Effects of thiopentone on median nerve somatosensory evoked potentials.

We have studied the effects of an i.v. bolus of thiopentone 4 mg kg-1 on the median nerve somatosensory evoked potentials (SSEP) in 15 unpremedicated patients. The latency and amplitude of the SSEP response over the second cervical vertebra (SC) and sensory cortex (P15, N20, P25) were recorded before and for 12 min after injection. Data were analysed at 0, 4, 8 and 12 min for time-related alterations. Cortical amplitude was variable, with a tendency to decrease (P less than 0.03). There was a statistically significant but clinically insignificant transient increase in latency of the cortical N20 (P less than 0.008), and interwave conduction times of SC to P15 (P less than 0.007) and SC to P25 (P less than 0.039). The relation of these results to the proposed mechanism of thiopentone action at synapses is discussed.