Purpose: The burst-suppression (BS) electroencephalographic (EEG) patterns induced by general anesthesia can react to somatosensory stimuli. We investigated this reactivity by studying the effect of peripheral nerve stimulation used for routine intraoperative spinal cord monitoring by somatosensory evoked potentials on BS patterns.
Methods: The relative time spent in suppression expressed as BS ratio (BSR) and mean burst duration (BD) were measured pre (BSRPre), during (BSRStim) and post (BSRPost) a 60-second repetitive electrical ulnar nerve stimulation in 9 patients under total intravenous general anesthesia with propofol. The BS reactivity was measured as BSRPre- BSRStim.
Results: We included 27 trials with BSRPre up to 77%, indistinguishable from BSRPost. During stimulation, the mean BSR transiently dropped from 42% to 35%. For each 1 % increase in BSRPre the BS reactivity increased with 0.6 % whereas the BD remained about 3 s. For BSRPre below 30% the BS reactivity was negligible.
Conclusions: Our data shows that somatosensory input can evoke bursts, altering the “spontaneous” deep BS patterns (BSRpre >30%). Further studies are necessary to objectively assess the clinical relevance of stimulus induced BS reactivity during deep general anesthesia.