The effect of low concentrations of halothane on the cerebrovascular circulation in young children

To determine the effect of halothane on cerebral blood flow velocity measur ed by transcranial Doppler, 23 healthy young children were studied during s urgery. Anaesthesia was induced with thiopental, fentanyl and vecuronium, a nd maintained with halothane in 70% nitrous oxide in oxygen. A continuous e pidural anaesthesia with 0.25% bupivacaine was performed. End-tidal carbon dioxide pressure, temperature, heart rate and systolic blood pressure were kept constant. Three minimal alveolar concentrations (MAC; 0.5, 1.0 and 1.5 ) of halothane were administered in stepwise increases. The cerebral blood flow velocity increased significantly at 1.0 (p < 0.01) and 1.5 MAC (p < 0. 001) compared with the value at 0.5 MAC. No further change in cerebral bloo d flow velocity was seen between 1.0 and 1.5 MAC. These data show that maxi mal changes in cerebral blood flow velocity are obtained at 1.0 MAC and tha t further increases in halothane concentration do not modify the cerebral c irculation. It is suggested that young children differ from adults in that the maximal effect of halothane occurs at lower concentrations.