IN SHORT, IONM IS THE MONITORING OF COMPONENTS OF THE NERVOUS SYSTEM OF A PATIENT DURING SURGERY.
Say you want to know if your friend can move and feel. You would just ask them, right? Now say that friend is asleep under anesthesia but you still want to know the same info. They obviously can’t talk back to you while unconscious and show you they can move their legs or feel you touching their arm. IONM is essentially a system of stimulating and recording electrodes placed on the patient that allow us to see that kind of information in data form. Here’s how we do it:
SSEPS
This is how we monitor sensation. Electrodes placed at the wrists and ankles (sometimes other sites too) deliver small electrical pulses that activate nerves. A sensory signal, say from the wrist, travels up its corresponding nerves within the arm, then through the spinal cord and into the brain where the signal is processed as “hey, something is buzzing my wrist!” That response in the brain is captured by recording electrodes placed at the scalp. This method of collecting sensory function data is called somatosensory evoked potentials, or SSEPs, and demonstrates the ability of the patient to feel.
TCMEPS
This is how we monitor motor function. Electrodes are placed on the scalp over the part of the brain that controls voluntary movement. Stimulation is delivered through these electrodes that causes the motor area of the brain to activate. A motor signal is sent out of the brain, down through the spinal cord, and delivered to muscles all over the body. Recording electrodes placed in some of those muscles in the arms and legs pick up the muscle “twitches” that result, allowing us to confirm that the motor signal from the brain is getting through. This method of collecting motor function data is called transcranial motor evoked potentials, or TcMEPs.
EMG
You may have heard of this one before. Those same electrodes placed in muscles to record muscle “twitches” from TcMEPs are also used to watch for any muscle activity that might be caused by irritation to the nerves that activate them. This helps us detect if the surgery is causing any unwanted nerve agitation. This is called electromyography, or EMG. We can also use EMG in the form of directly stimulating a nerve or area with a probe and seeing what muscle(s) are activated and how easily they’re activated. The surgeon can use this data to determine locations of nerves (sometimes they’re hard to see within tissue) or evaluate placement of screws in the vertebrae (for spinal fusions).
WHEN IS IOM USED?
Depending on the surgeon and style of surgery, IONM is most often used for spine, brain, and vascular surgeries that may put certain nervous structures at risk. Think of things like the spinal cord and its blood supply, nerve roots, or areas and vessels of the brain that could cause deficits if damaged. When the surgeon wants to have as much real-time information about the nervous system as possible, they’ll schedule us. We run neuromonitoring data on the nervous system throughout the surgery and let the surgeon know if we see any changes. In addition to SSEPs, TcMEPs, and EMG, there are many more techniques we use to assess additional nervous structures and functions.