Usefulness of transcranial motor evoked potentials during thoracoabdominal aortic surgery

Usefulness of Motor Evoked Potential Measurement and Analysis of Risk Factors for Spinal Cord Ischaemia from 300 Cases of Thoracic Endovascular Aortic Repair

OBJECTIVE

This study investigated the usefulness of motor evoked potentials (MEPs) for intra-operative monitoring to detect the risk of spinal cord ischaemia (SCI) during thoracic endovascular aortic repair (TEVAR). Risk factors for SCI in TEVAR were also analysed.

METHODS

Among 330 TEVARs performed from February 2009 to October 2018, 300 patients underwent intra-operative MEP monitoring. SCI risk groups were extracted based on MEP amplitude changes using a cutoff value of 50%. When the amplitude decreased to < 50% of the pre-operative value, intra-operative mean arterial pressure (MAP) was increased by about 20 mmHg using noradrenaline, whereas MAP was usually controlled to about 80 mmHg during surgery. Other efforts were also made to increase MEP amplitude by increasing cardiac output, correcting anaemia, and finishing the surgery promptly. Based on MEP amplitude data, SCI risk groups were extracted and risk factors for SCI in TEVAR were analysed.

RESULTS

A total of 283 non-SCI risk patients and 17 SCI risk patients by MEP monitoring were extracted; only 1.0% developed immediate paraplegia and none developed delayed paraplegia. Bivariable analysis showed significant differences in chronic kidney disease, haemodialysis, artery of Adamkiewicz closure, and stent graft (SG) covered length ≥ 8 vertebral bodies. Logistic regression analysis showed hyperlipidaemia (odds ratio [OR] 3.55, 95% confidence interval [CI] 1.08 - 11.67; p = .037), SG covered length ≥ 8 vertebral bodies (OR 1.35, 95% CI 1.02 - 1.78; p = .034), and haemodialysis (OR 27.78, 95% CI 6.02 - 128.22; p < .001) were the most influential risk factors for SCI in TEVAR.

CONCLUSION

MEPs might be a useful monitoring tool to predict SCI in TEVAR. In addition, hyperlipidaemia, SG covered length ≥ 8 vertebral bodies, and haemodialysis represent key risk factors for SCI during TEVAR.

Updated review on the use of neuromuscular blockade during intraoperative motor-evoked potential monitoring in the modern anesthesia era

Transcranial electrical stimulation motor-evoked potentials (Tc-MEP) monitoring is a common practice in neurosurgery to prevent postoperative neurological damage. However, the use of neuromuscular blocking agents (NMBAs) during Tc-MEP monitoring is a subject of controversy. In addition, the effectiveness of sugammadex, a selective reversal agent, in the context of Tc-MEP monitoring requires further investigation. This review aimed to clarify the considerations involved in achieving optimal Tc-MEP monitoring while ensuring patient safety. Preoperative patient selection, comorbidity assessment, motor power evaluation, and the nature of the planned surgery are critical factors. Accurate paralysis assessment, continuous NMBA infusion, and post-tetanic stimulation techniques are essential for achieving optimal partial NMB. The decision to administer an NMB during Tc-MEP monitoring necessitates a careful evaluation of the balance between accuracy and potential complications. This review emphasizes the challenges associated with NMB administration during Tc-MEP monitoring and highlights the need for personalized patient assessment.

Clinical feasibility and safety of transoesophageal motor-evoked potential monitoring

OBJECTIVES

Canine experiments have shown that transoesophageal motor-evoked potential monitoring is feasible, safe and stable, with a quicker response to ischaemia and a better prognostic value than transcranial motor-evoked potentials. We aimed to elucidate whether or not these findings were clinically reproducible.

METHODS

A bipolar oesophageal electrode mounted on a large-diameter silicon tube and a train of 5 biphasic wave stimuli were used for transoesophageal stimulation. Results of 18 patients (median age 74.5 years, 13 males) were analysed.

RESULTS

There were no mortalities, spinal cord injuries or complications related with transoesophageal stimulation. Transcranial motor-evoked potential could not be monitored up to the end of surgery in 3 patients for unknown reasons, 2 of whom from the beginning. Transoesophageal motor-evoked potential became non-evocable after manipulation of a transoesophageal echo probe in 2 patients. Strenuous movement of the upper limbs during transoesophageal stimulation was observed in 3 patients. In 14 patients who successfully completed both monitoring methods up to the end of surgery (11 thoraco-abdominal and 3 descending aortic repair), the final results were judged as false positives in 6 by transcranial stimulation and in 1 by transoesophageal stimulation. The stimulation intensity was significantly lower and the upper limb amplitude was significantly higher by transoesophageal stimulation, while the lower limb amplitude was comparable.

CONCLUSIONS

Transoesophageal motor-evoked potential monitoring is clinically feasible and safe with a low false positive rate. A better electrode design is required to avoid its migration by transoesophageal echo manipulation. Further studies may be warranted.

CLINICAL REGISTRATION NUMBER

UMIN000022320.

Bipolar transesophageal thoracic spinal cord stimulation: A novel clinically relevant method for motor-evoked potentials

Objective

Although transesophageal motor-evoked potential elicited by monopolar cervical cord stimulation is more stable and rapid in response to ischemia than transcranial motor-evoked potential in canine experiments, direct cervical alpha motor neuron stimulation precludes clinical application. We evaluated a novel stimulation method using a bipolar esophageal electrode to enable thoracic cord stimulation.

Methods

Twenty dogs were anesthetized. For bipolar transesophageal stimulation, the interelectric pole distance was set at 4 cm. Changes in amplitude in response to incremental stimulation intensity (100-600 V) were measured to evaluate stability. Spinal cord ischemia was induced by aortic balloon occlusion at the T8 to T10 level for 10 minutes to evaluate response time or at the T3 to T5 level for 25 minutes to evaluate prognostic value. Neurological function was evaluated using the Tarlov score at 24 and 48 hours postoperatively.

Results

Bipolar transesophageal stimulation was successful in all animals and their forelimb waveforms were identical to those after transcranial stimulation. The minimum stimulation intensity to produce >90% of the maximum amplitude was significantly lower in both monopolar and bipolar transesophageal stimulation than in transcranial stimulation (n = 5). Time to disappearance and recovery (>75%) of the hindlimb potentials were significantly shorter by both monopolar and bipolar transesophageal stimulation than by transcranial stimulation (n = 5). Correlation with neurological outcomes was comparable among all stimulation methods (n = 10).

Conclusions

Motor-evoked potential can be elicited by bipolar transesophageal thoracic cord stimulation without direct cervical alpha motor neuron stimulation, and its stability and response time are comparable to those elicited by monopolar stimulation.

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.

Reappearance of Motor-Evoked Potentials During the Rewarming Phase After Deep Hypothermic Circulatory Arrest

OBJECTIVE

Although motor-evoked potentials (MEPs) disappear in deep hypothermic circulatory arrest (DHCA), MEPs have been used to confirm whether motor function is intact after DHCA. It is crucial to know the timing, body temperature, and MEP amplitude at MEP reappearance to detect spinal cord ischemia after DHCA. However, data on these parameters are sparse. The authors investigated the characteristics of MEPs at reappearance after DHCA.

DESIGN

A retrospective observational study.

SETTING

Single national center.

PARTICIPANTS

Sixty-one patients who underwent descending aortic replacement and thoracoabdominal aortic replacement with DHCA between January 2013 and December 2015.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The authors extracted the following data: time to MEP reappearance after the end of lower extremity circulatory arrest, bladder temperature (BT) and nasopharyngeal temperature (NPT) when MEPs recovered, and %amplitude of MEPs relative to control values at MEP reappearance. The median time to MEP reappearance was approximately 70 minutes. BT at MEP reappearance ranged from 34.3°C to 34.6°C and NPT ranged from 36.2°C to 36.4°C. At MEP reappearance, %amplitude less than 50% of the control value was observed in more than 50% of patients. Time to MEP reappearance had a significant positive association with rewarming time (p < 0.01) and BT (p = 0.03).

CONCLUSIONS

There was a wide variation in MEP amplitude at reappearance during the rewarming phase. BT was approximately 34°C when MEPs in the leg recovered. The time to MEP reappearance is influenced significantly by rewarming time and BT.

Diagnostic and Prognostic Relevance of Magnetic Resonance Imaging and Electrophysiological Findings in Acute Spinal Ischemia

OBJECTIVE

Our purpose was to classify the rare entity of spontaneous spinal ischemia with clinical, magnetic resonance-tomographic, and electrophysiological parameters to determine criteria for outcome prediction.

METHODS

We analyzed the stroke registry database of the University Hospital Mannheim, Germany, from 2004 to 2010 for patients with a diagnosis of vascular spinal cord ischemia.

RESULTS

Ten patients were identified (mean age 65 years [range 50-83], 5 women). In 5 patients an etiology was found. Spinal diffusion-weighted magnetic resonance imaging revealed acute ischemia in 7 patients at initial imaging and this diagnosis was confirmed during the first week in the remaining 3 patients. Electrophysiological studies showed abnormal motor evoked potentials (MEPs) in 8 patients and abnormal somatosensory evoked potentials (SSEPs) in 7 patients. After rehabilitation, 5 patients had regained walking ability, whereas 5 patients stayed wheelchair bound. All patients with unfavorable outcome (American Spinal Injury Association (ASIA) Impairment score [AIS] score of ≤C) showed severe pyramidal tract lesions in MEPs during the first week. All patients with normal MEPs had an excellent outcome (AIS of E, P < .05).

CONCLUSIONS

Diffusion-weighted imaging (DWI) is a useful tool to confirm acute spinal ischemia suspected in patients within the first days after symptom onset. Poor outcome was associated with severe electrophysiological abnormalities in MEPs and SSEPs. Normal MEPs were significantly predictive of an excellent prognosis. A multimodal diagnostic approach combining DWI and electrophysiological evaluation facilitates the prediction of the individual clinical outcome.

Transesophageal versus transcranial motor evoked potentials to monitor spinal cord ischemia

OBJECTIVES

We have previously reported that transesophageal motor evoked potential is feasible and more stable than transcranial motor evoked potential. This study aimed to investigate the efficacy of transesophageal motor evoked potential to monitor spinal cord ischemia.

METHODS

Transesophageal and transcranial motor evoked potentials were recorded in 13 anesthetized dogs at the bilateral forelimbs, anal sphincters, and hindlimbs. Spinal cord ischemia was induced by aortic balloon occlusion at the 8th to 10th thoracic vertebra level. In the 12 animals with motor evoked potential disappearance, occlusion was maintained for 10 minutes (n = 6) or 40 minutes (n = 6) after motor evoked potential disappearance. Neurologic function was evaluated by Tarlov score at 24 and 48 hours postoperatively.

RESULTS

Time to disappearance of bilateral motor evoked potentials was quicker in transesophageal motor evoked potentials than in transcranial motor evoked potentials at anal sphincters (6.9 ± 3.1 minutes vs 8.3 ± 3.4 minutes, P = .02) and hindlimbs (5.7 ± 1.9 minutes vs 7.1 ± 2.7 minutes, P = .008). Hindlimb function was normal in all dogs in the 10-minute occlusion group, and motor evoked potentials recovery (>75% on both sides) after reperfusion was quicker in transesophageal motor evoked potentials than transcranial motor evoked potentials at hindlimbs (14.8 ± 5.6 minutes vs 24.7 ± 8.2 minutes, P = .001). At anal sphincters, transesophageal motor evoked potentials always reappeared (>25%), but transcranial motor evoked potentials did not in 3 of 6 dogs. In the 40-minute occlusion group, hindlimb motor evoked potentials did not reappear in 4 dogs with paraplegia. Among the 2 remaining dogs, 1 with paraparesis (Tarlov 3) showed delayed recovery (>75%) of hindlimb motor evoked potentials without reappearance of anal sphincter motor evoked potentials. In another dog with spastic paraplegia, transesophageal motor evoked potentials from the hindlimbs remained less than 20%, whereas transcranial motor evoked potentials showed recovery (>75%).

CONCLUSIONS

Transesophageal motor evoked potentials may be superior to transcranial motor evoked potentials in terms of quicker response to spinal cord ischemia and better prognostic value.

Is There Any Benefit of Neuromonitoring during Descending and Thoracoabdominal Aortic Aneurysm Repair?

Objective

Paraplegia remains the most feared and a devastating complication after descending and thoracoabdominal aneurysm operative repair (DTA and TAAAR). Neuromonitoring, particularly use of motor-evoked potentials (MEPs), for this surgery has gained popularity. However, ambiguity remains regarding its use and benefit. We systematically reviewed the literature to assess the benefit and applicability of neuromonitoring in DTA and TAAAR.

Methods

Electronic searches were performed on 4 major databases from inception until February 2014 to identify relevant studies. Eligibility decisions, method quality, data extraction, and analysis were performed according to predefined clinical criteria and end points.

Results

Among the studies matching our inclusion criteria, 1297 patients had MEP monitoring during DTA and TAAAR. In-hospital mortality was low (6.9% ± 3.6). Immediate neurological deficit was low (3.5% ± 2.6). In one third of patients (30.4% ± 14.2), the MEPs dropped below threshold, which were 30.4% and 29.4% with threshold levels of 75% and 50%, respectively. A range of surgical techniques were applied after reduction in MEPs. Most patients whose MEPs dropped and remained below threshold had immediate permanent neurological deficit (92.0% ± 23.6). Somatosensory-evoked potentials were reported in one third of papers with little association between loss of somatosensory-evoked potentials and permanent neurological deficit (16.7% ± 28.9%).

Conclusions

We demonstrate that MEPs are useful at predicting paraplegia in patients who lose their MEPs and do not regain them intraoperatively. To date, there is no consensus regarding the applicability and use of MEPs. Current evidence does not mandate or support MEP use.

Methodology of motor evoked potentials in a rabbit model

Spinal cord ischemia (SCI) is a devastating complication of aortic operations. Neuromonitoring using motor evoked potentials (MEPs) is a sensitive modality to detect SCI in humans. We describe a leporine SCI model using MEPs to test pharmaceutical therapeutics and other neuroprotective adjuncts. In 80 rabbits, methods to obtain MEPs in normotensive and ischemic rabbits were developed. The effects of isoflurane, propofol, apnea, and hypotension on lower extremity MEPs were studied. Lower extremity MEPs disappear upon SCI induction in 78 of 78 (100 %) rabbits. Prior to SCI induction and during apneic episodes, lower extremity MEPs were lost in all (100 %) and upper extremity MEPs in one (25 %). Isoflurane was used in four experiments, with loss of lower extremity MEPs in all four (100 %) and loss of upper extremity MEPs in zero. With propofol upper extremity, MEPs were obtainable in 80 of 80 rabbits (100 %) and lower extremity MEPs in 78 of 80 rabbits (97.5 %) prior to SCI induction. The presence of these lower extremity MEPs prior to SCI induction was not correlated with systolic or diastolic blood pressure. Disappearance of MEPs occurred in all 45 rabbits with postoperative lower extremity impairment. MEPs in the leporine model correlate closely with paraplegia. MEPs are influenced by inhaled anesthetics and apnea but not by hypotension alone. Propofol anesthesia provides reliable MEPs. This study provides the basis for a reproducible model of SCI to be used for novel therapeutic drug development.

A novel microwave sensor to detect specific biomarkers in human cerebrospinal fluid and their relationship to cellular ischemia during thoracoabdominal aortic aneurysm repair

Thoraco-abdominal aneurysms (TAAA) represents a particularly lethal vascular disease that without surgical repair carries a dismal prognosis. However, there is an inherent risk from surgical repair of spinal cord ischaemia that can result in paraplegia. One method of reducing this risk is cerebrospinal fluid (CSF) drainage. We believe that the CSF contains clinically significant biomarkers that can indicate impending spinal cord ischaemia. This work therefore presents a novel measurement method for proteins, namely albumin, as a precursor to further work in this area. The work uses an interdigitated electrode (IDE) sensor and shows that it is capable of detecting various concentrations of albumin (from 0 to 100 g/L) with a high degree of repeatability at 200 MHz (R(2) = 0.991) and 4 GHz (R(2) = 0.975).

Spinal cord injury following thoracic and thoracoabdominal aortic repairs

Objective

To discuss the currently available approaches to prevent spinal cord injury during thoracic and thoracoabdominal aortic repairs.

Methods

We carried out a PubMed search up to 2013 using the Medical Subject Headings: “aortic aneurysm/surgery” and “spinal cord ischemia”; “aortic aneurysm, thoracic/surgery” and “spinal cord ischemia”; “aneurysm/surgery” and “spinal cord ischemia/cerebrospinal fluid”; “aortic aneurysm/surgery” and “paraplegia”. All 190 original articles satisfying our inclusion criteria were analyzed for incidence, predictors, and other pertinent variables related to spinal cord injury, and we compared the results in recent publications with those in earlier reports.

Results

The mean age of the 38,491 patients was 65.3 ± 4.9 years. The overall incidence of paraplegia and/or paraparesis was 7.1% ± 6.1% (range 0%–32%). The incidence of spinal cord injury before 2000, from 2001 to 2007, and 2008–2013 was 9.0% ± 6.7%, 7.0% ± 6.1%, and 5.9% ± 5.2%, respectively ( p = 0.019). Various predictors of spinal cord injury were identified, extent of disease being the most common. Modification of surgical techniques, use of adjuncts, and better understanding of spinal cord perfusion physiology were attributed to the decrease in postoperative spinal cord injury in recent years.

Conclusions

Spinal cord injury after thoracic and thoracoabdominal aortic repair poses a real challenge to cardiovascular surgeons. However, with evolving surgical strategies, identification of predictors, and use of various adjuncts over the years, the incidence of spinal cord injury after thoracic/thoracoabdominal aortic repair has declined. Embracing a multimodality approach offers a good insight into combating this grave complication.

Transoesophageal spinal cord stimulation for motor-evoked potentials monitoring: feasibility, safety and stability

OBJECTIVES

Specificity of transcranial motor-evoked potentials (MEPs) is low because amplitude fluctuation is common, which seems due to several technical and fundamental reasons including difficulty in electrodes positioning and fixation for transcranial stimulation and susceptibility to anaesthesia. This study aimed to investigate the feasibility, safety and stability of our novel technique of transoesophageal spinal cord stimulation to improve the stability of MEPs.

METHODS

Ten anaesthetized adult beagle dogs were used. Transoesophageal stimulation was performed between the oesophageal luminal surface electrode (cathode) and a subcutaneous needle electrode (anode) at the fourth to fifth thoracic vertebra level. Stimulation was achieved with a train of five pulses delivered at 2.0-ms intervals. Compound muscle action potentials were recorded from four limbs and external anal sphincter muscles. Stability to anaesthetic agents was tested at varying speeds of propofol and remifentanil, and effects of varying concentration of sevoflurane inhalation were also evaluated.

RESULTS

Transoesophageal MEPs could be recorded without difficulty in all dogs. Fluoroscopic evaluation showed that electrodes misalignment up to 5 cm cranially or caudally could be tolerated. Stimulus intensity to achieve maximum amplitude of hindlimb muscle potentials on both sides was significantly lower by transoesophageal stimulation than by transcranial stimulation (383 ± 41 vs 533 ± 121 V, P = 0.02) and had less interindividual variability. Latency of transoesophageal MEPs was shorter than that of transcranial MEPs at every recording point. No arrhythmia was provoked during stimulation. Animals that were allowed to recover showed no neurological abnormality. In the two sacrificed animals, the explanted oesophagus showed no mucosal injury. Stability to varying dose of anaesthetic agents was similar between transoesophageal and transcranial stimulation, except for the potentials of forelimbs by transoesophageal stimulation that were resistant to anaesthetic depression.

CONCLUSIONS

Transoesophageal stimulation for MEPs monitoring was feasible without difficulty and safe. Although its stability to anaesthetic agents was similar to that of transcranial stimulation, its technical ease and small interindividual variability warrants further studies on the response to spinal cord ischaemia.

Changes of motor evoked potentials during descending thoracic and thoracoabdominal aortic surgery with deep hypothermic circulatory arrest

BACKGROUND

Paraplegia is a serious complication of descending and thoracoabdominal aortic aneurysms (dTAAs and TAAAs) surgery. Motor evoked potentials (MEPs) enable monitoring the functional integrity of motor pathways during dTAA and TAAA surgery. Although MEPs are sensitive to temperature changes, there are few human data on changes of MEPs during mild and deep hypothermia. Therefore, we investigated changes of MEPs in deep hypothermic circulatory arrest (DHCA) in dTAA and TAAA surgery.

METHODS

Fifteen consecutive patients undergoing dTAA and TAAA surgery using DHCA were enrolled. MEPs were elicited and recorded during each degree Celsius change in nasopharyngeal temperature during both the cooling and rewarming phases. Hand and leg skin temperature were also recorded simultaneously.

RESULTS

In the cooling phase MEP amplitude decreased lineally in both the hand and leg. The MEP disappeared at ~16°C in both the hand and leg in 10 of 15 patients, but was still elicited in 5 patients. In the rewarming phase MEP in the hand recovered before the temperature reached 20°C for eight patients and 25°C for the other seven patients. In contrast, MEP in the leg recovered below 20°C for two patients and 30°C for three patients. For the other eight patients MEP waves did not recover during the rewarming phase.

CONCLUSION

In the cooling phase of DHCA, MEP disappeared at ~16°C in some patients but was still elicited in others. MEP recovered below 25°C in the hand. Recovery of MEP in the leg was, however, extremely variable.

Can intraoperative motor-evoked potentials predict all the spinal cord ischemia during moderate hypothermic beating heart descending thoracic or thoraco-abdominal aortic surgery?

BACKGROUND AND AIM OF THE STUDY

Paraplegia is a serious complication of descending thoracic or thoraco-abdominal aortic aneurysm (DTAA or TAAA, respectively) surgery. The functional integrity of the spinal cord can be monitored with intraoperative motor-evoked potentials (MEPs). Herein, we evaluated the results and adequacy of MEP monitoring.

METHODS AND RESULTS

Between March 2006 and April 2009, 33 patients (24 males and 9 females) were monitored with MEPs and reviewed retrospectively. The mean age was 50.7 ± 15.2 years. Eighteen and 15 patients underwent TAAA and DTAA repairs, respectively. We routinely used femoro-femoral partial bypass and cerebrospinal fluid (CSF) drainage. If the MEP demonstrated a significant change, prompt protective interventions were performed. During the procedure, 31 patients (93.9%) had a detectable MEP, of whom four had significant MEP changes and only one had an accompanying alteration in the somatosensory-evoked potential. In-hospital mortality occurred in two patients (6.0%) because of mesenteric ischemia and sepsis, respectively. Postoperative paraplegia developed in two patients (6.0%), one with an undetectable MEP and another with no significant intraoperative MEP change. Both patients had hypotensive events and impaired CSF drainage in the immediate postoperative period. Permanent paraplegia persisted in one patient. In four patients with intraoperative MEP changes, paraplegia did not occur.

CONCLUSIONS

Although intraoperative monitoring of MEP has been shown to be effective in detecting cord ischemia during DTAA or TAAA surgery, it is not definitive and cannot predict all neurologic deficits. Other postoperative preventive strategies such as CSF drainage and maintaining a high blood pressure are important to prevent paraplegia.

Heat shock proteins as biomarkers for the rapid detection of brain and spinal cord ischemia: a review and comparison to other methods of detection in thoracic aneurysm repair

The heat shock proteins (HSPs) are members of highly conserved families of molecular chaperones that have multiple roles in vivo. We discuss the HSPs in general, and Hsp70 and Hsp27 in particular, and their rapid induction by severe stress in the context of tissue and organ expression in physiology and disease. We describe the current state of knowledge of the relationship and interactions between extra- and intracellular HSPs and describe mechanisms and significance of extracellular expression of HSPs. We focus on the role of the heat shock proteins as biomarkers of central nervous system (CNS) ischemia and other severe stressors and discuss recent and novel technologies for rapid measurement of proteins in vivo and ex vivo. The HSPs are compared to other proposed small molecule biomarkers for detection of CNS injury and to other methods of detecting brain and spinal cord ischemia in real time. While other biomarkers may be of use in prognosis and in design of appropriate therapies, none appears to be as rapid as the HSPs; therefore, no other measurement appears to be of use in the immediate detection of ongoing severe ischemia with the intention to immediately intervene to reduce the severity or risk of permanent damage.

A case of difficulty predicting neurological deficit during thoracoabdominal aortic surgery

Perioperative spinal cord injury associated with thoracoabdominal aorta (TAAA) surgery is a devastating complication. With variable results, the intraoperative use of neurophysiologic monitoring has been employed for the diagnosis and prevention of spinal cord ischemia. We present a case report of a patient undergoing TAAA surgery with the use of evoked potential monitoring. Intraoperatively, both sensory and motor evoked potentials were utilized and consequently the patient experienced changes in monitoring consistent with a new neurologic deficit. However, postoperatively these changes in evoked potentials never manifested in neurologic injury. We examine the utility of neurophysiologic monitoring as it pertains to TAAA surgery.

Endovascular repair in the thoracic and abdominal aorta: no increased risk of spinal cord ischemia when both territories are treated

PURPOSE

To evaluate the morbidity associated with thoracic and abdominal aortic repair using endovascular exclusion alone or combined endovascular and open repair.

METHODS

Between January 1998 and February 2007, 49 patients (36 men; mean age 70 years) underwent treatment for thoracic and abdominal aorta disease with descending thoracic aortic (DTA) stent-graft and abdominal aortic repair. Thirty-nine patients with coexisting thoracic and abdominal pathologies were classified with multilevel aortic disease (MLAD), whereas 10 patients presented with thoracoabdominal aneurysm. Patients were separated into 3 groups: 1: thoracic stent-grafts and open abdominal repair (n = 18), group 2: thoracic and abdominal stent-grafts (n = 21), and group 3: thoracic stent-grafts with visceral artery debranching (n = 10). Prior carotid-subclavian bypass was performed in 3 (6%) patients with a dominant left vertebral artery.

RESULTS

Stent-graft deployment was technically successful in all cases. Eight (16%) patients underwent emergent thoracic stent-graft placement. In 9 (18%) patients, the left subclavian artery was covered. No incidence of spinal cord ischemia was observed. The 30-day mortality was 4%, and overall mortality was 6% over a mean 33-month follow-up. The endoleak rate was 6% (1 type I, 1 type II, and 1 type III).

CONCLUSION

Conventional or endovascular abdominal open repair in combination with DTA stent-grafting is feasible and a safe alternative to traditional open repair. Management of MLAD did not show increased incidence of spinal cord ischemia and was associated with fewer complications and deaths than simultaneous or staged open thoracic and abdominal repairs.

Current approach on spinal cord monitoring: the point of view of the neurologist, the anesthesiologist and the spine surgeon

Optimal outcome in spine surgery is dependent of the coordination of efforts by the surgeon, anesthesiologist, and neurophysiologist. This is perhaps best illustrated by the rising use of intraoperative spinal cord monitoring for complex spine surgery. The challenges presented by neurophysiologic monitoring, in particular the use of somatosensory and motor evoked potentials, requires an understanding by each member for the team of the proposed operative procedure as well as an ability to help differentiate clinically important signal changes from false positive changes. Surgical, anesthetic, and monitoring issues need to be addressed when relying on this form of monitoring to reduce the potential of negative outcomes in spine surgery. This article provides a practical overview from the perspective of the neurophysiologist, the anesthesiologist, and the surgeon on the requirements which must be understood by these participants in order to successfully contribute to a positive outcome when a patient is undergoing complex spine surgery.