Prevention of paraplegia in pigs by selective segmental artery perfusion during aortic cross-clamping

Animal Models, Pathogenesis, and Potential Treatment of Thoracic Aortic Aneurysm

Thoracic aortic aneurysm (TAA) has a prevalence of 0.16-0.34% and an incidence of 7.6 per 100,000 person-years, accounting for 1-2% of all deaths in Western countries. Currently, no effective pharmacological therapies have been identified to slow TAA development and prevent TAA rupture. Large TAAs are treated with open surgical repair and less invasive thoracic endovascular aortic repair, both of which have high perioperative mortality risk. Therefore, there is an urgent medical need to identify the cellular and molecular mechanisms underlying TAA development and rupture to develop new therapies. In this review, we summarize animal TAA models including recent developments in porcine and zebrafish models: porcine models can assess new therapeutic devices or intervention strategies in a large mammal and zebrafish models can employ large-scale small-molecule suppressor screening in microwells. The second part of the review covers current views of TAA pathogenesis, derived from recent studies using these animal models, with a focus on the roles of the transforming growth factor-beta (TGFβ) pathway and the vascular smooth muscle cell (VSMC)-elastin-contractile unit. The last part discusses TAA treatment options as they emerge from recent preclinical studies.

Histological Findings After Aortic Cross-Clamping in Preclinical Animal Models

Spinal cord ischemic injury and paralysis are devastating complications after open surgical repair of thoracoabdominal aortic aneurysms. Preclinical models have been developed to simulate the clinical paradigm to better understand the neuropathophysiology and develop therapeutic treatment. Neuropathological findings in the preclinical models have not been comprehensively examined before. This systematic review studies the past 40 years of the histological findings after open surgical repair in preclinical models. Our main finding is that damage is predominantly in the grey matter of the spinal cord, although white matter damage in the spinal cord is also reported. Future research needs to examine the neuropathological findings in preclinical models after endovascular repair, a newer type of surgical repair used to treat aortic aneurysms.

Intravenous hydrogen sulfide does not induce neuroprotection after aortic balloon occlusion-induced spinal cord ischemia/reperfusion injury in a human-like porcine model of ubiquitous arteriosclerosis

Objective

In rodents, intravenous sulfide protected against spinal cord ischemia/reperfusion (I/R) injury during aortic balloon occlusion. We investigated the effect of intravenous sulfide on aortic occlusion-induced porcine spinal cord I/R injury.

Methods

Anesthetized and mechanically ventilated “familial hypercholesterolemia Bretoncelles Meishan” (FBM) pigs with high-fat-diet-induced hypercholesterolemia and atherosclerosis were randomized to receive either intravenous sodium sulfide 2 h (initial bolus, 0.2 mg kg body weight (bw)⁻¹; infusion, 2 mg kg bw⁻¹ h⁻¹; n = 4) or vehicle (sodium chloride, n = 4) prior to 45 min of thoracic aortic balloon occlusion and for 8 h during reperfusion (infusion, 1 mg kg bw⁻¹ h⁻¹). During reperfusion, noradrenaline was titrated to maintain blood pressure at above 80% of the baseline level. Spinal cord function was assessed by motor evoked potentials (MEPs) and lower limb reflexes using a modified Tarlov score. Spinal cord tissue damage was evaluated in tissue collected at the end of experiment using hematoxylin and eosin and Nissl staining.

Results

A balloon occlusion time of 45 min resulted in marked ischemic neuron damage (mean of 16% damaged motoneurons in the anterior horn of all thoracic motor neurons) in the spinal cord. In the vehicle group, only one animal recovered partial neuronal function with regain of MEPs and link motions at each time point after deflating. All other animals completely lost neuronal functions. The intravenous application of sodium sulfide did not prevent neuronal cell injury and did not confer to functional recovery.

Conclusion

In a porcine model of I/R injury of the spinal cord, treatment with intravenous sodium sulfide had no protective effect in animals with a pre-existing arteriosclerosis.

Treatment for thoracoabdominal aortic aneurysm by fenestrated endovascular aortic repair with physician-modified stent graft

Despite being widely used for several years, the endovascular aortic repair (EVAR) of a thoracoabdominal aneurysm (TAAA) remains challenging, particularly the revascularization of the abdominal aortic visceral branches. A 66-year-old male was admitted to hospital with abdominal bloating and pain. Computed tomographic angiography (CTA) confirmed a Crawford type III TAAA from the distal descending aorta to the suprarenal abdominal aorta that involved the celiac axis, accompanied with an occlusion of the left subclavian artery. Fenestrated-EVAR was performed successfully and 1 week later CTA showed a type III endoleak, which had resolved 3 months later, without stent migration or visceral artery occlusion. In this present case, the surgeons preferred to perform the procedure in three surgical stages, postponing the deployment of a covered stent in the CA fenestration to provide additional time for the development of collateral circulation to the spinal cord as a possible means of preventing postoperative paraplegia.

Erythropoietin preconditioning improves clinical and histologic outcome in an acute spinal cord ischemia and reperfusion rabbit model

OBJECTIVE

This study examined effects and functional outcome of recombinant human erythropoietin (rhEPO) and carbamylated erythropoietin fusion protein (cEPO-FC) preconditioning in a rabbit model for spinal cord ischemia and resulting paraplegia. This model was chosen because only a small surgical effect is needed to cause paraplegia in rabbits, which facilitates postoperative observation of animals.

METHODS

Anesthetized but spontaneously breathing New Zealand White rabbits randomly received cEPO-FC (50 μg/kg; n = 8), rhEPO (5000 IU/kg; n = 10), or vehicle (control; n = 10) 30 minutes before and after infrarenal aortic clamping. Ideal clamping time of 22 minutes was identified from preceding clamping tests (15-25 minutes). Postoperative observation time was 96 hours. Spinal cord function was assessed by neurologic evaluation of hind limb motor function every 12 hours using a modified Tarlov score. Spinal cord tissue damage was evaluated after 96 hours using hematoxylin and eosin, elastica van Gieson, Nissl, Masson-Goldner, and hemosiderin staining. Plasma levels of cell senescence markers stathmin, chitinase 1/3, elongation factor 1-α were determined.

RESULTS

Rabbits that received rhEPO showed significant improvement of spontaneous lower limb movements until 36 hours of reperfusion and improved histologic scores upon examination of the lumbar spinal cord compared with the control group. In contrast, cEPO-FC treatment showed comparable outcome to the control group concerning movements of the lower limbs and histology. Senescence markers were elevated in the control group, but not in the treatment groups, except for chitinase 3 in the rhEPO group. Only stathmin showed no significant effect. Markers for senescence might increase after acute ischemic injury. Attenuation of senescence markers might not come alone from improvement of the spinal cord.

CONCLUSIONS

Preconditioning with rhEPO attenuates ischemia/reperfusion injury of the spinal cord, whereas the carbamylated derivative (cEPO-FC) showed no positive effect on spinal cord function.

Nrf2 activation in astrocytes contributes to spinal cord ischemic tolerance induced by hyperbaric oxygen preconditioning

In this study, we investigated whether nuclear factor erythroid 2-related factor 2 (Nrf2) activation in astrocytes contributes to the neuroprotection induced by a single hyperbaric oxygen preconditioning (HBO-PC) against spinal cord ischemia/reperfusion (SCIR) injury. In vivo: At 24 h after a single HBO-PC at 2.5 atmospheres absolute for 90 min, the male ICR mice underwent SCIR injury by aortic cross-clamping surgery and observed for 48 h. HBO-PC significantly improved hindlimb motor function, reduced secondary spinal cord edema, ameliorated the reactivity of spinal motor-evoked potentials, and slowed down the process of apoptosis to exert neuroprotective effects against SCIR injury. At 12 h or 24 h after HBO-PC without aortic cross-clamping surgery, Western blot, enzyme-linked immunosorbent assay, realtime-polymerase chain reaction and double-immunofluorescence staining were used to detect the Nrf2 activity of spinal cord tissue, such as mRNA level, protein content, DNA binding activity, and the expression of downstream gene, such as glutamate-cysteine ligase, γ-glutamyltransferase, multidrug resistance protein 1, which are key proteins for intracellular glutathione synthesis and transit. The Nrf2 activity and downstream genes expression were all enhanced in normal spinal cord with HBO-PC. Glutathione content of spinal cord tissue with HBO-PC significantly increased at all time points after SCIR injury. Moreover, Nrf2 overexpression mainly occurs in astrocytes. In vitro: At 24 h after HBO-PC, the primary spinal astrocyte-neuron co-cultures from ICR mouse pups were subjected to oxygen-glucose deprivation (OGD) for 90 min to simulate the ischemia-reperfusion injury. HBO-PC significantly increased the survival rate of neurons and the glutathione content in culture medium, which was mainly released from asctrocytes. Moreover, the Nrf2 activity and downstream genes expression induced by HBO-PC were mainly enhanced in astrocytes, but not in neurons. In conclusion, our findings demonstrated that spinal cord ischemic tolerance induced by HBO-PC may be mainly related to Nrf2 activation in astrocytes.

Comparison of carbamylated erythropoietin-FC fusion protein and recombinant human erythropoietin during porcine aortic balloon occlusion-induced spinal cord ischemia/reperfusion injury

PURPOSE

Recombinant human erythropoietin (rhEPO) attenuated ischemia/reperfusion (I/R) injury-induced spinal cord damage. Since carbamylated EPO derivatives are stated to be devoid of rhEPO side effects, we tested the hypothesis that a newly developed carbamylated EPO-FC fusion protein (cEPO-FC) would compare favorably with rhEPO.

METHODS

Anesthetized and mechanically ventilated pigs randomly received cEPO-FC (50 μg kg(-1)), rhEPO (5,000 IU kg(-1)) or vehicle (n = 9 per group) 30 min prior to 30 min of aortic occlusion and over the 4 h of reperfusion. During aortic occlusion, mean arterial pressure (MAP) was maintained at 80-120% of baseline values by esmolol, nitroglycerin, and adenosine-5'-triphosphate (ATP). During reperfusion, noradrenaline was titrated to keep MAP at pre-ischemic levels. Spinal cord function was assessed by motor evoked potentials (MEP) and lower limb reflexes. Tissue damage was evaluated using hematoxylin and eosin, Nissl, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining. Plasma levels of interleukin-6, tumor necrosis factor-α, and 8-isoprostanes were measured as markers of systemic inflammation and oxidative stress.

RESULTS

While only cEPO-FC restored MEP amplitude to values close to pre-occlusion levels, both cEPO-FC and rhEPO comparably restored lower limb reflexes and reduced the percentage of damaged neurons. Infiltration of mononuclear inflammatory cells was moderate without intergroup difference; positive TUNEL staining was barely detectable in any group. I/R injury increased blood cytokine levels without intergroup difference, whereas both cEPO-FC and rhEPO significantly lowered 8-isoprostane levels.

CONCLUSIONS

In a porcine model of aortic balloon occlusion-induced spinal cord I/R injury, cEPO-FC and rhEPO comparably protected against ischemic spinal cord dysfunction and neuronal damage. This effect coincided with attenuated oxidative stress.

Left axillary arterial perfusion for cerebrospinal protection in proximal descending aortic aneurysm

A 73-year-old man presented with DeBakey type IIIa chronic aortic dissection. The aneurysm of the descending aorta was replaced using an open proximal technique with hypothermic circulatory arrest. For cerebrospinal protection, the left axillary artery was cannulated, which perfuses the vertebral artery and affects the Willis arterial circle, the anterior spinal artery, and the collateral blood supply to the spinal cord. Cannulation of the left axillary artery was a safe and effective surgical option for antegrade cerebral perfusion and spinal protection.

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.

Emergency surgery of the abdominal aorta in a porcine model: two sequential experiments

The aim of this study was to design an aggressive nonlethal animal model that would simulate surgical treatment of the abdominal aorta with a view to studying the systemic inflammatory response. Fourteen pigs were subjected to two sequential experiments. Experiment A was performed to determine the response to two degrees of hemorrhage: (A1) 40% bleeding; and (A2) 60% bleeding over 15 minutes followed by midline laparotomy and aortic dissection. Experiment B included two methods of aortic repair: (B1) aortic resection and replacement with a prosthesis; and (B2) aortic bypass without aortic resection. In the latter two groups, suprarenal aortic cross-clamping was placed for 30 minutes after a 40% hemorrhage. We analyzed various inflammatory markers and mortality. The 40% bleeding (vs. 60%) elicited a smaller decrease in mean arterial pressure (110 +/- 6 vs. 89 +/- 9 mmHg) but did not cause irreversible shock or mortality. After the 40% hemorrhage, the B1 aortic repair caused two cases of paraplegia. We have developed a model to study the combined effect of bleeding and aortic cross-clamping.

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.

The selective poly(ADP)ribose-polymerase 1 inhibitor INO1001 reduces spinal cord injury during porcine aortic cross-clamping-induced ischemia/reperfusion injury

OBJECTIVE

It is well-established that poly(ADP)ribose-polymerase (PARP) assumes major importance during ischemic brain damage, and the selective PARP-1 inhibitor PJ34 reduced spinal cord damage in murine aortic occlusion-induced ischemia/reperfusion injury. We investigated the effect of the PARP-1 inhibitor INO1001 on aortic-occlusion-related porcine spinal cord injury.

DESIGN AND SETTING

Prospective, randomized, controlled experimental study in an animal laboratory.

PATIENTS AND PARTICIPANTS

Ten anesthetized, mechanically ventilated, and instrumented pigs.

INTERVENTIONS

Animals underwent 45 min of thoracic aortic cross-clamping after receiving vehicle (n=5) or intravenous INO1001 (n=5, total dose 4 mg/kg administered both before clamping and during reperfusion). During reperfusion continuous intravenous norepinephrine was incrementally adjusted to maintain blood pressure at or above 80% of the preclamping level. Plasma INO1001 levels were analyzed by HPLC. After 4[Symbol: see text]h of reperfusion spinal cord biopsy samples were analyzed for neuronal damage (hematoxyline-eosine and Nissl staining), expression of the cyclin-dependent kinase inhibitor genes p21 and p27 (immunohistochemistry), and apoptosis (terminal deoxynucleotidyl transferase mediated nick end labeling assay).

MEASUREMENTS AND RESULTS

Plasma INO1001 levels were 0.8-2.3 and 0.30-0.76 mM before and after clamping, respectively. While 3-5% of the spinal cord neurons were irreversibly damaged in the INO1001 animals, the neuronal cell injury was three times higher in the control group. Neither p21 and p27 expression nor apoptosis showed any intergroup difference.

CONCLUSIONS

The selective PARP-1 inhibitor INO1001 markedly reduced aortic occlusion-induced spinal cord injury. Given the close correlation reported in the literature between morphological damage and impaired spinal cord function, INO1001 may improve spinal cord recovery after thoracic aortic cross-clamping.

Effects of a cantaloupe melon extract/wheat gliadin biopolymer during aortic cross-clamping

OBJECTIVE

We previously reported in healthy volunteers that a cantaloupe melon extract chemically combined with wheat gliadin (melon extract/gliadin) and containing SOD, catalase and residual glutathione peroxidase (GPx), protected against DNA strand-break damage induced by hyperbaric oxygen (HBO), a well-established model of DNA damage resulting from oxidative stress. Aortic cross-clamping is a typical example of ischemia/reperfusion injury-related oxidative stress, and therefore we investigated whether this melon extract/gliadin would also reduce DNA damage after aortic cross-clamping and reperfusion.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

Animal laboratory.

PATIENTS AND PARTICIPANTS

18 anesthetized, mechanically ventilated and instrumented pigs.

INTERVENTIONS

After 14 days of oral administration of 1250 mg of the melon extract/gliadin (n=9) or vehicle (n=9), animals underwent 30 min of thoracic aortic cross-clamping and 4 h of reperfusion.

MEASUREMENTS AND RESULTS

Before clamping, immediately before declamping, and at 2 and 4 h of reperfusion, we measured blood isoprostane (immunoassay) and malondialdehyde concentrations (fluorimetric thiobarbituric acid test), SOD, catalase and GPx activities (spectrophotometric kits), NO formation (nitrate+nitrite; chemoluminescence), DNA damage in whole blood samples and isolated lymphocytes exposed to hyperbaric oxygen (comet assay). Organ function was also evaluated. Kidney and spinal cord specimen were analysed for apoptosis (TUNEL assay). The melon extract/gliadin blunted the DNA damage, reduced spinal cord apoptosis and attenuated NO release, however, without any effect on lipid peroxidation and organ function.

CONCLUSIONS

Pre-treatment with the oral melon extract/gliadin may be a therapeutic option to reduce oxidative cell injury affiliated with aortic cross-clamping.

An alternative for descending thoracic aortic aneurysm repair

A simple technique termed "clamp test and spinal cord-plegia" for descending thoracic aortic aneurysm surgery is described. The clamp test is a passive method of creating ischemic conditions, whereas spinal cord-plegia is an active method of decreasing metabolism. This technique is a practical test that double-checks for critical feeding arteries and seems to have an excellent spinal cord-preserving effect.

The parp-1 inhibitor ino-1001 facilitates hemodynamic stabilization without affecting DNA repair in porcine thoracic aortic cross-clamping-induced ischemia/reperfusion

Inhibition of poly (ADP-ribose) polymerase 1 (PARP-1) improved hemodynamics and organ function in various shock models induced by sepsis or ischemia/reperfusion. PARP-1, however, is also referred to play a pivotal role for the maintenance of genomic integrity. Therefore, we investigated the effect of the PARP-1 blocker INO-1001 on hemodynamics, kidney function, and DNA damage and repair during porcine thoracic aortic cross-clamping. The animals underwent 45 min of aortic cross-clamping after receiving vehicle (n=9) or i.v. INO-1001 (n=9; total dose, 4 mg.kg, administered both before clamping and during reperfusion), data were recorded before clamping, before declamping, and 2 and 4 h after declamping. During reperfusion, continuous i.v. norepinephrine was incrementally adjusted to maintain blood pressure greater than or equal to 80% of the pre-clamping level. The plasma INO-1001 levels analyzed with high-pressure liquid chromatography were 1 to 1.4 micromol/L and 0.4 to 0.6 micromol/L before and after clamping, respectively. Although INO-1001-treated animals required less norepinephrine support, kidney function was comparable in the 2 groups. There was no intergroup difference either in the time course of DNA damage and repair (comet assay) as assessed both in vivo in whole blood before surgery, before clamping, before declamping, 2 h after declamping, and ex vivo in isolated lymphocytes (Ficoll gradient) sampled immediately before clamping and analyzed before, immediately, and 1 and 2 h after exposure to 4 bar 100% O2 for 2 h. There was no difference either in the expression of the cyclin-dependent kinase inhibitor gene, p27, in the kidney (immunohistochemistry). The reduced norepinephrine requirements during reperfusion suggest a positive inotropic effect of INO-1001, as demonstrated by other authors. In our model, INO-1001 proved to be safe with respect to DNA repair.

Spinal cord blood supply in patients with thoracoabdominal aortic aneurysms

OBJECTIVE

In patients with thoracoabdominal aortic aneurysms (TAAAs), the blood supply to the spinal cord is highly variable and unpredictable because of obstructed intercostal and lumbar arteries. This study was performed for the prospective documentation of patent segmental arteries during TAAA repair and the assessment of their functional contribution to the spinal cord blood supply.

METHODS

TAAA repair was performed in 184 consecutive patients (68 with type I aneurysm, 91 with type II, and 25 with type III) according to a protocol that included left heart bypass grafting, cerebrospinal fluid drainage, and the monitoring of motor-evoked potentials (MEPs). Patent intercostal and lumbar arteries were documented, and all reattached, selectively grafted, and oversewn segmental arteries were noted. MEP amplitude that decreased to less than 25% of baseline was considered an indication of critical spinal cord ischemia and prompted spinal cord revascularization.

RESULTS

Adequate MEP levels were encountered in 183 of 184 patients. One patient had early paraplegia (absent MEPs), two patients had delayed paraplegia develop, and two patients had temporary paraparesis, which accounted for an overall neurologic deficit of 2.7%. The median total number of patent intercostal and lumbar arteries in type I, II, and III aneurysms was three, five, and five, respectively. In eight of 68 type I cases, no segmental arteries were seen between the fifth thoracic vertebrae (T5) and the first lumbar vertebrae (L1) and MEP levels remained adequate because of distal aortic perfusion. In 18 of 91 type II cases, the aortic segment T5 to L1 did not contain patent arteries, and in six of these patients, the segment L1 to L5 did not have lumbar arteries either. In the latter patients, MEP levels depended on the pelvic circulation provided with the left heart bypass graft. In the other 12 of 91 type II cases, the only patent arteries were the lumbar arteries between L3 and L5. The loss of MEPs could be corrected with the reattachment of these arteries. In seven of 25 type III cases, the MEP levels also depended on lumbar arteries L3 to L5 and in three of 25 cases, no segmental arteries were available and MEP levels recovered after the reperfusion of the pelvic circulation. With the combination of the findings of type II and III cases, spinal cord perfusion was directed by lower lumbar arteries in 16% of the cases (19 of 116) and pelvic circulation in 8% of the cases (nine of 116).

CONCLUSION

In patients with TAAA, most intercostal and lumbar arteries are occluded and spinal cord perfusion depends on an eminent collateral network, which includes lumbar arteries and pelvic circulation. The monitoring of MEPs is a sensitive technique for the assessment of spinal cord ischemia and the identification of segmental arteries that critically contribute to spinal cord perfusion. Surgical strategies on the basis of this technique reduced the incidence rate of neurologic deficit to less than 3%.

Identification of the critical spinal arteries with F wave-polysynaptic response complex monitoring: an experimental study

PURPOSE

The main cause of paraplegia after surgery for descending thoracic aortic aneurysms and thoracoabdominal aortic aneurysms is spinal cord ischemia caused by ligation of the critical spinal arteries that are associated with the great radicular artery (GRA). In this experimental study, we attempted to identify the critical spinal arteries with F wave-polysynaptic response complex (FPC) monitoring. The FPC, which we are using as a monitor of spinal cord ischemia, is myogenic potentials evoked by the tibial nerve stimulation through the anterior horn cells.

METHOD

In 18 rabbits, infrarenal lumbar arteries were clamped until there was an FPC amplitude reduction (FPCAR) of at least 60%. The rabbits were classified according to the number of arteries clamped to produce the FPCAR (group A, 1 artery; group B, 2 arteries; group C, 3 arteries). Selective angiography of each lumbar artery was performed in all rabbits.

RESULTS

An FPCAR was observed in all 18 rabbits. In all nine rabbits in group A, the FPCAR was caused by the clamping of one particular lumbar artery. The GRA was shown by means of selective angiography to originate directly from this lumbar artery. In the nine rabbits in groups B and C, 11 FPCARs were observed. Of these, nine FPCARs in nine rabbits were caused by the clamping of lumbar arteries that included the vessel from which the GRA originated.

CONCLUSION

Temporary clamping of lumbar arteries with FPC monitoring can be used as a means of detecting the critical spinal arteries from which the GRA originates.

Active cooling during open repair of thoraco-abdominal aortic aneurysms improves outcome

OBJECTIVE

Evaluate impact of active cooling with partial cardiopulmonary bypass (CPB) and low systemic heparinization during open repair of thoracoabdoninal aortic aneurysms.

METHODS

Prospective analysis of 100 consecutive patients undergoing surgical repair of thoracoabdominal aortic aneurysms. Partial CPB and normothermic (36 degrees C) or hypothermic (29 degrees C) perfusion was selected in accordance to the surgeons preference. In the hypothermic group, aortic cross clamp was applied when the target temperature of the venous blood was achieved and rewarming was started after declamping.

RESULTS

52/100 patients (62.2+/-10.9 years) received normothermic and 48/100 patients hypothermic perfusion (63.8+/-10.6 years: NS). Emergent procedures accounted for 18/52 (35%) with normothermia vs. 21/48 (44%: NS) with hypothermia. The number of aortic segments (eight = maximum including arch and bifurcation) replaced was 3.9+/-1.5 with normothermia vs. 4.1+/-1.5 with hypothermia (NS); Crawford type II aneurysms accounted for 21/52 patients (40%) for normothermia vs. 20/48 (42%:NS) for hypothermia. Total clamp time was 38+/-21 min with normothermia vs. 47+/-28 min with hypothermia (P=0.05). Pump time was 55+/-28 min with normothermia vs. 84+/-34 min with hypothermia (P=0.001). Mortality at 30 days was 8/52 patients (15%) with normothermia vs. 2/48 (4%) with hypothermia (P=0.06; odds ratio = 4.1). Parapareses/plegias occurred in 4/52 patients (8%) with normothermia vs. 4/48 (8%) with hypothermia (NS). Revisions for bleeding were required in 4/52 patients (8%) with normothermia vs. 2/48 patients (4%) with hypothermia (P=0.38). Revisions for distal vascular problems were necessary in 5/52 patients (10%) with normothermia vs. 2/48 (4%) with hypothermia (P=0.25). Freedom from death, paraplegia, and surgical revision was 89.9% with normothermia vs. 94.8% with hypothermia (P=0.04; odds ratio 2.0).

CONCLUSIONS

Active cooling during repair of thoracoabdominal aortic aneurysms allows for longer cross-clamp times, more complex repairs and improves outcome.