Orthostasis during halothane anesthesia. A model situation for investigation of cerebrovascular autoregulation in infants

Halothane causes impairment of cerebrovascular reactivity and autoregulatio n. We used transcranial Doppler sonography (TCD) to investigate the reactio n patterns of cerebral blood flow velocities (CBFV) during a standardized o rthostatic maneuver after premedication and during halothane anesthesia in infants. After premedication orthostasis led to no significant changes in CBFV. Duri ng halothane anesthesia CBFV was significantly higher than after premedicat ion, and orthostasis induced a significant decrease in CBFV compared to val ues obtained in horizontal position. Heart rate and mean blood pressure wer e significantly lower than before medication during halothane anesthesia. T he observed changes in CBFV during halothane anesthesia represent a charact eristic pattern of impaired cerebral autoregulation. The changes in CBFV an d heart rate demonstrate that neither systemic nor cerebral hemodynamics co mpensate for hydrostatic inducement during halothane anesthesia. The tilting test is a useful tool for determining cerebral autoregulation c apacity in infants.