GB2260622A

GB2260622A - Control of fluid pressure in clinical procedures

Info

Publication number: GB2260622A
Application number: GB9122218A
Authority: GB
Inventors: John Gutridge
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-10-19
Filing date: 1991-10-19
Publication date: 1993-04-21
Also published as: GB9122218D0

Abstract

An assembly for infusion of a liquid in a patient's uterus or bladder includes a pump 11, a flow line 14 for delivery fluid from the pump 11 to the patient, a pressure transducer 16 for measuring pressure in the patient and control circuitry 18 capable of receiving and monitoring the pressure information from the transducer 16 and a functional parameter from the pump 11 and being adapted to control function of the pump in response to changes in the measured pressure to maintain a constant pressure supply to the patient. The transducer may be in a separate line such as a catheter. <IMAGE>

Description

Pump Assemblv This invention relates to an assembly for supplying liquid to a patient. The pump will usually be a peristaltic pump.

When infusing, for example, a patient's uterus or bladder with saline, glycol or the like which is necessary to allow certain clinical procedures to be carried out it is imperative that the pressure within these organs does not exceed the arterial pressure of the patient. If this happens and a blood vessel has been exposed/bleeds it can allow ingress of the fluid towards the patient. This can be potentially fatal and great efforts are made to prevent this from happening.

Normal peristaltic pumps having no regulation over their flow and can increase the pressure within an organ to an exceptionally high level. This is extremely dangerous. As a result surgeons have resorted to using what is called "hydro-static" pressure control. This involves a bag of saline or glycol on a drip stand being allowed to flow under gravity. In fact the bag is held at some 100cm above the height of the patient and this, by definition, restricts the delivered pressure to the height of the bag.

A known apparatus has a pump with an integral "within the cabinet" pressure sensor. Tubing is connected and "T-ed" into the main fluid line running to the patient. The other end of the transducer must be blocked to inhibit the flow of fluid. If fluid were to enter the equipment it would violate the sterility of the equipment. This is not allowed. Using a column of air to measure the pressure has intrinsic errors which are typically plus or minus 60% due to the compliance of the air column. There is in reality little correlation between the pressure in the organ and the pressure monitored. It is well established that pressure transducers monitoring fluid lines, as an example within a patient, can only produce accurate results when filled with a continuous column of fluid. A single air bubble within this fluid line would compromise the accuracy of the measuring device.

It is an object of the present invention, therefore, to provide an improved pump assembly for supplying liquid to a patient.

The invention provides a pump assembly, for delivering a liquid to a patient, including a pump, a flow line for delivering fluid from the pump to the patient, a pressure transducer for measuring pressure in the patient and control circuitry capable of receiving and monitoring the pressure information from the transducer and a functional parameter from the pump and being adapted to control function of the pump in response to changes in the measured pressure to maintain a constant pressure supply to the patient.

The invention also provides a pump assembly for delivering liquid to a patient including a supply of liquid to be delivered, a pump, and a line connecting the pump to the patient, and a pressure transducer being mounted in liquid connection with the patient, the transducer being connected to circuitry adapted to monitor and control the rate of operation of the pump so as to maintain a constant pressure supply to the patient.

The transducer can be in said line from the pump to the patient or can be in a separate liquid line leading to the patient.

The separate liquid line can be a catheter leading to the organ of the patient which to be treated.

As the nature and length of the flow passage(s) between the pump and the patient and the transducer and the patient may, in many instances vary from case to case, it is desirable that means be provided for calibrating the system before use. The assembly of the invention readily lends itself to such calibration as it can easily and simply be carried out during the initial line flushing sequence required to ensure that the lines are free of air before the procedure commences.

The assembly used can involve a through flow pressure transducer, in particular a through flow transducer sold under the trade mark TRANSPAC and manufactured by Abbot Laboratories Limited. This is an extremely accurate pressure transducer which is already used for routine diagnostic work in operating theatres and intensive care units. It is a sterile device, pre packed and costing only a few pounds. In its usual use arterial blood is caused to flow down a carefully calibrated passage surrounded by a pressure sensitive gel which is connected to sensors. This device is accurate in it stability and reproducibility, being typically plus or minus 2% between devices. No calibration of the assembly is thus required when transducers are substituted. With the invention the transducer is uniquely placed in series with the infused tubing line.

The delivered pressure can be displayed remotely, or indeed a surgeon or other person can have a remote hand held control allowing the target pressure to be remotely adjusted.

The.invention will be described further, by way of example, with reference to the accompanying drawings wherein.

Figure 1 is a schematic view illustrating a first preferred assembly of the invention; and Figure 2 is a similar view of a second preferred assembly.

Referring now to the drawings it will be seen that a first preferred assembly (10) of the invention includes a pump (11).

The pump (11) is shown to be peristaltic, as peristaltic pumps are usual in these environments. However other pumps can be used provided they meet the other criteria for surgical/medical use.

A supply (12) of a liquid to be infused, such as saline or glycol is fed by a line (13) to the pump (11) and leaves the pump (11) via a line (14) towards the patient on which an organ is indicated schematically at (15). Mounted in the line (14) is a transducer (16) which measures the pressure in the line (14) and gives an out put in the form of digital electrical pulses which are fed via a line (17) to a central control apparatus (18).

Apparatus (18) is connected to the pump (11) by circuitry indicated by lines (19) and can sense the rate of operation of the pump (for example in the case of the peristaltic pump it notes the rate of revolutions of the shaft by means of an infrared sensor) and can also control the supply of current to the pump (11) so as to vary its rate of operation. The apparatus (18) can add a pair of displays (20) (21) which can indicate the desired and actual pressures in the organ (15). In similar manner a remote control unit (22) can be connected by a link (23) (hard wired or a radio or like link) to the apparatus (18). This allows the surgeon to control the apparatus from a far if need be.

Figure 2 illustrates a modification.

In the assembly (24) shown in Figure 2, similar parts have been allotted similar reference numerals. The only difference from the Figure 1 assembly is that a transducer (25) similar to the transducer (16) is disposed not in the line (14) but in a separate line such as a catheter (26) leading to the organ (15).

The catheter (26) can have its other end connected to a supply of liquid to be infused as indicated at (27). This can be a small supply to prevent blockage of the catheter and during infusion.

In both the assemblies (10) and (24), it will be appreciated that the transducer (16/25) is measuring the pressure not actually in the patients organ (15) but at a position remote therefrom. The difference between the pressure at the transducer and in the organ will depend on the amount of conduit (14/16) between the pump and the transducer and the organ. As this will vary, the assembly cannot be permanently calibrated. It is, therefore, necessary that the assembly is calibrated whilst the system is being set up. In all such procedures, an initial line flushing sequences has to be carried out, preliminarily, to ensure that the lines are operating correctly and that no air bubbles have been incorporated. During this sequence it is quite easy to test the calibration and it has been found that after calibration there is a relationship between the pressure at the transducer and the pressure in the organ being infused.

In more detail, the tubing and taps etc. after the transducer represent an impedance and the combination of the flow and the resistance of the tubing creates an off-set giving a false base line. The present assembly automatically compensates for this base line off-set.

It will be appreciated that as the transducer is disposed in the fluid flow path from the pump to the organ being treated, the pressure which it senses will be dependent upon the rate of operation of the pump and the pressure in the organ. Ideally, the transducer would be mounted as close as possible to the position which pressure needs to be measured, namely at or in the organ. In practice of course this is impossible and the pressure transducer has to be a significant distance from the organ.

During periods of constant operation of the pump the pressure in the transducer is dependent in linear manner on the pressure in the organ and the computer can easily determine the pressure in the organ from the pressure given by the transducer. The precise relationship can be determined during the initial set up prior to the actual procedure.

The pressure indicated by the transducer is, of course, also dependent upon the rate of flow through the conduit. As has been mentioned, under constant pump conditions, that is to say a constant delivered volume at constant pressure, the pressure measured by the transducer would be directly proportional to the pressure in the organ. If the rate of operation on the pump should change, however, this change in pressure immediately down stream of the pump affects the pressure sensed by the transducer, even if the pressure in the organ remains constant.The relationship between the rate of operation of the pump and the pressure in the transducer is, of course, a characteristic of the system and therefore by measuring the rate of operation of the pump and correlating that information with the calibration information obtained during the initial set up routine, (in effected allowing for the relative impedances between the pump and the transducer and the transducer and the organ), it is possible to determine the relationship between the pressure sensed in the transducer and the pressure in the organ during different rates of pump flow. Thus, the computer in the apparatus (18) is able to ensure that the actual pressure in the organ is displayed irrespective of the rate of operation of the pump.Of course, in the case of a peristaltic pump, the rate of delivery is directly proportional to the speed of its shaft and therefore such changes can easily be measured by a tachometer or comparable device. If other pumps were to be used, a sensor capable of giving an output related to the volume flow of the pump would be necessary.

When supplying liquid to an organ such as a uterus, it is very important that the desired pressure is reached without any overshoot. If the pump were simply cut off when the desired pressure in the organ were reached there would be an undoubted overshoot due to the delay inherent in any system and this could cause unacceptable high pressure in the organs. For this reason, it is desirable if the rate of operation of the pump is, by means of the control apparatus (18), related to the difference between the actual measured pressure in the organ and the desired pressure. For example, it is most convenient if the rate of operation of the pump is chosen to be proportional to the difference between the desired pressure in the organ and the actual measured pressure.In this way, when the pressure in the organ is low the pump acts at a high rate in order to raise pressure quickly, but as the actual pressure is reached it operates more and more slowly so as to give the feed back through the system time to work and to ensure that there is no overrun once the desired operating pressure is reached. Indeed, an exponential relationship is desirable so that final pump action is very slow.

This slowing of the pump during final pressurisation of the organ gives a very satisfactory control of the problem of overshoot but in itsself lead to the problem that the measured pressure has to be corrected because of calibration shifts due to different pump operation rates. Such variations are taken care of by the computer which measures the rate of operation of the pump and using that information and the information from the transducer can calculate the actual pressure in the organ.

During the line flushing procedure the computer within the apparatus (18) measures the off-set produced by the tubing and recalibrates.

The overall behaviour of the pump is controlled by the data presented to the computer in the form of pressure information from the transducer and flow information from the tachometer on the motor drive. The use of an external pressure transducer (see figure 2) can, in an alternative arrangement, allow for extremely accurate monitoring of the pressure via the catheter (26). This gives even better results.

The pump can have a twelve roller rotor and be capable of producing flow rates of up to 1 litre a minute. In view of the control of the system, it is possible for the assembly to operate, in circumstances where control pressure is not a problem, as a constant flow device.

The assemblies of the invention are extremely useful in preventing injury and death to a patient. The mean arterial blood pressure of a patient may be typically l00mm of mercury.

If the pressure within a organ such as the uterus or bladder is allowed to exceed the this by 20% and a blood vessel should be exposed, fluid can enter the blood vessel with possible fatal results. Glycol is often used in diathermia and can cause congestive heart failure if it enters the blood stream.

The system of the invention is far more accurate than previous systems using pressure measurement, and with the inherent accurate measurement and control of the assembly and very significant improvement and performance can be obtained and the use of gravity bags with their relatively low flows can be eliminated.

The invention is not limited to the precise details of the foregoing and variations can be made thereto. For example, the pump can be of any convenient form, not necessary peristaltic.

Many other variations are possible.

Claims

1. A pump assembly, for delivering a liquid to a patient, including a pump, a flow line for delivering fluid from the pump to the patient, a pressure transducer for measuring pressure in the patient and control circuitry capable of receiving and monitoring the pressure information from the transducer and a functional parameter from the pump and being adapted to control function of the pump in response to changes in the measured pressure to maintain a constant pressure supply to the patient.

2. A pump assembly for delivering liquid to a patient including a supply of liquid to be delivered, a pump, and a line connecting the pump to the patient, a pressure transducer being mounted in liquid connection with the patient, the transducer being connected to circuitry adapted to monitor and control the rate of operation of the pump so as to maintain a constant pressure supply to the patient.

3. An assembly as claimed in claims 1 or 2 wherein the transducer is in said line from the pump to the patient.

4. An assembly as claimed in claim 1 or 2 wherein the transducer is in a separate liquid line leading to the patient.

5. An assembly as claimed in claim 4, wherein the separate liquid is a catheter leading to the organ of the patient which is to be treated.

6. An assembly as claimed in any preceding claim wherein means is provided for calibrating the system before use.

7. An assembly as claimed in any preceding claim wherein the assembly has a through flow pressure transducer.

8. An assembly as claimed in claim 7 wherein the transducer is a through flow transducer sold under the trade mark TRANSPAC and manufactured by Abbot Laboratories Limited.

9. An assembly as claimed in any preceding claim wherein the delivered pressure is displayed remotely.

10. An assembly as claimed in any preceding claim wherein a remote hand held control is provided allowing the target pressure to be remotely adjusted.

11. A pump assembly substantially as described with reference to the accompanying drawings.