EFFECT OF INCREMENTAL DOSES OF SEVOFLURANE ON CEREBRAL PRESSURE AUTOREGULATION IN HUMANS

We have examined cerebral pressure autoregulation while awake, and dur ing 0.5 and 1.5 MAC of sevoflurane anaesthesia in 10 patients undergoi ng non-intracranial neurosurgical procedures. All patients received a standardized anaesthetic comprising premedication with temazepam 20 mg orally, a sleep dose of propofol, fentanyl 1 mu g kg(-1) and vecuroni um 0.1 mg kg(-1) After tracheal intubation, the lungs were ventilated with a mixture of air and oxygen to mild hypocapnia. Routine monitors included ECG, continuous and intermittent non-invasive arterial pressu re, pulse oximetry and end-tidal capnography. In addition, blood flow velocity (vmca) was measured by insonating the middle cerebral artery transtemporally using a 2-MHz transcranial Doppler probe. Cerebral pre ssure autoregulation was tested by increasing mean arterial pressure ( MAP) by approximately 20 mm Hg using an infusion of phenylephrine and simultaneously recording vmca. The index of autoregulation (IOR) durin g each period of the study, calculated as the ratio of percentage chan ge in estimated cerebral vascular resistance (CVRe=MAP/vmca) to percen tage change in MAP, was compared using ANOVA. vmca during 0.5 and 1.5 MAC of sevoflurane anaesthesia was significantly lower than that while awake (mean 79 (so 24), 54 (15) and 51 (12) cm s(-1), respectively; P <0.05). There was no significant change in vmca with the increase in M AP while awake, or during 0.5 or 1.5 MAC of sevoflurane anaesthesia an d IOR was similar under the three conditions (0.82 (0.11), 0.83 (0.04) and 1.0 (0.03), respectively). We conclude that cerebral pressure aut oregulation remained intact during sevoflurane anaesthesia in humans.