Application of tetanic stimulation of unilateral tibial nerve prior to transcranial stimulation can augment the amplitudes of myogenic motor evoked potentials from the muscles in bilateral upper and lower limbs

Background: Recently, we reported a new technique to augment motor evoked potentials (MEPs) under general anesthesia, called as post-tetanic MEP (p-MEP), in which tetanic stimulation of peripheral nerve prior to transcranial stimulation enlarged amplitudes of MEPs from the muscle innervated by the nerve subjected to tetanic stimulation. In the present study, we tested whether tetanic stimulation of left tibial nerve can also augment amplitudes of MEPs from the muscles, which are not innervated by the nerve subjected to tetanic stimulation. Methods: Thirty patients undergoing spinal surgery under propofol-fentanyl anesthesia with partial neuromuscular blockade were examined. For conventional MEP (c-MEP) recording, transcranial stimulation with train-of-five pulses was delivered to C3-C4, and the compound muscle action potentials were bilaterally recorded from the abductor pollicis brevis (APB), abductor hallucis (AH), tibialis anterior (TA), and soleus (S) muscles. For p-MEP recording, tetanic stimulation (50Hz, 50mA of stimulus intensity) with a duration of 5 sec was applied to the left tibial nerve at the ankle 1 sec prior to transcranial stimulation. Transcranial stimulation and recording of compound muscle