Safety issues during surgical monitoring

Transcranial electric stimulation motor evoked potentials for cervical spine intraoperative monitoring complications: systematic review and illustrative case of cardiac arrest

PURPOSE

We show a systematic review of known complications during intraoperative neuromonitoring (IONM) using transcranial electric stimulation motor evoked potentials (TES-MEP) on cervical spine surgery, which provides a summary of the main findings. A rare complication during this procedure, cardiac arrest by cardioinhibitory reflex, is also described.

METHODS

Findings of 523 scientific papers published from 1995 onwards were reviewed in the following databases: CENTRAL, Cochrane Library, Embase, Google Scholar, Ovid, LILACS, PubMed, and Web of Science. This study evaluated only complications on cervical spine surgery undergoing TES-MEP IONM.

RESULTS

The review of the literature yielded 13 studies on the complications of TES-MEP IONM, from which three were excluded. Five studies are case series; the rest are case reports. Overall, 169 complications on 167 patients were reported in a total of 38,915 patients, a global prevalence of 0.43%. The most common complication was tongue-bite in 129 cases, (76.3% of all complication events). Tongue-bite had a prevalence of 0.33% (CI 95%, 0.28-0.39%) in all patients on TES-MEP IONM. A relatively low prevalence of severe complications was found: cardiac-arrhythmia, bradycardia and seizure, the prevalence of this complications represents only one case in all the sample. Alongside, we report the occurrence of cardiac arrest attributable to TES-MEP IONM.

CONCLUSIONS

This systematic review shows that TES-MEP is a safe procedure with a very low prevalence of complications. To our best knowledge, asystole is reported for the first time as a complication during TES-MEP IONM.

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.

Practice Guidelines for Canadian Neurophysiology Laboratories During the COVID-19 Pandemic

The COVID-19 pandemic has had a major impact on clinical practice. Safe standards of practice are essential to protect health care workers while still allowing them to provide good care. The Canadian Society of Clinical Neurophysiologists, the Canadian Association of Electroneurophysiology Technologists, the Association of Electromyography Technologists of Canada, the Board of Registration of Electromyography Technologists of Canada, and the Canadian Board of Registration of Electroencephalograph Technologists have combined to review current published literature about safe practices for neurophysiology laboratories. Herein, we present the results of our review and provide our expert opinion regarding the safe practice of neurophysiology during the COVID-19 pandemic in Canada.

State-of-the-Art Diagnostic Methods to Diagnose Equine Spinal Disorders, With Special Reference to Transcranial Magnetic Stimulation and Transcranial Electrical Stimulation

Spinal cord disorders are a common problem in equine medicine. However, finding the site of the lesion is challenging for veterinarians because of a lack of sensitive diagnostic methods that can assess neuronal functional integrity in horses. Although medical imaging is frequently applied to help diagnose corticospinal disorders, this approach does not reveal functional information. For the latter, transcranial magnetic stimulation (TMS) and more recently transcranial electrical stimulation (TES) can be useful. These are brain stimulation techniques that create either magnetic or electrical fields passing through the motor cortex, inducing muscular responses, which can be recorded either intramuscularly or extramuscularly by needle or surface electrodes. This permits the evaluation of the functional integrity of the spinal motor tracts and the nerve conduction pathways. The interest in TES in human medicine emerged these last years because unlike TMS, TES tends to bypass the motor cortex of the brain and predominantly relies on direct activation of corticospinal and extrapyramidal axons. Results from human medicine have indicated that TMS and TES recordings are mildly if not at all affected by sedation. Therefore, this technique can be reliably used in human patients under either sedation or full anesthesia to assess functional integrity of the corticospinal and adjunct motor tracts. This opens important new avenues in equine medicine.

Intraoperative direct cortical stimulation motor evoked potentials: Stimulus parameter recommendations based on rheobase and chronaxie

OBJECTIVE

To determine optimal interstimulus interval (ISI) and pulse duration (D) for direct cortical stimulation (DCS) motor evoked potentials (MEPs) based on rheobase and chronaxie derived with two techniques.

METHODS

In 20 patients under propofol/remifentanil anesthesia, 5-pulse DCS thenar MEP rheobase and chronaxie with 2, 3, 4 and 5ms ISI were measured by linear regression of five charge thresholds at 0.05, 0.1, 0.2, 0.5 and 1msD, and estimated from two charge thresholds at 0.1 and 1msD using simple arithmetic. Optimal parameters were defined by minimum threshold energy: the ISI with lowest rheobase²×chronaxie, and D at its chronaxie. Near-optimal was defined as threshold energy <25% above minimum.

RESULTS

The optimal ISI was 3 or 4 (n=7 each), 2 (n=4), or 5ms (n=2), but only 4ms was always either optimal or near-optimal. The optimal D was ∼0.2 (n=12), ∼0.1 (n=7) or ∼0.3ms (n=1). Two-point estimates closely approximated five-point measurements.

CONCLUSIONS

Optimal ISI/D varies, with 4ms/0.2ms being most consistently optimal or near-optimal. Two-point estimation is sufficiently accurate.

SIGNIFICANCE

The results endorse 4ms ISI and 0.2msD for general use. Two-point estimation could enable quick individual optimization.

Intraoperative neurophysiological monitoring of the spinal cord during spinal cord and spine surgery: a review focus on the corticospinal tracts

Recent advances in technology and the refinement of neurophysiological methodologies are significantly changing intraoperative neurophysiological monitoring (IOM) of the spinal cord. This review will summarize the latest achievements in the monitoring of the spinal cord during spine and spinal cord surgeries. This overview is based on an extensive review of the literature and the authors' personal experience. Landmark articles and neurophysiological techniques have been briefly reported to contextualize the development of new techniques. This background is extended to describe the methodological approach to intraoperatively elicit and record spinal D wave and muscle motor evoked potentials (muscle MEPs). The clinical application of spinal D wave and muscle MEP recordings is critically reviewed (especially in the field of Neurosurgery) and new developments such as mapping of the dorsal columns and the corticospinal tracts are presented. In the past decade, motor evoked potential recording following transcranial electrical stimulation has emerged as a reliable technique to intraoperatively assess the functional integrity of the motor pathways. Criteria based on the absence/presence of potentials, their morphology and threshold-related parameters have been proposed for muscle MEPs. While the debate remains open, it appears that different criteria may be applied for different procedures according to the expected surgery-related morbidity and the ultimate goal of the surgeon (e.g. total tumor removal versus complete absence of transitory or permanent neurological deficits). On the other hand, D wave changes--when recordable--have proven to be the strongest predictors of maintained corticospinal tract integrity (and therefore, of motor function/recovery). Combining the use of muscle MEPs with D wave recordings provides the most comprehensive approach for assessing the functional integrity of the spinal cord motor tracts during surgery for intramedullary spinal cord tumors. However, muscle MEPs may suffice to assess motor pathways during other spinal procedures and in cases where the pathophysiology of spinal cord injury is purely ischemic. Finally, while MEPs are now considered the gold standard for monitoring the motor pathways, SEPs continue to retain value as they provide specificity for assessing the integrity of the dorsal column. However, we believe SEPs should not be used exclusively--or as an alternative to motor evoked potentials--during spine surgery, but rather as a complementary method in combination with MEPs. For intramedullary spinal tumor resection, SEPs should not be used exclusively without MEPs.