Orthostasis in halothane anesthesia. A model situation for studying cerebrovascular autoregulation in infants]

Halothane causes impairment of cerebrovascular reactivity and autoregulation. We used transcranial Doppler sonography (TCD) to investigate the reaction patterns of cerebral blood flow velocities (CBFV) during a standardized orthostatic maneuver after premedication and during halothane anesthesia in infants. After premedication orthostasis led to no significant changes in CBFV. During halothane anesthesia CBFV was significantly higher than after premedication, and orthostasis induced a significant decrease in CBFV compared to values obtained in horizontal position. Heart rate and mean blood pressure were significantly lower than before medication during halothane anesthesia. The observed changes in CBFV during halothane anesthesia represent a characteristic pattern of impaired cerebral autoregulation. The changes in CBFV and heart rate demonstrate that neither systemic nor cerebral hemodynamics compensate for hydrostatic inducement during halothane anesthesia. The tilting test is a useful tool for determining cerebral autoregulation capacity in infants.