Spinal cord protection during thoracoabdominal aortic aneurysm repair: results of selective reconstruction of the critical segmental arteries guided by evoked spinal cord potential monitoring

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.

Intraoperative monitoring for spinal radiculomedullary artery aneurysm occlusion treatment: What, when, and how long?

BACKGROUND

Spinal radiculomedullary artery aneurysms are extremely rare. Treatment should be tailored to clinical presentation, distal aneurysm flow, and lesion anatomical features. When a surgical occlusion is planned, it is necessary to evaluate whether intraoperative monitoring (IOM) should be considered as an indispensable tool to prevent potential spinal cord ischemia.

METHODS

We present a patient with symptoms and signs of spinal subarachnoid hemorrhage resulting from the rupture of a T4 anterior radiculomedullary aneurysm who underwent open surgical treatment under motor evoked potential (MEP) monitoring.

RESULTS

Due to the aneurysmal fusiform shape and preserved distal flow, the afferent left anterior radiculomedullary artery was temporarily clipped; 2 minutes after the clamping, the threshold stimulation level rose higher than 100 V, and at minute 3, MEPs amplitude became attenuated over 50%. This was considered as a warning criteria to leave the vessel occlusion. The radiculomedullary aneurysm walls were reinforced and wrapped with muscle and fibrin glue to prevent re-bleeding. The patient awoke from general anesthesia without focal neurologic deficit and made an uneventful recovery with complete resolution of her symptoms and signs.

CONCLUSION

This paper attempts to build awareness of the possibility to cause or worsen a neurological deficit if a radiculomedullary aneurysm with preserved distal flow is clipped or embolized without an optimal IOM control. We report in detail MEP monitoring during the occlusion of a unilateral T4 segmental artery that supplies an anterior radiculomedullary artery aneurysm.

Organ Protection During Thoracoabdominal Aortic Surgery: Rationale for a Multimodality Approach

Surgical repair of thoracoabdominal aortic aneurysms (TAAAs) remains a technically challenging operation that requires a systematic approach to prevent ischemic complications and achieve excellent clinical outcomes. Techniques for organ protection have evolved substantially over the past 20 years. This review describes our current multimodality approach to organ protection during TAAA repair.

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.

Cerebrospinal fluid drainage for thoracic and thoracoabdominal aortic aneurysm surgery

BACKGROUND

During aortic aneurysm surgery, cross-clamping can lead to inadequate blood supply to the spinal cord resulting in neurological deficit. Cerebrospinal fluid drainage (CSFD) may increase the perfusion pressure to the spinal cord and hence reduce the risk of ischaemic spinal cord injury.

OBJECTIVES

To determine the effect of CSFD during thoracic and thoracoabdominal aortic aneurysm (TAAA) surgery on the risk of developing spinal cord injury.

SEARCH METHODS

For this update the Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (last searched May 31 2012) and CENTRAL (2012, Issue 5) for publications describing randomised controlled trials of cerebrospinal fluid drainage for thoracic and thoracoabdominal aortic aneurysm surgery. Reference lists of relevant articles were checked.

SELECTION CRITERIA

Randomised trials involving CSFD during thoracic and TAAA surgery.

DATA COLLECTION AND ANALYSIS

Both authors assessed the quality of trials independently. SNK extracted data and GS verified the data.

MAIN RESULTS

Three trials with a total of 287 participants operated on for Type I or II TAAA were included.In the first trial of 98 participants, neurological deficits in the lower extremities occurred in 14 (30%) of CSFD group and 17 (33%) controls. The deficit was observed within 24 hours of the operation in 21 (68%), and from three to 22 days in 10 (32%) participants. CSFD did not have a significant benefit in preventing ischaemic injury to the spinal cord.The second trial of 33 participants used a combination of CSFD and intrathecal papaverine. It showed a statistically significant reduction in the rate of postoperative neurological deficit (P = 0.039), compared to controls. Analysis was undertaken after only one third of the estimated sample size had entered the trial.In the third trial TAAA repair was performed on 145 participants. CSFD was initiated during the operation and continued for 48 hours after surgery. Paraplegia or paraparesis occurred in 9 of 74 participants (12.2%) in the control group versus 2 of 82 participants (2.7%) receiving CSFD (P = 0.03). Overall, CSFD resulted in an 80% reduction in the relative risk of postoperative deficits. Meta-analysis showed an odds ratio (OR) of 0.48 (95 % confidence interval (CI) 0.25 to 0.92). For CSFD-only trials, OR was 0.57 (95% CI 0.28 to 1.17) and for intention-to-treat analysis in CSFD-only studies, the OR remained unchanged.

AUTHORS' CONCLUSIONS

There are limited data supporting the role of CSFD in thoracic and thoracoabdominal aneurysm surgery for prevention of neurological injury. Further clinical and experimental studies are indicated.

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.

Risk of spinal cord injury after operations of recurrent aneurysms of the descending aorta

BACKGROUND

Degenerative disease of the aorta usually involves the occlusion of several intercostal and lumbar branches by mural thrombus or atherosclerotic plaques, suggesting that the blood supply to the spinal cord is mainly provided through collateral networks. Patients with previous abdominal aortic aneurysm repair and subsequent thoracoabdominal aortic reconstruction must undergo ligation of a number of these segmental arteries, presenting a greater risk of experiencing spinal cord ischemic injury.

METHODS

The records of 18 patients who had experienced abdominal aortic aneurysm graft replacement and who had undergone 19 operations for thoracoabdominal aortic repair were retrospectively evaluated. All patients were male. The mean age was 66 +/- 10 years (range, 36 to 75 years); the mean interval between the two operations was 79 +/- 69 months (range, 1 to 231 months). There were 18 (95%) cases of thoracoabdominal aortic aneurysms, and one (5%) case of acute dissection of the thoracoabdominal aorta. The origin of the Adamkiewicz artery was determined preoperatively by computed tomography. Measures to avoid spinal cord injury included monitoring of evoked spinal cord potentials and selective reconstruction of the intercostal arteries under hypothermic cardiopulmonary bypass.

RESULTS

There were three (16%) cases of permanent neurologic injury that included one cerebrovascular accident, one neurogenic bladder, and one paraparesis of the right lower limb. There were no cases of paraplegia or postoperative deaths.

CONCLUSIONS

Surgical reconstruction of the thoracoabdominal aorta in patients who previously underwent abdominal aortic graft replacement is not related to an increased probability of developing spinal cord ischemic injury.

Cerebrospinal fluid drainage for thoracic and thoracoabdominal aortic aneurysm surgery

BACKGROUND

During aortic aneurysm surgery, cross-clamping can lead to inadequate blood supply to the spinal cord resulting in neurological deficit. Cerebrospinal fluid drainage (CSFD) may increase the perfusion pressure to the spinal cord and hence reduce the risk of ischaemic spinal cord injury.

OBJECTIVES

To determine the effect of CSFD during thoracic and thoracoabdominal aortic aneurysm (TAAA) surgery on the risk of developing spinal cord injury.

SEARCH STRATEGY

The reviewers searched the Cochrane Peripheral Vascular Diseases Group Specialised Trials Register (last searched October 2003), the Cochrane Central Register of Controlled Trials (CENTRAL) database (last searched Issue 4, 2003), MEDLINE and EMBASE, and reference lists of relevant articles. Recent conference proceedings were scanned.

SELECTION CRITERIA

Randomised trials involving CSFD during thoracic and TAAA surgery.

DATA COLLECTION AND ANALYSIS

Both reviewers assessed the quality of trials independently. One reviewer (SNK) extracted data and the other reviewer (GS) verified the data.

MAIN RESULTS

Three trials, with a total of 287 participants operated on for type I or II TAAA, were included. In the first trial of 98 patients, neurological deficits in the lower extremities occurred in 14 (30%) CSFD and 17 (33%) controls. The deficit was observed within 24 hours of the operation in 21 (68%), and from 3 to 22 days in 10 (32%). CSFD did not have a significant benefit in preventing ischaemic injury to the spinal cord. The second trial of 33 patients used a combination of CSFD and intrathecal papaverine. It showed a statistically significant reduction in the rate of postoperative neurological deficit (p = 0.039), compared to controls. Analysis was undertaken after only one third of the estimated sample size had entered the trial. In the third trial TAAA repair was performed on 145 patients. CSFD was initiated during the operation and continued for 48 hours after surgery. Paraplegia or paraparesis occurred in 9 of 74 patients (12.2%) in the control group versus 2 of 82 patients (2.7%) with CSFD (p = 0.03). Overall, CSFD resulted in an 80% reduction in the relative risk of postoperative deficits. Meta-analysis showed an odds ratio (OR) of 0.48 (0.25 to 0.92; confidence interval (CI) 95%). For CSFD trials only OR was 0.57 (0.28 to 1.17) and for intention-to-treat in CSFD only studies OR remained unchanged.

REVIEWER'S CONCLUSIONS

There are limited data supporting the role of CSFD in thoracic and thoracoabdominal aneurysm surgery for prevention of neurological injury. Further clinical and experimental studies are indicated.

The use of an aortoiliac side-arm conduit to maintain distal perfusion during thoracoabdominal aortic aneurysm repair

Thoracoabdominal aneurysm repair continues to be associated with a significant risk of operative complications, many of which are related to the prolonged period of aortic cross clamping inherent in the procedure. A variety of adjuvant techniques have been used in attempts to decrease morbidity, including atriofemoral extracorporal bypass, subarachnoid drainage, epidural cooling, and preliminary axillofemoral bypass. Herein is described a method to maintain distal perfusion with a side-arm conduit, originating from the most proximal aspect of the aortic graft and terminating on the left iliac artery. The technique has the potential to minimize hemodynamic instability while decreasing the period of pelvic and lower extremity ischemia and simplifying reattachment of aortic branch vessels. This method provides another option that can be considered in these technically demanding operative procedures.

Effect of nitrous oxide on myogenic motor evoked potentials during hypothermia in rabbits anaesthetized with ketamine/fentanyl/propofol

BACKGROUND

A number of authors have reported that anaesthetics suppress myogenic motor evoked potentials (MEPs). However, the influence of hypothermia on these effects is unknown. Therefore we investigated the effects of hypothermia on nitrous oxide-induced suppression of myogenic MEPs.

METHODS

Twenty-two rabbits anaesthetized with ketamine, fentanyl and propofol were randomly allocated to one of three groups, with oesophageal temperatures of 40 degrees C (n = 8), 35 degrees C (n = 7) and 30 degrees C (n = 7). Myogenic MEPs in response to electrical stimulation of the motor cortex with a train of five pulses were recorded from the soleus muscle. Following the control recording, nitrous oxide was administered at concentrations of 30%, 50%, and 70% in random order, and MEPs were recorded. Control MEP amplitudes and percentage of control MEP amplitudes (%MEP amplitude) during the administration of nitrous oxide were compared between the three groups.

RESULTS

Control MEP amplitudes were similar between the three groups. Nitrous oxide suppressed MEPs in a dose-dependent manner in all groups. During the administration of nitrous oxide, % MEP amplitudes at 35 degrees C and 30 degrees C (hypothermia) were significantly lower than those at 40 degrees C (normothermia).

CONCLUSION

These results suggest that nitrous oxide-induced suppression of MEPs may be augmented during hypothermia.

Proinflammatory cytokines in cerebrospinal fluid in repair of thoracoabdominal aorta

BACKGROUND

Little is known about alterations of cytokine levels in cerebrospinal fluid (CSF) during thoracoabdominal aortic surgery. We measured perioperative CSF cytokine levels to determine their clinical significances.

METHODS

Perioperative serum and CSF levels of cytokine were measured in 15 adult patients undergoing repair of the descending thoracic aorta (n = 4) or thoracoabdominal aorta (n = 11). All patients underwent prosthetic replacement and perioperative CSF drainage. Serum and CSF levels of tumor necrosis factor-alpha, Interleukin- (IL-) 1beta, IL-6, IL-8, IL-10, and IL-12 were measured before operation and at 0, 6, 12, 18, 24, 48, and 72 hours postoperatively using enzyme-linked immunosorbent assays.

RESULTS

There were no hospital deaths, but 1 patient suffered paraplegia. Cerebrospinal fluid IL-8 levels peaked at immediately after operation (751.7 +/- 42.1 pg/mL versus preoperative levels, 54.9 +/- 24.6 pg/mL; p < 0.001), and the higher levels persisted for 72 hours. In contrast, serum IL-8 levels did not change and remained lower than CSF levels. The patient with paraplegia had the highest CSF IL-8 levels throughout the study period. Serum and CSF levels of tumor necrosis factor-alpha, IL-1beta, IL-6, and IL-12 did not significantly change. Serum and CSF levels of IL-10 were significantly elevated after operation compared with preoperative levels. In contrast to IL-8, serum IL-10 levels surpassed CSF levels.

CONCLUSIONS

Cerebrospinal fluid IL-8 levels are significantly elevated in thoracoabdominal aortic operation, and may be the most sensitive to the inflammatory response in the ischemic spinal cord injury. Persistent elevation of CSF IL-8 levels may be predictive of further development of neurologic deficits, and a reduction of proinflammatory cytokine levels may be a beneficial effect of CSF drainage, but this requires further investigation.

Monitoring of intrathecal oxygen tension during experimental aortic occlusion predicts ultrastructural changes in the spinal cord

OBJECTIVE

To study the correlation between intrathecal PO2 and ultrastructural changes in the spinal cord during thoracic aortic occlusion in pigs.

MATERIAL AND METHODS

In 18 pigs, online intrathecal oxygenation was monitored by a multiparameter Paratrend catheter (Biomedical Sensors, High Wycombe, United Kingdom) during 60 minutes' clamping of the proximal and distal descending thoracic aorta. The animals were randomly divided into 2 groups (A and B) depending on the level of distal aortic clamping. Distal aortic perfusion was restored through an aorto-iliac shunt, which also maintained low thoracic segmental perfusion of the spinal cord in group B. Perfusion-fixation technique was used before harvesting the spinal cord specimens, which later were evaluated with light and electron microscopy by an independent observer. Intrathecal parameters were interpreted as normal if PO2 was more than 0.8 kPa and PCO2 was less than 12 kPa, as intermediate ischemia if PO2 was 0.8 or less or PCO (2) was more than 12 kPa, and as absolute ischemia if PO2 was 0.8 or less and PCO2 was more than 12 kPa.

RESULTS

Among 6 animals with ultrastructural changes of absolute spinal cord ischemia-reperfusion injury, 5 also had absolute ischemia according to variables derived by the Paratrend catheter. The 2 methods were in agreement in 3 of 5 animals with intermediate ischemia-reperfusion changes and in 5 of 6 animals with normal findings. The accuracy of cerebrospinal fluid PO2 and PCO2 to predict electron microscopy-verified intermediate or absolute ischemia-reperfusion injury was 94%.

CONCLUSIONS

Monitoring of intrathecal PO2 after clamping of the descending aorta correlated with ultrastructural changes in the spinal cord in this pig model.

Selective perfusion of segmental arteries in patients undergoing thoracoabdominal aortic surgery

BACKGROUND

Reattachment of segmental arteries is one method used to prevent paraplegia associated with thoracoabdominal aortic repair. Nevertheless, even when important segmental arteries are reattached, ischemia causing spinal injury may occur during anastomosis.

METHODS

In 27 patients undergoing thoracoabdominal aortic repair, we attempted to perfuse the segmental arteries to be reattached with catheters connected to the distal bypass circuit. To identify perioperative risk factors for spinal ischemia, we examined changes in spinal somatosensory evoked potentials.

RESULTS

A median value of four segmental arteries were perfused in 20 (74%) of the 27 patients. Changes in somatosensory evoked potential indicative of spinal ischemia were observed in 13 patients (48%). The only risk factor associated with changes in evoked potentials revealed by a multivariate analysis was prolonged aortic cross-clamp time (> 120 minutes). Of the 2 patients who suffered paraplegia, one had the longest clamp time and the other showed spinal cord necrosis due to embolic shower.

CONCLUSIONS

Despite selective perfusion of segmental arteries, spinal ischemia associated with aortic cross-clamping may occur when clamping is prolonged over 120 minutes. Most of the changes appear to be reversible, however.

Lazaroid reduces production of IL-8 and IL-1 receptor antagonist in ischemic spinal cord injury

BACKGROUND

21-aminosteroids (lazaroids) have demonstrated the protective effect against cerebral ischemic injury through the inhibition of lipid peroxidation. We examined whether lazaroids affected the production of proinflammatory and antiinflammatory cytokines in ischemic spinal cord injury model.

MATERIALS

Anesthetized New Zealand white rabbits underwent a 20-minute infrarenal aortic cross-clamping (AXC) with pretreatment of either an intravenous 3 mg/kg lazaroid U74389G (group L; n = 10) or the same volume saline (group P; n = 10). Sham operation group (group S; n = 6) underwent only exposure of the aorta. Plasma concentrations of interleukin (IL)-8, -1beta, -1 receptor antagonist (IL-1ra) and tumor necrosis factor (TNF)-alpha were measured at four time points. Functional assessment with Tarlov score at 24 and 48 hours after pretreatment, pathologic assessment of the spinal cord, and measurements of cytokine levels in the spinal cord were performed.

RESULTS

The maximum elevation of plasma IL-8 and -1ra levels occurred at 1 hour after declamping in four measurement points. Plasma IL-8 and -1ra levels in group L were significantly lower than those in group P (*p < 0.05). Plasma TNFalpha peaked at 5 minutes after declamping, but decreased afterwards. Plasma TNFalpha levels were not different among three groups. Spinal IL-8 levels in group L (0.98 +/- 0.34 ng/g tissue) were lower than those in group P (7.26 +/- 2.26 ng/g tissue)(*p < 0.05). Spinal IL-1ra and TNFalpha were not significantly different. Tarlov score and pathologic assessment were better in group L.

CONCLUSIONS

Lazaroid U-74389G reduced the production of systemic IL-8 and -1ra and spinal IL-8 when AXC caused spinal cord injury. These results indicate that lazaroids may attenuate ischemic endothelial cell injury or activation of leukocytes.

Spinal cord monitoring

Over the past two decades, intraoperative spinal cord monitoring has matured into a widely used clinical tool. It is used when the spinal cord is at risk for damage during a surgical procedure. This includes orthopedic, neurosurgical, and certain cardiothoracic procedures. Both somatosensory evoked potential (SEP) and direct motor pathway stimulation techniques are available. The SEP techniques are used most widely, are generally accepted, and have been shown to reduce surgical morbidity. A large multicenter study has shown that SEP monitoring reduces postoperative paraplegia by more than 50-60%. Techniques and literature on clinical applications are reviewed in this report.

Thoracoabdominal aortic aneurysm repair with sequential visceral perfusion: A technical note

The aim of this study was to develop a method for type III and type IV thoracoabdominal aortic aneurysm (TAA) repair that reduces ischemia time to the abdominal viscera, spinal cord, and lower extremities. Over a 25-month period, five type IV TAAs and three type III TAAs were repaired with a trifurcated polytetrafluoroethylene (PTFE) graft to bypass three of four visceral vessels and another graft to reconstruct the thoracoabdominal aorta. The trifurcated graft was sewn end-to-side to an unaffected area of descending thoracic aorta. Sequential end-to-end bypasses to the left renal, superior mesenteric, and celiac arteries followed this anastomosis. The remaining TAA was then replaced with a Dacron tube or bifurcated graft by clamping distal to the trifurcated graft so as to maintain visceral and left renal artery perfusion. Implantation of the right renal artery into the Dacron graft completed visceral artery reconstruction. The postoperative results indicate the feasibility of type III and IV TAA repair using tangential thoracic aortic clamping, individual aortic branch vessel reconstruction, and separate distal revascularization. This operative technique decreases ischemia time to the abdominal viscera, spinal cord, and lower extremities.

Site of origin of spinal cerebrospinal fluid pulse wave

: Since vascular pulsation in the cerebrospinal fluid causes the cerebrospinal fluid pulse wave (CSFPW), spinal CSFPW may serve as a monitor of spinal cord blood flow. However, there are two possible sources of spinal CSFPW: brain and spinal cord pulsation, and it is unclear for which region spinal CSFPW provides blood flow information. To resolve this question, we analyzed changes in CSFPW caused by occlusion of the large vessels in mongrel dogs. The thoracic and abdominal aorta (TA group, n = 13; AA, n = 6), bilateral internal carotid arteries (ICA, n = 7), and superior and inferior vena cava (SVC, n = 6; IVC, n = 8) were occluded. The CSFPW was measured at the second cervical and sixth lumbar spine level. To eliminate the influence of hemodynamic changes caused by the occlusion, CSFPWs were decomposed into component frequencies, harmonic waves (HWs), and analyzed using the system analysis method. After occlusion, cervical CSFPW was decreased in groups ICA (change in the first HW, 38%; P < 0.05 by Wilcoxon signed-ranks test), TA (40%; P < 0.05), and SVC (53%; P < 0.05), while lumbar CSFPW was decreased in groups TA (71%; P < 0.01), AA (78%; P < 0.05), and IVC (48%; P < 0.05). These results show that spinal CSFPW provides information on the blood flow of a relatively localized region, and could be used to monitor spinal cord blood flow.

Cardiac function is a risk factor for paralysis in thoracoabdominal aortic replacement

PURPOSE

We studied factors that influence paralysis risk, renal function, and mortality in thoracoabdominal aortic replacement.

METHODS

We prospectively collected preoperative demographic and intraoperative physiologic data and used univariate and multivariate analyses to correlate this data with risk factors for paralysis. A mathematical model of paraplegia risk was used to study the efficacy of paraplegia reduction strategies. We analyzed preoperative and operative factors for paralysis risk, renal function, and mortality for 217 consecutive patients surgically treated from 1984 through 1996 for 176 thoracoabdominal and 41 thoracic aneurysms at the University of Wisconsin Hospital and Clinics. No patient had intercostal reimplantation or assisted circulation. One hundred fifty patients (group A) received cerebrospinal fluid drainage (CSFD) and low-dose naloxone (1 microg/kg/hour) as adjuncts to reduce the risk of paralysis. Sixty-seven patients (group B) did not receive CSFD and naloxone.

RESULTS

Seventeen deficits occurred in 205 surviving patients: 5 of the 147 in group A (expected deficits = 31) and 12 of the 58 in group B (expected deficits = 13) (p < 0.001). In a multivariate logistic regression model, acute presentation, Crawford type 2 aneurysm, group B membership, and a decrease in cardiac index with aortic occlusion remained significant risk factors for deficit (p < 0.0001). By odds ratio analysis, group A patients had 1/40th the risk of paralysis of group B. The only significant predictor of postoperative renal function was the preoperative creatinine level (p < 0.0001); renal revascularization significantly improved renal function. The mortality rate was 1.6% (2) for patients undergoing elective treatment and 21% (19) for patients who had acute presentations. Acute presentation, age, and the preoperative creatinine level were found to be significant factors for operative mortality in a logistic regression model (p < 0.001) and defined a group at high risk for death.

CONCLUSIONS

CSFD and low-dose naloxone significantly reduce the paralysis risk associated with thoracoabdominal aortic replacement. A decrease in the cardiac index with aortic occlusion is a previously unreported variable that defines a subset of patients at higher risk for paralysis.

Preliminary report on prediction of spinal cord ischemia in endovascular stent graft repair of thoracic aortic aneurysm by retrievable stent graft

OBJECTIVE

To predict spinal cord ischemia after endovascular stent graft repair of descending thoracic aortic aneurysms, temporary interruption of the intercostal arteries (including the aneurysm) was performed by placement of a novel retrievable stent graft (Retriever) in the aorta under evoked spinal cord potential monitoring.

METHODS

From February 1995 to October 1997, endovascular stent graft repair of descending thoracic aortic aneurysms was performed in 49 patients after informed consent was obtained. In 16 patients with aneurysms located in the middle and distal segment of the descending aorta, the Retriever was placed temporarily before stent graft deployment. The Retriever consisted of two units of self-expanding zigzag stents connected in tandem with stainless steel struts. Each strut was collected in a bundle fixed to a pushing rod, and the stent framework was lined with an expanded polytetrafluoroethylene sheet. The Retriever was delivered beyond the aneurysm through a sheath and was retracted into the sheath 20 minutes later. A stent graft for permanent use was deployed in patients whose predeployment test results with the Retriever were favorable. Evoked spinal cord potential was monitored throughout placement of the Retriever and stent grafting until the next day.

RESULTS

The Retriever was placed in 17 aneurysms in 16 patients. There were no changes in amplitude or latency of evoked spinal cord potential records obtained before or during Retriever placement. After withdrawal of the Retriever, all aneurysms were excluded from circulation immediately after permanent stent grafting. There were no changes in evoked spinal cord potential, nor were neurologic deficits seen after stent graft deployment in any patient.

CONCLUSIONS

These results suggest that predeployment testing with the Retriever under evoked spinal cord potential monitoring is promising as a predictor of spinal cord ischemia in candidates for stent graft repair of thoracic aortic aneurysms.

Prevention of spinal cord ischaemic complications after thoracoabdominal aortic surgery

Since the publication of prior reviews on this topic, substantial clinical experience with a variety of operative strategies to prevent ischaemic cord complications has been reported. The available data on angiographic localisation of critical intercostal vessels, and, in particular, the evoked potential response to cross-clamping in patients indicates that risk of paraplegia varies considerably even among patients with equivalent TAA extent. Factors such as individual development of the ASA, patent critical intercostals, and the particulars of collateral circulation when intercostal aortic ostia are already occluded likely account for this variability. Information available from SSEP monitoring relative to the dynamic course of cord ischaemia with cross-clamping, and the parallel, if not, frustrating experience with angiographic localisation and intercostal vessel reconstruction indicates that a narrow temporal threshold of cord ischaemia with clamping is present in many patients. This reinforces the importance of both expeditious clamp intervals, critical intercostal re-anastomoses, and the desirability of neuroprotective manoeuvres during cross-clamp induced cord ischemia. As suggested in compelling experimental work our contemporary clinical experience, and predicted by prior reviewers, regional cord hypothermia provides significant promise for limiting or eliminating, in particular, immediate perioperative deficits. Avoidance of postoperative hypotension, spinal cord oedema, and preservation of critical intercostal vessels are additional strategies necessary to impact the development of delayed deficits favourably.

Importance of intercostal artery reattachment during thoracoabdominal aortic aneurysm repair

PURPOSE

We studied the relationship of neurologic deficit to ligation, reimplantation, and preexisting occlusion of intercostal arteries to determine which arteries and consequent management are most critical to outcome in thoracoabdominal aortic aneurysm repair.

METHODS

From February 1991 to July 1996, 343 patients with thoracoabdominal aortic aneurysms underwent repair by one surgeon. In this study, only Crawford types I, II, and III (n = 264) were considered. Of these, 110 (42%) were type I, 116 (44%) type II, and 38 (14%) type III. The adjuncts of distal aortic perfusion and cerebrospinal fluid drainage were used in 164 patients (62%). Data were analyzed by contingency table and by multiple logistic regression.

RESULTS

Early neurologic deficit occurred in 23 patients (8.7%), and late deficit in 10 patients (3.8%). Neurologic deficit in patients with at least one reimplantation and no ligation of arteries T11 or T12 occurred in 19 of 147 (12.9%). Neurologic deficit for occlusion of the same arteries occurred in 11 of 111 (9.9%), whereas for ligation of T11 and T12 neurologic deficit occurred in three of six (50%; reimplantation, p < 0.03; occlusion, p < 0.006). In addition, reimplantation of intercostal arteries T9 or T10 was significantly associated with reduced late neurologic deficit in multivariate analysis (p = 0.05). No other intercostal artery status was associated with modification of the neurologic deficit rate. Multivariate analysis showed type II aneurysms and acute dissections to be significantly associated with an increased risk of postoperative neurologic deficit (p < 0.0009, 0.002, respectively). Adjuncts were protective (p < 0.007), most often in types II and III (14.1% neurologic deficit in type II with adjunct, 35.3% without; 0% in type III with adjunct, 20% without).

CONCLUSION

Patients with patent arteries at the T11/T12 level have highly variable outcomes depending on whether the arteries are reattached or ligated. Our data suggest that reimplantation of thoracic intercostal arteries T11 and T12 is indicated when these arteries are patent. Reimplantation of T9 and T10 lowers the risk of late neurologic deficit, probably by decreasing the spinal cord's vulnerability to changes in blood and cerebrospinal fluid pressure in the days after surgery. Adjuncts lower overall risk and provide adequate time for targeted intercostal artery reimplantation.

Spinal cord complications of thoracoabdominal aneurysm surgery

BACKGROUND

Although rare, paralysis secondary to spinal cord ischaemia after aortic aneurysm surgery is a devastating complication. Many papers have been published on this topic but without a clear consensus on the best way of minimizing the problem. Recent articles have included advanced pharmacological approaches and the literature has been reviewed in light of these.

METHODS

Relevant papers were identified by an extensive text word search of the Medline database and a review of quoted articles.

RESULTS

Spinal cord complications are commoner after the repair of Crawford type II aneurysms than less extensive aneurysms. The presence of dissection, rupture and prolonged clamp times are associated with an increased incidence. About a quarter of all cord problems develop over 24 h after surgery and this may be due to a reperfusion type injury, although the exact mechanisms are by no means clear.

CONCLUSION

A combination of rapid surgery, left heart bypass for the repair of more extensive aneurysms, free spinal drainage and the avoidance of postoperative hypoxia and hypotension help to minimize spinal cord ischaemia. No pharmacological agent has yet been shown conclusively to improve outcome in the clinical setting.

Clinical experience with epidural cooling for spinal cord protection during thoracic and thoracoabdominal aneurysm repair

PURPOSE

This report summarizes our experience with epidural cooling (EC) to achieve regional spinal cord hypothermia and thereby decrease the risk of spinal cord ischemic injury during the course of descending thoracic aneurysm (TA) and thoracoabdominal aneurysm (TAA) repair.

METHODS

During the interval July 1993 to Dec. 1995, 70 patients underwent TA (n = 9, 13%) or TAA (n = 61) (type I, 24 [34%], type II, 11 [15%], type III, 26 [37%]) repair using the EC technique. The latter was accomplished by continuous infusion of normal saline (4 degrees C) into a T11-12 epidural catheter; an intrathecal catheter was placed at the L3-4 level for monitoring of cerebrospinal fluid temperature (CSFT) and pressure (CSFP). All operations (one exception, atriofemoral bypass) were performed with the clamp-and-sew technique, and 50% of patients had preservation of intercostal vessels at proximal or distal anastomoses (30%) or by separate inclusion button (20%). Neurologic outcome was compared with a published predictive model for the incidence of neurologic deficits after TAA repair and with a matched (Type IV excluded) consecutive, control group (n = 55) who underwent TAA repair in the period 1990 to 1993 before use of EC.

RESULTS

EC was successful in all patients, with a 1442 +/- 718 ml mean (range, 200 to 3500 ml) volume of infusate; CSFT was reduced to a mean of 24 degrees +/- 3 degrees C during aortic cross-clamping with maintenance of core temperature of 34 degrees +/- 0.8 +/- C. Mean CSFP increased from baseline values of 13 +/- 8 mm Hg to 31 +/- 6 mm Hg during cross-clamp. Seven patients (10%) died within 60 days of surgery, but all survived long enough for evaluation of neurologic deficits. The EC group and control group were well-matched with respect to mean age, incidence of acute presentations/aortic dissection/aneurysm rupture, TAA type distribution, and aortic cross-clamp times. Two lower extremity neurologic deficits (2.9%) were observed in the EC patients and 13 (23%) in the control group (p < 0.0001). Observed and predicted deficits in the EC patients were 2.9% and 20.0% (p = 0.001), and for the control group 23% and 17.8% (p = 0.48). In considering EC and control patients (n = 115), variables associated with postoperative neurologic deficit were prolonged (> 60 min) visceral aortic cross-clamp time (relative risk, 4.4; 95% CI, 1.2 to 16.5; p = 0.02) and lack of epidural cooling (relative risk, 9.8; 95% CI, 2 to 48; p = 0.005).

CONCLUSION

EC is a safe and effective technique to increase the ischemic tolerance of the spinal cord during TA or TAA repair. When used in conjunction with a clamp-and-sew technique and a strategy of selective intercostal reanastomosis, EC has significantly reduced the incidence of neurologic deficits after TAA repair.

Operation for nondissecting aneurysm in the descending thoracic aorta

BACKGROUND

Little is known about the risks of mortality and morbidity after descending thoracic aortic aneurysm repair using left heart bypass and temporary arterioarterial bypass.

METHODS

A multicenter, retrospective study was performed on 120 patients who were admitted to one of nine cardiovascular centers between January 1988 and December 1993 and underwent operation for nondissecting thoracic aortic aneurysm. The present series included 10 patients with ruptured aneurysm. Graft replacement was performed in 95 patients, patch repair in 22, and suture of the ruptured aorta in 3. Venoarterial bypass was used in 45 patients, left heart bypass in 56, and temporary arterioarterial bypass in 19 as circulatory support. The mean postoperative follow-up period was 30 +/- 21 months.

RESULTS

Hospital mortality occurred in 7 patients (5.8%). Univariate analysis revealed that only aneurysmal rupture was related to hospital mortality. Brain or cord injury was observed in 4. Of nine deaths that occurred after discharge, five were related to aneurysm and two were due to vascular event. No significant difference was noticed in probability of survival according to the circulatory supporting method. Only aneurysmal rupture affected probability of survival. Multivariate analysis revealed that aneurysmal rupture was the only independent predictor for vascular death including hospital mortality.

CONCLUSIONS

The present study confirms that aneurysmal rupture is a significant predictor for mortality and morbidity in aortic operations for nondissecting descending thoracic aneurysm, and that a similarly good outcome would be expected when using left heart bypass, temporary arterioarterial bypass, or venoarterial bypass.

Improvement in results of repair of type IV thoracoabdominal aortic aneurysms

PURPOSE

Although management of extensive type I and II thoracoabdominal aortic aneurysms (TAA) remains a formidable challenge, results of repair of TAA originating in the distal thoracic aorta (type IV) appear to have improved significantly. To quantitate this perceived improvement, the following retrospective study was undertaken to examine the results of type IV TAA repair at the Brigham & Women's Hospital over the past 18-year period.

METHODS

From July 1977 to September 1994, nonruptured atherosclerotic type IV TAAs were repaired in 58 patients. The mean age was 70 years, and associated risk factors included smoking (91%), hypertension (86%), coronary artery disease (52%), and previous aortic surgery (38%). Mean follow-up was 2.4 years (median 2 years).

RESULTS

Overall 30-day mortality was 5.3% (two deaths). Morbidity included stroke (3.5%), paraplegia (1.8%), permanent paraparesis (1.8%), myocardial infarction (7%), pneumonia (8.8%), gastrointestinal bleeding (11%), intestinal ischemia (5.3%), wound infection (7.0%), peripheral ischemia (5.3%), in-hospital dialysis (8.8%), and permanent dialysis (1.9%). Overall 5-year survival was 50%. With univariate analysis, survival was positively correlated with more recent year of operation (p = 0.002), smaller volume of intraoperative blood transfusion (p = 0.02), decreased supraceliac ischemia time (p = 0.04), and the use of the retroperitoneal approach (p = 0.09). Multiple regression analysis revealed that the year of operation was the only independent predictor of survival (p = 0.003). Subgroup analysis of patients who underwent operation between 1977 and 1987 (n = 13) and 1988 and 1994 (n = 45) revealed statistically significant improvements in length of hospital stay (46 +/- 12 vs 21 +/- 4 days, p = 0.02), postoperative dysrhythmia (50% vs 16%, p = 0.03), postoperative maximum serum glutamic oxaloacetic-transaminase (516 +/- 234 vs 319 +/- 139 mg%, p = 0.04), incidence of hemorrhage requiring reexploration (33% vs 0%, p = 0.002), 30-day mortality (23% vs 0%, p = 0.009), and in-hospital mortality (39% vs 2.2%, p = 0.002).

CONCLUSIONS

The modern mortality, morbidity, and survival of surgical repair of type IV TAA in our institution approaches that of infrarenal abdominal aortic aneurysm.