FR2718643A1 - Extra-corporeal hepatodialyser using the liver taken from a living being. - Google Patents

Abstract

Hepato-dialysis apparatus comprising an extracorporeal circulatory system for a live liver placed outside the patient. The apparatus includes an infusion receptacle (6), with a thermostat, containing a liver (5) to be infused, and an extracorporeal blood circulation loop consisting of, firstly, an inflowing line (2) from an artery and including a portion which is devided into two branches (16) and (17), one of which directly supplies the portal vein and the other supplying the hepatic artery through a peristaltic pump (18) provided with a pressure regulator and, secondly, an outflowing line (10) including a debubbling device (45) and a pump (46) for reinjection into a patient's vein. A monitoring and operating controller (24) is also provided. The invention relates to the field of extracorporeal hepatic dialysis on a live liver.

Description

 The present invention relates to a hepato-dialyzer by extracorporeal perfusion of an external liver taken from a living being.

 Liver transplantation has revolutionized many treatments linked to liver diseases and in particular viral hepatitis.

 All of them are difficult and delicate to treat and some of them, called fulminants, worsen the patient's condition at such a speed that he dies before the transplant can be performed.

 If transplantation is the only hope in many cases, it remains an exceptional means because the shortage of human organs can only provide very incompletely the needs.

 It therefore appears highly important to be able to have a means of hepatic assistance making it possible to avoid transplantation while awaiting regeneration or at least to prolong the waiting phase for an allograft.

 The various known medical means which have been used in order to assist the failing liver have not scientifically proven their effectiveness.

 There are other means of external circulation, for example on dialysis columns on which hepatic cells are grown. Significant results are very difficult to obtain from this technique. Indeed, the liver cells do not develop well on this medium and die quickly. In addition, when they divide, they lose their properties.

 The object of the present invention is to propose an external hepato-dialyzer, minimally invasive for the patient, reproducing graft perfusion conditions close to physiology, and capable of operating with great security and restricted monitoring.

 The originality of this hepatodialyser is based on several essential characteristics.

 First of all, contrary to the teaching of certain previous experiments, the liver is perfused using arterial and non-venous blood despite its pulsating form with a large excursion of the pressure wave.

 The balance between the circuit relating to the external liver and the efferent circuit is achieved by the free flow of arterial blood out of the vena cava of the perfused organ to reinject it into a vein of the patient and by the total dissociation of the two circuits. .

 The hepatic artery is supplied with arterial blood regulated in pressure with respect to a set value.

 The cassette containing the perfused organ is placed in elevation relative to the patient's body to take advantage of a return static pressure and also to regulate the related portal pressure.

 For this purpose, the hepato-dialyzer is composed of a thermostatically controlled double-walled stainless steel tank or cassette, sterilizable and waterproof, specially designed. First of all, it allows the liver to be stored in the refrigerator at 4 "C in the preservation liquid, then to perfuse it by keeping the hepatic graft at 37" C away from any bacterial contamination and finally to reheat and recover the blood before reinjecting it.

This cassette is placed in fixed or adjustable elevation relative to the subject to be assisted by hepatic dialysis using the following means. an extra-corporeal blood circulation circuit
specially adapted consisting of flexible tubing, two peristaltic pumps, an air bubble detector, for example
ultrasonic, coupled to an electromagnetic valve and
an alarm, two diaphragm pressure sensors coupled to a
display system, a regulator allowing a control
computerized flow to pressure in the artery
hepatic,. a syringe pump to deliver at a rate
constant heparin in the circuit,. a thermostatic water bath allowing a contribution
stable and constant caloric in the infusion tank
of the graft.

 This circuit ensures the circulation of arterial blood taken from a radial or femoral artery of the patient, through an external liver, for example of pig, via the portal vein and the hepatic artery, and the blood return towards a vein, for example the jugular vein.

In order to perfuse the liver transplant under optimal physiological conditions, the system meets several imperatives. respect for the triple hepatic vascular supply
(hepatic artery, portal vein and vena cava) in order to
meet the oxygen requirements of the
parenchyma. Arterial vascularization of the graft
is an essential element for the proper functioning of
the bile tree and therefore the secretion of bile. The
portal vascularization ensures the
purification and synthesis functions while
bringing oxygen to the rest of the parenchyma.

. respect for physiological characteristics
hemodynamics i.e. flow rates, pressures
and physiological perfusion flows in each
vascular axes. The flow of blood passing to
across the liver should be lml / g of
parenchyma / minute. Infusion pressures should
be maintained at 17 +/- 3 mmHg for the portal vein,
and 110 +/- 10 mmHg average for the hepatic artery
and close to O mmHg for the vena cava. The flow
portal blood must have characteristics
venous hemodynamics, almost continuous without
strokes, while the arterial flow should be pulsed from
way to reproduce waveforms and durations
systolic and diastolic heart.

. respect for the distribution of blood mass in
the different vascular territories: two thirds
of blood mass and therefore oxygen must
be brought to the portal level, a third to the level of
the hepatic artery.

. compliance with temperature conditions at around 37 "C
and humidity necessary for the purification functions,
of synthesis and secretion of the pig graft.

 In an ongoing concern for simplicity and security, several original solutions have been developed to meet all of these requirements.

 First of all the choice of the vascular approach in the patient: it is advisable to choose a vessel capable of delivering 300 to 500 ml of blood per minute suitable for example for a piglet liver weighing from 300 to 500 grams. The use of an oxygenator, always potentially thrombogenic, being prohibited for a manipulation of several hours, which is more in a xenogenic model where the rejection is manifested by a massive activation of the coagulation phenomena, the blood is taken directly at the arterial level .

This alternative avoids the use of massive doses of heparin formally contraindicated in patients with hepatocellular insufficiency.

 Another originality of this circuit lies in the fact that the arterial blood flow pulsed at the puncture point, the pressure of which is that delivered by the patient (70 to 140 mmHg on average), is transformed into an almost continuous flow which can be adapted pressure (between 15 and 20 mmHg).

 Three factors allow this transformation. The first is linked to the diversion of part of the blood flow to the hepatic artery using one of the peristaltic pumps, which has the effect of "smoothing" the pressure wave. The second is linked to the gradual increase in the internal diameter of the tubing. Finally, the third is related to the difference in level between the blood collection site and the portal vein of the graft (adjustable up to 700mm).

Continuous monitoring of the portal pressure allows adjustments to be made according to the patient's blood pressure variations.

 Another major advantage of this device is the constant pressure perfusion of the hepatic artery. An electronic regulator allows a computerized control of the pump flow to the blood pressure in the circuit.

 This system allows on the one hand to avoid any overpressure in the arterial network of the graft and on the other hand to follow the rejection phenomena occurring during the infusion. The first witness to rejection of a graft being vascular thrombosis in the arterial network, the decrease in flow in the hepatic artery and then the stopping of the pump are determining factors to indicate the ideal moment to change grafts.

 The infusion cassette is mounted elevated relative to the patient's body. The difference in height represents the static reinjection pressure. This height can be adjustable in order to adjust the static return pressure to the specifics of the circuit and the patient.

 The blood carried in the portal vein and the hepatic artery crosses the liver to be purified there then flows freely by the vena cava left open at the bottom of the tank. The purified blood is then reheated on contact with the wall, then collected and transported slowly by means of a support in elevation from the bottom towards the outlet orifice and the return branch of the circuit comprising a trap and a bubble detector as well as monitoring and alarm for the presence of air in the return blood.

 The first work carried out on porcine (autologous) and simian (heterologous) models seems to show that this purification technique is fairly well tolerated by the treated animal, that it allows rapid neurological recovery in less than two hours for comatose subjects. and that the functions of purification, synthesis and secretion of the hepatic graft are good.

This invention is illustrated in a nonlimiting manner by the appended drawings in which. Figure 1 is the general block diagram of
1 hepatodialyser according to the invention,. Figure 2 is a schematic perspective view of
the cassette containing the perfused organ,. Figure 3 is the general diagram.

 The extracorporeal perfusion blood circulation circuit 1 is composed as follows.

 A first loop known as the related circuit 2 transports the patient's arterial blood 3 resting on a bed or table 4, preferably of height adjustable relative to the ground, to a liver 5 to be perfused, for example the liver of a pig.

 The liver 5 to be perfused is enclosed in a sealed perfusion cassette 6 and receives the patient's blood through his hepatic artery 7 and through his portal vein 8.

 The perfused blood is reinjected into a vein 9 of the patient's body, for example into the subclavian vein by a return loop of the blood circulation circuit called the efferent circuit 10.

 More particularly, the related circuit 2 has a first section 11 formed of a conduit 12 whose cross section gradually increases in the direction of circulation of the blood supply flow to the liver so as to dampen the blood pressure wave. This first section 11 begins at the point of puncture in the chosen artery 12 of the patient's body 3 either in the radial artery in termino-terminal, or in the femoral artery in latero-terminal and ends at the birth of a bypass 14.

 The injection of a fluidizing product, for example heparin, into this section is provided by an electric syringe 15.

 The bypass 14 divides the circuit into two parallel branches: a direct branch 16 and a constant pressure branch 17. The direct branch 16 is connected to the portal vein 8 of the liver 5 and the constant pressure branch 17 supplies the hepatic artery 7 through a pump 18 preferably of the peristaltic type comprising three rollers.

 The fact of using a pump head with three rollers makes it possible to obtain a slightly pulsed blood flow essential for the proper functioning of the hepatic arterial network.

 The pressure in each branch 16 and 17 is transmitted by a pressure sensor 19 and 20 respectively to a control unit 21 for example of the integral proportional electronic regulator type which allows a computerized control of the flow rate of the peristaltic pump 18 to the blood pressure in the related circuit, pressure, the value of which is reduced and maintained at a predetermined set value according to the hemodynamic characteristics known and necessary for normal functioning of the liver.

 This control unit 21 comprises, in the example shown, two indicators 22 and 23 corresponding to each sensor. It will be integrated into a general automated management and monitoring system for the hepato-dialyzer by an automated system 24 (Figure 3). The flow in branch 17 is generated by the peristaltic pump 18 with digital display controllable from the outside by a weak current. It is the regulator, which, by comparing the desired pressure, that is to say the set pressure to the real pressure prevailing in the hepatic artery given by the pressure sensor, will control the pump by modifying its flow to maintain pressure to the setpoint. In the event that the pressure measured is greater than the setpoint, the regulator will send a lower control current to the pump, which results in a reduction in the flow rate.

Conversely, if the actual pressure is lower than the setpoint, the flow will increase. The oscillations will quickly stabilize to an equilibrium point.

Of course, the control of the pump cannot be only proportional to the difference observed between the set value and the measured value. Indeed, at the point of equilibrium the speed of rotation of the pump would be zero. It is therefore necessary to involve an integration component, which makes it possible to maintain flow rates allowing a slight oscillation of the pressures around the set value.

 The branches of the related circuit are connected to the connection interface of the perfusion cassette 6, the detailed description of which is given below with the aid of the drawing in FIG. 2.

 The infusion cassette 6 is specially designed for this extracorporeal dialysis circuit. It is placed in a fixed or adjustable elevation in relation to the subject to be assisted by hepatic dialysis. It is a container 25 with a double wall of generally parallelepiped shape in stainless steel closed by a transparent cover 26, for example made of organic material.

 A suitable peripheral seal 27 disposed between the cover and the body of the cassette ensures the seal with respect to the external environment.

 The side wall of the perfusion cassette is double to delimit a closed peripheral compartment 28 for maintaining the interior volume at the desired constant temperature of 37 "C.

 In this peripheral compartment 28 circulates a heated liquid fluid, for example, water coming from an external reserve, for example, from a thermostatted water bath (not shown).

 Transversal connections are provided at each end of the compartment 28 for the connection with the supply conduits 29 and exit 30 of the heating fluid.

 The tank is equipped in its internal volume 31 near its bottom 32 with a support 33 of generally flat shape on which the perfused liver will rest. This support is held at a certain distance from the bottom by lugs such as 34 to 37 or any other equivalent elements.

 This support is transverse in free flow towards the bottom communicating with the outside for the blood freely leaving the perfused liver. It is of the grating or inclined plane type with four symmetrical slopes converging towards a central flow orifice 38 towards the bottom 32 as shown in FIG. 2.

 The cassette has on its front face a hydraulic connection interface 39 intended to provide the through passages and connections for supplying blood to the perfused liver and the flow connections. For this purpose connections of the quick-connect type are provided on both sides of each through conduit. There are, for example, two supply sections 40 and 41 and a discharge section 42 opening onto the bottom orifice 32.

 The cassette also includes a level indicator visible from the outside showing the level of a buffer reserve 43, of blood in the bottom 32 of the tank, for example in the form of a conduit 44 bent upwards.

 Thanks to this level indicator making it possible to follow the quantity of blood present in the tank, the adjustment of the rate of reinjection is done manually at the start of the infusion so that the flow of blood at the outlet is identical to that at the entry into the circuit.

 The buffer reserve 43 communicates via the discharge section 42 with a lower drain which is connected to a tube by a quick coupling to the loop 10 for return of the circuit in the patient's body 3.

 The extracorporeal circuit for circulation of the blood flow continues after the cassette 6 leaves by the return loop constituting the efferent circuit 10.

This consists of various tubes and tubing connecting a 45 effect bubble trap
Vortex to a reinjection pump 46, for example of the peristaltic type, to compensate for the pressure drops, then to a bubble detector 47 whose purge line comprises a pressure sensor acting as a detector for the controller 24 intended to monitor and to manage the overall operation. Thus, the detector is ultrasonic with evacuation and alarm as well as automatic closing of the circuit before reinjection into the patient's body 3.

 Various devices permanently indicate the quantities to be monitored characteristic of liver function and its quality. It is the production of bile by a test tube 49 visible in the figure representing the perfusion cassette 6. It is also an indicator 50 of the oxygen saturation rate provided by a probe making it possible to monitor the consumption of oxygen from the perfused liver.

 With the value of the perfusion pressures they allow to estimate the stage of rejection and determine the ideal moment to change the graft.

 All of these indications as well as the presence of bubbles signaled by the bubble detector will be taken into account by the operating and monitoring automaton 24 which will automatically cut the efferent circuit by the isolation valve when bubbles are present and will cause the 'evacuation of these.

 Between the direct branch 16 and the evacuation section 42, a bypass 51 has been provided for replacing the graft after the reduction in purification efficiency by the hepatic function without stopping the blood flows.

 It is a hydraulic bypass tube 52 between the direct branch and the outlet of the cassette intended to short-circuit the cassette.

 Conventionally, three isolation valves 53, 54 and 55 are provided at the appropriate locations in and near the branch 51.

 The general diagram shown in FIG. 3 explains the overall operation of the circuit from a manipulator or the automaton 24 and the functional links existing between different components.

Claims (11)

 1. Hepato-dialyser extra-corporeal by perfusion on a liver (5) taken from a living being characterized in that it comprises a hemodynamic circulation loop (1) comprising:  an associated circuit (2) for supplying the liver with arterial blood from a patient (3), a circuit formed by two distinct branches for supplying separately from an artery (13) of the patient, on the one hand hepatic artery (7) and on the other hand the portal vein (8) of the liver (5) with return in a vein (9) of the patient,  a sealed perfusion cassette containing the perfused liver (5) having an inner support (33) raised relative to the bottom on which the liver rests, a supply interface and a free evacuation of the perfused blood,  an efferent circuit (10) towards a vein (9) of the subject for the reinjection of the blood comprising a boiling device and a reinjection pump (46) in one of the veins of the patient,  an automaton (24) intended to monitor and manage the operation of the assembly.  2. Hepato-dialyzer according to claim 1 characterized in that the efferent circuit has a first section common to a narrowing section which divides into a direct branch (16) supplying the portal vein of the liver in a branch of overpressure (17) comprising a pump (18) with controlled operation, on each of the two branches grafting a pressure sensor (19) in connection with the control unit (21) for operating the pump.  3. Hepato-dialyzer according to claim 2 characterized in that the pump (18) is a peristaltic pump controlled at constant pressure by the control unit (21) from pressure sensors,  4. Hepato-dialyzer according to claim 3 characterized in that the peristaltic pump (18) is three rollers.  5. Hepato-dialyzer according to claim 1 and 5 characterized in that the cassette (6) comprises a thermostated jacket with perimeter compartment (28), an interior support (33) on which the liver (5) rests, said support ( 33) being raised relative to the bottom (32) and shaped so as to collect and then evacuate the blood by gravity towards the bottom, the said cassette comprising a hydraulic connection input interface (39) with double supply conduit for the liver on its portal vein (8) and its hepatic artery (7), a low outlet in communication with the bottom (32) and connected to the efferent circuit.  6. Hepato-dialyzer according to claim 1 and 5 characterized in that the cassette (6) is arranged in height relative to the subject (3).  7. Hepato-dialyzer according to claim 6 characterized in that the cassette (6) disposed in height relative to the patient (3) is at an adjustable height relative to the latter.  8. Hepato-dialyzer according to claim 1 characterized in that the operating table carrying the patient is of adjustable height relative to the ground.  9. Hepato-dialyzer according to claim 1 and 5 characterized in that at least the inlet conduit of the cassette (6) corresponding to the supply of the portal vein is connected to the outlet conduit of the cassette (6) by a bypass (51) in which is inserted a flow shut-off element (53).  10. Hepato-dialyzer according to claim 1 characterized in that the efferent circuit (10) comprises in series a Vortex type booster (45), a re-injection pump (46) and a bubble detector (47) whose line of purge includes a pressure sensor acting as a detector for the controller (24) for monitoring and managing overall operation.  11. Hepato-dialyzer according to claims 1 and 2 characterized in that the common section of the afferent circuit (2) is equipped with an electric syringe (15) for the injection of a fluidization product.