Cerebral vasomotor responsiveness to carbon dioxide is preserved during propofol and midazolam anesthesia in humans

Carbon dioxide reactivity, as measured by transcranial Doppler ultrasonography, was determined during total intravenous anesthesia with propofol or midazolam in comparison with an awake control group. Thirty ASA physical status I neurosurgical patients undergoing lumbar laminectomy participated in the study. In randomized order they were subjected to a CO2 reactivity challenge, either under an intravenous anesthesia technique or in the awake state. CO2 reactivity was calculated in each study group as a relative change in middle cerebral artery (MCA) flow velocity per mm Hg change in end-tidal CO2 (PETCO2) (%/mm Hg). The cerebrovascular response to changes in CO2 was preserved during intravenous anesthesia. There was a significant difference (P < 0.05) in the reactivity slopes between the awake and the anesthetized patients with a small but not significant difference between the propofol and the midazolam group. We conclude that hypocarbia is effective in reducing cerebral blood flow velocity (CBFV) during intravenous anesthesia, either with propofol or midazolam.