Spinal cord protection during aortic cross-clamping using retrograde venous perfusion

Targeted Temperature Management With Total Liquid Ventilation After Ischemic Spinal Cord Injury

BACKGROUND

Ischemic spinal cord injury is a devastating condition after aortic surgery. We determined whether ultrafast and short whole-body hypothermia provided by total liquid ventilation (TLV) attenuated lower limb paralysis after aortic cross-clamping with a targeted temperature management at 33°C versus 36°C.

METHODS

Anesthetized rabbits were submitted to infrarenal aortic cross-clamping during 15 min. A control group (n = 7) was maintained at normothermia (38°C to 38.5°C) with conventional mechanical ventilation. In TLV groups, TLV was started after reperfusion and maintained during 30 min with a target temperature at either 33°C or 36°C (TLV-33°C and TLV-36°C, respectively; n = 7 in each condition). After TLV, animals were resumed to conventional ventilation. Hypothermia was maintained during 120 min, before rewarming and awakening. Hind limb motor function was assessed with modified Tarlov score at day 2 and infarct size in the spinal cord was determined using triphenyltetrazolium chloride staining.

RESULTS

Target temperature was achieved within 20 minutes in the two TLV groups. At day 2, the modified Tarlov score was significantly lower in the control group, as compared with TLV-33°C and TLV-36°C groups (0.0 ± 0.0 versus 3.1 ± 0.7 and 2.6 ± 0.6, respectively). The infarct size of the spinal cord was also significantly higher in the control group compared with TLV-33°C and TLV-36°C groups (75% ± 10% versus 32% ± 7% and 28% ± 10%, respectively). Neither motor function nor infarct size differed significantly between TLV-33°C and TLV-36°C groups.

CONCLUSIONS

Ultrafast hypothermic TLV attenuates spinal cord injury when applied after ischemic insult. Neurological outcome was similar with targeted temperature management at either 33°C or 36°C.

Maximizing neuroprotection: where do we stand?

Brain and spinal cord traumas include blunt and penetrating trauma, disease, and required surgery. Such traumas trigger events such as inflammation, infiltration of inflammatory and other cells, oxidative stress, acidification, excitotoxicity, ischemia, and the loss of calcium homeostasis, all of which cause neurotoxicity and neuron death. To prevent trauma-induced neurological deficits and death, each of the many neurotoxic events that occur in parallel or sequentially must be minimized or prevented. Although neuroprotective techniques have been developed that block single neurotoxic events, most provide only limited neuroprotection and are only applied singly. However, because many neurotoxicity triggers arise from common events, an approach for invoking more effective neuroprotection is to apply multiple neuroprotective methods simultaneously before the many neurotoxic triggers and cascades are initiated and become irreversible. This paper first discusses some triggers of neurotoxicity and neuroprotective mechanisms that block them, including hypothermia, alkalinization, and the administration of adenosine. It then examines how the simultaneous application of these techniques provides significantly greater neuroprotection than is provided by any technique alone. The paper also stresses the importance of determining whether the neuroprotection provided by these techniques can be further enhanced by combining them with additional techniques, such as the systemic administration of glucocorticoids. Finally, the paper stresses the absolute critical importance of applying these techniques within the "golden hour" following trauma, before the many neurotoxic events and cascades are manifest and before the neurotoxic cascades become irreversible.

Combinatorial techniques for enhancing neuroprotection: hypothermia and alkalinization

Brain and spinal cord (CNS) trauma typically kill a number of neurons, but even more neurons are killed by secondary causes triggered by the initial trauma. Thus, a minor insult may rapidly cause the death of a vastly larger number of neurons and complete paralysis. The best mechanism for reducing the extent of neurological deficits is to minimize the number of neurons killed by post-trauma sequelae. Neuroprotection techniques take many diverse forms with a breadth too great for a short review. Therefore, this review focuses on the neuroprotection provided by hypothermia and a number of other neuroprotective techniques, when administered singly or in combination, because it is generally found that combinations of applications lead to significantly better neuroprotection than is achieved by any one alone. The combinatorial approach to neuroprotection holds great promise for enhancing the degree of neuroprotection following trauma, leading to maximum maintenance of neurological function.

Neuroprotection by hypothermia plus alkalinization of dorsal root ganglia neurons through ischemia

Brain and spinal cord (CNS) trauma typically directly kill some neurons leading to permanent neurological deficits. However, they also lead to a number of triggers which in turn frequently kill a vastly larger number of neurons than were killed by the initial insult. The best mechanism for reducing the extent of neurological deficits is to minimize the number of neurons that die immediately due to the trauma, and post-trauma sequelae. Neuroprotection techniques have taken many diverse forms with a breadth too great for a short review. Therefore, this review is focused on the roles of only a small number of neuroprotective agents, with its primary focus being on neuroprotection provided by hypothermia, alone and when combined with the other methods. Included are also recent results involving a novel neuroprotective technique, tested on adult human dorsal root ganglion neurons, comparing the influences of hypothermia and alkalinization singly, providing fourfold and eightfold increases in neuroprotection, respectively, but when combined providing a 26-fold increase in neuroprotection. This combinatorial approach to neuroprotection holds great promise for enhancing the degree of neuroprotection clinically following CNS trauma, leading to the preservation of maximal neurological functions.

The penile erection efficacy of a new phosphodiesterase type 5 inhibitor, mirodenafil (SK3530), in rabbits with acute spinal cord injury

Mirodenafil (SK3530) is a new potent and selective inhibitor of cGMP-specific phosphodiesterase type 5 (PDE5). Recent clinical trials have demonstrated that mirodenafil is an effective treatment for erectile dysfunction. Its mechanism of action is enhancement of nitric oxide (NO) induced cGMP formation resulting in significant relaxation of the corpus cavernosum (CC). The aim of this study was to investigate the oral efficacy of mirodenafil in an acute spinal cord-injured rabbit model. Mirodenafil or sildenafil citrate was given orally to male rabbits with a surgical transection of the spinal cord at the L2-L4 lumbar vertebra or ischemic-reperfusion spinal cord injury (SCI). Erections were evaluated in a time-course manner by measuring the length of the uncovered penile mucosa. In the transection SCI model, penile erections were induced at 0.3, 1 and 3 mg/kg of mirodenafil but sildenafil only showed an erectile response at 3 mg/kg. The effects of 1 and 3 mg/kg of mirodenafil were significantly increased by intravenous injection of sodium nitroprusside (SNP), a nitric oxide donor. In the ischemic-reperfusion injury model, 3 mg/kg of either mirodenafil or sildenafil produced a penile erection response. After injection of SNP, the lengths of immediate penile erections were significantly increased in the 1 and 3 mg/kg mirodenafil and 3 mg/kg sildenafil groups. The onset of erectile activity was faster with mirodenafil than with sildenafil citrate. These results demonstrate that mirodenafil may be useful for treating erectile dysfunction in patients with a spinal cord injury.

Spinal cord retrograde perfusion: review of the literature and experimental observations

BACKGROUND

Spinal cord damage represents a devastating complication of thoracic and thoracoabdominal aortic surgery. Retrograde perfusion as an alternative route to protect the spinal cord has recently been investigated with controversial results. We reviewed the literature and analyzed additional experimental observations.

METHODS

Ten juvenile pigs were divided into control and study groups (A and B, respectively). Through a lateral thoracotomy the distal aortic arch was cannulated and connected to a cardiotomy reservoir. All animals underwent 40-minute single cross-clamping of the proximal descending aorta while keeping proximal systolic arterial pressure above 100 mmHg. In group B, normothermic arterial blood was delivered retrogradely through the azygos vein, maintaining perfusion pressure within 25-30 mmHg. Animals were allowed to recover to perform a primary neurologic evaluation.

RESULTS

Flaccid paraplegia was uniformly observed in group A. In group B, all animals showed mild-to-moderate voluntary hind limb movements on awakening (p = 0.007). Controls also showed urine incontinence short after cross-clamping, and this was not observed in group B (p = 0.008). A different veno-arterial oxygen step-down was observed in blood collected from the excluded aorta in the two groups (p < 0.001).

CONCLUSIONS

Preliminary results indicate that controlled retrograde normothermic perfusion alone through the azygos system provides some degree of protection from spinal cord ischemia. Bladder dysfunction may represent a simple test to detect massive cord damage intraoperatively. Retrograde spinal cord perfusion warrants further investigation.

Functional and cytoarchitectural spinal cord protection by ATL-146e after ischemia/reperfusion is mediated by adenosine receptor agonism

BACKGROUND

ATL-146e protects the spinal cord from ischemia/reperfusion injury, presumably via adenosine A(2A) receptor activation, but this relationship remains unproven. We hypothesized that spinal cord functional and cytoarchitectural preservation from ATL-146e would be lost with simultaneous administration of the specific adenosine A(2A) antagonist ZM241385 (ZM), thus proving that adenosine A(2A) receptor activation is responsible for the protective effects of this compound.

METHODS

New Zealand White rabbits underwent 45 minutes of infrarenal aortic cross-clamping. Groups (n = 10) included sham, ischemia, ischemia plus ATL-146e (ATL-146E), ischemia plus ZM, or ischemia with both compounds (agonist-antagonist). Tarlov scores were recorded every 12 hours. After 48 hours, the spinal cord was fixed for histology and microtubule-associated protein 2 immunohistochemistry.

RESULTS

Tarlov scores at 48 hours were significantly better in the sham and ATL-146E groups (5.0 and 3.9, respectively) compared with the other three groups (all < or =1.3; P < .001). On hematoxylin and eosin, neuronal viability was higher in the sham, ATL-146E, and agonist-antagonist groups compared with the control and ZM groups (P < .05). Microtubule-associated protein 2 expression was preserved in the sham and ATL-146E groups but was lost in the ATL + ZM, ZM241385, and control groups.

CONCLUSIONS

ATL-146e preserves the spinal cord in terms of both cytoarchitecture and function after reperfusion of the ischemic spinal cord, but this preservation is not completely blocked by competitive adenosine A(2A) receptor antagonism. Although ATL-146e does seem to partially function through activation of the adenosine A(2A) receptor, the neuroprotective mechanism may not be limited to this particular receptor.

Cold spinoplegia and transvertebral cooling pad reduce spinal cord injury during thoracoabdominal aortic surgery

OBJECTIVE

We examined the protective effects of the new selective spinal cord cooling by using cold saline infusion into the cross-clamped aorta and a transvertebral cooling pad placed over the lumbar vertebral column from paraplegia caused by ischemic spinal cord injury on thoracoabdominal aortic surgery.

METHODS

Eighteen rabbits were divided into three groups: groups I, II, and III (n = 6 for each group). In group I (37 degrees C; 5 mL) and group II (3 degrees C; 5 mL), saline was infused into the isolated aortic segment twice, at 0 and 5 minutes after aortic cross clamping. In group III, a 3 degrees C saline solution plus cooling pads placed just after cross clamping were combined. The infrarenal aorta was then isolated proximally and distally by vascular clamps for 12 minutes. In our preliminary study, only the abdominal aorta just distal to the left renal artery was clamped. At 48 hours after reperfusion, the groups clamped for 12 and 15 minutes were all paraplegic. The time of clamping the aorta was set at 12 minutes as the critical point when paraplegia occurred upon simple clamping of the infrarenal aorta only. The spinal cord temperature was monitored at the L4 level continuously during the procedures in all three groups. At 8, 24, and 48 hours after the operation, hind limb function was estimated by using the Tarlov score, which is often used for evaluating motor function in animals. A histopathologic study using hematoxylin and eosin stains was also performed.

RESULTS

At 48 hours after the operation, the Tarlov scores in groups I, II, and III were 0 +/- 0, 2.0 +/- 1.9, and 4.0 +/- 0 (mean +/- SD), respectively. The Tarlov score and histopathologic analysis in group III were significantly superior to those of groups I (P < .01) and II (P < .05). The spinal cord temperature in groups II and III decreased by -1.8 degrees C and -4.3 degrees C at its minimum. The rabbits in group III were also protected from paraplegia.

CONCLUSIONS

Selective spinal cord cooling with cold saline infusion into the isolated aortic segment and transvertebral regional cooling can reduce the neurologic damage of spinal cord ischemia.

Immunosuppressants: neuroprotection and promoting neurological recovery following peripheral nerve and spinal cord lesions

No clinical techniques induce restoration of neurological losses following spinal cord trauma. Peripheral nerve damage also leads to permanent neurological deficits, but neurological recovery can be relatively good, especially if the ends of a transected nerve are anastomosed soon after the injury. The time until recovery generally depends on the distance the axons must regenerate to their targets. Neurological recovery following the destruction of a length of a peripheral nerve requires a graft to bridge the gap that is permissive to, and promotes, axon regeneration. But neurological recovery is slow and limited, especially for gaps longer than 1.5 cm, even using autologous peripheral nerve grafts. Without a reliable means of bridging long nerve gaps, such injuries commonly result in amputations. Promoting extensive neurological recovery requires techniques that simultaneously provide protection to injured neurons and increase the numbers of neurons that extend axons, while inducing more rapid and extensive axon regeneration across long nerve gaps. Although conduits filled with various materials enhance axon regeneration across short nerve gaps, pure sensory nerve graft remains the gold standard for use across long nerve gaps, even though they lead to only limited neurological recovery. Consistent results demonstrate that several immunosuppressive agents enhance the number of axons and the rate at which they regenerate. This review examines the roles played by immunosuppressants, especially FK506, with primary focus on its role as a neuroprotectant and neurotrophic agent, and its potential clinical use to promote improved neurological recovery following peripheral nerve and spinal cord injuries.

Effect of the free radical scavenger MCI-186 on spinal cord reperfusion after transient ischemia in the rabbit

OBJECTIVE

Paraplegia remains a serious complication of aortic operations. The production of free radicals during reperfusion after transient ischemia is believed to induce secondary spinal neuronal injury, resulting in paraplegia. The aim of the present study was to clarify the protective effect and method of administration of antioxidants on the neurological and histological outcome in the animal model for reperfusion injury after transient spinal cord ischemia.

METHODS

New Zealand white rabbits underwent surgical exposure of the abdominal aorta that was clamped for 15 minutes to achieve spinal cord ischemia. Group A animals received two 10 mg/kg doses of 3-methyl-1-phenyl-2-pyrazolin-5-one (MCI-186) at the time of release of the aortic clamp and 30 minutes later. In group B, MCI-186, 5 mg/kg, was given three times, at the time of aorta clamp release, 30 minutes and 12 hours later. In group C (control group), one dose of vehicle was administered. Neurological status was assessed using modified Tarlov's score until 168 hours after operation. Spinal cord sections were examined microscopically to determine the extent of ischemic neuronal damage.

RESULTS

Groups A and B animals had better neurological function than group C (p < 0.001). In contrast, group C animals exhibited paraplegia or paraparesis with marked neuronal necrosis. The number of surviving neurons within examined sections of the spinal cord was significantly greater in group B than in group C (p < 0.001).

CONCLUSION

In a 15-minute ischemia-reperfusion model using rabbits, systemic repetitious administration of MCI-186, a free radical scavenger, was found to have a protective effect on the spinal cord neurons both neurologically and histologically. We postulate that the drug minimizes the delayed neuronal cell death for reperfusion injury after transient ischemia by reducing the free radical molecules. Moreover, it was thought that we could protect delayed neuronal cell death more effectively by administering MCI-186 12 hours later.

Neuroprotection of adult rat dorsal root ganglion neurons by combined hypothermia and alkalinization against prolonged ischemia

Ischemia and ischemia-induced secondary events, such as acidosis and excessive activation of receptors by amino acids, trigger neuron death. The isolation and dissociation of dorsal root ganglion (DRG) involves time during which the neurons are ischemic due to being densely packed within the intact DRG and surrounded by a connective tissue coat. Thus, the longer the time between killing the host animal and when the DRG are dissociated, the longer the neurons are ischemic and exposed to ischemia-induced secondary causes of neuron death. It is well established that hypothermia and alkalinization each separately protect neurons from ischemia and ischemia-induced secondary causes of neuron death, but there are no data on the neuroprotection provided by simultaneous hypothermia and alkalinization. The present experiments were designed to determine the combination of hypothermic and alkaline conditions that yield the largest number of viable neurons dissociated from intact DRG maintained ischemic for up to 4 h. Hypothermia (20 degrees C>15 degrees C>37 degrees C) and alkalinization (pH 9.3>pH 8.3>pH 7.4) increased the yield of viable neurons compared with the yield from DRG maintained under physiological conditions. Hypothermia and alkalinization combined (20 degrees C/pH 9.3) provided the greatest neuroprotection with a yield of viable neurons after 1 h of ischemia 2.5-fold larger than that from DRG maintained under physiological conditions (37 degrees C/pH 7.6). Over 4 h of ischemia, the yield of viable neurons from DRG maintained under both hypothermic/alkaline and physiological conditions decreased in a linear manner, but those at 20 degrees C/pH 9.3 had a 4.5-fold greater yield of viable neurons than those at 37 degrees C/pH 7.6. Thus, combined hypothermia and alkalinization provide significantly greater protection against ischemia and ischemia-induced secondary causes of neuron death than either alone.

Efficacy of DA-8159, a new PDE5 inhibitor, for inducing penile erection in rabbits with acute spinal cord injury

DA-8159 is a pyrazolopyrimidinone derivative which exhibits potent and selective phosphodiesterase type 5 (PDE5) inhibition. The aim of this study was to investigate the effects of DA-8159 on inducing a penile erection in rabbits with an acute spinal cord injury (ASCI). DA-8159 was given either orally (1, 3, or 10 mg/kg) or intravenously (0.1 or 0.3 mg/kg) to conscious male albino rabbits with a surgical transection of the spinal cord at the L2-L4 lumbar vertebra or ischemic-reperfusion SCI rabbits. Erection was evaluated in a time-course manner by measuring the length of the uncovered penile mucosa. DA-8159 induced a dose-dependent erection in both transection and ischemic-reperfusion ASCI rabbits. The efficacy of DA-8159 was potentiated by an intravenous injection of sodium nitroprusside, a nitric oxide donor. Potentiation of the effect by nitric oxide donor implies that DA-8159 can enhance the erectile activity during sexual arousal. These results suggest that DA-8159 may be useful for treating erectile dysfunction in patients with an SCI.

The role of pharmacology in spinal cord protection during thoracic aortic reconstruction

Surgery of the thoracic aorta continues to have a significant risk of neurologic complication. Several strategies to minimize this risk are emerging. Pharmacologic protection from these complications continues to be researched, but at this point few medications are being used clinically. This article reviews the pathophysiology of ischemic spinal cord injury and summarizes the investigational pharmacology that may prevent these serious complications.

DA-8159, a new PDE5 Iihibitor, induces penile erection in conscious and acute spinal cord injured rabbits

OBJECTIVES

DA-8159 is a pyrazolopyrimidinone derivative showing potent and selective phosphodiesterase 5 (PDE5) inhibition. In the previous study, DA-8159 induced a dose-dependent increase in the intracavernous pressure (ICP) in anaesthetized dogs. The aim of this study was to investigate the effects of DA-8159 on penile erection in conscious and acute spinal cord injured (ASCI) rabbits.

METHODS

DA-8159 was given orally (0.3 to 10mg/kg) to normal rabbits and ASCI rabbits with a surgical transection of the spinal cord at the L2-L4 lumbar vertebra or ischemic-reperfusion. The erection was evaluated in a time-course manner by measuring the length of the uncovered penile mucosa in the absence or presence of intravenous sodium nitroprusside (SNP), a nitric oxide (NO) donor.

RESULTS

DA-8159 induced a dose-dependent penile erection in both the conscious and ASCI rabbits. The efficacy of DA-8159 was potentiated and the effective doses were significantly decreased by an intravenous injection of SNP. Potentiation of the effect by a nitric oxide donor implies that DA-8159 can enhance the erectile activity during sexual arousal.

CONCLUSION

These results demonstrate that DA-8159 may be a useful treatment option for erectile dysfunction in patients with or without a spinal cord injury, but further evaluation of the effects of DA-8159 on humans must be performed.

Complex blunt aortic injury or repair: beneficial effects of cardiopulmonary bypass use

OBJECTIVE

To compare the outcomes and associated morbidity in patients with blunt aortic injury (BAI) repaired using cardiopulmonary bypass versus no bypass. Special consideration is given to the influence of bypass in the outcome of complex injuries or repair circumstances.

SUMMARY BACKGROUND DATA

There are conflicting data concerning the utility of bypass techniques in the operative management of BAI, and controversy over the subject persists. During the last decade, surgeons at the authors' institution have undergone a change in philosophy concerning management of these injuries and began almost exclusively using cardiopulmonary bypass for the repair in 1996. This project explores the effects of this change in the management of BAI.

METHODS

The records of all patients with BAI admitted to a level 1 trauma center over a period of 12 years were reviewed for demographics, injury characteristics, operative technique, and outcome. The bypass group was compared to the no bypass group with respect to morbidity and mortality. Those with a complex injury or repair (CI/R) were examined as a subgroup. CI/R was defined as the presence of an injury with extension proximal to the subclavian artery, involvement of branch vessels, or requirement of maneuvers interfering with anastomosis construction, such as cardiac massage.

RESULTS

From January 1, 1990, to December 31, 2001, 91 patients were admitted to Wake Forest University Baptist Medical Center with BAI. Sixty-five of these underwent operative repair. Sixty (32 no bypass, 28 bypass) survived to the immediate postoperative period. Injury Severity Score was similar (33 no bypass, 31 bypass, P =.48), as was admission base deficit (-9.2 m Eq/L no bypass vs. -7.0 mEq/L B, P =.13). Paraplegia occurred in four (12%) of the no bypass group as opposed to 0 of the bypass group (P =.05). No patient in the bypass group experienced complications related to heparinization, and two (7%) experienced bypass-related complications (cerebral edema, femoral vein laceration). Mean clamp time for the entire group was 27 minutes. Examination of the 10 patients with CI/R who survived the operating room showed markedly longer clamp times (59 minutes vs. 22 minutes, P <.0001) and a higher rate of paraplegia/paresis (30% vs. 2%, P =.01) as compared to those without CI/R. Logistic regression demonstrated a significant relationship between increasing clamp time and the CI/R classification (P =.007). All three (100%) of the CI/R patients repaired via clamp-and-sew technique developed paraplegia, while none of the seven CI/R patients repaired on bypass developed neurologic changes (P =.008).

CONCLUSIONS

With the use of cardiopulmonary bypass in the repair of BAI, the incidence of paraplegia/paresis has fallen. While patients with typical injuries and uncomplicated repair can expect good results with either technique, cardiopulmonary bypass provides significant advantages in the repair of those with CI/R. With the use of bypass, no CI/R patient developed paraplegia, while all CI/R patients experienced paraplegia before bypass use. Although others have reported the importance of clamp time, in this series clamp time appeared largely to be a surrogate variable for complexity of injury.

Reduction of spinal cord injury with pentobarbital and hypothermia in a rabbit model

OBJECTIVES

to evaluate the effects of hypothermia and pentobarbital on spinal cord ischaemia induced in a rabbit model.

MATERIALS AND METHODS

thirty-two rabbits, allocated into four equal groups, had the infrarenal aorta clamped distal to the left renal artery and above the iliac bifurcation for 40 min. Groups 3 and 4 had infusion of 15 mg/kg of pentobarbital intravenously for 5 min, 15 min before the cross-clamping. Groups 2 and 4 had infusion of 20 ml of Ringer's lactate (LR) solution at 3 degrees C for 3 min during aortic cross clamp into the isolated aortic segment. Group 1 was untreated and served as control. Postoperative functions of spinal cord were assessed.

RESULTS

paraplegia occurred in all rabbits in Group 1, in one in each of Groups 2 and 3, whereas no paraplegia was observed in Group 4. In addition 2 and 3 animals of Groups 2 and 3, respectively revealed varying degree of neurological disturbances, whereas all animals of Group 4 had normal function. This difference between Groups 2, 3, and 4 vs Group 1 was significant (p<0.002). So was the difference between Groups 2 and 4 (p=0.03), whereas the difference between Groups 3 and 4 was not significant.

CONCLUSIONS

hypothermia and pentobarbital was more effective than hypothermia alone for prevention of spinal cord ischaemia in a rabbit model.

Left atrial-inferior vena cava bypass achieves retroperfusion of the porcine spinal cord: morphologic and preliminary physiologic studies

BACKGROUND

Spinal cord injury remains a devastating complication after procedures on the descending thoracic aorta. A new model for retrograde perfusion of the spinal cord during aortic cross-clamping was evaluated for its potential role in preventing spinal cord injury after thoraco-abdominal aortic surgery.

METHODS

Retrograde perfusion of the spinal cord was established in juvenile pigs using partial bypass from the left atrium to the isolated inferior vena cava. Flow was maintained for a 60-min period of aortic occlusion. Morphologic studies of spinal cord blood flow were obtained using injection of a dilute barium-gelatin-chromatin dye solution. Physiologic cooling of the spinal cord was achieved using varying degrees of hypothermic retroperfusion.

RESULTS

Five animals underwent a 30-min period of retroperfusion followed by dye injection. Dye was identified in spinal cord venules and capillaries, most heavily concentrated in the lumbar and lower thoracic cord. Thirteen animals underwent a 60-min period of normothermic (37 degrees C), mild hypothermic (27 degrees C), moderate hypothermic (17 degrees C), or deep hypothermic (7 degrees C) retroperfusion; mean spinal cord temperatures were 35.2, 32.2, 28.0, and 24.4 degrees C, respectively.

CONCLUSIONS

Retrograde perfusion of the porcine spinal cord using a left atrial to inferior vena cava partial bypass circuit can be accomplished and can be used with hypothermic perfusate to produce cooling of the spinal cord. This new technique warrants further investigation into spinal cord protection and potential application for operations on the descending thoracic aorta.

Adenosine A2A agonist reduces paralysis after spinal cord ischemia: correlation with A2A receptor expression on motor neurons

BACKGROUND

The adenosine A2A agonist ATL-146e ameliorates reperfusion inflammation, reducing subsequent paralysis and neuronal apoptosis after spinal cord ischemia. We hypothesized that neuroprotection with ATL-146e involves inducible neuronal adenosine A2A receptors (A2A-R) that are upregulated after ischemia.

METHODS

Eighteen rabbits underwent laparotomy, and 14 sustained spinal cord ischemia from cross-clamping the infrarenal aorta for 45 minutes. One group (ischemia-reperfusion [I/R] + ATL) received ATL-146e intravenously for 3 hours during spinal cord reperfusion. A second group (I/R) received equivolume intravenous saline solution for 3 hours and served as an ischemic control, and a third group (Sham) underwent sham laparotomy. At 48 hours, all subjects were assessed for motor impairment using the Tarlov scoring system (0 to 5). Lumbar spinal cord sections were immunolabeled for A2A-R and graded in a blinded fashion using light microscopy.

RESULTS

There was a significant improvement in Tarlov scores in I/R + ATL animals compared with the I/R group. Sham-operated animals demonstrated no A2A-R immunoreactivity. There was a dramatic increase in A2A-R immunoreactivity in neurons of lumbar spinal cord sections from I/R compared with I/R + ATL and sham-operated animals.

CONCLUSIONS

Reduction in paralysis in animals receiving ATL-146e correlates with the new finding of A2A-R expression on lumbar spinal cord motor neurons after ischemia. Adenosine A2A agonists may exert neuroprotective effects by binding to inducible neuronal A2A-R that are upregulated during spinal cord reperfusion, and reduced in response to administration of an A2A-R-specific agonist.

Adenosine A2A analogue improves neurologic outcome after spinal cord trauma in the rabbit

BACKGROUND

ATL-146e, an adenosine A2A agonist, reduces paralysis after spinal cord ischemia-reperfusion. We hypothesized that systemic ATL-146e could improve neurologic outcome after blunt spinal cord trauma.

METHODS

Twenty rabbits survived a thoracic spinal cord impact of 30 g-cm. One group received 0.06 microg/kg/min ATL-146e for the first 3 hours after impact (A2A group), whereas a second group received saline carrier (T/C group). Neurologic outcome was measured using the Tarlov scale (0-5). Histologic sections from the A2A and T/C groups were compared for neuronal viability.

RESULTS

There was significant improvement in Tarlov scores of A2A animals compared with T/C animals at 12 hours (p = 0.007), with a trend toward improvement at 36 (p = 0.08) and 48 (p = 0.09) hours after injury. There was decreased neuronal attrition in A2A animals (p = 0.06).

CONCLUSION

Systemic ATL-146e given after spinal cord trauma results in improved neurologic outcome. Adenosine A2A agonists may hold promise as a rapidly acting alternative to steroids in the early treatment of the spinal cord injured patient.

Adenosine A2A analogue ATL-146e reduces systemic tumor necrosing factor-alpha and spinal cord capillary platelet-endothelial cell adhesion molecule-1 expression after spinal cord ischemia

OBJECTIVE

Inflammation is likely a major contributor to spinal cord reperfusion injury after aortic reconstruction. Systemic 4-(3-[6-amino-9-(5-ethylcarbamoyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-9H-purin-2-yl]-prop-2-ynyl)-cyclohexanecarboxylic acid methyl ester (ATL-146e), a selective adenosine A(2A) agonist, has been shown to reduce paralysis after spinal cord ischemia. We hypothesized that ATL-146e reduces cytokine production during spinal cord reperfusion, curtailing inflammation and decreasing spinal cord capillary platelet-endothelial cell adhesion molecule-1 (PECAM-1) expression.

STUDY DESIGN

New Zealand White rabbits sustained spinal cord ischemia with 45-minute cross-clamping of the infrarenal aorta. One group of animals received intravenous ATL-146e at 0.06 microg/kg/min for 3 hours during reperfusion, beginning after 30 minutes of ischemia. A second group received saline solution vehicle alone for 3 hours, serving as an ischemic control. A third group served as sham-operated animals, undergoing laparotomy with anesthesia. Serum was assayed with enzyme-linked immunosorbent assay for tumor necrosing factor-alpha (TNF-alpha). Animals were allowed to recover for 48 hours and were evaluated for hind-limb motor function with the Tarlov (0 to 5) scoring system. At necropsy, animals from each group yielded spinal cords for immunohistochemical staining for PECAM-1. Data are expressed as mean +/- standard error of the mean, with statistical analysis with Student t test and Kruskal-Wallis nonparametric test.

RESULTS

Markedly improved Tarlov scores were seen in rabbits with ATL-146e (P <.001) during spinal cord reperfusion as compared with ischemic control animals. A significant reduction was found in TNF-alpha in the sera of rabbits with ATL-146e infusion (P <.01) as compared with ischemic control animals. Significantly reduced endothelial PECAM-1 staining intensity (P <.05) was seen in microscopic spinal cord sections from rabbits with ATL-146e.

CONCLUSION

ATL-146e, an adenosine A(2A) agonist, reduces spinal cord reperfusion injury. The mechanism of the protection may involve a reduction in circulating TNF-alpha during a critical 3-hour reperfusion interval and reduction in spinal cord endothelial PECAM-1 upregulation.

Spinal cord protection during aortic cross clamping: retrograde venous spinal cord perfusion, distal aortic perfusion, and cerebrospinal fluid drainage

OBJECTIVE

We investigated retrograde venous spinal cord perfusion (RVP), with the established adjuncts cerebrospinal fluid drainage (CSFD), and distal aortic perfusion (DAP) in the canine model. We then examined the clinical feasibility of RVP, DAP, and CSFD.

DESIGN

Canine study: Twenty dogs were randomized to four treatment groups. All animals underwent 60 min of complete aortic cross-clamp. Group 1 was the control and received only aortic cross-clamp; group 2 DAP and CSFD; group 3 DAP, CSFD, and RVP; and group 4 CSFD plus RVP. Human study: Five patients underwent aortic graft replacement of the descending or thoracoabdominal aorta, while receiving CSFD, DAP, and RVP.

RESULTS

Canine study: All animals in groups 1 and 4 awoke paralyzed. One animal each in groups 2 and 3 were paraparetic, with the remaining dogs neurologically intact. Groups 2 and 3 differed from groups 1 and 4 at p < 0.0001. Human study: No mortality or permanent complications were observed in this group.

CONCLUSION

While RVP did not reduce neurologic injury, neither did it increase morbidity. In humans the method is technically feasible and free from major problems. Further animal studies and randomized trials are underway at our center.

Systemic adenosine A2A agonist ameliorates ischemic reperfusion injury in the rabbit spinal cord

BACKGROUND

The adenosine A2A agonist ATL-146e (4-[3-[6-Amino-9-(5-ethylcarbamoyl-3,4-dihydroxytetrahydro-furan-2-yl)-9H-purin-2-yl]-prop-2-ynyl]-cyclohexanecarboxylic acid methyl ester) has been shown to prevent reperfusion injury in multiple organ systems through inhibition of activated leukocyte-endothelial interaction. We hypothesized that systemic ATL-146e could reduce spinal cord reperfusion injury after aortic clamping.

METHODS

Twenty-six rabbits underwent cross-clamping of the infrarenal aorta for 45 minutes. One group received intravenous ATL-146e for 3 hours during reperfusion. A second cohort received only vehicle and served as controls. Animals were assessed at 24 and 48 hours using the Tarlov (0 to 5) scoring system for hind limb function. To evaluate neuronal attrition, immunostaining of lumbar spinal cord sections was performed using anti-SMI 33 antibody against neurofilament.

RESULTS

Systemic ATL-146e was tolerated without hemodynamic lability. Animals that received ATL-146e had significantly improved neurologic outcomes 24 and 48 hours after spinal cord ischemia (p < 0.001). There was preservation of neuronal architecture in the ventral horn of spinal cord sections from animals receiving ATL-146e compared with control animals.

CONCLUSIONS

Intravenous ATL-146e given during reperfusion is tolerated without hemodynamic lability, and results in substantially improved spinal cord function after ischemia by preservation of ventral horn neurons.

An adenosine A2A agonist, ATL-146e, reduces paralysis and apoptosis during rabbit spinal cord reperfusion

BACKGROUND

We hypothesized that systemic ATL-146e, an adenosine A(2A) agonist, would decrease spinal cord reperfusion inflammatory stress and inhibit apoptosis and that these effects would correlate with improved neurologic functional outcome.

METHODS

Thirty rabbits underwent cross-clamping of the infrarenal aorta for 45 minutes. One group of animals (n = 14) received 0.06 microg/kg per minute of ATL-146e infused intravenously for 3 hours, beginning 15 minutes before reperfusion. A second group of animals (n = 16) underwent spinal cord ischemia with saline vehicle alone and served as ischemic controls. Animals (n = 9, 11) from each group survived for 48 hours and assessed for neurologic impairment with the Tarlov (0-5) scoring system. Four animals from each group were humanely killed at the end of the 3-hour treatment period, and the remainder killed after 48 hours' survival. In all animals, lumbar spinal cord tissue specimens were frozen for subsequent Western blot analysis of heat shock protein 70 (HSP 70), and for the p85 fragment of poly (ADP-ribose) polymerase (PARP). Neuronal viability indices were determined at 48 hours with hematoxylin and eosin staining.

RESULTS

There was improvement in neurologic function in rabbits receiving ATL-146e (P <.001) compared with ischemic controls. At the end of the 3-hour treatment period there was a 46% (P <.05) decrease in HSP 70 expression in the ATL-146e group compared with the control group, but no difference in PARP expression. At 48 hours, there was no difference between control and ATL-146e groups in HSP 70 expression, but there was a 65% (P <.05) reduction in PARP in the spinal cords of animals that had received ATL-146e. There was a significant improvement in neuronal viability indices in animals receiving ATL-146e compared with ischemic controls (P <.05).

CONCLUSIONS

Systemic ATL-146e infusion during reperfusion after spinal cord ischemia results in preservation of hindlimb motor function. There is evidence of decreased spinal cord inflammatory stress immediately after treatment with ATL-146e as indicated by reduced HSP 70 induction. Treatment with ATL-146e is associated with a reduction in neuronal apoptosis as suggested by a substantial decrease in the fragmentation of PARP at 48 hours. These results suggest that inflammation during reperfusion and subsequent apoptosis contribute to paralysis after restoration of blood flow to the ischemic spinal cord.

An intraaortic solution trial to prevent spinal cord injury in a rabbit model

OBJECTIVES

to evaluate the effectiveness of an intraaortic delivered solution on preventing spinal cord injury.

DESIGN

forty rabbits were allocated into five equal groups.

MATERIALS AND METHODS

one clamp was placed just distal to the left renal artery, and another was placed just above the iliac bifurcation for 40 min. Group 1 was not infused (control group). Through a 24G vascular catheter inserted into the isolated aortic segment, 20 ml of LR solution at room temperature (Group 2) 20 ml of LR solution at 3 degrees C (Group 3), and 20 ml of LR solution at 3 degrees C containing 30 mg/kg of methylprednisolone (Group 4) were infused over 3 min. In Group 5, 10 mg/kg of vitamins E and C were delivered two days before the experiment, and 20 ml of LR solution at 3 degrees C containing 30 mg/kg of methylprednisolone, and 10 mg/kg of vitamins E and C was infused at the operation. Postoperative spinal cord function was assessed using Tarlov's criteria.

RESULTS

the neurologic status of Groups 3, 4, and 5 was significantly superior to that of Groups 1 and 2. No paraplegia was observed in Groups 4 and 5. Spastic paraplegia occurred in all rabbits of Groups 1 and 2, and in 20% of Group 3. In the electron microscopic evaluation of spinal cord specimens, normal histologic structure was observed in Groups 4 and 5, whereas, some derangements were observed in all others.

CONCLUSIONS

intraaortic infusion of a hypothermic blended solution containing methylprednisolone, vitamins C and E provided best protection against postischaemic spinal cord dysfunction.

Adenosine analogue reduces spinal cord reperfusion injury in a time-dependent fashion

BACKGROUND

We hypothesized that inflammation during spinal cord reperfusion worsens ischemic injury. ATL-146e, an adenosine A(2A) agonist with known anti-inflammatory properties, was used to test this hypothesis at varied intervals to determine the time course of reperfusion injury.

METHODS

Forty rabbits underwent cross-clamping of the infrarenal aorta for 45 minutes. One group (n = 14 animals) received 0.06 microg/kg/min systemic ATL-146e over 3 hours, beginning after 30 minutes of ischemic time. A second group (n = 6 animals) received ATL-146e over 1.5 hours. A third group (n = 3 animals) received ATL-146e over 1 hour, and a fourth group (n = 17 animals) received saline solution. All animals were assessed at 48 hours for hind limb motor function (Tarlov scale, 0-5).

RESULTS

Animals that received ATL-146e for 3 hours (Tarlov score, 4.3 +/- 0.22; P <.001) or 1.5 hours (Tarlov score, 2.7 +/- 0.6; P <.05) had improved neurologic outcomes compared with rabbits that received saline solution (Tarlov score, 0.6 +/- 0.29). Animals that received ATL-146e for 1 hour (Tarlov score, 0.7 +/- 0.8) were not significantly different from those animals that received saline solution.

CONCLUSIONS

Systemic ATL-146e, given during reperfusion, results in time-dependent improvement in spinal cord function after ischemia. This implies that the mechanism of spinal reperfusion injury includes leukocyte-mediated inflammation at a critical post-ischemic time interval.

Retrograde venous perfusion with hypothermic saline and adenosine for protection of the ischemic spinal cord

PURPOSE

Spinal cord injury and the resultant postoperative paraplegia are devastating complications of thoracic aortic surgery, for which no widely accepted protective interventions exist. We hypothesized that retrograde venous perfusion-cooling of the spinal cord with a hypothermic saline and adenosine solution would protect it from ischemic injury caused by thoracic aortic occlusion.

METHODS

Adult domestic swine of either sex (weight range, 20 to 30 kg) were intubated and ventilated. A left thoracotomy was performed. The accessory hemiazygous vein was divided, and a catheter was inserted distally. The aorta was clamped at the left subclavian artery. The venous catheter was not used in the animals in the control group (n = 7); in the animals in the experimental group (n = 7), a cold (4 degrees C) saline and adenosine solution was infused into the accessory hemiazygous vein. After 30 minutes, the clamp and catheter were removed, and the chest was closed. A blinded observer evaluated the animals' hind-leg motor activity 24 hours later. The Tarlov scale was used: 0, complete paralysis; 1, minimal movement; 2, stands with assistance; 3, stands alone; 4, weak walk; 5, normal gait. The animals' rectal temperatures were measured at the end of the experiment, and blood pressure was measured throughout. Two other groups were studied to assess the effect of the intervention on spinal cord temperature.

RESULTS

The animals in the control group had a mean Tarlov score of 1.7 +/- 0.6; the animals in the experimental group had a mean Tarlov score of 4.9 +/- 0.1 (P <.01). The animals in the experimental group had a significantly greater drop in spinal cord temperature than those in the control group (4. 05 +/- 0.6 degrees C vs 0.58 +/- 0.12 degrees C; P <.01). No significant difference in rectal temperatures was found, nor did any arrhythmias or hypotensive episodes occur in either group. Perfusion of the spinal cord was confirmed with angiography by using this approach.

CONCLUSION

Retrograde venous perfusion-cooling of the spinal cord with a hypothermic saline and adenosine solution protects the cord from ischemic injury caused by clamping of the thoracic aorta.

Retrograde perfusion with a sodium channel antagonist provides ischemic spinal cord protection

BACKGROUND

Neuronal voltage-dependent sodium channel antagonists have been shown to provide neuroprotection in focal and global cerebral ischemic models. We hypothesized that retrograde spinal cord venous perfusion with phenytoin, a neuronal voltage-dependent sodium channel antagonist, would provide protection during prolonged spinal cord ischemia.

METHODS

In a rabbit model, spinal cord ischemia was induced for 45 minutes. Six groups of animals were studied. Controls (group I, n = 8) received no intervention during aortic cross-clamping. Group II (n = 8) received systemic phenytoin (100 mg). Group III (n = 4) received systemic phenytoin (200 mg). Group IV (n = 8) received retrograde infusion of room temperature saline (22 degrees C) only. Group V (n = 8) and group VI (n = 9) received retrograde infusion of 50 mg and 100 mg of phenytoin, respectively, (infusion rate: 0.8 mL x kg(-1) x min(-1) during the ischemic period). Mean arterial blood pressure was monitored continuously. Animals were allowed to recover for 24 hours before assessment of neurologic function using the Tarlov scale.

RESULTS

Tarlov scores (0 = complete paraplegia, 1 = slight lower limb movement, 2 = sits with assistance, 3 = sits alone, 4 = weak hop, 5 = normal hop) were as follows (mean +/- SEM): group I, 0.50 +/- 0.50; group II, 0.25 +/- 0.46; group IV, 1.63 +/- 0.56; group V, 4.13 +/- 0.23; and group VI, 4.22 +/- 0.22 (p < 0.0001 V, VI versus I, II, IV by analysis of variance). No differences in mean arterial blood pressure were observed. All animals in group III became profoundly hypotensive and died before the conclusion of the 45-minute ischemic time.

CONCLUSIONS

Retrograde venous perfusion of the spinal cord with phenytoin, a voltage-sensitive sodium channel blocker, is safe and provides significant protection during prolonged spinal cord ischemia.

Hypothermic retrograde venous perfusion with adenosine cools the spinal cord and reduces the risk of paraplegia after thoracic aortic clamping

OBJECTIVE

We evaluated the utility of retrograde venous perfusion to cool the spinal cord and protect neurologic function during aortic clamping. We hypothesized that hypothermic adenosine would preserve the spinal cord during ischemia.

METHODS

Six swine (group I) underwent thoracic aortic occlusion for 30 minutes at normothermia. Group II animals underwent spinal cooling by retrograde perfusion of the paravertebral veins with hypothermic (4 degrees C) saline solution during aortic occlusion. The spinal cords of group III animals were cooled with a hypothermic adenosine solution in a similar fashion. Intrathecal temperature was monitored and somatosensory evoked potentials assessed the functional status of spinal pathways.

RESULTS

Spinal cooling without systemic hypothermia significantly improved neurologic Tarlov scores in group III (4.8 +/- 0.2) and group II (3.8 +/- 0.4) when compared with group I scores (1.3 +/- 0.6) (P <.001). Furthermore, 5 of the 6 animals in group III displayed completely normal neurologic function, whereas only one animal in group II and no animals in group I did (P =.005). Somatosensory evoked potentials were lost 10.6 +/- 1.4 minutes after ischemia in group I. In contrast, spinal cooling caused rapid cessation of neural transmission with loss of somatosensory evoked potentials at 6.9 +/- 1.2 minutes in group II and 7.0 +/- 0.8 minutes in group III (P =.06). Somatosensory evoked potential amplitudes returned to 85% of baseline in group III and 90% of baseline in group II compared with only 10% of baseline in group I (P =.01).

CONCLUSIONS

We conclude that retrograde cooling of the spinal cord is possible and protects against ischemic injury and that adenosine enhances this effect. The efficacy of this method may be at least partly attributed to a more rapid reduction in metabolic and electrical activity of the spinal cord during ischemia.