Adequacy of ascending aorta-descending aorta shunt during cross-clamping of the thoracic aorta for prevention of spinal cord injury

Bypass Techniques for Descending Thoracic Aortic Surgery

The conduct of partial left heart bypass or partial car diopulmonary bypass (CPB) during surgery involving the descending thoracic aorta or thoracoabdominal aorta is one of the most unappreciated and misunder stood extracorporeal circulation procedures in cardio vascular surgery. It is different from conventional CPB, and although some uninitiated practitioners consider it simpler, it is in fact more complicated than conven tional CPB and involves different concepts. It requires expertise and skill in regulating the flow, pressure, and oxygenation of blood going to both the proximal and distal parts of the body and management of the special bypass or shunt procedures used, specialized monitor ing, and knowledge about the protection and preserva tion of organs both proximal and distal to the aortic clamping. It demands exquisite communication and un derstanding of the unique problems faced by the sur geon, anesthesiologist, and perfusionist.

Blood supply and vascular reactivity of the spinal cord under normal and pathological conditions

The authors present a review of spinal cord blood supply, discussing the anatomy of the vascular system and physiological aspects of blood flow regulation in normal and injured spinal cords. Unique anatomical functional properties of vessels and blood supply determine the susceptibility of the spinal cord to damage, especially ischemia. Spinal cord injury (SCI), for example, complicating thoracoabdominal aortic aneurysm repair is associated with ischemic trauma. The rate of this devastating complication has been decreased significantly by instituting physiological methods of protection. Traumatic SCI causes complex changes in spinal cord blood flow, which are closely related to the severity of injury. Manipulating physiological parameters such as mean arterial blood pressure and intrathecal pressure may be beneficial for patients with an SCI. Studying the physiopathological processes of the spinal cord under vascular compromise remains challenging because of its central role in almost all of the body's hemodynamic and neurofunctional processes.

Bridging circuit for the resection of retroperitoneal sarcoma involving the aorta and the IVC- veno-venous to veno-arterial perfusion

A 50-year-old female underwent surgery for removal of a massive retroperitoneal sarcoma (RPS) involving the right hepatic lobe and the inferior vena cava (IVC), abdominal aorta, right lung, right hemi-diaphragm and pericardium. Resection of the RPS necessitated cross-clamping of the abdominal aorta, IVC and the hepatic artery. Cross-clamp time cannot be predicted prior to tumour resection and vascular re-construction. To prevent complications of prolonged cross-clamp time and distal hypo-perfusion, circulatory support was sought to facilitate the procedure. A perfusion circuit was designed to accommodate an easy and immediate redirection of blood flow from venovenous bypass (VVB) to veno-arterial bypass (VAB) without requiring a change of circuit and with minimum heparin administration. Furthermore, this circuit provides the added safety of an oxygenator and a heat-exchanger. Utilising the circuit enabled successful resection of the RPS. The patient was discharged from the intensive care unit (ICU) seven days later without any post-operative complications. This case report of a design of a perfusion circuit for the resection of RPS made use of a perfusion approach that had not previously been described and allowed for a reduction in the duration of ischaemic time and retroperitoneal bleeding.

Overview of Great Vessel Trauma

Traumatic injury to the aorta and the brachiocephalic branches are potentially lethal injuries. Specialized preoperative imaging and medical management can lead to better outcomes in this group of patients. In addition, improved surgical techniques for spinal cord protection have led to decreased morbidity in surgical candidates. TEVAR remains a promising technique; however, long-term data currently are not available.

Management of Blunt Thoracic Aortic Injury

Blunt traumatic aortic transection (TAT) is an uncommon injury in clinical practice that is associated with a high morbidity and mortality. The approach to patients with such an injury is controversial with specific regard to the most effective diagnostic tools, timing of surgical intervention and mechanisms of spinal cord protection. Chest X-ray with widening of the mediastinum is unreliable as a diagnostic tool. Contrast enhanced helical CT Scan has replaced the traditional angiography as the screening diagnostic tool of choice Emergency thoracotomy and repair should be reserved for the few patients with isolated TAT without any major concomitant injuries. Delayed management approach with aggressive blood pressure control and serial radiological monitoring is a safe and recommended option for those with severe concomitant injuries or other medical co-morbidity that puts surgery at high risk. Active augmentation of the distal perfusion pressure during cross clamp offers the best protection against development of paraplegia during open surgical repair. Endovascular stenting offers a minimally invasive method of treatment but the long-term durability of the endovascular stent is still unknown. We feel that the greater feasibility of the endovascular repair in the acute phase of the thoracic injury is an advantage over the open surgery and should be the treatment of choice in patients with severe concomitant injuries.

Femoro-femoral partial bypass in the treatment of thoracoabdominal aneurysms

This article describes our rationale for the use of femoro-femoral bypass as a primary modality for perfusion in the repair of thoracoabdominal aortic aneurysms at Stanford University School of Medicine. Benefits and limitations of this method are discussed and compared with other described techniques.

Management of traumatic aortic rupture: a 30-year experience

OBJECTIVE

To present the authors' 30-year experience with traumatic aortic rupture (TAR).

SUMMARY BACKGROUND DATA

TAR is a highly lethal injury. Most institutions manage a small number of cases, and most surgeons receive only modest exposure during training.

METHODS

Between 1971 and 2001, the authors operated on 219 patients with a diagnosis of TAR. Diagnosis of TAR since 1994 has been based exclusively on the use of contrast-enhanced spiral computed tomography, with angiography reserved for equivocal cases (periaortic mediastinal hematoma without aortic wall abnormalities). Patients were divided according to surgical technique. Eighty-two patients (group A) were operated on with a clamp-and-sew technique. Sixty-four patients (group B) underwent surgery with the use of a passive shunt, and 73 patients (group C) were treated using heparin-less partial cardiopulmonary bypass.

RESULTS

Mortality was 18 patients for group A (21.9%), 23 patients for group B (35.9%), and 13 patients for group C (17.8%) (P =.03). Paraplegia occurred in 15 of 64 survivors in group A (23.4%), 7 of 41 survivors in group B (17%), and 0 of 60 survivors in group C ( P=.0005). Aortic occlusion without lower body perfusion for longer than 30 minutes (P =.004) and surgical technique without lower body bypass support (P =.0005) were associated with paraplegia.

CONCLUSIONS

Surgery for TAR based on spiral computed tomography screening and diagnosis is reliable. The use of heparin-less distal cardiopulmonary bypass in the authors' hands is safe and is associated with a reduced incidence of paraplegia.

Prevention of paraplegia in transluminally placed endoluminal prosthetic grafts for descending thoracic aortic aneurysms

OBJECTIVE

To evaluate the efficacy of a temporary balloon occlusion test for the prevention of paraplegia following transluminally placed endoluminal prosthetic grafts for descending thoracic aortic aneurysms.

SUBJECTS AND METHODS

Two occlusion balloons were inserted via the brachial and femoral arteries and positioned in the proximal and distal neck of the descending thoracic aortic aneurysms using fluoroscopy. After temporary occlusion of the thoracic aorta by inflation of both the proximal and distal balloons, the evoked spinal potential was measured for 15 mins. A maximum amplitude during temporary balloon occlusion test decreasing by more than 20% of the pre-balloon occlusion level was considered to be significant, enough to not perform transluminally placed endoluminal prosthetic grafts, but instead an open repair. The test was applied in 12 cases (9 males and 3 females, 50-86 years old). All aneurysms were located between the Th6 and Th12 with a maximum diameter of 40-70 mm, and average of 56 mm.

RESULTS

The changes in maximum amplitude of evoked spinal potential remained within 20% of the value before balloon occlusion in 11 cases. Transluminally placed endoluminal prosthetic grafts were performed in these 11 cases and no instance of paraplegia or other complication relating to the test was observed. Deployment of stent-grafts was successful in 10 cases (91%).

CONCLUSION

It is suggested that the preoperative measurement of evoked spinal potential during temporary balloon occlusion is clinically useful for the assessment of the risk to paraplegia occurring in transluminally placed endoluminal prosthetic grafts.

A prolonged spinal cord ischaemia model in pigs. Passive shunting offers stable central haemodynamics during aortic occlusion

OBJECTIVES

to evaluate the effect of a modified aortic shunt on central haemodynamic variables during experimental thoracic aortic occlusion in a prolonged spinal cord ischaemia model.

MATERIAL AND METHODS

central haemodynamic variables were evaluated during aortic cross-clamping. In the shunt group (n=11), after the placement of proximal and distal aortic clamps, distal aortic perfusion was restored through an aortoiliac shunt via the left subclavian artery. In the no-shunt group (n=11), spinal cord ischaemia was achieved with only proximal aortic cross-clamping. The clamping time was 60 minutes in the shunt group and 30 minutes in the no-shunt group.

RESULTS

in the no-shunt group, all animals needed inotropic support, vasodilators and buffers during the experiment. None of these drugs were needed in the shunt group. In the no-shunt group, cross-clamping caused a significant increase in mean arterial pressure and heart rate compared to baseline values. These variables were stable in the shunt group during aortic occlusion. In the reperfusion period cardiac output, heart rate and arterial pCO(2)were significantly higher in the no-shunt than in the shunt group.

CONCLUSION

the present experimental spinal cord ischaemia model, using double aortic cross-clamping with shunt, offers improved central haemodynamics. This enables the study of prolonged selective spinal cord ischaemia without interaction from vasoactive drugs or systemic reperfusion.

Surgery for descending thoracic aortic anastomotic aneurysms with a temporary external bypass method

The surgical treatment of descending thoracic aortic anastomotic aneurysms is technically challenging. The purpose of this study was to evaluate the use of a temporary external bypass method as an intraoperative measure in the surgical treatment of anastomotic aneurysms of the descending thoracic aorta. An analysis of five consecutive patients who had undergone surgery for a collective seven descending thoracic aortic anastomotic aneurysms in our university hospital over a period of 14 years was conducted. A temporary bypass technique was used as an intraoperative measure in all the operations, four of which were performed with a right axillary to left external iliac artery bypass, while other sites were used in the remaining three. Systemic heparinization was able to be avoided in six operations and was markedly reduced in the remaining one. Although the major postoperative complication was coagulated hemothorax after six procedures, all patients recovered well and are still alive after a mean follow-up period of 8.2+/-1.5 (SEM) years. The results of this analysis led us to conclude that our temporary bypass method for treating descending thoracic aortic anastomotic aneurysm prevented the risks of anticoagulant administration for circulatory support, which contributed to the success of the operation. This method can be used as adjunct treatment for anastomotic aneurysms in the descending thoracic aorta.

Traumatic aortic rupture: diagnosis and management

BACKGROUND

Traumatic aortic rupture is a relatively uncommon lesion that presents the cardiothoracic surgeon with unique challenges in diagnosis and management. To address controversial aspects of this disease, we reviewed our experience.

METHODS

The study was performed by retrospective chart review.

RESULTS

Forty-two patients with traumatic thoracic aortic ruptures were managed between January 1988 and June 1997. Nine arrived without vital signs and died in the emergency department. Admission chest radiographs were normal in 3 patients (12%) and caused significant delays in diagnosis. Four of 30 patients admitted with vital signs had rupture before thoracotomy and died. Twenty-six underwent aortic repair. In 1 patient repair was performed with simple aortic cross-clamping, whereas a second was managed with a Gott shunt. The remaining 24 patients had repair with partial left heart bypass. In 1 patient hypothermic circulatory arrest was required. Two patients (7.7%) died. There were no cases of new postoperative paraplegia in the bypass group. There was no morbidity directly attributable to the administration of heparin for cardiopulmonary bypass.

CONCLUSIONS

In a discrete group of patients with traumatic rupture of the aorta, the rupture will become complete during the first few hours of hospital admission; aggressive medical treatment with beta-blockade and vasodilators in the interval before the operation is an essential aspect of management. Active distal circulatory support with partial left-heart bypass provides the optimal means of preventing spinal cord ischemia during repair of acute traumatic aortic rupture.

Prevention of spinal cord ischaemic complications after thoracoabdominal aortic surgery

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

The efficacy of left atrial to femoral artery bypass in the prevention of spinal cord ischemia during aortic surgery

Surgical repair of traumatic lesions or aneurysmectomy of the descending thoracic aorta necessitates the interruption of distal aortic blood flow, a situation which invariably promotes proximal hypertension accompanied by a precipitous increase in cerebrospinal fluid pressure and distal hypoperfusion. All are significant determinants of postoperative paraplegia. The institution of aortic bypass, distal to cross-clamping, by either implantation of an extraluminal passive shunt or deployment of left atrial to femoral artery (LA-FA) cannulation with a centrifugal pump, is the most widespread modality to afford a means of proximal decompression and provide distal perfusion. Passive shunt techniques do not consistently provide optimal bypass efficiency, due to inherent limitations of device design and the inability to accurately monitor and control flow. The LA-FA bypass technique is superior to passive shunts in effecting proximal unloading by allowing for precise adjustment of blood flow to equilibrate proximal and distal aortic pressures. The concomitant use of cerebrospinal fluid drainage with LA-FA bypass can effectively reduce the incidence of postoperative paraplegia. Intraoperative monitoring of evoked potentials as a sensitive indicator of spinal cord ischemia should be considered an integral component of preserving cord function. The use of cerebrospinal fluid drainage and evoked potential monitoring in conjunction with LA-FA bypass is therefore highly advisable.

Monitoring of somatosensory evoked potentials: a primer on the intraoperative detection of spinal cord ischemia during aortic reconstructive surgery

The acute interruption of blood supply to the spinal cord during thoracic and thoracoabdominal aortic reconstructions, if unabated, inevitably causes neurological injury secondary to regional hypoxia. Techniques that address the multifactorial nature of spinal cord ischemic injury have evolved to preserve neuromotor function. However, the overall incongruity of the spinal cord's vascular anatomy makes it virtually impossible to predict, with any degree of certainty, the duration of aortic cross-clamping (AXC) that can safely be endured. The sensitivity of evoked potential monitoring to the disruption of spinal cord perfusion has led to the emergence of this modality as an effective tool at the surgeon's disposal for the intraoperative assessment of distal aortic perfusion and cord viability during proximal AXC. Somatosensory evoked potentials (SSEP) provide invaluable diagnostic data as to the status of cord function, through the continuous appraisal of signal amplitude and latency. A latency increase, as small as 10% of the pre-AXC value, is linked to a reduction of spinal cord perfusion pressure and thereby associated with a high incidence of neurological impairment. Four discrete types of SSEP responses have been identified to represent differing surgical scenarios during AXC. The Type I response (deterioration of SSEP within 3 to 5 minutes) is indicative of a failure to maintain a distal pressure of at least 60 mm Hg, whereas a Type II signifies adequate distal aortic perfusion. Sudden loss of signal as witnessed in a Type III SSEP implies compromised critical intercostal vessels and indicates their expeditious reimplantation. A gradual (30 to 50 minutes) SSEP "fadeout" corresponds to marginal distal perfusion, suggesting the presence of extensive pathology. Intraoperative evoked potential monitoring, in conjunction with distal aortic perfusion, permits rapid identification and correction of compromised spinal cord blood flow, permitting repair of aortic lesions without the added liability of time constraints.

Intraoperative adjuncts of spinal cord protection

Immediate neurological deficits as a complication of aortic surgery occur as the direct result of hypoxia, related to the acute deprivation of spinal cord blood supply inflicted by prolonged aortic cross-clamping (AXC). The etiology of spinal cord ischemia constitutes a series of progressive interdependent events which include proximal hypertension, increase in cerebrospinal fluid pressure, perioperative hypotension, inadequate perfusion to critical intercostal or lumbar vessels, extent of aortic pathology and duration of AXC. Several intraoperative interventions and strategies, which address the multifactorial nature of cord injury, are presented by the authors. Of critical importance is the role of adequate distal aortic perfusion, with either left atrium-femoral artery (LA-FA) bypass or arterial-arterial passive shunts, to control both central hypertension, through proximal unloading, and hypotension distal to AXC. Equally crucial is the increase in CSF pressure, secondary to proximal hypertension, which acts antagonistically to distal aortic pressure in regulating spinal cord perfusion pressure (SCPP). Cerebrospinal fluid drainage (CSFD) reduces CSF pressure to offset SCPP to favor cord perfusion. Pharmacological agents, such as papaverine and steroids in combination with CSFD, produce a synergistic benefit of extending the time interval of safe AXC. Encouraging results have also been realized with circulatory arrest and profound hypothermia which reduce oxygen demand of neural tissues and extend the safe duration of AXC interval. The use of distal bypass is most effective with CSFD as an integral component of a multimodality approach, which also incorporates the intraoperative monitoring of somatosensory evoked potentials (SSEP), to detect the onset of spinal cord ischemia and assess the adequacy of distal aortic perfusion and disposition of critical segmental vessels.

Ischemia-reperfusion injury in the spinal cord of rabbits strongly enhances lipid peroxidation and modifies phospholipid profiles

The effect of spinal cord ischemia (10, 20, and 40 min) and post-ischemic reperfusion (10, 30, and 60 min) on lipid peroxidation and phospholipids was investigated. Spinal cord ischemia was accompanied by lipolytic processes with significant changes in concentration of lipid peroxidation products (LPP). Reestablishment of the blood supply after 10 min ischemia was accompanied by significantly increased levels of thiobarbituric acid reactive substances (TBA-RS) after 10 and 30 min of reperfusion. Following 20 and 40 min ischemia a significant increase was observed at all reperfusion periods. Ischemia itself significantly reduced the concentration of phosphatidyl inositol (IP), phosphatidyl ethanolamine (EP) and ethanolamine plasmalogens (Epls). Significant changes were observed in concentration of phosphatidyl serine (SP) too, but only after 20 and 40 min of ischemia. The concentration of phosphatidic acid (PA) was significantly reduced only after 10 min of ischemia. The onset of reperfusion after ischemia was accompanied by a diverse pattern of changes in PA, IP, Epls and SP, while the concentration of EP remained at the above mentioned ischemic intervals.

Isoflurane versus sodium nitroprusside for the control of proximal hypertension during thoracic aortic cross-clamping: effects on spinal cord ischemia

OBJECTIVE

This study was designed to compare the effects of isoflurane and nitroprusside on spinal cord ischemia when they are used to control proximal hypertension during thoracic aortic cross-clamping (TACC).

DESIGN

Prospective, randomized, blinded experimental study.

SETTING

Laboratory and animal research facility.

PARTICIPANTS

Adult mongrel dogs.

INTERVENTIONS

Two groups of eight dogs had TACC for 45 minutes. Proximal aortic, distal aortic, and cerebrospinal pressure was calculated as the distal mean pressure minus the CSF pressure. Group 1 received nitroprusside and group 2 received isoflurane to control proximal hypertension during cross-clamping. The dogs were neurologically evaluated 24 and 48 hours later by an observer blinded as to the study group. Spinal cord segments were obtained for histopathologic examination.

MEASUREMENTS AND MAIN RESULTS

Distal perfusion pressure and spinal cord perfusion pressure were significantly higher in the isoflurane group (p < .005). At 24 hours, seven of eight dogs in group 1 had severe neurologic injury (ie, paraplegia), with the eight having mild neurologic injury. This is in contrast to group 2, where 6 of 8 dogs had either minimal or no injury, one had mild injury, and one had severe injury. Similar results were observed at 48 hours (p < .005).

CONCLUSIONS

Isoflurane, when used to control proximal hypertension during TACC, produces a higher spinal cord perfusion pressure and is associated with a lower incidence of neurologic injury than nitroprusside in this canine model.

Reducing morbidity of thoracoabdominal aneurysm repair by preliminary axillofemoral bypass

BACKGROUND

Thoracoabdominal aneurysm (TAA) repair continues to be associated with appreciable morbidity and mortality. To reduce the substantial cardiac afterload of thoracic aortic clamping, preserve visceral, renal, and lower-extremity perfusion, and reduce spinal cord ischemia, a right axillofemoral bypass was performed before TAA resection.

PATIENTS AND METHODS

Fifteen patients undergoing repair of their TAA had a preliminary axillofemoral bypass with an 8- to 10-mm externally supported polytetrafluoroethylene graft. Nine underwent elective repair and 6 were operated on emergently. All but 2 patients (both had type IV aneurysms) had spinal fluid drainage and all had moderate hypothermia induced (31 degrees C to 32 degrees C). All visible intercostal arteries were reimplanted.

RESULTS

Requirements for pharmacologic afterload reduction were minimal. Urine output was preserved during proximal aortic and intercostal anastomoses, and acidosis was minimal. Anticoagulation was not necessary unless the aortic bifurcation was replaced, and no patient had thrombotic complications. One (7%) patient died after repair of a ruptured aneurysm, and 1 (7%) developed paraplegia and required temporary dialysis.

CONCLUSION

Preliminary axillofemoral bypass avoids the profound hemodynamic and physiologic derangement caused by clamping of the thoracic aorta, and effectively reduces the morbidity of TAA repair.

Left atrial-aortic/femoral bypass with a centrifugal pump without systemic heparin during surgery on the descending aorta

Active or passive bypass to support the distal circulation during cross-clamping of the descending thoracic aorta has been reported to decrease the incidence of paraparesis, to reduce left ventricle afterload, and to preserve distal organ perfusion. The aim of this study was to describe and to evaluate a perfusion technique for surgery on the descending aorta in humans. Nine patients underwent surgery on the descending thoracic aorta. The left atrium was cannulated using a Carmeda bioactive surface cannula. Distal cannulation sites were the left common femoral artery or the aorta below the involved segment. The cannulae were connected to a BioMedicus centrifugal pump via Carmeda bioactive surface tubings and pump heads. No systemic heparin was used. Cross-clamp time was 51 +/- 6 min, and the pump flow was 2.3 +/- 0.2 L/min. The mean arterial pressure in the upper body was 81 +/- 4 mm Hg and 68 +/- 5 mm Hg in the lower. Seven patients were discharged from hospital. Two patients with aortic rupture died; one died on the operating table, and the other, neurologically intact, died 4 days postoperatively due to multiorgan failure. No patients suffered spinal cord injury. It is concluded that active bypass without systemic heparin during cross-clamping of the descending aorta is simple and safe.

Spinal cord protection in the absence of collateral circulation: meta-analysis of mortality and paraplegia

A meta-analysis of paraplegia complicating aortic surgery on patients having neither intercostal nor spinal collaterals, epitomized by patients with acute traumatic aortic rupture, was done. Index Medicus and Medline were searched for all suitable English publications between 1972 and 1992. New paraplegia occurred in 9.9% of 1492 patients who underwent surgery. However, 19.2% of patients undergoing surgery with only simple aortic cross-clamping developed paraplegia, in contrast to 6.1% if distal aortic perfusion was augmented by either "passive" or "active" methods (p < 0.00001). The risk of paraplegia increased progressively as cross-clamp times lengthened if simple aortic cross-clamping was used (p < 0.00001), but only once did the cross-clamp time exceed 30 minutes (p < 0.05). Paraplegia occurred in 8.2% of patients with "passive" shunts from the ascending aorta (p < 0.001 vs simple cross-clamping). Shunts from the left ventricular apex, however, had an incidence of paraplegia of 26.1% and, therefore, did not decrease the risk of paraplegia. "Active" augmentation of distal perfusion had the lowest risk of paraplegia: 2.3% (p < 0.00001 vs simple cross-clamping or "passive" shunts). Mortality, however, was higher in these potentially polytraumatized patients when they were perfused distally using methods requiring full systemic heparinization (18.2%), compared to mortality with methods not requiring heparin (11.9%; p < 0.01). In conclusion, simple aortic cross-clamping has a high risk of paraplegia if the cross-clamp time extends beyond 30 minutes. "Active" modalities of augmenting distal perfusion provide optimal spinal protection.

Traumatic aortic rupture: twenty-year metaanalysis of mortality and risk of paraplegia

A metaanalysis of articles concerning the surgical management of acute traumatic rupture of the descending thoracic aorta published in the English-language literature between 1972 and July 1992 was performed. The overall mortality of 1,742 patients who arrived at the hospital alive was 32.0%, one-third died before surgical repair was started. Paraplegia was noted preoperatively in 2.6% of these hospitalized patients, and paraplegia complicated the surgical repair in 9.9% of 1,492 patients who reached the operating room in a relatively stable condition. Patients then were analyzed according to the surgical intervention used. Simple aortic cross-clamping (n = 443) was associated with a hospital mortality of 16.0% and incidence of paraplegia of 19.2%, despite lower average mean cross-clamp times (32 minutes; p < 0.01 versus passive or active methods of providing distal perfusion). In a subset of 290 patients in whom individual data were available, the cumulative risk of paraplegia was shown to increase substantially if the duration of aortic cross-clamping exceeded 30 minutes, but only when distal perfusion was not augmented (p < 0.00001). "Passive" perfusion shunts (n = 424) were associated with a mortality of 12.3%, and the incidence of paraplegia decreased to 11.1% (p < 0.001). However, shunts inserted from the apex of the left ventricle had a contradictory high 26.1% incidence of paraplegia compared with shunts from the ascending aorta (8.2%; p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of altering cerebrospinal fluid pressure on spinal cord blood flow

Removal of cerebrospinal fluid (CSF) has been proposed as a means of protecting the spinal cord against ischemic injury during thoracoabdominal aneurysm operations. We investigated the effect of altering CSF pressure (CSFP) on lumbar spinal cord blood flow (SCBF) in an experiment using dogs. The SCBF was measured before and after withdrawal of CSF in settings with and without thoracic aortic clamping. Furthermore, SCBF was measured at the basal state and after elevation of CSFP to 20 mm Hg and to 40 mm Hg. The SCBF did not change significantly before and after removal of CSF in settings both with and without thoracic aortic clamping. Elevation of CSFP significantly reduced SCBF. Elevation of CSFP reduces SCBF, but lowering CSFP per se does not increase SCBF whether the thoracic aorta is occluded or not. This supports the notion that removal of CSF offers spinal cord protection only when CSFP is abnormally elevated.

Hufnagel revisited: a descending thoracic aortic valve to treat prosthetic valve insufficiency

In 1953 Hufnagel and Harvey reported their successful treatment of aortic valve insufficiency by the implantation of a ball-valve prosthesis into the descending thoracic aorta. Since then, great advances in technology, surgery, and anesthesia have made aortic valve replacement a more common procedure with relatively low mortality. This remains true for the vast majority of prosthetic valve replacements. However, cases requiring reoperation can be difficult, leading to a much higher degree of morbidity and mortality. In selected patients who require repeated approaches to the aortic root we propose that Hufnagel's original idea may still be of value to reduce the severity of aortic insufficiency. We report our experience in 4 cases of aortic prosthetic incompetence, all of which were improved by two New York Heart Association functional classes after a modification of Hufnagel's procedure.

Beneficial circulatory support by left heart bypass with a centrifugal (BioMedicus) pump for aneurysms of the descending thoracic aorta

A comparative study between left heart bypass with a centrifugal (BioMedicus) pump and with a temporary external shunt was performed to assess the efficacy of distal organ perfusion in the surgical treatment of 31 patients with aneurysm of the descending thoracic aorta. Eighteen patients were supported with a centrifugal pump, and the remaining 13 were supported by temporary shunt with either a Gott shunt or a Dacron graft. Heparinless bypass with a centrifugal pump provided a significant decrease of intraoperative blood loss and blood transfusion by the combined application of Cell-Saver. The pressure difference between upper and lower extremities decreased (p < 0.05) in the centrifugal pump group even with aortic cross-clamping, and the urine output increased during operation. Among 13 patients supported with the temporary shunt, 3 had postoperative renal failure, and 2 died of it. All patients with a centrifugal pump survived without any complications. It could be concluded that the left heart bypass with a centrifugal (BioMedicus) pump was safe and was favorable for support of the distal circulation during aortic cross-clamping and to prevent ischemic complications such as renal failure and spinal cord injury.

Partial left heart bypass with centrifugal pump and limited anticoagulation during the resection of coarctation of the aorta

Resection of coarctation of the aorta necessitates crossclamping of the descending aorta. Despite the existence of a collateral circulation, spinal cord ischaemia and intestinal ischaemia may occur associated with a prolonged crossclamp time and distal hypoperfusion during the operation. To prevent these severe complications and to control hypertension proximal to the clamp, circulatory support may be necessary.

We performed partial left heart bypass (PLHB) with limited anticoagulation in four patients, using a centrifugal pump in orderto sustain a mean arterial blood pressure of at least 60mmHg in the distal thoracic aorta below the clamped coarctated segment. The method is practical, simple and safe. It combines features of several methods of protection of the spinal cord: adequate distal perfusion of the aorta at a desired flow rate and blood pressure, avoidance of proximal hypertension, minimal aortic and cardiac manipulation and avoidance of bleeding tendency by limited heparinization. Vasodilating drugs with their adverse effect on distal aortic pressure are not necessary in this situation.

Postoperatively, neurological sequelae orvital organ damage did not occur in our patients.

Effect of partial ischemia on phospholipids and postischemic lipid peroxidation in rabbit spinal cord

Rabbit spinal cord, subjected to severe partial ischemia induced by abdominal aorta ligation tightly below the renal arteries, was analyzed for phospholipid composition and levels of lipid peroxidation products after 10, 20, and 40 min of the insult. Under conditions when spinal cord blood flow was decreased below 5% of control, concentrations of inositol and ethanolamine phospholipids were decreased by 30% and 10%, respectively. Phosphatidic acid concentration was also altered during ischemia. No accumulation of thiobarbituric acid reactive substances (TBA-RS), conjugated dienes and fluorescent lipid soluble material was found throughout the ischemic period. Pattern of TBA-RS, conjugated diene, and fluorophore formation during postischemic in vitro incubation without and with a peroxidation couple (Fe2+, ascorbic acid) showed increased susceptibility to postischemic lipid peroxidation in tissues after 20 and 40 min of ischemia.

Paraplegia following surgery of the descending thoracic aorta

Paraplegia remains an uncontrollable complication of aortic reconstructive surgery. Twenty-one consecutive patients undergoing surgery at the Royal Adelaide Hospital for lesions of the descending thoracic aorta were reviewed. Those patients suffering an acute traumatic transection had a much higher rate of postoperative paraplegia (40%) than those undergoing elective reconstruction of chronic aneurysms (10%). The incidence of paraplegia after surgery for an acute transection when bypass was not employed was greater than 50%. In contrast, the outcome was successful in all patients who underwent reconstruction using left heart extracorporeal bypass. Based on these findings, the routine use of bypass during reconstruction of the thoracic aorta is recommended, particularly for acute traumatic transection.

Comparison of superoxide dismutase, thiopental, and nimodipine for maintenance of somatosensory evoked responses during aortic cross-clamping and declamping in dogs

Paraplegia is a potential complication of aortic cross-clamping. The occurrence of this devastating sequela has caused increased interest in the use of somatosensory evoked responses (SER) to monitor spinal cord ischemia during aortic cross-clamping. This study was designed to examine changes in SERs during clamping and declamping of the canine aorta after injection of superoxide dismutase (SOD), thiopental (T), and nimodipine (N). In the control group, cross-clamping the aorta produced an increase in latency and a decrease in amplitude of the SER starting at two minutes. Isoelectric SERs were obtained after 16 minutes of aortic cross-clamping, but recovered with cross-clamp removal. When the aorta was clamped for more than 16 minutes in the control group, the isoelectric SERs obtained were irreversible. After the injection of SOD and T, SER latencies and amplitudes changed to a smaller degree with aortic cross-clamping and did not become isoelectric even after 20 minutes of clamping. During aortic cross-clamp removal in the control group, SERs initially improved and then showed signs of reperfusion ischemia, which disappeared after eight minutes. There were no significant SER changes due to reperfusion when SOD or T or the combination was given prior to aortic cross-clamping. There was no difference in SER changes from the control group during aortic cross-clamping and after release of cross-clamping when N was given. Nimodipine did not alter SER changes from aortic cross-clamping alone. In summary, SOD and T, alone or in combination, protect the spinal cord against ischemia during aortic cross-clamping and declamping.

Hypothermic regional perfusion for protection of the spinal cord during periods of ischemia

Ischemic spinal cord injury with resulting postoperative paraplegia is an inherent risk for operations on the thoracic aorta. The mechanism of injury is not clearly understood, and numerous adjuncts to avoid this complication have been suggested, with conflicting clinical results. A new technique of hypothermic regional perfusion of the spinal cord is described. Fifteen female pigs weighing 21 to 39 kg were used for the experiment. The control group consisted of 5 animals in which the thoracic aorta was clamped at the distal arch for 30 minutes. All of these animals sustained postoperative neurological damage. Eighty percent sustained postoperative paraplegia, and 20% had severe spasticity of the hind legs that precluded normal ambulation. The experimental group consisted of 10 animals in which hypothermic regional perfusion was performed for 30 minutes after cross-clamping of the distal arch. Perfusion cooling was followed by 30 minutes of ischemia in 5 animals and 45 minutes of ischemia in the remaining 5. All animals that underwent hypothermic regional perfusion were able to walk postoperatively, and no evidence of ischemic injury was found at postmortem examination of the spinal cords. This technique proved to be simple and effective in protecting the spinal cord for up to 45 minutes of ischemia in the experimental group. The clinical implications of this concept are promising for patients undergoing operations on the thoracic aorta.

Risk factors for the development of renal failure following the surgical treatment of traumatic aortic rupture

A retrospective study of 44 patients who were treated surgically for traumatic aortic rupture was undertaken to determine risk factors for the development of postoperative renal failure. Renal failure occurred in 11 of 41 patients (27%) eligible for analysis. The Pearson product-moment correlation showed no significant relationship between the occurrence of renal failure and the patient's age, injury severity score, initial blood pressure, or the interval between accident and thoracotomy. Renal failure was significantly correlated with cross-clamping only (r = .2751, p = .043). There was no relationship between renal failure and total cross-clamp times. The mortality rate was significantly higher for patients with renal failure.