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

We studied cerebral pressure autoregulation and carbon dioxide reactivity during propofol-induced electrical silence of the electroencephalogram (EEG) in 10 patients. Anaesthesia was induced with propofol 2.5 mg kg-1, fentanyl 3 micrograms kg-1 and vecuronium 0.1 mg kg-1, and a propofol infusion of 250-300 micrograms kg-1 min-1 was used to induce EEG silence. Cerebral pressure autoregulation was tested by increasing mean arterial pressure (MAP) by 24 (SEM 5) mm Hg from baseline with an infusion of phenylephrine and simultaneously recording middle cerebral artery blood flow velocity (vmca) using transcranial Doppler. Carbon dioxide reactivity was tested by varying PaCO2 between 4.0 and 7.0 kPa and recording vmca simultaneously. Although absolute carbon dioxide reactivity was reduced, relative carbon dioxide reactivity was within normal limits for all patients studied (mean 8.5 (SEM 0.8) cm s-1 kPa-1 and 22 (2)% kPa-1, respectively). No significant change in vmca (34 (2) and 35 (2) cm s-1) was observed with the increase in MAP (77 (4) to 101 (4) mm Hg) during autoregulation testing. We conclude that cerebral carbon dioxide reactivity and pressure autoregulation remain intact during propofol-induced isoelectric EEG.