Few experimental studies are available concerning whole organ liver homotransplantation, and all of these involve the use of dogs. Goodrich and his colleagues published the first extensive experiments on hepatic transplantation in 1956. The value of these investigations was limited by the fact that the organs were transplanted to the pelvis, without removal of the dog's own liver, Since then, Moore (4
) and Starzl (9
) and their colleagues have reported succcssful hepatic transplantation in dogs with anatomically normal placement of the homograft after removal of the recipient's own liver. These studies clarified the physiological and biochemical events which transpire during rejection of hepatic grafts. In addition. the investigations defined the specific difficulties which must be surmounted if operative failure is to be avoided.
The provision of a viable and minimally damaged homograft is undoubtedly the most important single factor in the determination of success. It is necessary to obtain the donated tissue from a cadaver. Yet the extraordinary sensitivity of the tissue to anoxia requires that an adequate hepatic circulation be present before death and that some form of hepatic preservation be instituted immediately after death before the onset of irreversible cellular injury. For the latter purpose, the hypothermic perfusion technique recently developed by Marchioro and his colleagues was used. It is possible with this method simultaneously to cool and perfuse the liver within a few minutes after death. before beginning its operative removal. The most effective means of postmortem preservation are futile, however, if the moribund state has been protracted. In Patient 1, the selection of a donor after prolonged cardiac massage was unwise. In contrast, the circumstances of death of the donors for Patients 2 and 3 were highly favorable.
Although the technique of hypothermic perfusion has made liver transplantation feasible, the method has definite limitations in extending the postmortem viability of hepatic tissue. Marchioro and his associates have shown that severe hepatocellular injury almost invariably occurs with perfusions of more than 2 hours. The policy of staging the operation in the recipients, which was followed in the last 2 patients, allows reduction of this time to a minimum. After preliminary mobilization of the diseased liver and preparation of the structures for subsequent anastomoses, the definitive second operation can be performed after the incision has been quickly reopened with a minimum of tedious time-consuming dissection.
The surgical details of implantation involve, for the most part. utilization of well standardized surgical methods. The vascular anastomoses frequently must be performed with short cuffs and with limited exposure, necessitating intraluminal suturing techniques (). The greatest hazard is in performance of the inferior vena caval anastomosis at the diaphragm. Both the donor and recipient segments of the vena cava often have orifices of small posterior phrenic tributaries which are unknowingly severed when the respective livers are removed. Such open orifices are located a short distance from the cut edge of and can only be seen from the inside of the vessel. Failure to suture the openings during the caval-caval anastomosis results in later hemorrhage at a time when the presence of the homograft makes secondary exposure of this area almost impossible. The double suture method developed in dogs for this anastomosis has virtually eliminated this problem ().
Reconstitution of internal biliary drainage in infants will probably be most effectively accomplished with a Roux-en-Y cholecystojejunostomy. In the 2 adults, choledochocholedochostomy was simple to perform by the stenting of the anastomosis with a T tube inserted through the recipient portion of the common duct ( ). Although the principal arterial supply to the common duct comes from retroduodenal sources, Parke, Michels, and Ghosh have demonstrated that vascular contributions, upon which viability of the donor common duct depends, also come from the hepatic arteries in the hilum of the liver.
One unique technical requirement is for decompression of the venous systems which must be temporarily occluded during the transplantation. In the dog, failure to obtain satisfactory drainage from these venous pools results in certain failure, particularly when any degree of venous hypertension is allowed to develop in the splanchnic bed. In man, the necessity for providing drainage from at least the portal system is probably not so important as in the dog. Child has demonstrated that acute occlusion of the portal vein in monkeys and man is usually well tolerated, presumably because collateral channels are more abundant in primates than in lower forms. Indeed, it was demonstrated in the presently reported 3 cases that drainage of the portal system was not necessary. In 2 of the 3 patients, external bypasses were not used, and in the third, flow ceased after a few minutes. The conclusion seems justified that a single effective bypass from the inferior vena cava to the superior vena cava is all that is required for adequate venous return to the heart from both the inferior vena caval and portal systems.
Experience with these 3 patients stresses the need for close control of the coagulation processes during and after transplantation. Profound clotting defects were demonstrated in all at the time of transplantation resulting in fatal hemorrhage in the first patient. The hemorrhagic tendency did not result from an acute deficiency of those clotting factors which are synthesized in the liver. Analysis of plasma fibrinogen during the liverless phase in Patients 2 and 3 did not reveal a clinically significant drop, a finding in accord with many experimental studies which show that a substantial decrease in clotting factors after total hepatectomy requires several hours to develop. Instead, the important finding appeared to be an explosive increase in the plasma fibrinolytic activity which developed within minutes, both during manipulation of the liver () and after its removal (). The exact cause of this change is open to some speculation. As a working hypothesis, it might be assumed that the liver normally elaborates a substance which inhibits conversion of plasminogen to plasmin (fibrinolysin) presumably by a deterrent action on a plasminogen activator. Absence of the liver or severe hepatic injury during operative manipulation could conceivably permit uncontrolled conversion of plasminogen to plasmin by removal of such a restraining influence on the activator system.
Whatever the explanation for the increased fibrinolytic activity, it is imperative to anticipate this tendency and to provide prophylactic treatment before a frank hemorrhagic diathesis develops. In the second and third patients, EACA was administered prophylactically, within a few minutes after removal of the recipient's liver. This drug, which prevents activation of plasminogen to plasmin by inhibiting plasminogen activators, apparently prevented the fibrinolytic crisis in these last 2 patients despite profound decreases in euglobulin lysis time. The administration of fibrinogen and fresh blood at the time of transplantation are probably also of significant value in reducing the danger of a hemorrhagic diathesis.
In view of the effort expended to define and prevent the hemorrhagic diathesis which led to the death of the first patient, it is ironic that Patients 2 and 3 should have died because of the late consequences of intravascular clotting. In both the latter paticnts, the immediate cause of death was multiple pulmonary emboli. In both, the characteristic clotting deficiency which was observed at the time of operation was sueceeded by a hypcrcoagulable state several days later, which may have been an important contributing factor in the formation and propagation of the emboli.
The source of the pulmonary emboli in Patients 2 and 3 is a matter of interest. It is encouraging that the vascular suture lines of the transplant itself did not have a selective tendency to develop thrombosis. Rather, the peripheral thrombosis in Patient 2 was in the right iliac vein and the terminal inferior vena cava, which led to the belief that protection from this complication would be afforded by the use of Spencer's vena caval plication procedure. In Patient 3, however, in which vena caval plication was performed, a peripheral focus of thrombus could not be found at autopsy. It is possible in this paticnt and in the second one as well that semi-fluid clots were originally formed in and passed through the external bypass system from the inferior to the superior vena cava during the transplantation. The early devcloprncnt of respiratory distress in both patients is compatible with such a sequence of events. In future attempts at hepatic homotransplantation, it is probable that these embolic complications can be prevented with well timed and accurately controlled heparin therapy, either at the time when the external bypass is in use or in the postoperative period.
This experience with humans has confirmed many previous experimental impressions of the functional behavior of the hepatic homograft. In dogs receiving liver homografts under optimal circumstances of cooling and minimal donor organ ischemia, there is a prompt resumption of hepatic metabolism with minimal immediate derangcment of function. Biochemical evidence of graft repudiation begins on the fourth or fifth day in the untreated animal, but this can be mitigated or prevented by the use of a therapeutic regimen similar to that employed in the clinical cases. The most useful measurements to follow the course of the rejection process are serum bilirubin, serum alkaline phosphatase, and serum glutamic oxalacetic acid transaminase. Under more adverse experimental conditions, simulating those necessary in a clinical setting, Marchioro and his colleagues have shown that there is a moderately severe ischemic injury to the canine liver, manifested by sharp rises in bilirubin, alkaline phosphatase and SGOT within the first 24 hours. Differentiation of the latter nonspecific changes from those due to rejection is an important aspect of the postoperative care.
Both of the patients who survived the operative procedure exhibited a functional pattern of acute parenchymal injury. Rises in SGOT to 950 to 1150 SF units occurred within the first day and then rapidly receded. Jaundice temporarily deepened. The subsequent curves of various function tests were in the direction of improvement until immediately before death, demonstrating the reversibility of these early changes.
The experiences in these cases have demonstrated that the immediate problems of clinical hepatic homotransplantation are subject to practical solution. They provide little information, however, concerning the feasibility of long term maintenance of liver homografts, although the progressive improvement of liver function and the degree of histologic preservation of the transplants after 7½ and 22 days are encouraging notations. In unpublished observations from our laborntorics, it has been found possible to obtain prolongation of survival of pharmacologically altered dogs with liver homografts, which has been comparable to that obtained in treated animals receiving renal homografts. Ultimately, it may be necessary to conclude that the treatment required to prevent rejection is significantly different with livers than with kidneys. At present, however, there is no evidence to support such a belief, and the further acquisition of experience in the treatment of these otherwise doomed patients appears to be justified.