Transcranial Motor Evoked Potentials during Spinal Deformity Corrections—Safety, Efficacy, Limitations, and the Role of a Checklist

Abstract

IntroductionIntraoperative neuromonitoring (IONM) has become a standard of care in spinal deformity surgeries to minimize the incidence of new onset neurological deficit. Stagnara wake up test and ankle clonus test are the oldest techniques described for spinal cord monitoring, but they cannot be solely relied upon as a neuromonitoring modality. Somatosensory evoked potentials monitor only dorsal tracts and give high false positive and negative alerts. Transcranial motor evoked potentials (TcMEPs) monitor the more useful motor pathways. The purpose of our study was to report the safety, efficacy, limitations of TcMEPs in spine deformity surgeries, and the role of a checklist.Study designRetrospective review of all spinal deformity surgeries performed with TcMEPs from 2011 to 2015.Materials and methodsAll patients were subjected to IONM by TcMEPs during the spinal deformity surgery. Patients were included in the study only if complete operative reports and neuromonitoring data and postoperative neurological data were available for review. An alert was defined as 80% or more decrement in the motor evoked potential amplitude, or increase in threshold of 100 V or more from baseline. The systemic and surgical causes of IONM alerts and the postoperative neurological status were recorded.ResultsIn total, 61 patients underwent surgery for spinal deformities with TcMEPs. The average age was 12.6 years (6–36 years) and male:female ratio was 1:1.3. Diagnoses included idiopathic scoliosis (n = 35), congenital scoliosis (n = 13), congenital kyphosis (n = 7), congenital kyphoscoliosis (n = 4), post-infectious kyphosis (n = 1), and post-traumatic kyphosis (n = 1). The average kyphosis was 72° (45°–101°) and the average scoliosis was 84° (62°–128°). There were in total 33 alerts in 22 patients (36%). The most common causes were hypotension (n = 7), drug induced (n = 5), deformity correction (n = 5), osteotomies (n = 3), tachycardia (n = 1), screw placement (n = 2), and electrodes disconnection (n = 1). Reversal of the inciting event cause resulted in complete reversal of the alert in 90% of the times. Three patients showed persistent alerts, out of whom one had a positive wake up test and woke up with neurodeficit, which recovered over few weeks, while the other patients showed persistent alerts but woke up without any deficit. Sensitivity and specificity of TcMEP in deformity correction surgery were 100 and 96.6%, respectively, in our study.ConclusionIONM alerts are frequent during spinal deformity surgery. In our study, more than 50% of the alerts were associated with anesthetic management. IONM with TcMEPs is a safe and effective monitoring technique and wake up test still remains a valuable tool in cases of a persistent alert.

The Impact of Neurophysiological Intraoperative Monitoring during Spinal Cord and Spine Surgery: A Critical Analysis of 121 Cases

“…To try and enhance the efficacy of intraoperative neuromonitoring, “checklists” are being developed that provide a methodology of utilizing this technology optimally during surgery [ 27 - 28 ]. These checklists describe what the surgeon, anesthesiologist, neurophysiologists, and technicians should perform to manage a significant alert given by the intraoperative neuromonitoring [ 27 ].…”

Intraoperative Fluid Management in Patients Undergoing Spine Surgery: A Narrative Review

“…These findings suggest that augmentation of cardiac output and oxygen delivery (DO 2 ) is more efficacious at restoring electrophysiological state after hemorrhagic hypotension than solely increasing MAP. A recent retrospective study conducted by Acharya et al (80) including 61 patients who underwent spine deformity surgery with TcMEPs monitoring, identified hypotension as the most common cause of TcMEP's alterations. These findings were timely correlated with spinal cord ischemia as hypotension correction resulted in reversal of TcMEPs changes (80).…”

“…A recent retrospective study conducted by Acharya et al (80) including 61 patients who underwent spine deformity surgery with TcMEPs monitoring, identified hypotension as the most common cause of TcMEP's alterations. These findings were timely correlated with spinal cord ischemia as hypotension correction resulted in reversal of TcMEPs changes (80). While the authors followed a protocol to increase MAP > 100 mmHg, they did not specify how this was achieved.…”

Loss of temperature and pain sensation as risk marker of neurological complications in surgical correction of severe spinal deformity

“…В настоящее время применение моторных транскраниально вызванных потенциалов (МВП) является важным составным элементом «золото-го стандарта» ИОНМ при коррекции деформаций позвоночника [8,[11][12][13][14][15], поскольку они чрезвы-чайно чувствительны к изменению кровотока в спинном мозге из-за гипотонии или сдавления (поражения) сосудов [8,9]. Изменения параметров МВП в ответ на хирургическую агрессию нередко обнаруживаются раньше, чем реакция соматосен-сорных вызванных потенциалов, что способствует более быстрой идентификации надвигающегося повреждения спинного мозга [8].…”