CHANGES IN SOMATOSENSORY-EVOKED POTENTIAL S AFTER SEVOFLURANE AND ISOFLURANE - A RANDOMIZED PHASE-III STUDY

Monitoring of somatosensory evoked potentials (SEP) is used to identif y critical phases of cerebral ischaemia by means of characteristic cha nges in the signal patterns. A correct interpretation of the results i s possible, however, only if the influence of drugs that act on the ce ntral nervous system is known. We were able to show that volatile anae sthetics have an impact on latencies and stimulus amplitudes. In this study, we examined the influence of sevoflurane as compared with isofl urane on the conduction of SEP by the median nerve at various concentr ations. In addition, we determined how the addition of nitrous oxide ( N2O) influenced the stimulus response of median-nerve SEP. Both isoflu rane and sevoflurane caused a dose-dependent increase in latency of th e primary cortical complex, while the influence on the cervical compon ents 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 cor tical stimulus response. Thus, it can be recommended that supplementat ion with N2O should be avoided in the presence of low initial amplitud es. Based on our results, the use of isoflurane and sevoflurane concen trations up to 1.0 MAC seems to be compatible with intraoperative moni toring of SEP.