Abstract
Objective: To determine optimal interstimulus interval (ISI) and pulse duration (D) for direct cortical stimulation (DCS) motor evoked potentials (MEPs) based on rheobase and chronaxie derived with two techniques. & para;& para;Methods: In 20 patients under propofol/remifentanil anesthesia, 5-pulse DCS thenar MEP rheobase and chronaxie with 2, 3, 4 and 5 ms ISI were measured by linear regression of five charge thresholds at 0.05, 0.1, 0.2, 0.5 and 1 ms D, and estimated from two charge thresholds at 0.1 and 1 ms D using simple arithmetic. Optimal parameters were defined by minimum threshold energy: the ISI with lowest rheobase(2) x chronaxie, and D at its chronaxie. Near-optimal was defined as threshold energy <25% above minimum.& para;& para;Results: The optimal ISI was 3 or 4 (n = 7 each), 2 (n = 4), or 5 ms (n = 2), but only 4 ms was always either optimal or near-optimal. The optimal D was similar to 0.2 (n = 12), similar to 0.1 (n = 7) or similar to 0.3 ms (n = 1). Two-point estimates closely approximated five-point measurements.& para;& para;Conclusions: Optimal ISI/D varies, with 4 ms/0.2 ms being most consistently optimal or near-optimal. Two-point estimation is sufficiently accurate.& para;& para;Significance: The results endorse 4 ms ISI and 0.2 ms D for general use. Two-point estimation could enable quick individual optimization. (C) 2017 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.