Effects of Anesthetic Regimens and Other Confounding Factors Affecting the Interpretation of Motor Evoked Potentials During Pediatric Spine Surgery

Intraoperative Neuromonitoring Auxiliary Significance of DNEP for MEP-positive Event During Severe Spinal Deformity Surgery

STUDY DESIGN

This was a retrospective analysis.

OBJECTIVE

The objective of this study was to assess the intraoperative neuromonitoring auxiliary significance of descending neurogenic-evoked potential (DNEP) for motor-evoked potential (MEP) during severe spinal deformity surgery when MEP-positive event occurs.

SUMMARY OF BACKGROUND DATA

MEP detection is the most widely applied neurological monitoring technique in spinal deformity surgery. MEP is quite vulnerable to anesthesia, blood pressure, and other intraoperative factors, leading to a high false-positive rate of MEP (3.2%-45.0%), which has greatly interfered with the surgical process. At present, the widely used "presence-or-absence" alarm criteria of MEP is not enough to solve the problem of false positive of MEP.

METHODS

A total of 205 cases undergoing severe spinal deformity correction were retrospectively studied. Overall, 74 MEP-positive cases were classified as 2 subgroups: DNEP (+) and DNEP (-) groups. The MEP recovery, wake-up test, and Frankle grade were used to assess the neurological functions. The perioperative and long-term neurological outcomes were assessed.

RESULTS

There were significant differences in preoperative scoliosis angle and kyphosis angle between DNEP (-) and DNEP (+) groups. Patients in DNEP (-) group showed more MEP improvement (81.5%), compared with the DNEP (+) group (53.2%). The Wake-up test showed 59.3% motor function deficit cases in DNEP (-) group, which was lower than the 87.2% in DNEP (+) group. More patients in DNEP (-) group had normal nerve function (Frankel level E) than those in DNEP (+) group immediately after surgery, as well as at follow-up.

CONCLUSIONS

MEP-positive cases with intraoperative DNEP (-) showed superior prognosis after severe spinal deformity surgery. Intraoperative DNEP could be regarded as an important quantitative tool to assist MEP to monitor neurological injury and can serve as a temporary substitution monitoring technique after MEP is lost.

Influence of hemorrhage and subsequent fluid resuscitation on transcranial motor-evoked potentials under desflurane anesthesia in a swine model

PURPOSE

Hemorrhage increases the effect of propofol and could contribute to false-positive transcranial motor-evoked potential (TcMEP) responses under total intravenous anesthesia (TIVA). We investigated the influence of hemorrhage and subsequent fluid resuscitation on TcMEPs under desflurane anesthesia.

METHODS

Sixteen swine (25.4 ± 0.4 kg) were anesthetized with a 4% end-tidal desflurane concentration (EtDes), which was incrementally increased to 6%, 8%, and 10% and then returned to 4% every 15 min. This procedure was repeated twice (baseline). After baseline measurements, animals were allocated to either the hemorrhage (n = 12) or control (n = 4) group. In the hemorrhage group, 600 ml of blood was removed and the EtDes protocol described above was applied. Hypovolemia was resuscitated using 600 ml of hydroxyethyl starch and the EtDes protocol was applied again. TcMEPs were measured at each EtDes. In the control group, measurements were performed without hemorrhage or fluid infusion.

RESULTS

TcMEP responses were observed in all conditions in all limbs with 4% EtDes (0.4 MAC). TcMEP amplitudes decreased according to the EtDes to a greater degree in the lower limbs compared with the upper limbs. Hemorrhage enhanced the effect of desflurane on TcMEP amplitudes, and decreased TcMEP by 41 ± 12% in upper limbs and 63 ± 17% in lower limbs compared with baseline. Subsequent fluid resuscitation did not reverse TcMEP amplitudes.

CONCLUSIONS

TcMEP amplitudes decrease during hemorrhage under desflurane anesthesia. This phenomenon might result from an enhanced effect of desflurane on the spinal motor pathway without increasing the desflurane concentration.

Practicalities of Total Intravenous Anesthesia and Target-controlled Infusion in Children

Propofol administered in conjunction with an opioid such as remifentanil is used to provide total intravenous anesthesia for children. Drugs can be given as infusion controlled manually by the physician or as automated target-controlled infusion that targets plasma or effect site. Smart pumps programmed with pharmacokinetic parameter estimates administer drugs to a preset plasma concentration. A linking rate constant parameter (keo) allows estimation of effect site concentration. There are two parameter sets, named after the first author describing them, that are commonly used in pediatric target-controlled infusion for propofol (Absalom and Kataria) and one for remifentanil (Minto). Propofol validation studies suggest that these parameter estimates are satisfactory for the majority of children. Recommended target concentrations for both propofol and remifentanil depend on the type of surgery, the degree of surgical stimulation, the use of local anesthetic blocks, and the ventilatory status of the patient. The use of processed electroencephalographic monitoring is helpful in pediatric total intravenous anesthesia and target-controlled infusion anesthesia, particularly in the presence of neuromuscular blockade.

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.

Establishment of a precise novel brain trauma model in a large animal based on injury of the cerebral motor cortex

BACKGROUND

Animal models are essential in simulating clinical diseases and facilitating relevant studies.

NEW METHOD

We established a precise canine model of traumatic brain injury (TBI) based on cerebral motor cortex injury which was confirmed by neuroimaging, electrophysiology, and a series of motor function assessment methods. Twelve beagles were divided into control, sham, and model groups. The cerebral motor cortex was identified by diffusion tensor imaging (DTI), a simple marker method, and intraoperative electrophysiological measurement. Bony windows were designed by magnetic resonance imaging (MRI) scan and DTI. During the operation, canines in the control group were under general anesthesia. The canines were operated via bony window craniotomy and dura mater opening in the sham group. After opening of the bony window and dura mater, the motor cortex was impacted by a modified electronic cortical contusion impactor (eCCI) in the model group.

RESULTS

Postoperative measurements revealed damage to the cerebral motor cortex and functional defects. Comparisons between preoperative and postoperative results demonstrated that the established model was successful.

COMPARISON WITH EXISTING METHOD(S)

Compared with conventional models, this is the first brain trauma model in large animal that was constructed based on injury to the cerebral motor cortex under the guidance of DTI, a simple marker method, and electrophysiology.

CONCLUSION

The method used to establish this model can be standardized to enhance reproducibility and provide a stable and precise large animal model of TBI for clinical and basic research.

Recent technological advances in pediatric brain tumor surgery

X-rays and ventriculograms were the first imaging modalities used to localize intracranial lesions including brain tumors as far back as the 1880s. Subsequent advances in preoperative radiological localization included computed tomography (CT; 1971) and MRI (1977). Since then, other imaging modalities have been developed for clinical application although none as pivotal as CT and MRI. Intraoperative technological advances include the microscope, which has allowed precise surgery under magnification and improved lighting, and the endoscope, which has improved the treatment of hydrocephalus and allowed biopsy and complete resection of intraventricular, pituitary and pineal region tumors through a minimally invasive approach. Neuronavigation, intraoperative MRI, CT and ultrasound have increased the ability of the neurosurgeon to perform safe and maximal tumor resection. This may be facilitated by the use of fluorescing agents, which help define the tumor margin, and intraoperative neurophysiological monitoring, which helps identify and protect eloquent brain.

Change in body surface temperature as an ancillary measurement to motor evoked potentials

STUDY DESIGN

Experimental study.

OBJECTIVES

To study the role of surface temperature as an adjunct to motor evoked potentials (MEPs) in rabbit spinal cord injury (SCI) model.

SETTING

Department of Orthopedics, Korea University Guro Hospital, Seoul, Korea.

METHODS

Rabbits (n =18) were divided into Complete (n = 9) and Incomplete (n = 9) SCI groups. Complete SCI was defined as being non-responsive to a wake-up test with loss of MEPs after transection of spinal cord. Incomplete SCI was defined as being responsive to a wake-up test with significant attenuation (⩾ 80%) of MEPs after impaction on spinal cord. Surface temperature of upper and lower extremities, core temperature and MEPs signals were checked before, during and after SCI for 20 min. A wake-up test was conducted and spinal cord was histologicaly evaluated.

RESULTS

Experimental conditions between the two groups were statistically similar (P > 0.005 for all values). After SCI, upper extremity temperatures did not change in either group (P > 0.005); however, the surface temperature of the lower extremities in the Complete SCI Group elevated to 1.7 ± 0.5°C in comparison to 0.5 ± 0.1°C in the Incomplete SCI Group (P < 0.001). The scores of wake-up test in the Incomplete SCI Group were significantly different from that of the Complete SCI Group (P < 0.001), while white and gray matter damage was variable on histology.

CONCLUSIONS

Monitoring of changes of body surface temperature of the lower extremities can be potentially used to identify the completeness of SCI in a rabbit model.

Fundamentals of clinical outcomes assessment for spinal disorders: study designs, methodologies, and analyses

Study Design A broad narrative review. Objective Management of spinal disorders is continuously evolving, with new technologies being constantly developed. Regardless, assessment of patient outcomes is key in understanding the safety and efficacy of various therapeutic interventions. As such, evidence-based spine care is an essential component to the armamentarium of the spine specialist in an effort to critically analyze the reported literature and execute studies in an effort to improve patient care and change clinical practice. The following article, part one of a two-part series, is meant to bring attention to the pros and cons of various study designs, their methodological issues, as well as statistical considerations. Methods An extensive review of the peer-reviewed literature was performed, irrespective of language of publication, addressing study designs and their methodologies as well as statistical concepts. Results Numerous articles and concepts addressing study designs and their methodological considerations as well as statistical analytical concepts have been reported. Their applications in the context of spine-related conditions and disorders were noted. Conclusion Understanding the fundamental principles of study designs and their methodological considerations as well as statistical analyses can further advance and improve future spine-related research.

Is hemifacial spasm a phenomenon of the central nervous system? --The role of desflurane on the lateral spread response

OBJECTIVE

A signature EMG feature of hemifacial spasm (HFS) is the lateral spread response (LSR). Desflurane is a common anesthetic with potent effects on synaptic transmission. We tested the hypothesis that the LSR is mediated by corticobulbar components by comparing the LSR during total intravenous anesthesia (TIVA) or TIVA plus desflurane during microvascular decompression (MVD) surgery.

METHODS

22 HFS patients undergoing MVD surgery participated in this prospective study. The LSR data was recorded from the o. oculi, o. oris and mentalis muscles prior to opening dura. LSR onset latencies and amplitudes were determined under TIVA and TIVA/desflurane (0.5 and 1MAC). Facial muscle LSRs and EEG were analyzed.

RESULTS

Desflurane (1MAC) significantly decreased the LSR amplitude in all 3 facial muscles (p<0.01). Pooled LSR data from all facial muscles showed desflurane inhibited the LSR amplitude by 43% compared to TIVA (p<0.001). No effects on the latency of the LSR or on EEG state were observed.

CONCLUSIONS

LSR inhibition by desflurane suggests a central mechanism involvement in the genesis of this signature HFS response.

SIGNIFICANCE

This study demonstrates that facial nerve vascular compression and plastic changes within the CNS are part of the pathophysiology of HFS.

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.