[Changes in somatosensory evoked potentials after sevoflurane and isoflurane. A randomized phase III study]

Monitoring of somatosensory evoked potentials (SEP) is used to identify critical phases of cerebral ischaemia by means of characteristic changes in the signal patterns. A correct interpretation of the results is possible, however, only if the influence of drugs that act on the central nervous system is known. We were able to show that volatile anaesthetics have an impact on latencies and stimulus amplitudes. In this study, we examined the influence of sevoflurane as compared with isoflurane on the conduction of SEP by the median nerve at various concentrations. In addition, we determined how the addition of nitrous oxide (N2O) influenced the stimulus response of median-nerve SEP. Both isoflurane and sevoflurane caused a dose-dependent increase in latency of the primary cortical complex, while the influence on the cervical components of the SEP with respect to increased latency was only slight. No significant difference was found between both study groups. Under the influence of N2O, there were marked reductions in amplitude of the cortical stimulus response. Thus, it can be recommended that supplementation with N2O should be avoided in the presence of low initial amplitudes. Based on our results, the use of isoflurane and sevoflurane concentrations up to 1.0 MAC seems to be compatible with intraoperative monitoring of SEP.