Integration of Intraoperative Neuromonitoring with Surgery to Save Thousands of Lives

Neurons comprise the basic working unit of our brain and act as a carrier of signals from the brain to the rest of the body. Not only our nervous system is delicate and unrepairable, but also it is a significant part of our body. Any damage to neurons would lead to paralysis, muscle weakness, and hearing loss. To reduce the risk of damaging the neurons while operating a person, intraoperative neurophysiological monitoring (IONM) or intraoperative neuromonitoring technology can be very helpful. This technology reduces the risk of damaging the nerve by detecting the injuries before they cause any complications after operation. The IONM also localizes anatomical structures such as sensorimotor and peripheral nerves that help the surgeons by guiding them during dissection. With the help of IONM, monitoring the changes in spinal cord, brain, and peripheral nerve fiction before they are damaged beyond repair is possible. 

IONM technology has been successfully integrated with various surgical procedures, which have increased the post-surgery mortality rate of patient. This was made possible with the help of availability of widespread computer networks and increase in the awareness about IONM. This technique has a wide range of applications, and is used alongside numerous surgeries to detect important neural structures during the surgery along with preventing postoperative damages. Few of these modalities consist of electromyography, somatosensory evoked potentials (SSEPs), visual evoked potentials (VEPs), electroencephalography (EEG), motor evoked potentials (MEPs), and brainstem auditory evoked potentials (BAEPs).  

• Electromyography (EMG)

It is possible to record the electrical activities produced by skeletal muscles with the help of EMG. With the help of free-running EMG, it is possible to detect metabolic and/or mechanical irritation of the nerves. By using free-running EMG monitoring, two types of discharge can be observed with different clinical significance. These two types of discharges are phasic and tonic discharge. Phasic charges are short and comparatively synchronous bursts of motor unit potential. This is mostly in association with the blunt mechanical trauma. In contrast, tonic charges comprise of repetitive and fixed episodes of activity of motor unit potentials. It can last from several seconds to minutes. The region affected is nerve ischemia and it is caused due to heat spread from irrigation with saline, electrocautery, or traction. For motor nerve condition studies, stimulation of EMG is preferred. It is performed by stimulation of the nerves electrically. Alongside, the action potential of resulting compound muscle in the inverted muscle is recorded. This informs the surgeons about the variation of the motor nerves of patients. It also informs about the functionality of different nerves, including motor and sensory that can be come across during the surgery. It offers the information of the proximity of the nerves that are prone to damage during surgeries such as pedicle screwing of the spine.

• Somatosensory evoked potential (SSEP)

SSEP is commonly stimulated in the median nerve and the posterior tibial nerve. SSEP is most effective when it is recorded in the cortical somatosensory area as it offers important data regarding intraoperative neural damage. SSEP can also be recorded from spine, Erb's point, primary cortical somatosensory area, or brainstem, but the recorded data is not as accurate. SSEP is a test opted for sensory pathways which ascend through the dorsal column of the spinal cord. The usage of SSEP prevents unwanted movement of the patients during the surgery. This technique is quantifiable and has comparatively low average intertrial variability. If the amplitude of SSEP decreases more than 50% and/or the latency increases more than 10% of the baseline, it is considered as “alarm critical” for intraoperative neural damage.

• Visual evoked potential (VEP)

VEP comprises of inducing brief visual stimuli to observe electrical potentials that are recorded from the scalp over the visual cortex. The visual pathway from the IONM offers in-depth information on diverse surgeries such as removal of tumors that lie near the optic radiation, aneurysm clipping of the posterior circulation, and transsphenoidal surgery.

• Electroencephalography

With the help of electroencephalography, a surgeon can observe the electrical activities from the scalp. This technique is used widely for monitoring anesthesia and assessing the degree of cerebral perfusion during vascular surgery and the degree of hypothermia for neuroprotection. Generally, EEG is used to detect the diffuse hypoperfusion states through CEA, but there can be a possibility that it won’t detect micro-emboli during CEA.

• Brainstem auditory evoked potentials (BAEPs)

By generating acoustic stimuli, a small electrical potential is generated. These potential responses are BAEPs. These potentials are useful for monitoring auditory structures and relatively resistant to surgical anesthesia. BAEPs can be interpreted by the amplitude or latency of its waves I-V, i.e., first five negative potentials. It alarms the system for intraoperative neural damage and subsequent postoperative hearing loss if the amplitude decreases more than 50% and/or latency remains more than 1 ms.  

As intraoperative neuromonitoring offers a wide range of utilities, many companies have started investing in this field. More investments are made for updating the technology for intraoperative neuromonitoring. This has significantly increased the market of intraoperative neuromonitoring. Allied Market Research has estimated that the intraoperative neuromonitoring market would reach $4.9 billion, growing at a CAGR of 7.0% by 2022. As the chronic disorders increases in the ageing population, the need for the application of IONM increases. This market shows a great potential in the field of medicine and will reach new heights as more technology develops to support this market.

Related Post