DK142803B - Blood oxygenation systems. - Google Patents

Description

(¾ \ * α / (11) PUBLICATION REPORT 1 ^ 2803 DENMARK, 5 ”| η, · αί A ®i 1.1 / 03” (21) Application No 5000/73 (22) Filed on 11 Sep 1973 (24) Running Day 11. βθρ. 1973 (44) The application submitted and the petition published on 2 February 1 9δΐ

DIRECTORATE OF J

PATENT AND TRADEMARKET (30> Priority requested from it

Sep 12 1972, 7232286, FR

<71) SOGIETE DES INDUSTRIES PLASTIQUES - SODIP, 7 Avenue Lionel Terr ay, 69330 Meyzieu, FR.

(72) Inventor: Andre Sausse, 12 Avenue Franklin Roosevelt, Sceaux, Hauts-de-Seine, FR.

(74) Plenipotentiary in the proceedings:

The engineering company Budde, Schou & Co._ __ (54) Blood oxygenation plant.

The present invention relates to a blood oxygenation system adapted to be placed outside a patient's body and at least comprising an oxygenator and two pumps, each pump being either peristaltic or tubular diaphragm and valves, and the pumps is connected in series on each side of the oxygenator, the system being arranged to be connected to the patient's vascular system so that the oxygenator and pumps are in flow-related connection therewith. Such a circuit serves to facilitate or replace pulmonary function, cardiac function or cardiovascular function.

Such blood circuits are known with two circulation pumps, which are connected in series on either side of a membrane oxygenated apparatus.

2 U2803

However, maintaining a certain pressure in the oxygenator, necessary to hold the blood in the form of thin barriers or films of constant thickness, requires either a conduit for partial recirculation of arterial blood in the oxygenator or complicated control systems.

It is an object of the invention to provide a facility of the kind in question which, by means of two pumps, connects an oxygenator to a patient's vascular system, where the system operates both simply and safely and, above all, does not require a bypass to balance blood flow.

This object is achieved according to the invention in that the pump chamber of each pump has an effective internal volume between two limits which is substantially proportional to the blood pressure at the pump inlet, this effective internal volume having its greatest value for the pump located at the inlet of the oxygenator. and its minimum value for the pump placed at the outlet of the oxygenator at a blood pressure at the inlet of the respective pump in the range ^ 20 mm Hg relative to atmospheric pressure.

In one embodiment, the system according to the invention may be characterized in that the two pumps are provided with drive means for simultaneous operation. This simplifies the control because the average blood flow for the two pumps is the same, while the operation is particularly economical.

According to the invention, the effective internal volume of the pump placed at the inlet of the oxygenator may have its greatest value at a blood pressure prevailing at the inlet of the pump which is lower than the atmospheric pressure. In this way, excessive pressure in the patient's blood vessels can be avoided.

According to the invention, the effective internal volume of the pump placed at the outlet of the oxygenator may be at least at a blood pressure prevailing at the pump inlet which is higher than the atmospheric pressure. In this way, the oxygenator can always maintain an accurate blood pressure.

According to the invention, the greatest effective outflow capacity of the pump located at the oxygenator outlet can be greater than the greatest effective outflow capacity of the pump located at the inlet of the oxygenator. This means that the pump placed at the outlet can operate at full capacity without risk.

According to the invention, the minimum effective outflow capacity of the pump located at the oxygenator outlet may be less than the least effective outflow capacity of the pump located at the inlet of the oxygenator. Hereby, especially in combination with the just mentioned embodiment of the invention, it is achieved that one can safely maintain the minimum blood pressure in the oxygenator for the desired period of time.

According to the invention, at least one of the two pumps connected in series on either side of the oxygenator may be a peristaltic pump whose outflow is affected by the pressure of the suction fluid. This can avoid both pulmonary edema and vascular collapse.

According to the invention, at least the pump located at the outlet of the blood oxygenator may be a pump with tubular diaphragm and valves. In this way one can particularly support the heart function.

According to the invention, the two series-connected pumps may be of peristaltic type and be provided with similar rotors mounted on the same shaft driven by a single motor at an adjustable speed. Here, too, cardiac function can be supported and construction is simple.

According to the invention, the first pipe, which is arranged at the inlet of the oxygenator, may have a circular cross-section, and the pipe for the other pumped at the outlet of the oxygenator may have a substantially elliptical cross-section, the inner circumference of the latter pipe being may be larger than the inner circumference of the pipe of the former pump. This construction is particularly simple and works particularly efficiently and economically.

The invention will be explained in more detail below with reference to the drawing, in which 1 schematically shows an embodiment of the system according to the invention; FIG. 2 shows a characteristic curve of the flow as a function of the pressure in a peristaltic pump which can be used in the system according to the invention; and FIG. 3 characteristic curves of the flow as a function of the pressure in two pumps placed on each side of the oxygenator.

By blood oxygenator is meant in this specification an apparatus for exchanging breath gases, i.e. oxygen, carbon dioxide, water vapor and nitrogen, and optionally gases or vapors with medical and / or anesthetic effects. The apparatus may also be a heat exchanger.

4 142803

In FIG. 1, it appears that the bloodstream located outside the body connects an apparatus 1 of a kind known per se to oxygenation of blood, which apparatus contains at least one membrane 2, with a vein artery system in a patient.

A cannula 3 is introduced e.g. in the lower caverns. Preferably, a cannula is used which has a non-closing extension at its end. This extension may consist of three elastic, radial branches 5 which press against the vein walls and keep them locally apart so that the opening of the cannula is exposed. Such a cannula prevents occlusion of the vein and prevents restriction of the outflow from the vein. The branches may advantageously be compressible so that the cannula can be inserted through a smaller diameter side vein 4, e.g. the femoral vein, which is cut for this purpose.

The cannula 3 is connected to the inlet of the oxygenator 1 through a flexible conduit 7, for example of silicone elastomer, to which a first pump 6 of peristaltic type or with tubular membrane and flaps, also called ventricular pump, is arranged.

A flexible conduit 11, also made of silicone elastomer, connects the outlet of the oxygenator 1 to a cannula inserted in an artery 9 or preferably to a funnel-shaped prosthesis 8 attached to the artery, preferably a femoral artery. Located on line 11. another pump 10, also of peristaltic type or with tubular diaphragm and flaps.

The artery is suitably opened longitudinally and the prosthesis 8 is sewn in an oblique position at the edges of the hole, whereby the inclination is laid in the preferred flow direction. The two sides of the prosthesis are separated under the influence of arterial pressure. After the prosthesis is removed, the hole in the artery is closed in the usual way.

A peristaltic auxiliary pump 13, which is connected to the suction line 7 of the pump 6, allows the remaining part of the vein 4 to drain additional blood into the extracorporeal circulation from a blood source such as a bottle 16 to compensate for any blood loss, and optionally introducing drugs in liquid form, e.g. heparin.

As, for example, the extracorporeal blood circulation shown is, it is necessary to regulate three different pressures, namely the blood pressure at the inlet to the pump 6, the pressure in the oxygenator and the patient's arterial pressure to maintain these pressures at desired values.

5 142803

A pressure gauge 17 is placed on line 7 in the immediate vicinity of the pump 6 inlet. This pressure gauge appropriately measures the blood pressure through the walls of the flexible conduit 7, reducing the risk of blood clotting. As a pressure gauge, the pressure gauge described in French Patent No. 2,163,936 can be used. On the basis of information on the blood pressure at the passage into the pump 6, it is possible to calculate the blood flow, as will be seen below.

A pressure gauge 14 allows the blood pressure in the oxygenator to be checked. In addition, a pressure gauge 21, which measures the patient's arterial pressure, allows it to be maintained at the desired level by either influencing the blood volume by means of the bottle 16 and pump 13 or influencing the patient's vascular resistance.

The blood should be introduced into the patient at a temperature close to 37 ° C. With this in mind one places, e.g. on line 11, means for reheating the blood and regulating its temperature. Conveniently, the reheating means may consist of a heating element having an electrical resistance 18 surrounding the conduit 11 or preferably inserted into its wall. This heater is, for example, of the kind described in French Patent Specification No. 2,165,269.

It is preferable to use two temperature sensors 19 and 20 of known type and located in the flow direction respectively after and at the level of the heater 18. The sensor 19 makes it possible to control and possibly control the re-heating of the blood. The sensor 20 allows to avoid local superheats of the blood which could occur by a decrease in blood flow or a temporary stop.

Preferably, the inner walls of the various organs of the bloodstream, in particular pump chambers, cannulas, and connectors which are in contact with the blood, are coated with a smooth organic silicon compound by coating method described in German Publication No. 2206608.

The mode of operation of the blood circulation is schematically represented as follows: Venous blood flows from the lower cavities, where it has a pressure close to the atmospheric pressure, through the cannula 3 and the conduit 7 up to the first peristaltic pump 6. This pump 6 pumps the blood into the the oxygenator 1 at a pressure sufficient to overcome the pressure drop in the apparatus. The blood chambers of the oxygenator are kept full, and the thickness of the blood film is kept substantially constant, thereby keeping the blood pressure within a predetermined interval on the pressure gauge 14. The oxygenated blood is removed from the oxygenator by the second peristaltic pump 10, which increases blood pressure to a value that allows the blood to enter the patient's arterial system through the prosthesis 8 after appropriate reheating in line 11.

The average blood flow common to the two pumps is provided by the patient's veins. This flow should be able to vary in such a way as to prevent any increase in venous pressure, as this could cause problems for the patient, especially acute pulmonary edema. To avoid this, it is expedient to increase the flow through the pumps 6 and 10. On the other hand, the pump flow is reduced if the venous pressure becomes too low, which could cause collapse of the veins or of venous cavities.

For this purpose, pumps are used whose pump chamber has an internal volume which varies with the blood pressure at the inlet, which is usually not the case for peristaltic type pumps or pumps of tubular membrane and flaps. According to the invention, pumps are used which, within the range of blood pressure used at the pump inlet, have an effective internal volume which is generally proportional to the blood pressure at the pump inlet.

As peristaltic pumps, such pumps as described in French Patent No. 2,063,677 are preferably used.

The two series connected peristaltic pumps are usually operated synchronously, at the same speed or at different speeds, to provide the same average flow. Preferably, they always rotate at the same mutual speed and are therefore conveniently mounted on the same drive shaft. The speed may be adjustable, but it is often of interest to maintain a constant speed.

The peristaltic pumps can also be operated at mutually equal speed by means of their own motor, whereby both motors have. the same speed / voltage characteristics, and both motors are supplied from a common voltage source which can be fixed or adjustable.

Pumps with tubular diaphragm and valves can also be used, including an inlet valve, the function of which can be automatic, ie. caused by the passage of the fluid to the interior of the pump, or preferably arbitrarily controlled, e.g. by a pneumatic action obtained by means of a pulse generator. The controlled outlet valve may be of the same type as the inlet valve. These pumps may be connected either to different pulse generators synchronized at the same frequency, or preferably to a common pulse generator.

7 142803

The 1, the peristaltic pumps shown suitably consist of a flexible peristaltic tube of a silicone elastomer, which tube is spaced between two fixed points and rotating rollers. The peristaltic tube usually has an elliptical cross section between the rollers which is more or less flattened depending on the pressure at the pump inlet. At constant velocity, the flow is a function of the pressure at the pump inlet, which is clearly shown in the FIG. 2 shows the flow curve as a function of the suction pressure in such a pump.

It will be seen that the pump at an operating pressure pA at the pump inlet, which lies between two limit values p ^ and p ^, gives a flow Qa between two limit values and (^. The flow in this range is substantially proportional to the inlet pressure pA · In the the following part of the description denotes pffl and p ^ denote the least effective pressure and the greatest effective pressure, respectively, at the pump inlet, and in the same way and QM denote the least, respectively, largest, effective flow.

The least effective flow is obtained when the inlet pressure is sufficiently low for the pipe to be compressed, thereby pushing its opposite walls against each other so that the cross section of the pipe takes the form of a dumbbell, thereby providing increased resistance to further deformation. If you go further, the tube is flattened further, but under the influence of much lower suction pressure at the pump inlet, which corresponds to a sudden change in the slope of the curve, since it is necessary to reduce pressure in the interior of the tube more and more to achieve a smaller illumination and thus a smaller throughput Q.

From the beginning, the diameter of the pipe is assumed to be elliptical. At regular increasing pressure, the cross-section of the pipe will assume a more and more circular shape, and then remain circular. This means that the greatest effective flow QM is obtained when the inlet pressure is sufficiently high for the cross-section of the pipe to become circular. If this limit is exceeded, the cross-sectional area of the pipe can only be increased by expanding the pipe, which requires considerably higher pressure and also corresponds to a sudden change in the slope of the curve.

In the embodiment of FIG. 1, the flow of the pump 6 varies for a given level depending on the venous pressure. Since the venous pressure at the level of the cannula 3 is close to the atmospheric pressure, and as the blood pressure at the inlet of the pump 6 differs from the venous pressure with the values of the pressure losses in the intermediate conduit 7, partially offset by the level difference between the cannula 3 and the pump 6, the blood 8 The pressure at the pump inlet is usually lower than the pressure of the atmosphere. Accordingly, one chooses a pump 6 whose characteristic flow pressure curve extends in a zone which preferably extends from pressure below atmospheric pressure up to this pressure. In FIG. 3 shows the characteristic curve of the pump 6. The effective zone of the curve lies between Bm and llv'by the boundary pressures pfflg and p ^ in the case shown are both lower than the atmospheric pressure, which is at the value 0 on the abscissa or at point 0. pMg, like the largest flow, is proportional to the rotational speed of pump 6.

It is desirable that the greatest effective pressure pg be somewhat lower than atmospheric pressure, generally less than 20 mm Hg and preferably less than 10 mm Hg below atmospheric pressure. This condition is provided by a pump whose thin-walled peristaltic tubes at rest have a circular cross-section (between the rollers, in the case of a rotary pump with rollers such as that shown in Fig. 1). This cross-section is the largest possible and allows for the greatest effective flow At a pressure of p with the same circumference and the corresponding flow is Qg.

When the pressure Pg becomes equal to the least effective pressure p ^ g, the peristaltic tube is further flattened and its cross-sectional area approaches 0, reducing the flow to the least effective flow Q ^ g.

The pump 10, which is connected in series with the pump 6, delivers exactly the same average flow. The flow of the pump 10 is thus determined by the pump 6, which again depends on the venous pressure. The pumps 6 and 10 are generally arranged at approximately the same level as the oxygen generator. The assembly of the pumps 6 and 10 and the oxygenator is usually positioned vertically below the patient so that the pressure losses in the flow direction in front of the pump can be partially compensated and thus adjust the blood flow to the desired mean.

It is necessary to keep the blood pressure in the oxygenator within a predetermined pressure range in order for the blood film to be substantially constant in thickness during its contact with the membrane and to allow a controlled pressure gradient through the membrane thickness.

Thus, in one of a stack of membranes alternating red intermediate plates comprising oxygenator, the relative blood pressure measured by the manometer 14 can be maintained within a predetermined range, e.g. between 0 and 200 mm Hg.

If in this oxygenator the oxygen pressure is kept below atmospheric pressure, the pressure difference between the blood and the oxygen pressure is always positive, which allows the use of microporous membranes with high gas permeability, which membranes also allow a good degassing of the blood, even in the case of foaming or if small bubbles appear. The apparatus thus serves as a safety degassing device. The membranes described in French Patent No. 1568120 are particularly suitable for this purpose. Furthermore, the maintenance of this positive pressure difference makes it possible to prevent the membranes from accidentally adhering to each other in an adhesive which can be difficult to lift.

If the blood pressure exceeds the oxygen pressure too much, the blood could break through the membrane or overcome the liquid density of the microporous membranes and penetrate the membranes, e.g. at a pressure of 800 mm Hg.

The blood pressure in the oxygenator can be maintained within a selected range by the pump 10, whose characteristic flow pressure curve extends in a pressure zone substantially above atmospheric pressure. In FIG. 3 shows the characteristic curve of the pump 10. The effective zone of the curve lies between the points Cm and CM, and the corresponding boundary pressures Pm ^ Q and Pj ^ q are in both cases higher than the atmospheric pressure.

It is desirable that the least effective pressure pm10 be equal to or slightly higher than atmospheric pressure, generally less than 20 mm Hg and preferably less than 10 mm Hg above atmospheric pressure. This condition is provided with a pump whose peristaltic tubes at rest have a flattened cross section. This cross-section is virtually minimal and allows for a minimum effective flow The pump 10 has a peristaltic tube with quite thin walls so that the greatest effective flow can be achieved at a maximum effective pressure PM1Q, which is usually less than 200 mm Hg and preferably ca. 50 mm Hg above atmospheric pressure. Thus, for each flow forced by the pump 6, the peristaltic tubes of the pump 10 get a more or less flattened cross section corresponding to pressure at the outlet of the oxygenator between 0 and e.g. 50 nun Hg above atmospheric pressure. The greatest pressure at the inlet of the oxygenator depends on the pressure losses in the apparatus, usually less than 100 mm Hg for blood flows of the order of 600 ml / min in an oxygenator with a surface of 0.5 m2.

To be sure that the average blood pressure in the oxygenator at any moment remains within the desired range, two conditions must be met simultaneously.

The first condition is that the largest effective flow for the pump 10, which is in the flow direction behind the oxygenator, is greater than the corresponding flow for the pump 6 in front of the oxygenator.

Since the pumps 6 and 10 of the invention are usually operated so that they operate simultaneously and stand still simultaneously, this condition can be fulfilled in any of the following ways:

The pump 10 can be operated at a higher speed than the pump 6, whereby the ratio of the speeds is fixed. In the case of a rotor peristaltic pump, the pump 10 can be provided with a rotor having a larger diameter than the rotor of the pump 6. Preferably, both pumps are provided with identical rotors which rotate at identical speed because they have a common shaft, and these rotors affect different pipes, whereby the internal circumference of the cross section of the pump 10 is greater than the internal circumference of the cross section of the pump. 6's tube. Of course, these different ways can be combined with one another.

The second condition is that the least effective flow of the pump 10 in the flow direction after the oxygenation apparatus is less than the least effective flow of the pump 6 before the oxygenator.

To fulfill this condition, a pipe with walls which is more flexible than the walls of the pipe of the pump 6 can be selected for pump 10. Thus, the cross-section of the pump 10 tube, which is discharged at a pressure close to the atmospheric pressure, has the shape of a dumbbell with a smaller surface than the cross-section of the pump 6's pipe at the least effective pressure above this pump. For the pump 10 one chooses a tube which is generally flat and which, if necessary, can assume dumbbell shape is more elastic than the tube 6 of the pump 6 which has a circular shape at rest. One can use a tube with thinner walls than for pump 6 and combine thin walls and flat shape.

Thus, it can be observed that according to the invention, both of the above-mentioned requirements can be fulfilled at one time.

In practice, when a steady state is achieved and the flow in the out-of-body circuit is satisfactory, it is appropriate to reduce the disturbances in the state of the blood to reduce the velocity of the pump 6 so that its true flow becomes approx. 4/5 of the largest flow. For this purpose, the pressure gauge 17 is used, which allows the actual flow to be calculated.

Preferably, peristaltic pumps are used to support cardiac or cardiac lung function. In the case of relief of cardiac lung function, however, a competition between the more or less pulsating flow from such pumps and the flow due to the patient's heartbeat can be feared.

If one wishes to take advantage of the diastolic phase by injecting the blood from the extracorporeal circulation and avoiding competition between this and the heart, it is therefore preferable to use pumps whose flow can be synchronized with the heart's cycle. Such pumps are usually selected from diaphragm pumps suitable for blood circulation. These pumps are known as ventricular or tubular diaphragm pumps and valves. Suitable pumps such as those described in French Patent Specification No. 2,175,274 can be used.

These pumps are provided with appropriately controlled valves arranged respectively in the flow direction before and after. The largest volume of the arterial cavity forming the pump 10 is at most 50% and preferably at most 20% larger than the largest volume of the venous cavity forming the pump 6. The pump chambers of these pumps, which are usually rigid, are suitably in opposite phases connected to one and the same pulse generator.

The onset of the chair can be initiated either by an electrocardiographic signal or preferably by the patient's arterial pressure falling below a certain threshold. The suction pressure of one or the other pump and the pump pressure can be controlled by regulating the pressure of the gaseous propellant fluid. A mode of operation comparable to the peristaltic pumps is found, whose flow is a function of the pressure in the direction of flow.

It is even possible, as in the latter, to guard against injection of air by placing the pumps vertically, whereby the blood flows through the pumps from below, and the air thus is confined at the level of the inlet flap which cannot be strictly sealed.

The use of two pumps with tubular diaphragm and flaps and a fluid pulse generator as described in French Patent 2,144,342 is particularly advantageous in resuscitation in an ambulance or helicopter, as this apparatus does not require electrical energy but can operate at expansion of the oxygen used for the oxygenator. With an oxygen bottle of 0.5 cm, self-control is satisfactory while keeping the weight and space requirements minimal.

In the foregoing, a device associated with a patient's vein artery system has been described, but the same aggregate is also applicable to venous-vein circulation or out-of-body artery-vein circulation.

The out-of-body circuit may comprise several parallel coupled auxiliaries, each consisting of a blood filtration apparatus with a pump 6 on one side and a pump 10 on the other side. Such auxiliary units are connected to the main circuit through valves 22 and 23 see fig. 1. They can be connected or short-circuited to quickly satisfy different needs of the patient.

Since in the external body according to the invention, pumps are used which give a very insignificant degree of hemolysis, and since any direct blood circulation is avoided, the apparatus can very well be used for a long time. Because the pumps are self-regulating, the circuit has the properties of simplicity, reliability and safety to a considerable extent, especially safety against the injection of air. The pumps act as gas traps.

When the blood oxygenator is equipped with microporous membranes and is flowed by a gas stream at a pressure lower than atmospheric pressure, it can remove any gas bubbles that may be introduced into the blood before it enters the oxygenator, and the better the finer the bubbles. When the oxygenator operates in this way, it behaves better than the commonly used gas traps, which act by gravity or buoyancy, as these work better the larger the bubbles. Therefore, under these particularly favorable conditions, such a gas trap can be used in the circuit.

The characteristics of the circuit according to the invention and the associated advantages will become even more apparent from the following embodiments: 13 142803

Example 1.

The circuit used is similar to that of FIG. 1 with the exception of the drive means for the pumps 6 and 10. The speeds at which the pumps are operated can be controlled between 0 and 40 rpm by means of direct current motors supplied from a common voltage source. The pumps 6 and 10 are of the type described in French Patent Specification No. 2,063,677. The peristaltic tubes consist of silicone elastomers. The pipe of pump 6 has an inside diameter of 10 mm and an outside diameter of 12.6 mm. The periphery of the rotor, which has three rollers, describes a circle with a diameter of 140 mm. The pump 10's pipe has an inner diameter of 11.25 mm and an outer diameter of 14.1 mm, while the periphery of the rotor describes a circle with a diameter of 140 mm. The pump 10 is located 50 cm above the oxygenator. The latter consists of two indigenous aggregates, each containing 16 microporous membranes and seven intermediate plates stacked and clamped between two end plates. The apparatus is of the type described in French Patent No. 1597874. The exchange area is 1 m. During permanent operation, the blood pressure drop in the device is 50 mm Hg.

This circuit was used to support a patient's heart-lung function over a 12-hour period. At the end of treatment, the hemolysis rate of the blood was found to be less than $ 0.5. The blood pressure ioxygenator interior was kept within the range 50-150 mm Hg. At an average blood flow of 800 ml / min, the transfer of oxygen was 40 ml / min and of carbon dioxide 60 ml / min.

Example 2.

The circuit and pumps 6 and 10 are the same as in Example 1 and correspond to FIG. 1. The rotors of pumps 6 and 10 are mounted on a common shaft driven by a single motor 12 at a speed which can be controlled between 0 and 40 rpm. Each rotor has three rollers arranged at an angular displacement of 120 °, and the two rotors are angularly displaced 60 ° to each other.

The pipe 6 of the pump 6 has a circular cross-section in the idle state.

The tube has an inside diameter of 15.8 mm and an outside diameter of 20 mm. The pipe 10 of the pump 10 has an elliptical cross-section in its resting state. The inner large and small axis of the ellipse are 24 and 4 mm, respectively. When deformed under pressure, this tube has a circular cross-section with an internal diameter of 16.8 mm and an outside diameter of 20v.mm.

The effective diameter of the pumps 6 and 10 is 190 mm. the oxygenator has a membrane area of 3 m.

This device partially replaces an adult patient's heart-lung operation for 52 hours. Blood flow is regulated to a mean value of 2 l / min and the average transfer of oxygen is 130 rol / min and of carbon dioxide 150 ml / min. The pressure conditions and hemolysis conditions are the same as in Example 1. Another apparatus is ready for use in the event that the transfer values should prove momentarily insufficient.

Claims (8)

Patent Claims. A blood oxygenation system, which is arranged to be placed outside a patient's body and at least comprises an oxygenator and two pumps, each pump being either peristaltic or with tubular diaphragm and valves, and the pumps being connected in series on each side of the oxygenator, the system being arranged to be connected to the patient's vascular system, so that the oxygenator and pumps are in flow communication therewith, characterized in that each pump's pump chamber has an effective internal volume between two limits. is substantially proportional to the blood pressure at the pump inlet, this effective internal volume having its greatest value for the pump placed at the inlet of the oxygenator and its minimum value for the pump placed at the outlet of the oxygenator at a blood pressure at the inlet of the respective pump in the interval - 20 mm Hg relative to atmospheric pressure. Installation according to claim 1, characterized in that the two pumps are provided with drive means for simultaneous operation. System according to claim 1 or 2, characterized in that the effective internal volume of the pump located at the inlet of the oxygenator has its greatest value at a blood pressure prevailing at the pump inlet which is lower than the atmospheric pressure. System according to any one of claims 1, 2 or 3, characterized in that the effective internal volume of the pump located at the outlet of the oxygenator is at least at a blood pressure prevailing at the pump inlet which is higher than the atmospheric pressure. Installation according to any one of the preceding claims, characterized in that the largest effective outflow capacity of the pump located at the outlet of the oxygenator is greater than the greatest effective outflow capacity of the pump located at the inlet of the oxygenator. Installation according to any one of the preceding claims, characterized in that the minimum effective outflow capacity of the pump located at the outlet of the oxygenator is less than the least effective outflow capacity of the pump located at the inlet of the oxygenator. Installation according to any one of the preceding claims, characterized in that at least one of the two pumps, which are connected in series on each side of the oxygenator, is a peristaltic pump whose discharge is influenced by the pressure of the suction fluid. System according to any one of the preceding claims, characterized in that at least it is used at the outlet of the blood oxygenator.