Modulation of somatosensory evoked potentials under various concentrations of desflurane with and without nitrous oxide.

Continuous measurement of somatosensory evoked potentials (SEP) by means of characteristic changes in the signal pattern makes it possible to identify cerebral or spinal cord ischemia during critical phases of the operative procedure. A correct interpretation of the measurements is only possible, however, if the influence of drugs acting on the central nervous system is known. The authors were able to show that inhaled anesthetics have an impact on latencies and response amplitudes. This study examined the influence of various concentrations of desflurane on the conduction of SEP of the Median nerve. In addition, the authors determined how the supplementation of nitrous oxide (N2O) influences the stimulus response of the medianus nerve's SEP. Desflurane has been shown to produce dose-dependent increases in SEP latency (data in part for latency N2O: 0.5 minimum alveolar concentration [MAC] = 20.8 +/- 0.9; 1.5 MAC = 22.2 +/- 1.5; 1.5 MAC/N2O= 23.8 +/- 1.5) and decreases in amplitude, whereas cervically recorded subcortical SEP components are minimally influenced by desflurane. When nitrous oxide is added, there were marked reductions in amplitude (p<0.01) of the cortical stimulus response (1.5 MAC = 2.4 +/- 0.9; 1.5 MAC/N2O = 1.1 +/- 1). It can therefore be recommended that supplementation with N2O should be avoided in the presence of low initial amplitudes. Based on the study's results, the use of desflurane (up to 1.0 MAC) seems to be compatible with intraoperative monitoring of median somatosensory evoked potentials.