Intraoperative somatosensory evoked potential monitoring decreases EEG burst suppression ratio during general anesthesia

Alexandru Calin 1, 2; Vshakhadatta Mathur Kumaraswamy2, Diana Braver2, Dinesh G. Nair2, Mihai Moldovan3, 1 and Mirela V. Simon 2 1Department for Functional Sciences, Division of Physiology and Neuroscience, "Carol Davila" University of Medicine and Pharmacy, Bucharest, Romania 2Intraoperative Neurophysiology Unit, Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, U.S.A. 3Neuroscience and Pharmacology, Panum, University of Copenhagen, Copenhagen, Denmark

NEURONUS 2013 IBRO & IRUN Neuroscience Forum, May 9-11th 2013, Jagiellonian University, Krakow. Poland
Friday May 10th, 2013


Purpose: The burst-suppression (BS) electroencephalographic (EEG) patterns induced by general anesthesia can react to somatosensory stimuli. We investigated to which extent peripheral nerve stimulation used for routine intraoperative spinal cord monitoring by somatosensory evoked potentials affects 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 suggest that during deep general anesthesia SSEP monitoring can evoke bursts, altering the “spontaneous” BS patterns. Such changes in the level of somatosensory input should be accounted for when BSR is used to target the anesthetic concentration or to estimate the changes in cortical excitability for procedures like neurophysiologic motor mapping.