**4. Discussion**

Liver transplantation in the rhesus monkey frequently uses the classical model because the inferior vena cava is embedded in the parenchyma of the posterior segment of the liver, making the anatomy unsuitable for piggyback liver transplantation. The rhesus monkey is fragile and often dies early following experimental transplantation. In this study, seven animals (66.7%) died within 6 hours after portal vein opening, seven died at 12–72 hours and eleven died at > 72 hours. The double-cuff method has been used extensively in established liver transplantation models. This model significantly shortens the duration of the anhepatic phase, decreases the incidence of portal vein bleeding and stenosis, and decreases the incidence of early death.

#### **4.1 Abdominal hemorrhage in rhesus monkeys following liver transplantation**

In this study, the main cause of death was abdominal hemorrhage in the early postoperative period (within 6 hours after portal vein opening). In small animals such as rats, abdominal hemorrhage is also the major cause of death after reduced-size liver transplantation. This bleeding is often from the inferior vena cava anastomosis above the liver but has also been observed from the ligation points, liver capsule, right adrenal vein, lumbar veins, portal vein and inferior vena cava below the liver. In this study, abdominal hemorrhage was most often from the anastomoses of the portal vein and the inferior vena cava below the liver, and was also observed from the anastomosis of the inferior vena cava above the liver, liver bed, liver capsule, right adrenal vein and lumbar veins, similar to the bleeding points observed in rats. Abdominal hemorrhage sometimes involved multiple sites in one animal. In this study, the animals did not tolerate bleeding well and showed signs of decreased peripheral circulation after a blood loss of 100 mL. Animals with abdominal hemorrhage commonly died within 6 hours after portal vein opening. Rhesus monkeys may also have a preoperative hypercoagulable state and a postoperative hypocoagulable state, greatly influencing the stability of this model. Hemostasis and fluid balance are therefore very important for successful liver transplantation in the rhesus monkey. As a variety of factors contribute to the development of abdominal hemorrhage, surgeons should be familiar with the surgical procedures used including microsurgical techniques. Our original model prior to

Causes of Death of Rhesus Monkeys Undergoing Liver Transplantation 541

incidence of thrombosis, (2) the rhesus monkey has a relatively low body mass, (3) a hypercoagulable state is common in the rhesus monkey and (4) rejection causes damage to the tunica intima, resulting in degeneration or necrosis and subsequent arterial thrombosis.

Pulmonary infection is one of the causes of early death following reduced-size liver transplantation in rats, and may be due to an infection focus prior to surgery or to aspiration during surgery. Kamada et al proposed that an anhepatic phase of 26 minutes was safe. Shortening of the anhepatic phase to restore organ perfusion and maintain hemodynamic function is one method to reduce the rate of pulmonary infection following reduced-size liver transplantation, as pulmonary infection is associated with prolonged blood vessels clamping. Prolonged clamping of the portal vein causes prolonged intestinal tract congestion, increasing the likelihood of enteric bacteria entering the circulation and of inflammation-induced lung injury. Preoperative intramuscular atropine to reduce respiratory secretions, small tidal volume anesthesia to reduce aspiration and comfortable living environment and surgical conditions can help to prevent pulmonary infection in rats. In this study, pulmonary infection caused one death in the short-term postoperative period

One animal in this study died due to primary nonfunction and one due to pneumothoraxinduced respiratory failure. Both these animals underwent transplantation using our original surgical model. The primary nonfunction may have been due to the significant fatty degeneration (> 50%) of the donor liver and the differences in weight between donor and recipient causing microhepatia. This animal underwent an anhepatic phase of approximately 1 hour with significant blood loss after portal vein opening, and deteriorated postoperatively with high bilirubin levels, hypoventilation, mydriasis, respiratory arrest and cardiac arrest. Autopsy showed no bleeding, a large amount of ascites in the abdominal cavity and gaseous distension of the gastrointestinal tract. In one animal, the diaphragm was damaged during surgery, resulting in pneumothorax. This animal died due to respiratory failure despite attempted treatment. Autopsy showed a normal liver, no abdominal bleeding or ascites, a bulging diaphragm, gas in the abdominal cavity and collapse of both lungs.

Compared with the rat model, establishment of an orthotopic liver transplantation model in large animal such as the monkey is more difficult. There are some important issues to consider to improve animal survival rate following liver transplantation. The quality of the donor liver is a key factor, and donation of an unhealthy liver is not appropriate. The weight of recipient and donor livers should be similar for the donor liver to function well. Intraoperative blood loss and injury to tissues and organs should be minimized. The modified cuff technique can minimize the duration of the anhepatic phase and of anesthesia, reducing circulatory and other systemic problems. Care should also be taken in perioperative management. This study analyzes the causes of death of rhesus monkeys at different stages following liver transplantation, which can help to modify models of liver transplantation to improve survival rate and to increase the quality of future

**4.4 Pulmonary infection** 

experimental studies.

and two deaths in the long-term postoperative period.

**4.5 Other causes of death following liver transplantation** 

modification used direct anastomosis, which is a complex and time-consuming process, increasing the duration of the anhepatic phase and resulting in circulatory and other systemic problems following portal vein opening. Liver transplantation may also lead to coagulation disorders, resulting in wound hematoma. In this study, seven animals (28%) died of abdominal hemorrhage following transplantation; five (71.4%) in the early postoperative period and two (28.6%) in the short-term postoperative period.
