WO2016065265A2

WO2016065265A2 - Anesthesia vaporizer and method

Info

Publication number: WO2016065265A2
Application number: PCT/US2015/057122
Authority: WO
Inventors: Jeffrey D. Marsh
Original assignee: Marsh Jeffrey D
Priority date: 2014-10-24
Filing date: 2015-10-23
Publication date: 2016-04-28
Also published as: WO2016065265A3

Abstract

Apparatus and method is disclosed for vaporizing a liquid anesthesia agent in a carrier gas for delivery to a patient such that the apparatus automatically establishes, monitors, and maintains a predetermined concentration level of the anesthesia agent in the carrier gas. The apparatus has an inlet and an outlet with a vaporization chamber therebetween, and a pump for dispensing small quantities of liquid anesthesia agent into the vaporization chamber. A first sensor senses the condition of the carrier gas upstream from the vaporization chamber and a second sensor senses the condition of the carrier gas/vaporized agent downstream from the vaporization chamber. A computer control system responsive to the sensors is configured to determine the concentration level of the agent delivered to the patient and to automatically increase or decrease the rate at which the pump is actuated to maintain the concentration level at the predetermined level.

Description

ANESTHESIA VAPORIZER AND METHOD

RELATED APPLICATIONS

[0001] This is application claims priority to U. S. Provisional Application No. 62/068,1 70, filed on October 24, 2014, and to U. S. Provisional Application No. 62/100,283, filed on January 6, 201 5, both of which are herein incorporated by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable.

BACKGROUND OF THE DISCLOSURE

[0003] This disclosure relates to an anesthesia vaporizer and a method of vaporizing a liquid anesthesia agent where the vaporized agent is mixed with a carrier gas, such as air, oxygen or other gaseous mixtures, to be delivered to a patient where the concentration of the anesthesia agent delivered to patient is accurately controlled and monitored.

[0004] An operating diagram of a typical prior art plenum-type anesthesia vaporizer is shown in Fig. 6. This vaporizer comprises a carrier gas flow path that is divided between a vapor flow path and a by-pass flow path. The incoming carrier gas is split between the two flow paths and is controlled by a suitable control valve, where a portion of the carrier gas is directed into the vapor flow path that in turn passes through a vaporizing chamber where a quantity of the liquid anesthesia agent is vaporized and mixed with the carrier gas flowing through the vapor flow path. The remaining portion of the carrier gas is directed through the bypass flow path. The carrier gas passing through the vaporizing chamber volatilizes the liquid anesthetic and is then mixed with the anesthetic-free carrier gas bypassing the chamber. Often, a bimetallic strip valve is provided in the carrier gas by-pass flow path to modulate the amount of carrier gas flowing through the by-pass flow path so as to compensate for temperature changes caused by vaporization of the liquid anesthesia agent in the vaporization chamber.

[0005] Examples of typical anesthesia agents include SeveFlurane, IsoFlurane, Halothane and other such liquid agents. The physical properties of such agents are well known to those skilled in the art. Typically, at standard temperature and pressure (STP), these agents are a liquid and must be vaporized in the vaporization chamber before being administered to a patient. The partial pressures of the carrier gas (e.g., air or oxygen) is such that the anesthesia vapors in the flow path through a vaporization chamber of the prior art vaporizer (as shown in Fig. 6) combine with the carrier gas in the vaporization chamber such that about 30% of the mixture is the anesthetic agent vapor and about 70% is the carrier gas. However, mixtures of this level of concentration are lethal to the patient such that the saturated mixture must be further mixed with pure carrier gas flowing through the by-pass channel to achieve concentration levels generally between 1 % and 7% - the intended concentration range to be supplied to a patient.

[0006] As is well-known, when a liquid is converted into a vapor, additional energy (known as the latent heat of vaporization) is required to transform the anesthesia agent from a liquid to a vapor with no change in temperature. This additional heat must come either from the immediate surroundings, such as the structure of the vaporizer, or from a heater. As shown in Fig. 6, large heat sinks are often provided in the vaporizer, which are in thermal conductive relation to the vaporization chamber and such the heat sinks provide sufficient heat to vaporize the agent without unduly cooling the structure of the vaporizer. However, even with the heat sinks, the vaporization of the agent causes the temperature of the vaporization chamber to cool and the partial pressure of the agent changes thus requiring that changes in the balance of the saturated vapor and carrier gas must be made to maintain the desired concentration levels delivered to the patient. This is a complex, constantly-varying dynamic condition. Certain vaporizers utilize electric resistance heaters to heat the vaporization chamber to maintain the temperature of the vaporization chamber at a constant temperature as the agent is vaporized, which adds more complexity to the situation to be monitored and controlled.

[0007] Other prior art vaporizers have employed open and closed loop control systems to compensate for the change in temperature as the liquid agent is vaporized. In recent years, other vaporizers, using control loops, employ gas analysis techniques to monitor and control the percentage of the vaporized anesthesia agent in the gas stream delivered to the patient. Certain of these newer techniques use infra-red absorption technology and ultrasonic flight time analysis.

[0008] Another well-known aspect of anesthesia vaporization is the fact that the two volumes of gasses (i.e., the agent vapor and the carrier gas) are additive and if a certain known volume of carrier gas is flowing and liquid agent is vaporized into the stream, the volume exiting the system is greater than the entering carrier gas. There has been a long-standing need for improvements in anesthesia vaporizers and the methods in which the vaporizer is accurately controlled in response to the concentration of the actual mixture of the agent/carrier gas that is delivered to the patient. Further, there has been a long-standing need for a small, portable, reliable, and simple to use device for field use as well as use in third-world countries.

SUMMARY OF THE INVENTION

[0009] The present disclosure utilizes a vaporizer body having an incoming flow channel or flow path for a carrier gas, such as air or oxygen or a mixture of gases, connected to a vaporization chamber within the vaporizer body which then connects to an outlet flow channel. In the incoming flow channel, a first sensor is located upstream of the vaporization chamber to determine the condition (e.g., the temperature, the mass flow rate, or both the temperature and the mass flow rate) of the gas passing by the sensor. The vaporization chamber has a means for removably attaching a supply (e.g., a bottle) of liquid anesthesia agent (typically about 250 ml_), such as a threaded socket in a portion of the vaporizer with a flow path from the bottle. The vaporizer has an electromechanical means (such as a pump or more particularly a so-called micro-quantity injection pump) for controlling or modulating the dispensing of the liquid agent into the vaporization chamber in order to achieve and/or to maintain a desired concentration level of anesthesia in the carrier gas supplied to the patient. Within the vaporization chamber, different techniques for vaporizing the liquid may be used. For example, a wick can be employed that is wetted with the liquid anesthesia agent over or through which the inlet carrier gas flows or by wetting of a prepared surface with the liquid agent will result in vaporization of the liquid agent. Other vaporization techniques can be used, such as the use of a heated evaporation plate or an ultrasonic disc to facilitate vaporization of the liquid agent. The vaporized agent and the carrier gas then continue to flow through the vaporization chamber and into the outlet channel where a second sensor determines the condition (e.g., the temperature, the mass flow rate, or both the temperature and the mass flow rate) of the exiting gas mixture of the carrier gas and the vaporized agent. From this information concerning the condition of the incoming carrier gas and the outgoing carrier gas and vaporized agent mixture, a computer control system may determine the concentration level of the outgoing mixture such that the concentration level can be compared to a predetermined concentration level so that the computer control system may utilize this information to control the electromechanical means (e.g., a micro-quantity pump) so as to vary the amount of liquid agent in a given length of time that is vaporized so as to maintain, adjust, or modulate the concentration of the vapor in the carrier gas delivered to the patient to insure that the concentration level of the anesthesia agent is within a preselected or predetermined range.

[0010] While it is possible to determine the concentration of the vaporized agent in the carrier gas stream delivered to the patient by only knowing the mass flow rate of the carrier gas into the inlet of the flow path and the volume or mass of the liquid agent delivered and vaporized in a given time, a preferred system and method utilizes sensors in the inlet and outlet portions of the flow path that monitor the mass flow of the carrier gas into the flow path and the expected mass increase of the exiting gas mixture due to the addition of the vaporized agent. This dual calculation method adds to the safety of the device to insure that the concentration of the agent remains within safe limits.

[0011] It will be particularly noted that the vaporizer and method of the present disclosure eliminate the need in prior art anesthesia vaporizers, such as shown in Fig. 6, for a by-pass flow path along with the need to compensate for temperature variations. The system and method of the present disclosure simplifies the vaporizer and allows for the direct control of the concentration of the agent in the carrier gas that is delivered to the patient and allows for direct control of the concentration of the anesthesia in the carrier gas as well as eliminating the need to produce a lethal mixture of anesthetic vapor prior to dilution by a stream of carrier gas.

[0012] The improvements described herein include the above- mentioned so-called "microinjection" pump which is under the control of the above-described computer controller to accurately inject a very small amounts of the anesthesia agent into the vaporization chamber of an anesthesia vaporization device so as to allow the computer control system to accurately control the concentration of the anesthesia agent in the gas stream delivered to the patient within a desired concentration range (e.g., concentrations ranging between about a 0.5% concentration of the anesthesia agent for each 0.25 liters of carrier gas and about a 5% concentration of the anesthesia agent for each 8 liters of carrier gas). Of course, this microinjection pump may be controlled so as to increase, decrease or terminate the flow of the anesthesia agent (and thus to control the concentration of anesthesia in the carrier gas) in response to an anesthesiologist or in response to predetermined parameters to establish and/or to maintain a predetermined concentration level or percentage.

[0013] The present disclosure describes apparatus for vaporizing a liquid anesthesia agent in a stream of a carrier gas for delivery to a patient such that the apparatus automatically maintains at a concentration level of the anesthesia agent relative to the carrier gas at a desired concentration level. The apparatus comprises a housing having a flow path therethrough, the flow path having an inlet and an outlet with a vaporization chamber therebetween. The flow path is configured to have a stream of a carrier gas flowing therethrough. A supply of a liquid anesthesia agent is provided, and means for modulating the dispensing of the liquid anesthesia agent into the vaporization chamber for vaporization of the liquid anesthesia agent within the vaporization chamber under the control of a computer control system is disclosed. A first sensor is located within an inlet portion of the flow path upstream from the vaporization chamber, and a second sensor is located downstream from the vaporization chamber. A modulating means (also referred to as a micro-quantity injection pump) is provided comprising an actuator under the control of the computer control system for injecting a micro-quality of liquid agent into the vaporization chamber each time the modulation means is actuated. The computer control system receives data from the first sensor related to the condition of the carrier gas in the inlet portion of the flow path upstream of the vaporization chamber and receives data from the second sensor related to the condition of the carrier gas and of the vaporized anesthesia agent downstream from the vaporization chamber. The computer control system is configured to calculate the concentration of the vaporized anesthesia agent in the flow path downstream of the vaporization chamber to be delivered to the patient and automatically increasing or decreasing the rate at which liquid anesthesia agent is delivered to vaporization chamber so as to maintain the concentration of the anesthesia agent to be delivered to the patient at a predetermined level. [0014] Another embodiment of such a micro-quantity pump is described in accord with the present disclosure for supplying a liquid anesthesia agent to an anesthesia vaporizer under the control of a computer control system so that the concentration of vaporized anesthesia agent in a carrier gas stream supplied to a patient may be controlled to be within a predetermined range of concentration levels. This other embodiment of the micro-quantity pump has a pump body having at least one cylinder and adapted to be supplied with a liquid anesthesia agent. The pump has an outlet from the supply of liquid agent to a proximal end of the cylinder. The outlet has a one-way check valve for allowing liquid agent to flow from the supply to the cylinder but preventing the back flow of liquid agent from the cylinder to the supply. The cylinder has an outlet passageway leading from the proximate end of each cylinder for the injection of liquid agent into the vaporizer, this outlet passageway having a second one-way check valve allowing liquid agent to flow toward the vaporizer but preventing the back flow of liquid agent from the outlet passageway the cylinder. The cylinder has a piston disposed therein in slidable, sealable engagement with the cylinder. A drive is operable in response to the computer control system for moving (advancing) the piston within its respective cylinder toward the proximate end thereof so as to inject a quantity of liquid anesthesia agent into the vaporizer as determined by the computer control system so as to establish or to maintain a desired concentration level of the vaporized agent relative to the carrier gas delivered to the patient. The drive is operable in reverse direction to retract the piston away from the proximal end of its cylinder to draw a quantity of liquid agent from the supply into the second cylinder.

[0015] A method of the present disclosure is disclosed for vaporizing a liquid anesthesia agent and for controlling the concentration level of the vaporized agent in a carrier gas stream delivered to a patient utilizing a vaporizer having a flow path through which a stream of a suitable carrier gas flows. The flow path has an inlet and an outlet with a vaporization chamber therebetween. A selectively operable pump is utilized for dispensing a desired or predetermined quantity of the liquid agent into the vaporization chamber in a predetermined time to provide a predetermined concentration level of the vaporized agent in the carrier gas delivered to a patient. A computer control system controls operation of the pump in response to the desired concentration level and the actual concentration level of the agent delivered to the patient. The method comprises determining the condition of the carrier gas in the inlet portion of the flow path, and determining the condition of the carrier gas and the vaporized agent entrained with the carrier gas in the outlet portion of the flow path. An anesthesiologist or other person or a protocol determines a desired concentration of the vaporized agent in the carrier gas to be delivered to the patient. The computer control system is configured to vary or modulate the amount of liquid agent dispensed into the vaporization chamber in a given time interval so as to result in the desired concentration level of the vaporized agent in the carrier gas being delivered to the patient.

[0016] A method of vaporizing a liquid anesthesia agent and controlling the concentration level of the vaporized agent in a carrier gas stream delivered to a patient to be at a predetermined concentration level is disclosed that utilizes a vaporizer having a flow path through which a stream of a suitable carrier gas flows. The flow path has an inlet and an outlet with a vaporization chamber therebetween. A supply of the liquid agent and a selectively operable pump are provided for dispensing a quantity of the liquid agent into the vaporization chamber, and a computer control system controls operation of the pump. The method comprises the steps of determining the condition of the carrier gas in the inlet portion of the flow path, determining the condition of the carrier gas and the vaporized agent in the outlet portion of the flow path, determining the concentration level of the vaporized agent in the carrier gas to be delivered to the patient; and operating the computer control system so as to vary the amount of liquid agent dispensed into the vaporization chamber in a given time so as to result in the predetermined concentration level being supplied to the patient.

[0017] Other objects and features of the disclosure will be specifically pointed out and will become apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Fig. 1 is a longitudinal cross-sectional diagrammatic view of a vaporizer of the present disclosure;

[0019] Fig. 2 is a perspective view of a vaporizer of the present disclosure, with a LCD display screen removed to show a compartment for housing a computer control system;

[0020] Fig. 3 is an enlarged cross-sectional view taken along line 3 - 3 of Fig. 2 illustrating an electro-mechanical system (e.g., a micro-quantity pump) for controlling the dispensing of a predetermined quantity of liquid anesthesia agent in a predetermined length of time into the vaporization chamber to be vaporized with the electro-mechanical system controlled by a computer control system so as to establish and to maintain a desired concentration level of the anesthesia agent in a carrier gas to be delivered to a patient;

[0021] Fig. 4 is a sensor amplifying circuit diagram for a flow sensor used in the present disclosure for signal conditioning of the output of the flow sensor that is used to determine the mass flow rate of the carrier gas passing by the flow sensor and, preferably, to determine the temperature of the carrier gas or the vaporized agent carried by the carrier gas mixture;

[0022] Fig. 5 is a block diagram of the computer control used to control the vaporizer of the present disclosure;

[0023] Fig. 6 is a diagram of a prior art plenum vaporizer;

[0024] Fig. 7A is a vertical cross sectional view of a so-called duck bill check valve used in the vaporizer of the present disclosure to permit a small quantity of liquid anesthesia agent to be dispensed into the vaporizer in response to actuation of the above-described electro-mechanical system or pump under the control of the computer control system and to prevent back flow of the liquid agent from the vaporizer to the pump;

[0025] Fig. 7B is a side elevational view of the duck bill valve shown in Fig. 7A;

[0026] Fig. 8 is a view showing an ultrasonically activated vaporization disk and its power supply for enhancing vaporization of drops of liquid agent dispensed onto a evaporator plate in the vaporization chamber of the vaporizer of the present disclosure;

[0027] Fig 9 is a perspective view of another embodiment of the vaporizer and of the micro-quantity pump of the present disclosure having a bottle of liquid anesthesia agent inserted in an inlet socket of the pump for supplying liquid anesthesia agent to the pump and for dispensing micro- quantities into the liquid agent vaporizer under the control of a computer control system for establishing and maintaining a desired concentration level of anesthesia delivered to a patient.;

[0028] Fig. 10 is an exploded perspective view of the micro-quantity pump shown in Fig. 9 illustrating the main components of the micro- quantity injection pump;

[0029] Fig. 1 1 is a bottom perspective view of the micro-quantity injection pump shown in Figs. 9 and 10;

[0030] Fig. 12 is a vertical cross section of the micro-quantity injection pump taken along line 12 - 1 2 of Fig. 9;

[0031] Fig. 13 is a top plan perspective view of the pump shown in Fig. 9 with the bottle of liquid agent shown in Fig. 9 removed;

[0032] Fig. 14 is a horizontal cross-sectional view taken along line 14 - 14 of Fig. 12;

[0033] Fig. 1 5 is a bottom perspective view of a collar on a somewhat larger scale carried on the neck of an anesthesia bottle having a plurality of lugs that engage corresponding notches in the pump housing, where each of the notches has an electrode associated therewith, and where the collar is unique for each type of agent being used and where such unique collar has a pattern of electrodes on its lugs, which in accordance with a truth table (as shown in Fig. 16) , identifies and communicates the particular anesthesia agent being used to the computer control system;

[0034] Fig. 1 6 is an electrical schematic illustrating how the components of the above-described pump and vaporizer of Figs. 9 - 15 are connected to the computer control system and how the computer control system identifies or verifies that a bottle of the desired anesthesia agent has been installed on the pump body;

[0035] Fig. 17 is a top perspective view of third embodiment of the vaporizer and micro-injection pump system of the present disclosure for supplying micro-quantities of the liquid agent to the vaporizer under the control of a computer control system to establish and to maintain a desired concentration level of the anesthesia supplied to a patient, with parts broken away for purposes of illustration of the liquid flow channels between the source bottle and the vaporization chamber and with four check valves (as shown in Figs. 1 8, 20 and 22) omitted for purposes of clarity;

[0036] Fig. 18 is an exploded perspective view of the micro-quantity pump shown in Fig. 17;

[0037] Fig. 19 is another exploded perspective view similar to Fig. 18 further illustrating certain aspects of the vaporizer and pump system shown in Fig. 18;

[0038] Fig. 20 is an exploded perspective view of the upper portion of the micro-injection pump shown in Figs. 17 - 19;

[0039] Fig. 21 is a vertical cross-sectional view taken along line 21 - 21 of Fig. 17 illustrating certain components of the system;

[0040] Fig. 22 is a partial vertical cross- sectional view taken along line 22 - 22 of Fig. 20 illustrating details of the preferred check valves used to establish the flow of micro-quantities of liquid agent dispensed from one cylinder of the micro-pump as a piston in the one cylinder is advanced one step and to admit micro-quantities of agent into the other cylinder of the micro-pump as the piston in the other cylinder is retracted one step; and [0041] Fig. 23 is a flow chart illustrating the control strategy and steps used to control a micro-injection pump of the present disclosure so as to establish and to maintain a predetermined concentration level of the anesthesia agent and the carrier gas supplied to a patient.

[0042] Corresponding reference characters represent corresponding parts of the present disclosure throughout the several views of the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0043] Referring now to the drawings, Figs. 1 - 3 illustrate a first embodiment of an anesthesia vaporizer and micro-quantity anesthesia agent dispensing pump system of the present disclosure, as generally indicated in its entirety by reference character 1 . The system 1 has a main body 3 having a flow path or channel 5 extending through the body. The flow channel has an inlet 7 and an outlet 9 with a vaporization chamber 1 1 therebetween. As generally indicated at 1 3, a screw socket or the like is provided in main body 3 for sealably receiving a supply (e. g., a bottle) 15 of liquid anesthesia agent, such as, for example, SeveFlurane, IsoFlurane, Halothane and other such liquid agents. As shown, with the vaporizer inverted from its position shown in Figs. 1 - 3, the bottle 15 may be screwed into socket 13 in the main body when the bottle and the main body 3 are inverted so as to seal the bottle with respect to the main body. Once the bottle is screwed into socket 13, the main body 3 may be turned over so that it is in the position shown in Figs. 1 - 3. An appropriate circular washer-type pliant seal (not shown) seals the mouth of the bottle with respect to the main body 3 when the neck of the bottle is screwed into the main body socket 13. A stopper 1 7 is sealably provided in the neck of bottle 15. The stopper has a liquid outlet passage 18, as shown in Fig. 3, allowing liquid to flow to the dispensing pump, as will be hereinafter described. An air inlet tube 19 also extends through the stopper and is in communication with the atmosphere to allow air into the bottle as the liquid anesthesia agent therein is withdrawn therefrom. As shown in Fig. 1 , when the vaporizer is in its operating position, the air inlet tube 19 extends upwardly within bottle 15 and stops just short of the base of the bottle to allow atmospheric air to enter the bottle as liquid is dispensed from the bottle. This allows the liquid to flow freely from the bottle in small quantities through outlet passage 1 8 in response to a micro-quantity of liquid being dispensed into vaporization chamber 1 1 .

[0044] The outlet passage 18 is in communication with an inlet check valve 45, as shown in Fig. 3, for purposes as will appear. As indicated at 21 in Figs. 1 and 3, an inclined evaporator plate is provided in the vaporization chamber 1 1 to receive small droplets of the liquid anesthesia agent dispensed from bottle 15, to evaporate the liquid droplets, and to entrain the vaporized anesthesia agent in the carrier gas stream flowing through the flow path 5. The evaporator plate may be provided with a wicking surface of increased surface area that will distribute the liquid agent and increase its surface area to promote vaporization of the liquid agent. Alternatively, the evaporator plate may be heated to a temperature to above ambient temperature by a suitable electrical resistance heater, or may be rendered resonant by an ultrasonic transducer, as shown in Fig. 8, to aid in vaporization of the agent.

[0045] An inlet mass flow rate and temperature sensor 23 (also referred to as a "first sensor") is installed in flow path 5 between the inlet 7 and the vaporization chamber 1 1 and an outlet mass flow rate and temperature sensor 25 (also referred to as a "second sensor") is mounted in the flow path downstream of the vaporization chamber. In a preferred embodiment, both sensors 23 and 25 may both be a sensor, such as a model FS5 commercially available from 1ST USA, 9516 W. Flamingo Rd, Suite 210, Las Vegas NV, 89147, that preferably senses both the temperature and the mass flow of the gas passing thereby. However, in accordance with the present disclosure, sensors 23 and 25 need only determine the mass flow rate of the carrier gas and the carrier gas/vaporized agent flowing therepast. As shown in Fig. 2, the vaporizer body 3 has a compartment 27 in which suitable computer control system 29, such as a Raspberry Pi computer commercially available from Newark Electronics, www.newark.com, may be housed. As shown in Fig. 5, how computer controller 29 is used in the system is disclosed. Fig. 23 illustrates the steps carried out by computer control system 29 to establish and to maintain a predetermined concentration level of the anesthesia agent in the carrier gas delivered to a patient using a proportional-integral-derivative controller well known to those skilled in the art, which will be further described hereinafter in regard to Fig. 23. A LCD display screen 30 driven by computer 29 may be provided to display information regarding the flow rates, concentrations, temperatures and other information. This LCD display screen may overlie compartment 27. Also as shown in Fig. 2, a battery compartment 31 is provided for housing a suitable battery (not shown) for powering the computer control system. Of course, other types of power supplies for the computer control system may be used, as are well known to those skilled in the art. It will be further appreciated that because in a preferred embodiment, the system 1 (or the other systems hereinafter described) uses a Raspberry Pi computer for computer controller 29, the systems of this disclosure have the ability to communicate with a remote patient management system so that various parameters of the system can be monitored.

[0046] Referring now to Fig. 3, the system 1 further comprises an electromechanical means (e.g., a pump), as generally indicated at 33, for dispensing small or micro-quantities of a liquid anesthesia agent into the vaporization chamber 1 1 and for modulating the flow of liquid anesthesia agent into vaporization chamber 1 1 over a given period of time so as to control and/or to modulate the concentration level of the agent in the carrier gas supplied to the patient so as to establish and maintain a predetermined concentration level of the agent in the carrier gas delivered to the patient. The term "micro-quantity" will be described hereinafter. This micro-quantity pump 33 is under the control of computer control system 29 for establishing and maintaining a desired or predetermined concentration level of the agent in the carrier gas delivered to the patient. Pump 33 dispenses a predetermined volume, preferably a plurality of "micro-quantities" of liquid anesthesia agent in a predetermined length of time (e.g., a second or two) into vaporization chamber 1 1 , in a manner as will become apparent.

[0047] More specifically, a first embodiment of the electromechanical means or pump 33 is a micro-quantity injection pump that includes a selectively actuable solenoid 37 or other actuator controlled by the computer controller 29 such that upon each actuation of the solenoid, a micro-quantity of liquid anesthesia is dispensed into the vaporization chamber 1 1 . Computer controller 29 may thus readily track the number of micro-quantities of liquid agent that are dispensed into the vaporization chamber in a given time so that the volume and thus the mass of the liquid agent dispensed in that time will be known to the computer controller, which information may be used to determine the concentration of the agent in the carrier gas/vaporized agent mixture that is supplied downstream of the vaporizer to a patient or the like. The portion of the vaporizer that mounts solenoid 37 and the solenoid along with the portion that includes socket 1 3 are preferably removable from the vaporizer body 3 as a unit. In that manner, a full bottle 1 5 of the anesthesia agent may be threaded into the socket 13 while the bottle is upright. The bottle may then be inverted as it is installed in the vaporizer body 3 so as to prevent leakage or spillage of the liquid anesthesia agent. As will be appreciated by those skilled in the art, by directly connecting the container (bottle 15) to the system 1 of the present disclosure, is no need to transfer the anesthesia agent from its original container to another container prior to use with system 1 .

[0048] As further shown in Fig. 3, solenoid 37 has a plunger 39 having an outer shaft 41 on the distal end of the plunger that has a sliding, sealing fit within an O-ring 43. When the solenoid is actuated under the control of computer control system 29, the plunger will be drawn into the body of the solenoid thus decreasing the pressure within cavity 35, which is filled with liquid anesthesia agent. This decrease in pressure within cavity 35 causes a small quantity of liquid agent to be drawn into cavity 35 through an upper check valve 45 that is in communication with the liquid passage 18 in stopper 17. In this manner, each time that solenoid 37 is actuated; a micro- quantity of liquid agent from within bottle is drawn into chamber 35. Upon the solenoid being de-energized, a return spring 47 returns the solenoid plunger 39 to its de-energized, relaxed state, as shown in Fig. 3. As the plunger returns to its relaxed state, the plunger moves into the cavity 35 thus increasing the pressure of the liquid agent within the cavity, which in turn positively closes the upper valve 45 and effects the momentary opening of a second check valve 49. As the second check valve 49 opens, a micro-quantity or small droplet of liquid agent is dispensed onto the inclined vaporization plate 21 where the liquid droplet of anesthesia agent will be substantially instantaneously evaporated or vaporized and the vaporized agent will be mixed with the carrier gas flowing through the vaporization chamber 1 1 . As the droplet is emitted by the lower check valve 49, the pressure within the cavity 35 is reduced thus terminating the flow from the lower valve after the droplet has been dispensed.

[0049] As the droplet of liquid agent dispensed from the lower check valve 49 is vaporized on plate 21 , the change of state of the agent from a liquid to a vapor will absorb heat due to the change in temperature and the latent heat of vaporization of the agent. The solenoid plunger 39 and the upper and lower check valves 45 and 47 thus operate together as a plunger-type microinjection pump where the displacement of each stroke of the plunger dispenses a known volume of liquid agent onto the evaporation plate 21 . By controlling the rate at which the solenoid 37 is actuated, the amount of liquid agent dispensed onto the evaporation plate can started, increased, decreased or stopped. The latent heat of vaporization for each anesthesia agent is a known physical property for the particular agent being used. By knowing the mass flow rate of the carrier gas flowing into the vaporization chamber 1 1 and by knowing the volume (mass) of the liquid agent dispensed into the vaporization chamber in a given time, the concentration of the anesthesia agent in the gas stream delivered to the patient may be determined. By controlling or varying the rate that anesthesia is injected into the vaporization chamber over a given time, the computer controller 29 will control the concentration to be within a desired or predetermined range of concentration levels, to be increased or decreased, and to be started and stopped. It will be appreciated that solenoid 37 may be actuated at a maximum rate of about 250 cycles/second, but preferably the cycling rate of the solenoid is maintained somewhat below its maximum cycling rate so that when the concentrate rate is at its highest predetermined level, the solenoid is not continuously actuated thereby allowing the system 1 to further modulate or control the concentration level.

[0050] The check valves 45 or 49, as shown in Figs. 7A and 7B, are so- called "duck bill" check valves. Specifically, check valve 45 is shown to comprise a one-piece valve body 45a made of a suitable flexible elastomeric material, such as an EPDM, i.e., ethylene propylene diene monomer, rubber and preferably an M-class synthetic rubber in about the 60 durometer range. Valve body 45a has a base 45b that is configured to sealably engage a bore in the part in which it is mounted. The valve 45 has two angled flapper valve members 45c and 45d extending from the base and converging toward one another. The distal ends of the flapper valve members are separate from one another and thus form a slit or opening 45e between their distal ends that is normally closed to block the flow of liquid from the slit. It will be appreciated that with the interior space between the flapper valve members 45c and 45d filled with liquid, a slight increase of pressure within this space causes slit 45e to open such that a micro- quantity or volume of liquid will be dispensed from the valve. Upon this small quantity of liquid being dispensed, the pressure within the valve will decrease and the "memory" of the flapper valve members will close and seal slit 45e. Further, it will be appreciated that an increase in pressure on the exterior of the flapper valve members will compress the flapper valve members thus insuring that the slit 45e is positively closed preventing the back flow of liquid into the check valve. Such duck bill check valves may be a Duckbill Valve DU027.002-154.01 Silicone (VMQ), commercially available from miniValve, 6100 Oak Tree Blvd, Suite 200, Cleveland, OH 44131

[0051] With the check valves 45 and 49 oriented as shown in Fig. 3, liquid is disposed within the interior of the angled flapper valve members 45c and 45d of both valves and the slits 45e are both closed thus preventing liquid from being discharged or dispensed from the slits. Upon actuation of solenoid 37, as above described, the retraction of plunger 41 decreases the pressure within cavity 35 to a pressure slightly below the liquid pressure within the flapper valve members 45c, 45d of the upper check valve 45 thus momentarily opening its slit 45e and thus enabling a small quantity of liquid to be dispensed from bottle 13 into chamber 35. Upon the solenoid 37 permitting plunger 41 to return to its final position, this will cause the pressure within cavity 35 to increase, which positively closes the slit of the upper check valve. This increase in pressure within cavity 35 causes the flapper valve members of the lower check valve to move apart from one another and to open its slit thus allowing a small quantity of liquid agent to be dispensed onto the evaporator plate 21 . Of course, upon this small quantity of liquid being dispensed from cavity 35, the pressure in cavity will correspondingly decrease thus allowing the memory of the flapper valve members 45c and 45d of the lower valve 49 to close thus terminating flow from the lower check valve into vaporization chamber 1 1 . Thus, for each cycle of solenoid 37, one droplet or micro- quantity of liquid anesthesia will be dispensed onto the vaporization plate 21 . The rate at which the solenoid is cycled is under the control of computer control system 29 such that the rate of dispensing liquid agent into the vaporizer can be controlled or modulated, where the computer control system, in response to the outputs of sensors 23 and 25 (or other sensors), can maintain or vary the concentration of the anesthesia in the carrier gas delivered to the patient so that a predetermined concentration level is established and maintained.

[0052] Fig. 4 depicts a circuit A for amplifying (increasing) the signal from the sensor 23 supplied to computer controller 29. The construction and operation of circuit A will be readily known to one of ordinary skill in the art. It will be understood that, depending of the signal from the sensors 23 and 25, such an amplifier may or may not be needed. The sensor a sensor signal amplifying circuit, as indicated at A, is shown for the inlet sensor 23. As shown, the sensor 23 has a sensing element (e.g., a thermocouple) for sensing the temperature of the carrier gas flowing through the inlet side 7 of flow path 5. The sensor 23 also has a hot wire type mass flow sensor for determining the mass flow rate of the carrier gas past the sensor. Other types of mass flow meters, such as a vane type flow sensor, may be used. The temperature and mass flow rate signals from the temperature/mass flow sensor are conditioned by the circuit A shown in Fig. 4 and are supplied to the computer controller 29, as shown in Fig. 5. A similar signal amplifying circuit A is provided for the downstream sensor 25 such that the mass flow and the temperature of the carrier gas and the vaporized agent flowing through the outlet portion 9 of the flow path may be determined.

[0053] Referring to Fig. 5, the components of system 1 and how they are connected to one another are shown. As will be appreciated, computer 29 is powered by a battery or other power source in the conventional manner. However, if system 1 is battery powered, it thus gives the system the capability to be used in a wide variety of applications where there is no power, such as in a field hospital or other remote areas. The computer receives data from sensors 23 and 25, which data is converted from analog to digital signals by the A/D converter 50. A control selector 51 is provided so that an anesthesiologist or the like may manually select the concentration level of the carrier gas/vaporized agent to be supplied to the patient. The concentration level so selected is provided to computer 29. Further, a selector 53 is provided so that the anesthesiologist may select the type of anesthesia agent being used. However, as disclosed in regard to systems 101 and 201 hereinafter described, the type of anesthesia agent being used may automatically be determined by the computer controller through the use of a special collar 145 or 229 affixed to each bottle of anesthesia agent, which collar provides an electrical signal to the computer to identify the agent being used. Computer 29 operates in accord with a program, as hereinafter described and as shown in Fig. 23, to control the operation of solenoid 37 via a digital power switching device 54, such as a model ULN2803A Darlington transistor array commercially available from Texas Instruments, Inc., of Dallas, Texas.

[0054] It will be understood that the rate at which solenoid 37 is actuated is controlled by computer control system 29. A concentration level of the vaporized agent in the carrier gas delivered to a patient may be selected or otherwise predetermined by an anesthesiologist or other medical practitioner by adjusting the % agent selector 51 (e.g., a potentiometer or the like), as shown in Fig. 5. The computer control system 29 will monitor the outputs of sensors 23 and 25 in the manner shown in Fig. 23 and will determine if more or less anesthesia agent needs to be vaporized and combined with the carrier gas flowing through the vaporizer to achieve the desired or predetermined concentration level. The computer control system will thus control the micro-injection pump 33 by increasing the rate at which solenoid 37 is operated so as to increase or decrease the amount of anesthesia agent dispensed into the vaporization chamber 1 1 in a given time thereby to control and/or modulate the concentration level so that the predetermined concentration level may be achieved and maintained.

[0055] Referring now to Fig. 8, in place of the evaporator plate 21 shown best in Fig. 3, an ultrasonic vaporization plate 21 a may be used. As shown in Fig. 8, an ultrasonic plate 29a may be mounted in vaporization chamber 1 1 in place of plate 21 to receive droplets or very small quantities of liquid anesthesia agent from the lower valve 49. This plate 21 a may have a small ultrasonic transducer affixed thereto, where the ultrasonic transducer is rendered resonant by a power supply and controller circuit, as generally indicated at 55, mounted outside of the vaporization chamber and connected to the transducer by means of suitable wires or the like. For example, such an ultrasonic system, identified by part number SMUTK4W3F190, is commercially available from Steiner & Martins, Inc. of 1371 5 SW 139 Court, Suite 102, Miami, FL. When the plate 21 a is rendered resonant and when a small drop of liquid agent drops onto the plate, the ultrasonic energy of the plate will break down the larger drop into very small droplets of about 4 microns in diameter, as reported by the manufacturer, Steiner & Martins, Inc. This small droplet size greatly increases the surface area of the drop and facilitates the more rapid vaporization of the liquid agent. This may be particularly helpful in vaporizing agents having a relatively high vapor pressure, as compared to lower vapor pressure agents. Energization and de-energization of the ultrasonic plate 21 a may be controlled by computer 29.

[0056] Referring now to Figs 9 - 16, a second embodiment of a microinjection pump of the present disclosure is indicated in its entirety at 101 and is shown to comprise a pump body 103 having a first pump body section 105 and a second pump body section 107 (also referred to as an anti-rotation body). A threaded socket 109 is provided in body section 105 for threadably, sealably receiving the threaded neck of a bottle or other container 13 of liquid anesthesia agent. To install a bottle of liquid anesthesia agent in socket 109, the micro-pump 101 is removed from vaporizer 3, the pump body 105 is inverted from its position shown in Fig. 9 so that socket 109 faces downwardly and the threaded neck of bottle 13 is threadably inserted into the socket and the bottle is rotated to tighten and seal the bottle with respect to the pump body. A compressible seal (not shown) may be provided between the mouth of the neck of the bottle and the body section 105 in which the socket 109 is formed. After the bottle is screwed in place, the pump body and the bottle are inverted to the position shown in Fig. 9 such that the liquid anesthesia agent in the bottle is gravity fed into socket 109 through a liquid dispensing passage 18 in stopper 17 (as shown in Fig. 13), which has two ports or passages, 1 1 0a, 1 10b (as shown in Figs. 12 and 13) that serve as the inlets to pump 103. An air inlet tube similar to tube 19, as described above and shown in Fig. 13 is preferably installed in stopper 1 7 so as to admit atmospheric air into the bottle such that liquid agent is free to exit the bottle. As shown in Fig. 13, each of the ports 1 10a, 1 10b is equipped with a respective one-way check valve 1 1 1 a, 1 1 1 b, such as a duck bill check valve similar to those described above or with another type of check valve such as hereinafter described, so as the pump 101 is operated, a micro-quantity of liquid anesthesia agent is drawn from bottle 13 and into passages or ports 1 10a, 1 10b, but where these valves block or check the back flow of liquid from these passages back into bottle 13.

[0057] As indicated at 1 12, a space is provided between pump body sections 1 05 and 107. Pair of gears 1 13a, 1 13b is rotatably mounted with respect to pump body 105 in space 1 1 2 and the gears are in mesh with one another with each of the gears having a respective hub 1 14a, 1 14b. A motor 1 1 5, preferably a reversible stepper motor, which is also referred to as an actuator (as shown in Fig. 12) under the control of computer control system 29 is mounted on a bracket 1 16, which in turn is mounted on the bottom of body 105. As best shown in Fig. 1 1 , motor 1 1 5 drives a pinion 1 17, which is in mesh with gear 1 13b. Thus, as the motor is energized, the pinion rotates gear 1 13b in one direction, and because gears 1 13a, 1 13b are in mesh with one another, gear 1 13a is rotated in the opposite direction. Of course, if the direction of motor 1 15 is reversed, the direction of rotation of the gears is also reversed. Hubs 1 14a, 1 14b each have a respective internally threaded center opening 1 1 6a, 1 16b therethrough (as shown in Figs. 12 and 14) which threadably receives a respective elongate externally threaded jack shaft 1 19a or 1 19b. The distal ends of the jack shafts are received in respective non-threaded bores 121 a, 1 21 b in the second body portion 107. The distal end of each jack shaft carries a respective stop pin 123a, 123b which is slidably received in a respective slot 1 24a, 124b in second body 107 (also referred to as the "anti-rotation" body) opening into a respective bore 121 a or 121 b. In this manner, upon rotation of gears 1 13a, 1 1 3b, the stop pins engage the sides of slots 124a, 124b to prevent rotation of the jack shafts as the gears 1 13a, 1 13b. This causes the jack shafts 1 19a, 1 19b to threadably advance into or to retract from body 1 05.

[0058] The proximate ends of jack shafts 1 19a, 1 19b are each received in a respective cylinder bore 1 25a, 125b in the first pump body portion 1 05 in axial register bores 121 a, 121 b. Each cylinder bore has a respective proximate end 126a, 126b, as best shown in Figs. 12 and 14. The proximate end of each jack shaft carries a respective piston 127a, 127b. Each of the pistons is in axial slidable, sealable relation with its respective cylinder bore 125a, 125b. The proximate end of each cylinder bore 125a, 125b is in communication with its respective inclined passage or port 1 10a, 1 10b in body 105 so as to receive liquid anesthesia agent from bottle 1 3 via its respective inlet check valve 1 1 1 a or 1 1 1 b as each respective piston is retracted in its cylinder bore. In operation, passages 1 10a, 1 10b and the portion of cylinders 1 25a, 125b between the proximate ends of pistons 127a, 127b are filled with liquid anesthesia agent supplied from bottle 1 3 that is threaded into socket 109 via a respective port 1 10a, 1 1 0b. Of course, as one of the pistons is advanced toward the proximate end of its cylinder bore; liquid agent in the bore will be dispensed into vaporization chamber 1 1 , in a manner as will appear.

[0059] It will be appreciated that pinion 1 17 and gears 1 1 3a, 1 13b constitute a transmission, as generally indicated at T, for simultaneously driving the jack shafts 1 19a, 1 19b in opposite axial directions within their respective cylinder bores 125a, 125b. Alternatively, a crankshaft arrangement (not shown) with opposing displacement cylinders (or two opposing journals and parallel cylinders) can be utilized for driving the pistons 127a, 127b in opposite directions in their respective cylinders in place of jack shafts 1 19a, 1 19b being threaded in the hubs of gears 1 13a, 1 13b by using a properly geared stepper motor to control rotation of the crank.

[0060] At the proximate end of each cylinder 125a, 125b, a respective outlet channel or passage 133a, 133b leads to a dispensing body 135, which has a dispensing passageway therein (not shown) leading to a hollow dispensing needle or tube 137. When pump 103 is installed on vaporizer body 3 (as shown in Fig. 9), needle 137 extends into vaporization chamber 1 1 so that droplets of liquid anesthesia may be dispensed onto the evaporation plate 21 .

[0061] As shown in Figs. 12 and 14, each outlet channel 133a, 1 33b is equipped with a respective one-way outlet check valve, as indicated at 136a, 1 36b. This one-way check valve may be a duck bill check valve, as described above, or another type of check valve as hereinafter described to permit a micro-quantity of liquid agent to be dispensed from the valve upon each step of stepper motor 1 15 and yet which effectively blocks back flow of the liquid agent into its respective cylinder 125a, 1 25b. With this arrangement, as piston 127a is advanced one step at a time by stepper motor 1 1 5 toward the proximate end 1 26a of its cylinder bore 125a, a micro-quantity of liquid anesthesia is forced through its respective check valve 136a, and then into channel 133a and into dispensing body 1 35 such that a micro-quantity of liquid agent is thus forced or dispensed from injection needle 137 and onto the evaporator plate 21 , as heretofore described. Preferably, the evaporator plate 21 of the vaporizer 1 has a surface that is treated (e.g., roughened or treated with a suitable hydrophilic chemical) so that when a micro-quantity of liquid anesthesia agent is dispensed from the tip of needle 137 and comes into contact with the surface of evaporation plate 21 , the liquid is substantially instantly vaporized. As above described, the evaporator plate may be heated or ultrasonically excited to enhance vaporization of the liquid agent on the plate.

[0062] Because gears 1 13a, 1 13b are in mesh with one another, as screw jack shaft 121 a and piston 127a are advanced toward the proximate end 126a of their respective cylinder bore 125a so as to inject a predetermined micro-quantity of liquid agent into passage 133a upon each actuation of motor 1 15, the inlet check valve 1 1 1 a in passage 1 10a prevents liquid agent from being forced back into bottle 1 3. Further, upon jack shaft 1 19a advancing its piston 1 27a toward the proximate end of cylinder bore 1 25a, jack shaft 1 19b and piston 127b are simultaneously moved away from (retracted) the proximate end of is respective cylinder 125b a distance similar to the distance that piston 127a is advanced. This retraction movement of piston 127b draws a similar micro-quantity of liquid agent from bottle 13 through its passage 1 1 0b and through its respective check valve 1 1 1 b into cylinder 125b. In this manner, the space within cylinder 125b is filled with liquid agent as the piston 127b is retracted. Of course, upon reversal of motor 1 15, cylinder 125b will be filled with liquid anesthesia agent so that as piston 127b is advanced to the proximate end of cylinder 1 25b, piston 127b will act as did piston 127a to dispense a micro-quantity of liquid agent through its respective check valve 1 36b into passage 133b upon each step of stepper motor 1 15.

[0063] As noted, motor 1 1 5 is preferably a reversible stepper motor or the like that is controlled by computer controller 29 such that upon energization of the motor through one or more steps, the gears 1 13a, 1 13b are rotated in opposite directions through a small incremental angle in proportion to the angle the gears are rotated, which in turn causes the jack shafts 1 19a, 1 19b to be axially advanced or retracted relative to the proximate ends 126a, 126b of their respective cylinder bores 125a, 125b. The computer controller 29 keeps track of the number of steps that motor 1 15 is actuated such that when a piston 127a, 127b becomes fully advanced, the computer controller will reverse the direction of rotation of motor 1 15, such that the previously advancing piston is retracted and such that the previously retracting piston is advanced. Also, because the computer knows the number of steps that motor 1 1 5 is actuated in a given time, the computer knows the total volume of agent dispensed into the vaporizer in that given time. This information is useful in determining the concentration level of the carrier gas/agent delivered to a patient or the like.

[0064] Fig. 13 is a top plan view of the pump 103 including the first body member 1 05 and the second body 107. As previously described, the body 105 has socket 109 therein for threadably, sealably receiving the threaded neck of bottle 13 of liquid anesthesia agent. As shown, the pump body 105 proximate socket 109 has one or more slots 141 a - 141 d with each slot receiving a corresponding lug 143a - 143d (as best shown in Fig. 15) on a collar 145, which is loosely fitted on the neck of a bottle 13 of a specified type of anesthesia agent. An electrode 142a - 142e is provided in the base of each slot 141 a - 141 e. It will be understood for each type of anesthesia agent (e.g., SeveFlurane, IsoFlurane, Halothane or the like), the bottle containing each such agent will have an agent identifying collar 145 received on its neck, where the collar is specific for the particular anesthesia contained in the bottle. Each lug 143a - 143e of collar 145 may or may not have a corresponding electrode 144a - 144e on its end that would engage a corresponding electrode 142a - 142e in the base of its corresponding slot 141 a - 141 e when the bottle is fully threaded into socket 109. In accord with the "truth table" shown in Fig. 16, computer controller will be provided with a signal from the electrodes 142a - 142d that make contact with an electrode 144a - 144d so as to identify the unique pattern of electrodes that make contact thus positively identifying the particular agent being used. Then, in accordance with data pre-loaded into the computer controller (that is, stored in the calibration and input/output tables shown in Fig. 23) for all types of agents, the physical characteristics (e.g., density, vaporization temperature, for the particular agent in the bottle 13 installed in socket 109 will be used by the computer controller to establish and to control the concentration level of the agent in the carrier gas delivered to the patient. Because the computer controller "knows" the agent being used and because the computer controller can determine the mass flow rates and the target ΔΤ, and the predetermined concentration level desired, the computer controller can readily control the rate at which stepper motor 1 15 is actuated in order to establish and maintain the desired concentration level. Of course, in place of collar 145, the type of agent being used may be entered into computer 29 by means of a controller switch 53, as described above in conjunction with system 1 .

[0065] Fig. 16 is an electrical schematic illustrating how computer controller 29 is connected to the first and second sensors 23 and 25, how the computer controller identifies the particular agent being used, and how the computer controller actuates stepper motor 1 15. Specifically, the computer controller 29 is programmed to establish and maintain a predetermined concentration level of the anesthesia agent in the carrier gas/anesthesia agent supplied to the patient at a predetermined the flow rate of the carrier gas supplied to inlet 7 of vaporizer 1 . As shown in Fig. 16, the first or inlet sensor 25 preferably senses the mass flow and inlet temperature of the incoming carrier gas stream. The signal of the sensor 23 is amplified by its amplifier A and is transmitted to an analog-to-digital converter A/D1 , such as an ADS1 1 15 analog-to-digital converter commercially available from Texas Instruments, Inc. of Dallas, TX, and then is communicated to computer 29. Likewise, the output of downstream signal of sensor 25 preferably indicates the temperature and mass flow of the carrier gas and the vaporized agent downstream of the vaporization chamber 1 1 . This downstream signal is amplified by its amplifier A and is transmitted to its analog-to-digital converter A/D2 (which is similar to A/D1 ) and is communicated to computer 29. The lines 1 8, 25 and 22 (as shown in Fig. 16) are connected to electrodes 142a - 142e in the bases of slots 141 a - 141 e surrounding socket 109, such that when contact is made with an electrode 144a - 144d provided on collar lugs 143a - 143d, the truth table shown in Fig. 16 will provide a signal to computer 29 indicating the particular anesthesia agent being used. In response to the signals from sensors 23 and 23, the computer controller will then determine the actual concentration level of the vaporized agent in the carrier gas supplied to the patient and will compare the actual concentration level with a predetermined or desired concentration level and will determine if more or less of the vaporized agent needs to be injected into vaporization chamber 1 1 to establish or maintain the desired concentration level. The control strategy shown in Fig. 23 may be used to control operation of pump 103 to insure that the predetermined concentration level is achieved and maintained. As shown in Fig. 16, leads 18, 25, 22, +5 v., 24, 23, 1 7, 4 and Grd are connected to pump 1 01 by a multi-pin connector C.

[0066] More specifically, the flow rate (and thus the mass) of the carrier gas (normally pure oxygen or air) entering the vaporizer 1 is sensed and quantified by sensor 23, which is preferably a heated wire mass flow sensor. Preferably, but not necessarily, sensor 23 also determines the temperature of the incoming carrier gas. The signal from sensor 23 is amplified by its amplifier A and then converted to a 24 or 32 bit digital value by its analog to digital converter A/D1 and is then communicated to computer 29. Knowing the type of agent used in the system by sensing lines #22, #25, and #1 8 (as shown in the truth table of Fig. 16), the program in the computer control system 29 actuates pump 103 at a previously established rate to achieve a desired concentration level of the agent in the carrier gas supplied to a patient. The pumping rate is achieved through a changing combination of on and off signals to the transistor array 146, such as ULN2803 Darlington IC transistor array (as shown in Fig. 16), which in turn operates stepper motor 1 15 in accord with the predetermined program to establish and maintain a predetermined concentration level to be delivered to a patient. Due to the addition of vaporized agent, the mass exiting the vaporizer chamber 1 1 will increase. Downstream sensor 25 monitors this expected change (by, for example, using a calibrated table look-up as shown in Fig. 23) and confirms the correct rate of steps/second of the motor 1 15 and thus of the injection pump 103. If the variance is excessive by some predetermined amount, an error signal is used to either speed up or slow down the stepper motor rate so as to control the concentration level and so as to insure that the predetermined concentration level is delivered to the patient. As a third verification check, the temperature change of the carrier gas and the addition of the vaporized agent is monitored by sensors 23 and 25, or a separate temperature sensor (not shown). Using an additional output of the Darlington transistor array 146, the evaporation plate 21 may be heated to a given temperature. Using the pulse rate to maintain the temperature as an indicator causes the vaporization plate to also function as a third mass flow sensor. That is, the heat or power required to maintain the evaporation plate 21 at a constant temperature is similar to the heat required to maintain the heated wires in mass flow sensors 23 and 25, and thus can be calibrated to establish the mass flow past the evaporation plate. This results in a triple redundancy check for the amount of agent delivered for a given inflow of carrier gas. Those skilled in the art will recognize that, as shown in Fig. 23, computer controller 29 uses a proportional-integral-derivative (PID) loop, as further described below.

[0067] It will be appreciated that the micro-injection pump 1 01 may be constructed and operated with only a single jack screw 199a, a single cylinder 125a, and a single piston 127a. This single piston embodiment would operate in the manner above described under the control of the computer control system to inject micro-quantities of an anesthesia agent into the vaporizer upon the forward movement of the piston in the cylinder. However, to intake additional agent from the bottle 13 into the single cylinder, the stepper motor 1 15 would be operated in the opposite direction (retracted) at high speed to fill the cylinder with liquid agent as the piston is retracted. Then, the computer control system would operate the motor 1 15 to inject micro quantities of the liquid agent to the vaporizer as previously -SO-

described. It will be appreciated that the intake of additional liquid agent is done in a short time (a few seconds) such that there is effectively little or no appreciable difference in the concentration of the agent relative to the carrier gas during the intake time while additional liquid agent is drawn into the single cylinder.

[0068] Also, in place of the duck bill valves 45, 49, 1 1 1 a, 1 1 1 b, 1 36a, and 1 36b previously described, small micro-ball check or other one-way check valves 249a, 249b (as hereinafter described in regard to Fig. 22) may be used to permit the one-way flow of micro-quantities of liquid agent may be used in place of the duck bill valves, as above described.

[0069] Referring to Figs. 1 7 - 22, another embodiment of a combination vaporizer/pump 201 of the present disclosure is shown to comprise a vaporizer 203 and a micro-injection pump 205 (also referred to as an electromechanical means) is similar to pump 101 . Pump 205 comprises a head block assembly 207 that mounts on or carries the vaporizer 203 and pump 205, and that receives a bottle 209 of liquid anesthesia agent in a manner similar to that described above in regard to pump 101 . Head block assembly 207 comprises a main or lower plate 21 1 , an intermediate plate 213, and an upper plate 215. A lower gasket 217 is sealably interposed between the upper face of main plate 21 1 and the lower face of intermediate plate 213. An upper gasket 219 is sealably interposed between the upper face of the intermediate plate 213 and the lower face of the upper plate 215. Gaskets 217 and 21 9 are preferably of a suitable elastomeric material, such as an EPDM rubber, as above described, that can form a seal between the plates when the plates and the gaskets are secured together by fasteners or the like (not shown).

[0070] In the underside of the lower plate 21 1 , a threaded socket 221 (as best shown in Figs. 18 and 20) is provided, where socket 221 is similar to socket 1 09 and threadably receives the threaded neck of bottle 209 so that the bottle is sealed with respect to the lower plate. A dip tube 223 (shown in Figs. 17 and 19) extends from socket 221 and is inserted through a stopper 224 (see Fig. 19) in the neck of bottle 209 and extends to the base of the bottle for withdrawing liquid agent from the bottle and into the head block assembly 207 upon pump 205 being operated to withdraw a micro-quantity of liquid agent from the bottle in a manner as will appear. Stopper 224 has an air vent (not shown) therein for allowing air to enter the bottle as liquid is withdrawn therefrom.

[0071] As shown in Figs. 1 8 and 20, socket 221 has notches 225a - 225d, similar to notches 141 a - 144d. Notches 225a - 225d are provided with corresponding electrodes 228a - 228d (one of which is shown in Fig. 20) for making electrical contact with a corresponding electrode (not shown) on a corresponding tab or lug 227a - 227d on a collar 229 carried by the neck of bottle 209. It will be appreciated that socket 221 , collar 229, tabs 227a - 227d, electrodes 228a - 228d, and the corresponding electrodes on tabs 227a - 227d on are similar to the socket 109 and collar 145 described above in regard to Figs. 9 - 16. The electrodes cooperate with one another in the same manner as the electrodes heretofore described in regard to collar 145 such that a detailed description of their construction and function is not required, but that computer 29 receives a signal indicating the particular type of anesthesia agent that is being dispensed. This information is then used by computer control system 29 in the manner as described above to control the pump 205 so as to inject a predetermined amount of the agent in a given time to insure that the predetermined concentration level of the particular agent in the carrier gas is supplied and maintained to the patient.

[0072] A first flow path, a portion of which is generally indicated by the centerline 231 a (as shown in Fig. 18), is provided in head assembly 207 for drawing liquid drawn out of bottle 209 via dip tube 223 and for supplying liquid agent to the inlet of pump 205. A second flow path, a portion of which is generally indicated by centerline 231 b, is also provided in head assembly 207 for dispensing micro-quantities of liquid from pump 205 into vaporizer 203 under the control of computer controller 29 so as to establish and to maintain a desired or predetermined concentration level of the agent in the carrier gas supplied to a patient. As best shown in Fig. 18, flow path 231 a provides communication between the liquid in bottle 209 via dip tube 223 to a first V-shaped passage 233 in gasket 219. This first V-shaped passage 233 includes passages 233a, 233b that converge and join at the apex 233c of the first V-shaped passage, which is supplied liquid agent from dip tube 223. The angled passageways 233a and 233b lead to a respective passage or ports 235a, 235b (as shown in Fig. 18) that extend through intermediate plate 213 and lead to a second V-shaped passage, as generally indicated at 237, in gasket 217. Passage 237 has a pair of angled passages 237a, 237b that meet at apex 237c. The closely spaced ends of passages 237a, 237b are each in communication with a respective port 235a, 235b in plate 213. A respective one-way check valve 239a or 239b (as best shown in Fig. 20) is provided in ports 235a or 235b in intermediate plate 21 3 for selectively admitting or blocking flow to and from passages 237a, 237b. The widely spaced ends of passages 237a, 237b are in communication with pump ports 241 a, 241 b in lower plate 21 1 . Each pump port 241 a, 241 b (as best shown in Figs. 18 and 20) is in communication with a corresponding pump cylinder 277a, 277b, as will be hereinafter described, for admitting liquid from bottle 209 into one respective pump cylinder when the piston in that cylinder is retracted to draw liquid into that cylinder and for injecting a micro-quantity of liquid from that pump cylinder into vaporizer 203 when the piston in that cylinder is advanced upon each actuation or step of pump 203 by motor 301 in a manner that will be more particularly described hereinafter.

[0073] Upon one of the pump cylinders 277a or 277b being operated to force liquid from the pump 205 to the vaporizer 203 via its respective port 241 a or 241 b in plate 21 1 and via a respective port 235a or 235b in plate 219, a corresponding increase in pressure in passages 237a or 237b positively closes a respective check valve 239a or 239b in ports 235a, 235b so as to block back flow of liquid to the bottle 209. The more closely spaced ends of passages 237a, 237b are in communication with respective ports 245a, 255b in intermediate plate 213, which in turn are in communication with the spaced ends of passages 245a, 245b of a third V- shaped passage, as generally indicated at 245, in gasket 219. These two angled passages 245a, 245b converge at a common collection point 245c generally at the apex of the third V-shaped passage 245. This collection point or port 245c is in communication with a passageway, as generally indicated at 247, that includes a port 247a in plate 213, a port 247b in gasket 217, and a port 247c in plate 21 1 leading to an anesthesia inlet 267 of vaporizer 203 (as shown in Figs. 17 and 21 ). In this manner, that micro- quantities of liquid agent from pump 205 may be selectively injected or dispensed into vaporizer 203 under the control of the computer controller 29 in order to establish and/or to maintain a predetermined concentration level of the anesthesia agent in the carrier gas delivered to the patient. Each port 243a, 243b has a respective one-way check valve 249a, 249b interposed between its port 243a, 243b and its respective passage 245a, 245b in gasket 219 for selectively blocking the flow of liquid to passage 245a, 245b when liquid is being drawn into a respective pump cylinder 277a, 277b and for admitting liquid from its respective pump cylinder when that pump cylinder is operated to inject liquid into the vaporizer.

[0074] Turning now to a description of the construction and operation of pump 205, this is another embodiment of the micro-injection pump 101 described in regard to Figs. 9 - 16. Pump 205 operates in a manner similar to pump 101 , but pump 205 is constructed so as to have a more compact construction. Like pump 101 , pump 205 injects "micro" quantities of liquid agent into vaporizer 203 upon each actuation of the pump so that a "micro" quantity of liquid agent (as hereinafter described) is injected into vaporizer 203 upon each actuation or step of pump 205, where the micro- quantity is substantially instantaneously vaporized in vaporizer 203 and mixed with the carrier gas flowing through the flow path of the vaporizer so that the resulting mixture of the vaporized agent and the carrier gas is controlled and maintained to be within a predetermined or desired range of concentration levels. Like pump 1 01 , pump 203 is controlled by computer controller 29, as above described, so as to inject an amount of liquid agent injected into vaporizer 203 in a given time to result in the desired or predetermined concentration level. Of course, the computer controller 29 may be operated in accord with a predetermined program (such as above described and such as shown in Fig. 23), which may be monitored or controlled by an anesthesiologist so as to maintain a predetermined or otherwise desired concentration level of anesthesia supplied to the patient.

[0075] As shown best in Figs. 18 - 20, pump 203 comprises a C- shaped mounting bracket 275 having an upper end or jaw 275a and a lower jaw 275b. Upper jaw 275a is mounted to the underside of plate 21 1 . Bracket 275 mounts a pair of pump cylinders, as generally indicated at 277a, 277b. Each of the pump cylinders includes a cylinder tube 279a, 279b, each having an outlet nipple 281 a, 281 b that is sealingly connected to a respective port 241 a, 241 b in lower plate 21 1 . The cylinder tubes are mounted in mounting holes 283a, 283b in the lower jaw 275b of bracket 275 and extend downwardly therefrom, and each cylinder tube has a respective cylinder bore 285a, 285b therein. However, as shown in Fig. 22, nipples 281 a, 281 b may be sealingly mounted directly to ports 241 a, 241 b in plate 21 1 such that the C-shaped mounting bracket 275 is not required. Each cylinder bore 285a, 285b has a respective piston 287a, 287b sealably, slidable in axial direction within each cylinder bore. These pistons are axially driven (reciprocated) in their respective cylinder bores by means of a drive or transmission, as generally indicated at 289, which is generally similar in construction and operation to drive T depicted in Figs. 9 - 14. Each piston is carried on the end of a threaded jack shaft 291 a, 291 b and the jack shafts are journalled by a respective bearings 293a, 293b received in a bearing a block 295. Each jack shaft 291 a, 291 b is threadably received in a threaded center opening in its respective drive gear 297a, 297b and is held against rotation by pins (not shown in Figs. 18 - 21 , but similar to pins 123a, 123b heretofore described) that move axially in a slot in an anti-rotation member 298 (as shown in Fig. 19) so that upon gears 297a, 297b being driven by a pinion 299, the jack shafts move axially in opposite directions relative to gears 297a, 297b. The pinion 299 is driven by a reversible motor 301 , preferably a stepper motor similar to motor 1 15, or other type of motor that may be energized to move a specified amount in response to commands or signals from the computer control system 29.

[0076] Motor 301 is shown in Fig.19 to be mounted on a bracket 303. It will be appreciated that because gears 297a, 297b are in mesh with one another the gears rotate in opposite directions such that the pistons 287a, 287b move axially in opposite direction upon energization of motor 301 . Thus, as piston 287a advances toward the proximate end of its cylinder 277a adjacent plate 21 1 , piston 287b retracts toward the distal end of its cylinder 277b. Each of the pistons is axially movable within its cylinder bore 285a, 285b through an axial stroke of predetermined length between a fully advanced position, in which the piston is proximate the end of its cylinder toward head block assembly 207, and a fully retracted position. It will be appreciated that with one of the pistons in its fully advanced position, the other piston is in its fully retracted position. Upon the computer control system 29 effecting the operation of stepper motor 301 to operate one step, one of the pistons will pump a micro-quantity of liquid agent from within its cylinder bore into its respective passage 241 , 241 b toward vaporizer 203 via passage 247, and the other piston substantially simultaneously draws a similar micro-quantity of liquid agent into its cylinder bore for each step of the motor.

[0077] It will be further understood that when one of the pistons reaches its fully advanced position, the direction of operation of motor 301 may be reversed by computer controller 29, which, in turn, will reverse the direction of axial travel of the pistons 287a, 287b in their respective cylinder bores. It will be further understood that upon reversal of motor 301 , there may be some "hysteresis" or lost motion in pump 205 before the one piston that was in its fully retracted position advances or moves from its fully retracted position and before that piston will inject a desired micro-quantity of liquid into vaporizer 203 upon each step of motor 301 . However, the computer control system 29 is programmed to accommodate such hysteresis by initially rapidly advancing the now advancing piston through a predetermined number of steps (which will depend on the design and dimensions of pump 205) to insure that the piston will pump a desired micro-quantity of liquid agent upon each subsequent actuation or step of motor 301 .

[0078] It will be further appreciated that because mass flow/temperature sensors 259 and 261 in vaporizer 203 (as hereinafter described and as shown in Fig. 21 ) continuously monitor the mass flow and preferably the temperature of the carrier gas moving through the flow path 253 of vaporizer 203 such that the concentration level of the carrier gas/agent delivered to the patient may be determined. If such initial advancement of a piston through such a predetermined number of steps to accommodate such hysteresis injects too much liquid agent into the vaporizer such that the concentration level momentarily exceeds a predetermined level, the control system 29 will sense that too much agent has been injected and will momentarily stop the dispensing of additional agent into the flow path while the carrier gas continues to flow until the concentration level returns to its a desired concentration level. It will also be appreciated that the quantity of liquid agent delivered to the vaporizer upon such correction for the hysteresis is sufficiently small such that the concentration level will only be marginally above its desired concentration level for a very short time such that the time that the concentration level is momentarily above its predetermined level will not harm the patient. Still further, those skilled in the art will understand that the hysteresis for each pump 205 must be calibrated and the results loaded into the calibration table shown in Fig, 23. Also, the hysteresis characteristics may change over the service life of pump 205 such that the pump should be periodically re-calibrated. [0079] Referring now to Fig. 21 , vaporizer 203 is shown to comprise a vaporizer body 251 having a serpentine flowpath 253 therethrough. Flowpath 253 has a carrier gas inlet 255 and a carrier gas/vaporized agent outlet 257. Inlet 255 and outlet 257 are each equipped with sensors 259 and 261 , respectively, where these sensors are similar to sensors 23 and 25 described above. Vaporizer body 251 is preferably of a suitable heat sink material, such as aluminum or the like, and has a cover 263 overlying and enclosing flowpath 253. As indicated at 265, a vaporizer chamber is included in flowpath 253. A passage 267 provides communication with passageway 247 in head block assembly 207 so that micro-quantities of liquid agent from pump 205 may be dispensed into vaporizer chamber 265. It will be understood that because vaporizer body 251 is made of a suitable heat sink material, the vaporizer body will have sufficient heat capacity to vaporize the liquid agent within flowpath 253 without the need for providing auxiliary heat to vaporize the liquid agent.

[0080] Referring now to Fig. 22, details regarding check valves 249a, 249b are shown. It will be understood that check valves 239a, 239b and 249a, 249b are of similar construction and operation such that only check valves 249a, 249b and their operation need be described in detail. Each check valve includes an O-ring seal 305, which serves as a valve seat, installed on a shoulder of its respective port 245a, 245b in the upper portion of intermediate plate 213. A sealing member or disk 307 is in sealing engagement with the upper surface of its respective O-ring seat 305. The O-ring seat 305 and the sealing member 307 are preferably of a suitable elastomeric material, such as an EPDM synthetic rubber of the type described above in regard to gaskets 217 and 219. A compression coil spring 309 is installed in blind bores 31 1 in the bottom face of upper plate 215. Each coil spring biases its respective sealing member 307 into sealing engagement with its respective O-ring seat 305 for blocking the flow of liquid through the valve. It will be appreciated that the biasing force that spring 309 exerts on its sealing member 307 maintains the sealing member in sealing relation with its respective O-ring seat 305. However, the force exerted by spring 309 is sufficiently low that upon an increase in pressure being applied to the face of the sealing member 307 on the side opposite the spring, the spring will compress thus allowing sealing member 307 to move clear of its O-ring seat thus allowing a micro-quantity of liquid to flow through the valve and to flow into a respective passage 245a, 245b of V-shaped slot 245 in gasket 219 for purposes as previously described. As soon as this pressure decreases, the spring will close the valve. Of course, if the pressure on the face of the sealing member 307 on the side opposite O-ring 305 is increased, the spring and the force exerted on the sealing member will block the flow of liquid through the valve.

[0081] As used in this disclosure, the term "micro-quantity" of liquid agent means a small quantity of liquid agent that is injected or dispensed into the vaporization chamber 1 1 upon each step or actuation of an anesthesia pump, such as pumps 33, 101 or 205, is a sufficiently small such that that multiple "micro-quantities" are needed in a suitable increment of time (e.g., 1 or 2 seconds) so that the concentration level delivered to the patient, even at low concentration levels, may be established and maintained by repeatedly actuating the pump, and yet such that such micro-quantities are sufficiently large such that the pump may establish and maintain the highest desired or predetermined concentration level at maximum flow rates without requiring the pump to run continuously so that control over the concentration level may be maintained. By way of one specific example, referring to pump 103, as shown in Figs. 9 - 1 6, if the diameter of cylinders 1 25a, 1 25b is 14.6 mm., and if the pitch of the threads on jack screws 1 19a, 1 1 9b is 1 .27 mm./revolution, one revolution of a jack screw 1 19a, 1 19b will displace about 212.76 mm³. If stepper motor 1 15 motor has 512 steps/revolution, and if the pitch diameter of the pinion 1 17 is one half the pitch diameter of gears 1 13a, 1 13b, there would be 1024 steps of pinion 1 1 7 for each revolution of gears 1 1 3a, 1 13b, such that one step of the motor would result in the injection of .066488 microliters of liquid anesthesia agent injected via needle 137 onto the vaporization plate 21 in vaporization chamber 1 1 so as to be substantially instantaneously vaporized.

[0082] Another example of a "micro-quantity" of liquid agent, and how the micro-pumps 33, 1 01 and 301 are operated to control the concentration level of the agent in the carrier gas stream supplied to a patient to, for example, provide a range of desired or predetermined concentration levels ranging between about a 0.5% concentration of the anesthesia agent in 0.25 liters/minute of carrier gas flow (e.g., O²) and a 5% concentration of the anesthesia agent in 8 liters/minute of carrier gas flow. Such a range of concentration levels would imply that the flow rate of the liquid agent to the vaporizer would have a flowrate range between about 0.0075 ml/minute and about 2.4 ml/minute. In order to achieve such a predetermined range of minimum and maximum flow rates of agent to the vaporizer by repeatedly actuating injecting micro-quantities of the agent into the vaporizer, the micro-quantity of agent dispensed upon each actuation of the solenoid 37 in regard to micro-pump 33 (or upon each actuation of stepper motor 1 1 5 for micro-pump 101 or stepper motor 301 for micro-pump 201 , as hereinafter described) must allow a sufficient number of steps in a time interval of several seconds such that the instantaneous peaks and valleys of concentration levels caused by the nearly instantaneous vaporization of discrete micro-quantities of liquid agent are smoothed. For example, over a time interval of 1 minute, if a micro-quantity of agent of about 0.000064 ml is dispensed for each step or actuation of the micro-pump, and if the pump 33, 101 or 301 is actuated at a rate of about 2 steps/second, the above-noted minimum flow rate of about 0.0075 ml/minute would be achieved. Likewise, in order to achieve the maximum agent flow rate of about 2.4 ml/minute, pump 33, 101 or 301 would be operated at about 601 steps/second, which actuation rates are well within the operating range of such pumps. It will be further understood that the amount of a micro- quantity of agent dispensed upon each actuation of pump 33, 101 or 301 is dependent upon the dimensions of the pump. Those skilled in the art will understand that the desirable volume of a micro-quantity of another micro- pump in accord with the present disclosure having different dimensions may be different. However, based on the above description, one skilled in the art will be able to readily determine the volume of a micro-quantity for such other micro-pump, and the number of cycles or steps in a given time to achieve another range of concentration levels.

[0083] As can be recognized by those skilled in the art, such small volumes discharged or dispensed by such a check valve may be difficult to measure or otherwise determine for each actuation of pumps 33, 101 or 205. One way to determine the average volume of liquid dispensed/cycle of the pump is through the use of a suitable gas analyzer that employs an IR absorption method. This is preferably done during calibration of the system.

[0084] It will be appreciated that in place of the above-described pump controlled and actuated by computer control system 29, other types of positive displacement pumps or variable orifices can be used to control the amount of liquid agent delivered to the vaporization chamber 1 1 .

[0085] Computer controller 29 is preferably a proportional-integral- derivative (PID) controller well known to those skilled in the art. As shown in Fig. 23, computer controller 29 continuously calculates an "error value" as the difference between the measured concentration level and a desired concentration level, as set either by control 51 , or by a pre-established concentration level.

[0086] Those skilled in the art will recognize that the concentration of the agent in the carrier gas stream exiting the flow path 5 may also be determined and controlled in accord with the system and method of the present disclosure by using two vane mass flow sensors, one located upstream of vaporization chamber 1 1 and the other downstream from the chamber. Still further, it would also be possible to determine and control the concentration using one vane mass flow sensor on the inlet side and a temperature sensor on the outlet side of the vaporization chamber. However, the redundancy of the system having both a temperature sensor and a mass flow sensor on the inlet side of the flow path and both a temperature sensor and a mass flow sensor on the outlet side of the flow path is preferred.

[0087] In accord with a preferred method of the present disclosure for controlling vaporization of the liquid anesthesia agent it is only necessary to determine the difference of mass flow rate of the carrier gas flowing through the inlet 7 and the mass flow rate of the carrier gas and the vaporized anesthesia agent flowing through the outlet 9 of flow path 5 to determine the concentration of the anesthesia agent delivered to the patient. Further in accord with the preferred method, if the mass flow of the carrier gas flowing into the vaporization chamber 1 1 is known and if the temperature change of the carrier gas along with the anesthesia agent vaporized in the chamber is determined, this data may be used by the computer control system 29 to control and monitor the concentration of the agent in the gas stream delivered to the patient. These two different methods of determining the concentration level are a redundant check of the concentration level of the anesthesia delivered to the patient.

[0088] The above-described method of controlling the concentration level of the carrier gas and the anesthesia agent carried thereby supplied to the patient have been demonstrated with different anesthesia agents at flow level ranges normally employed in surgeries. The parameters for these tests are easily measured on the scales involved. The original discussion of temperature change is reproduced below. This is a continuous flow consideration, but it can be approached from a fixed volume analysis. For example, if it is assumed that 2 liters/minute of 0₂ is flowing through the flow path 5 at STP, then in 1 minute we have two liters of 0₂ contained in hypothetical perfectly insulated container of a known fixed volume. Then, using the ideal gas law equation (PV=nRT) and recognizing that the molar mass of 0₂ = 32 , a mass flow rate of about 0.089 moles or 2.855 grams of 0₂/minute can be calculated by the computer controller 29. If it is desired to establish a 5% concentration of Isoflurane, (the molecular weight of Isoflurane is 184.5 g/mole), 0.05 X 2.855 = 0.142 grams of liquid Isoflurane would need to be at the same temperature would need to be introduced or dispensed into this last- mentioned container (or 0.142 X 184.5 = 0.00077 mole of Isoflurane). The liquid Isoflurane will totally vaporize due to its lower partial pressure and the resulting gas mixture will have cooled down. So then the resulting temperature of the gas mixture in the theoretical container must be determined. The partial pressure for 0₂ is 160 mm. The partial pressure for Isoflurane is 240 mm. The latent heat of vaporization Isoflurane at 20⁵ C, is 41 cal./gm. 1 calorie is 4.184 joules such that 41 cal/gm X 4.184joule/cal. X .142gm = 24.359 joules. Since the heat capacity of 0₂ (constant volume) is about 0.021 1 kJ /mole/K and since we have 0.089 moles of 0₂, the actual heat capacity of the volume can be calculated to be 0.021 1 kJ/m X .089 m = .001878 kj IK or 1 .878j/K. Thus, the temperature in the theoretical ideal container would lower by 24.359/1 .878 or 1 2.97 ⁵K or 23.344 ⁵F.

[0089] In operation, with cylinder bores 285a, 285b and with all passages in head block assembly 209 filled with liquid agent, with piston 287a advancing and with piston 287b retracting, upon computer control system 29 initiating operation of pump 207 to inject a micro-quantity of liquid agent into the vaporization chamber 265 of vaporizer 203, stepper motor 301 is actuated to advance one step. Assuming that the dimensions and gear ratios of pump 207 are the same as for pump 101 , a micro- quantity of liquid agent will be injected or dispensed into the vaporizer 207 upon each step of motor 301 . More specifically, upon stepper motor 301 being commanded by computer control 29 to operate one step, because the pitch diameter of pinion 299 is one-half the pitch diameter of gears 297a, 297b and because the stepper motor has 51 2 steps/revolution, the pinion rotates through an angle corresponding to a step of motor 301 (e.g., 1 /51 2 of a revolution), which in turn drives gears 297a, 297b through 1 /1024 of a revolution. The rotating gear 297a advances piston 287a and the rotating gear 297b simultaneously retracts piston 287b in their respective cylinders. The advancement of piston 287a one step or increment upon one step of motor 301 dispenses a micro- quantity of liquid agent from cylinder 277a into port 241 a, which increases the pressure in passageway 231 a and opens valve 249a and closes valve 249b. As valve 249a opens, a micro-quantity of liquid agent is communicated to passage 231 a, which in turn allows a micro-quantity of liquid to be directed to passageway 247, which in turn delivers a micro- quantity of liquid agent into vaporizer chamber 265 via passage 267. As will be appreciated, as piston 287b retracts, a corresponding volume of liquid agent will be drawn into cylinder 277b. Of course, upon the reversal of the direction of operation of motor 301 , after the above-discussed "hysteresis" has been accommodated, advancement of piston 287b by motor 310 will dispense similar micro-quantities of liquid agent into the vaporizer 209 and retraction of piston 287a draw liquid agent into cylinder 277a.

[0090] As described above in regard to pump 101 , the volume of a micro-quantity of liquid dispensed by either pump 1 01 or pump 205 may vary greatly, depending on number of steps of the stepper motors 1 15 or 301 used, the pitch diameters of the pinions 1 1 7, 299 and of the gears 125a, 125b or 297a, 297b, and the internal diameters of cylinders 125a, 125b or 279a, 279b. However, what is important with the vaporizer of the present disclosure is the amount of liquid dispensed into the vaporizer in a given length of time and the volume of carrier gas flowing through the vaporizer. One skilled in the art would recognize that the amount of liquid injected into the vaporizer upon each step of motor 1 15 or 301 should not be sufficiently large so as drastically increase the concentration level of the agent in the carrier gas such that an undesirably high concentration is delivered to the patient, and that the micro-quantity should not be so small that the stepper motors must operate continuously because if they do, the computer control system 29 will not effectively be able to control or modulate the concentration level. It has been found that micro-quantities of about 0.000064 ml/step of the stepper motors 1 15 or 301 allows the computer control system to control the concentration level to be within a desired predetermined range when using typical anesthesia agents, such as SeveFlurane, IsoFlurane, or Halothane.

[0091] It will be understood that in this disclosure and in the claims when it is described that the predetermined concentration level of the anesthesia agent is delivered to a patient that there need not be a patient connected to the system of the present disclosure, but rather this is merely a term that indicates the outlet concentration level of the agent in the carrier gas downstream of the vaporizer of the present disclosure.

[0092] As various changes could be made in the above constructions and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. Apparatus for vaporizing a liquid anesthesia agent in a stream of a carrier gas for delivery to a patient such that said apparatus automatically maintains at a predetermined concentration level of the anesthesia agent relative to the carrier gas, said apparatus comprising a flow path having an inlet and an outlet with a vaporization chamber therebetween, said flow path being configured to have a steam of a carrier gas flowing therethrough and to be connected to a supply of a liquid anesthesia agent, and means for modulating the dispensing of said liquid anesthesia agent into said vaporization chamber for vaporization of said liquid anesthesia agent within said vaporization chamber, a first sensor located in said flow path upstream from said vaporization chamber, a second sensor in said flow path downstream from said vaporization chamber, said modulating means comprising an actuator under the control of a computer control system, said computer control system receiving data from said first sensor related to the condition of said carrier gas upstream of said vaporization chamber and receiving data from said second sensor related to the condition of said carrier gas and of said vaporized anesthesia agent downstream from said vaporization chamber, in response to said sensors said computer control system determines the concentration of said vaporized anesthesia agent in said flow path downstream of said vaporization chamber to be delivered to the patient and to automatically increase or decrease the rate at which liquid anesthesia agent is delivered to vaporization chamber so as to maintain the predetermined concentration level of said anesthesia to be delivered to said patient.

2. Apparatus for vaporizing a liquid anesthesia agent in a stream of a carrier gas for delivery to a patient such that said apparatus automatically establishes, monitors, and maintains a desired concentration level of the anesthesia agent relative to the carrier gas at a desired concentration level, said apparatus comprising a flow path having an inlet and an outlet with a vaporization chamber therebetween, said flow path being configured to have a steam of a carrier gas flowing therethrough and to receive liquid anesthesia agent from a supply of a liquid anesthesia agent, and a pump for dispensing small quantities of said liquid anesthesia agent into said vaporization chamber for vaporization of said anesthesia agent, a first sensor located within an inlet portion of said flow path upstream from said vaporization chamber, a second sensor downstream from said vaporization chamber, a computer control system receiving data from said first sensor related to the mass flow rate of said carrier gas and receiving data from said second sensor related to the condition of said carrier gas and of said vaporized anesthesia agent downstream from said vaporization chamber, said computer control system being configured to calculate the concentration of said vaporized anesthesia agent to be delivered to the patient and to automatically increase or decrease the rate at which liquid anesthesia agent is dispensed by said pump into said vaporization chamber so as to maintain the concentration level to be delivered to said patient at a predetermined level.

3. Apparatus as set forth in claim 2 wherein said first and second sensors determines both the temperature and the mass flow of the gas stream flowing therepast.

4. Apparatus as set forth in claim 2 wherein said pump dispenses a plurality of micro-quantities of liquid agent into the vaporization chamber in a predetermined time so as to establish, modulate and maintain said concentration level at said predetermined level.

5. A pump for supplying small quantities of a liquid anesthesia agent to an anesthesia vaporizer under the control of a computer control system so that the concentration of vaporized anesthesia agent in a carrier gas stream supplied to a patient may be controlled to be with in a predetermined range of concentration levels, said pump comprising a pump body having at least one cylinder, a piston movable within said cylinder, and an actuator for moving said piston in discrete steps, said pump being configured to be connected to a supply of liquid anesthesia agent, an agent outlet from said supply of liquid agent to said cylinder, said agent outlet having a one-way check valve associated therewith for allowing liquid agent from said supply to be delivered to said cylinder but preventing the back flow of liquid agent from said cylinder to said supply, said cylinder having an outlet passageway for the injection of liquid agent into said vaporizer upon actuation of said pump, said outlet passageway having a second one-way check valve associated therewith allowing a small quantity of liquid agent to flow toward said vaporizer upon each actuation of said pump but preventing the back flow of liquid agent from said outlet passageway said pump, and a drive operable in response to said computer control system moving said piston within its respective cylinder so as to inject said small quantity of liquid anesthesia agent into said vaporizer as determined by said computer control system so as to establish and to maintain a predetermined concentration level of the vaporized agent relative to the carrier gas delivered to the patient, said drive being further operable to retract said piston so as to draw a small quantity of liquid agent from said supply into said second cylinder.

6. A pump for supplying micro-quantities of a liquid anesthesia agent to an anesthesia vaporizer during a time interval under the control of a computer control system so that the concentration of vaporized anesthesia agent in a carrier gas stream supplied to a patient may be established and controlled to be at a predetermined concentration level, said computer control system discretely actuating said pump to deliver a micro-quantity of said liquid agent to said vaporizer upon each actuation of said pump, said pump comprising a pair of cylinders configured to be connected to a supply of liquid anesthesia agent, a flowpath from said supply of liquid agent to each said cylinder, said supply flowpath for each said cylinder having a first one-way check valve associated therewith for allowing liquid agent to flow from said supply to its respective said cylinder but preventing the back flow of liquid agent from said cylinder to said supply, each of said cylinders having an outlet passageway leading from said cylinder for the injection of a micro-quantity of liquid agent into said vaporizer, each said outlet passageways having a second one-way check valve associated therewith allowing a micro-quantity of liquid agent to flow toward said vaporizer but preventing the back flow of liquid agent from said outlet passageway its respective cylinder, each of said cylinders having a piston disposed therein in slidable, sealable engagement with its respective cylinder, and a drive operable in response to said computer control system moving one of said pistons within its respective cylinder so as to inject a micro- quantity of liquid anesthesia agent into said vaporizer, said drive simultaneously retracting the other piston so as to draw a micro-quantity of liquid agent from said supply into said second cylinder.

7. A pump as set forth in Claim 6 wherein said drive is reversible so that said piston in said second cylinder may be operated to inject liquid agent into said vaporizer while simultaneously said first piston is retracted in its respective cylinder so as to draw liquid agent into said the last-said cylinder.

8. A pump as set forth in Claim 7 wherein said drive includes a stepper motor.

9. A pump as set forth in Claim 8 wherein said drive further comprises a shaft axially disposed in each of said cylinders, each said shaft having one of said pistons associated therewith, and a transmission between said stepper motor and said shaft for effecting axial movement of said pistons in their respective cylinders for each step said motor is actuated.

10. A pump as set forth in Claim 9 wherein said transmission comprises a pair of gears, each of which is in threadable engagement with a respective one of said shafts and with said gears being in mesh with one another, said motor being connected to one of said gears so that upon energization of said motor one of said shafts is axially within its respective cylinder so as to inject a micro-quantity of liquid agent into said vaporizer and the other of said shafts is axially retracted within its respective cylinder so as to draw liquid agent into its respective cylinder upon each step of said motor.

11. A pump as set forth in Claim 10 wherein said stepper motor has a pinion driven thereby with said pinion being in mesh with one of said gears.

12. A method of vaporizing a liquid anesthesia agent and controlling the concentration level of the vaporized agent in a carrier gas stream delivered to a patient to be at a predetermined concentration level, said method utilizing a vaporizer having a flow path through which a stream of a suitable carrier gas flows, said flow path having an inlet and an outlet with a vaporization chamber therebetween, a supply of said liquid agent, a selectively operable pump for dispensing a quantity of said liquid agent into said vaporization chamber, a computer control system controlling operation of said pump, said method comprising the steps of: a. Determining the condition of said carrier gas in said inlet portion of said flow path;

b. Determining the condition of said carrier gas and said vaporized agent in said outlet portion of said flow path;

c. Determining whether the concentration level of said vaporized agent in said carrier gas to be delivered to the patient; and d. Operating said computer control system so as to vary the amount of liquid agent dispensed into said vaporization chamber in a given time so as to result in the predetermined concentration level being supplied to the patient.

13. The method of Claim 12 wherein step "a" further includes determining the mass flow of the carrier gas in the inlet portion of the flow path.

14. The method of Claim 12 further comprising said computer control system effecting operation of said pump in discrete steps to inject a micro-quantity of liquid agent into said vaporization chamber upon each actuation step of said pump such that in a given time, the amount of liquid agent vaporized in said vaporization chamber results in the predetermined concentration level of said anesthesia agent being delivered to said patient.