Neurophysiological Detection of Impending Spinal Cord Injury During Scoliosis Surgery

Neuromonitoring changes in pediatric spinal deformity surgery: a single-institution experience

OBJECT

Intraoperative monitoring of the spinal cord has become the standard of care during surgery for pediatric spinal deformity correction. The use of both somatosensory and motor evoked potentials has dramatically increased the sensitivity and specificity of detecting intraoperative neurophysiological changes to the spinal cord, which assists in the intraoperative decision-making process. The authors report on a large, single-center experience with neuromonitoring changes and outline the surgical management of patients who experience significant neuromonitoring changes during spinal deformity correction surgery.

METHODS

The authors conducted a retrospective review of all cases involving pediatric patients who underwent spinal deformity correction surgery at Shriners Hospital for Children, Philadelphia, between January 2007 and March 2010. Five hundred nineteen consecutive cases were reviewed in which neuromonitoring was used, with 47 cases being identified as having significant changes in somatosensory evoked potentials, motor evoked potentials, or both. These cases were reviewed for patient demographic data and surgical characteristics.

RESULTS

The incidence of significant neuromonitoring changes was 9.1% (47 of 519 cases), including 6 cases of abnormal Stagnara wake-up tests, of which 4 had corroborated postoperative neurological deficits (8.5% of 47 cases, 0.8% of 519). In response to neuromonitoring changes, wake-up tests were performed in 37 (79%) of 47 cases, hardware was adjusted in 15 (32%), anesthesiology interventions were reported in 5 (11%), hardware was removed in 5 (11%), the patient was successfully repositioned in 3 (6%), and the procedure was aborted in 13 (28%). In 1 of the 4 patients with new postoperative deficits, the deficit had fully resolved by the last follow-up; the other 3 patients had persistent neurological impairment as of the most recent follow-up examination. The authors observed a sensitivity of 100% for intraoperative neuromonitoring.

CONCLUSIONS

Due to the profound risks associated with spinal deformity surgery, intraoperative neurophysiological monitoring is an integral tool to warn of impending spinal cord injury. Intraoperative neuromonitoring appears to provide a safe and useful warning mechanism to minimize spinal cord injury that may arise during scoliosis correction surgery in pediatric patients.

Effect of dexmedetomidine-etomidate-fentanyl combined anesthesia on somatosensory- and motor-evoked potentials in patients undergoing spinal surgery

This aim of the present study was to evaluate the effects of dexmedetomidine (DEX) on the intraoperative monitoring of somatosensory-evoked potentials (SEPs) and motor-evoked potentials (MEPs) in patients undergoing spinal surgery. A total of 36 patients who received spinal surgery under general anesthesia were randomly divided into two groups (n=18 per group), group C, the test group and group D, the control group, and these groups were subjected to a matching anesthesia induction. In brief, the anesthesia was administered via injection of etomidate and fentanyl; once the patients were unconscious, a laryngeal mask airway (LMA) was inserted, SEPs and MEPs were monitored and the collected data were considered to be basic data. Cisatracurium was subsequently injected and an endotracheal tube (7#) was inserted to replace the LMA. The following procedures were conducted for anesthesia maintenance: Group C, the anesthesia was maintained via target-controlled infusion of etomidate and intermittent injection of fentanyl; and group D, DEX (0.5 μg/kg) was injected over a duration of 10 min and then pumped at a rate of 0.5 μg/kg/h. In the two groups, all of the other drugs used were the same and a muscle relaxant was not administered. The bispectral index was maintained between 45 and 55 during surgery, and the SEPs and MEPs were monitored continuously until the surgery was completed. No significant difference in duration and amplitude of the SEPs (P15-N20) was identified between group C and D (P>0.05). Furthermore, the MEPs were monitored in the two groups at specific durations and no significant difference was observed between the two groups (P>0.05). The SEPs and MEPs were maintained in the patients who were administered with the DEX-etomidate-fentanyl combined anesthesia during spinal surgery.

A prospective evaluation of hemodynamic management in acute spinal cord injury patients

STUDY DESIGN

Prospective observational study of acute spinal cord-injured (SCI) patients.

OBJECTIVES

To determine how effectively mean arterial blood pressure (MAP) and spinal cord perfusion pressure (SCPP) are maintained at target levels in acute SCI patients.

SETTING

Single-institution study at a Canadian level-one trauma center.

METHODS

Twenty-one individuals with cervical or thoracic SCI were enrolled within 48 h of injury. A lumbar intrathecal drain was inserted for monitoring intrathecal cerebrospinal fluid pressure (ITP). The MAP was monitored concurrently with ITP, and the SCPP was calculated. Data was recorded hourly from the time of first assessment until at least the end of the 5th day post injury.

RESULTS

All subjects had at least one recorded episode with a MAP below 80 mm Hg, and 81% had at least one episode with a MAP below 70 mm Hg. On average, subjects with cervical injuries had 18.4% of their pressure recordings below 80 mm Hg. Subjects with thoracic cord injuries had on average 35.9% of their MAP recordings <80 mm Hg.

CONCLUSION

It is common practice to establish MAP targets for optimizing cord perfusion in acute SCI. This study suggests that even in an acute SCI referral center, when prospectively scrutinized, the actual MAP may frequently fall below the intended targets. Such results raise awareness of the vigilance that must be kept in the hemodynamic management of these patients, and the potential discrepancy between routinely setting target MAP according to 'practice guidelines' and actually achieving them.

Effect of Hemorrhage and Hypotension on Transcranial Motor-evoked Potentials in Swine

Background:

Transcranial motor-evoked potentials (TcMEPs) monitor spinal cord motor tract integrity. Using a swine model, the authors studied the effects of vasodilatory hypotension, hemorrhage, and various resuscitation efforts on TcMEP responses.

Methods:

Twelve pigs were anesthetized with constant infusions of propofol, ketamine, and fentanyl. Animals were incrementally hemorrhaged, until bilateral tibialis anterior TcMEP amplitude decreased to less than 40% of baseline or until 50% of the blood volume was removed. Mean arterial pressure (MAP), cardiac output (CO), and oxygen delivery (DO2) were examined. Resuscitation with phenylephrine, epinephrine, and colloid were evaluated. In seven animals, vasodilatory hypotension was examined. Paired comparisons and multivariate analysis were performed.

Results:

Hemorrhage significantly reduced (as a percentage of baseline, mean ± SD) TcMEPs (left, 33 ± 29%; right, 26 ± 21%), MAP (60 ± 17%), CO (49 ± 12%), and DO2 (43 ± 13%), P value less than 0.001 for all. Vasodilation reduced MAP comparably, but TcMEPs, CO, and DO2, were not significantly lowered. After hemorrhage, restoration of MAP with phenylephrine did not improve TcMEPs, CO, or DO2, but similar restoration of MAP with epinephrine restored (to percentage of baseline) TcMEPs (59 ± 40%), and significantly increased CO (81 ± 17%) and DO2 (72 ± 19%) compared with both hemorrhage and phenylephrine, P value less than 0.05 for all. Resuscitation with colloid did not improve TcMEPs. Multivariate analysis revealed that changes in TcMEPs were more closely associated with changes in CO and DO2 as compared with MAP.

Conclusions:

Hypotension from hemorrhage, but not vasodilation, is associated with a decrease in TcMEP amplitude. After hemorrhage, restoration of TcMEPs with epinephrine but not phenylephrine indicates that CO and DO2 affect TcMEPs more than MAP. Monitoring CO may be beneficial in major spine surgery when using TcMEP monitoring.

Efficacy of intraoperative monitoring of transcranial electrical stimulation–induced motor evoked potentials and spontaneous electromyography activity to identify acute-versus delayed-onset C-5 nerve root palsy during cervical spine surgery

Object

Deltoid muscle weakness due to C-5 nerve root injury following cervical spine surgery is an uncommon but potentially debilitating complication. Symptoms can manifest upon emergence from anesthesia or days to weeks following surgery. There is conflicting evidence regarding the efficacy of spontaneous electromyography (spEMG) monitoring in detecting evolving C-5 nerve root compromise. By contrast, transcranial electrical stimulation–induced motor evoked potential (tceMEP) monitoring has been shown to be highly sensitive and specific in identifying impending C-5 injury. In this study the authors sought to 1) determine the frequency of immediate versus delayed-onset C-5 nerve root injury following cervical spine surgery, 2) identify risk factors associated with the development of C-5 palsies, and 3) determine whether tceMEP and spEMG neuromonitoring can help to identify acutely evolving C-5 injury as well as predict delayed-onset deltoid muscle paresis.

Methods

The authors retrospectively reviewed the neuromonitoring and surgical records of all patients who had undergone cervical spine surgery involving the C-4 and/or C-5 level in the period from 2006 to 2008. Real-time tceMEP and spEMG monitoring from the deltoid muscle was performed as part of a multimodal neuromonitoring protocol during all surgeries. Charts were reviewed to identify patients who had experienced significant changes in tceMEPs and/or episodes of neurotonic spEMG activity during surgery, as well as those who had shown new-onset deltoid weakness either immediately upon emergence from the anesthesia or in a delayed fashion.

Results

Two hundred twenty-nine patients undergoing 235 cervical spine surgeries involving the C4–5 level served as the study cohort. The overall incidence of perioperative C-5 nerve root injury was 5.1%. The incidence was greatest (50%) in cases with dual corpectomies at the C-4 and C-5 spinal levels. All patients who emerged from anesthesia with deltoid weakness had significant and unresolved changes in tceMEPs during surgery, whereas only 1 had remarkable spEMG activity. Sensitivity and specificity of tceMEP monitoring for identifying acute-onset deltoid weakness were 100% and 99%, respectively. By contrast, sensitivity and specificity for spEMG were only 20% and 92%, respectively. Neither modality was effective in identifying patients who demonstrated delayed-onset deltoid weakness.

Conclusions

The risk of new-onset deltoid muscle weakness following cervical spine surgery is greatest for patients undergoing 2-level corpectomies involving C-4 and C-5. Transcranial electrical stimulation–induced MEP monitoring is a highly sensitive and specific technique for detecting C-5 radiculopathy that manifests immediately upon waking from anesthesia. While the absence of sustained spEMG activity does not rule out nerve root irritation, the presence of excessive neurotonic discharges serves both to alert the surgeon of such potentially injurious events and to prompt neuromonitoring personnel about the need for additional tceMEP testing. Delayed-onset C-5 nerve root injury cannot be predicted by intraoperative neuromonitoring via either modality.

Effects of vertebral column distraction on transcranial electrical stimulation-motor evoked potential and histology of the spinal cord in a porcine model

BACKGROUND

Spinal cord injury can occur following surgical procedures for correction of scoliosis and kyphosis, as these procedures produce lengthening of the vertebral column. The objective of this study was to cause spinal cord injury by vertebral column distraction and evaluate the histological changes in the spinal cord in relationship to the pattern of recovery from the spinal cord injury.

METHODS

Global osteotomy of all three spinal columns was performed on the ninth thoracic vertebra of sixteen pigs. The osteotomized vertebra was distracted until transcranial electrical stimulation-motor evoked potential (TES-MEP) signals disappeared or decreased by >80% compared with the baseline amplitude; this was defined as spinal cord injury. The distraction distance at which spinal cord injury occurred was measured, the distraction was released, and the TES-MEP recovery pattern was observed. A wake-up test was performed, two days of observations were made, and histological changes were evaluated in relationship to the recovery pattern.

RESULTS

Spinal cord injury developed at a distraction distance of 20.2 ± 4.7 mm, equivalent to 3.6% of the thoracolumbar spinal length, and the distraction distance was correlated with the thoracolumbar spinal length (r = 0.632, p = 0.009). No animals exhibited complete recovery according to TES-MEP testing, eleven exhibited incomplete recovery, and five exhibited no recovery. During the two days of observation, all eleven animals with incomplete recovery showed positive responses to sensory and motor tests, whereas none of the five animals with no recovery had positive responses. On histological evaluation, three animals that exhibited no recovery all showed complete severance of nerve fibers (axotomy), whereas six animals that exhibited incomplete recovery all showed partial white-matter injury.

CONCLUSIONS

Parallel distraction of approximately 3.6% of the thoracolumbar length after global osteotomy resulted in spinal cord injury and histological evidence of spinal cord damage. The pattern of recovery from the spinal cord injury after release of the distraction was consistent with the degree of axonal damage. Axotomy was observed in animals that exhibited no recovery on TES-MEP, and only hemorrhagic changes in the white matter were observed in animals that exhibited incomplete recovery.

Intraoperative neurophysiological monitoring in spine surgery: indications, efficacy, and role of the preoperative checklist

Spine surgery carries an inherent risk of damage to critical neural structures. Intraoperative neurophysiological monitoring (IONM) is frequently used to improve the safety of spine surgery by providing real-time assessment of neural structures at risk. Evidence-based guidelines for safe and efficacious use of IONM are lacking and its use is largely driven by surgeon preference and medicolegal issues. Due to this lack of standardization, the preoperative sign-in serves as a critical opportunity for 3-way discussion between the neurosurgeon, anesthesiologist, and neuromonitoring team regarding the necessity for and goals of IONM in the ensuing case. This analysis contains a review of commonly used IONM modalities including somatosensory evoked potentials, motor evoked potentials, spontaneous or free-running electromyography, triggered electromyography, and combined multimodal IONM. For each modality the methodology, interpretation, and reported sensitivity and specificity for neurological injury are addressed. This is followed by a discussion of important IONM-related issues to include in the preoperative checklist, including anesthetic protocol, warning criteria for possible neurological injury, and consideration of what steps to take in response to a positive alarm. The authors conclude with a cost-effectiveness analysis of IONM, and offer recommendations for IONM use during various forms of spine surgery, including both complex spine and minimally invasive procedures, as well as lower-risk spinal operations.

Concurrent tethered cord release and growing-rod implantation-is it safe?

Study Design Retrospective case series from one institution with a comparison control group. Objective To evaluate the safety of concomitant tethered cord release and growing-rod insertion in individuals with early onset scoliosis. Methods We retrospectively reviewed patients who underwent concurrent tethered cord release and growing-rod insertion. We compared our data to a comparison control group of eight patients who underwent staged tethered cord release and growing-rod insertion. Results We identified three patients meeting criteria. There were no neurological complications in the three patients who underwent concomitant surgery. Average immediate postoperative curve correction was 43.3 degrees (47.6%). We identified seven patients who underwent staged surgery from a multicenter prospective database. No neurological complications were reported, and average immediate postoperative correction was 35.1 degrees (46.2%). Conclusion We believe that concurrent tethered cord release and growing-rod insertion can be performed safely with the use of multimodality neurophysiological monitoring techniques.

Intraoperative neurophysiologic monitoring: are we really that bad?

STUDY DESIGN

Retrospective review of a prospectively collected, multicenter database.

OBJECTIVE

To assess the rates of new neurologic deficit (NND) associated with spine surgery.

SUMMARY OF BACKGROUND DATA

New neurologic deficit is a potential complication of spine surgery but previously reported rates are often limited by small sample size and single-surgeon experiences.

METHODS

The Scoliosis Research Society morbidity and mortality database was queried for spinal surgery cases complicated by NND from 2004 to 2007, including nerve root deficit, cauda equina deficit, and spinal cord deficit. Use of neuromonitoring was assessed. Recovery was stratified as complete, partial, or none. Rates of NND were stratified based on diagnosis, age (pediatric, <21 years; adult, ≥21 years), and surgical parameters.

RESULTS

Of the 108,419 cases reported, NND was documented for 1,064 (1.0%), including 662 nerve root deficits, 74 cauda equina deficits, and 293 spinal cord deficits (deficit not specified for 35 cases). Rates of NND were calculated on the basis of diagnosis. Revision cases had a 41% higher rate of NND (1.25%) compared with primary cases (0.89%; P < 0.001). Pediatric cases had a 59% higher rate of NND (1.32%) compared with adult cases (0.83%; P < 0.001). The rate of NND for cases with implants was more than twice that for cases without implants (1.15% vs. 0.52%; P < 0.001). Neuromonitoring was used for 65% of cases, and for cases with new nerve root deficit, cauda equina deficit, and spinal cord deficit, changes in neuromonitoring were reported in 11%, 8%, and 40%, respectively. The respective percentages of no recovery, partial, and complete recovery for nerve root deficit were 4.7%, 46.8%, and 47.1%, respectively; for cauda equina deficit, they were 9.6%, 45.2%, and 45.2%, respectively; and for spinal cord deficit, the percentages were 10.6%, 43%, and 45.7%, respectively.

CONCLUSION

Our data demonstrate that even among skilled spinal deformity surgeons, NNDs are inherent potential complications of spine surgery. These data provide general benchmark rates for NND with spine surgery as a basis for patient counseling and for ongoing efforts to improve safety of care.

Spinal cord infarction remote from maximal compression in a patient with Morquio syndrome

Morquio syndrome, or mucopolysaccharidosis type IV, is a rare enzyme deficiency disorder and results in skeletal dysplasia. Odontoid dysplasia is common among affected patients, resulting in atlantoaxial instability and spinal cord compression. Surgical treatments include decompression and prophylactic fusion, during which intraoperative neuromonitoring is important to alert the surgical team to changes in cord function so that they can prevent or mitigate spinal cord injury. This report describes a 16-year-old girl with Morquio syndrome who developed paraplegia due to thoracic spinal cord infarction during foramen magnum and atlantal decompression. This tragic event demonstrates the following: 1) that patients with Morquio syndrome are at risk for ischemic spinal cord injury at levels remote from areas of maximal anatomical compression while under anesthesia in the prone position, possibly due to impaired cardiac output; 2) the significance of absent motor evoked potential responses in the lower limbs with preserved upper-limb responses in an ambulatory patient; 3) the importance of establishing intraoperative neuromonitoring baseline assessments prior to turning patients to the prone position following induction of anesthesia; and 4) the importance of monitoring cardiac output during prone positioning in patients with chest wall deformity.

Effects of intrathecal morphine on transcranial electric motor-evoked potentials in adolescents undergoing posterior spinal fusion

BACKGROUND

Intrathecal morphine (ITM) provides effective analgesia after posterior spinal fusion (PSF). Although most anesthetic drugs have well-characterized effects on evoked potentials, there is little data on the effects of ITM on transcranial electric motor-evoked potentials (tceMEPs). We performed this study to assess the effects of ITM on tceMEPs in the first 30 minutes after administration. We hypothesized that administration of ITM in doses currently used at our institution would not significantly affect mean tceMEP amplitudes and latencies of an ITM study group relative to control patients who did not receive the drug.

METHODS

tceMEPs were recorded before ITM injection and 5, 10, 20, and 30 minutes after injection in 14 subjects ages 11 through 18 years undergoing PSF. These recordings were compared to an age-matched control group undergoing PSF in which ITM was not injected. The effects of ITM on tceMEP amplitude and latency were compared between the 2 groups.

RESULTS

Fourteen subjects were enrolled in the ITM group and 16 served as controls. There were no significant differences in the baseline mean response amplitudes of the 2 groups for any of the 8 muscles studied. Mean response amplitudes over the 30-minute posttreatment period in the ITM group did not differ significantly from those of the control subjects. Average response amplitudes collapsed across all muscles for each subject were not significantly different during the baseline period (95% CI = -38% to 45%; P = 0.783), nor were they significantly different between the 2 groups during the posttreatment period (95% CI = -30% to 78%; P = 0.640). There also were no significant differences in the mean response latencies of the 2 groups in either the baseline or posttreatment periods. Average response latencies collapsed across all muscles for each subject were 4% larger for the ITM group than for controls during the baseline period (95% CI = -5% to 13%; P = 0.377), and 3% larger for the ITM group than for controls during the posttreatment period (95% CI = -4% to 12%; P = 0.359).

CONCLUSIONS

Administration of ITM in doses currently used at our institution did not cause more than a 70% attenuation of mean tceMEP amplitudes or latency changes of an ITM study group relative to control subjects during the 30-minute period after injection. Further studies are required to determine if there are delayed effects after this initial time period.

The effects of spinal cord injury induced by shortening on motor evoked potentials and spinal cord blood flow: an experimental study in Swine

BACKGROUND

Spinal cord injury due to spinal shortening is disastrous, but the amount that the spine can be shortened without injury is unknown. We assessed spinal cord injury and changes in spinal cord blood flow after spinal shortening in swine.

METHODS

Ten pigs underwent pedicle screw instrumentation between T10 and T13 followed by a T11 and T12 vertebrectomy resulting in spinal shortening. Spinal cord function and spinal cord blood flow were monitored simultaneously with use of transcranial motor evoked potentials and laser Doppler flowmetry, respectively. A staged shortening procedure was performed: phase 1 resulted in no morphological change in the spinal cord, phase 2 resulted in buckling of the spinal cord, and phase 3 resulted in kinking of the spinal cord. After loss of motor evoked potential signals, which was considered to indicate spinal cord injury, the spinal instrumentation was tightened. The motor evoked potentials and spinal cord blood flow were monitored for an additional thirty minutes, and a wake-up test was then performed. Finally, a spinal cord specimen was obtained and evaluated histologically.

RESULTS

The motor evoked potential data demonstrated no evidence of spinal cord injury during phases 1 and 2. However, the signals were lost during phase 3, indicating spinal cord injury. The mean shortening was 35 ± 2.7 mm, which was similar to the mean vertebral body height at the thoracolumbar level (33.6 ± 1.9 mm), indicating that spinal cord injury resulted from shortening equivalent to the height of one vertebra. Spinal shortening did not cause injury if the amount of shortening was less than the mean segmental height of the entire spinal column (27.7 ± 1.6 mm for T1-L6). The spinal cord blood flow increased slightly (by 11.6% ± 20.6%) during phase 2, but decreased by 43.1% ± 11.4% during phase 3. The wake-up test performed after thirty minutes revealed no movement in the lower limbs.

CONCLUSIONS

Spinal shortening of =104.2% of one vertebral body height at the thoracolumbar level caused spinal cord injury, but shortening of =73.8% did not result in injury. swine.

Somatosensory Evoked Potential Monitoring During Endoscopic Endonasal Approach to Skull Base Surgery: Analysis of Observed Changes

BACKGROUND:

Intraoperative neurophysiological monitoring, including upper- and lower-extremity somatosensory evoked potentials (SSEPs), has been used to identify and prevent injury to neurovascular structures during conventional skull base surgery. The expanded endonasal approach (EEA) is a novel minimally invasive approach to skull base surgery. However, it carries the risk of injury to neurovascular structures, including the internal carotid artery, anterior cerebral artery, and cranial nerves.

OBJECTIVE:

To evaluate the value of SSEP monitoring to predict and/or prevent neurovascular deficits during EEA to skull base surgery.

METHODS:

We retrospectively identified 999 consecutive patients who had intraoperative neurophysiological monitoring during EEA skull base surgery at our institution. A total of 976 patients had SSEP monitoring and a documented postoperative neurological examination.

RESULTS:

The incidence of changes in SSEP during the procedure was 20 of 976 (2%). The incidence of new postoperative neurological deficits was 5 of 976 (0.5%). The positive and negative predictive values of SSEPs during EEA to predict neurovascular deficits were 80.00% and 99.79%, respectively.

CONCLUSION:

Intraoperative SSEP monitoring was able to identify impending risk to neurovascular structures to prevent permanent postoperative neurological deficits. We advocate a comprehensive approach to neurophysiological monitoring during EEAs, including SSEPs, spontaneous and triggered electromyography of the cranial nerves III through XII, brainstem auditory evoked potentials, and electroencephalogram, depending on the surgical approach and location of the neural structures at risk.

Impact of multimodal intraoperative monitoring during correction of symptomatic cervical or cervicothoracic kyphosis

OBJECT

surgical correction of symptomatic cervical or cervicothoracic kyphosis involves the potential for significant neurological complications. Intraoperative monitoring has been shown to reduce the risk of neurological injury in scoliosis surgery, but it has not been well evaluated during surgery for cervical or cervicothoracic kyphosis. In this article, the authors review a cohort of patients who underwent kyphosis correction with multimodal intraoperative monitoring (MIOM).

METHODS

twenty-nine patients were included in the study. Preoperative and postoperative Cobb angles were measured to determine the extent of correction. Multimodal intraoperative monitoring consisted of somatosensory evoked potentials, transcranial motor evoked potentials (tMEPs), and electromyography activity. Sensitivity, specificity, positive predictive values (PPVs), and negative predictive values (NPVs) were assessed for each monitoring modality.

RESULTS

the mean patient age was 58.0 years, and 20 patients were female. The mean pre- and postoperative sagittal Cobb angles were 41.3° and 7.3°, respectively. A total of 8 intraoperative monitoring alerts were observed. Transcranial MEPs yielded a sensitivity of 75%, specificity of 84%, PPV of 43%, and NPV of 95%. Somatosensory evoked potentials had a sensitivity of 25%, specificity of 96%, PPV of 50%, and NPV of 88%. Electromyography resulted in a sensitivity of 0%, specificity of 93%, PPV of 0%, and NPV of 96%. Changes in tMEPs led to successful intervention in 2 cases. There was 1 case in which a C-8 palsy occurred without any changes in MIOM.

CONCLUSIONS

in contrast to sensitivity and PPV, specificity and NPV were generally high in all 3 monitoring modalities. Both false-positive and false-negative results occurred. Transcranial MEP monitoring was the most useful modality and appeared to allow successful intervention in certain cases. Larger, prospective comparative studies are necessary to determine whether MIOM truly decreases the rate of neurological complications and is therefore worth the added economic cost and intraoperative time.

A Multi-Centre Multi-National Survey of Anaesthetists Regarding the Range of Anaesthetic and Surgical Practices for Paediatric Scoliosis Surgery

Institutional responses to a detailed multi-national survey were used to characterise the range of current anaesthetic and surgical practices for paediatric scoliosis surgery. Questions addressed surgical practice, anaesthetic agents, blood-sparing techniques, neurophysiological monitoring used and recalled major complications. Twenty-seven (87%) institutions responded. The median number of cases of these institutions was 40 per year (range 5 to 700). Common practices included inhaled volatile anaesthetic maintenance (80%), omission of nitrous oxide (81%), intravenous remifentanil (88% [range 0.05 to 2.00 μg.kg-1.min-1]), and double intravenous antiemetic agent prophylaxis (59%); multimodal analgesia with paracetamol and parenteral opioids, non-steroidal anti-inflammartory drugs and epidural local anaesthetic or opioid infusion (UK) and intrathecal opioids and sub-anaesthetic doses of intravenous ketamine by infusion (Australia); use of cell-saver (81%), controlled hypotension (77%) and antifibrinolytic agents (74%) (intravenous aprotinin [59%] or tranexamic acid [44%]); and epidural somatosensory (92%), neurogenic motor-evoked (32%), compound motor action (31%) and transcranial motor-evoked potential monitoring (54%), with routine wake-up test used infrequently (19%). Fifty-four neurological or cardiac adverse events or deaths were recalled. While institutional practices varied, common themes were identified. The information obtained may suggest new strategies to various centres and could be useful for planning multi-centre audits and trials.

Hospital cost analysis of adolescent idiopathic scoliosis correction surgery in 125 consecutive cases

BACKGROUND

Although achieving clinical success is the main goal in the surgical treatment of adolescent idiopathic scoliosis, it is becoming increasingly important to do so in a cost-effective manner. The goal of the present study was to determine the surgical and hospitalization costs, charges, and reimbursements for adolescent idiopathic scoliosis correction surgery at one institution.

METHODS

We performed a retrospective review of 16,536 individual costs and charges, including overall reimbursements, for 125 consecutive patients who were managed surgically for the treatment of adolescent idiopathic scoliosis by three different surgeons between 2006 and 2007. Demographic, surgical, and radiographic data were recorded for each patient. Stepwise multiple linear regression analysis was employed to assess independent correlation with total cost and charge. Nonparametric descriptive statistics were calculated for total cost with use of the Lenke curve-classification system.

RESULTS

The mean age of the patients was 15.2 years. The mean main thoracic curve measured 50 degrees, and the thoracolumbar curve measured 41 degrees. The cost varied with Lenke curve type: $29,955 for type 1, $31,414 for type 2, $31,975 for type 3, $60,754 for type 4, $32,652 for type 5, and $33,416 for type 6. Independently significant increases for total cost were found in association with the number of pedicle screws placed, the total number of vertebral levels fused, and the type of surgical approach (R(2) = 0.35, p <or= 0.03). Independently significant increases for reimbursement were found in association with the number of pedicle screws placed and the type of surgical approach (R(2) = 0.12, p <or= 0.02). The hospital was reimbursed 53% of total charges and 120% of total costs. Reimbursement was highly correlated with charge (r = 0.45, p < 0.001). For rehospitalizations, the hospital was reimbursed 65% of charges and 93% of costs.

CONCLUSIONS

The largest contributors to overall cost were implants (29%), intensive care unit and inpatient room costs (22%), operating room time (9.9%), and bone grafts (6%). There were three significant independent predictors of increased total cost: the surgical approach used, the number of pedicle screws placed, and the number of vertebral levels fused. This study characterizes the relative contributions of factors that contribute to total costs, charges, and reimbursements that can, in time, identify potential areas for cost reduction or redistribution of resources in the surgical treatment of adolescent idiopathic scoliosis.

Intraoperative neurophysiological monitoring during complex spinal deformity cases in pediatric patients: methodology, utility, prognostication, and outcome

INTRODUCTION

Complex spinal deformity (CSD) problems in pediatric patients result from a wide variety of congenital, acquired, neoplastic, or traumatic abnormalities that result in a combination of spinal deformity and spinal cord impingement. While these problems are rare, decompression, correction, instrumentation, and fusion are quite hazardous. Intraoperative neurophysiological monitoring (IONM) seems particularly beneficial in these patients.

METHODOLOGY

Somatosensory evoked potentials, transcranial electrical motor evoked potentials (MEPs), direct waves, and electromyography were used in a variety of CSD cases over a period when IONM was routine for most spinal cases. Examples of cases in which IONM provided important intraoperative information and significantly affected the course of the operation are illustrated.

RESULTS

IONM is a useful tool particularly in CSD cases in pediatric patients but requires special expertise and anesthetic considerations. Loss of MEP appears to have particularly important adverse prognostic information. Conversely, maintenance of IONM provides significant reassurance that the spinal cord function is being maintained. Preserved but persistently diminished MEPs usually predict a neurological injury that will significantly improve and possibly completely recover. Issues concerning training, certification, oversight, standardization of equipment, and technique are partially but incompletely resolved.

DISCUSSION

IONM is an extremely valuable tool for management of CSD pediatric patients. The utility of IONM is such and the detection of unexpected or unanticipated neurological injury frequent enough that a strong argument that it be used in every spinal surgery case can be made.

Intramedullary spinal cord tumor surgery: can we do it without intraoperative neurophysiological monitoring?

OBJECTIVE

The objective of this review is to discuss the utilization of intraoperative neurophysiological monitoring (IONM) during spinal cord tumor surgery.

DISCUSSION

The literature generally supports the use of intraoperative monitoring during surgery for spinal cord lesions.

CONCLUSION

We argue that IONM should be the standard of care for the treatment of such pathology, and a number of issues supporting this argument are discussed.

Multimodal intraoperative neuromonitoring in corrective surgery for adolescent idiopathic scoliosis: Evaluation of 354 consecutive cases

BACKGROUND

Multimodal intraoperative neuromonitoring is recommended during corrective spinal surgery, and has been widely used in surgery for spinal deformity with successful outcomes. Despite successful outcomes of corrective surgery due to increased safety of the patients with the usage of spinal cord monitoring in many large spine centers, this modality has not yet achieved widespread popularity. We report the analysis of prospectively collected intraoperative neurophysiological monitoring data of 354 consecutive patients undergoing corrective surgery for adolescent idiopathic scoliosis (AIS) to establish the efficacy of multimodal neuromonitoring and to evaluate comparative sensitivity and specificity.

MATERIALS AND METHODS

The study group consisted of 354 (female = 309; male = 45) patients undergoing spinal deformity corrective surgery between 2004 and 2008. Patients were monitored using electrophysiological methods including somatosensory-evoked potentials and motor-evoked potentials simultaneously.

RESULTS

Mean age of patients was 13.6 years (+/-2.3 years). The operative procedures involved were instrumented fusion of the thoracic/lumbar/both curves, Baseline somatosensory-evoked potentials (SSEP) and neurogenic motor-evoked potentials (NMEP) were recorded successfully in all cases. Thirteen cases expressed significant alert to prompt reversal of intervention. All these 13 cases with significant alert had detectable NMEP alerts, whereas significant SSEP alert was detected in 8 cases. Two patients awoke with new neurological deficit (0.56%) and had significant intraoperative SSEP + NMEP alerts. There were no false positives with SSEP (high specificity) but 5 patients with false negatives with SSEP (38%) reduced its sensitivity. There was no false negative with NMEP but 2 of 13 cases were false positive with NMEP (15%). The specificity of SSEP (100%) is higher than NMEP (96%); however, the sensitivity of NMEP (100%) is far better than SSEP (51%). Due to these results, the overall sensitivity, specificity and positive predictive value of combined multimodality neuromonitoring in this adult deformity series was 100, 98.5 and 85%, respectively.

CONCLUSION

Neurogenic motor-evoked potential (NMEP) monitoring appears to be superior to conventional SSEP monitoring for identifying evolving spinal cord injury. Used in conjunction, the sensitivity and specificity of combined neuromonitoring may reach up to 100%. Multimodality monitoring with SSEP + NMEP should be the standard of care.

Risk factors for spinal cord injury during surgery for spinal deformity

BACKGROUND

Spinal cord monitoring is now considered standard care during surgery for spinal deformity. Combined somatosensory and motor evoked potential monitoring allows the detection of early spinal cord dysfunction in most patients. The purpose of the current study was to identify clinical factors that increase the risk of intraoperative electrophysical changes and to provide management recommendations.

METHODS

The records of 162 consecutive patients who underwent surgery for the treatment of spinal deformity at a tertiary referral center were reviewed. Electrophysical monitoring of these patients was considered to have been successful if reproducible signals had been obtained. Relevant electrophysical changes included a reduction, as compared with baseline, of >50% in the amplitude of the somatosensory evoked potentials; an increase, as compared with baseline, of >10% in the latency of the somatosensory evoked potentials; a loss of motor evoked potentials; and an abrupt decrease of >75% in the motor evoked potentials.

RESULTS

One hundred and fifty-one (93%) of the 162 patients were monitored successfully. Four of the eleven patients with unsuccessful monitoring had neuromuscular scoliosis. Twelve of the 151 successfully monitored patients had a true electrophysical event, and two of them were found to have new postoperative neurologic deficits that represented a change from the findings of their preoperative neurologic examination. The determined causes of these electrophysical events included curve correction in eight patients, hypotension in two, direct cord trauma in one, and malposition of a pedicle screw in one. The patients with a true electrophysical event had a significantly higher rate of neurologic events than did the patients who did not have a true electrophysical event (p < 0.001). The rate of true electrophysical events was significantly higher in the patients with cardiopulmonary comorbidities than it was in the patients with no comorbidities (p = 0.011).

CONCLUSIONS

Combined somatosensory and motor evoked potential monitoring effectively prevents neurologic injury in most children undergoing surgery for spinal deformity. Despite the potential for false-positive results, we recommend setting a low threshold for defining relevant electrophysical changes. Rapid intervention can reverse these changes and avoid potentially serious neurologic complications. Patients with cardiopulmonary comorbidities may be at a higher risk for having relevant electrophysical events.

Thoracolumbar spinal deformity: Part II. Developments from 1990 to today: historical vignette

In the first part of this 2-part historical review, the authors outlined the early diagnostic and therapeutic strategies used in the management of spinal deformity. In this second part, they expand upon those early innovations and further detail the advances from 1990 to the modern era.

Recommendations for the clinical use of somatosensory-evoked potentials

The International Federation of Clinical Neurophysiology (IFCN) is in the process of updating its Recommendations for clinical practice published in 1999. These new recommendations dedicated to somatosensory-evoked potentials (SEPs) update the methodological aspects and general clinical applications of standard SEPs, and introduce new sections dedicated to the anatomical-functional organization of the somatosensory system and to special clinical applications, such as intraoperative monitoring, recordings in the intensive care unit, pain-related evoked potentials, and trigeminal and pudendal SEPs. Standard SEPs have gained an established role in the health system, and the special clinical applications we describe here are drawing increasing interest. However, to prove clinically useful each of them requires a dedicated knowledge, both technical and pathophysiological. In this article we give technical advice, report normative values, and discuss clinical applications.