Effects of midazolam on median nerve somatosensory evoked potentials

We have studied the effect of i.v. midazolam on median nerve somatosensory evoked potentials (SSEP) in 10 unpremedicated adults. Anaesthesia was induced with midazolam by bolus administration (0.2 mg kg-1) followed by infusion (5 mg h-1). The latency and amplitudes of the SSEP responses over the second cervical vertebrae (SC2) and sensory cortex (P17, N20, P25) were recorded before and for 10 min after induction. Data were analysed over that period for time-related alterations. Small but statistically significant increases in latency of the cortical N20 (P less than 0.005) and P25 (P less than 0.001) waves and interwave conduction times of SC2 to P25 (P less than 0.005) and N20 to P25 (P less than 0.021) were observed. Cortical amplitude (N20-P25) decreased significantly (P less than 0.012), to approximately 60% of baseline. These results demonstrated that midazolam produced a depression of cortical SSEP amplitude without clinically significant alterations in latency.