Strategies to prevent neurologic deficit based on motor-evoked potentials in type I and II thoracoabdominal aortic aneurysm repair

Intraoperative neurophysiologic monitoring in thoracoabdominal aortic aneurysm surgery can provide real-time feedback for strategic decision making

OBJECTIVES

Despite the introduction of several adjuncts to improve spinal perfusion, spinal cord ischemia (SCI) remains a devastating complication of thoracoabdominal aortic aneurysm (TAAA) repair. Our aim was to assess the effects on clinical outcome of interventions triggered by motor evoked potentials (MEP) alerts. Furthermore, we want to assess whether a multimodal intraoperative neurophysiologic monitoring (IONM) protocol is helpful for stratifying patients according to the risk of SCI at the end of the vascular phase of surgery.

METHODS

We prospectively studied one-hundred consecutive patients who underwent TAAA repair. We applied a multimodal IONM including MEP, somatosensory evoked potentials (SEP) and peripheral nerve monitoring techniques. Signal deteriorations were classified as reversible/irreversible according to whether they recovered or not at the end of monitoring (EOM), set at the end of the vascular phase of surgery. Significant MEP changes drove a series of corrective measures aimed to improve spinal perfusion.

RESULTS

The rate of immediate postoperative motor deficits consistent with SCI was significantly higher with irreversible MEP deteriorations compared to reversible ones. The interpretation of MEP findings at the EOM led to the development of risk categories for SCI, based on the association between MEP results and motor outcome.

CONCLUSIONS

Our data seem to justify interventions made to reverse MEP deterioration in order to improve the clinical outcome. A multimodal IONM protocol could improve MEP interpretation at the end of the vascular phase of surgery, supporting the surgeon in their decision-making, before concluding vascular maneuvers.

Neuromonitoring during descending aorta procedures

Thoraco-abdominal aneurysm (TAA) repair carries a significant risk of spinal cord infarction. The latter results from irreversible changes in the spinal cord arterial network, e.g., sacrifice of the segmental arteries. Intra-operative neurophysiology with somatosensory and especially motor evoked potential (SEP and MEP respectively) monitoring, has emerged as an effective tool to assess the efficiency of the collateral blood flow, detect reversible spinal cord ischemia and guide the peri-operative multidisciplinary management to prevent postoperative paraplegia. The main roles of such monitoring include diagnosis of spinal cord vs peripheral limb ischemia, titration of mean arterial pressure during aortic clamping, the guidance of selective re-implantation of critical segmental arteries, and management of hemodynamics in the immediate postoperative period. In addition, manipulation of the aortic arch and proximal descending aorta, adds the risk of cerebral infarction from both low flow state and/or thromboembolic events. As such, EEG monitoring may be a useful add-on for either assessment of the efficiency of cerebral cooling as a neuroprotective method and/or for detection and treatment of reversible cerebral ischemia. This chapter presents the multimodality approach to open TAA monitoring as a versatile tool for the prevention of devastating postoperative neurologic deficits.

"Awake" Spinal Cord Monitoring Under Local Anesthesia and Conscious Sedation in Fenestrated and Branched Endovascular Aortic Repair

INTRODUCTION

Endovascular repair of thoracoabdominal aortic aneurysms carries a risk of spinal cord ischemia, the causes of which remain uncertain. We hypothesized that local anesthesia (LA) with conscious sedation could abrogate the potential suppressive cardiovascular effects of general anesthesia (GA) and facilitate intraoperative monitoring of neurological function. Here, we examine the feasibility of this technique during fenestrated (FEVAR) or branched endovascular aortic repair (BEVAR).

MATERIALS AND METHODS

Consecutive patients undergoing FEVAR or BEVAR under LA and conscious sedation by a team at a single center were analyzed. Patients received conscious sedation using intravenous remifentanil and propofol infusions in conjunction with a local anesthetic agent. No patient had a prophylactic spinal drain inserted. Outcome measures included conversion to GA, need for vasopressors and/or spinal drainage, length of stay, complications, and patient survival.

RESULTS

A total of 44 patients underwent FEVAR or BEVAR under LA and conscious sedation. The cohort included thoracoabdominal aortic aneurysms (n=41) and pararenal aneurysms treated with endografts covering the supraceliac segment (n=3). Four patients (9%) required conversion to GA at a median operative duration of 198 minutes (range 97-495 minutes). Vasopressors were required intraoperatively in 3 of the cases that were converted to GA. No patient developed spinal cord ischemia and none had insertion of a spinal drain. The median hospital length of stay was 4 days (range 2-41 days). Postoperative delirium and hospital-acquired pneumonia was seen in 7% of patients. All patients survived to 30 days, with 95% alive at a median follow-up of 15 months (range 3-26 months).

CONCLUSION

LA and conscious sedation is a feasible anesthetic technique for the endovascular repair of thoracoabdominal aortic aneurysms.

Case report: Keeping a cool head - A delayed open repair of a ruptured TAAA

INTRODUCTION

The limited resources available for complex surgical procedures during the nightshift can influence the postoperative outcome and are associated with increased complication rates and 30-day mortality. On the other hand, cases of the nightshift are often urgent and demand prompt reaction.

PRESENTATION OF CASE

Hereby we report a patient with a ruptured thoracoabdominal aortic aneurysm, who was admitted during nightshift and was operated 12 h later to gain optimal conditions for such a complex surgical treatment and bypass the nightshift-effect.

DISCUSSION

A review of the literature shows a significant short-term mortality increase on elective procedures performed during the weekend or during the nightshift, however it remains undecisive on the impact of the weekend-effect on emergent procedures.

CONCLUSION

The fortunate recovering of the patient during his hospital stay as well as in the following months emphasizes the importance of critical risk assessment during emergency management, which may justify a delayed surgical treatment.

Arteriogenesis of the Spinal Cord-The Network Challenge

Spinal cord ischemia (SCI) is a clinical complication following aortic repair that significantly impairs the quality and expectancy of life. Despite some strategies, like cerebrospinal fluid drainage, the occurrence of neurological symptoms, such as paraplegia and paraparesis, remains unpredictable. Beside the major blood supply through conduit arteries, a huge collateral network protects the central nervous system from ischemia—the paraspinous and the intraspinal compartment. The intraspinal arcades maintain perfusion pressure following a sudden inflow interruption, whereas the paraspinal system first needs to undergo arteriogenesis to ensure sufficient blood supply after an acute ischemic insult. The so-called steal phenomenon can even worsen the postoperative situation by causing the hypoperfusion of the spine when, shortly after thoracoabdominal aortic aneurysm (TAAA) surgery, muscles connected with the network divert blood and cause additional stress. Vessels are a conglomeration of different cell types involved in adapting to stress, like endothelial cells, smooth muscle cells, and pericytes. This adaption to stress is subdivided in three phases—initiation, growth, and the maturation phase. In fields of endovascular aortic aneurysm repair, pre-operative selective segmental artery occlusion may enable the development of a sufficient collateral network by stimulating collateral vessel growth, which, again, may prevent spinal cord ischemia. Among others, the major signaling pathways include the phosphoinositide 3 kinase (PI3K) pathway/the antiapoptotic kinase (AKT) pathway/the endothelial nitric oxide synthase (eNOS) pathway, the Erk1, the delta-like ligand (DII), the jagged (Jag)/NOTCH pathway, and the midkine regulatory cytokine signaling pathways.

Neuromonitoring Using Motor and Somatosensory Evoked Potentials in Aortic Surgery

BACKGROUND

Motor evoked potentials (MEP) and somatosensory evoked potentials (SSEP) are established methods of neuromonitoring aimed at preventing paraplegia after descending or thoracoabdominal aortic repair. However, their predictive impact remains controversial. The aim of this study was to evaluate our single-center experience using this monitoring technique.

METHODS

Between 2009 and 2014, 78 patients (mean age 66 ± 12, 53% male) underwent either descending or thoracoabdominal aortic repairs. Of these, 60% had an aortic aneurysm, 30% dissection, and 10% other etiologies. Intraoperatively, MEPs and SSEPs were monitored and, if necessary, clinical parameters (blood pressure, hematocrit, oxygenation) were adjusted in response to neuromonitoring signals. This analysis is focused on the neurological outcome (paraplegia, stroke) after the use of intraoperative neuromonitoring.

RESULTS

Thirty-day mortality was 10 (12.8%). All patients with continuously stable signals or signals that returned after signal loss developed no spinal cord injury, whereas two out of six of the evaluable patients with signal loss (without return) during the procedure suffered from postoperative paraplegia (one transient and one permanent). Sensitivity and specificity of use of MEP and SSEP were 100% and 94.20% regarding paraplegia, respectively.

CONCLUSIONS

(1) Preservation of signals or return of signals is an excellent prognostic indicator for spinal cord function. (2) Intraoperative modifications in direct response to the signal change may have averted permanent paralysis in the patients with signal loss without neurologic injury. We have found MEP and SSEP neuromonitoring to be instrumental in the prevention of paraplegia. doi: 10.1111/jocs.12739 (J Card Surg 2016;31:383-389).

Extended Motor Evoked Potentials Monitoring Helps Prevent Delayed Paraplegia After Aortic Surgery

OBJECTIVE

Motor evoked potentials (MEPs) monitoring can promptly detect spinal cord ischemia (SCI) from aortic clamping during open thoracoabdominal aneurysm repair (OTAAR) with distal aortic perfusion (DAP) and thus help decrease the risk of immediate postoperative SCI (IP-SCI). However, neither stable MEPs during aortic clamp interval (ACI) nor absence of IP-SCI eliminate the possibility of delayed postoperative SCI (DP-SCI). We hypothesized that extension of MEPs monitoring beyond ACI can also help decrease the risk of DP-SCI.

METHODS

We identified 150 consecutive patients at our institution between April 2005 and October 2014 who underwent OTAAR with DAP and MEPs monitoring and had no IP-SCI. Using logistic regression analysis, we studied the independent effect of extended MEPs monitoring on the risk of developing DP-SCI. We used a propensity score analysis to adjust for potential confounders, such as poorly controlled hypertension, previous aneurysm surgery, splenectomy, acute aortic dissection, aneurysm type, older age, and history of diabetes and smoking.

RESULTS

From the 150 patients, 129 (86%) remained neurologically intact whereas 21 (14%) developed DP-SCI. Nineteen of these twenty-one patients (90%) had no extended monitoring. Fifty-seven of fifty-nine (97%) patients who benefited from extended monitoring had no DP-SCI (p = 0.003). Extended MEPs monitoring was independently associated with decreased risk of DP-SCI (odds ratio = 0.14; 95% confidence interval: 0.03, 0.65; p = 0.01).

INTERPRETATION

MEPs detect the lowest systemic blood pressure that ensures appropriate spinal cord perfusion in the postoperative period. Thus, they inform the hemodynamic management of patients post-OTAAR, particularly in the absence of a reliable neurological exam.

Neuromonitoring, Cerebrospinal Fluid Drainage, and Selective Use of Iliofemoral Conduits to Minimize Risk of Spinal Cord Injury During Complex Endovascular Aortic Repair

Purpose: To review outcomes of continuous motor/somatosensory-evoked potential (MEP/SSEP) monitoring, cerebrospinal fluid drainage, and selective use of iliofemoral conduits in patients undergoing endovascular repair of descending thoracic aneurysm (DTA) and thoracoabdominal aortic aneurysms (TAAAs). Methods: The clinical data of 49 patients (mean age 75±8 years; 38 men) who underwent endovascular repair of DTA and TAAAs (2011–2014) were reviewed. All patients had cerebrospinal fluid drainage, permissive hypertension (mean arterial pressure ≥80 mm Hg), and MEP/SSEP monitoring. There were 44 (90%) patients with TAAAs and 5 (10%) with DTA. Types I and II TAAAs were repaired in staged procedures. Iliofemoral conduits were used for small iliac arteries and to minimize time of lower extremity ischemia in patients with difficult anatomy. In patients with changes in MEP/SSEPs, a standardized protocol was employed to optimize spinal cord perfusion and restore lower extremity blood flow. Endpoints were mortality, spinal cord injury (SCI), and lower extremity ischemic complications. Results: Sixteen (33%) patients had staged TAAA repair. A total of 163 visceral arteries were targeted by fenestrations and branches (mean 3.7±1.0 vessels/patient). Temporary iliofemoral conduits were used in 16 limbs/14 patients. A stable MEP/SSEP was achieved in all patients. Thirty-one (63%) patients had a ≥75% decrease in MEP/SSEP amplitude in 50 limbs starting on average 75±28 minutes after obtaining vascular access. MEP/SSEP amplitude improved with maneuvers in 12 (39%) patients and returned to baseline with restoration of lower extremity flow in all except 1 patient who developed immediate SCI. Thirty-day mortality was 4%. Three (6%) patients had SCI, 2 permanent and 1 temporary at 14 days. There were no lower extremity ischemic complications. Conclusion: Neuromonitoring predicted immediate SCI and allowed use of a protocol to optimize spinal cord and lower extremity perfusion during complex endovascular aortic repair. Larger clinical experience is needed to evaluate the efficacy of neuromonitoring to prevent SCI.

Intraoperative Changes in Cerebrospinal Fluid Gas Tensions Reflect Paraplegia During Thoracoabdominal Aortic Surgery

Background:

In this study, gas tensions in cerebrospinal fluid (CSF) were prospectively evaluated as intraoperative markers for the detection of neurological deficits.

Methods:

Spinal fluid, serum, and heart lung machine (HLM) perfusate were monitored for gas tensions (po2/pCo2) and related parameters (pH, lactate, and glucose) during thoracoabdominal aortic repair and correlated with perioperative neurological examination and electrophysiological testing.

Results:

Forty-seven patients were assessed for the study, and 40 consecutive patients were finally included. The patients were divided into 3 groups: group A (23 patients, 57.5%): no clinical or laboratory signs of neurological damage; group B (14 patients, 35%) who developed subclinical deficits; and group C (3 patients, 7.5%) who had paraplegia. Significant intraoperative changes in CSF gas tensions were observed with postoperative paraplegia. Glucose ratio between serum and CSF showed higher variability in group C, confirming a damage of the blood–brain barrier (BBB).

Conclusion:

Major neurological damage is reflected by early changes in CSF gas tensions and glucose variability, suggesting damage of the BBB in these patients.

Intraoperative neurophysiological monitoring during resection of intradural extramedullary spinal cord tumors: experience with 100 cases

BACKGROUND

Intradural-extramedullary spinal cord tumor surgery is common. Unlike intramedullary spinal cord tumor surgery, where intraoperative neurophysiological monitoring (IONM) has been described extensively, the application of IONM has not been described in this context, and its relevance has not been investigated.

METHODS

From 2001 to 2012, 100 patients underwent intradural-extramedullary spinal cord tumor resection with IONM. Preoperative and postoperative clinical evaluations were completed retrospectively, using a modified McCormick grading scale and correlated with IONM monitorability and dynamics. IONM consisted of transcranial motor evoked potentials (tcMEP), spinal (D wave) and muscle generators, somatosensory evoked potentials (SSEP), and electromyography (EMG). Both short-term and long-term clinical evaluations were performed. Patient demographics, tumor type, span, location, and morphologic complexity were analyzed.

RESULTS

Surgeries were performed for resection of schwannomas (33 %), meningiomas (22 %), ependymomas (12 %), and other pathologies (20 %); pathology was unknown in 13 % of patients. Tumor locations were cervical in 21 %, thoracic in 46 %, thoracolumbar in 7 %, lumbar 20 %, and not specified in 6 %. Tumors spanned an average of 2.2 spinal levels. Monitorability was 97 and 67 % with tcMEP and SSEP modalities respectively. D waves were monitorable in 73 % of attempts. Intraoperative tcMEP changes were reported in 29 cases with 14 resolved intraoperatively, There were one false-negative outcome and five true-positive outcomes. For SSEP, 13 changes were noted and three resolved; there were three false-negative results and one true-positive result. For D wave monitoring there were two intraoperative changes with none resolved leading to one false negative and one true positive result. With a multimodality approach incorporating any change in evoked potential, IONM demonstrated sensitivity of 0.82, specificity of 0.95, positive predictive value of 0.82, and a negative predictive value of 0.95.

CONCLUSIONS

IONM is feasible and useful in the context of intradural-extramedullary spinal cord surgery for identifying iatrogenic injury to the spinal cord.

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.

Setting up and utilizing a service for measuring perioperative transcranial motor evoked potentials during thoracoabdominal aortic surgery and thoracic endovascular repair

OBJECTIVES

Paraplegia is a complication that may occur following surgery or endovascular stenting of thoracic and thoracoabdominal aortic pathology. Measuring transcranial motor evoked potentials (tcMEPs) has been shown to provide a reliable measure of spinal cord function during such procedures allowing interventions to protect cord function. In the spirit of sharing experience and eliminating the learning curve for others, this manuscript describes our experience of setting up a service for tcMEP monitoring as well as the documents and algorithms for measuring, recording and acting on the patient data, the so-called 'MEP Pathway'.

METHODS

Recording and interpretation of tcMEP during thoracoabdominal aortic intervention requires training of staff and close team working in the operating theatre and postoperative intensive care unit. Providing consistent, reliable, specific and sensitive information on spinal cord function and its safe and effective use to alter patient outcomes requires a protocol. The MEP pathway was developed by medical and paramedical staff at our institution based on clinical experience and literature reviews over a 1-year period (2012-2013).

RESULTS

The tcMEP pathway comprises six documents that guide staff in: (a) assessing suitability of patients, (b) setting up hardware, (c) preparing algorithms for management, (d) documenting intervention (left heart bypass, cardiopulmonary bypass or endovascular stenting) as well as (e) documenting postoperative intensive care processes.

CONCLUSIONS

The tcMEP pathway acts as a guide for safe introduction and use of tcMEPs in thoracoabdominal aortic interventions. tcMEP-led guidance of intraoperative and postoperative management in thoracic aortic surgery is an important adjunct in caring for this patient group.

Intraoperative neurophysiologic monitoring: basic principles and recent update

The recent developments of new devices and advances in anesthesiology have greatly improved the utility and accuracy of intraoperative neurophysiological monitoring (IOM). Herein, we review the basic principles of the electrophysiological methods employed under IOM in the operating room. These include motor evoked potentials, somatosensory evoked potentials, electroencephalography, electromyography, brainstem auditory evoked potentials, and visual evoked potentials. Most of these techniques have certain limitations and their utility is still being debated. In this review, we also discuss the optimal stimulation/recording method for each of these modalities during individual surgeries as well as the diverse criteria for alarm signs.

Transcranial electric motor evoked potential monitoring during spine surgery: is it safe?

STUDY DESIGN

Retrospective review.

OBJECTIVE

To report on the safety of repetitive transcranial electric stimulation (RTES) for eliciting motor-evoked potentials during spine surgery.

SUMMARY OF BACKGROUND DATA

Theoretical concerns over the safety of RTES have hindered broader acceptance of transcranial electric motor-evoked potentials (tceMEP), despite successful implementation of spinal cord monitoring with tceMEPs in many large spine centers, as well as their apparent superiority over mixed-nerve somatosensory-evoked potentials (SSEP) for detection of spinal cord injury.

METHODS

The records of 18,862 consecutive patients who met inclusion criteria and underwent spine surgery with tceMEP monitoring were reviewed for RTES-related complications.

RESULTS

This large retrospective review identified only 26 (0.14%) cases with RTES-related complications; all but one of these were tongue lacerations, most of which were self-limiting.

CONCLUSIONS

The results demonstrate that RTES is a highly safe modality for monitoring spinal cord motor tract function intraoperatively.

Effect of chronic dissection on early and late outcomes after descending thoracic and thoracoabdominal aneurysm repair

OBJECTIVE

Although chronic aortic dissection (CD) has traditionally been considered a predictor of perioperative morbidity and mortality after descending thoracic/thoracoabdominal aneurysm repair (thoracoabdominal aortic aneurysm [TAA]), recent reports have rejected this assertion. Still, few contemporary studies document late outcomes after TAA for CD, which is the goal of this study.

METHODS

From August 1987 to December 2005, 480 patients underwent TAA; 73 (15%) CD and 407 (85%) degenerative aneurysms (DA). Operative management consisted of a clamp-and-sew technique with adjuncts in 53 (78%) CD and 355 (93%) DA patients (P < .001). Epidural cooling was used to prevent spinal cord injury (SCI) in 51 (70%) CD and 214 (53%) DA patients (P = .007). Study end points included perioperative SCI/mortality, freedom from reintervention, and long-term survival.

RESULTS

CD patients were younger (mean age 64.5 years CD vs 72.5 years DA, P < .001) and more frequently had a family history of aneurysmal disease (23% CD vs 6% DA, P < .001). Forty-three (59%) CD patients had elective TAA (vs 322 (79%) DA, P = .001). Eleven (15%) CD patients had Marfan's syndrome (vs 0% DA, P < .001), and 17 (23%) CD patients had a prior arch or ascending aortic repair (vs 16 [4%] DA, P < .001). CD patients were more likely to have Crawford type I & II thoracoabdominal aneurysms (44 [60%] vs 120 [29%] DA, P < .001), while only two (3%) CD patients had type IV aneurysms (vs 99 [24%] DA). There was no difference in perioperative mortality between the two groups (11% CD vs 8.6% DA, P = .52), nor was there a difference in flaccid paralysis, which occurred in five (7%) CD and 22 (5%) DA patients (P = .92). At 5 years, 70% of CD patients were free from reintervention versus 74% of DA (P = .36). The actuarial survival was 53% and 32% at 5 and 10 years for CD versus 47% and 17% for DA (P = .07).

CONCLUSIONS

Despite increased operative complexity, CD does not appear to increase perioperative SCI or mortality after TAA when compared with DA. Long-term freedom from aneurysm-related reintervention is similar for both groups as is survival, despite patients with CD being of younger age at presentation.

Human motor evoked potential responses following spinal cord transection: an in vivo study

Motor evoked potential (MEP) monitoring has been used increasingly in conjunction with somatosensory evoked potential monitoring to monitor neurological changes during complex spinal operations. No published report has demonstrated the effects of segmental spinal cord transection on MEP monitoring.

The authors describe the case of an 11-year-old girl with lumbar myelomeningocele and worsening thoracolumbar scoliosis who underwent a T11–L5 fusion and spinal transection to prevent tethering. Intraoperative MEP and somatosensory evoked potential monitoring were performed, and the spinal cord was transected in 4 quadrants. The MEPs were lost unilaterally as each anterior quadrant was sectioned.

This is the first reported case that demonstrates the link between spinal cord transection and MEP signaling characteristics. Furthermore, it demonstrates the relatively minor input of the ipsilateral ventral corticospinal tract in MEP physiology at the thoracolumbar junction. Finally, this study further supports the use of MEPs as a specific intraoperative neuromonitoring tool.

Surgical treatment of aortic aneurysm and aortic dissection: a retrospective analysis of 122 cases

The study summarizes the clinical experience of surgical treatments of various types of thoracic aneurysm and aortic dissection. Clinical data of 122 patients with thoracic aneurysm and aortic dissection during July 2005 to July 2008 were retrospectively analyzed. The elective operations were performed in 107 patients while emergency surgery was done in 15 cases. Different surgical strategies were employed on the basis of diseased region, including simple ascending aortic replacement (n=3), aortic root replacement (n=43), hemi-arch replacement /total arch replacement+elephant trunk technique (n=32), thoracic/thoracoabdominal aortic replacement (n=8) and endovascular repair (n=36). In this series, there is 4 cases of perioperative death due to massive cerebral hemorrhage (n=1), respiratory failure (n=1) and multiple organ dysfunction syndrome (MODS) (n=2). Three cases developed post-operative massive cerebral infarction and the relatives of the patients abandoned treatment. Instant success rate of endovascular repair was 100%. The intimal rupture was sealed. Blood flow was unobstructed in true lumen and no false lumen was visualized. It was concluded that aggressive surgery should be considered in the patients with thoracic aneurysm and aortic dissection. Surgical procedures should vary with the location and the nature of the lesions.

Erythropoietin during porcine aortic balloon occlusion-induced ischemia/reperfusion injury

BACKGROUND

Aortic occlusion causes ischemia/reperfusion injury, kidney and spinal cord being the most vulnerable organs. Erythropoietin improved ischemia/reperfusion injury in rodents, which, however, better tolerate ischemia/reperfusion than larger species. Therefore, we investigated whether erythropoietin attenuates porcine aortic occlusion ischemia/reperfusion injury.

MATERIALS AND METHODS

Before occluding the aorta for 45 mins by inflating intravascular balloons, we randomly infused either erythropoietin (n = 8; 300 IU/kg each over 30 mins before and during the first 4 hrs of reperfusion) or vehicle (n = 6). During aortic occlusion, mean arterial pressure was maintained at 80% to 120% of baseline by esmolol, nitroglycerine, and adenosine 5'-triphosphate. During reperfusion, noradrenaline was titrated to keep mean arterial pressure >80% of baseline. Kidney perfusion and function were assessed by fractional Na-excretion, p-aminohippuric acid and creatinine clearance, spinal cord function by lower extremity reflexes and motor evoked potentials. Blood isoprostane levels as well as blood and tissue catalase and superoxide dismutase activities allowed evaluation of oxidative stress. After 8 hrs of reperfusion, kidney and spinal cord specimens were taken for histology (hematoxylin-eosin, Nissl staining) and immunohistochemistry (TUNEL assay for apoptosis).

RESULTS

Parameters of oxidative stress and antioxidative activity were comparable. Erythropoietin reduced the noradrenaline requirements to achieve the hemodynamic targets and may improve kidney function despite similar organ blood flow, histology, and TUNEL staining. Neuronal damage and apoptosis was attenuated in the thoracic spinal cord segments without improvement of its function.

CONCLUSION

During porcine aortic occlusion-induced ischemia/reperfusion erythropoietin improved kidney function and spinal cord integrity. The lacking effect on spinal cord function was most likely the result of the pronounced neuronal damage associated with the longlasting ischemia.

Hybrid procedures for thoracoabdominal aortic aneurysms and chronic aortic dissections - a single center experience in 28 patients

OBJECTIVE

We report our 6-year experience with the visceral hybrid procedure for high-risk patients with thoracoabdominal aortic aneurysms (TAAA) and chronic expanding aortic dissections (CEAD).

METHODS

Hybrid procedure includes debranching of the visceral and renal arteries followed by endovascular exclusion of the aneurysm. A series of 28 patients (20 male, mean age 66 years) were treated between January 2001 and July 2007. Sixteen patients had TAAAs type I-III, one type IV, four thoracoabdominal placque ruptures, and seven patients CEAD. Patients were treated for asymptomatic, symptomatic, and ruptured aortic pathologies in 20, and 4 patients, respectively. Two patients had Marfan's syndrome; 61% had previous infrarenal aortic surgery. The infrarenal aorta was the distal landing zone in 70%. In elective cases, simultaneous approach (n = 9, group I) and staged approach (n = 11, group II) were performed. Mean follow-up is 22 months (range 0.1-78).

RESULTS

Primary technical success was achieved in 89%. All stent grafts were implanted in the entire thoracoabdominal aorta. Additionally, three patients had previous complete arch vessel revascularization. Left subclavian artery was intentionally covered in three patients (11%). Thirty-day mortality rate was 14.3% (4/28). One patient had a rupture before the staged endovascular procedure and died. Overall survival rate at 3 years was 70%, in group I 80%, and in group II 60% (P = .234). Type I endoleak rate was 8%. Permanent paraplegia rate was 11%. Three patients required long-term dialysis (11%). Peripheral graft occlusion rate was 11% at 30 days. Gut infarction with consecutive bowel resection occurred in two patients. There was no significant difference between group I and II regarding paraplegia and complications.

CONCLUSIONS

Early results of visceral hybrid repair for high-risk patients with complex and extended TAAAs and CEADs are encouraging in a selected group of high risk patients in whom open repair is hazardous and branched endografts are not yet optional.

Alarm criteria for motor-evoked potentials: what's wrong with the "presence-or-absence" approach?

STUDY DESIGN

Combined prospective and retrospective.

OBJECTIVE

Evaluate 2 published criteria for interpreting motor-evoked potentials (MEP) in response to repetitive transcranial electrical stimulation (rTES) during surgery.

SUMMARY OF BACKGROUND DATA

There is controversy regarding how to interpret MEPs elicited by rTES. Many centers warn the surgical team only if the MEP is lost entirely ("Presence-or-Absence" method). Alternatively, we monitor the stimulus energy needed to elicit a minimal evoked EMG response; significant increases in this energy reflect impending motor tract injury and serve as the basis for warning the surgical team ("Threshold-Level" method).

METHODS

We documented target muscle thresholds for rTES throughout each subject's surgical procedure. The time (in hours) between intraoperative threshold change and (a) complete loss of response or (b) until the end of the surgical procedure was determined. Short-term postoperative motor status was documented by either direct physical examination or by chart review.

RESULTS

We enrolled 903 subjects, from whom intraoperative rTES-evoked responses could be elicited in 859 subjects. Of these, 93 subjects sustained intraoperative damage to central motor pathways. Significant increases in target muscle thresholds were often noted many minutes, and sometimes hours before complete signal loss. In other cases, thresholds increased significantly without ever losing the muscle response.

CONCLUSION

The Threshold-Level method is highly sensitive and specific to deterioration in central motor function, and provides early warning of such an event. Conversely, in some cases the Presence-or-Absence method may fail to detect episodes of partial loss, and in other cases typically introduces a delay between the times when motor dysfunction begins to occur and when the response is lost (at which time an alarm is triggered). We conclude that use of the Presence-or-Absence alarm criteria for interpreting MEPs during surgery is often incompatible with the requirement for accurate and early warning of impending injury to central motor pathways, and should be avoided.

The value of motor evoked potentials in reducing paraplegia during thoracoabdominal aneurysm repair

OBJECTIVE

Paraplegia after thoracoabdominal aortic aneurysm (TAAA) repair mainly occurs in patients with Crawford extent I and II. We assessed the impact of monitoring spinal cord integrity and the subsequent adjusted surgical maneuvers on neurologic outcome in repairs of type I and II TAAAs.

METHODS

Surgical repair of TAAAs was performed in 112 consecutive patients with extent type I (n = 42) and type II (n = 70) aneurysms. The surgical protocol included cerebrospinal fluid drainage, moderate hypothermia, and left heart bypass with selective organ perfusion. Spinal cord function was assessed by means of monitoring motor evoked potentials (MEPs). Significant decreased MEPs always generated adjustments, including raising distal aortic and mean arterial pressure, reattachment of visible intercostal arteries, or endarterectomy of the excluded aortic segment with revascularization of back bleeding intercostal arteries.

RESULTS

Motor evoked potential monitoring could be achieved in all patients. By maintaining a mean distal aortic pressure of 60 mm Hg, MEPs were adequate in 82% of patients. Increasing distal aortic pressure restored MEPs in all patients. In 19 patients (17%), MEPs decreased significantly during aortic cross-clamping because of critical spinal cord ischemia. MEPs returned in all patients after spinal cord blood flow was re-established except in three patients with type II TAAA in whom MEPs could not be restored, and absent MEPs at the end of the procedure corresponded with neurologic deficit. Delayed paraplegia developed in two patients owing to hemodynamic instability with insufficient mean arterial blood pressure to maintain adequate spinal cord perfusion.

CONCLUSION

Monitoring MEPs is a highly reliable technique to assess spinal cord ischemia during TAAA repair. A surgical protocol including cerebrospinal fluid drainage, left heart bypass, and monitoring of MEPs can reduce the paraplegia rate significantly. Adjusted hemodynamic and surgical strategies induced by changes in MEPs could restore spinal cord ischemia in most patients, preventing early and late paraplegia in all type I patients. In type II patients, early paraplegia occurred in 4.2% and delayed neurologic deficit in 2.9%. Despite all available measures, complete prevention of paraplegia in type II aneurysms seems to be unrealistic.

Role of Somatosensory Evoked Potentials in Predicting Outcome During Thoracoabdominal Aortic Repair

BACKGROUND

Clinical utility of somatosensory evoked potentials (SSEP) in descending thoracic and thoracoabdominal aortic repair is debated. We reviewed our practical experience with SSEP in descending thoracic and thoracoabdominal aortic repairs.

METHODS

Between January 2000 and April 2005, we used SSEP monitoring in 444 patients (270 thoracoabdominal aorta and 174 descending thoracic aorta). Median age was 68 years; 36% were female. Only changes of spinal origin were analyzed. Changes were classified as (1) no change, (2) transient changes that returned to baseline by the end of the procedure, or (3) persistent changes that did not return to baseline by the end of the procedure.

RESULTS

Somatosensory evoked potential changes occurred in 87 (19.6%) patients; 22 (25%) of these did not return to baseline. Immediate neurologic deficit occurred in 8 of 444 patients (1.8%); five deficits (5 of 87; 5.8%) occurred in patients with SSEP changes, compared with three deficits (3 of 357; 0.8%) in patients without changes. Odds ratio for this comparison was 7.2 (p < 0.002). Somatosensory evoked potential was a poor screening tool for neurologic deficit, with a sensitivity of 62.5% and specificity 81.2%. Negative predictive value was 99.2%, indicating a very low event probability in the absence of SSEP changes. Delayed neurologic deficit occurred in 3.2% and was not related to SSEP changes. Somatosensory evoked potential changes were also associated with increased 30-day mortality and low glomerular filtration rate.

CONCLUSIONS

Intraoperative SSEP monitoring was reliable in ruling out spinal injury in descending thoracic and thoracoabdominal aortic repair, but had a low sensitivity. It did not predict delayed neurologic deficit. Spinal SSEP change was an independent predictor of mortality and correlated with low preoperative glomerular filtration rate.

Spinal cord ischemia after endovascular repair of the descending thoracic aorta in a sheep model

OBJECTIVES

Spinal cord ischemia remains a devastating complication after thoracic aortic surgery. The aim of this study was to investigate the pathophysiology of spinal cord ischemia after thoracic aortic endografting and the role of intercostal artery blood supply for the spinal cord in a standardized animal model.

METHODS

Female merino sheep were randomized to either I, open thoracotomy with cross-clamping of the descending aorta for 50 min (n=7), II, endograft implantation (TAG, WL Gore & Ass.), (n=6) or III open thoracotomy with clipping of all intercostal arteries (n=5) . CT-angiography was used to assess completion of surgical protocol and assess the fate of intercostal arteries. Tarloy score was used for daily neurological examination for up to 7 days post-operatively. Histological cross sections of the lumbar, thoracic and cervical spinal cords were scored for ischemic damage after stained with Hematoxylin-Eosin, Klüver-Barrrera and antibodies. Exact Kruskall-Wallis-Test was used for statistical assessment (p<0.05).

RESULTS

Incidence of paraplegia was 100% in group I and 0% in group II (p=0.0004). When compared to the endovascular group, there was a higher rate of histological changes associated with spinal cord ischemia in the animals of the control group (p=0.0096). Group III animals showed no permanent neurological deficit and only 20% infarction rate (p=0.0318 compared to group I).

CONCLUSIONS

In sheep, incidence of histological and clinical ischemic injury of the spinal cord following endografting was very low. Complete thoracic aortic stent-grafting was feasible without permanent neurologic deficit. Following endovascular coverage or clipping of their origins, there is retrograde filling of the intercostal arteries which remain patent.

Prolonged loss of leg myogenic motor evoked potentials during thoracoabdominal aortic aneurysm repair, without postoperative paraplegia

No postoperative paraplegia occurred in a patient whose leg myogenic motor evoked potentials (mMEPs) disappeared during thoracoabdominal aortic aneurysm repair. A 69-year-old man underwent resection and repair of a type III (Crawford classification) thoracoabdominal aneurysm. An epidural catheter was placed into the epidural space for epidural cooling, and a Swan-Ganz catheter was placed into the subarachnoid space for cerebrospinal fluid (CSF) drainage. Continuous CSF pressure and temperature measurement was carried out the day before surgery. The mMEPs gradually disappeared 10 min after proximal double aortic clamping and complete aortic transection. Selective perfusion of intercostal arteries was started about 20 min after the loss of the mMEPs, but the mMEPs were not restored. Possibly, spinal cord hyperemia, induced by selective perfusion of the intercostal vessels, narrowed the subarachnoid space so that CSF could not be satisfactorily drained during surgery. The spinal cord hyperemia may have decreased spinal function and suppressed the leg mMEPs. The persistence of the loss of mMEPs was undeniably due to the influence of the anesthetic agent or a perfusion disorder in the lower-extremity muscles. Of note, moderate spinal cord hypothermia and postoperative CSF drainage probably resulted in improved lower-limb motor function.

Thoracic and Thoracoabdominal Aneurysm Repair: Is Reimplantation of Spinal Cord Arteries a Waste of Time?

BACKGROUND

The impact of different strategies for management of intercostal and lumbar arteries during repair of thoracic and thoracoabdominal aortic aneurysms (TAA/A) on the prevention of paraplegia remains poorly understood.

METHODS

One hundred consecutive patients with intraoperative monitoring of motor evoked potentials (MEP) and somatosensory evoked potentials (SSEP) during TAA/A repair involving serial segmental artery sacrifice (October 2002 to December 2004) were reviewed.

RESULTS

Operative mortality was 6%. The median intensive care unit stay was 2.5 days (IQ range: 1-4 days), and the median hospital stay 10.0 days (IQ range: 8-17 days). Potentials remained unchanged during the course of serial segmental artery sacrifice, or could be returned to baseline levels by anesthetic and blood pressure manipulation, in 99 of 100 cases. An average of 8.0 +/- 2.6 segmental artery pairs were sacrificed overall, with an average of 4.5 +/- 2.1 segmental pairs sacrificed between T7 and L1, where the artery of Adamkiewicz is presumed to arise. Postoperative paraplegia occurred in 2 patients. In 1, immediate paraplegia was precipitated by an intraoperative dissection, resulting in 6 hours of lower body ischemia. A second ambulatory patient had severe paraparesis albeit normal cerebral function after resuscitation from a respiratory arrest.

CONCLUSIONS

With monitoring of MEP and SSEP, sacrifice--without reimplantation--of as many as 15 intercostal and lumbar arteries during TAA/A repair is safe, resulting in acceptably low rates of immediate and delayed paraplegia. This experience suggests that routine surgical implantation of segmental vessels is not indicated, and that, with evolving understanding of spinal cord perfusion, endovascular repair of the entire thoracic aorta should ultimately be possible without spinal cord injury.

Transcutaneous near-infrared spectroscopy for detection of regional spinal ischemia during intercostal artery ligation: Preliminary experimental results

OBJECTIVE

Real-time information about regional spinal cord ischemia can guide intraoperative management and reduce the risk of paraplegia after thoracic aortic surgery. We hypothesized that near-infrared spectroscopy could provide such information during intercostal and lumbar artery ligation in pigs.

METHODS

Transcutaneous near-infrared spectroscopic sensors were placed in the midline over the upper and lower thoracic vertebrae of 4 progressively larger pigs (weight range 21-70 kg). After the entire aorta was exposed, segmental arteries from T6 through L1 were sequentially ligated while regional oxygen saturation was monitored. Decreases in regional oxygen saturation were calculated as percentage changes from baseline. The degrees of ischemia in the upper and lower spinal cord were compared histopathologically.

RESULTS

Baseline regional oxygen saturations were similar in the upper (68.8% +/- 9.0%) and lower (68.0% +/- 11.5%, P = .82) cord. After ligation, however, regional oxygen saturation levels were significantly lower in the lower cord (41.3% +/- 10.1%) than in the upper cord (64.8% +/- 9.3%, P = .037). The regional oxygen saturation had decreased by 39.0% +/- 11.5% in the lower cord but only by 6.3% +/- 7.6% in the upper cord (P = .026). This difference was confirmed microscopically: upper-cord sections had fewer ischemic neurons (8.8 +/- 9.4) than did lower-cord sections (21.3 +/- 13.6, P = .002).

CONCLUSION

Intraoperative spinal cord ischemia was detectable with near-infrared spectroscopy in pigs weighing as much as 70 kg. The potential utility of this technique in patients undergoing thoracic aortic surgery warrants investigation.