Determining the safety of the tobacco cembranoid (1S,2E,4R,6R,7E,11E)-Cembratriene-4,6-diol (4R): A translational study in nonhuman primates.

The tobacco cembranoid known as (1S,2E,4R,6R,7E,11E)-2,7,11-cembratriene-4,6-diol (4R) has been shown to offer neuroprotection against conditions such as brain ischemia, systemic inflammation, Parkinson's disease, and organophosphate toxicity in rodents. Previous safety studies conducted on male and female Sprague Dawley rats revealed no significant side effects following a single injection of 4R at varying concentrations (6, 24, or 98 mg/kg of body weight). This study aimed to assess the potential of 4R for clinical trials in neurotherapy in male nonhuman primates. Ten macaques (Macacca mulatta) were randomly separated into two groups of 5 and then intravenously injected with 4R or vehicle for 11 consecutive days at a dose of 1.4 mg/kg. Throughout the study, we monitored brain activity by electroencephalogram, somatosensory evoked potentials, and transcranial motor evoked potentials on days 0, 4, 8, and 12 and found no significant changes. The spontaneous behavior of the primates remained unaffected by the treatment. Minor hematological and blood composition variations were also detected in the experimental animals but lacked clinical significance. In conclusion, our results reinforce the notion that 4R is non-toxic in nonhuman primates under the conditions of this study.

Utility of transcranial motor-evoked potential changes in predicting postoperative deficit in lumbar decompression and fusion surgery: a systematic review and meta-analysis.

PURPOSE: The primary aim of this study was to evaluate whether TcMEP alarms can predict the occurrence of postoperative neurological deficit in patients undergoing lumbar spine surgery. The secondary aim was to determine whether the various types of TcMEP alarms including transient and persistent changes portend varying degrees of injury risk. METHODS: This was a systematic review and meta-analysis of the literature from PubMed, Web of Science, and Embase regarding outcomes of transcranial motor-evoked potential (TcMEP) monitoring during lumbar decompression and fusion surgery. The sensitivity, specificity, and diagnostic odds ratio (DOR) of TcMEP alarms for predicting postoperative deficit were calculated and presented with forest plots and a summary receiver operating characteristic curve. RESULTS: Eight studies were included, consisting of 4923 patients. The incidence of postoperative neurological deficit was 0.73% (36/4923). The incidence of deficits in patients with significant TcMEP changes was 11.79% (27/229), while the incidence in those without changes was 0.19% (9/4694). All TcMEP alarms had a pooled sensitivity and specificity of 63 and 95% with a DOR of 34.92 (95% CI 7.95-153.42). Transient and persistent changes had sensitivities of 29% and 47%, specificities of 96% and 98%, and DORs of 8.04 and 66.06, respectively. CONCLUSION: TcMEP monitoring has high specificity but low sensitivity for predicting postoperative neurological deficit in lumbar decompression and fusion surgery. Patients who awoke with new postoperative deficits were 35 times more likely to have experienced TcMEP changes intraoperatively, with persistent changes indicating higher risk of deficit than transient changes. LEVEL OF EVIDENCE II: Diagnostic Systematic Review.

Intraoperative transabdominal MEPs: four case reports.

Four recent cases utilizing transabdominal motor-evoked potentials (TaMEPs) are presented as illustrative of the monitoring technique during lumbosacral fusion, sciatic nerve tumor resection, cauda equina tumor resection, and lumbar decompression. Case 1: In a high-grade lumbosacral spondylolisthesis revision fusion, both transcranial motor-evoked potentials (TcMEPs) and TaMEPs detected a transient focal loss of left tibialis anterior response in conjunction with L5 nerve root decompression. Case 2: In a sciatic nerve tumor resection, TcMEPs responses were lost but TaMEPs remained unchanged, the patient was neurologically intact postoperatively. Case 3: TaMEPs were acquired during an L1-L3 intradural extramedullary cauda equina tumor resection utilizing a unique TaMEP stimulation electrode. Case 4: TaMEPs were successfully acquired with little anesthetic fade utilizing an anesthetic regimen of 1.1 MAC Sevoflurane during a lumbar decompression. While the first two cases present TaMEPs and TcMEPs side-by-side, demonstrating TaMEPs correlating to TcMEPs (Case 1) or a more accurate reflection of patient outcome (Case 2), no inference regarding the accuracy of TaMEPs to monitor nerve elements during cauda equina surgery (Cases 3) or the lumbar decompression presented in Case 4 should be made as these are demonstrations of technique, not utility.

Safe use of subdermal needles for intraoperative monitoring with MRI.

OBJECTIVE: The purpose of this study was to develop safe, site-specific procedures for placing and leaving subdermal needle leads for intraoperative monitoring (IOM) during intraoperative MRI procedures. METHODS: The authors tested a variety of standard subdermal needle electrodes designed and FDA-approved for IOM in the conventional operating room. Testing was used to determine the conditions necessary to avoid thermal injury and significant image artifacts with minimal disruption of IOM and MRI procedures. Phantom testing was performed with a fiber optic (lead) temperature monitoring system and was followed by testing of leads placed in a healthy volunteer. The volunteer testing used electrode placements typical of standard IOM cases, together with radiofrequency (RF) coil placement and imaging sequences routinely employed for these case types. Lead length was investigated to assess heating effects for electrodes placed within the RF coil. RESULTS: The authors found that conventional stainless steel (SS) and platinum/iridium (Pt/Ir) subdermal needles can be used safely without significant heating when placed outside the RF coil, and this accounts for the majority or entirety of electrode placements. When placed within the RF coil, Pt/Ir leads produced minimal image artifacts, while SS leads produced potentially significant artifacts. In phantom testing, significant heating was demonstrated in both SS and Pt/Ir leads placed within the RF coil, but only during high-resolution T2-weighted scanning. This problem was largely, but not completely, eliminated when leads were shortened to 25 cm. Human testing was unremarkable except for nonpainful heating detected in a few electrodes during thin-slice (1.5 mm) FLAIR scanning. Transient irritation (skin reddening along the needle tract) was noted at 2 of the electrodes with detectable heating. CONCLUSIONS: The authors were satisfied with the safety of their site-specific procedures and have begun with off-label use (following institutional review board approval and obtaining patient informed consent) of tested monitoring leads in cases that combine IOM and MRI. The authors recommend that all facilities perform their own site-specific testing of monitoring leads before proceeding with their routine use.

The value of multimodality intraoperative neurophysiological monitoring in treating pediatric Chiari malformation type I.

INTRODUCTION: Chiari malformation type I is defined as a descent of cerebellar tonsils below the level of the foramen magnum. The traditional treatment for symptomatic patients is foramen magnum decompression (FMD) surgery. Intraoperative neurophysiological monitoring (INM) is an established surgical adjunct, which is proposed to reduce the potential risk of various surgical procedures. Though INM has been suggested as being helpful in patient positioning and in determining the optimal surgical extent of FMD (i.e., duroplasty, laminectomy, tonsillectomy), its shortcomings include prolongation of anesthesia and surgery as well as monetary costs. Multimodality INM including transcranial-electric motor evoked potential (TcMEP) is not routinely employed in most practices. This study evaluates efficacy of multimodality INM during FMD. METHODS: This work is a retrospective analysis of prospectively collected data. Twenty-two FMD surgeries in 21 pediatric patients (aged 1-18 years) were performed at our center utilizing multimodality INM. All patients presented Chiari malformation type I, 18 of which had presented with syringomyelia, underwent posterior fossa decompression (FMD + C1 laminectomy), accompanied in some with additional cervical laminectomies, duroplasty, and partial tonsillectomies. TcMEP and somatosensory evoked potentials (SSEP) were monitored throughout the procedure including before and after positioning. INM alarms were correlated with perioperative and long-term patient outcomes. RESULTS: INM data remained stable during 19 operations. Three cases displayed significant attenuation in the monitoring signals, all concomitant with patient positioning on the surgical table. One case showed attenuation in SSEP data only, which remained attenuated following repositioning. Another displayed altered TcMEP concomitant with positioning which partially stabilized following repositioning and resolved following bony decompression. The third case showed unilateral attenuation of both TcMEP and SSEP data, which did not rectify until closure. In each of these three cases, no new neurological deficits were observed post operatively. CONCLUSIONS: Multimodality INM can be useful in FMD surgery, particularly during patient positioning. TcMEP attenuations may occur independent of SSEPs. The clinical implications of these monitoring alerts have yet to be defined. There is a need to establish an optimal, cost-effective monitoring protocol for FMD.

A novel mouthpiece prevents bite injuries caused by intraoperative transcranial electric motor-evoked potential monitoring.

PURPOSE: Intraoperative transcranial motor-evoked potential monitoring causes contraction of the masseter muscles, which may cause injuries to the oral cavity and damage to the orotracheal tube. We developed a mouthpiece made from vinyl-silicone impression material to prevent these injuries. The purpose of this study was to examine its efficacy and safety. METHODS: Twenty-two patients undergoing spinal surgery under transcranial motor-evoked potential monitoring were fitted with bespoke vinyl-silicone mouthpieces by dentists before surgery. On induction of general anesthesia and orotracheal intubation, the mouthpiece was attached to the upper and lower dental arches. A lateral cervical X-ray was taken at the end of surgery to examine the condition of the orotracheal tube. The incidence of endotracheal tube deformation was compared with an historic control group of 20 patients in whom a conventional gauze bite block had been previously used before induction of the mouthpiece. The oral cavity was examined by a dentist the day before surgery and 3 days postoperatively, and intraoral injuries were recorded. RESULTS: No endotracheal tube deformation was found in 22 patients fitted with the new mouthpiece. The incidence of tube deformation (none of 22 patients, 0 %) was significantly lower than in those who had been fitted with the gauze bite block (9 of 20 patients, 45.0 %; p < 0.001). Application of the mouthpiece resulted in no tongue or tooth injuries. CONCLUSION: A novel mouthpiece reduced the incidence of damage to the endotracheal tube caused by intraoperative transcranial motor-evoked potential monitoring.

Chronologic Changes in Transcranial Motor Evoked Potential During Anterior Temporal Lobectomy in Patients with Temporal Lobe Epilepsy: A Single-Center Cross-Sectional Analytic Study.

OBJECTIVE: Despite the benefits of anterior temporal lobectomy with amygdalohippocampectomy in patients with temporal lobe epilepsy (TLE), approximately up to 5% may have hemiparesis as its postoperative complication. This paper aims to describe which step/s of the anterior temporal lobectomy with amygdalohippocampectomy have the highest probability of having the greatest decrease in motor evoked potential (MEP) amplitude. METHODS: This study used a cross-sectional design of obtaining data from TLE patients who underwent anterior temporal lobectomy with amygdalohippocampectomy with transcranial MEP monitoring. Each of the following steps were evaluated for reduction in MEP amplitude: 1) dural opening, 2) opening the inferior horn, 2) vertical temporal lobe resection 3) subpial dissection, 4) temporal lobe stem resection, 5) lateral temporal lobe resection, 6) hippocampal resection, 7) amygdala resection, 8) uncus resection, and 9) dural closure. RESULTS: Nineteen patients were included in the study. Based on the Friedman Test, 1 or more steps had significantly different average MEP amplitude reductions (Friedman = 50.7, P = 0.0001). When compared with baseline (100%, cutoff P = 0.005), hippocampal resection (z = -3.81, P < 0.0001), T1 subpial dissection (z = -3.2, P = 0.0010), uncus resection (z = -3.48, P = 0.0002), temporal stem resection (z = -3.26, P = 0.001), lateral temporal lobe resection (z = -3.13, P = 0.002), and amygdalectomy (-z = -3.37, P = 0.0005) were significantly lower. Of these, hippocampal resection, uncus resection, and amygdalectomy were deemed highly significant. CONCLUSIONS: MEP amplitude tends to decrease during amygdala, hippocampal, and uncal resection because of surgical manipulation of anterior choroidal arteries, which can potentially cause hemiparesis. Careful attention should be paid to changes in MEP during these steps.

Failure to Obtain Baseline Signals of Transcranial Motor-Evoked Potentials in Spine Surgery: Analysis of the Reasons.

OBJECTIVE: Among the various intraoperative neurophysiologic monitoring (IONM) techniques, transcranial motor-evoked potential (Tc-MEP) has recently become the most widely used method to monitor motor function. However, we often find that Tc-MEP is not sufficiently detected at the start of surgery. Therefore, we aimed to analyze the reasons and risk factors for not detecting sufficient baseline signal of Tc-MEP from the beginning of spinal surgery. METHODS: We categorized IONM data from 1058 patients who underwent spine surgeries at a single institution from 2014 to 2020 and categorized them into 2 groups: 1) "poor MEP" if Tc-MEP could not be sufficiently obtained and 2) "normal MEP" if Tc-MEP could be sufficiently obtained from the surgery. We analyzed the patient's age, gender, underlying disease, operation type, level numbers, baseline motor function, existence of pathologic reflex, myelopathy, and duration from the onset and clinical diagnosis. RESULTS: The rate of failure to obtain sufficient baseline Tc-MEP signals in spine surgery was 21.8% (231/1058). Multivariate analysis showed significant associations of existence of diabetes mellitus, myelopathy, thoracic spine surgery, baseline motor deficit and tumor, and trauma disease with loss of meaningful and interpretable signals in baseline Tc-MEP (P < 0.05). Only 15 of 231 patients (6.4%) showed a trend of signal recovery after decompression procedures. CONCLUSIONS: Various factors (myelopathy, diabetes mellitus, thoracic surgery, baseline motor deficit, tumor, and trauma) were closely related to not obtaining sufficient baseline signals for Tc-MEP. When operating on patients with these considerations, we need to consider the efficacy and usefulness of Tc- MEP.

Cathodal Genesis of Ipsilateral Hand (Crossover) Motor Evoked Potentials: Evidence from a Patient with Previous Stroke.

A case is described where baseline transcranial electrical motor evoked potentials (TcMEP) and somatosensory evoked potentials (SSEP) results were unilaterally absent in a patient with previous hemispheric stroke undergoing a right-sided carotid endarterectomy. SSEP data confirmed right cortical pathology and excluded a technical rationale for absent motor evoked responses. Attempts at generating left-hand (contralateral) TcMEP from right cortical anodal stimulation failed despite high stimulus intensities. However, TcMEP responses from anodal stimulation of the right cortex were recorded from the right-hand (ipsilateral) which were attributed to "crossover." Ipsilateral TcMEP onset latencies derived from the stimulus-response data supports the idea that crossover is a product of cathodal stimulation initially acting on pericortical motor pathways.

The Use of Intraoperative Neuromonitoring for Cervical Spine Surgery: Indications, Challenges, and Advances.

Intraoperative neuromonitoring (IONM) has become an indispensable surgical adjunct in cervical spine procedures to minimize surgical complications. Understanding the historical development of IONM, indications for use, associated pitfalls, and recent developments will allow the surgeon to better utilize this important technology. While IONM has shown great promise in procedures for cervical deformity, intradural tumors, or myelopathy, routine use in all cervical spine cases with moderate pathology remains controversial. Pitfalls that need to be addressed include human error, a lack of efficient communication, variable alarm warning criteria, and a non-standardized checklist protocol. As the techniques associated with IONM technology become more robust moving forward, IONM emerges as a crucial solution to updating patient safety protocols.

Direct Wave Intraoperative Neuromonitoring for Spinal Tumor Resection: A Focused Review.

At present, surgical resection of primary intramedullary spinal cord tumors is the mainstay of treatment. However, given the dimensional constraints of the narrow spinal canal and dense organization of the ascending and descending tracts, intramedullary spinal cord tumor resection carries a significant risk of iatrogenic neurological injury. Intraoperative neurophysiological monitoring (IONM) and mapping techniques have been developed to evaluate the functional integrity of the essential neural pathways and optimize the surgical strategies. IONM can also inform on impending harm to at-risk structures and can correlate with postoperative functional recovery if damage has occurred. Direct waves (D-waves) will provide immediate feedback on the integrity of the lateral corticospinal tract. In the present review, we have provided an update on the utility of D-waves for spinal cord tumor resection. We have highlighted the neuroanatomical and neurophysiological insights from the use of D-wave monitoring, the technical considerations and limitations of the D-wave technique, and multimodal co-monitoring with motor-evoked potentials and somatosensory-evoked potentials. Together with motor-evoked potentials, D-waves can help to guide the extent of tumor resection and provide intraoperative warning signs and alarm criteria to direct the surgical strategy. D-waves can also serve as prognostic biomarkers for long-term recovery of postoperative motor function. We propose that the use of D-wave IONM can contribute key findings for clinical decision-making during spinal cord tumor resection.

Utility of evoked potentials during anterior cerebral artery and anterior communicating artery aneurysm clipping.

Objective: To investigate the optimal combination of somatosensory- and transcranial motor-evoked potential (SSEP/tcMEP) modalities and monitored extremities during clip reconstruction of aneurysms of the anterior cerebral artery (ACA) and its branches. Methods: A retrospective review of 104 cases of surgical clipping of ruptured and unruptured aneurysms was performed. SSEP/tcMEP changes and postoperative motor deficits (PMDs) were assessed from upper and lower extremities (UE/LE) to determine the diagnostic accuracy of each modality separately and in combination. Results: PMDs were reported in 9 of 104 patients; 7 LE and 8 UE (3.6% of 415 extremities). Evoked potential (EP) monitoring failed to predict a PMD in 8 extremities (1.9%). Seven of 8 false negatives had subarachnoid hemorrhage. Sensitivity and specificity in LE were 50% and 97% for tcMEP, 71% and 98% for SSEP, and 83% and 98% for dual-monitoring of both tcMEP/SSEP. Sensitivity and specificity in UE were 38% and 99% for tcMEP, and 50% and 97% for tcMEP/SSEP, respectively. Conclusions: Combined tcMEP/SSEP is more accurate than single-modality monitoring for LE but is relatively insensitive for UE PMDs. Significance: During ACA aneurysm clipping, multiple factors may confound the ability of EP monitoring to predict PMDs, especially brachiofacial hemiparesis caused by perforator insufficiency.

Poor derivation of Tc-MEP baseline waveforms in surgery for ventral thoracic intradural extramedullary tumor: Efficacy of use of the abductor hallucis in cases with a preoperative non-ambulatory status.

Most thoracic intradural extramedullary tumors (IDEMT) are benign lesions that are treated by gross total resection and spinal cord decompression. Intraoperative transcranial-motor evoked potential (Tc-MEP) monitoring is important for reducing postoperative neurological complications. The purpose of this study is to examine the characteristics of Tc-MEP waveforms in surgery for thoracic IDEMT resection based on location of the tumor relative to the spinal cord. The subjects were 56 patients who underwent surgery for thoracic IDEMT from 2010 to 2018. The waveform derivation rate for each lower muscle was examined at baseline and intraoperatively. 56 patients had a mean age of 61.7 years, and 21 (38%) were non-ambulatory before surgery. The tumors were schwannoma (n = 28, 50%), meningioma (n = 25, 45%), and neurofibroma (n = 3, 5%); and the lesions were dorsal (n = 29, 53%) and ventral (n = 27, 47%). There was a significantly higher rate of undetectable waveforms in all lower limb muscles in the ventral group compared to the dorsal group (15% vs. 3%, p < 0.05). In non-ambulatory cases, the derivation rate at baseline was significantly lower for ventral thoracic IDMETs (47% vs. 68%, p < 0.05). The abductor hallucis (AH) had the highest waveform derivation rate of all lower limb muscles in non-ambulatory cases with a ventral thoracic IDMET. Spinal cord compression by a ventral lesion may be increased, and this may be reflected in greater waveform deterioration. Of all lower limb muscles, the AH had the highest derivation rate, even in non-ambulatory cases with a ventral IDEMT, which suggests the efficacy of multichannel monitoring including the AH.

Neurophysiological monitoring during anterior cervical discectomy and fusion for ossification of the posterior longitudinal ligament.

OBJECTIVE: This study aimed to investigate the value of intraoperative neurophysiological monitoring (IONM) in anterior cervical spine discectomy with fusion (ACDF) for ossification of the posterior longitudinal ligament (OPLL). METHODS: Patients who underwent multimodal IONM (transcranial electrical motor-evoked potentials [tcMEP], somatosensory-evoked potentials, and continuous electromyography) for ACDF from 2009 to 2019 were compared to historical controls from 2003 to 2009. The rates of postoperative neurological deficits, neurophysiological warnings, and their characteristics were analyzed. RESULTS: Among 196 patients, postoperative neurological deficit rates were 3.79% and 14.06% in the IONM and historical control (non-IONM) groups, respectively (p < 0.05). The use of IONM (OR: 0.139, p = 0.003) and presence of myelopathy (OR: 8.240, p = 0.013) were associated with postoperative neurological complications on multivariate regression. In total, 23 warnings were observed during IONM (17 tcMEP and/or electromyography; six electromyography). Sensitivity and specificity of IONM warnings for detecting neurological complications were 84.2% and 93.7%, respectively. CONCLUSIONS: IONM, especially multimodal IONM, may be a useful tool to detect neurological damage in ACDF for high-risk conditions such as OPLL with pre-existing myelopathy. SIGNIFICANCE: The utility of IONM in ACDF for OPLL has not been evaluated due to its rarity. This study supports the use of IONM in cervical OPLL with myelopathy.

Neurophysiological monitoring of spinal cord function during spinal deformity surgery: 2020 SRS neuromonitoring information statement.

The Scoliosis Research Society has developed an updated information statement on intraoperative neurophysiological monitoring of spinal cord function during spinal deformity surgery. The statement reviews the risks of spinal cord compromise associated with spinal deformity surgery; the statement then discusses the various modalities that are available to monitor the spinal cord, including somatosensory-evoked potentials, motor-evoked potentials, and electromyographic (EMG) options. Anesthesia considerations, the importance of a thoughtful team approach to successful monitoring, and the utility of checklists are also discussed. Finally, the statement expresses the opinion that utilization of intraoperative neurophysiological spinal cord monitoring in spinal deformity surgery is the standard of care when the spinal cord is at risk.

The efficacy of somatosensory evoked potentials in evaluating new neurological deficits after spinal thoracic fusion and decompression.

OBJECTIVE: Posterior thoracic fusion (PTF) is used as a surgical treatment for a wide range of pathologies. The monitoring of somatosensory evoked potentials (SSEPs) is used to detect and prevent injury during many neurological surgeries. The authors conducted a study to evaluate the efficacy of SSEPs in predicting perioperative lower-extremity (LE) neurological deficits during spinal thoracic fusion surgery. METHODS: The authors included patients who underwent PTF with SSEP monitoring performed throughout the entire surgery from 2010 to 2015 at the University of Pittsburgh Medical Center (UPMC). The sensitivity, specificity, odds ratio, and receiver operating characteristic curve were calculated to evaluate the diagnostic accuracy of SSEP changes in predicting postoperative deficits. Univariate analysis was completed to determine the impact of age exceeding 65 years, sex, obesity, abnormal baseline testing, surgery type, and neurological deficits on the development of intraoperative changes. RESULTS: From 2010 to 2015, 771 eligible patients underwent SSEP monitoring during PTF at UPMC. Univariate and linear regression analyses showed that LE SSEP changes significantly predicted LE neurological deficits. Significant changes in LE SSEPs had a sensitivity and specificity of 19% and 96%, respectively, in predicting LE neurological deficits. The diagnostic odds ratio for patients with new LE neurological deficits who had significant changes in LE SSEPs was 5.86 (95% CI 2.74-12.5). However, the results showed that a loss of LE waveforms had a poor predictive value for perioperative LE deficits (diagnostic OR 1.58 [95% CI 0.19-12.83]). CONCLUSIONS: Patients with new postoperative LE neurological deficits are 5.9 times more likely to have significant changes in LE SSEPs during PTF. Surgeon awareness of an LE SSEP loss may alter surgical strategy and positively impact rates of postoperative LE neurological deficit status. The relatively poor sensitivity of LE SSEP monitoring may indicate a need for multimodal neurophysiological monitoring, including motor evoked potentials, in thoracic fusion surgery.

Intraoperative monitoring of corticospinal tracts in anterior cervical decompression and fusion surgery: Excitability differentials of lower extremity muscles.

OBJECTIVE: This study examines and compares excitability characteristics of tibialis anterior (TA) and abductor hallucis (AH) transcranial motor evoked potentials (tcMEP) during anterior cervical decompression and fusion (ACDF) surgery. METHODS: Electrophysiological and clinical data of 89 patients who underwent ACDF procedure were retrospectively reviewed. TcMEP data of TA and AH muscles from 178 limbs were analyzed for availability, robustness and stability during the procedure. RESULTS: TA tcMEP was available at 83% whereas AH tcMEP was available at 99% of the monitored lower limbs at preposition baseline. Availability of both TA and AH tcMEP was demonstrated in 147/178 limbs. The baseline amplitude of AH tcMEP was significantly greater than that of TA tcMEP recorded from the same limb (744.6 ±â€¯54.0 and 326.9 ±â€¯33.3 µV, respectively). Simultaneous deterioration of TA and AH tcMEP data was demonstrated in 10/147 limbs. Deterioration of either TA or AH tcMEP data accompanied by unchanged tcMEP data from the other lower limb muscle was noted in 32/147 compared to 1/147 limbs, respectively. The deteriorated TA and AH tcMEP data returned to baseline before closing at incidence of 17% compared to 46%, respectively. No new lower extremity (LE) neurological deficit was presented postoperatively in any patient. CONCLUSIONS: AH tcMEP is a more reliable candidate than TA tcMEP for intraoperative LE monitoring in ACDF procedure. SIGNIFICANCE: The excitability differentials in LE tcMEP in ACDF is a variable that need to be considered while interpreting intraoperative neurophysiological data.

Characteristics of false-positive alerts on transcranial motor evoked potential monitoring during pediatric scoliosis and adult spinal deformity surgery: an "anesthetic fade" phenomenon.

OBJECTIVE: Transcranial motor evoked potential (TcMEP) monitoring may be valuable for predicting postoperative neurological complications with a high sensitivity and specificity, but one of the most frequent problems is the high false-positive rate. The purpose of this study was to clarify the differences in the risk factors for false-positive TcMEP alerts seen when performing surgery in patients with pediatric scoliosis and adult spinal deformity and to identify a method to reduce the false-positive rate. METHODS: The authors retrospectively analyzed 393 patients (282 adult and 111 pediatric patients) who underwent TcMEP monitoring while under total intravenous anesthesia during spinal deformity surgery. They defined their cutoff (alert) point as a final TcMEP amplitude of ≤ 30% of the baseline amplitude. Patients with false-positive alerts were classified into one of two groups: a group with pediatric scoliosis and a group with adult spinal deformity. RESULTS: There were 14 cases of false-positive alerts (13%) during pediatric scoliosis surgery and 62 cases of false-positive alerts (22%) during adult spinal deformity surgery. Compared to the true-negative cases during adult spinal deformity surgery, the false-positive cases had a significantly longer duration of surgery and greater estimated blood loss (both p < 0.001). Compared to the true-negative cases during pediatric scoliosis surgery, the false-positive cases had received a significantly higher total fentanyl dose and a higher mean propofol dose (0.75 ± 0.32 mg vs 0.51 ± 0.18 mg [p = 0.014] and 5.6 ± 0.8 mg/kg/hr vs 5.0 ± 0.7 mg/kg/hr [p = 0.009], respectively). A multivariate logistic regression analysis revealed that the duration of surgery (1-hour difference: OR 1.701; 95% CI 1.364-2.120; p < 0.001) was independently associated with false-positive alerts during adult spinal deformity surgery. A multivariate logistic regression analysis revealed that the mean propofol dose (1-mg/kg/hr difference: OR 3.117; 95% CI 1.196-8.123; p = 0.020), the total fentanyl dose (0.05-mg difference; OR 1.270; 95% CI 1.078-1.497; p = 0.004), and the duration of surgery (1-hour difference: OR 2.685; 95% CI 1.131-6.377; p = 0.025) were independently associated with false-positive alerts during pediatric scoliosis surgery. CONCLUSIONS: Longer duration of surgery and greater blood loss are more likely to result in false-positive alerts during adult spinal deformity surgery. In particular, anesthetic doses were associated with false-positive TcMEP alerts during pediatric scoliosis surgery. The authors believe that false-positive alerts during pediatric scoliosis surgery, in particular, are caused by "anesthetic fade."

Impact of total propofol dose during spinal surgery: anesthetic fade on transcranial motor evoked potentials.

OBJECTIVEIntraoperative neuromonitoring may be valuable for predicting postoperative neurological complications, and transcranial motor evoked potentials (TcMEPs) are the most reliable monitoring modality with high sensitivity. One of the most frequent problems of TcMEP monitoring is the high rate of false-positive alerts, also called "anesthetic fade." The purpose of this study was to clarify the risk factors for false-positive TcMEP alerts and to find ways to reduce false-positive rates.METHODSThe authors analyzed 703 patients who underwent TcMEP monitoring under total intravenous anesthesia during spinal surgery within a 7-year interval. They defined an alert point as final TcMEP amplitudes ≤ 30% of the baseline. Variations in body temperature (maximum - minimum body temperature during surgery) were measured. Patients with false-positive alerts were classified into 2 groups: a global group with alerts observed in 2 or more muscles of the upper and lower extremities, and a focal group with alerts observed in 1 muscle.RESULTSFalse-positive alerts occurred in 100 cases (14%), comprising 60 cases with global and 40 cases with focal alerts. Compared with the 545 true-negative cases, in the false-positive cases the patients had received a significantly higher total propofol dose (1915 mg vs 1380 mg; p < 0.001). In the false-positive cases with global alerts, the patients had also received a higher mean propofol dose than those with focal alerts (4.5 mg/kg/hr vs 4.2 mg/kg/hr; p = 0.087). The cutoff value of the total propofol dose for predicting false-positive alerts, with the best sensitivity and specificity, was 1550 mg. Multivariate logistic analysis revealed that a total propofol dose > 1550 mg (OR 4.583; 95% CI 2.785-7.539; p < 0.001), variation in body temperature (1°C difference; OR 1.691; 95% CI 1.060-2.465; p < 0.01), and estimated blood loss (500-ml difference; OR 1.309; 95% CI 1.155-1.484; p < 0.001) were independently associated with false-positive alerts.CONCLUSIONSIntraoperative total propofol dose > 1550 mg, larger variation in body temperature, and greater blood loss are independently associated with false-positive alerts during spinal surgery. The authors believe that these factors may contribute to the false-positive global alerts that characterize anesthetic fade. As it is necessary to consider multiple confounding factors to distinguish false-positive alerts from true-positive alerts, including variation in body temperature or ischemic condition, the authors argue the importance of a team approach that includes surgeons, anesthesiologists, and medical engineers.

Surgical management of complex spinal cord lipomas: how, why, and when to operate. A review.

This review summarizes the classification, anatomy, and embryogenesis of complex spinal cord lipomas, and it describes in some detail the new technique of total lipoma resection and radical reconstruction of the affected neural placode. Its specific mission is to tackle two main issues surrounding the management of complex dysraphic lipomas: whether total resection confers better long-term benefits than partial resection and whether total resection fares better than conservative treatment-i.e., no surgery-for asymptomatic lipomas. Accordingly, the 24-year progression-free survival data of the author and colleagues' series of over 300 cases of total resection are compared with historical data from multiple series (including the author and colleagues' own) of partial resection, and total resection data specifically for asymptomatic lesions are compared with the two known series of nonsurgical treatment of equivalent numbers of patients. These comparisons amply support the author's recommendation of total resection for most complex lipomas, with or without symptoms. The notable exception is the asymptomatic chaotic lipoma, whose peculiar anatomical relationship with the neural tissue defies even this aggressive surgical approach and consequently projects worse results (admittedly of a small number of cases) than for the other two lipoma subtypes of dorsal and transitional lesions. Prophylactic resection of asymptomatic chaotic lipomas is therefore not currently endorsed.