Intraoperative Neurophysiologic Monitoring Reducing Risk of Post-Operative Neurologic Deficits
I have devoted most of 29 years in neurology to this cause. There are many modalities and techniques available to this end; however, prevention of symptoms and deficits is one of the most relevant and vital areas of neurology. Intraoperative Neurophysiologic Monitoring (IONM) has become the standard of care in the United States to prevent and minimize insults to the nervous system during surgery. IONM is used most often, but not limited to, in spinal surgeries. There are estimates of more than 3 million spine procedures performed worldwide per year and only a fraction of them are monitored with IONM.
There is, unfortunately, a shortage of trained technical staff both in the United States and more so throughout the world that can implement IONM. We are witnessing a move toward globalization of healthcare, improving quality of care and minimizing risk in the medical community worldwide.
The medical tourism sector has taken a lead in this arena. With this trend, modalities including IONM need to be implemented and patients, facilitators and medical staff need to be trained in their utility and importance.
What is Intraoperative Neurophysiologic Monitoring (IONM)?
IONM is the real-time monitoring of the integrity of the nervous system during any surgery that could place operation at risk. Continuous testing and evaluation of the function of the peripheral and central nervous system are performed from the time the patient is placed under anesthesia to the completion of surgery. A technologist is present in the room and communicates directly and immediately with surgical staff, who are alerted to any changes or abnormalities of the testing within seconds.
With this alert, the surgeon or anesthesiologist may intervene and alter their approach to avoid any temporary or permanent nervous system compromise. A neurologist specializing in IONM is routinely available online or, in some cases, in the operating room to supervise and complement the technical staff performing the procedure.
More than 3 million spinal procedures are performed worldwide per year and only a fraction of them are monitored with IONM.
Why Perform IONM?
I think of the risk to the nervous system during surgery as being a two-part process. One is the anatomy of the nervous system and risks from patient positioning with potential external compression. The second is the surgery itself.
Anatomy and Positioning as Risk
Various parts of the nervous system are susceptible to injury by virtue of location. Some of the reasons are:
- Superficial location of peripheral nerves making them more amenable to compression.
- Various nerves cross different joints that can, if flexed or extended, cause traction on the nerves.
- The spinal cord is tightly encased within the spinal column. If there is narrowing of this canal from degenerative changes, such as disc bulges and arthritic processes, the spinal cord can become compressed, especially if incorrectly positioned. The cervical spine (neck region) is most susceptible.
During surgery, the patient is placed in one position which typically does not change for the duration of the procedure. The head and neck can be extended or rotated and the extremities, especially the arms, can be flexed. This can cause mechanical stress to the nervous system or can even lead to lack of blood flow to the spine and peripheral nerves.
Many safeguards are used by the surgical staff to prevent stress including padding and careful inspection; however, some patients have a low threshold of injury and are more susceptible than others. Some surgical procedures can also last for several hours compounding the mild compressive stress. Even in shorter durations, surgeries can be enough to place the nervous system at risk.
Surgical Procedure as Risk
Any surgery that takes place on or near the brain, spine or peripheral nerves pose a potential risk. Depending on the surgery, the approach to the area of interest and the procedure itself may require that peripheral nerves be retracted out of the surgical field.
The instrumentation used, such as screws, plates and pins, are also potential threats. Surgeons are exceptionally skilled at avoiding injury to the nervous system; however, as stated earlier each patient has a different threshold of injury.
IONM during surgery can identify an evolving threat to the nervous system and alert the surgeon prior to reaching that patient’s threshold for injury. Either during the positioning process or during the surgery itself, IONM is another line of protection.
IONM is also utilized to assist the surgeon in localizing vital neurologic structures. Peripheral nerves or nerve roots near the spine can be stimulated and identified. Surgery on the brain may also require the IONM team to identify and localize vital structures that either need to be avoided or corrected.
What Types of Surgery Require IONM?
- Spinal surgeries including some disc removals, fusions, corrections (scoliosis) and fractures;
- Neurosurgery, if peripheral nerves, spine or brain are at risk or need to be identified including removal of certain brain tumors, peripheral tumors and aneurysm clipping;
- Vascular surgery including aortic aneurism repair, carotid endarterectomy and certain coronary bypass procedures;
- Orthopedic surgery including any repair of a joint where a peripheral nerve may be at risk, hip revisions and pelvic fractures;
- Plastic and reconstructive surgery if nervous system is involved;
- ENT (ear nose throat); especially if nervous structures in the neck are at risk;
- Any long duration surgery, bariatric surgery, or any procedure where patient positioning may be an issue either due to patient body habitus or the type of positioning needed.
How is IONM Performed?
IONM is actually not one type of test, but can be comprised in several different types of well-established neurophysiologic tests. These include somatosensory (SEP) and motor evoked potentials (MEP), electroencephalography (EEG), electromyography (EMG), auditory brainstem responses (ABR), and triggered nerve stimulation.
The basic concept is to stimulate a part of the nervous system and elicit a response that is reproducible and can be measured, recorded and followed. Any deviation outside of a normal range would prompt an alert to the surgeon. The stimulation can be in the form of an electrical impulse given over a peripheral nerve in the case of the somatosensory responses (SEP) or over the scalp to stimulate the brain to trigger a motor response in the case of the motor evoked responses (MEP).
An auditory click stimulus is used to obtain an auditory brainstem response (ABR). Passive recording of electrophysiologic activity is also performed to record the electrical activity of the brain (EEG) or of the mucles (EMG).
IONM during surgery can identify an evolving threat to the nervous system and alert the surgeon prior to reaching that patient’s threshold for injury.
Various structures, such as peripheral nerves, can be stimulated for the purpose of proper identification. Instrumentation, such as hardware used in spinal fusion surgery, can also be stimulated to assess location and safety of its placement.
A technologist routinely greets the patient immediately prior to surgery in the hospital. They will take a brief history and speak with the surgical staff to be able to formulate a testing plan for that specific patient and procedure. Anesthesia staff is then informed of the type of testing that will be performed so that the proper agents used do not affect the use of IONM as much as possible.
The technologist then explains the testing procedure to the patient. In the operating room, after the patient is under anesthesia, electrodes will be applied to the patient and the testing begins. The electrodes are a combination of adhesive pads and sub-dermal needles, which are like small pins with a wire attached.
IONM is one of the safest testing modalities available. The patient under anesthesia during the set up and implementation of the testing does not feel any pain or discomfort. The electrodes are all removed at the end of the surgery prior to the patient awakening.
There have been rare cases reported of minor skin burns from the electrical stimulation pads; although, I have personally not seen this happen on my patients in more than 20 years of IONM practice.
Risks from not Using IONM
The nervous system is extremely fragile, highly dependent on proper blood flow and very susceptible to mechanical and chemical irritation.
Once injured, the brain and nerves may undergo some amount of self-repair; however, the incidence of any degree of permanent nerve damage is high.
The peripheral nerves have a fine network of blood vessels that bring oxygenated blood to the nerve itself. Some of these vessels are finer than a human hair.
They are easily compressed leading to potentially permanent damage. Any surgical procedure poses a certain risk to the nervous system.
Some more than others, such as those already mentioned. While the patient is under anesthesia, we have little information on the condition of the nervous system, especially the peripheral nerves.
IONM is the only way to accurately and immediately assess its integrity. Nervous tissue can suffer irreversible damage within seconds to minutes of an insult.
Medical Tourism and IONM
Best practices are the worldwide trend in healthcare, especially in the medical tourism community. Medical professionals worldwide are responsible for sharing and teaching their skills to the healthcare community. We also have a responsibility to offer the best care possible and level the playing field, such that patients have access to state-of-the-art care no matter where they obtain it.
Given that spine surgery is one of the fastest growing specialties in medical tourism, modalities, such as IONM, should be made available to these patient and hospitals. More complex surgeries are being performed and patients are becoming better informed about what is available.
Recent trends show that availability and quality are primary drivers in medical tourism decision-making, and not just cost. IONM should be a part of the movement toward improving medical and surgical outcomes. Medical tourism patients often act as both the consumer and decision-maker regarding their choices of care.
Technology, such as IONM, should be readily available and patients, facilitators, hospitals and medical staff should be educated about its importance and implementation.
About the Author
Dr. Joseph J. Moreira received his medical degree from St. George’s University School of Medicine in 1988. For the past 20 years, he has focused on Neurophysiology and Intraoperative Neurophysiologic Monitoring. Dr. Moreira was one of the first neurologists to use motor-evoked testing in the operating room during clinical practice in New York and presented his technique for monitoring scoliosis surgery at the American Academy of Neurology. Dr. Moreira, currently the clinical director of Intraoperative Monitoring, serves a group of more than 30 neurosurgeons and orthopedic practitioners. Dr. Moreira has a keen interest in bringing Intraoperative Monitoring to the medical tourism community and educating and training hospital staff in this specialty. He believes in helping the global medical community in attaining best practices and widening his field of expertise so that patients around the world have access to the best care they can attain and a better understanding of risk.