Abstract
Intraoperative monitoring is performed to provide real-time assessment of the neural structures that can be at risk during spinal surgery. Somatosensory evoked potentials (SEPs) are the most commonly used modality for intraoperative monitoring. SEP stability can be affected by many factors during the surgery. This study is a prospective review of SEP recordings obtained during intraoperative monitoring of instrumented spinal surgeries that were performed for chronic underlying neurologic and neuromuscular conditions, such as scoliosis, myelopathy, and spinal stenosis. We analyzed multiple montages at the baseline, and then followed their development throughout the procedure. Our intention was to examine the stability of the SEP recordings throughout the surgical procedure on multiple montages of cortical SEP recordings, with the goal of identifying the appropriate combination of the least number of montages that gives the highest yield of monitorable surgeries. Our study shows that it is necessary to have multiple montages for SEP recordings, as it reduces the number of non-monitorable cases, improves IOM reliability, and therefore could reduce false positives warnings to the surgeons. Out of all the typical montages available for use, our study has shown that the recording montage Cz-C4/Cz-C3 (Cz-Cc) is the most reliable and stable throughout the procedure and should be the preferred montage followed throughout the surgery.
Highlights
The ultimate goal of intraoperative neurophysiological monitoring (IOM) is to reduce the risk of adverse events that can occur during surgeries that put neural structures at risk in an attempt to prevent permanent neurological injury
Our study shows that it is necessary to have multiple montages for Somatosensory evoked potentials (SEP) recordings, as it reduces the number of non-monitorable cases, improves IOM reliability, and could reduce false positives warnings to the surgeons
Despite the addition of other monitoring modalities, SEPs continue to be the standard modality used in IOM for various reasons, most importantly that they can be run frequently, and are not susceptible to overstimulation and neuromuscular blockade use
Summary
The ultimate goal of intraoperative neurophysiological monitoring (IOM) is to reduce the risk of adverse events that can occur during surgeries that put neural structures at risk in an attempt to prevent permanent neurological injury. Somatosensory evoked potentials (SEP) have been used for IOM since their inception in the late 60s and 70s [1,2,3,4,5]. The field of IOM has been improved by the addition of other modalities, such as electromyography (EMG) and motor evoked potentials (MEP); SEP recording have continued to remain the gold standard. False-positive SEP changes during surgery can transiently occur due to various causes, such as change in anesthesia delivery, blood loss, blood pressure, body temperature, accumulation of anesthetic in the patient’s body, and various technical interferences in the operating room. For the purposes of conducting IOM, it is very important to distinguish real SEP changes from sources of interference, such as technical problems or noise, which may lead to an increase in number of false positive changes.
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