Hemodynamic effects of high dose pentobarbital: studies in elective neurosurgical patients.

High dose barbiturate therapy has been used clinically for about 10 years. However, the hemodynamic consequences of such therapy have not been well defined in humans. We therefore examined the effects of a brief (30-minute), high dose (0.6 mg/kg/minute or 18 mg/kg total) infusion of pentobarbital in nine otherwise healthy patients (aged 20 to 30) scheduled to undergo operation for the removal of large or deeply seated arteriovenous malformations. Monitored variables included intravascular pressures, cardiac output, arterial and mixed venous blood gases and hematocrit, and the electroencephalogram (EEG). After a brief rest period and the collection of control data, pentobarbital infusion was begun, muscle relaxants were given, and normocarbia was maintained by mask ventilation. Because our primary intent was to examine the effects of the drug on the heart and arterial circulation, lactated Ringer's solution was infused continuously to keep pulmonary capillary wedge pressure (PCWP) at control values in an attempt to keep constant the ventricular "preload" (although PCWP is only an approximation of the true preload). Drug infusion resulted in progressive EEG suppression ending in a pattern of deep burst suppression (1 to 3 bursts/minute) at t = 30 minutes, with measured plasma pentobarbital concentrations (in four patients) of 34 +/- 4 micrograms/ml (mean +/- SD). There were no changes in PaO2, PaCO2, or pH, nor were there any changes in PCWP. The cardiac index did not change.(ABSTRACT TRUNCATED AT 250 WORDS)