ObjectiveA recent report suggested that, for hypotensive patients, tissue acidemia is best monitored by simultaneous estimates of arterial pH, mixed venous pH, and bicarbonate. This method of detecting tissue acidemia may therefore apply to fulminant hepatic failure patients, who are known to have a high frequency of covert tissue hypoxia. In the present study, both arterial pH and mixed venous pH and bicarbonate were compared in 22 patients with fulminant hepatic failure. Blood samples were drawn from the pulmonary artery and radial artery and this blood was analyzed to determine oxygen delivery and consumption. The arterial pH, mixed venous pH, and bicarbonate were compared using an oxygen flux test to determine the optimal method of demonstrating tissue hypoxia in this group of patients.DesignA prospective study.SettingThe Liver Unit of our institution.PatientsPatients (n = 22) with fulminant hepatic failure admitted between January 1989 and January 1990.InterventionsPatients were studied before and after an infusion of prostacyclin.Measurements and ResultsThe findings of this study suggest that pH and bicarbonate differences in arterial and mixed venous blood samples were not indicative of tissue hypoxia in patients with fulminant hepatic failure. By contrast, measurement of oxygen consumption after the infusion of prostacyclin, with the demonstrated increase in oxygen uptake, provided a more accurate indication of covert tissue hypoxia.ConclusionsIn critically ill patients with a hyperdynamic circulation, such as those patients with fulminant hepatic failure, an oxygen flux test remains the best method of determining the presence of covert tissue hypoxia.