Effect of Time and Dose on Scalp-Recorded Somatosensory Evoked Potential Wave Augmentation by Etomidate

Effects of different concentrations of sevoflurane and desflurane on subcortical somatosensory evoked responses in anaesthetized, non-stimulated patients

Twenty-four patients were recruited and given either sevoflurane or desflurane as their sole anaesthetic. Each patient was given sequentially increasing or decreasing doses at 0.5 MAC intervals, and the median nerve somatosensory evoked response recorded after an equilibration at each concentration. The N20-P25 and P25-N35 amplitudes decreased with increasing agent concentration. However, for both agents the P15-N20 amplitude response was quadratic in shape. The peak inflection points were at 3.2% for sevoflurane and 4.9% for desflurane. There were no differences between the ascending and descending groups. This increase in activity in the midbrain at 'surgical' end-tidal anaesthetic concentrations suggests more complex neuroelectrical responses to anaesthesia than simple global suppression.

Drug induced double peak waveforms in the N20-component of somatosensory evoked potentials

The double peak waveform of the N20 component of the early somatosensory evoked potentials is a rare finding. In the present paper we investigated 9 patients (mean age +/- SD: 31.3 +/- 11.3 years; range 18-52 years) with the phenomenon of the two subcomponents of the primary cortical complex, after stimulation of the median nerve in a retrospective analysis. The results of the heterogenous patient group showed that the generation of the second subcomponent is not pathognomonic for patients with severe head injury, that it could be reversible and that pharmacological induced effects are presumably responsible for this phenomenon.