Splanchnic circulation and metabolism in patients with acute liver failure.

Acute liver failure is associated with mortality of around 50%. The aim of the present studies was to examine the circulatory and metabolic state of the splanchnic region in acute liver failure. This had not been studied previously and it could be expected that improved understanding of the pathophysiology of acute liver failure could lead to improved therapy. Hepatic plasma flow was estimated in patients with acute liver failure after development of hepatic encephalopathy grade III, by the use of liver vein catheterization and continuous infusion of sorbitol. The method was evaluated against the prerequisites of Fick's principle. Hepatic plasma flow could be estimated with sorbitol but not in all patients and the standard error of the estimated hepatic blood flow was higher than in other patient groups. In 20 patients with acute liver failure, mean hepatic blood flow was increased. At the same time, the systemic and the peripheral hemodynamics were examined. The ratio hepatic blood flow/cardiac output was increased in many patients. Lower extremity blood flow was within normal limits. Thus, low systemic vascular resistance index in acute liver failure was likely to be a consequence of vasodilatation in the muscular resistance vessels and, in particular, in the splanchnic resistance vessels. Intervention with high-volume plasmapheresis changed systemic and splanchnic hemodynamics differently, suggesting that the splanchnic vasodilatation in liver failure may by caused by a specific mechanism different from the one that leads to peripheral vasodilatation. Infusion of dopamine increased mean arterial pressure, cardiac output, and hepatic blood flow in acute liver failure. The splanchnic exchange of substrates for oxidative metabolism was examined. Splanchnic oxygen consumption was increased. The ratio splanchnic oxygen consumption/systemic oxygen consumption indicated that 1/3 of the oxygen used in the whole body in acute liver failure was used in the splanchnic region. The splanchnic metabolism of fuel substrates was abnormal. Lactate and pyruvate was released and there were no detectable gradients of free fatty acids or of the sum of amino acids. There was a small release of ketone bodies. The data suggested that the energy needs of the failing liver was covered by intracellular fat. The hypothesis of splanchnic tissue hypoxia was examined from different approaches. The normal hepatic venous oxygen saturation, the splanchnic release of both lactate and pyruvate, and a normal hepatic venous pyruvate/lactate ratio in the presence of low acetoacetate/hydroxybutyrate ratio rather indicated high substrate turnover than splanchnic tissue hypoxia. Amino acid and ammonia metabolism was examined. It was observed that arterial ammonia concentration measured after institution of mechanical ventilation was associated with cerebral herniation 1-5 days later. The background for hyperammonemia was that ammonia was released from the splanchnic circulation. The data implied that glutamine was deamidated in the gut and alanine and ammonia was released into the portal vein as during normal circumstances. Then due to severely decreased hepatic function the liver was unable to remove ammonia and alanine as it normally would. Further, the data implied that urea synthesis was impaired. Exchange of ammonia in muscle tissue was studied in 7 patients with acute liver failure and muscle tissue seems to play a major role in ammonia detoxification in acute liver failure. Treatment with high-volume plasmapheresis decreased arterial ammonia, which was likely due to increased urea production or stimulation of glutamine synthesis in muscle tissue. These findings add to our understanding of the pathophysiology and have implications for the management of acute liver failure.