Intraoperative Monitoring: Improving Patient Safety with Improved Surgical Outcomes

By Steven J. Anglés, Attorney at Law

Patients who have been traumatically and severely injured as a result of another person’s negligence may ultimately need surgery to get long-lasting relief from their pain, symptoms and residuals. One common concern shared by our clients and their providers alike is the question of safety during a surgical procedure. Patients undergoing operations under general anesthesia may have little idea of multi-faceted measures in place to improve patient outcomes by monitoring their condition during surgery.  The fields of medicine and technology have combined in many ways, and one in particular is the use of intraoperative neurophysiological monitoring (IOM or IONM).

IOM is the monitoring of nerve health and function in the spine and the brain for patients undergoing vascular surgery, neurosurgery, or orthopedic surgery. IOM can be used for operations including:

  • Operations of the spine, including fusion, discectomy, or laminectomy;
  • Operations of the brain, including craniotomies;
  • Vascular surgery;
  • Facial nerve surgery

The first documented use of this of monitoring was in 1935, primarily for patients suffering from epilepsy.[1] The potential applications for this technology grew over the years, and advances in computer networking and integrated communication systems helped IOM to evolve.

Through IOM, neurodiagnostic procedures can help determine whether any nerves have become compressed, or if the brain or spinal cord has any reduced vascular flow, allowing the surgical team to take immediate and corrective actions to prevent a bad outcome. Essentially, IOM acts as an early warning system for surgeons to gain reliable insight into a patient’s condition during surgery, adding a layer of safety to the measures already in place that monitor cardiac and respiratory function while a patient is anesthetized. For example, the diagram below shows normal brainstem electrical response.  If the amplitude, shape, or timing of the responses were to change from a patient’s “baseline” response during surgery, it could signal a neurological dysfunction.


Normal brainstem auditory evoked potentials (BAEP)[2]


How it Works:

The IOM team is typically composed of the surgeon, clinical neurophysiologist, anesthesiologist, and an IOM monitoring technologist.[3] The neurophysiologist is a specialist trained in bioelectrical activity that attaches sensors to the patient to monitor the activity of the muscles, nerves, and brain. The neurophysiologist and surgeon receive information from the technologist who observes and records using monitoring equipment, and interpret the results in real time during the course of the procedure. Interestingly, some members of the team, such as the technologist, can monitor the patient’s neurological activity remotely, even from another location entirely. The information received also assists the anesthesiologist, who may not only need to make adjustments during the course of the operation, but also gives the anesthesiologist information on which anesthetics to use prior to surgery. (Anesthetics can affect the brain’s metabolism, which can alter recordings of brainwaves, causing interference with intraoperative monitoring.)[4]

IOM uses a number of different methods each with very specific applications.  Several modalities or methods of monitoring can also be used together within the same surgery. For example, electrodes on a patient’s scalp during an electroencephalography test (EEG) to evaluate brain waves can be used in conjunction with an electromyography test which monitors the peripheral nervous system. In this way, a surgical team could simultaneously monitor the patient’s brain activity as well as the bundles of nerve fibers or axons conducting information to and from the central nervous system.


Since the use of IOM is normally reserved for more complex surgeries, its availability may be limited. Different medical organizations will have specific guidelines as to when IOM use is necessary or appropriate, and not all organizations may offer it as an option for patients. Additionally, adding IOM to the cost of a surgical procedure may not necessarily qualify for reimbursement under some insurance policies. For example, one large national health insurance provider specifies in its plans that “IOM billed by the surgeon, assistant surgeon, or anesthesiologist will be denied as included in the surgical or anesthesia reimbursement…” but “IOM performed by a physician (MD or DO), other than the surgeon, assistant surgeon, or anesthesiologist…may be eligible for reimbursement.”[5] Remote IOM by a physician may only be eligible for reimbursement to the monitoring physician if the time spent does not exceed a certain number of minutes and a technician is physically present in the operating room.

While intraoperative neurophysiological monitoring may not be required or recommended by surgeons in a majority of cases, it continues to be an important safety consideration worthy of discussion with patients.


[1] Kim S-M, Kim SH, Seo D-W, Lee K-W. Intraoperative Neurophysiologic Monitoring: Basic Principles and Recent Update. Journal of Korean Medical Science. 2013;28(9):1261-1269. doi:10.3346/jkms.2013.28.9.1261.

[2] Intraoperative Neurophysiological Monitoring, Medscape, Mar 17, 2016

[3] Kim S-M, Kim SH, Seo D-W, Lee K-W. Intraoperative Neurophysiologic Monitoring: Basic Principles and Recent Update. Journal of Korean Medical Science. 2013;28(9):1261-1269. doi:10.3346/jkms.2013.28.9.1261.

[4] American Clinical Neurophysiological Soceity; Guideline 11A: Recommended standards for neurophysiologic intraoperative monitoring – principles; 2009.