Effects of halothane on somatosensory evoked potentials recorded in the extradural space.

We studied the effects of supplementing anaesthesia with halothane (up to 1.5%, inspired) on the somatosensory evoked potential recorded in the extradural space of six patients before corrective surgery for idiopathic adolescent scoliosis. A further six patients in whom anaesthesia was supplemented with thiopentone acted as a control group. Halothane 1.5% resulted in a significant decrease in overall amplitude (P less than 0.05) from the left leg only. Halothane had no significant effect on overall amplitude, first peak amplitude, second peak amplitude and first peak latency. We conclude that halothane is unlikely to alter the interpretation of somatosensory evoked potentials recorded extradurally during scoliosis surgery. A possible unilateral effect of halothane on the concave side in idiopathic adolescent scoliosis needs further investigation.