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 sevofluraneor desflurane as their sole anaesthetic. Each patient was givensequentially increasing or decreasing doses at 0.5 MAC intervals,and the median nerve somatosensory evoked response recordedafter an equilibration at each concentration. The N₂₀-P₂₅ andP₂₅-N₃₅ amplitudes decreased with increasing agent concentration.However, for both agents the P₁₅-N₂₀ amplitude response wasquadratic in shape. The peak inflection points were at 3.2%for sevoflurane and 4.9% for desflurane. There were no differencesbetween the ascending and descending groups. This increase inactivity in the midbrain at ‘surgical’ end-tidalanaesthetic concentrations suggests more complex neuroelectricalresponses to anaesthesia than simple global suppression. Br J Anaesth 2001; 86: 59–62