The effect of isoflurane on cerebral blood flow and metabolism in humans during craniotomy for small supratentorial cerebral tumors.

Fourteen patients were studied during craniotomy for small supratentorial cerebral tumors. Cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) were measured twice by a modification of the Kety-Schmidt technique using 133Xe intravenously. Anesthesia was induced with thiopental 5-7 mg X kg-1, fentanyl 0.2 mg, and pancuronium, and maintained with 0.75% inspired isoflurane concentration in 67% nitrous oxide, and moderate hypocapnia. In one group of patients (n = 7), the inspired isoflurane concentration was maintained at 0.75% throughout anesthesia. One hour after induction of anesthesia, CBF and CMRO2 averaged 31 +/- 3 ml X 100 g-1 X min-1 and 2.1 +/- 0.2 ml O2 X 100 g-1 X min-1 (X +/- SEM), respectively. During repeat studies 1 h later, CBF and CMRO2 were unchanged. In a second group of patients (n = 7), an increase in the inspired isoflurane concentration from 0.75% to 1.5% was associated with a significant decrease in CMRO2 from 2.4 +/- 0.1 to 1.9 +/- 0.1 ml O2 X 100 g-1 X min-1, and no change in CBF. It is concluded that this anesthetic regimen is safe to use in patients with small supratentorial tumors in whom only a small midline shift has occurred.