When to Use Neuromonitoring in Spine Surgery

Intraoperative neuromonitoring in spine surgery: How effectively does it prevent complications? When should your team be using it? Our expert answers these questions and more.

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Spine surgery, as with any surgery, carries the risk of complications. Though rare, neurological injury has the potential of incurring serious sensory and motor injuries. Due to the nature of complications that can occur with spine surgery, intraoperative neurophysiological monitoring (IONM), or neuromonitoring, is increasingly being used to avoid post-surgical neurological complications.

Surgeon using neuromonitoring in spine surgeryWhen should your surgical team use neuromonitoring? How effectively does it prevent neurological complications. Our expert answers those questions and more.

While many surgeons prefer using neuromonitoring for all spinal surgeries in an effort to reduce potential complications, controversies exist regarding its use in routine procedures because of its high cost, as well as its effectiveness.

History of Neuromonitoring

Neuromonitoring is a technology that allows the surgeon to assess spinal cord function during surgery through real-time feedback from individual nerve roots, motor tracts, and sensory tracts. After the introduction of the first commercial intraoperative neuromonitoring (IONM), the procedure became popular in the 1980s. However, the concept of electrical stimulation for the purpose of collecting data about the nervous system first arose in the 1930s.

Though technology was invented in Japan in 1972 that utilized the spinal cord evoked potential (SCEP) after direct stimulation of the spinal cord, in the United States, surgeons had to "rig" their own machines to collect this type of data, which was inefficient and often unwieldy. The introduction of the first IONM machine in the 1980s changed this landscape in the United Kingdom and United States. 

All these methods monitored sensory mediated tracts in the spinal cord; but, at that time, the only way to monitor motor function was by using the “Wake up test” developed by Vauzelle and Stagnara (1973). In 1980, Merton and Morton reported a technology to stimulate the brain transcranially and opened the doors for motor tract monitoring.

In 1990, The American Society of Neurophysiological Monitoring was founded to serve the expanding IONM field. According to the society’s definition, IONM “includes any measure employed to assess the ongoing functional integrity of the central or peripheral nervous system in the operating theatre or other acute care setting.” 

The multidisciplinary support of hardware and software development and the evolution of anesthesiology has not only made neuromonitoring possible in the present, but routine.

An Expert’s History with Neuromonitoring

Dr. Michael G. Fehlings, Professor of Neurosurgery and Vice Chair Research, Department of Surgery at the University of Toronto and Toronto Western Hospital has a long history using neuromonitoring, “I was first exposed to neuromonitoring during the last couple of years of my neurosurgery residency in Toronto in the late 1980s,” he says. “At that time we were using SSEPs for complex spinal procedures and brainstem auditory evoked potentials and facial nerve monitoring for certain skull base operations including vestibular schwannoma resections.

“At New York University Medical Centre during my fellowship from 1991-1992, I was exposed to the combined use of motor and somatosensory evoked potentials during delicate spinal cord operations including resection of intramedullary spinal cord tumors,” he continues.

“Since coming on staff at Toronto Western Hospital in 1992, I have used neuromonitoring on most spinal procedures. Initially, this mainly involves SSEPs but over the years we have added various forms of multimodality monitoring.”

Types of Neuromonitoring

No single method adequately covers the complex functions of the spinal cord. Multimodality combinations of currently available technologies are considered necessary for effective neuromonitoring. The three most common types of neuromonitoring modalities used are:

  • Somatosensory evoked potentials (SSEPs): SSEP is the most frequently used intraoperative spinal monitoring modality. Peripheral stimulating electrodes generate cortical responses. This process allows the surgeon to monitor sensory pathways and detect any perioperative neurologic changes.
  • Transcranial motor evoked potentials (MEPs): MEPs, also called transcranial MEPs (tcMEPs), generate a stimulus either at the level of the spinal cord or at the motor cortex. Using electrodes, the signal is measured at predetermined peripheral upper and lower extremity muscle group sites by recording electrodes.
    • Pros: Monitoring and tracking of the corticospinal tract activity during the operative procedure is a bit pro, as well as MEPs’ reliability in detecting new postoperative deficits.
    • Cons: MEPs have extreme sensitivity to inhaled volatile gases, which prevents the usage of routine anesthesia and instead requires the use of intravenous anesthetic agents. Also, a triggered stimulus to register the MEP is required, which prevents continuous monitoring.
  • Spontaneous and triggered electromyography (EMG): EMG actually has two forms: stimulated or spontaneous (sEMG) and triggered (tEMG). tEMG recordings are obtained when the center of the tulip of the pedicle screw is stimulated, generating a response that is then recorded from the applicable muscle group.
    • Pros: EMG is a valuable for neuromonitoring specific nerve roots that may be at risk of injury during spinal instrumentation. sEMG is recorded continuously, which provides the surgeon the advantage of real-time feedback throughout the entire procedure. Since its introduction, this technique has also been shown to be an effective tool for detecting cortical bone breaches during pedicle screw insertion.
    • Cons: To obtain a proper sEMG response, neuromuscular blockade is prohibited with sEMG, but not tEMGs. Lower thresholds in tEMGs might indicate a cortical breach, putting the nerve root at risk.

Best Method(s) for Surgery

Dr. Fehlings explains that neuromonitoring goes beyond normal vitals, “by providing monitoring of neural function. In the compromised cord, multimodality Eps can also provide an indirect read-out of spinal cord perfusion.” And, “In principle, multimodality electrophysiological recording where both motor and sensory tracts are monitored provides the best accuracy and sensitivity/specificity.”

The following spinal procedures benefit most from neuromonitoring, says Dr. Fehlings:

  • Posterior cervical and thoracic decompressions
  • Intradural spinal cord surgery (e.g. intradural intra and extramedullary tumors; tethered cord release; syringomyelia surgery)
  • Spinal deformity surgery
  • Complex revision surgery

Should Neuromonitoring be Used for All Spinal Surgeries?

There is controversy in the current health climate as to whether neuromonitoring should be used for all spinal surgeries. There are some surgeons who feel that if the technology exists, there’s no reason not to use it. On the other hand, due to high cost and efficiency others argue that it should only be used for specific surgeries.

Dr. Fehlings’ experience in this area adds credence to both points of view. “Neuromonitoring is likely not necessary for all surgeries. For example, a one- or two-level ACDF and simple lumbar decompressions for stenosis or disc pathology are low risk procedures and neuromonitoring likely adds very little to the safety of the procedure,” says Dr. Fehlings

“However,” he continues, “in our unit, we are fortunate to have a dedicated in-house neuromonitoring team with 4 skilled full-time neurophysiology technologists. As such, we use neuromonitoring for virtually all cases—the techs get very good at interpreting normal variations in EP signals due to anesthetics. This knowledge is helpful in interpreting changes which occur in more complex cases. In addition, we sometimes pick up nerve compression from positioning issues (e.g. ulnar or peroneal nerve compression) with EP monitoring—this can then be readily corrected intraoperatively,” says Dr. Fehlings

According to one study, however, for a new surgical intervention to be cost-effective, any additional costs must show benefits that can either reduce long-term associated costs or improve surgical outcomes. At this time, there is not enough research on the cost-effectiveness of neuromonitoring and more research is needed to determine the long-term health and cost benefits before suggesting an expanded use.

Should Neuromonitoring Ever Not Be Used?

Aside from cost concerns and given the benefit of neuromonitoring, it’s easy to see where surgeons may fall on the side of always using neuromonitoring. But there may be drawbacks for certain facilities and surgeons. “There is a learning curve to using neurophysiological monitoring and the team needs to work together to understand variations that can occur due to technical issues or anesthetic effects,” says Dr. Fehlings

However, Dr. Fehlings sees very few drawbacks, “With frequent use, the setup for EP monitoring should add very little if any time to the OR set-up. For MEPs. the total intravenous anesthetic (TIVA) protocol does require added skill and familiarity by the anesthetic team. In many cases, we recommend converting from TIVA to inhalational anesthetic during wound closure, after the critical phases of surgery are completed, to allow more rapid awakening from the anesthetic.”

Should Your Practice Use Neuromonitoring?

Despite the need for more evidence-based research, that body of evidence is growing in support of the effectiveness of neuromonitoring in detecting adverse outcomes during spinal surgery. Without enough prospective studies with high-level evidence that validate efficacy of neuromonitoring, its use is largely left to surgeon preference and the policies and recommendations of specific institutions where neuromonitoring may be employed. Overall, future studies are needed to explore new treatments, develop clinical practice guidelines, and synthetize all previous literature.

According to Dr. Fehlings, the use of neuromonitoring should be expanded. It is also considered, “the standard of care of deformity surgery, intradural spinal cord surgery and complex spinal instrumentation surgery.” Depending on your practice, the benefits may outweigh cost and efficiency concerns, especially given the data that can be obtained on improving its effectiveness in future surgeries.

 

Updated on: 03/11/21
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Managing Neurological Complications in Pediatric Spinal Deformity Surgery
Michael G. Fehlings, MD, PhD, FRCSC, FACS
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