[Effects of nitrous oxide and halothane on somatosensory evoked potentials after stimulation of the median nerve].

In 10 healthy adult subjects cervical and cortical somatosensory evoked responses (SEP) after median nerve stimulation were recorded. The recordings were performed before and after inhalation of 66 2/3% nitrous oxide (and 33 1/3% oxygen) and during additional inhalation of halothane in concentrations ranging from 0,5 to 2,0 vol%; end tidal paCO2 and tympanic membrane temperature were kept constant. Nitrous oxide caused a 50% amplitude reduction of the cortical responses while latencies remained unchanged. Latency of the primary cortical response N20 and central conduction time increased continuously with increasing halothane concentration, amplitude N20P25 and amplitude ratio R showed a further decrease. The sensitivity of SEP components to halothane anaesthesia increased with peak latency: Cervical SEP remained relatively constant even during deep anaesthesia, early cortical potentials showed latency prolongation and amplitude reduction, middle and long latency components were progressively diminished with increasing halothane concentration. These changes have to be considered, when interpreting cervical and cortical SEP recorded intraoperatively.