Differential effects of hyperventilation on cerebral blood flow velocity after tourniquet deflation during sevoflurane, isoflurane, or propofol anesthesia.

The purpose of this study was to compare the degree of increase in middle cerebral artery (MCA) blood flow velocity after tourniquet deflation when modulating hyperventilation during orthopedic surgery under sevoflurane, isoflurane, or propofol anesthesia. Twenty-four patients undergoing elective orthopedic surgery were randomly divided into sevoflurane, isoflurane, and propofol groups. Anesthesia was maintained with sevoflurane, isoflurane, or propofol administration with 33% oxygen and 67% nitrous oxide at anesthetic drug concentrations adequate to maintain bispectral values between 45 and 50. A 2.0-MHz transcranial Doppler probe was attached to the patient's head at the temporal window, and mean blood flow velocity in the MCA (V (mca)) was continuously measured. The extremity was exsanguinated with an Esmarch bandage, and the pneumatic tourniquet was inflated to a pressure of 450 mmHg. Arterial blood pressure, heart rate, V (mca) and arterial blood gases were measured every minute for 10 min after release of the tourniquet in all three groups. Immediately after tourniquet release, the patients' respiratory rates were increased to tightly maintain end-tidal carbon dioxide (PetCO(2)) at 35 mmHg. No change in partial pressure of carbon dioxide in arterial blood (PaCO(2)) was observed pre- and posttourniquet deflation in any of the three groups. Increase in V (mca) in the isoflurane group was greater than that in the other two groups after tourniquet deflation. In addition, during the study period, no difference in V (mca) after tourniquet deflation was observed between the propofol and sevoflurane groups. Hyperventilation could prevent an increase in V (mca) in the propofol and sevoflurane groups after tourniquet deflation. However, hyperventilation could not prevent an increase in V (mca) in the isoflurane group.