Abstract: Objective To compare the effects of different muscle relaxation levels (T1 response of the train-of-four (TOF) stimulation 5%-15% versus T1 response 45%-55% of baseline) the electrophysiological monitoring of the spinal cord during the spinal cord surgery, and then to explore the reasonable anesthesia program matched with electrophysiological monitoring.Methods Twenty-three patients undergoing selective spinal surgery with electrosurgical monitoring were enrolled in this study. Total intravenous anesthesia using propofol plus remifentanil and muscle relaxation provided by atracurium were maintained. Somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) were used to monitor the spinal cord function, and TOF stimulation at adductor pollicis muscle represented the muscle relaxation.The amplitude and latency of SEP and MEP were recorded at the level of NMB₁ (T1 5% to 15% base) and NMB₂ level (T1 45% to 55% base). Spontaneous breathing and severe motor motility under transcranial electrical stimulation were also recorded.Results There were no significant differences between the amplitudes and the latencies of SEP at different NMB levels(P>0.05). The latencies of MEP were similar under different muscle relaxation levels(P>0.05). The amplitudes of MEP had significant difference on the left upper limbs and the right lower limbs, whereas not on the left upper limbs and the right lower limbs. The incidence of severe motility at NMB₂ level was much higher than that at NMB₁ level (P<0.05). No spontaneous breathing was detected.Conclusion The use of muscle relaxant is not contraindicated during spinal surgeries that need intraoperative neurophysiology monitoring. For high risk spinal surgery, T1 response at 45%-55% of baseline may be the appropriate neuromuscular blockade level.

Key words: spinal cord function monitoring, neuromuscular blockade, somatosensory evoked potentials, motor evoked potentials