Effects of propofol on cerebral blood flow and the metabolic rate of oxygen in humans

Background: Effects of propofol on human cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2 ), and blood flow-metabolism coupling have not been fully evaluated. We therefore assessed the effects of propofol on total-CBF and CMRO2 in patients without noxious stimuli and neurologic disorders. Methods: General anesthesia was induced with midazolam (0.2 mg/kg) and fentanyl (5 mug/kg) in 10 patients (ASA physical status I) undergoing knee joint endoscopic surgery. Epidural anesthesia was also performed to avoid noxious stimuli during surgery. Cerebral blood flow (CBF) and cerebral arteriovenous oxygen content difference (a-vDO(2) ) was measured using the Kety-Schmidt method with 15% N-2 O as a tracer before and after propofol infusion (6 mg/kg/h for 40 min), and the CMRO2 was also calculated. Results: CBF decreased following propofol infusion from 34.4 ml/100 g/min (range 28.4-52.0) to 30.0 ml/100 g/min (range 20.2-42.4) (P =0.04). Although there was no significant change in a-vDO(2) , CMRO2 decreased following propofol infusion from 2.7 ml/100 g/min (range 2.2-4.3) to 2.2 ml/100 g/min (range 1.4-3.0) (P =0.04). There was a strong linear correlation between CBF and CMRO2 (r= 0.90). Conclusion: Propofol proportionally decreased CBF and CMRO2 without affecting a-vDO(2) in humans, suggesting that normal cerebral circulation and metabolism are maintained.