GB2268286A

GB2268286A - Synchronised intermittent infusion system

Info

Publication number: GB2268286A
Application number: GB9218529A
Authority: GB
Inventors: Simon John Caswell
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-05-06
Filing date: 1992-09-01
Publication date: 1994-01-05
Also published as: GB9218529D0; GB9209779D0

Abstract

A medical syringe driver (6) provides a slow steady rate infusion of fluid which is broken into an intermittent bolus infusion by provision of a compressible chamber (4) in the fluid pathway which is allowed to fill with fluid, being compressed intermittently under electronic control by an external piston (3). A timing pulse from a ventilator device or other appropriate source (16) is modified by a control circuit (15) so as to allow the instillation of fluid to be precisely related to the cycle of the timing device, both in time and frequency, in order to control the infusion of the fluid into the patient's respiratory system. Alternatively, a valve system allows the compression system to pump the fluid as well as dividing the flow. <IMAGE>

Description

SiNCHRON-ISED INTERMITTENT - INFUSION SYSTEM l ,is invention relates to a synchronised intermittent infusion system.

There is a frequent need in modern medical practice to infuse fluids into the body in precise amounts. Several pump devices have been produced which enable exact control of this process. Examples are roller pumps, peristaltic pumps, volumetric pumps and syringe drivers. These devices are excellent for controlling the intermittent infusion of moderate to large (20ml+) amounts or, in the case of the syringe driver, the constant infusion of small (2my+) amounts. No device has been produced which will synchronise the infusion of small amounts of fluid with the operation of an external support system or with the action of a body function such as breathing or pulse.

The introduction of intra-tracheal drug therapy has led to the need for new infusion devices to make best use of this new route of administration. The nebuliser is eommonly used to provide an aerosol suspension of a drug for administration into the respiratory system and this can be adapted for use with mechanical ventilators in intensive care situations. However, it is hard to avoid losing a proportion of the drug in the administration tubing and there are some drugs for which nebulisation is not appropriate. One such is the artificial surfactant used to treat premature babies with the condition known as respiratory distress syndrome. At present these drugs are administered manually via a syringe, the drug being driven into the lungs by the airflow from a mechanical ventilator.

I propose a new type of infusion system which will allow automatic control of the timing and size of the very small boluses of fluid infused in this manner without interfering with the ventilator or other aspects of treatment. I envisage that this pump will also be useful for instilling drugs into the respiratory system of patients with other conditions and may also be useful for controlling intermittent infusions in other situations. I call this device the "synchronised intermittent infusion system. " SYNCHRONISED INTERMITTENT INFUSION SYSTEM .ni!:-ording to the present invention there is provided a system for the intermittent infusion of fluids into body systems under the control of an external timing circuit.It comprises a reservoir of fluid instilled into the patient through a sterilised tubing system with a . compressible chamber, by the intermittent compression of which the fluid may be instilled in timed boluses, the timing being synchronised with the function of a body system or patient support system or other suitable timing cycle, using a suitable circuit to select, time and operate the chamber compression unit.

DESCRIPTION OF TYPICAL EXAMPLE A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows the operating unit including the connections to the syringe driver and the patient ventilator tubing.

Figure 2 shows the hinged lid with its recessed location channels for the tubing and flexible chamber.

Figure 3 shows, in principle, a motorised actuating device (a) using a cam, and a solenoid actuator (b).

Figure 4 shows a compressible chamber in plan (a) and elevation (b) views.

Figure 5 shows a valve operated pump which dispenses with the syringe driver, using the action of the piston to provide the pumping effect Figure 6 shows a simple circuit diagram for the timing and control circuitry to operate either a servo (a) or relay (b) output.

SYNCHRONISED INTERMITTENT INFUSION SYSTEM }?figure 7 shows the relationships of the signal timing at various stages of the control circuit as follows: Line 1- Input signal from ventilator or other timing device.

Line 2- Signal from impulse divider (output digit 0).

Line 3- Signal from delay chip (22).

Line 4- Signal from operating timer chip (24).

Line 5- Signal from servo control chip (30) (impulses shown extended in time by way of illustration).

There are 3 components to the pump: a) The reservoir and infusion path.

b) The compression chamber unit.

c) The control unit.

The Reservoir and Infusion Path The syringe driver (6) is a standard device for pumping fluids from a reservoir in the form of a medical syringe. The syringe is clamped to the pump and a motorised device presses the plunger at a rate selected by the user to deliver the fluid at a known steady rate. This method is usually used for quantities between lml and 50ml, this being the standard size range of medical syringes. The infusion path consists of narrow bore flexible tubing (7) so as to convey the fluid from the pump to the patient with the minimum dead space and consequent wastage of fluid. All the tubing and connections are sterilised before use so as to prevent contamination of the fluid by micro-organisms. I propose an additional component to be inserted in this path, being a chamber (4) which could be a length of compressible tubing or a purpose-made chamber as in Fig 4.In this example the fine flexible tubing is bonded to a chamber consisting of two layers of thin flexible material such as plastic sheet, the circumference of the chamber being sealed by heat or other means so that the fluid can easily fill the chamber under low pressure and can easily be expelled from the chamber by compressing SYNCHRONISED INTERMITTENT INFUSION SYSTEM the chamber from outside. The tubing leads from the syringe driver to this chamber and thence to the ventilator tubing (9). An adaptor (8) is used so that the fluid is pumped into the air tubing as close to the patient as possible.A nozzle and valve may be incorporated to control the aerolisation of the fluid, although in the case of the surfactant treatment of premature babies, aerolisation is not considered necessary at the present time.

AF. a variation, the syringe driver could be dispensed with and the intermittent piston operation could also provide the pumping action. In this variation, the fluid would be contained in a sterile reservoir such as an infusion bag and the piston would be part of a volumetric pump. In the illustration (Fig 3b) a modified syringe is used, connected to the motor or servo (1) so that each action of the pump pushes the syringe plunger in to deliver the bolus, and withdraws it to refill the syringe from the reservoir prior to the next pumping action. A valve system (12) combined with a three-way connector completes the pump.Whereas in the syringe driver method, the average infusion rate is set by the driver rate, in the volumetric method the size of each bolus is fixed by the piston volume and the total infusion rate by the product of bolus size and instillation frequency.

The Compression Chamber Unit z Ite compression chamber unit comprises a framework or box (10) in which the infusion tubing is firmly held with means for removing the tubing and reinserting it, in this case a hinged lid (11) with locating recesses for the tubing and a flat backing for the chamber. There is a means for fixing the compression chamber in place so that the piston (3) will compress it in the same manner on each occasion of use. I1le piston is held by guides (2) and connected to the actuating device so that the action of the actuator will compress the flexible chamber. The actuating device is a suitable means of operating the piston. In the illustration (Fig 1) an electronically controlled servo (1) is used, in this case a pulse-controlled radio control servo, but alternative devices could be a motorised device, either a stepper motor or a motor controlled to move one revolution per activation using a cam (14) or pin connection: In these cases the servo control circuit (30) would be replaced by a suitable relay device (33). Alternative means of action could be devised as long as the piston could be reliably controlled by the control unit, for example a solenoid (17) or electrostatic piston.

SYNCHRONISED INTERMITTENT INFUSION SYSTEM The Control Unit Thes control unit (15) comprises a circuit taking the timing pulse from the ventilator or other patient treatment device and manipulating this pulse to select, time, and operate the pump. In the case of surfactant treatment, the ventilator control unit must be adapted to output a signal pulse coinciding with the beginning of the inspiratory phase of the respiratory cycle. Since not all ventilators will be fitted with means for sending such a signal to an external device, an alternative signal could be used. For example, a pressure switch (16) connected to the ventilator tubing could detect the increase in pressure associated with inspiration and supply the signal or other timing signals could be used.In the case of a "trigger" ventilator the drop in pressure of the patients respiratory effort could equally be used.

In its simplest form, standard timer ICs such as the 555 or 7210 perform the timing function. Pulse selection can be performed by a 4017 decade counter and the servo operation by a 555 in astable mode. Fig 4 shows a simple circuit which will perform the required functions. The timing pulse is applied at the input socket (21) where it increments the 4017 (22). The counter outputs 2 to 6 are connected via the multi-position switch (23) to the reset pin, thus selecting the frequency of operation. A switchable bypass can isolate this component to enable operation on every pulse (not shown for simplicity). Output O is used to send a pulse to the 7210 timer (24) in delayed release mode. The potentiometer (25) controls the delay time. When using a pressure sensor to provide the synchronisation pulse, the delay chip can be bypassed through an inverter (34).The 7210 or inverter output sends a logic 0 pulse to a second 7210 (26) in one shot mode. This is also controlled by a potentiometer (27) thus sending a pulse of the required length. This pulse is applied to the transistor (28) which partially shorts out the parallel resistor (29). By this means the discharge time of the 555 (30) is reduced and the servo control signal from the 555 output sends a series of short pulses ( < lms) causing the servo to operate. When the signal from (26) ceases the 555 reverts to the longer pulses (1.5-2 ms) which keep the servo in the resting position. The potentiometer (31) controls this resting position. The inverter (32) changes the negative output pulses from the 555 to positive ones. This can be omitted if negative pulses are required. In any case the output stage will be tailored to the precise operating device used in any particular version of the invention.

It would be possible to add sophistication by incorporating feedback sensors to control the piston movement or to use digital timers to control the delay function without affecting the basic principle of the pump. The SYNCHRONISED INTERMITTENT INFI;SIOt9T SYSTEM servo controller could easily be replaced by a relay device (Fig 5b) to operate a solenoid (17) or motorised piston, whether this is operated by a stepper motor or a motor designed to operate a single revolution at a time or any other type of motorised actuator and whether a cam (13) or pin or any other type of connection connects the actuator to the piston.

Claims

SYNCHRONISED INTERMITTENT INFUSION SYSTEM

CLAIMS 1) A synchronised intermittent infusion system being a. system for the intermittent infusion of fluids into body systems under the control of an external timing circuit comprising a reservoir of fluid instilled into the patient through a sterilised tubing system with a compressible chamber, by the intermittent compression of which the fluid may be instilled in timed boluses, the timing being synchronised with the function of a body system or patient support system or other suitable timing cycle, using a suitable circuit to select, time and operate the chamber compression unit.
2) A synchronised intermittent infusion system as claimed in claim 1 where the reservoir comprises a medical syringe emptied at a controlled rate using any standard syringe pump or syringe driver.
3) A synchronised intermittent infusion system as claimed in claim 1 where the reservoir comprises an infusion bag or other similar container and a valve system is incorporated with the compressible chamber so that the compression of the chamber also provides the pumping action to instil the fluid.
4) A synchronised intermittent infusion system as claimed in claim 3 where the chamber is constructed or adapted so that the volume of each bolus can be measured and determined.
5) A synchronised intermittent infusion system as claimed in claims 1-4 where a motorised actuator operates the compression piston.
6) A synchronised intermittent infusion system as claimed in claim 5 where the actuator is operated by a stepper motor.
7) A synchronised intermittent infusion system as claimed in claim 5 where the actuator is operated by an electric motor constructed or adapted to perform one revolution per actuation.
8) A synchronised intermittent infusion system as claimed in claim 5 where the actuator is operated by a servo motor.
SYNCHRONISED INTERMITTENT INFUSIONT SYSTEM 9) A synchronised intermittent infusion system as claimed in claims 5-8 where the actuator comprises a cam and a spring loaded piston.
10) A synchronised intermittent infusion system as claimed in claims 5-8 where the actuator comprises a rotating arm or disc conected to the piston by a pin or other attachment converting the rotation to reciprocating action of the piston.
11) A synchronised intermittent infusion system as claimed in claims 1-4 where a solenoid or other electromagnetic or electrostatic means is used to operate the piston.
12) A synchronised intermittent infusion system as claimed in claims 1-11 constructed or adapted for the instillation of fluids into the respiratory system of patients on an artificial ventilator.
13) A synchronised intermittent infusion system as claimed in claim 12 where the ventilator device provides a signal to synchronise the operation of the system with the inspiratory cycle of the ventilator.
14) A synchronised intermittent infusion system as claimed in claim 12 where a pressure sensor responds to the airway pressure of the ventilator system so as to synchronise the operation of the system with the inspiratory cycle of the ventilator.
15) A synchronised intermittent infusion system as claimed in claims 12-14 constructed or adapted for the administration of artificial surfactant in babies with respiratory distress syndrome.
16) A synchronised intermittent infusion system as claimed in claims 1-11 constructed or adapted for infusion of fluids into the circulatory system.
17) A synchronised intermittent infusion system as claimed in claims 1-11 constructed or adapted for infusion of fluids into any other body system.
18) A synchronised intermittent infusion system substantially as described herein with reference to figures 1-1|)of of the accompanying drawings.