Alterations in cerebral blood flow, oxygen metabolism, and electrical activity produced by high dose sodium thiopental.

High dose barbiturate therapy is being used with increasing frequency in the management of a widening spectrum of neurological disorders. Accurate regulation of the barbiturate dose is essential to maximize cerebral vasoconstriction and reduce brain metabolism while avoiding the cardiovascular depressant side effects of the drug. The purpose of this study was to determine whether the electroencephalogram (EEG) could be used to regulate administration of the agent. In nine mongrel dogs cerebral blood flow (CBF) was determined using the radioactive microsphere technique. After the determination of control CBF, a slow infusion of sodium thiopental was begun. CBF determinations were repeated when the periods of burst suppression in the EEG over several minutes averaged 30, 60, 120, and 240 seconds. CBF and oxygen metabolism showed a nearly identical pattern of a precipituos drop from control levels reaching a plateau at burst suppression between 30 and 60 seconds. Changes in cerebrovascular resistance were of a similar but opposite nature. Significant increases in heart rate occurred with burst suppression of 30 seconds, whereas the arterial pressure and cardiac index decreased with burst suppression between 30 and 60 seconds. In this study cerebral metabolic depression and vasoconstriction from sodium thiopental reached a plateau when sufficient barbiturate was administered to produce EEG burst suppression of between 30 and 60 seconds. At this level there was no important cardiovascular depression. Administration of additional barbiturates significantly decreased systemic arterial pressure and cardiac output, but produced no further decrement in the cerebral metabolic rate of oxygen or the CBF. There was no predictable relationship between cerebral metabolism or cardiovascular function and blood levels of sodium thiopental.