Cerebral Circulation and Metabolism during Enflurane Anesthesia in Humans

Abstract

The effects of enflurane anesthesia on cerebral blood flow (CBF) and cerebral metabolic rate for O2 (CMRO2) were studied in 17 patients. The patients were divided into 2 groups according to the depth of anesthesia. Cerebral perfusion pressure was maintained above 60 mmHg with phenylephrine. Group 1 (arterial enflurane concentration, 15 mg/dl) patients were studied before surgery while in group 2 (enflurane concentration, 27 mg/dl), the measurements were performed before and during surgery. In group 1, mean CBF and CMRO2 were 53 and 2.8 ml/100 g per min, respectively. These values were not significantly different from CBF (46 ml/100 per min) and CMRO2 (3.1 ml/100 g per min) values previously obtained in awake patients. In group 2 before surgery, mean CBF and CMRO2 were 61 and 2.6 ml/100 g per min, respectively, and were significantly different from the awake values, while the EEG showed frequent spikes and suppression. In group 2 during surgery, mean CBF and CMRO2 did not differ from the values obtained before surgery, despite significant EEG changes. Apparently, enflurane is a cerebral vasodilator and causes an increase in CBF and a decrease in CMRO2 in humans at an anesthetic level characterized by frequent spikes and suppression on the EEG.