Cerebral blood flow and oxygen consumption during isoflurane and halothane anesthesia in man.

In 13 patients, the effects on cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) of isoflurane and halothane administered in a clinically relevant situation were studied. Measurements were performed during fentanyl/nitrous oxide (65%) anesthesia together with moderate hyperventilation (PaCO2 approx 4.5 kPa), and repeated after addition of 0.65 MAC of isoflurane (n = 6) or halothane (n = 7). CBF was measured after intravenous administration of 133xenon and CMRO2 was calculated from the arterial venous differences of oxygen content (AVDO2) determined in arterial and jugular venous bulb blood. CBF and CMRO2 (means +/- s.e. mean) determined prior to administration of volatile agents were 28 +/- 5 ml x 100(-1) x min-1 and 2.0 +/- 0.3 ml x 100 g-1 x min-1, respectively, in the isoflurane group. In the halothane group, CBF was 25 +/- 0.4 ml x 100 g-1 x min-1 and CMRO2 was 2.0 +/- 0.4 ml x 100 g-1 x ml-1. There were no significant intergroup differences. Isoflurane did not change CBF, whereas halothane produced an increase of 36% (P less than 0.05) compared to values obtained during fentanyl/N2O anesthesia. In addition, isoflurane caused a further decrease in CMRO2 of 12% (P less than 0.01) as compared to a 20% increase (P less than 0.05) with halothane. The cerebral metabolic depression caused by the short-acting anesthetic induction agents would be expected to decrease with time, and could partly explain the observed increase in CMRO2 produced by halothane. The study suggests that the cerebrovascular and metabolic properties of isoflurane differ from those of halothane, also in man.