For MEPs, volatile anesthetic agents suppress excitability of the motor cortex, resulting in diminished amplitudes. MEPs and SSEPs are susceptible to the effects of intraoperative environmental factors. Noteworthy, patients with scoliosis are neurologically intact in general, compared to those undergoing surgery for intramedullary or extramedullary spinal cord disorders. In addition, somatosensory-evoked potentials (SSEP) monitor the ascending dorsal column pathways of the posterior cord. Motor-evoked potentials (MEPs) are routinely recorded during intraoperative monitoring (IOM) for spinal surgery to ensure integrity of the descending motor tracts. Early recognition of MEPS is important to prevent false positives in the course of IOM for spinal surgery. However, our findings favor anesthetic before surgical intervention as a proposed protocol. This study suggests that in susceptible individuals, MEPS may rarely occur unpredictably, independent of surgical or anesthetic intervention. None of the patients had suppression of SSEPs intraoperatively. In addition, neither the duration of time to the first surgical manoeuver nor the duration of surgical manoeuver to MEPS were related to recovery of MEPS. However, spontaneous MEPS recovery was also seen in group 4, suggesting that in certain circumstances, both surgical and anesthetic intervention was not required. For group 3, spontaneous MEPS recovery despite the lack of surgical intervention suggests that anesthetic intervention may play a role in this process. However, comparison of groups 1 and 2 suggests that neither the duration of anesthesia nor speed of surgical or anesthetic intervention were associated with recovery to a level beyond the criteria for MEPS. All 12 patients did not sustain any neurological deficits postoperatively. Our results show that four distinct groups of MEPS were encountered over the study period. Over a 5-year period, 250 patients with adolescent idiopathic scoliosis (AIS) who underwent corrective surgery with IOM were retrospectively analyzed for MEP suppression (MEPS). Motor- (MEP) and somatosensory-evoked potentials (SSEP) are susceptible to the effects of intraoperative environmental factors.
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