Alarm Value of Somatosensory Evoked Potential in Idiopathic Scoliosis Surgery

BackgroundSomatosensory evoked potential (SSEP) monitoring is performed to examine postoperative clinical findings when a monitoring event was noted intraoperatively and to ascertain the alarm threshold for intraoperative neural damage.MethodsThe tibial SSEP of both lower limbs was recorded intraoperatively in patients with idiopathic scoliosis. Change of SSEP amplitude as opposed to the baseline was categorized into 4 levels: decrease <40%, decrease of 40%–50%, decrease of 50%–60%, and decrease >60%. Postoperative neurologic function of patients was examined and compared with SSEP data.ResultsThe baseline amplitude before incision was significantly different from the amplitude after spine exposure. An amplitude reduction of >60% during scoliosis correction procedures was observed in 6 legs, and 4 of them had postoperative deterioration in motor status. As the measure of threshold for alarm, an amplitude reduction of >50% compared with baseline resulted in more false-positive outcomes compared with amplitude attenuation of >60%.ConclusionsCompared with the traditional SSEP baseline before skin incision, the baseline acquired after spine exposure results in more accurate monitoring. A >60% decrease in SSEP amplitude could be a more suitable alarm threshold.