Haemodynamics and function of the isolated perfused pig liver
Casey ND., Friend P., Butler A.
Over the past forty years extensive work has been carried out in the field of liver perfusion and function in an effort to understand its mechanisms and to enable us a develop methods of treatment for the injured ad failing liver. One problem we face with a patient in liver failure is that the livers reduced function inhibits its ability to regenerate and thus it is thought that a method of resting the liver or supporting its function would enable it to recover sufficiently to independently support the patient or suffice as a bridge to transplantation. Several world-wide centres in the late 1960s' attempted this by placing an animal liver in an isolated extracorporeal perfusion circuit and then connecting this to a patient via veno-veno bypass. This succeeded in reversing hepatic coma to varying degrees but ultimately failed in all cases due to, presumably, immunological complications with the patient and the gradual failure of the isolated animal liver. The progressive failure of the isolated perfused liver was also evident when the animal liver was not connected to the patient. With the considerable advancements in understanding and the technology of extracorporeal perfusion combined with our better understanding of the physiology of the liver and the immune system we set out to see if we could make this old principle work in practice. The initial study group of eleven pigs were selected, their livers mobilised and harvested in the standard manner for transplantation. Cannulac were then placed into the upper and lower inferior vena cava, hepatic artery portal vein and bile duct. The cystic duct was ligated and them connected to the perfusion circuit. The Perfusion circuit copsisted of a Medtronic paediatric Minimax oxygenator/heat exchanger, Medtronic Biomedicus paediatric BP50 centrifugal pump, Medtronic 1/4″ ID PVC tubing and an Avecor paediatric 500ml soft-shell venous reservoir. The circuit was primed with litter matched pig blood. The circuit was designed to deliver physiological flows and pressures to the liver with normal temperature, blood gases and electrolytes. Once the initial runs dealing with technique and methodology were completed we progress to isolated perfusion runs lasting in excess of twenty four hours with no apparent reduction in liver function or quality. Unlike our predecessors we did not create a progressive portal hypertension and in one perfusion run, where our initial liver preservation was far from ideal resulting in an acidotic and partially perfused liver, we managed over time to reverse the acidosis and regain full function to the liver thus resuscitating it. The next sudy group, that we are working on at the moment, will be where we connect the isolated perfused liver to another pig that has been placed in liver failure in an attempt to reverse hepatic coma and allow paracorporeal liver support until native liver funtion returns!