Advancing Intraoperative Neurophysiological Monitoring With Human Reflexes.

Human reflexes are simple motor responses that are automatically elicited by various sensory inputs. These reflexes can provide valuable insights into the functioning of the nervous system, particularly the brainstem and spinal cord. Reflexes involving the brainstem, such as the blink reflex, laryngeal adductor reflex, trigeminal hypoglossal reflex, and masseter H reflex, offer immediate information about the cranial-nerve functionality and the overall state of the brainstem. Similarly, spinal reflexes such as the H reflex of the soleus muscle, posterior root muscle reflexes, and sacral reflexes provide crucial information about the functionality of the spinal cord and peripheral nerves. One of the critical benefits of reflex monitoring is that it can provide continuous feedback without disrupting the surgical process due to no movement being induced in the surgical field. These reflexes can be monitored in real time during surgical procedures to assess the integrity of the nervous system and detect potential neurological damage. It is particularly noteworthy that the reflexes provide motor and sensory information on the functional integrity of nerve fibers and nuclei. This article describes the current techniques used for monitoring various human reflexes and their clinical significance in surgery. We also address important methodological considerations and their impact on surgical safety and patient outcomes. Utilizing these methodologies has the potential to advance or even revolutionize the field of intraoperative continuous monitoring, ultimately leading to improved surgical outcomes and enhanced patient care.

Unexpected median SEPs fluctuations during brain cavernous malformation resection with no post-operative deficit.

Median nerve somatosensory evoked potentials (SEPs) may present changes during cavernous malformation (CM) resection unrelated to new post-operative sensory deficits. We performed intraoperative neurophysiological monitoring of median SEPs (m-SEPs) in three patients who underwent CM resection (surgery) near the sensory-motor cortex. The only preoperative clinical manifestations in all patients were seizures. All patients presented m-SEPs alterations on the side of the lesion during the procedure. Two patients presented permanent changes in the cortical potentials. In the third patient, the cortical and subcortical components suffered temporal fluctuations to return to baselines at the end of the surgery. None of these patients developed new post-operative clinical deficits. During brain cavernous malformation resection, significant fluctuations in the amplitude of different components of m-SEPs may occur. These changes may be due to excitability variations on m-SEP generators and do not translate into new post-operative neurological deficits.

Median nerve somatosensory evoked potential alarm related to head and neck positioning for carotid surgery.

Head positioning in carotid surgery represents an often overlooked but sensitive period in the surgical plan. A 53-year-old male presented a significant decrement in median nerve somatosensory evoked potential (mSEP) following head and neck positioning for carotid pseudoaneurysm repair before skin incision.Neurophysiological monitoring was performed with mSEP and electroencephalography early during the patient's preparation and surgery. Within five minutes after rotation and extension of the head to properly expose the surgical field, the contralateral m-SEP significantly decreased in both cortical (N20/P25) and subcortical (P14/N18) components. Partial neck correction led to m-SEP improvement, allowing to proceed with the carotid repair. We discuss possible underlying pathophysiological mechanisms responsible for these changes and highlight the relevance of an early start on monitoring to avoid neurological deficits.

Methodology for eliciting the brainstem trigeminal-hypoglossal reflex in humans under general anesthesia.

OBJECTIVE: Brainstem trigeminal-hypoglossal reflexes (THRs), also known as the jaw-tongue reflexes, coordinate the position of the tongue in the mouth in relation to the jaw movement during oromotor behaviors such as mastication, swallowing, vocalization, and breathing. Their use in brainstem surgery however, has never been assessed in spite of its potential benefit possibly due to the lack of a methodology to elicit these reflexes under general anesthesia. METHODS: We proposed a technique to elicit the THRs during total intravenous anesthesia (TIVA) consisting on a V3 infrazygomatic train stimulation paradigm and recording from the Styloglossus (31 patients) and the Genioglossus (21 patients) muscles to elicit long latency responses. RESULTS: The THR was successfully recorded using the V3 stimulation point in 82.1% of patients, of which 96.9% presented a response on the Styloglossus muscle (Jaw-opening reflex) while 0.06% presented a response on the Genioglossus muscle instead (Jaw-closing reflex). CONCLUSIONS: The THRs can be successfully recorded in surgery under general anaesthesia with the predominant reflex seen being the jaw-opening reflex. SIGNIFICANCE: We provide a novel method to elicit the THRs during general anesthesia, which could be of aid in brainstem surgery.

Clarifying optimal outcome measures in intermittent and continuous laryngeal neuromonitoring.

BACKGROUND: Intraoperative neuromonitoring (IONM) techniques have evolved over the past decade into intermittent IONM (I-IONM) and continuous IONM (C-IONM) modes of application. Despite many prior publications on both types of IONM, there remains uncertainty about what outcomes should be measured for each form of IONM. The primary objective of this paper is to define categories of benefit for I-IONM/C-IONM and to clarify and standardize their reporting outcomes. METHODS: Expert review consensus statement utilizing modified Delphi methodology. RESULTS: I-IONM provides diagnosis, classification, and prevention of nerve injury through accurate and early nerve identification. C-IONM provides real-time information on nerve functional integrity and thus may prevent some types of nerve injury but cannot assist in nerve localization. Sudden mechanisms of nerve injury cannot be predicted or prevented by either technique. CONCLUSIONS: I-IONM and C-IONM are complementary techniques. Future studies evaluating the utility of IONM should focus on outcomes that are appropriate to the type of IONM being utilized.

Optimizing the methodology for saphenous nerve somatosensory evoked potentials for monitoring upper lumbar roots and femoral nerve during lumbar spine surgery: technical note.

The demand for intraoperative monitoring (IOM) of lumbar spine surgeries has escalated to accommodate more challenging surgical approaches to prevent perioperative neurologic deficits. Identifying impending injury of individual lumbar roots can be done by assessing free-running EMG and by monitoring the integrity of sensory and motor fibers within the roots by eliciting somatosensory (SEP), and motor evoked potentials. However, the common nerves for eliciting lower limb SEP do not monitor the entire lumbar plexus, excluding fibers from L1 to L4 roots. We aimed to technically optimize the methodology for saphenous nerve SEP (Sap-SEP) proposed for monitoring upper lumbar roots in the operating room. In the first group, the saphenous nerve was consecutively stimulated in two different locations: proximal in the thigh and distal close to the tibia. In the second group, three different recording derivations (10-20 International system) to distal saphenous stimulation were tested. Distal stimulation yielded a higher Sap-SEP amplitude (mean ± SD) than proximal: 1.36 ± 0.9 µV versus 0.62 ± 0.6 µV, (p < 0.0001). Distal stimulation evoked either higher (73%) or similar (12%) Sap-SEP amplitude compared to proximal in most of the nerves. The recording derivation CPz-cCP showed the highest amplitude in 65% of the nerves, followed by CPz-Fz (24%). Distal stimulation for Sap-SEP has advantages over proximal stimulation, including simplicity, lack of movement and higher amplitude responses. The use of two derivations (CPz-cCP, CPz-Fz) optimizes Sap-SEP recording.

Quadriplegia, an Unusual Outcome After Anterior Cervical Discectomy and Fusion: A Case Report.

CASE: A 68-year-old woman who underwent a C5 to C6 anterior cervical discectomy and fusion (ACDF) surgery presented with new-onset postoperative quadriplegia. During discectomy, intraoperative neurophysiological monitoring alerted of a spinal cord (SC) dysfunction. The surgery was halted, and measures to ensure adequate SC perfusion were initiated. In the next 2-week follow-up, patient's motor deficit progressively improved. CONCLUSIONS: We report an unusual and devastating outcome of new-onset quadriplegia after an elective ACDF and highlight the relevance of intraoperative monitoring during cervical spine surgery to early recognize and treat SC impending injury.

Continuous neuromonitoring during radiofrequency ablation of benign thyroid nodules provides objective evidence of laryngeal nerve safety.

INTRODUCTION: The recurrent laryngeal nerves(RLN) run immediately posterior to the thyroid capsule and could be injured during thyroid radiofrequency ablation(RFA). This study assesses whether RLN functional integrity is altered during RFA using continuous intraoperative neuromonitoring(CIONM). METHODS: Prospective case series of twenty nodules treated with RFA under general anesthesia utilizing the laryngeal adductor reflex(LAR) for CIONM. RESULTS: Thirteen nodules abutted the posterior thyroid capsule and 'danger triangle' for RLN injury. The ablative field did not breach the posterior capsule; 40 W was the maximal power used adjacent to the capsule. No patient experienced significant LAR amplitude alterations. Pre and postoperative laryngoscopy and voice assessments were comparable. At 12 months' median follow-up, no patient displayed posterior nodule regrowth. CONCLUSIONS: This prospective case series supports the premise that benign nodule RFA is safe with regards to RLN functional integrity provided the posterior capsule is not breached by the ablation zone and posterior power is ≤ 40 W.

Effects of Hepatitis C Virus (HCV) Eradication on Bone Mineral Density in Human Immunodeficiency Virus/HCV-Coinfected Patients.

BACKGROUND: Little is known about the effects of eradication of hepatitis C virus (HCV) on bone mineral density (BMD) and biomarkers of bone remodeling in human immunodeficiency virus (HIV)/HCV-coinfected patients. METHODS: We prospectively assessed standardized BMD (sBMD) at the lumbar spine and femoral neck, World Health Organization BMD categories at both sites, and plasma concentrations of soluble receptor activator of NF-κß ligand (sRANKL), and osteoprotegerin (OPG) at baseline (the date of initiation of anti-HCV therapy) and at 96 weeks. RESULTS: A total of 238 patients were included. The median age was 49.5 years, 76.5% were males, 48.3% had cirrhosis, 98.3% were on antiretroviral therapy, median CD4+ cell count was 527 cells/µL, and 86.6% had HIV-1 RNA <50 copies/mL. The prevalence of osteoporosis at baseline at the lumbar spine (LS) and femoral neck (FN) was 17.6% and 7.2%, respectively. Anti-HCV therapy comprised pegylated interferon (peg-IFN) and ribavirin (RBV) plus 1 direct-acting antiviral in 53.4%, peg-IFN/RBV in 34.5%, and sofosbuvir/RBV in 12.2%. A total of 145 (60.9%) patients achieved sustained virologic response (SVR). No significant effect of SVR was observed on sBMD for the interaction between time and SVR either in the LS (P = .801) or the FN (P = .911). Likewise, no significant effect of SVR was observed in plasma levels of sRANKL (P = .205), OPG (P = .249), or sRANKL/OPG ratio (P = .123) for the interaction between time and SVR. No significant correlation was found between fibrosis by transient elastography, and LS and FN sBMD, at baseline and week 96. CONCLUSIONS: SVR was not associated with significant changes in BMD nor biomarkers of bone remodeling in HIV/HCV-coinfected persons.

Intraoperative Neurophysiologic Monitoring Correlates with Neurologic Outcome After Endovascular and Surgical Treatment of a Cervical Arteriovenous Malformation.

BACKGROUND: The treatment of spinal intramedullary arteriovenous malformations (AVMs) presents the risk of spinal cord ischemia because of the vascular nidus and their feeding arteries involving and supplying the spinal cord parenchyma. The multimodal approach includes endovascular embolization and microsurgical excision, both benefiting from intraoperative neurophysiologic monitoring. We present a case study of a patient who underwent several staged embolizations and open surgery for microsurgical excision. PATIENT: A 32-year-old man who presented with a recurrent glomus-type intramedullary AVM in the cervical spinal cord, located at the C5-C6 segment, with progressive neurologic deterioration. METHODS: Somatosensory evoked potentials (SEPs) and transcranial motor evoked potentials (MEPs) were performed during three embolizations, a provocative test, and surgery, in addition to D-wave during microsurgical excision. RESULTS: Abolished hand MEP and drop in SEP during a provocative test guided the surgeon to embolize from a safer vessel with no acute neurologic deficit after three embolizations. Before surgery, an angiography showed the left posterior spinal artery supplying the AVM. After resecting the vascular nidus from the spinal parenchyma, left-hand MEP decreased in amplitude and later abolished, and SEP decreased. Interestingly, no D-wave or distal MEPs were affected. Weakness in the left hand immediately and 2 weeks postoperatively advocates for metameric spinal cord ischemia with preservation of long spinal cord pathways. CONCLUSIONS: Intraoperative neurophysiologic monitoring correlates with neurologic outcome after endovascular and surgical treatment of a cervical AVM. Intraoperative monitoring provides continuous functional information of long and metameric spinal cord pathways, which is critical when deciding on the vessel to be embolized and during microsurgical excision where the surgeon is in less control of the AVM hemodynamic flow.

Continuous Laryngeal Adductor Reflex Versus Intermittent Nerve Monitoring in Neck Endocrine Surgery.

OBJECTIVE: Intraoperative neuromonitoring (IONM) techniques aim to identify and potentially prevent nerve injury during surgeries. Prior studies into the efficacy of recurrent laryngeal nerve (RLN) IONM convey mixed results, with some claiming equivalence between IONM and no monitoring at all. The goal of the current study was to compare continuous RLN monitoring using the laryngeal adductor reflex (LAR) to intermittent RLN monitoring (intermittent IONM) to determine whether continuous monitoring reduces the incidence of intraoperative RLN injury during neck endocrine surgeries. METHODS: In this observational, historical case-control study, a historical cohort of patients monitored with intermittent-IONM (group 1, n = 130) were compared to prospectively collected data from consecutive nerves-at-risk monitored continuously with the LAR (LAR-CIONM, group 2, n = 205), at a single center by a single surgeon. The test benefit ratio and relative risk reduction (RRR) for LAR-CIONM over intermittent IONM were calculated. RESULTS: For group 1, nine nerves at risk exhibited intraoperative LOS with transient postoperative vocal fold (VF) hypomobility (n = 2) or immobility (VFI, n = 7). For group 2, two nerves at risk (0.98%) had sudden intraoperative LAR LOS following bipolar cautery, resulting in postoperative transient VFI (P = .004). In each group, there was one case of permanent postoperative VFI. The test benefit rate ratio for LAR-CIONM demonstrated a dramatic effect at 5.23, with an RRR of 81.0%. CONCLUSION: LAR-CIONM significantly decreased rates of postoperative transient VF paralysis and paresis over intermittent IONM alone (P = .004). Surgeons should be aware of the benefits and limitations of intermittent IONM versus CIONM. Intermittent IONM, although useful in nerve mapping and intraoperative decision making, has minimal benefit for the prevention of nerve injury, whereas CIONM can potentially reduce nerve injury rates and improve patient outcomes. LEVEL OF EVIDENCE: 3 Laryngoscope, 131:230-236, 2021.

Neurophysiological monitoring of the laryngeal adductor reflex during cerebellar-pontine angle and brainstem surgery.

OBJECTIVE: To correlate intraoperative changes of the laryngeal adductor reflex (LAR), alone or in combination with corticobulbar motor evoked potential of vocal muscles (vocal-CoMEPs), with postoperative laryngeal function after posterior fossa and brainstem surgery. METHODS: We monitored 53 patients during cerebellar-pontine angle and brainstem surgeries. Vocal-CoMEPs and LAR were recorded from an endotracheal tube with imbedded electrodes or hook-wires electrodes. A LAR significant change (LAR-SC) defined as ≥ 50% amplitude decrement or loss, was classified as either transient or permanent injury to the vagus or medullary pathways by the end of the surgery. RESULTS: All patients with permanent LAR loss (n = 5) or LAR-SC (n = 3), developed postoperative laryngeal dysfunction such as aspiration/pneumonia and permanent swallowing deficits (5.6%). Vocal-CoMEP findings refined postoperative vocal motor dysfunction. All seven patients with transient LAR-SC or loss, reverted by changing the surgical approach, did not present permanent deficits. CONCLUSIONS: Permanent LAR-SCs or loss correlated with postoperative laryngeal dysfunction and predicted motor and sensory dysfunction of the vagus nerve and reflexive medullary pathways. In contrast, a LAR-SC or loss, averted by a timely surgical adjustment, prevented irreversible damage. SIGNIFICANCE: Monitoring of the LAR, with vocal-CoMEPs, may enhance safety to resect complex posterior fossa and brainstem lesions.

Mortality risk assessment in Spain and Italy, insights of the HOPE COVID-19 registry.

Recently the coronavirus disease (COVID-19) outbreak has been declared a pandemic. Despite its aggressive extension and significant morbidity and mortality, risk factors are poorly characterized outside China. We designed a registry, HOPE COVID-19 (NCT04334291), assessing data of 1021 patients discharged (dead or alive) after COVID-19, from 23 hospitals in 4 countries, between 8 February and 1 April. The primary end-point was all-cause mortality aiming to produce a mortality risk score calculator. The median age was 68 years (IQR 52-79), and 59.5% were male. Most frequent comorbidities were hypertension (46.8%) and dyslipidemia (35.8%). A relevant heart or lung disease were depicted in 20%. And renal, neurological, or oncological disease, respectively, were detected in nearly 10%. Most common symptoms were fever, cough, and dyspnea at admission. 311 patients died and 710 were discharged alive. In the death-multivariate analysis, raised as most relevant: age, hypertension, obesity, renal insufficiency, any immunosuppressive disease, 02 saturation < 92% and an elevated C reactive protein (AUC = 0.87; Hosmer-Lemeshow test, p > 0.999; bootstrap-optimist: 0.0018). We provide a simple clinical score to estimate probability of death, dividing patients in four grades (I-IV) of increasing probability. Hydroxychloroquine (79.2%) and antivirals (67.6%) were the specific drugs most commonly used. After a propensity score adjustment, the results suggested a slight improvement in mortality rates (adjusted-ORhydroxychloroquine 0.88; 95% CI 0.81-0.91, p = 0.005; adjusted-ORantiviral 0.94; 95% CI 0.87-1.01; p = 0.115). COVID-19 produces important mortality, mostly in patients with comorbidities with respiratory symptoms. Hydroxychloroquine could be associated with survival benefit, but this data need to be confirmed with further trials. Trial Registration: NCT04334291/EUPAS34399.

Application of different thresholds for instrumentation device testing in minimally invasive lumbosacral spine fixation.

The main aim of this study was evaluating the reliability of stimulus-evoked electromyography (using different thresholds for stimulation of the instrumentation devices) for minimally invasive pedicle screw placement in the lumbosacral spine. A threshold of 5 mA was applied for the pedicle access needle. 7 mA was applied for the tapscrew and pedicle screw stimulation. The existence of threshold differences between vertebral levels was also assessed. All patients underwent postoperative computed tomography (CT) to determine the accuracy of pedicle screw placement. A total of 172 percutaneous pedicle screws were placed in 52 patients. 94.1% of screws were placed at L4, L5 and S1 vertebral levels. No statistically significant differences existed in thresholds of the pedicle access needles, tapscrews and pedicle screws between vertebral levels. In four instances, the pedicle access needle stimulation had a threshold of 5 mA (no breaches were associated). In the rest of occasions, the pedicle access needles had stimulation thresholds above 5 mA. In all instances, tapscrew and pedicle screw thresholds were above 7 mA; the tapscrews and pedicle screws had significantly greater thresholds than the pedicle access needles. No statistically significant differences existed in thresholds between tapscrews and pedicle screws. Postoperative CT imaging revealed one lateral pedicle violation. Both breach rate and false negative rate were 0.5%. No false positive cases were observed. No patients experienced postoperative pedicle screw-related neurologic deficits. A threshold of 5 mA for the pedicle access needle stimulation seems to be safe. Greater than 7 mA should be used for the tapscrew and pedicle screw stimulation.

Intraoperative mapping and monitoring of sensory vagal fibers during vagal schwannoma resection.

Vagal schwannomas are rare, benign tumors. Intermittent intraoperative neuromonitoring via selective stimulation of splayed motor fibers running on the schwannoma surface to elicit a compound muscle action potential has been previously reported as a method of preserving vagal motor fibers. In this case report, vagal sensory fibers are mapped and continuously monitored intraoperatively during high vagus schwannoma resection using the laryngeal adductor reflex (LAR). Mapping of nerve fibers on the schwannoma surface enabled identification of sensory fibers. Continuous LAR monitoring during schwannoma subcapsular microsurgical dissection enabled sensory (and motor) vagal fibers to be monitored in real time with excellent postoperative functional outcomes. Laryngoscope, 129:E434-E436, 2019.

A novel approach to neurologic function sparing surgical management of vagal schwannomas: Continuous intraoperative nerve monitoring of the laryngeal adductor reflex.

BACKGROUND: Vagal schwannomas are rare, benign tumors of the head and neck. Nerve damage during surgical resection is associated with significant morbidity. A new technique of continuous intraoperative nerve monitoring (IONM) that allows for real-time intraoperative feedback has recently been used for thyroid and cervical spine surgeries but has not previously been used in vagal schwannoma surgery. METHODS: Case series of three patients who underwent vagal schwannoma excision utilizing this novel IONM technique. The recurrent laryngeal and vagus nerves were monitored via the laryngeal adductor reflex (LAR) using an electromyographic endotracheal tube. RESULTS: Three patients with suspected vagal schwannomas were treated surgically using the intracapsular enucleation approach with a combination of intermittent IONM and continuous IONM of the LAR. CONCLUSION: This combination of continuous and intermittent IONM can be used to preserve vagal laryngeal innervation and function and may represent the future standard of care for vagal schwannoma excision.

Vagal schwannomas of the head and neck: A comprehensive review and a novel approach to preserving vocal cord innervation and function.

BACKGROUND: Schwannomas, benign tumors arising from neurolemmocytes, are the most common type of peripheral nerve tumors. Extracranial schwannomas are most often found in the parapharyngeal space, commonly involving the vagus nerve to cervical sympathetic trunk. Vagal schwannomas present several unique clinical and therapeutic challenges. METHODS: A comprehensive literature review was conducted on 197 articles reporting 235 cases of cervical vagal schwannomas. Presenting symptoms, treatment approach, and postoperative outcomes were recorded and analyzed. RESULTS: Vagal schwannomas commonly present as asymptomatic neck masses. When they become symptomatic, surgical resection is the standard of care. Gross total resection is associated with higher postoperative morbidity compared to subtotal resection. Initial reports using intraoperative nerve monitoring have shown improved nerve preservation. Recurrence rates are low. CONCLUSION: The combination of intermittent nerve mapping with novel continuous vagal nerve monitoring techniques may reduce postoperative morbidity and could represent the future standard of care for vagal schwannoma treatment.

Continuous Vagal Neuromonitoring Using the Laryngeal Adductor Reflex: Can Preincision Dyssynchrony Predict Intraoperative Nerve Behavior?

OBJECTIVE: The laryngeal adductor reflex (LAR) is an airway-protective response triggered by sensory laryngeal receptors and resulting in bilateral vocal fold adduction. The normal morphology of the early R1 response resembles that of the compound muscle action potential (CMAP). However, in a small subset of patients, the morphology is dyssynchronous with multiple peaks. This study investigates whether preoperative LAR dyssynchrony predicts intraoperative nerve behavior during thyroid surgeries. STUDY DESIGN: Retrospective case-control study. SETTING: US academic health center. SUBJECTS AND METHODS: Opening and closing LAR waveforms from 200 patients with normal preoperative laryngeal examinations monitored continuously during thyroid surgeries using the LAR were analyzed. Area under the curve (AUC) and number of "events" during surgery (defined as any transient decline in AUC >50% baseline) were determined for patients who demonstrated opening dyssynchronous LAR traces compared to demographically matched controls. RESULTS: Six patients had opening dyssynchronous LAR traces. These patients had significantly greater declines in R1 AUC than demographically matched patients with opening synchronized R1 traces (P = .007). Upon thyroid removal, 1 patient converted from a dyssynchronous to synchronous trace. CONCLUSIONS: Preincision dyssynchronous LAR waveforms may indicate subclinical, potentially reversible, neuropathy of the recurrent laryngeal nerve (RLN) and predict intraoperative RLN behavior. Preincision knowledge of R1 dyssynchrony can facilitate surgical planning as such patients may glean particular benefit from continuous intraoperative nerve monitoring, frequent tissue relaxation, and saline irrigation as means to minimize nerve stress intraoperatively.