Safe transcranial electric stimulation motor evoked potential monitoring during posterior spinal fusion in two patients with cochlear implants

Intraoperative Monitoring of Scoliosis Surgery in Young Patients

SUMMARY

Intraoperative neurophysiologic monitoring has added substantially to the safety of spinal deformity surgery correction since its introduction over four decades ago. Monitoring routinely includes both somatosensory evoked potentials and motor evoked potentials. Either modality alone will detect almost all instances of spinal cord injury during deformity correction. The combined use of the two modalities provides complementary information, can permit more rapidly identification of problems, and enhances safety though parallel redundancy should one modality fail. Both techniques are well established and continue to be refined. Although there is room for provider preference, proper monitoring requires attention to technical detail, understanding of the underlying physiology, and familiarity with effects of commonly used anesthetic agents.

Intraoperative neurophysiological monitoring in scoliosis surgery: literature review of the last 10 years

INTRODUCTION

Patients with spinal deformities undergoing corrective surgery are at risk for iatrogenic spinal cord injury (SCI) and subsequent neurological deficit. Intraoperative neurophysiological monitoring (IONM) allows early detection of SCI which enables early intervention resulting in a better prognosis. The primary aim of this literature review was to search if there are threshold values of TcMEP and SSEP in the literature that are widely accepted as alert during IONM. The secondary aim was to update knowledge concerning IONM during scoliosis surgery.

METHOD

PubMed/MEDLINE and Cochrane library electronic databases were used to search publication from 2012 to 2022. The following keywords were used: evoked potential, scoliosis, surgery, intraoperative monitoring and neurophysiological. We included all studies dealing with SSEP and TcMEP monitoring during scoliosis surgery. Two authors reviewed all titles and abstracts to identify studies that met the inclusion criteria.

RESULTS

We included 43 papers. Rates of IONM alert and neurological deficit varied from 0.56 to 64% and from 0.15 to 8.3%, respectively. Threshold values varied from a loss of 50 to 90% for TcMEP amplitude, whereas it seems that a loss of 50% in amplitude and/or an increase of 10% of latency is widely accepted for SSEP. Causes of IONM changes most frequently reported were surgical maneuver.

CONCLUSION

Concerning SSEP, a loss of 50% in amplitude and/or an increase of 10% of latency is widely accepted as an alert. For TcMEP, it seems that the use of highest threshold values can avoid unnecessary surgical procedure for the patient without increasing risk of neurological deficit.

Monopolar Cautery Use in Pediatric Cochlear Implant Users

OBJECTIVES

To determine the incidence and impact of monopolar cautery use in a cohort of pediatric cochlear implant (CI) users.

STUDY DESIGN

Case series from a retrospective chart review and a systematic review of the literature.

SETTING

Tertiary academic referral center.

METHODS

CI patient charts from 2012 to 2021 were reviewed from a single pediatric hospital system to determine if monopolar cautery was used during a subsequent surgical procedure. In addition, a systematic review of the literature was performed to identify additional, relevant patients. Postoperative CI function was the primary outcome measure.

RESULTS

In total, 190 patients underwent a surgical procedure following cochlear implantation in a single pediatric hospital system. Fifteen patients (7.9%) and 17 distinct surgical procedures were identified in which monopolar cautery was used. Seven of these 17 cases (41.2%) involved the head and neck, and 10 were performed below the clavicles. No patients experienced a device failure or a decline in CI performance following surgery. A systematic review identified an additional 4 patients who underwent a surgery that used monopolar cautery following cochlear implantation, and no change in CI function was identified.

CONCLUSIONS

The present study adds additional support to the notion that monopolar cautery does not necessarily injure CI functionality. While the most risk adverse strategy when planning a surgical procedure for a CI patient is to avoid monopolar cautery use altogether, the use of cautery should not immediately be associated with implant dysfunction.

Does the presence of programmable implanted devices in patients with early onset scoliosis alter typical operative and postoperative practices? A survey of spine surgeons

PURPOSE

Operative and postoperative management of early onset scoliosis (EOS) patients with programmable implanted devices has not been well characterized in the literature. The aim of this study was to describe current practices for pediatric spine surgeons who operate on patients with these devices.

METHODS

An electronic survey was distributed to 167 pediatric spine surgeons between January and March of 2021. The survey queried participants on operative and postoperative management of patients with the following implanted devices: vagal nerve stimulators, ventriculoperitoneal shunts, intrathecal baclofen pumps, pacemakers, and cochlear implants. Descriptive statistics were used to assess survey data.

RESULTS

Fifty-three respondents (31.7% response rate) with a mean 16.5 (SD 12.0) years in practice completed the survey. Depending on the type of device present, surgeons report changing their operative plan anywhere from 28.6 to 60.1% of the time when inserting magnetically controlled growing rods. Most respondents reported performing transcranial motor evoked potentials (80.0-98.0%) and monopolar cautery (70.0-92.9%) across implanted devices. Only 10% (n = 5) of surgeons reported complications related to operative and/or postoperative management of these patients. No complications were related to cautery, neuromonitoring, or surgical placement of MCGRs.

CONCLUSIONS

This study demonstrates variation in operative and postoperative management of these patients with various programmable implanted devices. Much of this inconsistency in practice is likely due to decades old case reports, constantly changing device manufacturer recommendations, and/or published simulation studies. Reported heterogeneity in management across surgeons necessitates development of published guidelines regarding proper operative and postoperative management of patients with EOS and implanted devices.

Neurophysiological Intraoperative Monitoring in Patients with Cochlear Implant Undergoing Posterior Spinal Fusion: A Case Report

CASE

Transcranial electric stimulation motor-evoked potentials (tcMEPs) are the most sensitive technique in multimodality intraoperative neuromonitoring (IONM) for posterior spinal fusion (PSF). The presence of a cochlear implant (CI) is considered a contraindication to IONM because of theoretical risk of implant device and local tissue damage from voltages induced by tcMEPs. We present the case of a 10-year-old girl with CI who underwent successful PSF with tcMEP and monopolar electrocautery (MoEC) without perioperative complications or CI damage.

CONCLUSION

With proper precautions, such as MoEC usage at a minimal voltage, motor-evoked potential monitoring can be safely performed in pediatric patients with CI undergoing PSF.

Safety issues during surgical monitoring

While intra-operative neuro-physiologic assessment and monitoring improve the safety of patients, its use may also introduce new risks of injuries. This chapter looks at the electric safety of equipment and the potential hazards during the set-up of the monitoring. The physical and functional physiologic effects of electric shocks and stimulation currents, standards for safety limits, and conditions for tissue damage are described from basic physical principles. Considered are the electrode-tissue interface in relation to electrode dimensions and stimulation parameters as applied in various modalities of evoked sensory and motor potentials as to-date used in intra-operative monitoring, mapping of neuro-physiologic functions. A background is given on circumstances for electric tissue heating and heat drainage, thermal toxicity, protection against thermal injuries and side effects of unintended activation of neural and cardiac tissues, adverse effects of physiologic amplifiers from transcranial stimulation (TES) and excitotoxicity of direct cortical stimulation. Addressed are safety issues of TES and measures for prevention. Safety issues include bite and movement-induced injuries, seizures, and after discharges, interaction with implanted devices as cardiac pacemaker and deep brain stimulators. Further discussed are safety issues of equipment leakage currents, protection against electric shocks, and maintenance.

Spinal cord monitoring

Spinal cord surgery carries the risk of spinal cord or nerve root injury. Neurophysiologic monitoring decreases risk of injury by continuous assessment of spinal cord and nerve root function throughout surgery. Techniques include somatosensory evoked potentials (SEPs), transcranial electrical motor evoked potentials (MEPs), and electromyography (EMG). Baseline neurophysiologic data are obtained prior to incision. Real-time signal changes are identified in time to correct compromised neural function. Such monitoring improves postoperative neurologic functional outcomes. Challenges in neurophysiologic intraoperative monitoring (NIOM) include effects of anesthetics, neuromuscular blockade, hypotension, hypothermia, and preexisting neurological conditions, e.g., neuropathy or myelopathy. Technical factors causing poor quality data must be overcome in the electrically noisy operating room environment. Experienced monitoring teams understand tactics to obtain quality recordings and consider confounding variables before raising alarms when change occurs. Once an alert is raised, surgeons and anesthesiologists respond with a variety of actions, such as raising blood pressure or adjusting retractors. In experienced hands, NIOM significantly reduces postoperative neurological deficits, e.g., 60% reduction in risk of paraplegia and paraparesis. A technologist in the operating room sets up the NIOM procedure. An experienced clinical neurophysiologist supervises the case, either in the operating room or remotely on-line continuously in real time.

Spinal Surgery With Electrically Evoked Potential Monitoring and Monopolar Electrocautery: Is Prior Removal of a Cochlear Implant Necessary?

: Transcranial electric stimulation to generate motor evoked potentials in lower limb muscles is the standard technique used to monitor spinal cord efferent pathways during surgical correction for spinal deformities. Monopolar electrical cauterization is also used by default in the thoracic and lumbar area of the spine during this kind of surgery to prevent major blood loss. Owing to the high levels of current used, both techniques are considered contraindicative if the patient has a cochlear implant (CI). Here, we present a CI patient who underwent corrective spinal fusion surgery for a severe kyphoscoliotic spinal deformity on whom both techniques were used without any negative effects on the CI function. A major improvement in sagittal body balance was achieved with no loss in implant-aided hearing levels. These results add to reports that CI manufactures should review their evidence underlying recommendations that transcranial electric stimulation and upper thoracic monopolar electrical cauterization are high risk for CI users, possibly initiating verification studies.

Safe Intraoperative Neurophysiologic Monitoring During Posterior Spinal Fusion in a Patient With Cochlear Implants

OBJECTIVE

Cochlear implants are generally considered a contraindication for any procedure requiring electrical stimulation near the implant. We present a case of a patient undergoing intraoperative transcranial electrical motor-evoked potential monitoring with a cochlear implant without adverse outcomes.

PATIENT

A 12-year-old girl with a history of VACTERL presented with worsening congenital kyphosis and bilateral severe-to-profound hearing loss. Since age 7 the patient used a cochlear implant in the right ear and hearing aid in the left ear. Physical examination and magnetic resonance imaging in 2016 revealed a left-sided 66-degree thoracolumbar kyphosis at T11 making the patient a candidate for surgical correction.

INTERVENTIONS

She underwent a posterior spinal fusion surgery, performed with intraoperative transcranial electrical motor-evoked potential monitoring. Steps were taken to mitigate electrical stimulation of the patient's cochlear implant.

MAIN OUTCOME MEASURES

Postoperative impedance of individual channels, audiometry, and neural response testing were compared with preoperative measurements.

RESULTS

Significant (>10%) impedance changes were observed postoperatively in channels 1, 2, 4, and 6; however, the net variation across all the channels was low (3%). The patient reported no hearing changes, and no significant changes in hearing threshold were seen in postoperative audiometric testing or neural response testing.

CONCLUSION

We present a case of successful posterior spinal fusion with intraoperative neurophysiological monitoring via transcranial electrical stimulation, in a patient with a cochlear implant. With proper precautions, motor-evoked potential monitoring can be safely performed in a patient with a cochlear implant.

Journal of clinical monitoring and computing 2016 end of year summary: anesthesia

Clinical monitoring and computing are essential during general anesthesia. As a result it would be impossible to review all the articles published in the Journal of Clinical Monitoring and Computing that are relevant to anesthesia. We therefore will limit this summary to those articles that are uniquely related to anesthesia. The topics include: anesthesia machines; ensuring the airway; anesthetic depth; neuromuscular transmission monitoring; locoregional anesthesia; ultrasound; and pain.