Within patient variability of lower extremity muscle responses to transcranial electrical stimulation with pulse trains in aortic surgery

Intraoperative recording of myogenic motor responses evoked by transcranial electrical stimulation is a method of controlling the integrity of the mot or pathways during clamping of the aorta. It is important to know the withi n patient variability of the transcranial motor evoked potential (tcMEP), b efore changes within the variability range are interpreted as abnormal duri ng the period of aortic cross clamping. Lower limb muscle responses were ob tained in 11 patients, following transcranial electrical stimulation with p ulse trains, of 4, 6 and 8 pulses. Under the conditions of partial neuromus cular blockade and a stable low dose propofol/fentanyl/nitrous oxide anaest hetic state, this study shows that multipulse transcranial electrical stimu lation reliably produces muscle responses of the lower limb in all patients tested with a coefficient of variation (CV) of around 20%. Eight pulses in the stimulation train produce neurophysiological facilitation that exceeds a 4 pulse train in terms of area under the curve (AUC) and response durati on. The use of multipulse stimulation rather than double or single pulse st imulation is recommended in order to increase the clinical efficacy of tcME P monitoring in aortic surgery. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.