What Is Intraoperative Neurophysiological Monitoring?

Intraoperative neurophysical monitoring is one way surgeons can make sure they aren't severing nerves by accident during delicate surgeries.

Intraoperative neurophysiological monitoring is the continuous evaluation of a patient’s nervous system during surgery, especially procedures involving the brain and spinal cord. Electrical and electromagnetic sensors connected to the patient via adhesive electrodes or needles transmit information from the nervous system that can be monitored on a computer screen.

Intraoperative neurophysiological monitoring keeps the surgeon and the anesthesiologist aware of the proper functioning of the patient’s nervous system during surgeries in real time. The neurophysiological monitoring devices alert the surgeon to any change in the patient’s nervous system to prevent irreversible nerve damage.

Intraoperative neurophysiological monitoring was first used in the 1930s during an epilepsy surgery. Since the 1980s, intraoperative neurophysiological monitoring techniques have been widely used during many surgical operations.

Before the advent of intraoperative neurophysiological monitoring, nerve functions were assessed by “wake up” tests during spinal surgeries. The anesthesia levels were periodically reduced to check the nerve function, but this did not provide continuous information.

With technological advancement in the monitoring devices and computerized analysis, intraoperative neurophysiological monitoring now has evolved into an integral part of many surgical procedures. It has become possible to access and selectively remove and treat even deep-seated tumors and lesions, which was not possible before these refined techniques.

Intraoperative neurophysiological monitoring is performed mainly to prevent permanent damage to the nervous system from surgeries involving the nervous system.

Intraoperative neurophysiological monitoring is performed to:

• Continuously monitor the functional integrity of neural pathways 
• Map and identify the affected region requiring surgery
• Avoid injury to the adjacent nerve tissues
• Detect and repair any nerve injury before the damage becomes irreversible
• Minimize risks of permanent post-surgical functional impairments such us:
  • Paralysis
  • Muscle weakness
  • Tingling
  • Chronic pain 
  • Numbness
  • Loss of bowel and bladder control

Intraoperative neurophysiological monitoring is usually performed by a technician who operates the device and is supervised by a neurophysiologist. Electrodes or needles attached to the patient’s relevant anatomy continuously transmit information to the device which can be viewed in a monitor.

During the surgery the neurophysiologist constantly observes and analyzes the information on the monitor and alerts the surgeon when any abnormality is observed. This helps the surgeon in real time, to navigate in the operative area and avoid accidental damage to the normal neural tissues and other vital organs and blood vessels in the area.

Various modalities are used to monitor the patient’s neurophysiological function during an operation.

• Electromyography (EMG): Recording of a muscle’s electrical activity in response to electrical stimulation, which makes the muscle contract.
• Evoked Potentials: Recording of the time taken for the brain’s response to sensory stimulus through sight, sound or touch.
• Electroencephalography (EEG): Recording of electrical activity in the brain with electrodes placed on the scalp.
• Electrocorticography: Recording of the brain’s electrical activity by placing electrodes inside the brain’s cortical region.