CEREBRAL PRESSURE AUTOREGULATION AND CARBON-DIOXIDE REACTIVITY DURINGPROPOFOL-INDUCED EEG SUPPRESSION

We studied cerebral pressure autoregulation and carbon dioxide reactiv ity during propofol-induced electrical silence of the electroencephalo gram (EEG) in 10 patients. Anaesthesia was induced with propofol 2.5 m g kg(-1), fentanyl 3 mu g kg(-1) and vecuronium 0.1 mg kg(-1), and a p ropofol infusion of 250-300 mu g kg(-1) min(-1) was used to induce EEG silence. Cerebral pressure autoregulation was tested by increasing me an arterial pressure (MAP) by 24 (SEM 5) mm Hg from baseline with an i nfusion of phenylephrine and simultaneously recording middle cerebral artery blood flow velocity (vmca) using transcranial Doppler. Carbon d ioxide reactivity was tested by varying Pa-CO2 between 4.0 and 7.0 kPa and recording vmca simultaneously. Although absolute carbon dioxide r eactivity was reduced, relative carbon dioxide reactivity was within n ormal 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 (7 7 (4) to 101 (4) mm Hg) during autoregulation testing. We conclude tha t cerebral carbon dioxide reactivity and pressure autoregulation remai n intact during propofol-induced isoelectric EEG.