Impact of anesthesia on transcranial electric motor evoked potential monitoring during spine surgery: a review of the literature

Clinical Application and Research Progress of Remimazolam for Pediatric Patients

Remimazolam is a novel ultrashort-acting benzodiazepine that allosterically modulates γ-aminobutyric acid type A (GABAA) receptors to exert sedative effects. Remimazolam has the properties of controllable sedation, rapid onset, and a short duration of action, along with minor depression of circulation and respiration. Remimazolam has been approved for clinical use since 2020 in Japan, and it has been applied for procedural sedation, general anesthesia induction and maintenance, and sedation in ICU patients, and has been proven to be safe and effective. Currently, no consensus has been reached on the clinical application of remimazolam in pediatric patients. This review introduces the clinical research progress and limitations of remimazolam in recent years, aiming to supply scientific guidance and a theoretical reference for the application of remimazolam in pediatric anaesthesia.

Evolving trends in the surgical, anaesthetic, and intensive care management of acute spinal cord injuries in the UK

PURPOSE

We surveyed the treatment of acute spinal cord injuries in the UK and compared current practices with 10 years ago.

METHODS

A questionnaire survey was conducted amongst neurosurgeons, neuroanaesthetists, and neurointensivists that manage patients with acute spinal cord injuries. The survey gave two scenarios (complete and incomplete cervical spinal cord injuries). We obtained opinions on the speed of transfer, timing and aim of surgery, choice of anaesthetic, intraoperative monitoring, targets for physiological parameters, and drug treatments.

RESULTS

We received responses from 78.6% of UK units that manage acute spinal cord injuries (33 neurosurgeons, 56 neuroanaesthetists/neurointensivists). Most neurosurgeons operate within 12 h for incomplete (82%) and complete (64%) injuries. There is a significant shift from 10 years ago, when only 61% (incomplete) and 30% (complete) of neurosurgeons operated within 12 h. The preferred anaesthetic technique in 2022 is total intravenous anaesthesia (TIVA), used by 69% of neuroanaesthetists. Significantly more intraoperative monitoring is now used at least sometimes, including bispectral index (91%), non-invasive cardiac output (62%), and neurophysiology (73-77%). Methylprednisolone is no longer used by surgeons. Achieving at least 80 mmHg mean arterial blood pressure is recommended by 70% neurosurgeons, 62% neuroanaesthetists, and 75% neurointensivists.

CONCLUSIONS

Between 2012 and 2022, there was a paradigm shift in managing acute spinal cord injuries in the UK with earlier surgery and more intraoperative monitoring. Variability in practice persists due to lack of high-quality evidence and consensus guidelines.

Effects of Anesthetic Choice on the Incidence of Transcranial-Motor Potential-Induced Oral Trauma

Transcranial motor-evoked potentials (TcMEPs) play an integral role in assessing motor tract function in surgical procedures where motor function is at risk. However, transcranial stimulation creates a risk for oral trauma. Several studies have reported on distinct factors that can influence the rate of TcMEP-induced oral trauma, but little is known about how an anesthetic regimen can influence this rate. In this retrospective review, we investigated the incidence of oral injury under total intravenous anesthesia (TIVA) and balanced anesthesia in 66,166 cases from 2019 to 2021. There were 295 oral injuries in our sample, yielding an incidence of 0.45%, which is in line with ranges reported in the literature. A total of 222 of the injured patients were sedated with balanced anesthesia, while the remaining 73 were under TIVA anesthetics. This difference in distribution was statistically significant (p < 0.0002). Our findings suggest TIVA is associated with lower risk of oral trauma when TcMEPs are monitored, thereby improving patient safety.

Updated review on the use of neuromuscular blockade during intraoperative motor-evoked potential monitoring in the modern anesthesia era

Transcranial electrical stimulation motor-evoked potentials (Tc-MEP) monitoring is a common practice in neurosurgery to prevent postoperative neurological damage. However, the use of neuromuscular blocking agents (NMBAs) during Tc-MEP monitoring is a subject of controversy. In addition, the effectiveness of sugammadex, a selective reversal agent, in the context of Tc-MEP monitoring requires further investigation. This review aimed to clarify the considerations involved in achieving optimal Tc-MEP monitoring while ensuring patient safety. Preoperative patient selection, comorbidity assessment, motor power evaluation, and the nature of the planned surgery are critical factors. Accurate paralysis assessment, continuous NMBA infusion, and post-tetanic stimulation techniques are essential for achieving optimal partial NMB. The decision to administer an NMB during Tc-MEP monitoring necessitates a careful evaluation of the balance between accuracy and potential complications. This review emphasizes the challenges associated with NMB administration during Tc-MEP monitoring and highlights the need for personalized patient assessment.

Pain Management, Functional Recovery, and Stress Response Expressed by NLR and PLR after the iPACK Block Combined with Adductor Canal Block for Total Knee Arthroplasty-A Prospective, Randomised, Double-Blinded Clinical Trial

INTRODUCTION

This study aimed to investigate pain management, functional recovery, and stress response expressed by the neutrophile-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) after the popliteal artery and posterior knee capsule infiltration (iPACK) block combined with adductor canal block (ACB) in total knee arthroplasty (TKA).

PATIENTS AND METHODS

This was a prospective, double-blinded, randomised, controlled trial in a tertiary referral hospital. Three hundred and sixty-six patients were randomly allocated into the sham block group and iPACK combined with the ACB group. The primary outcome was postoperative pain scores. The secondary outcomes were opioid consumption, functional recovery expressed by a range of motion, and quadriceps strength. Also, the neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) were calculated.

RESULTS

There were significant differences between the sham block and iPACK + ACB group in pain scores p < 0.0001 at all time points. Therefore, there was a significant difference in opioid consumption (p < 0.0001) and functional recovery (p < 0.0001). Also, NLR and PLR levels 12 h (p < 0.0001) and 24 h (24 h) after surgery (p < 0.0001) were much lower in the iPACK + ACB group.

CONCLUSION

After total knee arthroplasty, the iPACK combined with ACB block group improved pain management, functional recovery, and stress response. Therefore, we strongly recommend this technique as a part of a multimodal analgesia protocol in knee surgery.

Comparison of Motor Evoked Potentials Neuromonitoring Following Pre- and Postoperative Transcranial Magnetic Stimulation and Intraoperative Electrical Stimulation in Patients Undergoing Surgical Correction of Idiopathic Scoliosis

The relationships between the results of pre- and intraoperative motor evoked potential recordings during neuromonitoring and whether idiopathic scoliosis (IS) surgical correction improves the spinal efferent transmission have not been specified in detail. This study aims to compare the results of surface-recorded electromyography (EMG), electroneurography (ENG, M, and F-waves), and especially motor evoked potential (MEP) recordings from tibialis anterior muscle (TA) bilaterally in 353 girls with right idiopathic scoliosis (types 1-3 according to Lenke classification). It has not yet been documented whether the results of MEP recordings induced by transcranial single magnetic stimulus (TMS, pre- and postoperatively) and trains of electrical stimuli (TES; intraoperatively in T0-before surgery, T1-after pedicle screws implantation, and T2-after scoliosis curvature distraction and derotation following two-rod implantation) can be compared for diagnostic verification of the improvement of spinal cord neural transmission. We attempted to determine whether the constant level of optimal anesthesia during certain surgical steps of scoliosis treatment affects the parameters of MEPs recorded during neuromonitoring procedures. No neurological deficits have been observed postoperatively. The values of amplitudes but not latencies in MEP recordings evoked with TMS in IS patients compared before and after surgery indicated a slight improvement in efferent neural transmission. The results of all neurophysiological studies in IS patients were significantly asymmetrical and recorded worse on the concave side, suggesting greater neurological motor deficits at p = 0.04. The surgeries brought significant improvement (p = 0.04) in the parameters of amplitudes of sEMG recordings; however, the consequences of abnormalities in the activity of TA motor units were still reflected. ENG study results showed the symptoms of the axonal-type injury in peroneal motor fibers improving only on the concave side at p = 0.04, in parallel with F-wave parameters, which suggests that derotation and distraction might result in restoring the proper relations of the lumbar ventral roots in the spinal central canal, resembling their decompression. There were no significant differences detected in the amplitudes or latencies of MEPs induced with TMS or TES when comparing the parameters recorded preoperatively and intraoperatively in T0. The amplitudes of TES-evoked MEPs increased gradually at p = 0.04 in the subsequent periods (T1 and T2) of observation. A reduction in MEP latency at p = 0.05 was observed only at the end of the IS surgery. Studies on the possible connections between the level of anesthesia fluctuations and the required TMS stimulus strength, as well as the MEP amplitude changes measured in T0-T2, revealed a lack of relationships. These might not be the factors influencing the efferent transmission in spinal pathways beside the surgical procedures. Pre- (TMS-evoked) and intraoperative (TES-evoked) recordings are reliable for evaluating the patient's neurological status before and during surgical scoliosis correction procedures. An increase in MEP amplitude parameters recorded on both sides after scoliosis surgery proves the immediate improvement of the total efferent spinal cord transmission. Considering comparative pre- and postoperative sEMG and ENG recordings, it can be concluded that surgeries might directly result in additional lumbar ventral root decompression. We can conclude that MEP parameter changes are determined by the surgery procedures during neuromonitoring, not the anesthesia conditions if they are kept stable, which influences a decrease in the number of false-positive neuromonitoring warnings.

Effect of Ketamine and Dexmedetomidine as Adjuvant to Total Intravenous Anesthesia on Intraoperative Cranial Nerve Monitoring in the Patients Undergoing Posterior Fossa Craniotomies-A Randomized Quadruple Blind Placebo-Controlled Study

Objectives  Total intravenous anesthesia (TIVA) is used during surgery with intraoperative neurophysiological monitoring. Addition of adjuvant may minimize suppression of potentials by reducing doses of propofol. We studied the effect of addition of ketamine or dexmedetomidine to propofol-fentanyl-based TIVA on corticobulbar motor evoked potential (CoMEP) in patients undergoing posterior fossa surgeries. Materials and Methods  Forty-two patients were assigned to three groups ( n  = 14 each), Group S-saline, Group D-dexmedetomidine (0.25 μg/kg/h), and Group K-ketamine (0.25 mg/kg/h). Patients received propofol and fentanyl infusions along with study drugs. CoMEPs were recorded from muscles innervated by cranial nerves bilaterally at predefined intervals (T baseline , T 2 , T 3 , T 4 , and T 5 ). Effect on amplitude and latency of CoMEPs was assessed. Results  A significant fall in CoMEP amplitude was observed across all analyzed muscles at time T 4 and T 5 in saline and dexmedetomidine group as compared with ketamine group, p -value less than 0.05. A significant increase in latency was observed at T4 and T5 among groups ( p -value, D vs. K = 0.239, D vs. S = 0.123, and K vs. S = 0.001). Conclusion  Both ketamine and dexmedetomidine provide and allow effective recording of CoMEPs. Ketamine emerges as a better agent especially when prolonged surgical duration is expected as even propofol-fentanyl-based TIVA adversely affects CoMEPs when used for long duration.

Anesthesia of a patient with congenital cataract, facial dysmorphism, and neuropathy syndrome for posterior scoliosis: A case report

BACKGROUND

Congenital cataract, facial dysmorphism, and neuropathy (CCFDN) syndrome is an extremely rare multiorgan disorder. Characteristics include congenital cataracts, facial deformation, extremity deformities, and demyelinating neuropathy. CCFDN syndrome is associated with increased risk during anesthesia including rhabdomyolysis or epileptic seizures. There is a lack of published information about difficult airways in these patients. Difficult airways during intubation represent one of the most dreaded anesthesia complications: A "can not intubate, can not oxygenate" scenario. Presented herein is the first described successful endotracheal intubation of a CCFDN syndrome patient.

CASE SUMMARY

We report the anesthetic management of a 13-year-old girl with CCFDN syndrome scheduled for posterior neuromuscular scoliosis correction surgery. The patient suffered from extensive progressive neuromuscular scoliosis with a Cobb angle of 83°. Her limitations included neuropathy and a scoliotic curve. This condition negatively impacted her quality of life. This case reflects the potential anesthetic complications for posterior scoliosis correction and CCFDN syndrome. The challenge for our anesthetic team was the limited amount of data about anesthetic management of this condition. In total, one case report without any data about endotracheal intubation of patients with this condition was available. Endotracheal intubation in our case was uncomplicated. Another focus of our case was the prevention of possible complications associated with this syndrome, including rhabdomyolysis and seizures. Rhabdomyolysis can be triggered by some types of anesthetic agents like suxamethonium or volatile anesthetics, especially in patients with certain types of myopathies.

CONCLUSION

Adequate understanding of the anesthetic management of CCFDN syndrome can reduce perioperative complications and improve patient outcome after surgery.

Spinal fusion with motor evoked potential monitoring using remimazolam in Alström syndrome: A case report

RATIONALE

Alström syndrome is a rare genetic disorder characterized by obesity, diabetes mellitus, cardiomyopathy, and liver dysfunction. Further, scoliosis, a common symptom of Alström syndrome, often requires surgical intervention for functional impairments. Motor evoked potential (MEP) monitoring and other electrophysiological tests are essential when performing surgery for functional scoliosis. However, there are few reports on how to maintain general anesthesia in Alström syndrome. Here, we describe a patient with Alström syndrome who underwent surgery for scoliosis under general anesthesia with remimazolam and MEP monitoring.

PATIENT CONCERNS

A 17-year-old woman (height, 140 cm, weight, 64.5 kg) diagnosed with Alström syndrome was scheduled for a posterior spinal fusion for functional scoliosis. Other associated comorbidities of Alström syndrome present were dilated cardiomyopathy, type 2 diabetes mellitus, obesity (body mass index, 32.1 kg/m2), amblyopia (light perception), and hearing impairment (speech awareness threshold 50 dBHL in each ear).

DIAGNOSES, INTERVENTIONS, AND OUTCOMES

Posterior spinal fusion was planned for functional scoliosis. While investigating the dilated cardiomyopathy, transthoracic echocardiography showed global wall hypokinesis, with 45% left ventricular ejection fraction. The left ventricle was dilated, with left ventricular end-diastolic and end-systolic diameters of 55 and 42 mm, respectively. This finding along with the hypertriglyceridemia associated with Alström syndrome led us to conclude that propofol should be avoided. Thus, we induced general anesthesia using remimazolam. MEP monitoring was performed, and the patient experienced no motor impairments during the surgery.

LESSONS

Myocardial and hepatic dysfunction determine the prognosis of patients with Alström syndrome. Thus, anesthesia that preserves liver function should be selected in such cases. In patients with hypertriglyceridemia, propofol should be avoided, and using remimazolam, an ultrashort-acting benzodiazepine, may be appropriate. In this case, reviewing the Patient State Index with SedLine allowed us to perform MEP monitoring uneventfully, and the posterior spinal fusion was completed without any motor impairment.

Intraoperative Remifentanil Dosage in Surgery for Adolescent Idiopathic Scoliosis Does Not Increase Postoperative Opioid Consumption When Combined With Epidural Analgesia: A Retrospective Cohort Study

Background In adults, high-dose remifentanil during surgery has been reported to increase postoperative opioid consumption, but this has not been well documented in children. Multimodal analgesia is recommended in the perioperative period for adolescent idiopathic scoliosis (AIS), but no report has examined opioid consumption under epidural analgesia, which is one of the most common types of analgesia. Aims To investigate the association between intraoperative remifentanil dosage and postoperative opioid consumption in AIS in the setting of combined epidural analgesia for postoperative multimodal analgesia. Methods In this retrospective cohort study, patients aged 10-18 years who underwent surgery for scoliosis and epidural analgesia for postoperative pain between July 2012 and April 2019 were included. The primary endpoint was the association between intraoperative cumulative weight-adjusted remifentanil dosage and logarithmic transformation of cumulative weight-adjusted fentanyl consumption in the intensive care unit (ICU). Nonopioid analgesics were investigated as secondary endpoints. An epidural catheter was inserted by the surgeon intraoperatively, and a local anesthetic was administered at the end of the surgery. Multivariate linear regression analysis with adjustment for confounders was performed for all analyses. Results In total, 142 patients were included, and the median intraoperative remifentanil dosage for all patients was 0.27 (interquartile range, 0.24-0.34) µg/kg/min. No association was observed between cumulative weight-adjusted intraoperative dosage of remifentanil and fentanyl, even after adjusting for potential confounders (slope = -1.25; 95% confidence interval [CI], -4.35 to 1.85; P = 0.43). No association was observed between nonopioid analgesic use and intraoperative remifentanil dosage. Conclusion No association was noted between remifentanil dosage during surgery for AIS and postoperative opioid consumption with epidural analgesia. However, this study has limitations due to its retrospective design; thus, further prospective studies are warranted.

Perioperative Care of Patients Undergoing Major Complex Spinal Instrumentation Surgery: Clinical Practice Guidelines From the Society for Neuroscience in Anesthesiology and Critical Care

Evidence-based standardization of the perioperative management of patients undergoing complex spine surgery can improve outcomes such as enhanced patient satisfaction, reduced intensive care and hospital length of stay, and reduced costs. The Society for Neuroscience in Anesthesiology and Critical Care (SNACC) tasked an expert group to review existing evidence and generate recommendations for the perioperative management of patients undergoing complex spine surgery, defined as surgery on 2 or more thoracic and/or lumbar spine levels. Institutional clinical management protocols can be constructed based on the elements included in these clinical practice guidelines, and the evidence presented.

Effect of dexmedetomidine on evoked-potential monitoring in patients undergoing brain stem and supratentorial cranial surgery

BACKGROUND

Dexmedetomidine is used as adjuvant in total intravenous anaesthesia (TIVA), but there have been few studies concerning its effect on intraoperative neurophysiological monitoring (IONM) during cranial surgery. Our aim was to study the effect of dexmedetomidine on IONM in patients undergoing brain stem and supratentorial cranial surgery.

METHODS

Two prospective, randomized, double-blind substudies were conducted. In substudy 1, during TIVA with an infusion of propofol and remifentanil, 10 patients received saline solution (SS) (PR group) and another 10 (PRD group) received dexmedetomidine (0.5 mcg/kg/h). Total dosage of propofol and remifentanil, intensity, latency and amplitude of motor-evoked potentials following transcranial electrical stimulation (tcMEPs) as well as somatosensory-evoked potentials (SSEP) were recorded at baseline, 15, 30, 45 minutes, and at the end of surgery. In order to identify differences in the same patient after dexmedetomidine administration, we designed substudy 2 with 20 new patients randomized to two groups. After 30 minutes with TIVA, 10 patients received dexmedetomidine (0.5 mcg/kg/h) and 10 patients SS. The same variables were recorded.

RESULTS

In substudy 1, propofol requirements were significantly lower (P = .004) and tcMEP intensity at the end of surgery was significantly higher in PRD group, but no statistically significant differences were observed for remifentanil requirements, SSEP and tcMEP latency or amplitude. In substudy 2, no differences in any of the variables were identified.

CONCLUSIONS

The administration of dexmedetomidine at a dosage of 0.5 mg/kg/h may reduce propofol requirements and adversely affect some neuromonitoring variables. However, it can be an alternative on IONM during cranial surgeries. REDEX EudraCT: 2014-000962-23.

Evaluation of the Effect of Continuous Infusion of Dexmedetomidine or a Subanesthetic Dose Ketamine on Transcranial Electrical Motor Evoked Potentials in Adult Patients Undergoing Elective Spine Surgery under Total Intravenous Anesthesia: A Randomized Controlled Exploratory Study

Study Design

Prospective, randomized, placebo-controlled, double-blind exploratory study.

Purpose

To compare effects of dexmedetomidine or a subanesthetic dose of ketamine on the amplitude and latency of transcranial electrically generated motor evoked potentials.

Overview of Literature

Total intravenous anesthesia (TIVA) is a standard anesthesia technique for transcranial electrical motor evoked potential monitoring in spine surgery. We aimed to determine whether the use of dexmedetomidine and ketamine as a component of TIVA exerted any beneficial effect on the quality of monitoring.

Methods

A total of 90 American Society of Anesthesiologist grade I-III patients, aged 18-65 years, with a motor power of ≥4/5 grade as per the Medical Research Council Scale in all four limbs who were scheduled for elective spine surgery under transcranial electrical motor evoked potential monitoring were enrolled. The subjects were randomly allocated into the following three groups: group PD who received 0.5 μg/kg/hr dexmedetomidine infusion, group PK who received 0.5 mg/kg/hr ketamine infusion, and group PS who received normal saline infusion, along with standard propofol-fentanyl based TIVA regime. Amplitude and latency of bilateral motor evoked potentials of the tibialis anterior and abductor halluces muscle were recorded at Ti (at train-of-four ratio >90%), T30 (30 minutes post-Ti), T60 (60 minutes post-Ti), and Tf (at the end of spine manipulation).

Results

Baseline median amplitudes were comparable among the study groups. In group PK, we noted a gradually enhanced response by 24%-100% from the baseline amplitude. The median amplitudes of all the muscles were higher in group PK than those in groups PS and PD at time points T60 and Tf (p <0.05).

Conclusions

The present study demonstrated that compared with dexmedetomidine and control treatment, a subanesthetic dose of ketamine caused gradual improvement in amplitudes without affecting the latency.

Intraoperative neurophysiological monitoring in paediatric neurosurgery

Intraoperative neurophysiological monitoring (IONM) is commonly used in various surgical procedures in adults, but with technological and anaesthetic advancements, its use has extended to the paediatric population. The use of IONM in children poses a unique set of challenges considering the anatomical and physiological differences in this group of patients. The use of IONM aids in the localization of neural structures and enables surgeons to preserve the functional neural structures leading to decreased incidence of postoperative neurological deficits and better patient outcomes. In this article, we review the use of IONM in paediatric patients undergoing various spinal and cranial neurosurgical procedures. We discuss the patient characteristics, type of surgeries, and technical and anaesthetic considerations about IONM in this population.

Effect of reversal of residual neuromuscular blockade on the amplitude of motor evoked potentials: a randomized controlled crossover study comparing sugammadex and placebo

PURPOSE

To compare the amplitude changes in motor evoked potentials (MEP) with reversal of residual neuromuscular blockade using sugammadex or placebo in patients with cervical myelopathy.

METHODS

In this prospective randomized double-blind, placebo-controlled crossover trial, 38 patients with cervical myelopathy undergoing posterior cervical decompression and fusion were randomized to either sugammadex (2mg/kg) or placebo. The primary outcome measure was the increase in amplitude of the MEP in the first dorsal interossei (FDI) muscle at 3 min. Mann-Whitney U test was used to analyze the primary outcome measure.

RESULTS

There was a significant increase in the amplitude of MEP at 3 min with sugammadex when compared to placebo group. The median (IQR) increase in MEP amplitude (μV) at 3 min from the left FDI in sugammadex and placebo group was 652.9 (142:1650) and 20.6 (-183.5:297.5) (p <0.001), respectively. Corresponding values from right FDI were 2153.4 (1400:4536.8) and 55(-65.2:480.8) (p=<0.001).

CONCLUSION

Our study showed that there was a 200% increase in the MEP amplitude in the first dorsal interosseous muscle at 3 min following reversal of residual neuromuscular blockade with sugammadex. By ensuring that maximal MEP amplitude is recorded at baseline, early commencement of neuromonitoring can be achieved.

TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION

The study was registered at http://clinicaltrials.gov , ID NCT03087513, Feb 5^th 2018.

Navigated TMS in the ICU: Introducing Motor Mapping to the Critical Care Setting

Navigated transcranial magnetic stimulation (nTMS) is a modality for noninvasive cortical mapping. Specifically, nTMS motor mapping is an objective measure of motor function, offering quantitative diagnostic information regardless of subject cooperation or consciousness. Thus far, it has mostly been restricted to the outpatient setting. This study evaluates the feasibility of nTMS motor mapping in the intensive care unit (ICU) setting and solves the challenges encountered in this special environment. We compared neuronavigation based on computed tomography (CT) and magnetic resonance imaging (MRI). We performed motor mappings in neurocritical patients under varying conditions (e.g., sedation or hemicraniectomy). Furthermore, we identified ways of minimizing electromyography (EMG) noise in the interference-rich ICU environment. Motor mapping was performed in 21 patients (six females, median age: 69 years). In 18 patients, motor evoked potentials (MEPs) were obtained. In three patients, MEPs could not be evoked. No adverse reactions occurred. We found CT to offer a comparable neuronavigation to MRI (CT maximum e-field 52 ± 14 V/m vs. MRI maximum e-field 52 ± 11 V/m; p = 0.6574). We detailed EMG noise reduction methods and found that propofol sedation of up to 80 mcg/kg/h did not inhibit MEPs. Yet, nTMS equipment interfered with exposed pulse oximetry. nTMS motor mapping application and use was illustrated in three clinical cases. In conclusion, we present an approach for the safe and reliable use of nTMS motor mapping in the ICU setting and outline possible benefits. Our findings support further studies regarding the clinical value of nTMS in critical care settings.

Multi-Site Optical Monitoring of Spinal Cord Ischemia during Spine Distraction

Optimal surgical management of spine trauma will restore blood flow to the ischemic spinal cord. However, spine stabilization may also further exacerbate injury by inducing ischemia. Current electrophysiological technology is not capable of detecting acute changes in spinal cord blood flow or localizing ischemia. Further, alerts are delayed and unreliable. We developed an epidural optical device capable of directly measuring and immediately detecting changes in spinal cord blood flow using diffuse correlation spectroscopy (DCS). Herein we test the hypothesis that our device can continuously monitor blood flow during spine distraction. Additionally, we demonstrate the ability of our device to monitor multiple sites along the spinal cord and axially resolve changes in spinal cord blood flow. DCS-measured blood flow in the spinal cord was monitored at up to three spatial locations (cranial to, at, and caudal to the distraction site) during surgical distraction in a sheep model. Distraction was halted at 50% of baseline blood flow at the distraction site. We were able to monitor blood flow with DCS in multiple regions of the spinal cord simultaneously at ∼1 Hz. The distraction site had a greater decrement in flow than sites cranial to the injury (median -40 vs. -7%,). This pilot study demonstrated high temporal resolution and the capacity to axially resolve changes in spinal cord blood flow at and remote from the site of distraction. These early results suggest that this technology may assist in the surgical management of spine trauma and in corrective surgery of the spine.

Neuroanesthesia Guidelines for Optimizing Transcranial Motor Evoked Potential Neuromonitoring During Deformity and Complex Spinal Surgery: A Delphi Consensus Study

STUDY DESIGN

Expert opinion-modified Delphi study.

OBJECTIVE

We used a modified Delphi approach to obtain consensus among leading spinal deformity surgeons and their neuroanesthesiology teams regarding optimal practices for obtaining reliable motor evoked potential (MEP) signals.

SUMMARY OF BACKGROUND DATA

Intraoperative neurophysiological monitoring of transcranial MEPs provides the best method for assessing spinal cord integrity during complex spinal surgeries. MEPs are affected by pharmacological and physiological parameters. It is the responsibility of the spine surgeon and neuroanesthesia team to understand how they can best maintain high-quality MEP signals throughout surgery. Nevertheless, varying approaches to neuroanesthesia are seen in clinical practice.

METHODS

We identified 19 international expert spinal deformity treatment teams. A modified Delphi process with two rounds of surveying was performed. Greater than 50% agreement on the final statements was considered "agreement"; >75% agreement was considered "consensus."

RESULTS

Anesthesia regimens and protocols were obtained from the expert centers. There was a large amount of variability among centers. Two rounds of consensus surveying were performed, and all centers participated in both rounds of surveying. Consensus was obtained for 12 of 15 statements, and majority agreement was obtained for two of the remaining statements. Total intravenous anesthesia was identified as the preferred method of maintenance, with few centers allowing for low mean alveolar concentration of inhaled anesthetic. Most centers advocated for <150 μg/kg/min of propofol with titration to the lowest dose that maintains appropriate anesthesia depth based on awareness monitoring. Use of adjuvant intravenous anesthetics, including ketamine, low-dose dexmedetomidine, and lidocaine, may help to reduce propofol requirements without negatively effecting MEP signals.

CONCLUSION

Spine surgeons and neuroanesthesia teams should be familiar with methods for optimizing MEPs during deformity and complex spinal cases. Although variability in practices exists, there is consensus among international spinal deformity treatment centers regarding best practices.

LEVEL OF EVIDENCE

5.

Feasibility of Full Neuromuscular Blockade During Transcranial Motor Evoked Potential Monitoring of Neurosurgical Procedures

BACKGROUND

Transcranial motor evoked potential (TcMEP) monitoring is conventionally performed during surgical procedures without or with minimal neuromuscular blockade (NMB) because of its potential interference with signal interpretation. However, full blockade offers increased anesthetic management options and facilitates surgery. Here, the feasibility of TcMEP interpretation was assessed during full NMB in adult neurosurgical patients.

METHODS

Patients undergoing cervical or lumbar decompression received a rocuronium bolus producing 95% or greater blockade by qualitative train-of-four at the ulnar nerve. TcMEPs were recorded in bilateral thenar-hypothenar and abductor hallucis muscles. Adequacy of response for reliable signal interpretation was determined on the basis of repeatability and clarity, assessed by coefficient of variation and signal-to-noise ratio, respectively.

RESULTS

All patients had at least 3 of 4 measurable TcMEP limb responses present during full NMB, and 70.8% of patients had measurable responses in all 4 limbs. In total, 82.2% of thenar-hypothenar responses and 62.8% of abductor hallucis responses were robust enough for reliable signal interpretation on the basis of clarity. In addition, 97.8% of thenar-hypothenar responses and 79.1% of abductor hallucis responses met the criteria for reliable signal interpretation on the basis of consistency. Patient demographics, medical comorbidities, and preoperative weakness were not predictive of absent responses during full NMB.

CONCLUSIONS

TcMEP interpretation may be feasible under greater levels of NMB than previously considered, allowing for monitoring with greater degrees of muscle relaxation. Consideration for monitoring TcMEP during full NMB should be made on a case-by-case basis, and baseline responses without blockade may predict which patients will have adequate responses for interpretation.

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

•

Lower extremity (LE) muscles demonstrate intraoperative excitability differences.

•

Abductor hallucis is a suitable LE muscle for monitoring the corticospinal tract (CST).

•

CST monitoring with two LE muscles includes advantages but also practical limitations.

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 ± 54.0 and 326.9 ± 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.

Feasibility of intraoperative monitoring of motor evoked potentials obtained through transcranial electrical stimulation in infants younger than 3 months

OBJECTIVE

This study aimed to investigate the feasibility and safety of intraoperative motor evoked potential (MEP) monitoring in infants less than 3 months of age.

METHODS

The authors investigated 25 cases in which infants younger than 3 months (mean age 72.8 days, range 39-87) underwent neurosurgery between 2014 and 2017. Myogenic MEPs were obtained through transcranial electrical stimulation. In all cases, surgery was performed under total intravenous anesthesia, maintained with remifentanil and propofol.

RESULTS

MEPs were documented in 24 infants, the sole exception being 1 infant who was lethargic and had 4-limb weakness before surgery. The mean stimulation intensity maintained during monitoring was 596 ± 154 V (range 290-900 V). In 19 of 24 infants MEP signals remained at ≥ 50% of the baseline amplitude throughout the operation. Among 5 cases with a decrease in intraoperative MEP amplitude, the MEP signal was recovered in one during surgery, and in the other case a neurological examination could not be performed after surgery. In the other 3 cases, 2 infants had relevant postoperative weakness and the other did not show postoperative neurological deficits. Postoperative weakness was not observed in any of the 20 infants who had no deterioration (n = 19) or only temporary deterioration (n = 1) in MEP signal during surgery.

CONCLUSIONS

Transcranial electrical MEPs could be implemented during neurosurgery in infants between 1 and 3 months of age. Intraoperative MEP monitoring may be a safe adjunct for neurosurgical procedures in these very young patients.

A motor evoked potential trending system may discriminate outcome: retrospective application with three cases

This report presents a method for tracking Motor Evoked Potential (MEP) amplitudes over the course of a case using a moving least squares linear regression (LSMAs). During a case, newly obtained MEP amplitudes are compared to those predicted by a just previous linear regression (least squares moving average or LSMA). When detected by this comparison, a set criterion amplitude loss will then trigger linear regression of ensuing MEP amplitudes on an expanding step function which tracks the persistence of the amplitude loss for the remainder of the case. Three cases are presented. One in which the patient woke up with a newly acquired weakness in the left tibialis anterior and another in which MEP amplitudes were suddenly lost from the right foot, but after intervention, they were restored again. In a third case the patient again woke up with a new post-operative deficit, but MEP trial sampling had been more limited and variable than in the first two cases. When the linear trending method was applied to the affected myotome in the first case, the expanding step function regression was triggered after the moment of MEP loss and remained at a high level until the end of case. In the second case, the expanding step function regression was also triggered in the relevant myotome at the time of the reported MEP change, but diminished by end of case. In the third case the tracking method again successfully triggered a predictive R-Square despite the limited number of pre-event trials. The R-Square value of the expanding step function regression appears to have discriminative capability with regard to new post-op deficit. Given the importance of the intra-operative MEP for monitoring motor functioning and the high degree of variability that can affect it, the development of new quantitative, statistical methods to detect real from apparent MEP change will be necessary.

Laser safety in fiber-optic monitoring of spinal cord hemodynamics: a preclinical evaluation

The prevention and treatment of spinal cord injury are focused upon the maintenance of spinal cord blood flow, yet no technology exists to monitor spinal cord ischemia. We recently demonstrated continuous monitoring of spinal cord ischemia with diffuse correlation and optical spectroscopies using an optical probe. Prior to clinical translation of this technology, it is critically important to demonstrate the safety profile of spinal cord exposure to the required light. To our knowledge, this is the first report of in situ safety testing of such a monitor. We expose the spinal cord to laser light utilizing a custom fiber-optic epidural probe in a survival surgery model (11 adult Dorset sheep). We compare the tissue illumination from our instrument with the American National Standards Institute maximum permissible exposures. We experimentally evaluate neurological and pathological outcomes of the irradiated sheep associated with prolonged exposure to the laser source and evaluate heating in ex vivo spinal cord samples. Spinal cord tissue was exposed to light levels at ∼18  ×   the maximum permissible exposure for the eye and ∼  (  1  /  3  )    ×   for the skin. Multidisciplinary testing revealed no functional neurological sequelae, histopathologic evidence of laser-related injury to the spinal cord, or significant temperature changes in ex vivo samples. Low tissue irradiance and the lack of neurological, pathological, and temperature changes upon prolonged exposure to the laser source offer evidence that spinal cord tissues can be monitored safely with near-infrared optical probes placed within the epidural space.

Motor-Evoked Potential Analysis of Femoral Nerve Status During the Direct Anterior Approach for Total Hip Arthroplasty

BACKGROUND

During the direct anterior approach for total hip arthroplasty, a retractor is placed on the anterior wall of the acetabulum to retract the iliopsoas muscle. This step with the retractor has been reported to put the patient at risk for femoral nerve damage. The present study aimed to clarify the effects of the anterior acetabular retractor on the status of the femoral nerve during the direct anterior approach on the basis of transcranial motor-evoked potential (MEP) analysis.

METHODS

Between July 2016 and February 2017, 22 patients underwent primary total hip arthroplasty via the direct anterior approach with MEP analysis. The integrity of the femoral nerve was tested at 3 time points: preoperatively, as a control (first period); just after retractor placement on the anterior wall of the acetabulum (second period); and after the procedure (third period). The association between operative time and femoral nerve status was examined. Postoperative femoral nerve damage was determined by the presence of causalgia and the results of a manual muscle test (MMT) for strength of knee extension.

RESULTS

The mean amplitude of the femoral nerve was significantly reduced, from 100% in the first period to 54% (range, 5% to 100%) in the second period (p < 0.01), but then significantly improved to 77% (range, 20% to 100%) in the third period (p < 0.01). In 17 (77%) of the 22 patients, the amplitude of the femoral nerve in the second period was reduced, while only 5 patients (23%) showed no reduction. The mean operative time was 83 minutes (range, 63 to 104 minutes), and no significant correlation was observed between operative time and improvement of femoral nerve status between the second and third periods (p = 0.83 and r = -0.05). All 22 patients had a postoperative MMT grade of 5 for knee extension without causalgia of the femoral nerve.

CONCLUSIONS

On the basis of the MEP analysis, 17 (77%) of the 22 patients showed a significant reduction of the femoral nerve amplitude despite careful placement of the retractor on the anterior wall of the acetabulum. Although this reduction appears reversible, placement of an anterior retractor should be performed with careful attention to the femoral nerve.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Do intra-operative neurophysiological changes predict functional outcome following decompressive surgery for lumbar spinal stenosis? A prospective study

Background

To analyse the relation between immediate intraoperative neurophysiological changes during decompression and clinical outcome in a series of patients with lumbar spinal stenosis (LSS) undergoing surgery.

Methods

Twenty-four patients with neurogenic intermittent claudication (NIC) due to LSS undergoing decompressive surgery were prospectively studied. Intra operative trans-cranial motor evoked potentials (tcMEPs) were recorded before and immediately after surgical decompression. Lower limb normalised tcMEP improvement was used as primary neurophysiological outcome. Clinical outcome was assessed using the Zurich Claudication Questionnaire (ZCQ) self-assessment score, before surgery (baseline) and at an average of 8 and 29 months post-operatively.

Results

We found a moderate positive correlation between tcMEP changes and ZCQ at early follow-up (R=0.36). At late follow-up no correlation was found between intra-operative tcMEP and ZCQ changes. Dichotomizing the data showed a statistically significant relationship between tcMEP improvement and better functional outcome at early follow-up (P=0.013) but not at later follow-up (P=1).

Conclusions

Our findings suggest that intra-operative neurophysiological improvement during decompressive surgery may predict a better clinical outcome at early follow-up although this is not applicable to late follow-up possibly due to the observed erosion of functional improvement with time.

Sevoflurane affects evoked electromyography monitoring in cerebral palsy

Background

To explore the effect of sevoflurane inhalation anesthesia on evoked electromyography monitoring of spinal nerve root in children associated with cerebral palsy.

Methodology

Children with cerebral palsy (n=40) were selected and further divided into 1MAC (minimum alveolar concentration) sevoflurane group and 2MAC sevoflurane group. Following the induction of anesthesia, Nicolet Endeavor-CR16 channel electrophysiological monitor was used to implement three times of successive electrical stimulation with interval of 5 sec at 3.50 mA.

Results

Our results suggested a statistical significance of amplitude retention ratio and latency in the sevoflurane inhalation time (P<0.01), with an interaction effect between the sevoflurane inhalation time and concentration for amplitude retention ratio (P<0.01), while there is no interaction effect between the sevoflurane inhalation time and concentration for latency (P>0.05). Compared to 1MAC sevoflurane group, the amplitude retention ratio of 2MAC sevoflurane group decreased remarkably (P<0.01) and the latency of 2MAC sevoflurane group extended at T3 and T4 (P<0.05 or P<0.01).

Conclusions

In evoked electromyography monitoring of spinal nerve root in children with cerebral palsy, with the increasing of concentration and duration of sevoflurane inhalation, evoked electromyogram retention ratio reduces gradually, latency extends and the retention ratio has more changes than the latency.

Repeated sugammadex reversal of muscle relaxation during lumbar spine surgery with intraoperative neurophysiological multimodal monitoring

Intraoperative neurophysiological monitoring during spine surgery is usually acomplished avoiding muscle relaxants. A case of intraoperative sugammadex partial reversal of the neuromuscular blockade allowing adequate monitoring during spine surgery is presented. A 38 year-old man was scheduled for discectomy and vertebral arthrodesis throughout anterior and posterior approaches. Anesthesia consisted of total intravenous anesthesia plus rocuronium. Intraoperatively monitoring was needed, and the muscle relaxant reverted twice with low dose sugammadex in order to obtain adequate responses. The doses of sugammadex used were conservatively selected (0.1mg/kg boluses increases, total dose needed 0.4mg/kg). Both motor evoqued potentials, and electromyographic responses were deemed adequate by the neurophysiologist. If muscle relaxation was needed in the context described, this approach could be useful to prevent neurological sequelae. This is the first study using very low dose sugammadex to reverse rocuronium intraoperatively and to re-establish the neuromuscular blockade.

Effects of Dexmedetomidine on motor- and somatosensory-evoked potentials in patients with thoracic spinal cord tumor: a randomized controlled trial

Background

We hypothesized that the addition of dexmedetomidine in a clinically relevant dose to propofol-remifentanil anesthesia regimen does not exert an adverse effect on motor-evoked potentials (MEP) and somatosensory-evoked potentials (SSEP) in adult patients undergoing thoracic spinal cord tumor resection.

Methods

Seventy-one adult patients were randomized into three groups. Propofol group (n = 25): propofol-remifentanil regimenand the dosage was adjusted to maintain the bispectral index (BIS) between 40 and 50. DP adjusted group (n = 23): Dexmedetomidine (0.5 μg/kg loading dose infused over 10 min followed by a constant infusion of 0.5 μg/kg/h) was added to the propofol-remifentanil regimen and propofol was adjusted to maintain BIS between 40 and 50. DP unadjusted group (n = 23): Dexmedetomidine (administer as DP adjusted group) was added to the propofol-remifentanil regimen and propofol was not adjusted. All patients received MEP, SSEP and BIS monitoring.

Results

There were no significant changes in the amplitude and latency of MEP and SSEP among different groups (P > 0.05). The estimated propofol plasma concentration in DP adjusted group (2.7 ± 0.3 μg/ml) was significantly lower than in propofol group (3.1 ± 0.2 μg/ml) and DP unadjusted group (3.1 ± 0.2 μg/ml) (P = 0.000). BIS in DP unadjusted group (35 ± 5) was significantly lower than in propofol group (44 ± 3) (P = 0.000).

Conclusions

The addition of dexmedetomidine to propofol-remifentanil regimen does not exert an adverse effect on MEP and SSEP monitoring in adult patients undergoing thoracic spinal cord tumor resection.

Trial registration

The study was registered with the Chinese Clinical Trial Registry on January 31st, 2014. The reference number was ChiCTR-TRC-14004229.

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.

Neuromonitoring Using Motor and Somatosensory Evoked Potentials in Aortic Surgery

BACKGROUND

Motor evoked potentials (MEP) and somatosensory evoked potentials (SSEP) are established methods of neuromonitoring aimed at preventing paraplegia after descending or thoracoabdominal aortic repair. However, their predictive impact remains controversial. The aim of this study was to evaluate our single-center experience using this monitoring technique.

METHODS

Between 2009 and 2014, 78 patients (mean age 66 ± 12, 53% male) underwent either descending or thoracoabdominal aortic repairs. Of these, 60% had an aortic aneurysm, 30% dissection, and 10% other etiologies. Intraoperatively, MEPs and SSEPs were monitored and, if necessary, clinical parameters (blood pressure, hematocrit, oxygenation) were adjusted in response to neuromonitoring signals. This analysis is focused on the neurological outcome (paraplegia, stroke) after the use of intraoperative neuromonitoring.

RESULTS

Thirty-day mortality was 10 (12.8%). All patients with continuously stable signals or signals that returned after signal loss developed no spinal cord injury, whereas two out of six of the evaluable patients with signal loss (without return) during the procedure suffered from postoperative paraplegia (one transient and one permanent). Sensitivity and specificity of use of MEP and SSEP were 100% and 94.20% regarding paraplegia, respectively.

CONCLUSIONS

(1) Preservation of signals or return of signals is an excellent prognostic indicator for spinal cord function. (2) Intraoperative modifications in direct response to the signal change may have averted permanent paralysis in the patients with signal loss without neurologic injury. We have found MEP and SSEP neuromonitoring to be instrumental in the prevention of paraplegia. doi: 10.1111/jocs.12739 (J Card Surg 2016;31:383-389).

Successful intraoperative electrophysiologic monitoring of the recurrent laryngeal nerve, a multidisciplinary approach: The Massachusetts Eye and Ear Infirmary monitoring collaborative protocol with experience in over 3000 cases

BACKGROUND

Although intraoperative nerve monitoring (IONM) is utilized increasingly, the information on the related anesthesia technique is limited. This study presents an up-to-date clinical algorithm, including setup and troubleshooting of an IONM system, endotracheal tube placement, and anesthetic parameters. To our knowledge, this is the first interdisciplinary collaborative protocol for monitored neck surgery based on the published evidence and clinical experience.

METHODS

The Departments of Otolaryngology Head and Neck Surgery, Anesthesiology, and Audiology collaboratively developed a protocol for IONM of the recurrent laryngeal nerve (RLN) based on published evidence and our experience with 3000 patients over a 16-year period.

RESULTS

No complications related to monitoring or endotracheal tube placement were noted when the IONM protocol was implemented at Massachusetts Eye and Ear Infirmary (MEEI). The IONM protocol has proven to be vital in standardizing care and in avoiding intraoperative errors.

CONCLUSION

An IONM system entails an anesthesiologist who understands the challenges posed by this technique; muscle relaxation must be minimized/eliminated to optimize IONM. © 2016 Wiley Periodicals, Inc. Head Neck 38: First-1494, 2016.

Use of Posterior Root-Muscle Reflexes in Peripheral Nerve Surgery: A Case Report

It is well established that a mixed-agent general anesthetic regimen of volatile gas and intravenous anesthetic or total intravenous anesthetic (TIVA) is required to obtain adequate transcranial motor-evoked potentials (TcMEPs) to detect and hopefully prevent injury during brain, spinal cord, and peripheral nerve surgery. But even under ideal general anesthetic conditions, TcMEPs are not always detectable in every muscle monitored, and are prone to anesthetic fade, especially when neuropathic or injured tissue is monitored. TcMEP sensitivity to general anesthesia can be especially problematic during peripheral nerve surgery where there is often only one or a few essential muscles required to provide adequate monitoring; thus, maximum fidelity is essential. However, there is an anesthetic-resistant high-fidelity modality available to successfully monitor the motor component of distant peripheral nerves originating from the cauda equina. Percutaneus transabdominal electrical stimulation elicits a relatively anesthetic-resistant, robust motor response in muscles innervated by cauda equina nerve roots. We report the successful use of posterior root-muscle (PRM) reflex to monitor the decompression of the sciatic nerve at its bifurcation in a 22-year-old female with a history of severe sciatic nerve neuropathic pain and muscle weakness following benign thigh tumor resection.

Transient and reproducible loss of motor-evoked potential signals after intravenous levetiracetam in a child undergoing craniotomy for resection of astrocytoma

Transcranial electrical motor-evoked potential (tceMEP) monitoring is used in complex intracranial and spinal surgeries to detect and prevent neurological injury. We present a case of transient, reproducible loss of tceMEPs after an infusion of levetiracetam during craniotomy and tumor resection in a child. Cessation of the infusion resulted in restoration of baseline tceMEPs. When the infusion was resumed at the end of the procedure, a similar decrease in tceMEPs was seen as before, after the infusion was stopped. The surgery and postoperative course proceeded without incident, and the patient experienced a full recovery.

Propofol: a review of its role in pediatric anesthesia and sedation

Propofol is an intravenous agent used commonly for the induction and maintenance of anesthesia, procedural, and critical care sedation in children. The mechanisms of action on the central nervous system involve interactions at various neurotransmitter receptors, especially the gamma-aminobutyric acid A receptor. Approved for use in the USA by the Food and Drug Administration in 1989, its use for induction of anesthesia in children less than 3 years of age still remains off-label. Despite its wide use in pediatric anesthesia, there is conflicting literature about its safety and serious adverse effects in particular subsets of children. Particularly as children are not "little adults", in this review, we emphasize the maturational aspects of propofol pharmacokinetics. Despite the myriad of propofol pharmacokinetic-pharmacodynamic studies and the ability to use allometrical scaling to smooth out differences due to size and age, there is no optimal model that can be used in target controlled infusion pumps for providing closed loop total intravenous anesthesia in children. As the commercial formulation of propofol is a nutrient-rich emulsion, the risk for bacterial contamination exists despite the Food and Drug Administration mandating addition of antimicrobial preservative, calling for manufacturers' directions to discard open vials after 6 h. While propofol has advantages over inhalation anesthesia such as less postoperative nausea and emergence delirium in children, pain on injection remains a problem even with newer formulations. Propofol is known to depress mitochondrial function by its action as an uncoupling agent in oxidative phosphorylation. This has implications for children with mitochondrial diseases and the occurrence of propofol-related infusion syndrome, a rare but seriously life-threatening complication of propofol. At the time of this review, there is no direct evidence in humans for propofol-induced neurotoxicity to the infant brain; however, current concerns of neuroapoptosis in developing brains induced by propofol persist and continue to be a focus of research.

Monopolar-probe monitoring during spinal surgery with expandable prosthetic ribs

BACKGROUND

Intraoperative monitoring (IOM) has been proven to decrease the risk of neurological injury during scoliosis surgery. The vertical expandable prosthetic titanium rib (VEPTR) is a device that allows spinal growth. However, injuries to the spinal cord and brachial plexus have been reported after VEPTR implantation in 2 and 5% of patients, respectively. Simultaneous monitoring of these two structures requires the use of multiple time-consuming and complex methods that are ill-suited to the requirements of paediatric surgery, particularly when repeated VEPTR lengthening procedures are needed. We developed a monopolar stimulation method derived from Owen's monitoring technique. This method is easy to implement, requires only widely available equipment, and allows concomitant monitoring of the spinal cord and brachial plexus. The primary objective of this study was to assess the reliability of our technique for brachial plexus monitoring by comparing the stability of neurogenic mixed evoked potentials (NMEPs) at the upper and lower limbs.

HYPOTHESIS

We hypothesised that the coefficients of variation (CVs) of NMEPs were the same at the upper and lower limbs.

MATERIAL AND METHODS

Twelve VEPTR procedures performed in 6 patients between 1st January 2012 and 1st September 2014 were monitored using a monopolar stimulating probe. NMEPs were recorded simultaneously at the upper and lower limbs, at intervals of 150 s. The recording sites were the elbow over the ulnar nerve and the popliteal fossa near the sciatic nerve. Wilcoxon's test for paired data was used to compare CVs of the upper and lower limb NMEPs on the same side.

RESULTS

Mean CV of NMEP amplitude at the lower limbs was 16.34% on the right and 16.67% on the left; corresponding values for the upper limbs were 18.30 and 19.75%, respectively. Mean CVs of NMEP latencies at the lower limbs were 1.31% on the right and 1.19% on the left; corresponding values for the upper limbs were 1.96 and 1.73%. The risk of type I error for a significant difference between the upper and lower limbs was 0.5843 on the right and 0.7312 on the left for NMEP amplitudes and 0.7618 on the right and 0.4987 on the left for NMEP latencies.

CONCLUSION

Using an epidural active electrode and a sternal return electrode allows simultaneous stimulation of the cervical spinal cord and brachial plexus roots. The NMEPs thus obtained are as stable (reliable) at the upper limbs as at the lower limbs. This easy-to-implement method allows simultaneous monitoring of the upper and lower limbs. It seems well suited to VEPTR procedures.

LEVEL OF EVIDENCE

IV, retrospective single-centre non-randomised study.

Early detection of pedicle screw-related spinal cord injury by continuous intraoperative neurophysiological monitoring (IONM)

Pedicle screw placement has a high risk of damaging the motor and sensory pathways due to the close proximity to the spinal cord and nerve roots. Early detection and prevention of injury can be achieved by utilizing Somatosensory Evoked Potentials (SSEP) and Transcranial electrical Motor Evoked Potentials (TCeMEP) during a scoliosis surgery. A 19-year-old female presented for correction of scoliosis. After intubation, electrodes were placed for upper and lower SSEPs, EMGs and TCeMEPs. Total intravenous anesthesia was used. Baseline SSEP and TCeMEP responses were present in all limbs. Eight pedicle screws were placed. After placing the last screw, TCeMEP signals were lost bilaterally in lower extremities. Surgery was paused. After removing all the screws TCeMEP responses returned to baseline in left lower limb but remained absent in right lower limb. A wake-up test was performed which was positive in her right leg. Blood pressure was increased and bolus of steroids was given. There was no improvement in right lower limb TCeMEP responses. Surgeon was advised to stop the surgery and proceed for MRI and follow-up. SSEP signals remained stable in all four-extremities. The surgical correction was cancelled. MRI revealed intramedullary spinal cord ischemic changes at T11. After extubation, patient was unable to move her right lower extremity with flaccid paralysis. She also complained about severe burning in her left lower extremity. The patient was taken for rehabilitation exercises. One week post-op, she was moving hip flexors and two weeks later had afull motor function, bilaterally. Real-time IONM was useful in early identification of spinal cord injury. Significant changes were seen in TCeMEP, without any change in SSEP. We highly recommend utilizing continuous TCeMEP and SSEP monitoring during pedicle screw placement for prevention of injury to the spinal cord. In this case, the patient would have been paralyzed post-operatively without the use of IONM.

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.