Left Atrial–Inferior Vena Cava Bypass Achieves Retroperfusion of the Porcine Spinal Cord: Morphologic and Preliminary Physiologic Studies

Background. Spinal cord injury remains a devastating complication after procedures on the descending thoracic aorta. A new model for retrograde perfusion of the spinal cord during aortic cross-clamping was evaluated for its potential role in preventing spinal cord injury after thoraco-abdominal aortic surgery. Methods. Retrograde perfusion of the spinal cord was established in juvenile pigs using partial bypass from the left atrium to the isolated inferior vena cava. Flow was maintained for a 60-min period of aortic occlusion. Morphologic studies of spinal cord blood flow were obtained using injection of a dilute barium–gelatin–chromatin dye solution. Physiologic cooling of the spinal cord was achieved using varying degrees of hypothermic retroperfusion. Results. Five animals underwent a 30-min period of retroperfusion followed by dye injection. Dye was identified in spinal cord venules and capillaries, most heavily concentrated in the lumbar and lower thoracic cord. Thirteen animals underwent a 60-min period of normothermic (37°C), mild hypothermic (27°C), moderate hypothermic (17°C), or deep hypothermic (7°C) retroperfusion; mean spinal cord temperatures were 35.2, 32.2, 28.0, and 24.4°C, respectively. Conclusions. Retrograde perfusion of the porcine spinal cord using a left atrial to inferior vena cava partial bypass circuit can be accomplished and can be used with hypothermic perfusate to produce cooling of the spinal cord. This new technique warrants further investigation into spinal cord protection and potential application for operations on the descending thoracic aorta.