Neuromonitoring Using Motor and Somatosensory Evoked Potentials in Aortic Surgery

Anesthetic Considerations for Repair of Thoracoabdominal Aortic Aneurysms

Anesthetic management of open thoracoabdominal aneurysm (TAAA) repair poses a number of challenges for even the most experienced of cardiovascular anesthesiologists. This procedure encompasses a large number of unique anesthetic techniques, including one-lung ventilation, invasive hemodynamic monitoring, left-heart bypass, massive transfusion, selective renal and visceral perfusion, and central nervous system monitoring with CSF drainage. In this article, we aim to describe the anesthetic management for thoracoabdominal aortic aneurysm repair, including preoperative workup, intraoperative management, as well as postoperative concerns in the intensive care unit.

Use of Neurophysiological Monitoring during MR Imaging-Guided Ablation Procedures at 1.5 T: Workflow and Safety Considerations

PURPOSE

To evaluate the feasibility of intraoperative neurophysiological monitoring (IONM) during magnetic resonance (MR) imaging-guided ablations and identify strategies to reduce IONM electrode radiofrequency (RF) heating during MR imaging.

MATERIALS AND METHODS

Ex vivo experiments with a porcine tissue phantom simulating a typical high RF heating risk IONM setup during an MR imaging-guided ablation procedure on the shoulder were performed using a 1.5-T scanner. Mutual interference between MR imaging and IONM was evaluated. To assess RF heating risks, 4 pairs of IONM electrodes were inserted into the phantom at regions corresponding to the shoulders, midarm, and wrist. MR imaging of the "shoulder" was performed at 3 different specific absorption rates (SARs) with electrode wires positioned in various geometric configurations. Different combinations of electrode connections to the IONM system were investigated. Temperatures of each electrode were recorded using fiber-optic sensors.

RESULTS

Simultaneous IONM readout and MR imaging resulted in distortion of the IONM signal, but interleaving MR imaging and IONM without moving electrodes was feasible. During MR imaging, temperature elevations greater than 60°C at the electrode insertion sites were observed. Temperature reductions were achieved by routing electrode wires along the scanner central axis, reducing the wire length within the scanner bore, or lowering the SAR of the imaging sequence. Altering the electrode connection with the IONM system did not result in consistent changes in RF heating.

CONCLUSIONS

With electrodes in the scanner bore, interleaving IONM and MR imaging is desired to avoid signal interference, and several strategies identified herein can reduce risk of electrode RF heating during MR imaging-guided ablation.

Motor-Evoked Potential Monitoring With Multi-train Electrical Stimulation During Thoracoabdominal Aortic Aneurysm Surgery: A Case Report

Intraoperative motor-evoked potentials (MEPs) are measured for assessing motor function during surgery. MEP monitoring is often performed in thoracoabdominal aortic aneurysm (TAAA) surgery, but false positives are common and amplification methods are needed to obtain waveforms under severe conditions to assess proper spinal cord function. One method of amplitude amplification in transcranial-stimulated MEP monitoring is multitrain stimulation. There are few reports on multitrain-stimulated MEP monitoring for this surgery. A 57-year-old woman underwent open repair of the thoracoabdominal aorta due to a dissecting aortic aneurysm. After opening the chest, the aneurysm was incised proximally, and anastomosis with an artificial vessel was initiated. The lumbar artery leading to the Adam-Kiewicz artery was reconstructed at a body temperature of 25 °C. However, the single-train stimulation did not produce MEPs. When the measurement was switched to multitrain stimulation, MEPs were elicited in the lower extremity muscle groups and the waveforms were maintained until the end of the measurement. This case illustrates that MEP monitoring using multitrain stimulation during descending thoracic aortic aneurysm surgery can effectively elicit MEPs under challenging conditions, in which conventional single-train stimulation may be insufficient.

The role of intraoperative extensor digitorum brevis muscle MEPs in spinal surgery

PURPOSE

Intraoperative muscle motor evoked potentials (m-MEPs) are widely used in spinal surgery with the aim of identifying a damage to spinal cord at a reversible stage. Generally, lower limb m-MEPs are recorded from abductor hallucis [AH] and the tibialis anterior [TA]. The purpose of this work is to study an unselected population by recording the m-MEPs from TA, AH and extensor digitorum brevis (EDB), with the aim of identifying the most adjustable and stable muscles responses intraoperatively.

METHODS

Transcranially electrically induced m-MEPs were intraoperative recorded in a total of 107 surgical procedures. m-MEPs were recorded by a needle electrode placed in the muscle from TA, AH and EDB muscles in the lower extremities.

RESULTS

Overall monitorability (i.e., at least 1 Lower Limb m-MEP recordable) was 100/107 (93.5%). In the remaining 100 surgeries in 3 cases, the only muscle that could be recorded at baseline was one AH, and in other 2 the EDB. Persistence (i.e., the recordability of m-MEP from baseline to the end of surgery) was 88.7% for TA, 89.8% for AH and 93.8% for EDB.

CONCLUSION

In our series, EDB m-MEPs have demonstrated a recordability superior to TA and a stability similar to AH. The explanations may be different and range from changes in the excitability of the cortical motor neuron to the different sensitivity to ischemia of the spinal motor neuron. EDB can be used alternatively or can be added to TA and AH as a target muscle of the lower limb in spinal surgery.

The anesthesiologist's perspective on emergency aortic surgery: Preoperative optimization, intraoperative management, and postoperative surveillance

The management of emergencies related to the aorta requires a multidisciplinary approach involving various health care professionals. Despite technological advancements in treatment methods, the risks and mortality rates associated with surgery remain high. In the emergency department, definitive diagnosis is usually obtained through computed tomography angiography, and management focuses on controlling blood pressure and treating symptoms to prevent further deterioration. Preoperative resuscitation is the main focus, followed by intraoperative management aimed at stabilizing the patient's hemodynamics, controlling bleeding, and protecting vital organs. After the operation, factors such as organ protection, transfusion management, pain control, and overall patient care must be taken into account. Endovascular techniques are becoming more common in surgical treatment, but they also present new challenges in terms of complications and outcomes. It is recommended that patients with suspected ruptured abdominal aortic aneurysms be transferred to facilities with both open and endovascular treatment options and a track record of successful outcomes to ensure the best patient care and long-term results. To achieve optimal patient outcomes, close collaboration and regular case discussions between health care professionals are necessary, as well as participation in educational programs to promote a culture of teamwork and continuous improvement.

Thoracic aortic emergencies involving the aortic arch: An integrated cardiovascular surgical treatment approach

Thoracic aortic emergencies involving the aortic arch are potentially fatal conditions that require the entire surgical repertoire of conventional surgery, such as complete aortic arch replacement using the frozen-elephant-trunk technique, through hybrid procedures, to full surgical endovascular options with conventional or delivered/fenestrated stent-grafts. An interdisciplinary aortic team should choose the optimal treatment of the pathologies of the aortic arch, considering the morphology of the entire aorta, from the root to beyond the bifurcation, as well as the clinical comorbidities. The treatment goal is a complication-free postoperative result and lasting freedom from aortic reinterventions. Irrespective of the selected therapy method, patients should then be connected to a specialized aortic outpatient clinic. The aim of this review was to provide an overview of pathophysiology and current treatment options in emergencies of the thoracic aorta, also involving the aortic arch. We wanted to summarize the preoperative considerations, intraoperative settings, and strategies, as well the postoperative follow-up.

Near-infrared spectroscopy to monitor spinal cord oxygenation in οpen thoraco-abdominal aortic surgery. A case series

Objectives. We adopted the near-infrared spectroscopy (NIRS) technology to monitor the spinal oxygen supply through the paraspinous muscles oxygenation in agreement with the concept of “collateral network” circulation. We retrospectively investigated our database of subjects who underwent thoraco-abdominal aorta open repair assessing for the reliability of this monitoring to predict spinal cord injury. Methods. Consecutive patients who underwent elective thoraco-abdominal aorta open repair between March 2019 and September 2021. In addition to standard monitoring, patients received the monitoring of the paraspinous muscles oxygenation by NIRS. Results. In one patient a significant drop of the mean arterial pressure (49 mmHg) and the spinal-cord perfusion pressure (31 mmHg) occurred after the aortic clamping, with a contemporary lowering of the left-side oxygenation of paraspinous muscles (<40%). Both the blood pressure and the spinal cord perfusion pressure were restored within 10 minutes, but the oxygenation remained at an unsafe level (<55%) until the end of the surgery. This same patient experienced a lower-limb paralysis post-operatively. It did not happen in the other 11 cases of the sample. Conclusions. The main finding of our retrospective analysis indicates reliability of this technology to monitor the spinal cord oxygenation during open thoraco-abdominal aortic surgery and possibly predict spinal cord injury. Still, several questions need to be addressed about the suitability of this technology to the anatomic and pathophysiology of the spinal cord circulation

Optimization of factors for the prevention of spinal cord ischemia in thoracic endovascular aortic repair

OBJECTIVES

Spinal cord ischemia following thoracic endovascular aortic repair (TEVAR) is a devastating complication. This study seeks to demonstrate how a standardized protocol to prevent spinal cord ischemia affects incidence in patients undergoing TEVAR.

METHODS

Using CPT codes 33880 and 33881, all TEVAR procedures performed at a single tertiary care center from January 2017 to December 2018 were examined. Patients who had concomitant ascending aortic repairs or a TEVAR for traumatic indications were excluded from analysis, leaving 130 TEVAR procedures. Comorbid conditions, procedural characteristics, extent of coverage, peri-procedural management strategies, and post-operative outcomes were collected and analyzed retrospectively.

RESULTS

One hundred thirty patients undergoing TEVAR were examined for four perioperative variables: postoperative hemoglobin greater than 10 g/dL, subclavian revascularization, preoperative spinal drain placement, and somatosensory evoked potential monitoring (SSEP). All conditions were met in 46.2% (60/130) of procedures; 37.8% (28/74) in emergent/urgent cases and 61.5% (32/52) in elective cases. Of patients who required subclavian coverage, 87.1% (54/62) underwent subclavian revascularization; 70.8% (92/130) of patients received spinal drains preoperatively; 68.5% (89/130) of patients had SSEP monitoring; 73.8% (93/130) of patients obtained a postoperative hemoglobin of >10 g/dL. Out of all patients, two (1.5%) developed spinal cord ischemia.

CONCLUSION

Incidence of spinal cord ischemia in our cohort was low at 1.5% (2/130). Individual and bundled interventions for the prevention of spinal cord ischemia were unable to demonstrate a statistically significant effect given the low rate. Nonetheless, we advocate for a proactive approach for the prevention of spinal cord ischemia given our experience in this complex population.

Spinal cord protection in thoracoabdominal aortic aneurysm surgery: a multimodal approach

Spinal cord injury (SCI) is one major complication of open and endovascular thoracic and thoracoabdominal aortic aneurysm repair. Despite numerous neuroprotective adjuncts, the incidence of SCI remains high. This review article discusses established and novel adjuncts for spinal cord protection, including priming and preconditioning of the paraspinal collateral network, intraoperative systemic hypothermia, distal aortic perfusion, motor- and somatosensory evoked potentials and noninvasive cnNIRS monitoring as well as peri- and postoperative drainage of cerebrospinal fluid. Regardless of the positive influence of many of these strategies on neurologic outcome, to date no strategy assures definitive preservation of spinal cord integrity during and after aortic aneurysm repair.

Safety of perioperative cerebrospinal fluid drain as a protective strategy during descending and thoracoabdominal open aortic repair

Objective

We present our experience with routine application of the cerebrospinal fluid (CSF) drain (CSFD) during open aortic repair.

Methods

We retrospectively reviewed 100 patients with descending thoracic aortic aneurysm (DTAA) or thoracoabdominal aortic aneurysm (TAAA) or who underwent CSFD insertion before open repair between 2006 and 2017. All CSFDs were inserted by the cardiovascular anesthesia team. The goal was to keep intracranial pressure <10 mm Hg during the surgical procedure by draining CSF at a rate of 20 to 30 mL/h. Postoperatively, CSFD was set to maintain the lumbar pressure <10 mm Hg to reduce the risk of postoperative paraplegia. CSFD was part of our standard cord protection regimen.

Results

The mean patient age was 65.4 ± 11.7 years, and 60 (60%) were male. A CSFD was successfully inserted in all patients. The mean hospital length of stay was 11.9 ± 11.8 days, and hospital mortality was 6%. Postoperative transient paresis was observed in 4 patients (4%), and permanent paraplegia was seen in 2 (2%). CSFD-related complications were reported in 14 patients (14%). Complications included persistent CSF leakage and blood-tinged CSF with and without intracranial hemorrhage and spinal cutaneous fistula in 7 (7%), 9 (9%), and 1 (1%), respectively. Long-term survival was excellent (68.4% at 10 years).

Conclusions

CSFD is a safe practice when applied routinely as an adjunct strategy to prevent paraplegia in surgical management of DTAA and TAAA. We feel that this contributed to good early and late clinical results.

Utility of neuromonitoring in hypothermic circulatory arrest cases for early detection of stroke: Listening through the noise

OBJECTIVE

Stroke remains a potentially devastating complication of aortic arch intervention. The value of neurophysiologic intraoperative monitoring (NIOM) in the early identification of stroke is unclear. We evaluated the utility of NIOM for early stroke detection in aortic arch surgery.

METHODS

Across 8 years at our institution, 365 patients underwent aortic arch surgery with hypothermic circulatory arrest, and 224 cases utilized NIOM. One patient was excluded for intraoperative death. In the remaining cohort, we reviewed the incidence, timing, and location of strokes, and the incidence and nature of NIOM alerts.

RESULTS

Hemiarch was performed in 154 patients and total arch replacement in 69 patients. Stroke occurred in 6.3% of all cases (14 out of 223), 15.9% of total arches (11 out of 69), and 2.0% of hemiarches (3 out of 154). There were 33 NIOM alerts (14.8%), and 9 patients had both alerts and stroke. Of these, NIOM deficits plausibly correlated with imaging findings in 7 cases (78%). Of the 5 stroke patients without NIOM alerts, 2 developed neurologic symptoms 3 days or more postoperatively, and infarcts in 3 patients did not result in sensory or motor deficits. Excluding 2 patients with late stroke, the sensitivity of NIOM for stroke detection was 75%, specificity was 88.5%, positive predictive value was 27.3%, and negative predictive value was 97.4%.

CONCLUSIONS

Despite a low positive predictive value requiring a high level of discrimination when interpreting abnormal findings, NIOM has high sensitivity and specificity for the early stroke detection. Furthermore, its high negative predictive valve is reassuring for low risk of stroke in the absence of alerts.

Clinical Utility of Intraoperative Motor-Evoked Potential Monitoring to Prevent Postoperative Spinal Cord Injury in Thoracic and Thoracoabdominal Aneurysm Repair: An Audit of the Japanese Association of Spinal Cord Protection in Aortic Surgery Database

BACKGROUND

Spinal cord ischemic injury is the most devastating sequela of descending and thoracoabdominal aortic surgery. Motor-evoked potentials (MEPs) have been used to intraoperatively assess motor tract function, but it remains unclear whether MEP monitoring can decrease the incidence of postoperative motor deficits. Therefore, we reviewed multicenter medical records of patients who had undergone descending and thoracoabdominal aortic repair (both open surgery and endovascular repair) to assess the association of MEP monitoring with postoperative motor deficits.

METHODS

Patients included in the study underwent descending or thoracoabdominal aortic repair at 12 hospitals belonging to the Japanese Association of Spinal Cord Protection in Aortic Surgery between 2000 and 2013. Using multivariable mixed-effects logistic regression analysis, we investigated whether intraoperative MEP monitoring was associated with postoperative motor deficits at discharge after open and endovascular aortic repair.

RESULTS

We reviewed data from 1214 patients (open surgery, 601 [49.5%]; endovascular repair, 613 [50.5%]). MEP monitoring was performed in 631 patients and not performed in the remaining 583 patients. Postoperative motor deficits were observed in 75 (6.2%) patients at discharge. Multivariable logistic regression analysis revealed that postoperative motor deficits at discharge did not have a significant association with MEP monitoring (adjusted odds ratio [OR], 1.13; 95% confidence interval [CI], 0.69-1.88; P = .624), but with other factors: history of neural deficits (adjusted OR, 6.08; 95% CI, 3.10-11.91; P < .001), spinal drainage (adjusted OR, 2.14; 95% CI, 1.32-3.47; P = .002), and endovascular procedure (adjusted OR, 0.45; 95% CI, 0.27-0.76; P = .003). The sensitivity and specificity of MEP <25% of control value for motor deficits at discharge were 37.8% (95% CI, 26.5%-49.5%) and 95.5% (95% CI, 94.7%-96.4%), respectively.

CONCLUSIONS

MEP monitoring was not significantly associated with motor deficits at discharge.

Open Replacement of the Thoracoabdominal Aorta: Short- and Long-term Outcomes at a Single Institution

Background  Despite much progress in the surgical and endovascular treatment of thoracoabdominal aortic diseases (TAADs), there is no consensus regarding the optimal approach to minimize operative mortality and end-organ dysfunction. We report our experience in the past 16 years treating TAAD by open surgery. Methods  A retrospective review of all TAAD patients who underwent an open repair since January 2000 was performed. The primary endpoints included early morbidity and mortality, and the secondary endpoints were overall death and rate of aortic reintervention. Results  There were 112 patients treated by open surgery for TAAD. Mean age was 66 ± 10 years and 61 (54%) were male. Seventy-seven (69%) patients had aneurysmal degeneration without aortic dissection and the remaining 35 (31%) had a concomitant aortic dissection. There were 12 deaths (10.7%) and they were equally distributed between the aneurysm and dissection groups ( p  = 0.8). The mortality for elective surgery was 3.2% (2/61). The rate of permanent paraplegia and stroke were each 2.6% (3/112). The rate of cerebrovascular accident was significantly higher in the dissection group (8.5% vs. 1.2%, p  = 0.05). The survival at 1, 5, and 10 years was 80.6, 56.1, and 32.7%, respectively. Conclusion  Our data confirm that open replacement of the thoracoabdominal aorta can be performed in expert centers quite safely. Different aortic pathologies (degenerative aneurysm vs. dissection) do not influence the short- and long-term outcomes. Open surgery should still be considered the standard in the management of TAAD.

Changes in transcranial electrical motor-evoked potentials during the early and reversible stage of permanent spinal cord ischemia predict spinal cord injury in a rabbit animal model

The present study examined changes in the transcranial electrical motor-evoked potentials (TceMEP) waveform to predict neurological deficits and histopathological changes during the early and reversible stage of different levels of permanent spinal cord ischemic injury in a rabbit animal model. A total of 24 New Zealand rabbits were randomly divided into four groups of 6 rabbits each. Group 1 underwent a ligation of the lumbar artery at three levels (L1-L3), group 2 underwent a ligation of the lumbar artery at four levels (L1-L4) and group 3 underwent a ligation of the lumbar artery at five levels (L1-L5). The sham group contained 6 rabbits and did not receive ligation. TceMEP was recorded within 5 min of ligation and, 2 days later, motor function was assessed and the spinal cords were removed for histological examination. Following spinal cord injury, the relationship between variations in the TceMEP waveform and motor function and pathological damage was analyzed. It was observed that the amplitude of TceMEP began to decrease within 1 min of lumbar artery ligation and that the amplitude stabilized within 5 min. These amplitude changes that occurred within 5 min of different levels of permanent spinal cord ischemic injury were positively related to changes in motor function following recovery from anesthesia and 2 days after ligation. The Pearson correlation coefficient was 0.980 and 0.923 for these two time points, respectively (P<0.001). In addition, the amplitude changes were positively related to pathological damage, with a Pearson correlation coefficient of 0.945 (P<0.001). The results of the present study suggested that amplitude changes in TceMEP are particularly sensitive to ischemia. Ischemia may be detected within 1 min and the amplitude changes begin to stabilize within 5 min following ligation of the lumbar artery. The use of intraoperative monitoring of TceMEP allows for the detection of spinal cord ischemic injury with no time delay, which may allow for protective measures to be taken to prevent the occurrence of irreversible spinal cord injury.