What is IONM?

Intraoperative neuromonitoring (IONM) is the use of electrophysiological methods to assess, monitor, and map the function of nervous system structures (the brain, the spinal cord, and all the nerves that branch from those structures) in order to improve surgical outcomes.

IONM provides surgeons with real-time data during complex surgeries so that potential neurological injuries can be prevented. IONM includes several modalities that are sensitive to different nerve networks to indicate the likelihood of possible damage. These modalities include Somatosensory Evoked Potential (SSEP) and Motor Evoked Potential (MEP). 

The signals of these modalities during surgical procedures offer an early warning in the event that neural injury is imminent. This is especially significant given that nerve damage can be long-term and debilitating. When informed by IONM, surgeons can correct course to avoid incidents, and patients can experience better outcomes.

How IONM Modalities Function During Complex Surgeries

According to StatPearls, here’s a snapshot of how each of the aforementioned IONM modalities function to reduce risks during complex surgeries:

• Somatosensory Evoked Potential (SSEP). This modality is one of the oldest and most common. SSEPs monitor the peripheral and central pathway that relays tactile discrimination, vibration, and proprioception. Most commonly during spinal operations, SSEPs are stimulated at the median and ulnar nerves in the upper extremities, and the posterior tibial and peroneal nerves in the lower extremities.
• Motor Evoked Potential (MEP). This modality monitors the corticospinal pathway, from the primary motor area of the brain, through the brainstem and spinal cord, and out to the peripheral nervous system.  Responses can be recorded from the spinal cord or from muscles.

Research shows that monitoring these modalities makes surgery safer, especially when it comes to spinal, intracranial, and vascular surgeries. IONM reduces risks and allows surgeons to work with confidence as nerve system data is continuously reported. In a systematic review of over 100,000 spinal surgery cases, Global Spinal Journal reports that these modalities “have diagnostic utility in successfully detecting impending or incident intraoperative neurologic injuries.”

Language Mapping. While SSEP and MEP focus on sensory and motor pathways, language mapping is another vital application of IONM—especially during brain surgeries where speech function is at risk. This technique helps surgeons identify and preserve areas of the brain responsible for language, such as Broca’s and Wernicke’s areas.

Example Story: How Language Mapping Protects Critical Function During Surgery

Meet Bob. His MRI showed a tumor near Broca’s area, the part of the brain responsible for speech. This was especially concerning because Bob has a passion for public speaking in his day-to-day life. To avoid damaging his ability to talk, his surgeon ordered additional tests—and confirmed the tumor was in his language-dominant hemisphere.

Before surgery, a neurophysiologist met with Bob to prep for language mapping. Using simple flashcards—like pictures of a toilet or a tree—they asked Bob to name each one using his normal words. During surgery, as the surgeon stimulated areas near the tumor, Bob was shown the same cards again.

If Bob suddenly paused, stuttered, or said a different word (“loo” instead of “toilet”), it signaled that the area being stimulated controlled language. A neuropsychologist in the OR helped interpret these subtle signs to guide the surgeon.

Thanks to this approach, the surgical team was not only able to protect Bob’s ability to speak, but also had the confidence to achieve a more complete tumor resection. IONM doesn’t just reduce the risk of neurological injury—it empowers surgeons to make informed decisions that optimize patient outcomes.

The Importance of a Collaborative IONM Team

SpecialtyCare is a team of passionate, driven people dedicated to making a difference in healthcare. We are one of the nation’s leading providers of outsourced surgical services and one of the largest providers of outsourced intraoperative neuromonitoring in the United States. Currently we provide IONM services to over 800 hospitals and support more than 2,500 surgeons in over 130,000 surgeries each year. Contact us today to see how we can bring IONM into your OR.