NEUROLOGICAL OUTCOME IN A PORCINE MODEL OF DESCENDING THORACIC AORTIC-SURGERY - LEFT ATRIAL FEMORAL-ARTERY BYPASS VERSUS CLAMP REPAIR/

Background and Purpose In a porcine model of thoracic aortic cross-cla mping (AoXC), we compared the incidence and severity of paraplegia wit h two surgical techniques: left atrial-femoral artery (LA-FA) bypass ( BP group; n=9) and clamp/repair (CR group; n=8). The descending thorac ic aorta was clamped near its origin and distal to the third intercost al artery for 30 minutes. The intervening three intercostal arteries w ere ligated and divided. Methods All animals received methohexital ane sthesia and were hyperventilated to a Paco(2) of 28 to 32 mm Hg. Anima ls in the CR group received mannitol, and after AoXC, proximal hyperte nsion was controlled with phlebotomy. In the BP group, proximal hypert ension was controlled with LA-FA bypass using a centrifugal pump (Biom edicus 520C). Proximal mean arterial pressure, distal mean arterial pr essure, central venous pressure, and cerebrospinal fluid pressure were measured; radioactive microspheres were injected at baseline, at AoXC + 5 minutes, at AoXC + 20 minutes, at AoXC off + 5 minutes, and after resuscitation. Neurological function was assessed at 24 hours. The an imals were killed, and the spinal cord was removed to determine spinal cord blood flow. Histological cross sections of the lumbar spinal cor d were stained with cresyl violet/acid fuchsin and then examined with light microscopy to determine the ratio of altered to total spinal cor d neurons. Results Fifteen animals survived (one death in each group) and were assessed neurologically at 24 hours after AoXC. Despite bette r distal perfusion and lumbar spinal cord blood how in the BP group, d uring AoXC, and at AoXC off + 5 minutes, there was no significant diff erence in the severity of spinal cord ischemic injury between groups a s assessed neurologically by Tarlov score (P=.90, Mann-Whitney U test) . As well, the ratio of altered to total lumbar spinal cord neurons di d not differ between groups (P=.24). Conclusions In this chronic porci ne model, distal circulatory support with LA-FA bypass afforded better distal perfusion and improved lumbar spinal cord blood Bow but did no t influence the severity of spinal cord ischemic injury when compared with a clamp/repair technique.