Recordings of long-latency trigeminal somatosensory-evoked potentials in patients under general anaesthesia.

Objective: The reliability of intra-operative recordings of trigeminal scalp-induced somatosensory-evoked potentials (T-SSEP) is controversial. This investigation aimed to provide evidence that T-SSEP recordings are stable using standardised neurophysiological methodology and anaesthesiological regime.

Methods: We investigated 99 patients undergoing carotid endarterectomy under total intravenous anaesthesia (propofol/remifentanil infusion). Long-latency T-SSEPs were recorded from the scalp after simultaneously stimulating 2nd and 3rd branches of the trigeminal nerve. The analysis included visual assessments of traces and measurements of latencies and amplitudes of the N13 and P19 peaks of T-SSEP. Furthermore, additional groups of patients were investigated to identify changes in the parameters of T-SSEP that might correspond to different states of anaesthesia and artificial muscle activity.

Results: We reproducibly recorded T-SSEP responses in 99 patients with a mean latency of 12.4 ms (SD=0.93) and amplitude of 5.7 μV (SD=4.7). Collateral investigations concerning changes of T-SSEP caused by neuromuscular blockade improved independence of T-SSEP recordings to muscle relaxation in contrast to facial and cervical muscle activity.

Conclusions: We demonstrated the reliability of recording stable intra-operative T-SSEP responses with standardised electrophysiological and anaesthesiological regimes.

Significance: We provided evidence of the non-muscular origin of T-SSEPs recorded from the scalp.