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 measured by transcranial Doppler, 23 healthy young children were studied during surgery. Anaesthesia was induced with thiopental, fentanyl and vecuronium, and maintained with halothane in 70% nitrous oxide in oxygen. A continuous epidural 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 blood flow velocity was seen between 1.0 and 1.5 MAC. These data show that maximal changes in cerebral blood flow velocity are obtained at 1.0 MAC and that further increases in halothane concentration do not modify the cerebral circulation. It is suggested that young children differ from adults in that the maximal effect of halothane occurs at lower concentrations.