IntraOperative (Neurophysiology) Monitoring (IOM) is the recording of the bioelectrical activity (whether spontaneous or triggered) of the central and peripheral nervous system, in order to assess objectively and effectively the functional integrity of neural structures during surgery.

The use of electrophysiological methods dates back to 1937 when direct cortical stimulation was first used. Ever since, and especially in the past three decades, there have been very rapid advances in computer technology, biomedical engineering and the recording of electrophysiological data. As a consequence, IOM has blossomed from an interesting investigational procedure, to a widely used and clinically valid procedure to protect patients from neurologic injury during surgical intervention.

IOM is being used to:

• Ιdentify specific neural structures and landmarks that cannot be easily recognized on anatomical grounds only (for example to locate cranial nerves during skull base surgery)
• Τest the function of these structures,
• Detect and quantify early (if not prevent) any intraoperative injury, allowing for immediate corrective measures to prevent any postoperative deficit and restore normal function As a result, the surgeon can feel comfortable about the patient’s neurologic safety during surgery, and therefore go forward to provide a more thorough procedure. Moreover, with IOM the surgeon can feel more confident about a procedure’s safety, allowing surgery on a high-risk patient who might otherwise be turned away.

The most common signals/procedures involved in IOM are:

• The Electroencephalogram (EEG), which represents the spontaneous electrical activity of the brain
• · The Electromyogram (EMG), representing the spontaneous electrical activity of the muscles
• · Motor Evoked Potentials (MEPs), the recording of the peripheral response (e.g. at a leg nerve or muscle) to a stimulus delivered centrally (e.g. at the cortex)
• · Somatosensory Evoked Potentials (SSEPs), the recording of the central response to a stimulus delivered peripherally
• · Brainstem Auditory Evoked Responses (BAERs), the recording of the brain’s response to an auditory stimulation
• · Visual Evoked Potentials (VEPs), the recording of the brain’s response to a sensory stimulation of the patient’s visual field
• · Triggered EMG (tEMG), representing the activity recorded from a muscle after direct electrical stimulation of the motor nerve (or nerve root) that innervates that muscle
• · Nerve Conduction Study (NCS), the evaluation of the function (especially the ability of electrical conduction) of motor and sensory nerves in the upper and lower extremities
• · Transcranial Doppler (TCD), the measurement of the velocity of blood flow through the brain’s blood vessels.

Applications involve, but are not limited to:

• Neurosurgery (spinal surgery and most brain surgeries)
• Carotid endarterectomy;
• ENT procedures (acoustic neuroma resection etc.)
• Peripheral nerve surgery (carpal tunnel syndrome)
• TAAA (thoracic-abdominal aortic aneurysms)
• Thyreoid surgery
• Cardiothoracic surgery

The selection of IOM equipment is critical. A typical system should consist of a portable, computer-controlled unit that has the capacity to perform all the necessary operations: recording, stimulation, display, signal processing, and data storage.

However, as neurophysiological recordings are not only affected by surgical manipulation (ischemia or mechanical injury) but also by perisurgical factors (body temperature, blood pressure and/or the anesthesia regime) as well as artifacts (related to electrical interference, equipment failure etc.), what is far more important is the technologist’s ability to differentiate between all of the above and correctly interpret the recordings he obtains during the course of surgery.

We at Nucleomed take real pride in both!