Early ischemic preconditioning without hypotension prevents spinal cord injury caused by descending thoracic aortic occlusion

Preparing the spinal cord - priming or preconditioning? A systematic review of experimental studies

Objectives. Paraplegia is devastating complication associated with thoracic and thoracoabdominal aortic aneurysm repair. Vast evidence has been gathered on pre-, peri- and postoperative protective adjuncts aiming to minimize spinal cord ischemia. This review focuses on the pretreatment phase of open surgical or endovascular aortic procedures and gathers the experimental data on the interventional preconditioning and priming methods that increase the spinal cord ischemic tolerance. Design. By the start of March 2021, a systematic review was performed in PubMed, Scopus and Web of Science core collection to identify the articles that reported (i) either an ischemic preconditioning, remote ischemic preconditioning or priming method prior to (ii) experimental spinal cord ischemia performed in endovascular or open surgical fashion mimicking either thoracic, abdominal or thoracoabdominal aortic aneurysm procedures. (iii) The outcomes were reported via neurological, motor-evoked potential, somatosensory-evoked potential, histopathological, immunohistochemical, physiological analysis, or in different combinations of these measurements. Results. The search yielded 7802 articles, and 57 articles were included in the systematic review. The articles were assessed by the evaluated species, the utilized pretreatment, the measured protective effects, and the suggested underlying mechanisms. Conclusions. The reviewed articles showed several possible mechanisms in ischemic and remote ischemic preconditioning for prevention of spinal cord ischemia. The main suggested method for priming was arteriogenetic stimulus. Future studies should confirm these hints of arteriogenetic stimulus with more precise quantification of the protective recruitment process.

Remote Ischemic Preconditioning in Spinal Cord Protection: A Surviving Porcine Study

Surgical repair of thoracic aorta can compromise blood flow of the spinal cord. To mitigate spinal cord ischemia (SCI) additional protection methods are needed. In experimental studies remote ischemic preconditioning (RIPC) has proven to be an effective method of protecting organs from ischemia. The aim of the study was to assess efficacy of RIPC in spinal cord protection in a chronic porcine model. Sixteen piglets were assigned into the RIPC group (8) and the control group (8). RIPC was performed using blood pressure cuff in a 5-minute ischemia followed by a 5-minute reperfusion repeating cycles 4 times. The left subclavian artery and all segmental arteries above diaphragm were ligated at 5-minute intervals to accomplish SCI. The follow-up comprised a 4-hour intensive monitoring and a 7-day recovery phase. Blood samples were obtained, motor-evoked potentials and near-infrared spectroscopy (NIRS) of longitudinal back muscles were measured. Paraplegia was assessed every day postoperatively. Histopathological analysis of the spinal cord was performed after 7 days. NIRS values 4 hours after SCI were higher in the RIPC group, 45.5 (44.5-47.0), than in the control group, 41.5 (40.5-44.0) (P = 0.042). Nadir value of NIRS was 43.4 (39.3-46.0) in the RIPC group and 38.9 (38.-40.0) in the control group (P = 0.014). On the first postoperative day the RIPC group reached modified Tarlov score of 3 (2-3) vs 2 (1-2) in the control group (P = 0.024). RIPC hastens the recovery from SCI during the first postoperative day.

Lazaroid (U-74389G) ameliorates lung injury due to lipid peroxidation and nitric oxide synthase-dependent reactive oxygen species generation caused by remote systematic ischemia-reperfusion following thoracoabdominal aortic occlusion

INTRODUCTION

Lung ischemia-reperfusion injury after thoracoabdominal aortic occlusion represents a major complication, which increases morbidity and mortality. In the present study we hypothesized that lazaroid U-74389G intravenous administration protects from lung ischemia-reperfusion injury through lipid peroxidation inhibition.

MATERIALS AND METHODS

A total of 24 pigs were randomized in three groups. Group I (n = 8) underwent sham operation, group II (n = 8) underwent thoracoabdominal aortic occlusion for 45min and received placebo and group III (n = 8) received 3 doses of lazaroid (3 mg/kg) 60 and 30min before thoracoabdominal aortic occlusion and at 30min during thoracoabdominal aortic occlusion (duration 45min). Aortic occlusion was performed with aortic balloon-catheters under fluoroscopic guidance. All animals were sacrificed at the 7 t h postoperative day and lung specimens were harvested for molecular analysis.

RESULTS

mRNA levels of leukotrienes LB4 (LTB4R2), LC4 (LTC4S) and nitric oxide synthase (NOS) isoforms including iNOS, nNOS and eNOS were determined with real-time RT-qPCR. Nitric oxide can either induce (iNOS) or inhibit (nNOS and eNOS) lipid peroxidation based on its specific isoform origin. Group III showed significantly reduced mRNA levels of LTB4R2 (-63.7%), LTC4S (-35.9%) and iNOS (-60.2%) when compared with group II (P < 0.05, for all). The mRNA levels of nNOS was significantly increased (+37.4%), while eNOS was slightly increased (+2.1%) in group III when compared with group II (P < 0.05 and P = 0.467 respectively).

CONCLUSION

Lazaroid U-74389G may represent an effective pharmacologic intervention in reducing lung ischemia-reperfusion injury following thoracoabdominal aortic occlusion.

Aprikalim a potassium adenosine triphosphate channel opener reduces neurologic injury in a rabbit model of spinal cord ischemia

BACKGROUND

Potassium adenosine triphosphate (KATP) channel openers have been involved in the enhancement of ischemic tolerance in various tissues. The purpose of the present study is to evaluate the effects of aprikalim, a specific KATP channel opener, on spinal cord ischemic injury.

METHODS

Fifty-four rabbits were randomly assigned to three groups: group 1 (n = 18, sham operation), group 2 (n = 18, 30 min of normothermic aortic cross-clamping) and group 3 (n = 18, aprikalim 100 μg/kg was administered 15 min before 30 min of normothermic aortic cross-clamping). Neurologic evaluation was performed according to the modified Tarlov scale. Six animals from each group were sacrificed at 24, 48 and 168 h postoperatively. The lumbar spinal cords were harvested and examined histologically. The motor neurons were counted and the histologic lesions were scored (0-3, 3: normal).

RESULTS

Group 3 (aprikalim group) had better Tarlov scores compared to group 2 at all-time points (P < 0.025). The histologic changes were proportional to the Tarlov scores and group 3 had better functional outcome as compared to group 2 at 168 h (number of neurons: 21.2 ± 4.9 vs. 8.0 ± 2.7, P < 0.001 and histologic score: 1.67 ± 1.03 vs. 0.50 ± 0.55, P = 0.03). Although aprikalim exhibited improved effect on clinical and histologic neurologic outcome when compared to normothermic spinal cord ischemia, animals in group 3 had worse Tarlov score, reduced number of motor neurons and worse histologic score when compared to group 1 (sham operation) at 168 h (P = 0.003, P = 0.001 and P = 0.019 respectively).

CONCLUSION

Aprikalim reduces the severity of spinal cord ischemic injury in a rabbit model of spinal cord ischemia.

Effects of remote ischemic preconditioning on biochemical markers and neurologic outcomes in patients undergoing elective cervical decompression surgery: a prospective randomized controlled trial

BACKGROUND

Remote ischemic preconditioning (RIPC) may protect the spinal cord from ischemic injury. This randomized clinical trial was designed to assess whether a large clinical trial testing the effect of RIPC on neurologic outcome in patients undergoing spine surgery is warranted. This trial was registered with ClinicalTrials.gov, number NCT00778323.

METHODS

Forty adult cervical spondylotic myelopathy patients undergoing elective decompression surgery were randomly assigned to either the RIPC group (n=20) or the control group (n=20). Limb RIPC consisted of three 5-minutes cycles of upper right limb ischemia with intervening 5-minute periods of reperfusion. Neuron-specific enolase and S-100B levels were measured in serum at set time points. Median nerve somatosensory-evoked potentials (SEPs) were also recorded. Neurologic recovery rate was evaluated using a Japanese Orthopaedic Association scale.

RESULTS

RIPC significantly reduced serum S-100B release at 6 hours and 1 day after surgery, and reduced neuron-specific enolase release at 6 hours, and then at 1, 3, and 5 days after surgery. No differences were observed in SEP measurements or the incidence of SEP changes during surgery between the control and RIPC groups. Recovery rate at 7 days, and at 1 and 3 months after surgery was higher in the RIPC group than in the control group (P<0.05).

CONCLUSIONS

Our results for markers of neuronal ischemic injury and rate of recovery suggest that a clinical trial with sufficient statistical power to detect an effect of RIPC on the incidence of neurologic complications (paresis, palsy, etc) due to spinal cord ischemia-reperfusion injury after spine surgery is warranted [corrected].

Ischemia as a possible effect of increased intra-abdominal pressure on central nervous system cytokines, lactate and perfusion pressures

INTRODUCTION

The aims of our study were to evaluate the impact of increased intra-abdominal pressure (IAP) on central nervous system (CNS) cytokines (Interleukin 6 and tumor necrosis factor), lactate and perfusion pressures, testing the hypothesis that intra-abdominal hypertension (IAH) may possibly lead to CNS ischemia.

METHODS

Fifteen pigs were studied. Helium pneumoperitoneum was established and IAP was increased initially at 20 mmHg and subsequently at 45 mmHg, which was finally followed by abdominal desufflation. Interleukin 6 (IL-6), tumor necrosis factor alpha (TNFa) and lactate were measured in the cerebrospinal fluid (CSF) and intracranial (ICP), intraspinal (ISP), cerebral perfusion (CPP) and spinal perfusion (SPP) pressures recorded.

RESULTS

Increased IAP (20 mmHg) was followed by a statistically significant increase in IL-6 (p = 0.028), lactate (p = 0.017), ICP (p < 0.001) and ISP (p = 0.001) and a significant decrease in CPP (p = 0.013) and SPP (p = 0.002). However, further increase of IAP (45 mmHg) was accompanied by an increase in mean arterial pressure due to compensatory tachycardia, followed by an increase in CPP and SPP and a decrease of cytokines and lactate.

CONCLUSIONS

IAH resulted in a decrease of CPP and SPP lower than 60 mmHg and an increase of all ischemic mediators, indicating CNS ischemia; on the other hand, restoration of perfusion pressures above this threshold decreased all ischemic indicators, irrespective of the level of IAH.

Delayed pharmacological pre-conditioning effect of mitochondrial ATP-sensitive potassium channel opener on neurologic injury in a rabbit model of spinal cord ischemia

BACKGROUND

Diazoxide, pharmacological openers of mitochondrial ATP-sensitive potassium channels have been shown to induce early pre-conditioning in the spinal cord. Here, the authors investigated whether diazoxide also induce delayed pre-conditioning and thereby reduce neurologic complications using a rabbit model of spinal cord ischemia.

METHODS

Infrarenal blood flow was interrupted for 20 min in 21 rabbits. Non-treated control animals received no pre-treatment. Diazoxide (5 mg/kg) were given 48 h before 20 min ischemia in the 48-h DZ group, whereas 15-min DZ group received diazoxide (5 mg/kg) 15 min before 20-min ischemia. Neurological functions were evaluated using Johnson scores for 3 days after reperfusion, after which, spinal cords were procured for hematoxylin and eosin staining for cell counting.

RESULTS

Johnson scores revealed a marked improvement in both the diazoxide-treated groups vs. the non-treated control group at 3, 24, 48, and 72 h after reperfusion (P<0.01). The histologic changes were proportional to the Johnson scores, with better preservation of motor neuron numbers in the animals of the 48-h DZ and 15-min DZ group relative to the non-treated controls (81+/-12, 90+/-10, 50+/-23 motor neurons, respectively, P<0.01). No difference was found between the 48-h DZ group and 15-min DZ group with respect to the Johnson scores or neuron numbers.

CONCLUSIONS

The study demonstrates that pre-treatment with diazoxide 48 h before ischemia, induce delayed pharmacological pre-conditioning, thereby significantly improving clinical neurologic scores and histologic findings in this animal model.

Preconditioning and protection against ischaemia-reperfusion in non-cardiac organs: a place for volatile anaesthetics?

There is an increasing body of evidence that volatile anaesthetics protect myocardium against ischaemic insult by a mechanism termed 'anaesthetic preconditioning'. Anaesthetic preconditioning and ischaemic preconditioning share several common mechanisms of action. Since ischaemic preconditioning has been demonstrated in organs other than the heart, anaesthetic preconditioning might also apply in these organs and have significant clinical applications in surgical procedures carrying a high risk of ischaemia-reperfusion injury. After a brief review on myocardial preconditioning, experimental and clinical data on preconditioning in non-cardiac tissues will be presented. Potential benefits of anaesthetic preconditioning during non-cardiac surgery will be addressed.

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.

Effect of ischemic post-conditioning on spinal cord ischemic-reperfusion injury in rabbits

OBJECTIVES

To investigate the potential protective effect of ischemic post-conditioning (Post-con) on ischemia-reperfusion injury of the rabbit spinal cord, and to determine if there is an additive neuroprotective effect when ischemic preconditioning (IPC) and Post-con are combined.

METHODS

Forty New Zealand white rabbits were randomly divided into four groups: group Control (C; n=10), aortic occlusion (AOC; for 30 min; group IPC (n=10) three cycles of three-minute AOC plus three-minute reperfusion before the 30-min AOC; group Post-con (n=10), three cycles of three-minute reperfusion plus three-minute AOC immediately upon reperfusion after 30-min AOC; group IPC+Post-con (n=10), where animals were subjected to both IPC and Post-con. At six hours, 24 hr and 48 hr following reperfusion, neurological function was assessed according to Tarlov scores, and at 48 hr, the spinal cords were procured for the histopathologic evaluation, by comparing the number of intact alpha-motor neurons in the anterior horn.

RESULTS

The median count (and quartiles) of intact alpha-motor neurons was greatest in group Post-con 73 (69-76) and group IPC+Post-con 29 (22-42) compared to the numbers of viable alpha-motor neurons in groups C 6 (4-9) and IPC 15 (11-18) (P < 0.001). The numbers of animals who developed paraplegia according to Tarlov criteria were 7/10 in groups Post-con and IPC+Post-con, compared to 9/10 animals in each of groups C and IPC.

CONCLUSIONS

This laboratory investigation provides histological evidence that Post-con may protect the spinal cord from moderate to severe ischemia reperfusion injury. Ischemic preconditioning conferred no additional benefits in this rabbit model. The results have potential clinical implications for patients undergoing thoracoabdominal aortic reconstructive surgery.

Evolution of Spinal Cord Injury in a Porcine Model of Prolonged Aortic Occlusion

BACKGROUND

Spinal cord injury and subsequent paraplegia remains an unpredictable and devastating complication of thoracoabdominal aortic surgery. The aim of this study was to investigate spinal cord injury due to prolonged thoracoabdominal aortic occlusion.

MATERIALS AND METHODS

We used a highly reproducible porcine model of 45-min thoracoabdominal aortic occlusion, which was accomplished by two balloon occlusion catheters. Neurological evaluation after the end of experiment was performed by an independent observer according to the Tarlov scale. The lower thoracic and lumbar spinal cords were harvested at 10, 48, and 120 h (n = 6 animals per time point) and examined histologically with hematoxylin and eosin (H&E) stain and TUNEL method. Tarlov scores, number of neurons, and the grade of inflammation were analyzed.

RESULTS

H&E staining revealed reduction in the number of motor neurons which occurred in two phases (between 0 and 10 h and between 48 and 120 h of reperfusion), as well as development of inflammation in spinal cord sections during the reperfusion period, reaching a peak at 48 h. TUNEL reaction was negative for apoptotic neurons at any time point.

CONCLUSIONS

In this porcine model, we demonstrated that, after 45 min of thoracoabdominal aortic occlusion, motor neuron death seems to occur in two phases (immediate and delayed). Inflammation was a subsequent event of transient prolonged spinal cord ischemia and possibly a major contributor of delayed neuronal death. Using TUNEL straining we found no evidence of neuronal apoptosis at any time point of reperfusion.

Onlay Patch for Complete Intercostal Artery Preservation During Thoracic and Thoracoabdominal Aortic Aneurysm Repair

BACKGROUND

Replacement of the thoracic aorta is associated with a potential for interruption of the blood supply to the spinal cord leading to paralysis. Techniques have been proposed to ameliorate this risk, including reimplantation of the intercostal arteries. We present a technique to simplify this approach.

METHODS

In patients with extensive aneurysmal disease, a standard approach to the thoracic aorta via a left thoracotomy is performed. The patient is placed on full cardiopulmonary bypass with moderate hypothermia. The proximal anastomosis is performed unclamped with circulatory arrest. After completing the proximal and distal anastomosis separately, an onlay patch of Dacron is created and placed along the entire back wall of the aorta to cover all of the intercostal arteries. A side-to-side anastomosis between the patch and the distal graft is then performed and subsequently the anastomosis tested by retrograde flow.

RESULTS

The technique allows direct inspection of all suture lines, tested to an adequate pressure, so that postoperative bleeding is minimal.

CONCLUSION

Techniques to lessen the risk of paraplegia associated with aortic surgery include reimplantation of the intercostal arteries. This technique allows each suture line to be tested and easily visually inspected prior to closure of the chest.

Superiority of early relative to late ischemic preconditioning in spinal cord protection after descending thoracic aortic occlusion

OBJECTIVE

We previously showed that ischemic preconditioning significantly reduced spinal cord injury caused by 35-minute aortic occlusion. In this study we investigated the effect of ischemic preconditioning on spinal cord injury after 45-minute aortic occlusion.

METHODS

Thirty-two pigs were divided as follows: group 1 (n = 6) underwent sham operation, group 2 (n = 6) underwent 20 minutes of aortic occlusion, group 3 (n = 6) underwent 45 minutes of occlusion, group 4 (n = 6) underwent 20 minutes of occlusion and 48 hours later underwent an additional 45 minutes, and group 5 (n = 8) underwent 20 minutes of occlusion and 80 minutes later underwent an additional 45 minutes. Aortic occlusion was accomplished with two balloon occlusion catheters placed fluoroscopically after the origin of the left subclavian artery and at the aortic bifurcation. Neurologic evaluation was by Tarlov score. The lower thoracic and lumbar spinal cords were harvested at 120 hours and examined histologically with hematoxylin-eosin staining. The number of neurons was counted, and the inflammation was scored (0-4). Statistical analysis was by Kruskal-Wallis and 1-way analysis of variance tests.

RESULTS

Group 5 (early ischemic preconditioning) had better Tarlov scores than group 3 ( P < .001) and group 4 (late ischemic preconditioning, P < .001). The histologic changes were proportional to the Tarlov scores, with the least histologic damage in the animals of group 5 relative to group 3 (number of neurons P < .001, inflammation P = .004) and group 4 (number of neurons P < .001, inflammation P = .006).

CONCLUSION

Early ischemic preconditioning is superior to late ischemic preconditioning in reducing spinal cord injury caused by the extreme ischemia of 45 minutes of descending thoracic aortic occlusion.