IONM

Intraoperative neuromonitoring (IONM) is the use of neurophysiological techniques during surgery to assess the functional integrity of the nervous system in real time. The aim is to reduce the risk of postoperative neurological deficits by providing immediate feedback to the surgical team and guiding intraoperative decisions.

Common modalities in IONM include somatosensory evoked potentials (SSEPs), which monitor the dorsal column pathways by stimulating peripheral nerves and recording signals in the cortex or brainstem; motor evoked potentials (MEPs), which test motor pathways by stimulating the motor cortex or spinal cord and recording muscle responses; electromyography (EMG), including free-running and triggered forms to detect nerve irritation or injury; brainstem auditory and visual evoked potentials; and electroencephalography (EEG) for overall cortical activity. The specific combination of modalities is chosen based on the procedure and regional anatomy.

IONM is typically used in high-risk surgeries such as spine and cranial nerve procedures, brain tumor resections, vascular operations near the brain or spinal cord, and complex orthopedic deformity corrections. A trained monitoring team, usually including an IONM technologist and a supervising physician or neurophysiologist, establishes baseline measurements before incision and provides continuous or intermittent data during the operation. Any significant change in signal quality or amplitudes prompts communication and recommended intraoperative actions to the surgical team.

Limitations exist: signals can be affected by anesthesia, temperature, blood pressure, and patient factors; not all injuries are detectable; and false positives or negatives can occur. IONM is considered an adjunct to surgical technique and decision-making, not a guarantee of preserved function. Professional guidelines and institution-specific protocols govern implementation and interpretation.