Apico-aortic shunt: A support technique during surgery on the descending thoracic aorta
Department of Cardiovascular Surgery, Akita University School of Medicine, Japan.The Journal of cardiovascular surgery (Impact Factor: 1.46). 07/1997; 38(3):271-6.
To find out whether apico-aortic shunt may become an alternative support technique during surgery on the descending thoracic aorta, performance between apico-aortic shunt and aorto-aortic shunt was compared. In 5 sheep weighing 20-25 kg, apico-aortic shunt and aorto-aortic shunt were instituted with covalently bonded heparin coated polyvinyl tube (internal diameter 5 mm). After clamping the descending thoracic aorta, apico-aortic shunt and aorto-aortic shunt were opened for 30 minutes each. Proximal pressure was elevated to 200 mmHg and distal pressure was fallen to 55 mmHg after clamping the descending thoracic aorta. Opening of apico-aortic shunt and aorto-aortic shunt decreased proximal pressure to 178 +/- 14.8 and 173 +/- 12.0 mmHg, respectively (p = 0.57), and raised distal pressure to 82.4 +/- 7.8 and 90.0 +/- 3.5 mmHg, respectively (p = 0.83). The baseline blood flow of the descending thoracic aorta was 1.4-1.5 l/min. Apico-aortic shunt and aorto-aortic shunt were 0.76 +/- 0.16 and 0.80 +/- 0.22 l/min, respectively (p = 0.67). Blood gas tension, pH and BE measurement showed no significant change and difference between apico-aortic shunt and aorto-aortic shunt, and before and after clamping the descending thoracic aorta. Using apico-aortic shunt, interposition of bioprosthetic valved conduit in the descending thoracic aorta in 10 sheep was successfully performed without paraplegia and any other complications. We concluded that apico-aortic shunt may become an alternative support technique during surgery on the descending thoracic aorta in some specific situations.
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ABSTRACT: Postoperative paraplegia caused by ischemic injury of the spinal cord is the most disabling complication of thoracoabdominal surgery, particularly when repair of the descending thoracic aorta is involved. We describe the case of a 59-year-old man who underwent emergency surgery for placement of a Dacron prosthesis to repair a ruptured descending thoracic aorta aneurysm, using an aortic cross-clamping technique plus aortic-femoral partial bypass with normothermia and an ischemic time of 165 minutes. The early postoperative course included complete spinal syndrome with motor and sensory loss below T5, with consequent respiratory insufficiency of neuromuscular origin. The result was a difficult postoperative course including prolonged mechanical ventilation and recurrent respiratory infections. Possible causes include prolonged time of ischemia, inadequate monitoring of distal aortic pressure and inappropriate surgical technique related to the absence of angiographic data on spinal vascularization. We conclude that ischemic time should be kept to under 30 minutes whenever possible. In cases of prolonged ischemia, bypass techniques with outflow to the distal aortic segment are more effective whenever mean blood pressure at this point rises to 60 mmHg or more. Vasodilator use should be reserved for cases of severe arterial hypertension and left ventricular failure and/or life-threatening increases in aortic wall stress even if not leading to dangerous decreases in distal aortic pressure. Finally, angiographic study to obtain anatomical details of spinal blood flow is advisable.
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ABSTRACT: Sheep are recommended by the United States Food and Drug Administration as a model for testing cardiovascular tissue, but are particularly prone to spinal cord ischemia and subsequent paralysis during aortic cross-clamping. A shunt consisting of a 9 cm long phosphorylcholine coated 1/4 in. (i.d.) polyvinylchloride tube was inserted through the aortotomy into the aorta to provide blood flow across the operative site. Blood pressure and flow in the distal aorta were measured continuously with an indwelling femoral artery catheter and an ultrasonic aortic flow probe. The hemodynamic effects were measured in seven 45 to 55 kg Suffolk sheep. This shunt was then used to implant decellularized pulmonary artery patches into 25 animals. Occlusion of the aorta reduced the distal mean aortic pressure from 86.4 +/- 4.6 mmHg to 1.79 +/- 0.4 mmHg (P < 0.001) and opening the intra-aortic shunt restored the distal mean aortic pressure to 67.9 +/- 7.3 mmHg (P = 0.053). Blood flow in the distal aorta was 2.35 +/- 0.37 L/min at baseline and was reduced to -0.01 +/- 0.01 L/min (P < 0.001) with the aorta cross-clamped and returned to 2.49 +/- 0.36 L/min (P = 0.945) when the shunt was opened. Use of this shunt prevented hind leg paralysis in all 24 animals surviving the procedure. A simple intra-aortic shunt was effective in restoring blood pressure and flow in the aorta distal to the operative site and prevented hind leg paralysis associated with aortic clamping.
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