Intraoperative neurophysiologic monitoring (IOM) is an umbrella of techniques used to detect evolving neural compromise during surgery and includes EEG, electrocorticography (ECoG), brainstem auditory evoked potentials (BAEP/92585), motor evoked potentials (MEP), somatosensory evoked potentials (SEP), nerve conduction studies, and electromyography (EMG). These modalities are selected based on the anatomical structures and neural pathways at risk so that intraoperative changes can prompt immediate corrective actions by the surgical team (for example EEG for cerebral ischemia during carotid surgery; SEP/MEP for spinal cord integrity).
High-quality randomized controlled trials are limited for IOM; the supporting evidence base is composed primarily of observational studies, large multicenter series and formal technology assessments. Examples in the literature include multicenter SEP studies showing substantial reductions in paraplegia risk in spinal surgery and technology assessments recommending combined SEP/MEP monitoring when cord injury risk exists. Case series and retrospective analyses also document IOM’s role in predicting and preventing neurologic deficits in carotid, aortic, spinal and tumor surgeries.
Procedures in which monitoring has demonstrated benefit include carotid endarterectomy (EEG monitoring to detect cerebral ischemia), spinal deformity/corrective and other spinal surgeries (SEP/MEP to detect cord compromise), aortic/thoracoabdominal procedures (monitoring to identify spinal ischemia), and cortical/brain tumor resections (ECoG, functional cortical mapping and MEP/SEP as appropriate). EMG is additionally valuable for selective dorsal rhizotomy and peripheral nerve procedures where identifying specific roots or nerve function guides intraoperative decisions.
Realization of clinical benefit depends on appropriate modality selection, strict attention to recording conditions (including coordinated anesthesia and muscle relaxation), and experienced personnel. The policy emphasizes that monitoring should be performed by a well-trained technologist physically present in the operating room with continuous availability of a supervising clinical neurophysiologist (personal or remote as allowed by specific codes), and that monitoring is not medically necessary when the procedure poses no plausible risk to neural structures.