The cerebral metabolic effects of a massive dose of thiopental (177 mg/kg) were investigated in seven dogs. The systemic circulation was supported with an extracorporeal circuit. At an infusion rate of 2 mg/kg/min, cerebral oxygen consumption (CMRO2) decreased progressively until cerebral electrical silence was produced. This occurred after a mean dose of 72 mg/kg, which caused a mean decrease in CMRO to 58 per cent of the control value (measured at 1.5 per cent halothane inspired). Thereafter, despite continued infusion at 4 mg/kg/ min, CMRO2 did not decrease further. The oxygen-glucose index never changed during the infusion period and, at the termination of the infusion, brain assays for ATP, phosphocreatine, lactate, and pyruvate revealed normal concentrations. It is concluded that there was no alteration in normal cerebral metabolic pathways, that cerebral metabolic effects of thiopental are secondary to functional effects, that thiopental would provide no cerebral protection during hypoxia sufficient to abolish cerebral function, and that thiopental does not uncouple oxidative phosphorylation in vivo.
(C) 1974 American Society of Anesthesiologists, Inc.