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.     

Drip retrograde coronary sinus perfusion for myocardial protection during aortic cross-clamping.

Moderate hypothermia is one of the methods utilized for myocardial protection when the aortic root is cross-clamped but not opened. A combination of low-pressure, low-flow retrograde coronary sinus perfusion (RCSP) with oxygenated blood at moderate hypothermia (29 degrees C.) was demonstrated to yield significantly better protection to left ventricular function in dogs than does moderate hypothermia alone. Ventricular function was recorded before and after 1 hour of aortic cross-clamping at identical preloads and heart rates. Aortic pressure was returned to a level as close to base line as possible by constriction of the descending aorta. The average mean aortic pressure of the animals perfused retrograde at 29 degrees C. was returned to within 4 per cent of base line. By contrast, in the animals protected with moderate hypothermia alone, the pressure could be returned only to a level which was 37 per cent lower than base line. In animals protected with moderate hypothermia alone, cardiac output dropped 62 per cent, left ventricular stroke work (LVSW) 75 per cent, and peak dp/dt 44 per cent. In the animals protected with RCSP and moderate hypothermia, the cardiac output dropped 6 per cent, LVSW 9 per cent, and peak dp/dt 5 per cent. The differences in the changes noted between these two groups were significant for LVSW and dp/dt at a level of p less than 0.01 and for cardiac output and aortic pressure at a level of p less than 0.05. These results suggest that RCSP may be indicated when moderate hypothermia is otherwise chosen to be the sole source of myocardial protection.     

Spinal cord protection during thoracoabdominal aortic aneurysm repair; efficacy of distal aortic perfusion and segmental aortic clamping

Despite improvement in adjuncts for thoracoabdominal aortic aneurysms (TAAA) repairs, many devastating complications remains after the surgery. Our experience with these aneurysms has been reviewed in order to identify those methods at risk of major morbidity, as well as which further improvements required. During last 16 years, 53 consecutive patients were operated on TAAA. The mean age was 58 years. Twenty patients had dissecting aneurysms and 13 patients had had prior aortic surgery. A femoro-femoral bypass was used to maintain distal aortic perfusion in most patients. Reimplantation of intercostal or lumbar arteries under the multi-segmental aortic clamping is consistent in our technique. Motor evoked potentials (MEP) were measured to monitor spinal cord protection since 2000. The hospital mortality was 9.4% (5/53), 22.2% (2/9) for emergency operation and 15.4% (2/13) for patients with prior aortic surgery. The mortality for the first and elective operations was 3.2% (1/31). No any neurologic dysfunction was observed in all patients including the hospital deaths. In view of clinical results, our adjuncts and techniques are useful for prevention of spinal cord ischemia during the TAAA surgery.     

Effect of sodium nitroprusside on spinal cord perfusion and paraplegia during aortic cross-clamping

To evaluate the effects of sodium nitroprusside (SNP) on hemodynamics, cerebrospinal fluid dynamics, and neurological outcome after 30 minutes of thoracic aortic occlusion, we monitored proximal and distal blood pressure, cerebrospinal fluid pressure, spinal cord blood flow, and somatosensory evoked potentials. In group 1 (n = 6), no attempts were made to control proximal hypertension, whereas in group 2 (n = 6), proximal blood pressure was controlled with intravenous infusion of SNP. There was no significant difference in proximal or distal blood pressure or cerebrospinal fluid pressure between the two groups at baseline. During the crossclamp interval, the mean proximal aortic pressure rose from 108 +/- 21 to 146 +/- 14 mm Hg (p less than 0.001) in the control group, whereas the mean blood pressure in the SNP group was maintained at 99.8 +/- 12 mm Hg (p = not significant compared with baseline blood pressure). Mean distal aortic pressure decreased from systemic values to 23 +/- 7 mm Hg in control animals and to 11 +/- 5 mm Hg in the SNP group (p less than 0.005). In the latter group, cerebrospinal fluid pressure increased significantly from 10.6 +/- 1.9 to 20.1 +/- 5.5 mm Hg (p less than 0.005). In animals receiving SNP, spinal cord blood flow was decreased in the lower spinal cord segments and increased in the upper cord segments. When compared with controls, this difference did not reach significance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spinal cord protection during descending thoracic and thoracoabdominal aortic surgery

The incidence of postoperative paralysis after thoracic and thoracoabdominal aortic operations has decreased, but is still high in comparison with other operations. The analysis of the mechanism involved in the ischemic tolerance of the spinal cord could contribute to the protection of the spinal cord from ischemia. The identification of the Adamkiewicz artery and the predictive factors for postoperative paralysis in the preoperative period, the use of motor evoked potential, several adjuncts to keep the spinal cord circulation, the stabilization of the hemodynamics with good oxygenation, and hypothermia contribute to the prevention of the spinal cord ischemia. The anesthetics appropriate for the monitoring of the motor-evoked potential are propofol and fentanyl with or without ketamine. Among the anesthetic drugs, narcotics might exacerbate the motor function after the spinal cord ischemia. The analgesic drugs which do not aggravate the spinal cord dysfunction would be expected. Good cooperation of surgeons and anesthesiologists greatly contributes to the finding of the spinal cord ischemia during this operation.     

Spinal cord perfusion and protection during descending thoracic and thoracoabdominal aortic surgery: the collateral network concept

In the last two decades, as an increasing number of patients with descending thoracic and thoracoabdominal aneurysms are being diagnosed and treated, a more sophisticated understanding of spinal cord perfusion has become important in the attempt to minimize the frequency of spinal cord injury. The synthesis of information from laboratory studies and clinical experience has led to the collateral network concept, a framework for understanding spinal cord perfusion and thereby improving spinal cord protection during treatment of aneurysmal disease of the aorta distal to the left subclavian artery. Application of principles based on the collateral network concept has resulted in falling rates of spinal cord injury, which now approach 1% in descending thoracic aneurysm resection and less than 10% in extensive thoracoabdominal resections. These accomplishments suggest that, with further investigation, routine sacrifice of segmental aortic branches can be carried out in a way that will allow surgical and endovascular therapy of extensive distal aortic aneurysms without neurologic injury.     

Cerebral protection using retrograde cerebral perfusion during hypothermic circulatory arrest

Background

Retrograde cerebral perfusion through the superior vena cava (SVC) has been proposed to protect the brain from ischaemic injury during profound hypothemnic circulatory arrest (PHCA). Its contribution to cerebral protection is unclear. Furthermore, the addition of anaesthetic or vasodilating agents to the SVC perfusate to enhance brain protection, has never been described.

Methods

In three patients undergoing repair of the ascending aorta utilizing PHCA, the upper body was retrogradely perfused with cold (16°C) blood through the SVC by the cardiopulmonary bypass pump. Electroencephalographic activity was monitored using a computenzed electroencephalographic monitor (Cerebro Trac 2500, SRD). Perfusion pressure was measured at a port in the cannula connector. Etomidate or thiopentone was injected into the SVC perfusate to arrest reappearing electroencephalographic activity. Nitroglycerin or nitroprusside was injected into the perfusate to increase retrograde flow and maintain a constant perfusion pressure.

Results

During PHCA penods of up to 61 min, recurrent electroencephalographic activity was abolished by the retrograde administration of small boluses of etomidate (total 50 mg) or thiopentone (total 500 mg). Nitroprusside (100 μg) and nitroglycerin (2 μg · kg^?1 · min^?1) increased retrograde flow from 220 to 550 and 660 ml · min^?1, respectively, while maintaining perfusion pressure (25–26 mmHg). Recovery from anaesthesia and surgery was uneventful, with no adverse neurological sequelae.

Conclusion

Injection of anaesthetic agents into the retrograde SVC perfusate during PHCA, can suppress reoccumng electroencephalographic activity and retrograde injection of vasodilators can facilitate an increase in perfusion. It is suggested that both may augment brain protection.     

Spinal cord protection during aortic occlusion: efficacy of intrathecal tetracaine

Spinal cord ischemia and resultant paraplegia are devastating sequelae in up to 40% of patients undergoing repair of thoracoabdominal aneurysms. We investigated the effect of intrathecal tetracaine on the neurological sequelae of spinal cord ischemia and reperfusion with aortic occlusion. Cocaine-derived anesthetics (lidocaine and its analogues) have been shown to decrease neuronal cell metabolism and also have specific neuronal membrane stabilizing effects. New Zealand white rabbits were anesthetized and spinal cord ischemia was then induced by infrarenal aortic occlusion. Animals were divided into six treatment groups. Tetracaine (groups 2 and 4) or normal saline solution (group 5) was administered intrathecally before aortic cross-clamping. Groups 1 and 3 functioned as controls. Group 6 animals received intravenous thiopental. Rabbits were classified as either neurologically normal or injured (paralyzed or paretic). Among controls, 25 minutes of aortic occlusion produced varied neurological sequelae (group 1, 3/6 injured, 50%) whereas 30 minutes resulted in more consistent injury (group 3, 5/6 injured, 83%). All rabbits that received intrathecal saline solution were paralyzed (group 5, 4/4 injured, 100%). Animals treated with intrathecal tetracaine and aortic occlusion of 30 minutes (group 4) showed significantly better preservation of neurological function (6/7 normal, 86%) than controls and saline-treated animals (groups 3 and 5). All animals treated with intrathecal tetracaine and aortic occlusion for 25 minutes (group 2) showed no signs of injury (5/5 normal, 100%), but this was not significant versus controls (group 1). Intravenous thiopental (group 6, 5/5 injured, 100%) had no beneficial effect. Intrathecal tetracaine significantly and dramatically abrogated the neurological injury secondary to spinal cord ischemia and reperfusion after aortic occlusion at 30 minutes in the rabbit model.     

Simple hypothermic retrograde cerebral perfusion for brain protection during aortic arch surgery]

We have recently found that retrograde cerebral perfusion can be performed by simply elevating central venous pressure to 15 mmHg in the Trendelenburg position when the aortic arch is open during aortic arch surgery. During deep hypothermic (15 degrees C) perfusion of the lower half of the body with the descending aorta occluded, and with single cannulation of the right atrium for drainage, oxygen-saturated venous blood perfuses the brain retrogradely, supplying it with oxygen. This method renders clamping of the aortic arch and the arch vessels unnecessary. Eleven cases of aortic arch aneurysm (9 males, 2 females; 5 true aneurysms, 5 dissecting aneurysms, one combined aneurysm; mean age, 63 years) were operated using this technique, whose clinical significance was then evaluated. Median sternotomy was performed in 4 cases, left thoracotomy in 7. Patch replacement was performed in 2 cases and graft replacement in 9 cases (the proximal arch in 2, the whole arch in 2, the distal arch in 5). In two cases coronary artery bypass surgery using the internal thoracic artery was performed simultaneously via lateral thoracotomy. Operation time was 517 +/- 139 min, pump time was 211 +/- 34 min, cardiac arrest time was 84 +/- 34 min and the lowest rectal temperature was 15.7 +/- 1.1 degrees C. In the venous return, PO2 was 188 +/- 136 mmHg, and SO2 97.5 +/- 2.9%, the respective values in the retrogradely perfused blood in the aortic arch being 46 +/- 12 mmHg and 68.8 +/- 18.8%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spinal cord metabolism during thoracic aortic cross-clamping in pigs with special reference to the effect of allopurinol.

OBJECTIVE: investigate the metabolic response of the spinal cord and the effect of allopurinol following cross clamping of the descending thoracic aorta in a porcine model. DESIGN: experimental animal study. MATERIALS: twelve domestic swine. Six pigs were pre-treated with allopurinol, while six pigs served as controls. METHODS: measurement of extracellular concentrations of glucose, pyruvate, lactate, glycerol and glutamate using microdialysis in the lumbar spinal cord. Measurement of lumbar spinal blood flow using laser Doppler technique. RESULTS: for all animals there was a significant decrease in concentrations of glucose and pyruvate together with a significant increase in the lactate-pyruvate ratio during aortic cross clamping. There was also a significant increase in glycerol concentrations 60 min after cross clamping, and a significant decrease in glutamate concentrations after 50 min. No differences in concentrations of glucose, pyruvate, lactate and glutamate or the glutamate-pyruvate ratio were observed between animals used as controls and those treated with allopurinol. The laser Doppler flux decreased to 40% of pre cross-clamp level, returning to normal values at declamping. CONCLUSION: the changes in energy-related metabolites reflect a considerable ischaemia in the spinal cord tissue but there was no convincing effect of allopurinol on the lumbar spinal cord metabolism during thoracic aortic cross clamping in this model.     

Cerebrospinal fluid drainage and steroids provide better spinal cord protection during aortic cross-clamping than does either treatment alone

We investigated whether intravenous methylprednisolone (30 mg/kg) before 30 minutes of aortic cross-clamping and after 4 hours could enhance the effects of cerebrospinal fluid drainage on spinal cord perfusion pressure and postoperative paraplegia when proximal blood pressure was controlled with sodium nitroprusside and partial exsanguination. Dogs were randomized into three groups: group 1 (n = 6), control; group 2 (n = 7), steroids; and group 3 (n = 6), steroids with cerebrospinal fluid drainage. During aortic cross-clamping, blood pressure proximal to the clamp decreased significantly in each group compared with baseline (p less than 0.05), but did not differ among groups (group 1 = 82.2, group 2 = 82.1, group 3 = 86.6 mm Hg, p greater than 0.05). Mean distal pressure decreased from systemic values to 8.4, 8.5, and 3.7 mm Hg, respectively, after aortic cross-clamping (p less than 0.05); these values did not differ from one another (p greater than 0.05). During aortic cross-clamping, cerebrospinal fluid pressure in groups 1 and 2 did not differ significantly compared with baseline (12.2 versus 8.2, 14.2 versus 10.7 mm Hg, p greater than 0.05), whereas in group 3 the baseline cerebral spinal fluid pressure of 10.7 mm Hg decreased to 0.4 mm Hg (p less than 0.05). Spinal cord perfusion pressure in group 3 was significantly higher than in groups 1 and 2 (3.3 versus -3.9 and -5.7 mm Hg, p less than 0.05), but did not differ between groups 1 and 2 (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Influence of retrograde cerebral perfusion during aortic arch procedures

BACKGROUND: Recent reports suggest dramatic improvement in outcome using retrograde cerebral perfusion (RCP) during operations on the arch; however, most investigators have compared contemporary results with historic controls. The purpose of this study was to determine the impact of RCP within the same patient population and time period. METHODS: From 1996 to 2000, 72 consecutive patients underwent an aortic arch procedure using hypothermic circulatory arrest (HCA) (31 acute dissection or rupture, 41 chronic dissection or aneurysm). Supplemental RCP was used in 36 patients, whereas 36 patients had HCA alone. The groups were similar in age, emergent status, and cardiopulmonary bypass time (p > 0.08), but HCA time was higher with RCP (40 +/- 15 minutes versus 29 +/- 14 minutes; p < 0.001). RESULTS: Operative mortality was 10% +/- 4% (+/- 70% confidence limit), and adverse outcomes (death or cerebrovascular accident) occurred in 14% +/- 4%, but there was no difference between HCA alone (8% +/- 5%, 14% +/- 6%) and HCA with RCP (11% +/- 5%, 14% +/- 6%) (p > 0.73). The incidence of transient neurologic dysfunction was also similar (HCA alone, 11% +/- 5%; HCA with RCP, 17% +/- 6%; p > 0.73). Multivariate risk factors for mortality included emergency operation and HCA time (p < 0.02). Risk factors for adverse outcome included emergency operation and atheromatous ascending aorta (p < 0.03). Risk factors for transient neurologic dysfunction included preexisting cerebrovascular disease and rewarming retrograde (femoral) rather than antegrade (through the graft) (p < 0.03). CONCLUSIONS: Supplemental RCP during HCA did not decrease mortality or neurologic complications. Retrograde rewarming through the femoral artery after completion of the distal anastomosis increased transient neurologic dysfunction. Therefore, RCP remains optional, but reperfusion should be antegrade to improve neurologic recovery.