Evaluation of reliability of post-tetanic motor-evoked potential monitoring during spinal surgery under general anesthesia.

STUDY DESIGN: A prospective research. OBJECTIVE: Compare the reliability of post-tetanic motor-evoked potential (p-MEP) monitoring in the detection of motor injury during spinal surgery with that of conventional MEP (c-MEP). SUMMARY OF BACKGROUND DATA: Myogenic MEPs are sensitive to suppression by anesthetics and neuromuscular blockade. Recently, we reported a new technique for MEP recording, called "p-MEP" in which MEP amplitude can be enlarged by tetanic stimulation of peripheral nerve before transcranial stimulation in comparison with that of c-MEP. The purpose of this study is to compare the reliability of p-MEP monitoring in the detection of motor injury during spinal surgery with that of c-MEP. METHODS: Eighty patients undergoing elective spinal surgery were enrolled in the study. Both c-MEP and p-MEP monitoring were performed throughout the operation in each patient. For recording c-MEPs, transcranial electrical train of five pulses stimulation with an interstimulus interval of 2 milliseconds was performed and compound muscle action potentials were bilaterally recorded from abductor pollicis brevis, abductor hallucis, tibialis anterior, and soleus muscles. For recording p-MEPs, tetanic stimulation (50 Hz, 50 mA, 5 sec) was applied to the left median nerve and bilateral tibial nerves 1 second before transcranial stimulation and compound muscle action potentials were recorded from the same muscles. The false positive, false negative, and accuracy of MEP monitoring in the detection of change in motor function were compared between p-MEP and c-MEP. RESULTS: At the baseline, success rates of baseline c-MEP and p-MEP recording were 66.3% (53/80) and 92.5% (74/80), respectively. The false positive, false negative, and accuracy of p-MEP monitoring were 0%, 0%, and 100%, respectively, whereas c-MEP were 4%, 20%, and 95%, respectively. CONCLUSION: The results indicate that p-MEP is a more reliable method to detect changes in motor function during spinal surgery under general anesthesia in comparison with c-MEP.