Learning and memory is preserved after induced asanguineous hyperkalemic hypothermic arrest in a swine model of traumatic exsanguination

Background. Induced asanguineous hypothermic metabolic arrest (suspended animation) could provide valuable time to repair major vascular injuries if safely induced in patients with trauma. We report a novel method of doing this in a swine model of uncontrolled lethal hemorrhage (ULH) that resulted in preservation of learning ability and memory. Methods. Yorkshire swine (100 to 125 lb) underwent ULH before rapid intra-aortic infusion of a hypothermic (4degreesC), hyperkalemic (70 mEq/L) organ preservation solution by a left thoracotomy. Cooling continued until core temperature reached 10degreesC, and this was maintained for 60 minutes using low-flow cardiopulmonary bypass. Vascular injuries were repaired during this state of suspended animation, which was then reversed, and the animals were observed for 6 weeks. Cognitive functions were tested by training animals to retrieve food from color-coded boxes. Postoperatively, the ability to remember this task and a 75-point objective neurologic scale were used to test neurologic function. In experiment I, ULH was caused by lacerating thoracic aorta (n = 9). Five preoperatively untrained animals were trained to perform the task and compared with control animals (n = 15), and 4 preoperatively trained animals were tested for memory retention postoperatively. In experiment II, ULH was induced by creating an iliac artery and vein injury (n = 15). Animals were kept in shock for 15, 30, and 60 minutes before the induction of hypothermia. Results. In experiment I, surviving animals (719) were neurologically intact, and their capacity to learn new skills was no different than for control animals. All pretrained animals demonstrated complete memory retention. In experiment II, survival with 15, 30, and 60 minutes of shock were 80%, 60% and 80%, respectively. All animals (except 1) in the 60-minute group were neurologically intact and displayed normal learning capacity. Conclusions. Induction of hypothermic metabolic arrest (by thoracotomy) for repair of complex traumatic injuries is feasible with preservation of normal neurologic function, even after extended periods of shock from an intra-abdominal source of uncontrolled hemorrhage.