Changes in CMRO2, EEG and concentration of etomidate in serum and brain tissue during craniotomy with continuous etomidate supplemented with N2O and fentanyl.

Fourteen patients with supratentorial cerebral tumours were anaesthetized with continuous etomidate infusion (30 or 60 micrograms kg-1 min-1) supplemented with N2O 67% and fentanyl. Peroperatively cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) were measured twice by the Kety and Schmidt method. Simultaneously with the CBF measurements, blood for serum etomidate was sampled and EEG was recorded in 2-min periods in 12 patients. In 10 patients a brain biopsy for etomidate was taken peroperatively and correlated with the other data. The results indicate a dose-dependant increase in serum etomidate and brain tissue etomidate, a decrease in CMRO2 and suppression of EEG activity. In individual studies an increase in serum etomidate or a decrease in CMRO2 correlated to a suppression of the EEG activity, and vice versa. However, the wide variations in these relationships within and between patients make any conclusion regarding CMRO2 impossible from the EEG recording, infusion rate of etomidate or serum concentration of etomidate.