Perils of intraoperative neurophysiological monitoring: analysis of "false-negative" results in spine surgeries.

BACKGROUND CONTEXT: Although some authors have published case reports describing false negatives in intraoperative neurophysiological monitoring (IONM), a systematic review of causes of false-negative IONM results is lacking. PURPOSE: The objective of this study was to analyze false-negative IONM findings in spine surgery. STUDY DESIGN: This is a retrospective cohort analysis. PATIENT SAMPLE: A cohort of 109 patients with new postoperative neurologic deficits was analyzed for possible false-negative IONM reporting. OUTCOME MEASURES: The causes of false-negative IONM reporting were determined. MATERIALS AND METHODS: From a cohort of 62,038 monitored spine surgeries, 109 consecutive patients with new postoperative neurologic deficits were reviewed for IONM alarms. RESULTS: Intraoperative neurophysiological monitoring alarms occurred in 87 of 109 surgeries. Nineteen patients with new postoperative neurologic deficits did not have an IONM alarm and surgeons were not warned. In addition, three patients had no interpretable IONM baseline data and no alarms were possible for the duration of the surgery. Therefore, 22 patients were included in the study. The absence of IONM alarms during these 22 surgeries had different origins: "true" false negatives where no waveform changes meeting the alarm criteria occurred despite the appropriate IONM (7); a postoperative development of a deficit (6); failure to monitor the pathway, which became injured (5); the absence of interpretable IONM baseline data which precluded any alarm (3); and technical IONM application issues (1). CONCLUSIONS: Overall, the rate of IONM method failing to predict the patient's outcome was very low (0.04%, 22/62,038). Minimizing false negatives requires the application of a proper IONM technique with the limitations of each modality considered in their selection and interpretation. Multimodality IONM provides the most inclusive information, and although it might be impractical to monitor every neural structure that can be at risk, a thorough preoperative consideration of available IONM modalities is important. Delayed development of postoperative deficits cannot be predicted by IONM. Absent baseline IONM data should be treated as an alarm when inconsistent with the patient's preoperative neurologic status. Alarm criteria for IONM may need to be refined for specific procedures and deserves continued study.

Neurophysiological Monitoring During Spinal Cord Stimulator Placement Surgery.

OBJECTIVES: The objective of this retrospective study was to study the frequency of intraoperative neuromonitoring (IONM) alerts during the spinal cord stimulator (SCS) placement surgery, postoperative neurological complications and effectiveness of Somatosensory evoked potential (SSEP) and electromyography (EMG) methods to determine laterality of the SCS lead placement. MATERIALS AND METHODS: Records of 111 consecutive SCS placement surgeries monitored by a commercial IONM company between August 1, 2013 and December 31, 2013 were reviewed. IONM alerts, surgical interventions, and patient outcomes were assessed. RESULTS: Significant decreases of lower extremity SSEPs following the placement of the SCS paddle electrodes into the epidural space were recorded in two (1.9%) patients prompting alerts to the surgeons and removal of the electrode. Somatosensory system dysfunction due to stimulated limb malpositioning was identified by continuous SSEP in four cases (3.8%). All waveform changes resolved and SSEP waveforms returned back to baselines in all six patients after adjustments were made. There was no evidence of sustained neurological injury in any patients in this study. The location of the stimulator was adjusted based on IONM feedback in 8/43 (18.6%) cases. CONCLUSIONS: IONM is an effective tool in detecting potential neurological event and facilitating lead placement and potentially avoiding revision surgery.

Differential rates of false-positive findings in transcranial electric motor evoked potential monitoring when using inhalational anesthesia versus total intravenous anesthesia during spine surgeries.

BACKGROUND CONTEXT: False-positive loss of transcranial electrical motor evoked potentials (TCe-MEPs) limits the efficacy of motor tract monitoring during spine surgery. Although total intravenous anesthesia (TIVA) is widely regarded as the optimal regimen for TCe-MEPs, inhalational anesthesia is an alternative regimen. PURPOSE: To compare the rates of false-positive TCe-MEPs during spine surgery for patients anesthetized with TIVA and inhalation anesthesia. STUDY DESIGN: A retrospective analysis of data collected from consecutive patients undergoing TCe-MEP monitoring during spinal surgery. PATIENT SAMPLE: Consecutive adult patients from multiple surgical centers undergoing spine surgery inclusive of cervical or thoracic spinal levels during 2008-2009 who received TIVA or inhalation anesthesia. OUTCOME MEASURES: The primary outcome measure was the rate of false-positive alerts using TCe-MEPS, defined as a persistent loss of 90% or greater of the amplitude of TCe-MEP in one or more muscles not attributed to technical or transient systemic factors (hypotension or hypoxia) and not associated with any postoperative neurologic deficit. METHODS: Patients were divided into two groups according to anesthetic regimen: those anesthetized with one or more inhalational agents (n=1,303) and patients anesthetized with TIVA (n=511). The Fisher exact test and unpaired t test were used to compare group characteristics and false-positive rates. Each group was further subdivided by spinal region (cervical, thoracic, and thoracolumbar) and by presence of preoperative motor deficit. A Pearson chi-squared test was used to identify differences according to spinal region. This study was not supported by any financial sources nor do the authors have any financial relationships to disclose. RESULTS: Patient with inhaled anesthesia showed significantly higher rates of false-positive TCe-MEP changes (15.0% vs. 3.2%) compared with the TIVA group. These differences were significant across all surgical subgroups. The inhaled group had a larger number of patients with preoperative motor deficits compared with TIVA (45.0% vs. 37.4%), a potential confounder for false-positive results. However, a significantly higher rate of false-positive TCe-MEP changes was still observed in the inhaled group (11.4% vs. 0.6% for TIVA) when analyzing only those patients without preoperative motor deficits. CONCLUSIONS: Use of inhalation anesthesia during adult spinal surgery is associated with significantly higher rates of false-positive changes compared with TIVA during TCe-MEP monitoring. This relationship appears independent of preoperative motor status. Further study and multivariate analysis of anesthetic agents, diagnosis, and symptoms is necessary to elucidate the impact of these variables. The potential confounding effects of inhalational anesthesia on TCe-MEP monitoring should be considered when determining anesthetic regimen.

Quality assurance and performance improvement in intraoperative neurophysiologic monitoring programs.

Quality assurance (QA) as it relates to intraoperative neurophysiological monitoring (IONM) can be defined as the systematic monitoring, evaluation, and modification of the IONM service to insure that desired standards of quality are being met. In practice, that definition is usually extended to include the concept that the quality of the IONM service will be improved wherever possible and, although there are some differences in the two terms, in this article the term QA will be understood to include quality improvement (QI) processes as well. The measurement and documentation of quality is becoming increasingly important to healthcare providers. This trend is being driven by pressures from accrediting agencies, payers, and patients. The essential elements of a QA program are described. A real-life example of QA techniques and management relevant to IONM providers is presented and discussed.

Neurophysiological monitoring with brainstem evoked potentials can be a valuable tool for patients undergoing vertebrobasilar stenting and angioplasty-initial experience.

INTRODUCTION: Brainstem auditory evoked potentials (BAEPs) are routinely used during a variety of intracranial surgeries involving the posterior fossa and endovascular procedures including coiling of cerebral aneurysms. However, use of BAEPs has not been reported in vertebrobasilar stenting. METHODS: Six patients underwent stenting and angioplasty of the basilar artery (four) or the dominant vertebral artery (two) for symptomatic stenosis. All the patients received stenting and angioplasty with Wingspan stent and Gateway balloon, respectively. Continuous real time BAEPs were recorded in all patients, and somatosensory evoked potentials in five patients. RESULTS: All the patients had successful stenting and angioplasty in their target vessels. All the procedures were done under general anesthesia. In five patients, there were no significant changes in the BAEP responses during the predilation, stenting, and postdilation. There were no postprocedural neurological deficits in these patients. In one patient, there was a 1-ms increase of latency of wave V at the time of predilation angioplasty. No changes in the amplitude of wave V were noted. This patient had immediate postprocedure left hemiplegia, which improved to power of 3/5 in both upper and lower limbs at the time of discharge and to 4/5 at 3-month follow-up. Computed tomography scan did not show any evidence of hemorrhage. CONCLUSIONS: Brainstem auditory evoked potentials may be a valuable monitoring tool in patients undergoing stenting and angioplasty of vertebrobasilar system. Early signs of brainstem dysfunction can be identified to modify the procedure and reduce neurological deficits. Large studies are needed to validate the use of BAEP during this procedure.