Anesthetic Management for Pediatric Spinal Fusion: Implications of Advances in Spinal Cord Monitoring

Intraoperative responses of motor evoked potentials to the novel intravenous anesthetic remimazolam during spine surgery: a report of two cases

Background

Remimazolam is a novel short-acting benzodiazepine characterized by metabolism independent from organ function. We report intraoperative MEP responses of two patients who underwent spine surgery under general anesthesia using remimazolam.

Case presentation

In case 1, MEP monitoring was successfully performed with the use of a fixed dose of remimazolam at 0.5 mg/kg/h and remifentanil at 0.2 μg/kg/min. In case 2, an increasing dose of remimazolam from 0.5 to 1.5 mg/kg/h during the operation did not affect MEP signals. In both cases, remimazolam was titrated to maintain the values of entropy electroencephalogram (EEG) monitoring at 40–60.

Conclusions

General anesthesia using remimazolam and remifentanil can be a valuable alternative for spine surgery with MEP monitoring by EEG to assess the optimal dose.

Is routine intraoperative neuromonitoring necessary in growing rod lengthening procedures? A retrospective, observational study

PURPOSE

To investigate whether intraoperative neuromonitoring (IONM) may be avoided in growing rod lengthening procedures in early onset scoliosis (EOS).

METHODS

A total of 636 primary growing rod surgeries and lengthening procedures were performed in 112 patients with EOS. Traditional growing rods (TGR) or magnetically controlled growing rods (MCGR) were implanted and subsequent lengthening procedures were done at stipulated intervals. Combined multi-modality IONM was used in all index surgeries-but was only used in lengthening procedures in patients with existing spinal cord abnormality or a history of neurosurgical procedure for the same, patients with prior history of a neuromonitoring alert in their index surgery and when lengthening was accompanied by an implant exchange/revision. All the remaining growing rod lengthening procedures were carried out without IONM. Hospital records and operation notes were retrospectively reviewed with focus on details of neurological events/complications.

RESULTS

In 112 primary growing rod applications (TGR = 96, MCGR = 16) and 524 lengthening procedures (TGR = 444, MCGR = 80), intraoperative neuromonitoring 'alerts' were encountered in 6/112 index surgeries and temporary postoperative neurological deficits were seen in 2/112 index surgeries. No intraoperative neuromonitoring event or postoperative neurological complication was encountered in 524 lengthening procedures-irrespective of whether they were carried out along with implant exchange, or in patients with spinal cord abnormality or prior neuromonitoring event during index surgery.

CONCLUSION

While IONM should be used in primary growing rod application surgeries, its use may be avoided in lengthening and implant exchange procedures in a resource-limited setting.

LEVEL OF EVIDENCE

Level 3.

Clonidine administration during intraoperative monitoring for pediatric scoliosis surgery: Effects on central and peripheral motor responses

OBJECTIVE

To study the effect of clonidine administrated as a co-analgesic during scoliosis surgery, on the neuromonitoring of spinal motor pathways.

METHODS

Using standardized intraoperative monitoring, we compared the time course of peripherally and transcranially electrically evoked motor potentials (TcEMEPs) before and after injection of a single bolus of clonidine in children under total intravenous anesthesia (TIVA). MEP data were obtained from 9 patients and somatosensory evoked potentials (SSEPs) were obtained from 2 patients. The potential effect of clonidine on mean blood pressure (BP) was controlled.

RESULTS

TcEMEPs from upper and lower limbs rapidly showed significant drops in amplitude after the injection of clonidine. Amplitudes reached minimal values within five minutes and remained very weak for at least 10-20minutes during which monitoring of the central motor pathways was severely compromised. SSEPs were not altered during maximal amplitude depression of the TcEMEPS.

CONCLUSIONS

This is the first report showing that clonidine severely interferes with neuromonitoring of the spinal cord motor pathways. The results are discussed in light of the literature describing the effects of dexmedetomidine, another α-2 adrenergic agonist. The experimental and literature data point to central mechanisms taking place at both the spinal and cerebral levels. Therefore, clonidine as well as other α-2 adrenergic agonists should be used with extreme caution in patients for whom neuromonitoring of the motor pathways is required during surgery.

Intraoperative Neurophysiological Monitoring for Endoscopic Endonasal Approaches to the Skull Base: A Technical Guide

Intraoperative neurophysiological monitoring during endoscopic, endonasal approaches to the skull base is both feasible and safe. Numerous reports have recently emerged from the literature evaluating the efficacy of different neuromonitoring tests during endonasal procedures, making them relatively well-studied. The authors report on a comprehensive, multimodality approach to monitoring the functional integrity of at risk nervous system structures, including the cerebral cortex, brainstem, cranial nerves, corticospinal tract, corticobulbar tract, and the thalamocortical somatosensory system during endonasal surgery of the skull base. The modalities employed include electroencephalography, somatosensory evoked potentials, free-running and electrically triggered electromyography, transcranial electric motor evoked potentials, and auditory evoked potentials. Methodological considerations as well as benefits and limitations are discussed. The authors argue that, while individual modalities have their limitations, multimodality neuromonitoring provides a real-time, comprehensive assessment of nervous system function and allows for safer, more aggressive management of skull base tumors via the endonasal route.

Neuromonitoring During Surgery for Paediatric Spinal Deformity in Canada (2007)

Background:

Neuromonitoring during paediatric (and adult) spinal deformity surgery helps to reduce the risk of both permanent and short term neurological damage. A shortage of neurophysiologists and technicians limits the availability of this service. Not all surgeons believe neuromonitoring offers neuroprotection during spinal surgery. This study aimed to document the degree to which paediatric patients undergoing spinal deformity correction surgery have their spinal cord function monitored.

Methods:

A questionnaire was sent electronically to all of the surgical members of the Canadian Paediatric Spinal Deformity Study Group.

Results:

Results were received from 9/9 centres indicating that monitoring was performed in 7/9 centres, with one further centre awaiting staffing. Whilst half of those centres that do monitor only monitor sensory and motor evoked potentials, the remaining centres also use EMG and EEG to assess the state of the patient intraoperatively.

Conclusions:

Despite a shortage of staff, most paediatric spinal deformity surgeons in Canada who wish to, are able to neurophysiologically monitor their surgical cases. Neuromonitoring appears to be becoming a standard of care, at least for paediatric spinal deformity surgery. There is an urgent need for the establishment of national standards for both technologists and interpreters, as well as training programmes for both these groups.

Neurologic risk in growing rod spine surgery in early onset scoliosis: is neuromonitoring necessary for all cases?

STUDY DESIGN

Retrospective case series from a multicenter database.

OBJECTIVE

To evaluate the risk of neurologic injury during growing rod surgeries and to determine whether intraoperative neuromonitoring is necessary for all growing rod procedures.

SUMMARY OF BACKGROUND DATA

Although the use of growing rod constructs for early-onset spinal deformity has become a commonly accepted treatment, the incidence of neurologic events during growing rod surgeries remains unknown.

METHODS

We reviewed data from a multicenter database on 782 growing rod surgeries performed in 252 patients. VEPTR devices and any constructs with rib attachments were excluded. A questionnaire was sent to all surgeons contributing cases requesting detailed information about all neurologic events associated with any growing rod surgery.

RESULTS

There were 782 growing rod surgeries performed on 252 patients including 252 primary growing rod implantations, 168 implant exchanges, and 362 lengthenings. Five hundred sixty-nine of 782 (73%) cases were performed with neuromonitoring. Only one clinical injury occurred in the series, resulting in an injury rate of 0.1% (1/782). This deficit occurred during an implant exchange while attempting pedicle screw placement, and resolved within 3 months. There were 2 cases with neuromonitoring changes during primary implant surgeries (0.9%, 2/231), 1 change during implant exchanges (0.9%, 1/116), and 1 neuromonitoring change during lengthenings (0.5%, 1/222). The single monitoring change that occurred during a lengthening was in a child with an intracanal tumor who also had a monitoring change during the primary surgery. There are anecdotal cases (outside this study group series) of neuromonitoring changes during simple lengthenings in children with uneventful primary implantations.

CONCLUSION

Based on our study, the largest reported series of growing rod surgeries, the rate of neuromonitoring changes during primary growing rod implantation (0.9%) and exchange (0.9%) justifies the use of intraoperative neuromonitoring during these surgeries. As there were no neurologic events in 361 lengthenings in patients with no previous neurologic events, the question may be raised as to whether intraoperative neuromonitoring is necessary for simple lengthenings in these patients. However, caution should be maintained when interpreting our results as anecdotal cases of neurologic changes from simple lengthenings do exist outside of this series.

Neurologic injury in the surgical treatment of idiopathic scoliosis: guidelines for assessment and management

Iatrogenic spinal cord injury resulting from surgical treatment of spinal deformity is a relatively uncommon but devastating complication. Publications on the prevalence of spinal cord injury following surgery are numerous, but no definitive review with clinically pertinent treatment guidelines exists. Methods to reduce the risk of neurologic complications with scoliosis surgery include adequate patient evaluation and preoperative planning, intraoperative preparation, intraoperative neuromonitoring, and postoperative management. Treatment algorithms may be useful in the clinical setting to manage intraoperative or postoperative neurologic injury.

Upper-limb somatosensory evoked potential monitoring in lumbosacral spine surgery: a prognostic marker for position-related ulnar nerve injury

BACKGROUND CONTEXT

Somatosensory evoked potential (SSEP) is used to monitor integrity of the brain, spinal cord, and nerve roots during spinal surgery. It records the electrical potentials from the scalp after electrical stimulation of the peripheral nerves of the upper or lower limbs. The standard monitoring modality in lumbosacral spine surgery includes lower-limb SSEP and electromyography (EMG). Upper-limb SSEP monitoring has also been used to detect and prevent brachial plexopathy and peripheral nerve injury in thoracic and lumbosacral spine surgeries. We routinely monitor lower-limb SSEP and EMG in lumbosacral spine procedures at our institution. However, a few patients experienced postoperative numbness and/or pain in their ulnar distribution with uneventful lower-limb SSEP and EMG.

PURPOSE

We hypothesized that the postoperative upper extremity paresis in lumbosacral surgeries may result from compression and/or stretch of the brachial plexus and/or ulnar nerve while the patients were in prone position. Using upper-limb SSEP, we investigated whether we observe any significant change in the SSEP, and if so, whether we can prevent or reduce frequency of postoperative upper extremity deficits.

STUDY DESIGN/SETTING

In this prospective study, we monitored upper-limb SSEP, in addition to lower-limb SSEP and EMG, in 230 elective, posterior lumbosacral spinal procedures. All operations were performed by a group of four neurosurgeons.

PATIENT SAMPLE

One hundred and thirty-one female and 99 male with an age range of 28 to 86 years between January 2004 and December 2005 were studied.

OUTCOME MEASURES

Amplitude and latency of upper-limb or ulnar SSEP were continuously compared with those of the baseline. A greater than or equal to 50% decrease in SSEPs amplitude and/or a greater than or equal to 10% increase in latency were considered to be significant.

METHODS

After intubation, patients were positioned prone on Jackson or Andrews spinal table. Anesthesia was maintained with inhalant gas (desflurane or sevoflurane) and propofol infusion with and without minimal infusion of narcotics (fentanyl, sufentanyl, or remifentanil). Intraoperative neurophysiologic monitoring of upper-limb or ulnar SSEP was achieved by continuously recording cortical and subcortical responses after alternate stimulation of the ulnar nerve at the wrist. In our institutional protocol, a greater than or equal to 50% decrease in SSEPs amplitude and/or a greater than or equal to 10% increase in latency were considered to be significant to alert the operating surgeons. When significant changes occurred, the surgeon was immediately notified. Also, reevaluation of vital signs, depth of anesthesia, and patient's position, and technical troubleshootings were subsequently followed.

RESULTS

We observed a greater than or equal to 50% decrease in amplitude of ulnar SSEP in 10 patients without significant changes in lower-limb SSEP (peroneal or posterior tibial nerve SSEP) or EMG during surgery. Eight patients had changes in unilateral limbs, and two patients had changes in bilateral limbs. Two patients with significant changes in unilateral limbs showed changes twice. The mean SSEP amplitude for the 14 changes was 29.2+/-3.1% (mean+/-SEM, standard error of mean) of the baseline value at the average surgical time of 60+/-1.5 minutes. With repositioning of the arms, the amplitudes were immediately restored with the average of 70.2+/-7.1% (n=14) of the baseline value. The mean amplitude of upper-limb SSEP was 73.4+/-8.7% (n=12) of the baseline at wound closure. The average surgical time was 154+/-29.2 minutes per case for the 10 patients. There was no documented postoperative upper extremity paresis in all 230 patients.

CONCLUSIONS

The present study demonstrates that upper-limb SSEP monitoring could detect position-related ulnar neuropathy in 5.2% of the patients undergoing lumbosacral spine surgery.