Intraoperative Monitoring of the External Urethral Sphincter Reflex: A Novel Adjunct to Bulbocavernosus Reflex Neuromonitoring for Protecting the Sacral Neural Pathways Responsible for Urination, Defecation and Sexual Function.

PURPOSE: Intraoperative bulbocavernosus reflex neuromonitoring has been utilized to protect bowel, bladder, and sexual function, providing a continuous functional assessment of the somatic sacral nervous system during surgeries where it is at risk. Bulbocavernosus reflex data may also provide additional functional insight, including an evaluation for spinal shock, distinguishing upper versus lower motor neuron injury (conus vs. cauda syndromes) and prognosis for postoperative bowel and bladder function. Continuous intraoperative bulbocavernosus reflex monitoring has been utilized to provide the surgeon with an ongoing functional assessment of the anatomical elements involved in the S2-S4 mediated reflex arc including the conus, cauda equina and pudendal nerves. Intraoperative bulbocavernosus reflex monitoring typically includes the electrical activation of the dorsal nerves of the genitals to initiate the afferent component of the reflex, followed by recording the resulting muscle response using needle electromyography recordings from the external anal sphincter. METHODS: Herein we describe a complementary and novel technique that includes recording electromyography responses from the external urethral sphincter to monitor the external urethral sphincter reflex. Specialized foley catheters embedded with recording electrodes have recently become commercially available that provide the ability to perform intraoperative external urethral sphincter muscle recordings. RESULTS: We describe technical details and the potential utility of incorporating external urethral sphincter reflex recordings into existing sacral neuromonitoring paradigms to provide redundant yet complementary data streams. CONCLUSIONS: We present two illustrative neurosurgical oncology cases to demonstrate the utility of the external urethral sphincter reflex technique in the setting of the necessary surgical sacrifice of sacral nerve roots.

Analyzing the value of IONM as a complex intervention: The gap between published evidence and clinical practice.

OBJECTIVE: Intraoperative neurophysiological monitoring (IONM) was investigated as a complex intervention (CI) as defined by the United Kingdom Medical Research Council (MRC) in published studies to identify challenges and solutions in estimating IONM's effects on postoperative outcomes. METHODS: A scoping review to April 2022 of the influence of setting on what was implemented as IONM and how it influenced postoperative outcomes was performed for studies that compared IONM to no IONM cohorts. IONM complexity was assessed with the iCAT_SR tool. Causal graphs were used to represent this complexity. RESULTS: IONM implementation depended on the surgical procedure, institution and/or surgeon. "How" IONM influenced neurologic outcomes was attributed to surgeon or institutional experience with the surgical procedure, surgeon or institutional experience with IONM, co-interventions in addition to IONM, models of IONM service delivery and individual characteristics of the IONM provider. Indirect effects of IONM mediated by extent of tumor resection, surgical approach, changes in operative procedure, shorter operative time, and duration of aneurysm clipping were also described. There were no quantitative estimates of the relative contribution of these indirect effects to total IONM effects on outcomes. CONCLUSIONS: IONM is a complex intervention whose evaluation is more challenging than that of a simple intervention. Its implementation and largely indirect effects depend on specific settings that are usefully represented in causal graphs. SIGNIFICANCE: IONM evaluation as a complex intervention aided by causal graphs and multivariable analysis could provide a valuable framework for future study design and assessments of IONM effectiveness in different settings.

Foundations for evidence-based intraoperative neurophysiological monitoring.

In this review, we recommend means to enhance the evidence-base for intraoperative neurophysiological monitoring (IONM). We address two preliminary issues: (1) whether IONM should be evaluated as a diagnostic test or an intervention, and (2) the state of the evidence for IONM (as presented in systematic reviews, for example). Three reasons may be suggested to evaluate at least some IONM applications as interventions (or as part of an "interventional cascade"). First, practical barriers limit our ability to measure IONM diagnostic accuracy. Second, IONM results are designed to be correlated with interventions during surgery. Third, IONM should improve patient outcomes when IONM-directed intervention alters the course of surgery. Observational evidence for IONM is growing yet more is required to understand the conditions under which IONM, in its variety of settings, can benefit patients. A multi-center observational cohort study would represent an important initial compromise between the pragmatic difficulties with conducting controlled trials in IONM and the Evidence-Based Medicine (EBM) view that large scale randomized trials are required. Such a cohort study would improve the evidence base and (if justified) provide the rationale for controlled trials.

Pelvic autonomic neuromonitoring: present reality, future prospects.

Currently, the means to assess the autonomic nervous system primarily depend on end organ functional measurement: intravesical pressure, skin resistance, and penile strain gauge tension, for example. None of these measures has been generally accepted in the operating room. Nevertheless, the segmental and peripheral pelvic autonomic nerve supply is placed at risk during both pelvic and lower spine surgery. In this difficult era of suboptimal post-prostatectomy outcomes, the urological literature does reveal the salutary development of safer dissection techniques about the peri-prostatic and cavernous plexus. Means of reliably specific nerve identification remain elusive. The need for actual nerve monitoring (not just identification) has only recently been proposed. Data from the animal lab reinforce an appreciation of the intimate and elegant interconnectedness of autonomic and somatic structures, particularly at the segmental level. Also, the biochemistry of erectile tissue engorgement (in both sexes) is very well understood (the electrophysiology increasingly so). Understanding these principles should permit parallel investigation and implementation of neurophysiological techniques which both identify and monitor pelvic autonomic function. The predicates for these proposed new approaches in the operating room are discussed in this review.

Intraoperative neuromonitoring alerts that reverse with intervention: treatment paradox and what to do about it.

Intervention-mediated recovery from adversely changed evoked potential recordings may provide evidence for improved outcomes during neurophysiological intraoperative monitoring. However, these reversible signal changes (RSCs) are ambiguous because the patient's neurologic status cannot be known either at signal decline or after intervention. This article describes methods to reduce this ambiguity. Randomized control trials are not always possible or ethical. Recent thought on grading evidence has acknowledged that guidelines first described by Sir Austin Bradford Hill may support evidence for causation. Causality guidelines identified RSCs most likely to be truly positive in three reported studies. Diagnostic statistics were revised accordingly. A range of revised positive predictive values and likelihood ratios was calculated in the three studies, using causality guidelines. The revised data were similar to those reported for other diagnostic tests used in medicine. The RSCs may be assessed using causality guidelines for more accurate reporting of diagnostic statistics while preserving information related to surgical intervention and recovery that is lost with end of surgery diagnostics or when RSCs are ignored. A method is described for including RSCs in diagnostic statistics. This approach will more readily permit assessment of the value of neurophysiological intraoperative monitoring in prediction and prevention of neurologic deficits.

Surface electrodes are not sufficient to detect neurotonic discharges: observations in a porcine model and clinical review of deltoid electromyographic monitoring using multiple electrodes.

OBJECTIVE: In order to define the preferred electromyographic monitoring method during spine surgery, (1) a porcine model of neurotonic generation after lumbar root compression was developed and (2) intraoperative use of deltoid muscle intramuscular needle, subdermal needle, and surface electrodes was retrospectively reviewed. METHODS: In pigs, an array of intramuscular needle, subdermal needle, and surface electrode derivations was differentially amplified at identical gain and filter settings. Nerve root compression generated neurotonic discharges whose amplitudes were compared at each derivation. Clinically, 25 deltoid muscles in 13 patients were simultaneously monitored (during cervical spine surgery at the C4-C5 level) with surface, subdermal needle, and intramuscular needle electrode pairs, differentially amplified at identical gain and filter settings. Non-repeating neurotonic discharges were assigned, by amplitude and morphology, to best derivation (intramuscular, subdermal, surface or combination); coincident amplitudes were measured at the maximum deflection among the three derivations. Actual voltage detected between clinical methods was analyzed with Friedman's test and any detection versus none by general estimating equations(GEE) using SAS. The advantage of two needles over one in detection of any voltage was assessed using McNemar's test. RESULTS: Compressed porcine lumbar roots generated neurotonics which were identifiable at intramuscular sites only. Clinically, 31 neurotonics were identified: 20/31 at intramuscular, 5/31 at subdermal, and 6/31 equally well at intramuscular and subdermal derivations. Intramuscular detected neurotonics better than subdermal derivations (z = 2.9, P < .004). No voltage was recorded at the surface in 16/31 neurotonics. For detection of any voltage, intramuscular was better than subdermal (z = -1.5, P = .04) or surface electrodes (z = -2.7, P < .001). CONCLUSIONS: Electromyographic moni- toring of spine surgery should not be done by surface electrodes. Because sensitive neurotonic detection requires near field recording, intramuscular electrodes are preferred. Monitoring of a myotome at particularly increased risk may suggest multiple intramuscular electrodes.

The initial use of free-running electromyography to detect early motor tract injury during resection of intramedullary spinal cord lesions.

OBJECTIVE: The resection of intramedullary spinal cord lesions (ISCLs) can be complicated by neurological deficits. Neuromonitoring has been used to reduce intraoperative risk. We have used somatosensory evoked potentials (SEPs) and muscle-derived transcranial electrical motor evoked potentials (myogenic TCE-MEPs) to monitor ISCL removal. We report our retrospective experience with the addition of free-running electromyography (EMG). METHODS: Thirteen patients underwent 14 monitored ISCL excisions. Anesthesia was maintained with minimal inhalant to reduce motoneuron suppression and enhance the myogenic TCE-MEPs. Free-running EMG was examined in the four limbs for evidence of abnormal bursts, prolonged tonic discharge, or sudden electrical silence. Warning of an electromyographic abnormality or myogenic TCE-MEP loss prompted interventions, including blood pressure elevation, a pause in surgery, a wake-up test, or termination of surgery. Pre- and postoperative neurological examinations determined the incidence of new deficits. RESULTS: The combined use of free-running EMG and myogenic TCE-MEPs detected all eight patients with a new motor deficit after surgery; there was one false-positive report. In three of the eight true-positive cases, an electromyographic abnormality immediately anticipated loss of the myogenic TCE-MEPs. Two patients with abnormal EMGs but unchanged myogenic TCE-MEPs experienced mild postoperative worsening of motor deficits; myogenic TCE-MEPs alone would have generated false-negative reports in these cases. CONCLUSION: During resection of ISCLs, free-running EMG can supplement motor tract monitoring by TCE-MEPs. Segmental and suprasegmental elicitation of neurotonic discharges can be observed in four-limb EMG. Abnormal electromyographic bursts, tonic discharge, or abrupt electromyographic silence may anticipate myogenic TCE-MEP loss and predict a postoperative motor deficit.