Intraoperative Neurophysiological Monitoring and Mapping, often abbreviated neuromonitoring or IONM, is defined as the clinical practice and scientific study of human neurophysiology applied in the surgical or procedural setting. Neurophysiology is a branch of neuroscience that is focused on nervous system function. So, the field of neuromonitoring has a very specific focus on the clinical evaluation of nervous system function during surgical and interventional procedures. As both a clinical practice and a scientific study, the field of neuromonitoring includes the following:
- Educational programs at various levels.
- Professional societies that hold meetings and conferences (ASNM, ACNS, ASET)
- Peer-reviewed journals that publish cutting-edge research (TNJ, JCN, CN).
- Careers for practitioners that include scientists, physicians, technologists and technicians
Practitioners of neuromonitoring at all levels, ranging from technologist to doctor, may be employed by hospitals, private practices, group practices and corporations of all sizes.
How it Works
From a practical perspective, neuromonitoring involves the use of physiological techniques (e.g., recording electrical activity from the nervous system), during high risk surgical or interventional procedures in order to guide the surgical team and/or mitigate the risk for injury to the nervous system (e.g., causing muscle weakness, paralysis, hearing loss, and other loss of normal body functions). So, neuromonitoring significantly reduces the risk of iatrogenic injury to the nervous system, thereby optimizing surgical outcomes.
Neuromonitoring is typically performed by a team which includes 1) a certified technologist who works in the operating room to conduct the tests and document the findings in the context of the surgery, and 2) a doctoral-level neurophysiologist who works remotely via telemedicine to supervise the technologist and interpret the results of the physiologic tests. The neurophysiologist doesn’t have to be a physician (MD/DO), but he/she must be board-certified in the supervision and interpretation of neuromonitoring. So, a PhD neurophysiologist certified by the American Board of Neurophysiologic Monitoring is highly qualified to supervise and interpret neuromonitoring.
The physiological techniques mentioned above involve the application of different tests, or modalities, that allow one to identify nervous system structures and evaluate their function during surgery. These modalities often engage specific divisions of the nervous system. For example, some tests engage structures involved in sensation, while other tests engage structures involved in movement. The modalities employed for a given surgery are determined by the parts of the nervous system that are considered to be at risk. You can learn more about the most common test modalities by clicking the links on the right side of this page (on a mobile device, check the bottom of the page).
The neuromonitoring data from the different tests are shared between the technologist and the neurophysiologist via a HIPAA-compliant screen-sharing platform, and interpretation is done and communicated to the OR in real time. Communication between the technologist and the neurophysiologist most frequently occurs via internet-based chat.
The types of surgical procedures during which neuromonitoring is employed vary greatly and include: brain, spine, ENT, orthopedic, cerebrovascular and cardiovascular surgery.
Difference Between Mapping & Monitoring
Most people use the term neuromonitoring to describe both mapping and monitoring, but there is an important difference.
Monitoring refers to real-time, and preferably constant, evaluation of the nervous system. The primary goal is to minimize or prevent post-operative neurological deficits through early detection of evolving injury and timely intervention. Monitoring is based on the premise that neurophysiological activity changes in a measurable and reversible way before the onset of permanent neurological deficit, opening a window of opportunity for correction.
Changes in signal characteristics may suggest evolving injury to the nervous system and may reveal clues to identify the cause. The job of the neurophysiologist is to:
- Correctly determine if a change in data is real.
- Correctly determine if a change in data is important.
- Correctly determine what is causing the change in data.
- Do something about it, or recommend that someone else does.
When we determine that a change in data is real and important, we call this an “alert” because we immediately alert the surgeon. The alerted surgeon should perform all interventions that could prevent or limit neurologic deficits. Whenever possible an intervention is immediately performed in an effort to prevent a negative outcome, or at least limit the severity. Examples of interventions include: pause, irrigate, remove retractor, elevate blood pressure, abort surgery, etc. Not all changes/injuries can be reversed with intervention.
Mapping refers to periodic, or as-needed, identification of nervous system structures, ruling out non-neural structures, and/or navigation through and targeting nervous system structures. Sometimes tumors and other pathology can distort the nervous system, making it challenging to identify critical structures. So, the primary goals of mapping include characterization of tissue, preservation of function and accurately targeting neural structures.
Some parts of the nervous system lend themselves to identification due to their baseline electrical activity, or to how they can respond to local, regional or distant electrical stimulation. Physiologic stimulation/recording methods can be used to identify critical regions, as well as rule-out non-neural tissue and non-critical brain regions. Also, recording methods can be used to navigate through the nervous system and find the correct location. For example, placement of Deep Brain Stimulating (DBS) electrodes for treatment of Parkinson’s disease is accomplished with neuro-navigation and microelectrode recordings (MER).