Distal circulatory support for thoracic aortic operations: effects on intracranial pressure

Aneurysm formation after patch aortoplasty repair (Vossschulte): reoperation in adults with and without hypothermic circulatory arrest

BACKGROUND

Aortic aneurysm formation is common after patch aortoplasty repair of coarctation of the aorta. Its incidence varies between 5% and 38%. The majority of patients show progressive aneurysmal dilation within 6 to 18 years and reoperation is necessary to avoid rupture of the aneurysm.

METHODS

Ten patients were reoperated on for patch aneurysm formation. Femorofemoral cardiopulmonary bypass (CPB) with a heparinized system was used in all patients. Decision to initiate hypothermic circulatory arrest (HCA) was made intraoperatively. All patients received a Dacron graft replacement of the aneurysmatic thoracic aorta.

RESULTS

HCA was initiated in 5 patients owing to extreme adhesions in vicinity to the aneurysm. There was no significant intergroup difference regarding time interval after first operation, age, operation time, and postoperative blood loss. Only minor neurologic events were present in 2 patients with cross-clamping the aorta.

CONCLUSIONS

Patch aneurysms after Vossschulte aortoplasty can safely be operated on with femorofemoral CPB. Initiation of HCA is recommended to prevent rupture of the aneurysm during preparation and injury of adjacent nerves and vessels.

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.

Recent clinical experience with left heart bypass using a centrifugal pump for repair of traumatic aortic transection

OBJECTIVE

To analyze the indications, results, and limitations of using left atrial to femoral artery (LA-FA) bypass to provide distal perfusion during repair of traumatic aortic injuries.

SUMMARY BACKGROUND DATA

There is no consensus about the best method for repair of traumatic aortic transection. Distal aortic perfusion with LA-FA bypass and a centrifugal pump has been the authors' preferred technique for injuries to the aortic isthmus and descending thoracic aorta.

METHODS

From 1988 to 1998, the authors operated on 30 patients with traumatic aortic transection using LA-FA bypass. The mean age of the group was 36+/-2 years. The mechanism of injury was from a motor vehicle accident in 97% of the cases. Distal aortic perfusion was maintained at 50 to 75 mm Hg with flow rates of 1.5 and 3 L/min. The mean aortic cross-clamp time was 38+/-2 minutes, and the mean bypass time was 49+/-2 minutes.

RESULTS

No complications related to cannulation, arterial thromboembolism, renal failure, mesenteric ischemia, or hepatic insufficiency occurred. There were no cases of postoperative paraplegia and no deaths.

CONCLUSION

Left atrial to femoral artery bypass is a safe, simple, and effective adjunct to the repair of traumatic injuries to the thoracic aorta. Active distal aortic perfusion preserves spinal cord, mesenteric, and renal blood flow and eliminates the potential catastrophic consequence of spinal cord ischemia from an unexpectedly prolonged aortic cross-clamp time.

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.

Spinal cord protection during surgical procedures on the descending thoracic and thoracoabdominal aorta: a critical overview

During the past three decades, significant advances have been made in the surgical treatment of the diseases affecting the aorta. Despite these important advances, paraplegia remains a devastating complication of the surgical procedures on the thoracic and thoracoabdominal aorta. Paraparesis and paraplegia occur as a direct result of the interruption of blood flow to the spinal cord during the surgical procedures. A number of techniques have been advocated for the prevention of spinal cord ischemic injury. This article critically reviews our current understanding of the extent of this problem, the mechanism of injury, and the methods that have been devised to reduce the frequency of paraplegia following surgical procedures on the descending aorta.

Control of proximal hypertension during aortic cross-clamping: its effect on cerebrospinal fluid dynamics and spinal cord perfusion pressure

Postoperative paraplegia remains the most devastating complication of surgery of the descending and thoraco-abdominal aorta. Control of the proximal hypertension that follows cross-clamping of the thoracic aorta to repain aneurysms of the descending and thoraco-abdominal aorta is necessary to prevent left ventricular failure, myocardial infarction, and hemorrhagic cerebral events. Both pharmacological and mechanical modalities used to control central hypertension during aortic occlusion affect cerebrospinal fluid dynamics and spinal cord perfusion pressure. Sodium nitroprusside (doses >5 microg/kg/min), the most widely used pharmacological agent, decreases spinal cord perfusion pressure because it increases cerebrospinal fluid pressure and decreases blood pressure distal to the aortic cross-clamp. This effect cannot be prevented by drainage of cerebrospinal fluid. Nitroglycerin also decreases spinal cord perfusion pressure, but its effects on cerebrospinal fluid dynamics can be countered by drainage of cerebrospinal fluid. Active distal perfusion with left atrial-femoral artery bypass can provide adequate perfusion of the circulation distal to the aortic cross-clamp while simultaneously reducing cerebrospinal fluid pressure. This approach can maintain mesenteric and spinal cord blood flow, therefore preventing the multiple organ dysfunction syndrome caused by release of cytokines from the splanchnic district and decreasing the incidence of postoperative paraplegia from spinal cord ischemia. In cases of limited retroperfusion, partial exsanguination and cerebrospinal fluid drainage can be used in conjunction with left atrial-femoral artery bypass to prevent rises in cerebrospinal fluid pressure and maintain spinal cord blood flow above the threshold necessary to prevent neurological injury. The use of oxygenated perfluorocarbons in the subarachnoid space to provide passive oxygenation of the spinal cord during aortic occlusion remains experimental and requires further investigation.