Significant Alerts in Intraoperative Neurophysiologic Monitoring during Severe Spinal Deformity Surgeries- A Categorical Description Experience in Tertiary Care Referral Center from the Subcontinent
Authors: Gupta Pravin , Acharya Shankar , Kalra Kashmiri Lal , Chahal Rupinder Pal Singh , Kohli Manish 
Published: April 2016

Introduction

Intraoperative Neurophysiological monitoring (IONM) has become a standard of care in spinal deformity surgeries to minimize the incidence of new onset neurological deficit. It has largely averted the use of historic intraoperative wake-up test. The risk of new neurologic deficit, in such cases, is high and frequency of significant alerts in neuro-monitoring can distress the surgeon so it is essential for the surgeon to know about the various categories of alerts and their management.

Study Design

Retrospective review of all spinal deformity surgeries performed with IONM in an Indian hospital over a period from 2011–2015.

Material and Methods

All except two patients were subjected to IONM by transcranial electrical motor evolked potentials (TCeMEP) during the spinal deformity surgery. These two patients were monitored with SSEP. Patients were included in the study only if complete demographic data, operative reports and neuromonitoring data and post-operative neurological data were available for review. A significant IONM alert during MEP monitoring was defined as 80% or more decrement in the MEP amplitude, or Increase in threshold of 100 V or more from baseline. During SSEP monitoring, significant alert was defined as 50% or greater decrease from baseline in the amplitude or latency prolongation by 10% or more. A full neurologic recovery was defined as a return to baseline for all MEP and SSEP signals. The systemic and surgical causes of IONM alerts and the postoperative neurological status were recorded.

Results

Total 43 patients underwent the surgery for severe spinal deformities with neuromonitoring. The average age was 13.2 years (6–38), and male:female ratio was 11:32. Diagnoses included idiopathic scoliosis (26), congenital scoliosis (6), congenital kyphosis (5), congenital kyphoscoliosis (2), post-infectious kyphosis (3), and post-traumatic kyphosis (1). The average kyphosis was 84; (45–136); the average scoliosis was 89; (62–128). There were total 21 IONM alerts in 16 patients (37%). The most common causes were Hypotension (5), drug induced (4), distraction (4), deformity correction (3), SPO/Ponte/PSO osteotomies (2), Tachycardia (2) and Screw placement (1). Reversal of the inciting cause resulted in complete reversal of the alert in 90% of the times. Two patients wake up with neurodeficit (Screw placement and deformity correction) which recovered over few weeks. One patient showed persistent alerts but wake up without any deficit.

Conclusion

IONM alerts are frequent during severe spinal deformity surgery. In our study more than 50% of the alerts were associated with anesthetic management (hypotension, drugs and tachycardia). So in case of significant alert, surgeon should not get stressed out but to analyze whether the cause is systemic and the first step is to maintain the mean blood pressure. However, the most common cause of persistent IONM alert were screw malposition and deformity correction. Careful surgical technique supported by IONM and their interpretation can reduce neurologic mishaps.