Repetitive vs. single transcranial electrical stimulation for intraoperative monitoring of motor conduction in spine surgery

We studied the effectiveness of single and repetitive transcranial electrical stimulation to activate motor tracts under partial neuromuscular blockade and total intravenous anesthesia. During spinal surgery, in 10 patients, the latency and amplitude of the evoked abductor pollicis brevis muscle response after cortical stimulation was calculated and compared. The number of responses evoked by the double (pair) pulse stimulation was significantly higher (p = 0.0191) than single pulse stimulation. Repetitive stimulation caused more responses than single (p = 0.0001) or double stimulation (p = 0.0253). An increase of interstimulus interval from 1-3 msec did not significantly increase the motor response with the double pulse or repetitive stimulations. Varying the number of electrical pulses per train stimulation from 3-9 did not significantly change latency (P > 0.05) or amplitude (P > 0.05) of the motor response. The findings suggest that use of repetitive stimulation of the motor cortex is an effective method to activate motor pathway during spinal surgery.