Transcranial Doppler sonography: effects of halothane, enflurane and isoflurane on blood flow velocity in the middle cerebral artery.

Systolic, diastolic, and mean blood flow velocity in the middle cerebral artery (Vs,mca; Vd,mca; Vm,mca) and pulsatility (Vs-Vd)/Vm of the waveform obtained were recorded in 51 patients before, during and after general anaesthesia. Transcranial Doppler (TCD) sonographic variables were measured in the awake patient and after induction of anaesthesia with thiopentone 5-6 mg kg-1. After tracheal intubation, 17 patients received 0.8% halothane and 66% nitrous oxide in oxygen for 30 min (15 min normoventilation; 15 min hyperventilation). The inspired halothane concentration was then increased to 1.6% for 45 min (15 min normoventilation; 15 min hyperventilation; 15 min normoventilation with nitrous oxide replaced by oxygen). Enflurane (1.7% for 30 min and 3.4% for 45 min) was given to another 17 patients; 17 other patients received isoflurane (1.2% and 2.4%). Mean arterial pressure (MAP), nasopharyngeal temperature, end-tidal carbon dioxide concentration, inspired and end-tidal anaesthetic agent concentrations, haemoglobin concentration, PVC and TCD variables were measured at the end of each 15 min period. After recovery from anaesthesia, TCD variables were measured again. There were no intergroup differences in changes in MAP, nasopharyngeal temperature, haemoglobin concentration and PCV. Halothane, enflurane and isoflurane at low doses and normoventilation had little influence on TCD variables compared with awake values. In large concentrations with nitrous oxide in oxygen and normoventilation, there were differences between the volatile agents. Halothane increased blood flow velocities, but enflurane and isoflurane caused little change. Hyperventilation always decreased blood flow velocities and increased pulsatility.(ABSTRACT TRUNCATED AT 250 WORDS)