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Intraoperative Neurophysiological Monitoring – Growing Pains of a New Medical Technology

By Tyler Goldberg-Hoss and Tom Degan

If you undergo spine surgery, one of the most important medical providers may not be in the operating room. He or she may be in an office across town or even in another state. A neurophysiologist or similarly trained doctor is sitting at a computer screen monitoring signals from the spine or other neural structures to determine whether an injury is occurring. If the signals indicate a problem, the surgeon and anesthesiologist can be notified and take action to reverse or correct the problem before a nerve or spinal cord injury becomes permanent.

This is a new specialty in medicine called Intraoperative Neurophysiological Monitoring (IONM), and it is becoming a routine part of major surgeries involving risk to nerves or the spinal cord. While it has the potential for preventing permanent nerve damage, including paralysis, improper use of, or reliance upon, IONM can result in significant injury and give rise to medical negligence claims.

How Does IONM Work?

The human nervous system contains roughly 100 billion neurons, connected in elaborate networks that transmit information from one location in the body to another. The central nervous system, which consists of the brain and spinal cord, interprets sensory input, initiates muscle contraction, and carries out all other cognitive tasks. The nerves that communicate messages between the central nervous system and the rest of the body compose the peripheral nervous system.

Despite the enormous complexity of the human nervous system, there are aspects of neuron function that can be understood through simple physical principles. One of those aspects is the transmission of electrical signals along neurons. Neurons are able to respond to stimuli by generating an electrical signal. This electrical signal is then transmitted through the nervous system to the brain. In transmitting the electrical signal, the neurons act like classical electrical circuits. The electrical signals generated by the nervous system in response to sensory stimuli are called Evoked Potentials.

Somatosensory Evoked Potentials (SEP) are the electrical signals traveling through the nervous system to the brain related to the perception of touch, pressure, pain, temperature, position, movement, and vibration. SEPs can be elicited by electrically stimulating the nerves. When electronically stimulated, the SEP can be visualized on IONM equipment as a series of waves. The waveforms reflect the sequential activation of the neural structures along the nerve structure. If the neural pathway is injured, the injury can be observed as a change, or loss, of the waveform.

Monitoring for changes in the electrical impulses allows surgeons to detect injuries to the nervous system before they become permanent. Basically, IONM is an early warning system, which is used to alert surgeons that injury to the nervous system is occurring in time to prevent permanent damage.

The Invention and Evolution of IONM

The advent of using electrical currents to stimulate the nervous system can be traced back to the late 1800s. However, the development of IONM as it is currently used began in the 1970s, when surgeons began using SEP to monitor the main sensory pathways. IONM improved in the 1980s and became more and more common in spinal and facial surgery. Indeed, development and increasing use of IONM was largely fueled through its increasing use in spine surgery. In 1991 Medicare established a specific billing code for IONM, which opened the door for insurance reimbursement, which also spurred growth.

By the turn of the century, use of IONM evolved to the point where now some consider it a requirement to meet the standard of care in certain complex spinal surgeries.1 Indeed, IONM has been widely studied in spinal surgery, and literature supports significant benefits including a reduction in paralysis and death.2 However, research also indicates that other types of surgeries benefit from IONM. The surgical specialties where IONM is currently being used include: orthopedic, neurosurgical, cardiac, otolaryngological, plastic (peripheral nerve), and urologic.

IONM’s Utilization In Current Medical Practice

IONM is normally performed by technologists and interpreted by a PhD neurophysiologist, neurologist, or other physician.3 Technologists are the medical providers who set up the IONM equipment, place electrodes on the patient, and physically operate the IONM equipment. The neurophysiologist or physician is responsible for determining what monitoring is appropriate for a given surgical case, and interprets the IONM data, or waveforms, during surgery.

While the technologists and interpreting physician each have separate roles, both must understand the other’s job. The interpretive professional must understand all aspects of the equipment being used and the technical problems that might arise, since technical issues can interfere with signal acquisition. In addition, technologists need to understand how to interpret the data they are obtaining, because when changes in the waveforms occur they need to act quickly in order to prevent permanent injury to the patient. As the individual responsible for collecting IONM data during surgery, technologists must also be able to recognize when the waveform changes from the patient’s baseline, and then alert the surgeon or interpreting physician so the changes can be interpreted quickly.

The technologist and interpreting physician should both be knowledgeable about the surgical procedure being performed, and capable of recognizing critical periods during the surgery where IONM’s role is crucial. Thus, in addition to coordination between IONM team members, successful IONM requires coordination between the entire surgical team. This includes sharing expectations and protocols in advance of surgery, and ongoing discussions between the monitoring, surgical and anesthesia teams during the procedure.

For example, various anesthesia drugs interfere with certain types of monitoring. Therefore, the IONM team needs to communicate with the anesthesiologist and the surgeon regarding the types of monitoring that will be used, the type of drugs that will be used and when, and the effects of the drugs on the monitoring.

What Regulations and Practice Guidelines Exist for IONM Professionals?

In the 1980s, research hospitals and other cutting edge medical institutions hired skilled PhD neurophysiologists and/or physicians to interpret IONM data. These hospitals also trained technicians to set up the electrodes and equipment in their operating rooms. Thus, IONM was provided by hospitals in-house. As demand increased, the hospitals’ IONM neurophysiologist/physician would often oversee several technologists in numerous operating rooms at the same time. As demand continued to grow, the physicians and technicians providing in-house IONM service to these hospitals realized there was a market for their services and began starting their own businesses.

The departure of IONM professionals and technologists occurred in concert with new developments in telemedicine. The advances in telemedicine allowed the neurophysiologist/physician to oversee technologists from locations other than within the confines of a hospital. With remote monitoring, the neurophysiologist/physician is able to monitor several surgeries at the same time occurring at different locations. This new IONM industry is lucrative and the number of private IONM companies has grown exponentially over the past decade. However, while IONM utilization expanded, oversight of the physicians and technologists involved in providing IONM has struggled to keep pace.

At present, there is no formal state or federal licensing of IONM technologists. Indeed, there is really no concrete specific educational pathway for technologists seeking to specialize in IONM. What exists is a variety of certificates related to IONM technologists, signifying varying degrees of education and competence.4

There is also no standard for credentialing IONM physicians. While various boards and societies offer subspecialty certifications, there really is no standard certification, and hospitals are left to create their own credentialing criteria.5 Because no standard exists for identifying “qualified” IONM firms or technologists, hospitals must create their own criteria and standards to confirm that the IONM firm it utilizes is actually qualified to perform the job.6

Evaluation and Prosecution of IONM Medical Malpractice Cases

IONM records read in conjunction with an operative report can help determine whether or not a surgeon was appropriately alerted to changes in waveform, and if so, whether or not the surgeon took appropriate action. IONM data can be invaluable to practitioners when evaluating potential medical malpractice cases involving spinal surgery.

While it goes without saying that in any medical malpractice case, all of the client’s medical records should be obtained, hospitals routinely fail to provide certain records related to IONM. Therefore, attorneys should tailor their records requests to specifically request all IONM records, including chat logs showing communications between the technologists in the OR and the off-site interpreting physician, and the raw data from the IONM system itself (the machine that provides the electrical stimulation and records the data).

In addition, once a lawsuit is commenced, discovery should include specific requests for the following:

While very few reported medical malpractice cases implicating IONM exist, most successful cases involve a breakdown in communication within the IONM team (between the technologist and monitoring physician), or between the IONM team and the surgical team. Therefore, it is imperative to discover who was involved in IONM, what occurred, and when.

In a Massachusetts case, a lack of communication between the IONM technician and the neurologist monitoring the IONM data led to a significant settlement.7 In that case plaintiff learned through discovery that the technician was unsupervised by the neurologist for most of the surgery and failed to transmit any data to the neurologist in real-time. Plaintiff also discovered that after the surgery, the monitoring service and IONM technician either intentionally or negligently destroyed portions of the patient’s IONM data. This case illustrates the importance of obtaining the IONM raw data, which is recorded in every case.

The plaintiff in a California case asserted claims against her surgeon and the IONM technologists involved in her surgery.8 During the surgery, there was a loss of waveform indicating an injury to her spine, but the procedure continued without any action being taken about it. Plaintiff settled her claims against the surgeon, and proceeded to trial against the IONM technologists.

At trial, plaintiff was able to show the jury that two neurodiagnostic technologists performed IONM without the supervision of a physician. One technologist was in the operating room and the other technologist was interpreting the IONM data from a remote location. In addition, Plaintiff’s surgeon testified that he would never have performed surgery had he known that a physician was not interpreting the IONM data. The surgeon also testified that he was not notified about the loss of waveform that occurred during surgery, and had he been notified he would have taken steps to mitigate plaintiff’s injury. The case resulted in an eight-figure jury verdict against the IONM technologists.

This case illustrates how to create liability both through a lack of communication between IONM providers, and a hospital using an unqualified interpreting doctor. In addition, it demonstrates that it is possible in IONM cases for surgeons—who would otherwise be hostile to medical malpractice claims—to become strong advocates for their patients against negligent IONM defendants.

Given the rapid adoption and evolution of this technology, medical malpractice practitioners should prepare to see an increasing number of cases where IONM is used. Undertaking these types of cases requires a good understanding of IONM and how surgeons use it. Proper case evaluation may require consultation with a variety of specialists including surgeons, neurologists, and neurophysiologists. A good resource for understanding IONM and best practices, as well as a resource for potential expert witnesses, is an article published by members of the American Society of Neurophysiological Monitoring titled “Practice guidelines for the supervising professional: intraoperative neurophysiological monitoring.”9

1 McCann, Kelley et al, Somatosensory Evoked Potential Monitoring in Surgery for Pediatric Spinal Deformity, 2005 Proceedings of the AAOS, Washington, D.C.

2 See eg, Epstein et al., 1993, SPINE 18(6): 737-74.

3 In 2008 the American Medical Association passed Resolution 201, which stated that the supervision and interpretation of IONM “constitutes the practice of medicine, which can be delegated to non-physician personnel who are under the direct or online real time supervision of the operating surgeon or another physician trained in, or who has demonstrated competence, in neurophysiologic techniques and is available to interpret the studies and advise the surgeon during the surgical procedures.” Thus, a physician is always responsible for the supervision and interpretation of IONM data.

4 The most widely accepted is the American Board of Registration of Electro­encephalographic and Evoked Potential Technologists (ABRET), offers a Certifi­cation in Neurophysiologic Intra­operative Monitoring (CNIM). In addition to a CNIM certificate, the American Board of Neurophysiological Monitoring (ABNM) offers an advanced certification called the Diplomates of the Board of Neuro­physiological Monitoring (DABNM).

5 The American Board of Clinical Neurophysiology (ABCN) offers a certification in intraoperative monitoring, and American Board of Psychiatry and Neurology (APPN) both offer subspecialty certifications in clinical neurophysiology.

6 Various medical societies have issued guidelines to assists Hospitals and Medical Centers. The American Academy of Neurology (AAN) ((, ABRET-LAB ((, and American Board for Neurophysiologic Monitoring Programs (ABNMP) (( have each issued policies regarding the practice of IONM. The ASNM has published a white paper regarding credentialing and IONM ((

7 41 MLW 1853; Massachusetts Lawyers Weekly, July 1, 2013, p. 5.

8 ( (accessed 2/19/2016)

9 J Clin Monit Comput., 2014; 28(2): 103–111. Available online at: (

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