Cerebral metabolism of ammonia and amino acids in patients with fulminant hepatic failure

Background & Aims: High circulating levels of ammonia have been suggested to be involved in the development of cerebral edema and herniation in fulminant hepatic failure (FHF). The aim of this study was to measure cerebral metabolism of ammonia and amino acids, with special emphasis on glutamine metabolism. Methods: The study consisted of patients with FHF (n = 16) or cirrhosis (n = 5), and healthy subjects (n = 8). Cerebral blood flow was measured by the Xe-133 washout technique. Blood samples for determination of ammonia and amino acids were drawn simultaneously from the radial artery and the internal jugular bulb. Results: A net cerebral ammonia uptake was only found in patients with FHF (1.62 +/- 0.79 mu mol . 100 g(-1) . min(-1)). The cerebral glutamine efflux was higher in patients with FHF than in the healthy subjects and cirrhotics, -6.11 +/- 5.19 vs. -1.93 +/- 1.17 and -1.50 +/- 0.29 mu mol . 100 g(-1) . min(-1), respectively (P < 0.05). Patients with FHF who subsequently died of cerebral herniation (n = 6) had higher arterial ammonia concentrations, higher cerebral ammonia uptake, and higher cerebral glutamine efflux than survivors. Intervention with short-term mechanical hyperventilation in FHF reduced the net cerebral glutamine efflux, despite an unchanged net cerebral ammonia uptake. Conclusions: Patients with FHF have an increased cerebral glutamine efflux, and shortterm hyperventilation reduces this eff lux. A high cerebral ammonia uptake and cerebral glutamine efflux in patients with FHF were associated with an increased risk of subsequent fatal intracranial hypertension.