Cerebral pressure autoregulation and carbon dioxide reactivity during propofol-induced EEG suppression

We studied cerebral pressure autoregulation and carbon dioxidereactivity during propofol-induced electrical silence of theelectroencephalogram (EEG) in 10 patients. Anaesthesia was inducedwith propofol 2.5 mg kg^–1, fentanyl 3 µg kg^–1and vecuronium 0.1 mg kg^–1, and a propofol infusion of250–300 µg kg^–1 min^–1 was used to induceEEG silence. Cerebral pressure autoregulation was tested byincreasing mean arterial pressure (MAP) by 24 (SEM 5) mm Hgfrom baseline with an infusion of phenylephrine and simultaneouslyrecording middle cerebral artery blood flow velocity (vmca)using transcranial Doppler. Carbon dioxide reactivity was testedby varying Pa_co2 between 4.0 and 7.0 kPa and recording vmcasimultaneously. Although absolute carbon dioxide reactivitywas reduced, relative carbon dioxide reactivity was within normallimits for all patients studied (mean 8.5 (SEM 0.8) cm s^–1kPa^–1 and 22 (2)% kPa^–1, respectively). No significantchange in vmca (34 (2) and 35 (2) cm s^–1) was observedwith the increase in MAP (77 (4) to 101 (4) mm Hg) during autoregulationtesting. We conclude that cerebral carbon dioxide reactivityand pressure autoregulation remain intact during propofol-inducedisoelectric EEG.