To the Editor: The authors of the Guidelines for the Use of Intraoperative Monitoring for Surgery of the Human Spinal Column and Spinal Cord1 are pleased to respond to the authors of the Letter to the Editor.2 We wish to apologize to these authors for calling them “prominent electrophysiologists” when they are clearly not. Our information was incorrect, but perhaps we can be forgiven for this considering that the first author “is the former medical director for Surgical Neuromonitoring Associates and Surgical Neuromonitoring, PLLC, companies that perform intraoperative monitoring.”3 We also regret that they are “quite disappointed” in our work, and we confess to being confused regarding the stated reasons for their disappointment, to which we will attempt responses below. First of all, our publication1 was a “guideline,” and by definition not “research,” so we are unclear as to why the authors of the Letter2 were under the impression that we were attempting to classify our publication as “original research.” They go on to say that “The authors failed to follow their own inclusion and exclusion criteria, so no systematic review was conducted.” Their case in point to illustrate this claim is that we did use their cited letter and commentary4 when we said we would not use such information. The authors are confusing information cited within the document as scientific foundation or contextual information used as background, with the evidence used in generating the guidelines, which can be found in the evidentiary tables. Their “letter and commentary” is not found in the evidentiary tables, and therefore, we did not fail to follow our inclusion and exclusion criteria. They have noted that none of their publications on cost effectiveness can be found in any of the evidentiary tables, either. There are reasons for this, which we are happy to address. In 2012, Ney et al5 published a preliminary cost-effectiveness analysis of intraoperative neurophysiological monitoring during spinal surgery. They concluded that “multimodal intraoperative neuromonitoring (IONM) reduces the relative risk of postoperative neurological complications by an estimated 49.4% at a cost of $63 387 per neurological deficit averted.”5 Although an admirable attempt, even the authors declare that “accepting of the conclusions of the study requires some suspension of disbelief regarding the model's assumptions.” In their model, baseline neurological complication rate had the strongest correlation with reduction in neurological complications. Based on pooled analysis, they utilized a 5.0% baseline neurological complication rate for spinal surgeries. We argue that this grossly overestimates the rate of neurological complication with spinal surgery (particularly those performed most frequently). Furthermore, their analysis assumes “a generic postoperative neurological deficit,” which is unrealistic and further contributes to the inaccuracy of the model output. Lastly, the authors failed to include costs associated with false positive intraoperative monitoring (IOM) alerts. A false positive alert that results in abortion or prolongation of the procedure may carry significant cost that should be included in the model. In summary, Ney et al made a valiant attempt but fell short due to suboptimal data/inputs and we did not feel that another Class III study provided any further important data for our guidelines. The following year, Ney et al6 published a cost-benefit analysis of intraoperative neurophysiological monitoring in spinal surgery using a Monte Carlo simulation based upon the published literature. This is a hypothesis-generating study rather than an evidentiary exercise that could be used in guideline development. They reported that intraoperative monitoring is cost saving for spinal surgeries in a theoretical model based on the current published literature. While their sensitivity analysis does argue for cost savings at a neurological complication rate exceeding 0.3%, the data inputs from the then-current published literature weakens the model's integrity. To quote the authors themselves (in spite of their denial in their Letter), “ideally, data should be obtained in a randomized clinical trial for the efficacy of IONM in spinal procedures, where patient costs and quality of life are tracked alongside clinical data, with follow-up data for years after the initial operation.”5 In summary, this study also provided no usable information for the development of evidence-based guidelines. In 2015, Ney et al3 once again published an analysis of the National Inpatient Sample data, similar to that reported by James et al7 the previous year. The authors included only those patients who underwent “noncomplex” spinal procedures, including laminectomies and noninstrumented fusions. They reported a significant reduction in the rate of neurological complication in the monitored group, odds ratio = 0.6. While cost data are reported (IOM results in a 9%-39% increase in hospital charges depending on the regression model used), this study is more appropriately categorized as an observational analysis (Class III medical evidence) of the therapeutic effect of IOM. While the study reports ostensibly positive results, the authors note that the “sample sizes are enormous and can overemphasize minor differences in the data.”3 Further overemphasis comes from the use of relative risk reduction in the setting over a very small baseline incidence. The authors report a 0.6% absolute risk reduction associated with the use of IOM. The results of this study are curious. Ney et al3 included only “noncomplex” spinal procedures, presumably those with the least risk for neurological complication and those least likely to benefit from the use of IOM. Using the same database but including all procedure types, James et al7 reported no significant difference in the rate of neurological complication between the monitored and unmonitored groups. Such profound discrepancies using very similar datasets clearly demonstrate the need for more effective and scientifically robust research on this topic. Cost-effectiveness analysis necessarily requires assumptions based on the existing medical evidence. Our guideline acknowledges the robust evidence for the use of IOM as a diagnostic tool. However, our analysis reveals a paucity of quality data evaluating the use of IOM as a therapeutic adjunct. Demonstrating a positive therapeutic effect is a prerequisite for demonstrating cost effectiveness. If we are unable to demonstrate a consistent beneficial therapeutic impact, there is little utility (or validity) in theoretical mathematical models based on low-quality data inputs. This is not to say that such analyses should not be conducted; only that significant caution is warranted when interpreting their results. Lastly, the guideline1 authors want to reiterate that our work in no way discourages the use of intraoperative monitoring during spinal surgery. The objective of any guideline document is to report, to the best of our ability, the existing medical evidence, making recommendations on the topic in question based on this evidence-based synthesis and analysis. It is entirely possible that IOM does provide a therapeutic benefit in select patient populations and select procedures. What we reported is the lack of evidence in the published literature that we found of a therapeutic benefit to the use of IOM, while acknowledging evidence for a diagnostic role in spinal surgery. As previously stated in the conclusion of our guideline, we support the letter authors’ call for future research on this topic. However, to date there is insufficient evidence to require its use or to classify it as an evidence-based standard of care. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Hadley MN, Shank CD, Rozzelle CJ, Walters BC. Guidelines for the use of electrophysiological monitoring for surgery of the human spinal column and spinal cord. Neurosurgery . 2017; 81( 5): 713- 732. Google Scholar PubMed 2. Ney JP, van der Goes DN. Letter: Guidelines for the use of electrophysiological monitoring for surgery of the human spinal column and spinal cord. Neurosurgery . 2018. doi: 10.1093/neuros/nyy206 [published online ahead of print]. 3. Ney JP, van der Goes DN, Nuwer MR. Does intraoperative neurophysiologic monitoring matter in noncomplex spine surgeries? Neurology . 2015; 85( 24): 2151- 2158. Google Scholar CrossRef Search ADS PubMed 4. Ney JP, van der Goes DN, Nuwer MR. Letters. Spine . 2015; 40( 9): 667. Google Scholar CrossRef Search ADS PubMed 5. Ney JP, van der Goes DN, Watanabe JH. Cost-effectiveness of intraoperative neurophysiological monitoring for spinal surgeries: beginning steps. Clin Neurophysiol . 2012; 123( 9): 1705- 1707. Google Scholar CrossRef Search ADS PubMed 6. Ney JP, van der Goes DN, Watanabe JH. Cost-benefit analysis: intraoperative neurophysiological monitoring in spinal surgeries. J Clin Neurophysiol . 2013; 30( 3): 280- 286. Google Scholar CrossRef Search ADS PubMed 7. James WS, Rughani AI, Dumont TM. A socioeconomic analysis of intraoperative neurophysiological monitoring during spine surgery: national use, regional variation, and patient outcomes. Neurosurg Focus . 2014; 37( 5): E10. Google Scholar CrossRef Search ADS PubMed Copyright © 2018 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)
Neurosurgery – Oxford University Press
Published: May 22, 2018
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