CA2326822A1 - Anesthetic breathing circuit - Google Patents

Abstract

The invention is directed to an improved anesthesia system comprises:
i) an essentially circular breathing circuit having an inspiratory limb for introducing gases to a patient and an expiratory limb for receiving patient exhaled gases the inspiratory and expiratory limbs being connected to a patient breathing device, means for introducing fresh anesthetic gas from a vaporizer directly into the inspiratory limb and bypassing a C02 absorption canister of an anesthetic machine and downstream of an inspiratory check valve, ii) the improvement comprising positioning the means for introducing fresh anesthetic gas in the inspiratory limb upstream of the patient's breathing device a sufficient distance to develop in the inspiratory limb a fresh anesthetic gas accumulator of sufficient volume to induce a patient in one or two breaths.

Description

ANESTHETIC BREATHING CIRCUIT
Field of the Invention The present invention relates to a novel anesthetic delivery system s which is particularly useful for the delivery of sevoflurane but which may also be applied to other inhalant anesthetics. More particularly, it relates to a method of inducing a patient by delivering fresh anesthetic gas to the inspiratory limb of a circle breathing circuit.
Background of the Invention 1 o Anesthetics which can be inhaled are commonly used in a variety of operating room scenarios. They are particularly useful in situations where the patient has a fear of needles. The early inhalable anesthetics were typically volatile substances with relatively low boiling points and high vapor pressures. Ether was one of the first inhalant anesthetics to be used widely.
A
1 s major impediment to the widespread use of inhalation inductions has been the pungency of the available volatile anesthetics. Halogenated isopropyl derivatives of ether have become increasingly popular due to their excellent anesthetic properties and relatively low pungency. Of these, the fluorinated isopropyl ethers are the most popular. Sevoflurane (fluoromethyl-1,1,1,3,3,3-2 o hexafluro-2-propyl ether)which is marketed under the trademark, ULTANE, by Abbott Laboratories is one of the most widely used inhalant anesthetics.
Sevoflurane has a relatively low blood-gas solubility and a relative absence of pungency that makes inhalation induction feasible. Furthermore, sevoflurane is a volatile liquid that is nonflammable in air at ambient temperatures and has 2 5 a low flammability limit in oxygen making it safe to use. United States Patent 3,683,092 to Regan et al. discloses the use of sevoflurane as an anesthetic and Canadian Patent Application No. 2,155,002 discloses deuterated sevoflurane as an inhalant anesthetic with fewer side effects. Other inhalant anesthetics used in the medical and/or veterinary fields include halothane, desflurane, 3 o enflurane and isoflurane.

Sevoflurane and other inhalant anesthetics are delivered in liquid form to an anesthetic vaporizer which disperses the anesthetic with other gases.
Typical anesthetic vaporizer systems are described in Canadian Patent Application No. 2,186,891 and United States Patent No. 5072726.
s Ventilators and anesthetic systems are typically equipped with a number of safety features. United States Patent No. 5,694,924 describes an anesthetic system that has an inspiratory line, an expiratory line and a connecting line, which together form a closed system. Check valves are arranged in the connecting line to control the direction of gas flow. The 1 o system further comprises two gas reservoirs that are functionally interconnected so that an increase in volume of one results in a corresponding reduction in the volume of the other.
United States Patent No. 4,989,597 describes a gas switching unit or exchanger device in the anesthesia circuit. This reference also describes as 1 s prior art the injection of fresh anesthetic gas very close to the patient's mask.
United States Patent No. 5,619,986 discloses a reinhalation system for an anesthetic apparatus that includes inhalation and exhalation branches connected to each other. The object of this patent is to provide an apparatus that enables automatic adjustment to the desired concentration of anesthetic 2 o gas flowing throughout the system.
United States Patent No.5,044,361 describes the injection of fresh anesthetic gas very close to the patient mask and considerably downstream of an anesthetic gas absorber and desorber of the patient circuit.
While various improvements have been made to anesthesia systems, 2 s especially those in which exhaled gases are recycled, problems still exist. A
major problem is that the incoming fresh anesthetic gas is mixed with other gases and therefore diluted before it reaches the patient. In addition, high flow rates are required to prime the system so that there is a consistent concentration of anesthetic gas throughout the system. The present invention 3 o addresses these problems and provides a novel system that includes methods and apparatus for more efficient and rapid induction of patients with inhaled anesthetics.
Summarx of the Invention The present invention provides for a method and apparatus, which s enhances the efficiency of inhalant anesthetic delivery.
An object of one aspect of the present invention is to provide a means for delivering sevoflurane, or other inhalant anesthetics, to a patient in a manner such that the patient is anesthetized rapidly, i.e within a few breaths.
Another object of an aspect of the invention is to reduce costs by 1 o providing a breathing apparatus system that does not require priming of the entire circuit.
According to one aspect of the invention, there is provided, in an anesthesia system for providing anesthesia to a patient which comprises:
an essentially circular breathing circuit having an inspiratory 1 s limb for introducing gases to a patient and an expiratory limb for receiving patient exhaled gases said inspiratory and expiratory limbs being connected to a patient breathing device, means for introducing fresh anesthetic gas from a vaporizer directly into said inspiratory limb and bypassing a C02 absorption canister of an anesthetic machine and downstream of an inspiratory check 2 0 valve, the improvement comprising positioning said means for introducing fresh anesthetic gas in said inspiratory limb upstream of said patient's breathing device a sufficient distance to develop in said inspiratory limb a fresh anesthetic gas accumulator of sufficient volume to induce a 2 s patient in one or two breaths.
According to another aspect of the invention, there is provided a method of delivering anesthetic gas to a patient comprising the steps of:
i) supplying anesthetic gas to the inspiratory limb downstream of an inspiratory check valve and upstream of a patient mask;

ii) accumulating the gas in the inspiratory limb between the check valve and the mask; and iii) applying the mask to a patient and instructing the patient to breathe.
s Brief Descr.~tion of the Drawings Preferred embodiments of the invention are described below, reference being made to the drawings, wherein:
Figure la is a schematic of a conventional prior art circle breathing system;
1 o Figure lb is a schematic of a modified circle breathing system of the present invention;
Figure 2 is a prior art illustration of a typical prior art anesthesia delivery system;
Figure 3 is an enlarged view of the gas flows in a typical prior art s s anesthesia system;
Figure 4 is a schematic illustration of the anesthesia delivery system of the present invention;
Figures Sa and SB are illustrations comparing fresh gas flow in known systems and the system of the present invention; and 2 o Figure 6 is an exploded view of the connecting components of the present invention.
The present invention provides a system for the delivery of fresh anesthetic gas to a patient connected to a circle circuit anesthetic delivery 2 5 system. Throughout this specification the term "fresh gas" is used to refer to gas coming directly from an anesthetic vaporizer.
As shown in Figure la, the basic components of a conventional, prior art type of circle breathing circuit 10 are an inspiratory limb 12 and an expiratory limb 14, each with a unidirectional valve 16, 18, respectively. The 3 o circuit also includes a reservoir bag or counterlung 20 moving reciprocally with the patient's lungs. The principles of a circle breathing system can be found in Anesthesia Equipment: Principles and Applications, Mosby 1993 p100-101. The counterlung 20 may be connected to the system via a T-piece 21 and the patient is usually connected via a Y-piece 25. The positioning of s the valves 16, 18 within the limbs is not necessarily fixed. Additional components usually found in a circle circuit include a carbon dioxide absorber 28, a fresh gas inflow site 30 and an adjustable pressure limiting valve 32 for venting excess gas. The carbon dioxide absorber may be located in either the inspiratory limb or in the expiratory limb. The fresh anesthetic gas inflow is 1 o traditionally located in the inspiratory limb upstream from the carbon dioxide absorber and the pop-off valve is usually downstream from the expiratory valve near the bag.
It is apparent that, in a typical system such as that illustrated in Figure la, the fresh gas which enters the inspiratory limb at 30 will be mixed and 1 s diluted with gas returning from the expiratory limb 14 through the C02 absorber 28. Thus, there is a need for a large volume of fresh anesthetic gas in order to prime the entire circuit to a sufficient extent that the patient receives an inducing amount of the anesthetic.
The present invention improves upon the principles of a circle system 2 o to deliver an anesthetic such as sevoflurane in an efficient, cost-effective and patient friendly manner. As can be seen in simplified schematic form in Figure lb, in the present invention a fresh gas inlet 31 is located in the inspiratory limb downstream of the inspiratory check valve 16, but a reasonable distance upstream of the patient connector Y-piece 25. In a 2 s preferred embodiment, the fresh gas inlet is positioned at a distance of from about 60 to about 80 inches upstream from the patient connector, most preferably at a distance of 72 inches or 180 cm.
. This placement of the fresh gas inlet 31 has the surprising advantage that the fresh gas from the vaporizer can be provided to the patient without 3 o being diluted by recirculated gases. The introduction of anesthetic gas through the fresh gas inlet 31 is believed to cause back pressure on the inspiratory check valve 16 which prevents backflow of the fresh gas into the circle circuit. The fresh gas inlet is positioned at a sufficient distance from the patient connector 25 such that fresh gas accumulates in this portion of the inspiratory limb between the inlet 31 and the patient connector 25 to provide a reservoir of anesthetic gas is readily available for inhalation by the patient.
The amount of anesthetic gas required to fill the accumulator portion of the inspiratory limb is relatively small compared with the amounts required to prime the entire circuit. When the patient breathes in they receive a sufficient 1 o concentration of fresh anesthetic gas from the accumulator portion of the limb 12 to be induced within a few breaths.
While Figures lA and 1B illustrates the basic principles of a circle breathing system in simplified form, Figures 2 and 3 illustrate a typical anesthesia system such as those commonly used in operating rooms. Figure 2 schematically illustrates an anesthesia system 38 connected to a patient. In this system, the anesthetic is dispensed in liquid form to a vaporizer 40 that mixes the anesthetic with oxygen and nitrous oxide. The gaseous mixture from the vaporizer is directed to the common gas outlet 42 where it enters the fresh gas conduit 44. The fresh gas conduit delivers the gas to the inlet port 2 0 45 of the inhalation chamber 54 where it is mixed with exhaled gases returning from the expiratory limb 48 through the carbon dioxide absorber 46. The mixed gases then enter the inspiratory limb 52 for delivery to the patient.
An enlarged view of the gas flow within the carbon dioxide absorber 2 5 46 is shown in Figure 3. Fresh gas from the anesthesia system enters the common gas inlet 45 via the fresh gas conduit (not shown) then flows through the inhalation chamber 54 (also shown in Figure 2) where it is mixed with gases from the carbon dioxide absorber cannister. These mixed gases flow through the inspiratory valve 56 and out the inhalation port 58 to the 3 o inspiratory limb 52 of the patient breathing device. Upon exhalation, gas returns from the expiratory limb 48 through the expiratory valve 60 and into the exhalation chamber 62. Gas flows from the exhalation chamber to the breathing bag 64. Upon compression of the breathing bag, excess gas is vented through the excess gas outlet 66 and the remaining volume of gas s indicated by arrows 68 enters the canister 46 and travels downward for carbon dioxide absorption. Although the system is illustrated with a breathing bag, it is clearly apparent to one skilled in the art that the device may also be connected to a respirator. Gas returning from the bottom of the canisters, indicated by arrows 70, enters the inhalation chamber 54 and joins fresh 1 o anesthetic gas incoming from the vaporizer. Thus, the fresh gas is diluted with the recirculated gases before it goes to the patient.
Furthermore, in this type of prior art circuit one must prime the circuit, i.e. the concentration of anesthetic gas must be made uniform throughout the entire circuit. This includes the inhalation chamber, the 15 breathing bag, the carbon dioxide absorber canister and the associated connectors. This requires a high volume of gas and it takes considerable time and effort to prime the circuit so that the anesthetic gas is uniform throughout as is required for delivery of a sufficient concentration of anesthetic gas to the patient for rapid loss of consciousness.
2 o Thus, while the current anesthesia systems have proved useful, a major drawback is the large volumes of gases required to prime the system in the first place. There are also continuing dilution effects on the anesthetic gases from the recirculated gases.
Previous attempts have been made to increase the efficiency of 2 s anesthetic delivery by delivering the volatile liquid anesthetic by directly injecting it into the circle system (Lowe H.J. and Ernst E.A. "History of Closed Circuit Anesthesia" . The Quantitative Practice of Anesthesia- Use of Closed Circuit, Chapter 1, pp.3-10. Williams and Wilkins, Baltimore, MD,1981). The basic equipment used in this technique is simple, readily 3 o available and inexpensive, requiring little more than a syringe. While this technique is interesting and economical, this method requires careful dosing and is not readily adaptable for use in the average anesthesiologist's practice.
It has been generally held by anesthesiologists that the way to deliver a uniform concentration of an inhalant anesthetic is to provide a uniform s concentration throughout the entire breathing circle.
The present invention challenges those assumptions and illustrates that fresh anesthetic gas can be efficiently and safely delivered to the patient without the dilution effect encountered in traditional circle breathing systems.
This is achieved by providing means to deliver fresh anesthetic gas directly 1 o into the inspiratory limb downstream of the inspiratory check valve but considerably upstream of the patient mask or connector whereby this portion of the inspiratory limb acts as an accumulator or reservoir.
Referring now to Figure 4, this figure illustrates a preferred embodiment for delivering anesthetic gas directly from the common gas outlet 15 t0 the inspiratory limb of the breathing system. The fresh gas conduit 44, which normally acts as a conduit for delivery of anesthetic gas from the fresh gas outlet 42 to the gas inlet 45, is disconnected from the outlet 42 and plugged. Preferably, a clearly visible plug 47 is used and the free end of the tubing is hung on a hook or other holding means. In a preferred embodiment 2 o the plug is bright red. In this manner, it is clearly apparent to one looking at the anesthesia machine that the conduit 44 is not connected. Rather, a fresh gas tubing 74 is connected at one end to the fresh gas outlet 42 and the other end of the tubing is connected to the fresh gas inlet arm 76 of a connector 78.
It will be clearly apparent to one skilled in the art that various types of 2 s connectors, such as, for example, an Ayre's T-connector or a Washington T-piece could be used to achieve the same result. Alternatively, the inspiratory limb could be manufactured with an integral inlet port for fresh gas.
The fresh gas enters the circuit downstream of the inspiratory check valve 56. This causes back pressure on the valve and prevents any backflow 3 0 of the fresh gas. Preferably, the gas inlet is positioned a sufficient distance from the patient such that a reservoir of fresh gas accumulates in the portion of the inspiratory limb 52 between the inlet 76 and the patient Y-connector 80 without being diluted. In a preferred embodiment there is a distance of approximately 72 inches between the gas inlet and the patient Y-connector.
s The accumulated anesthetic gas is then inhaled by the patient. Thus, this portion of the inspiratory limb acts as an accumulator and, upon inhalation, the patient receives fresh anesthetic gas from the accumulator. The fresh gas flow generally exceeds the recirculated gas flow thereby allowing a greater concentration of anesthetic to reach the patient. When the patient exhales, the 1 o fresh anesthetic gas continues to fill the inspiratory limb. This results in increased pressure in the inspiratory limb, which causes back pressure on the check valve and promotes the filling of the inhalation tubing reservoir again.
The inspiratory limb gas will be eventually diluted somewhat by recirculated gas but not as diluted as in a conventional set-up and, most importantly, only 15 after the patient has already lost conciousness. The present system has the advantage that for the first few breaths, the patient receives essentially undiluted fresh gas from the accumulator reservoir that is formed in the inspiratory limb and thus, the time of induction is significantly decreased.
This is because the concentration of anesthetic gas does not get diluted to the 2 o same degree as conventional systems. There should be a sufficient distance between the gas inlet and the patient connector such that the size of the accumulator portion of the inspiratory limb is large enough to accumulate enough anesthetic gas that the patient is induced in one or two breaths. When using an inhalation induction agent, such as Sevoflurane, a two minute or 2 s greater difference which can be achieved by using the present invention, as compared to conventional techniques, is significant.
Typically, concentrations of gases found in a circuit are dependent upon two factors. The first factor is the concentration of the anesthetic gas mixture delivered into the circuit. This is usually accomplished by setting a 3 o flow of oxygen and nitrous oxide/air via the flow controllers. The gases are 1~
mixed with the anesthetic agent in the vaporizer and this mixture is delivered to the circuit. The concentration of the anesthetic agent is adjusted using a dial on the vaporizer. The second factor is the anesthetic uptake by the patient. A state of equilibrium is ultimately established in the gas s concentration between the patient uptake and the concentration of anesthetic gas mixture delivered.
In the present invention, the placement of the anesthetic gas inlet into the inspiratory lirizb on the patient side of the inspiratory check valve has the surprising result that the inspiratory limb acts as an accumulator which can be 1 o filled with a high concentration of anesthetic in a very short, almost instantaneous, time period. This positioning of the inlet also allows the inspiratory limb to act as a reservoir that continues to supply the patient with high concentration gases upon subsequent inspirations by the patient. This delivery of high concentration gases in the initial phase promotes surprisingly 15 rapid induction using sevoflurane. Similar results would be expected using other inhalant anesthetics.
A further surprising advantage of the present invention is that the positioning of the anesthetic inlet creates a slight back pressure which keeps the inspiratory valve closed. This further impedes dilution of the anesthetic 2 o gas by the gases returning via the carbon dioxide absorber canister.
Because the valve is kept closed with back pressure, flow returned via the carbon dioxide absorber is limited and the fresh anesthetic gas flow exceeds the recirculated gas flow. In this way, the patient's initial and important first few breaths are loaded with high concentration anesthetic gas allowing for rapid 2 s loss of consciousness. This is important for patient-controlled induction (PCI) or autoinduction as well as for vital capacity induction (VCII) as will be discussed in further detail below.
Thus, the present invention has significant advantages in terms of pharmacoeconomics, patient satisfaction and ease of use for the anesthesiologist.

The improved efficiency of the anesthesia system of the present invention can easily be recognized by comparing the gas flows in Figures SA
and SB. Figure SA is representative of the known methods of delivering inhalant anesthetics. The system includes a vaporizer 120 and a counterlung s equivalent 122. Fresh gas 124 from the vaporizer and returning gases 126 from the expiratory limb 132 are mixed in the the carbon dioxide absorber 128 and then proceed into the inspiratory limb 130 of the circuit.
Figure SB, on the other hand, illustrates how the fresh gas 124 from the vaporizer 120 can bypass the inlet of the carbon dioxide absorber 128 and 1 o enter into the inspiratory limb 130 downstream of the check valve 134 through an inlet 136. This has the significant advantage that the entire system does not have to be primed resulting in more rapid onset of unconsciousness and reduction in costs due to the lower amounts of anesthetic required.
Figure 6 illustrates how this effect can be achieved by connecting 1 s conduit tubing 135 from the fresh gas outlet to an inlet 136 of a tubing connector 138. Although a Washington T-piece has been illustrated for exemplary reasons, it would be clear to one skilled in the art that various other types of connectors could be used to achieve the same result. Another inlet 140 is connected to an adapter 142 which connects to the inhalation port.
2 o The outlet port 144 of the T-piece is adapted to fit over a complementary protrusion 146 on the end 148 of the inspiratory tubing 150.
The present invention encompasses a kit for use with a standard anesthesia machine. The kit includes inspiratory tubing and expiratory tubing which terminate in a Y-connector at the patient end of the tubing as well as a 2 5 tubing connector and conduit tubing. The tubing connector is attached at the distal end of the inspiratory tubing. The tubing connector has two inlets and an outlet. One inlet is adapted to be attached to the inspiratory port of an anesthesia machine. The other inlet is adapted to be connected to one end of a conduit tubing and the other end of the conduit tubing is adapted to be 3 o attached to the fresh gas outlet of the anesthesia machine. In a preferred embodiment, the kit also includes a clearly visible plug adapted to seal off the end of the tubing which is attached to the fresh gas outlet in a conventional anesthesia set-up.
While the present invention has been illustrated with connecting parts, s it is clearly apparent to one skilled in the art that the conduit tubing, the tubing connector and the inspiratory tubing can be provided as an integral unit without departing from the spirit of the invention.
The delivery of anesthetic gas directly into the inspiratory limb in accordance with the present invention provides for several surprising to advantages over known devices and methods. There is no need to prime the entire circuit as in standard systems. This results in increased ease of use for anesthetists and time between induction and surgical start time is reduced.
The induction times using this methodology compare favorably with traditional techniques and the cost savings related to the absence of priming 1 s the circuit are significant since the inspiratory limb acts as an anesthetic gas reservoir.
Furthermore, in the case of patient controlled induction or autoinduction, the patient has increased control of a situation which is often anxiety provoking. There is also a significant decrease in total induction time 2 o and thus decreased time to onset of surgery. As well, there is a significant decrease in anesthetic induction costs when compared to currently used intravenous induction regimes or standard inhalation induction techniques.
Traditionally, autoinduction has not been widely used due to problems of cost and efficiency. The present invention addresses these issues and provides for 2 s a cost efficient, pleasant method of autoinduction.
The present invention provides for efficient inhalant anesthetic delivery by delivering the fresh gas directly into the inspiratory limb downstream of the inspiratory check valve. This has real benefits for the patient in that an effective concentration of the anesthetic accumulates in the inspiratory limb and thus can be delivered more rapidly that with traditional methods and devices. This enhances quicker onset of unconsciousness and thus less exposure to the stresses of the operating room environment. There are also benefits to the anesthesiologist in terms s of time saved and ease of patient induction and there are also significant advantages to the health care provider in terms of cost savings due to the more efficient delivery of the anesthetic gas which results in lower consumption of anesthetic.
~.xam~e_s 1 o The above disclosure generally describes the present invention. A
more complete understanding can be obtained by reference to the following specific examples. These examples are described solely for the purpose of illustration and are not intended to limit the scope of the invention. Changes in form and substitution of equivalents are contemplated as circumstances 1 s might suggest or render expedient. Although specific terms have been employed herein, such terms are intended in a descriptive sense and not for purposes of limitation.
xa_ ple 1 Vital Capacity Breath techniaue With current anesthetic systems the anesthesia circuit must be primed 2 o as described before. Of extreme importance is the lack of priming the anesthetic circuit when using this novel methodology.
For example, in a typical procedure, the anesthesia circuit is primed with 8 % sevoflurane and 75 % N20 in 02 at 8 Llmin (6:2) until the inspired limb drug concentration measures > 6 % . This typically requires three 2 s flll/empty cycles of the occluded anesthesia circuit (approximately 45 sec.) The patient is brought into the operating room after informed consent of the technique of induction. It is explained to the patient that they will be required to take a slow, deep breath and then to hold their breath. When the patient can no longer hold that breath they are instructed to exhale fully and take another slow,deep breath. They are then instructed to hold that second breath. Under normal circumstances the patient will have been induced by the end of the first or second breath.
The patient lies on the operating table and standard monitors including s ECG, blood pressure and pulse oximetry are all placed. Depending on the vein status of the patient and comfort of the anesthetist an intravenous may be placed prior to induction or after induction. The standard vital capacity breath technique is then carried out. The patient may be optionally preoxygenated for 3 minutes prior to the induction. With the novel 1 o methodology of the present invention, there is no need to prime the system.
With the mask in place, the total gas flows are adjusted to approximately 8 L/min. with nitrous oxide at 6 Llmin or 4 L/min and oxygen at 2 L/min or 4 Llmin and the sevoflurane vaporizer is adjusted to approximately 8 % of the volume. Induction will usually take place within 1-2 breaths.
1 s Once the patient has lost consciousness and if the patient has gone apneic (ceased to breathe) then the patient will be assisted with positive pressure ventilation until spontaneous ventilation has recurred. In this time period the patient may have his airway maintained either with facemask andlor oral airway, Laryngeal mask airway (LMA) or intubation of the 2 o trachea. A time interval based on clinical judgment must be present for the last two adjuncts to be placed.
After induction of the patient, the patient is prepared for surgery.
Surgery is then carried forth.
F__x_ample 2 Patient Controlled Induction or 2 s Autoinduction:
A very important distinction is required with this technique. No priming is required at all with the patient controlled or autoinduction.
The patient is brought into the operating room after informed consent of the technique of induction. It is explained to the patient that he will be 3 o required to breathe via a facemask that he will hold. The patient lies on the operating table and standard monitors including ECG, blood pressure and pulse oximetry are all placed. The patient is then given the facemask and proper fit is assured. Patients generally feel more relaxed if they can hold the mask themselves and breath normally. The induction process begins as soon s as the patient is given the mask to hold. This involves the anesthetist turning the gas flows to approximately 1 L/min each of nitrous oxide and oxygen and sevoflurane at 8 % . Slowly, as the anesthetist is beginning to look for an appropriate intravenous site, with the patient breathing the anesthetic gas mixture, the patient will become more relaxed and in a very smooth fashion 1 o become induced. This usually coincides with the final securing of the intravenous .
As the patient continues to hold the mask and becomes induced he will usually continue to hold the facemask in a tonic fashion with airway maintained while the rest of his body is flaccid. This gradually gives way 1 s once the anesthetic depth deepens.
Once the patient has lost consciousness and if the patient has gone apneic (ceased to breathe) which is much less often with this form of induction, then the patient will be assisted with positive pressure ventilation until spontaneous ventilation has recurred. In this time period the patient may 2 o have his airway maintained either with facemask andlor oral airway, Laryngeal mask airway (LMA) or intubation of the trachea. A time interval based on clinical judgment must be present for the last two adjuncts to be placed.
This type of induction has the surprising result that patients usually 2 s react to this technique with an apparent sense of relief as they are in control of their induction.
After induction of the patient, the patient is prepared for surgery.
Surgery is then carried forth Example 3 Pharmacoeconomics of the methodology.
The following examples merely indicate representative values in Canadian dollars and are not intended as a statistical analysis of numerous studies. It is apparent, however, that significant cost savings can be achieved s by using the device and methodology of the present invention. For example, the cost of autoinduction of a patient at 2 L/min. is less than one quarter (22 % ) of the cost of traditional sevoflurane induction.
Costs of using Sevoflurane l o Gas Flow(l/min~ Sevoflurane % Cost l$/miW
1 1.5 0.085 2 2 0.25 2 8 0.90 15 60 minutes of Sevoflurane at 211min and 2 % - $15 .00 60 minutes of Sevoflurane at lllmin and 1.5 % - $ 5.10 Induction costs standard methodoloQv Cost of Propofol for 200 mg vial - Ave. induction 2 0 ~ $4.00 Cost of Sevoflurane vital capacity breath with "prime"
$7.20 Methodolo~v~~f the present invention Cost of Sevoflurane vital capacity breath at 811min average 1 min 2 s ~ $3.60**
Cost of Sevoflurane autoinduction at 211min, average lmin 45 sec --$1.60**
Thus, unexpected savings can be achieved using the present methodology for either vital capacity induction or patient controlled induction or autoinduction 3 o versus the traditional prime technique, propofol IV and other standard methods. This assumes no other adjuncts to be added with propofol or to traditional sevoflurane single breath induction technique which would increase even further their costs.
Although preferred embodiments of the invention have been described s herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.

Claims (10)

1. In an anesthesia system for providing anesthesia to a patient which comprises:
i) an essentially circular breathing circuit having an inspiratory limb for introducing gases to a patient and an expiratory limb for receiving patient exhaled gases said inspiratory and expiratory limbs being connected to a patient breathing device, means for introducing fresh anesthetic gas from a vaporizer directly into said inspiratory limb and bypassing a CO2 absorption canister of an anesthetic machine and downstream of an inspiratory check valve, ii) the improvement comprising positioning said means for introducing fresh anesthetic gas in said inspiratory limb upstream of said patient's breathing device a sufficient distance to develop in said inspiratory limb a fresh anesthetic gas accumulator of sufficient volume to induce a patient in one or two breaths.

2. In the system of claim 1 wherein said means to introduce fresh anesthetic gas comprises:
i) a source of anesthetic gas;
ii)an inlet port in said inspiratory limb;
and iii)a conduit interconnecting said source of anesthetic gas and said inlet port.

3. In the system of claim 2 wherein said inlet port is positioned between 65 and 75 inches upstream of said patient breathing device.

4. In the system of claim 1 wherein the anesthetic used is sevoflurane.

5. In the system of claim 4 wherein the sevoflurane is delivered at a flow rate of about 2 L/min to about 8 L/min.

6. An anesthetic gas delivery kit comprising:
i) inspiratory tubing and expiratory tubing each terminating in a patient connector;
ii) a tubing connector having a first inlet adapted for connection to an inspiratory port on an anesthesia machine, a second inlet for introduction of fresh anesthetic gas into said tubing connector, and an outlet adapted for connection to the free end of the inspiratory tubing; and iii) conduit tubing having a first end adapted for connection to said second inlet and a second end adapted for connection to a fresh gas outlet on an anesthesia machine.

7. The kit of claim 6, wherein the inspiratory tubing and the tubing connector are integral with each other.

8. The kit of claim 6, wherein the tubing connector and the conduit tubing are integral with each other.

9. The kit of claim 6 further comprising a plug adapted to seal off tubing of the anesthetic machine that was connected to the fresh gas outlet.

10. A method of delivering anesthetic gas to a patient comprising the steps of:
i) supplying anesthetic gas to the inspiratory limb downstream of an inspiratory check valve and upstream of a patient mask;
ii) accumulating the gas in the inspiratory limb between the check valve and the mask; and iii) applying the mask to a patient and instructing the patient to breathe.