The influence of nicardipine-, nitroglycerin-, and prostaglandin E1-induced hypotension on cerebral pressure autoregulation in adult patients during propofol-fentanyl anesthesia

We investigated the influence of drug-induced hypotension at a mean arterial pressure (MAP) of 60-70 mm Hg on cerebral pressure autoregulation in 45 adult patients during propofol-fentanyl anesthesia. Time-averaged mean blood flow velocity in the right middle cerebral artery (Vinca) was continuously measured at a PaCO2 of 39-40 nun Hg by using transcranial Doppler ultrasonography. Hypotension was induced and maintained with a continuous infusion of nicardipinc, nitroglycerin, or prostaglandin E-1. Cerebral autoregulation was tested by a slow continuous infusion of phenylephrine to induce an increase in MAP of 20-30 nun Hg. From the simultaneously recorded data of Vmca and MAP, cerebral vascular resistance (CVR) was calculated as MAP/Vmca. Furthermore, the index of autoregulation (IOR) was calculated as DeltaCVR/DeltaMAP, where DeltaCVR = change in CVR and DeltaMAP = change in MAP. The test was performed twice for each condition on each patient: baseline and hypotension. The IOR during baseline was similar among the groups. During nitroglycerin- and prostaglandin E-1-induced hypotension, IOR was not different from baseline. In contrast, during nicardipine-induced hypotension, IOR significantly decreased compared with baseline (0.37 +/- 0.08 versus 0.83 +/- 0.07, P < 0.01). In conclusion, nicardipine, but not nitroglycerin or prostaglandin E-1, significantly attenuates cerebral pressure autoregulation during propofol-fentanyl anesthesia.