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Factors Associated With Inadequate Intraoperative Baseline Lower Extremity Somatosensory Evoked Potentials

Chen, Jonathan H.; Shilian, Parastou; Cheongsiatmoy, Justin; Gonzalez, Andres A.

Journal of Clinical Neurophysiology: September 2018 - Volume 35 - Issue 5 - p 426–430
doi: 10.1097/WNP.0000000000000494
Original Research

Purpose: Intraoperative neurophysiologic monitoring involves the use of various modalities, including somatosensory evoked potentials (SEP), to assess the integrity of the at-risk nervous system during surgeries. Reliable baseline tracings are important because they are data against which future tracings are compared to detect potential injury. In some cases, adequate baselines may be difficult to achieve. Therefore, we analyzed several patient-specific factors to determine which variables are associated with inadequate intraoperative SEP baseline signals.

Methods: This is a single-center, retrospective chart review of 631 consecutive patients who underwent spine or cranial surgeries between 2010 and 2011. Variables analyzed included age, glucose levels, diabetes mellitus type 2, hypertension, hyperlipidemia, height, weight, sex, smoking, preexisting neurologic conditions, surgical history, lower extremity edema, and neurologic examination findings. Association between these patient factors and baseline lower extremity SEP signals were analyzed.

Results: Height, weight, neurologic deficits, lower extremity edema, and history of neurologic disease are each associated with inadequate baseline lower extremity SEPs after controlling for confounding variables. Baseline signals were able to be acquired in 94.1% of patients.

Conclusions: Adequate baselines are paramount for successful intraoperative neurophysiologic monitoring. However, certain patient-specific factors are associated with inadequate baseline SEP signals. Physical examination findings and a detailed chart review can be done to identify these factors and guide expectations during monitoring. Further research related to patient-specific factors amenable to modification can further improve our capacity to protect the nervous system during surgery.

Division of Intraoperative Neurophysiological Monitoring, Keck Hospital of University of Southern California, Los Angeles, California, U.S.A.

Address correspondence and reprint requests to Jonathan H. Chen, MD, 1500 San Pablo St #3108, Los Angeles, CA 90033 3, U.S.A.; e-mail:

The authors have no funding or conflicts of interest to disclose.

Chen J, Gonzalez A, Shilian P, Tran AT. Predictive factors determining poor baseline lower extremity somatosensory evoked potentials during surgery. Poster presented at American Clinical Neurophysiology Society Annual Meeting & Courses, Orlando, FL, February 12–14, 2016.

© 2018 by the American Clinical Neurophysiology Society