Mild hypothermia protects the spinal cord from ischemic injury in a chronic porcine model

Objectives: During thoracoabdominal aortic aneurysm repair, prolonged compromise of spinal cord blood Supply can result in irreversible spinal cord injury. This study investigated the impact of mild hypothermia during aortic cross-clamping on postoperative paraplegia in a chronic porcine model. Methods: The thoracic aorta was exposed and cross-clarn ped in 30juvenile pigs (20-22 kg) for different intervals at normothermia (36.5 degreesC), and during mild hypothermia (32.0 degreesC). Three pi,as were evaluated at each time and temperature. Myogenic motor-evoked potentials (MEPs) were monitored. and postoperative recovery evaluated using a modified Tarlov score. Results: There were no significant hemodynamic or metabolic differences between individual animals. and the groups had equivalent arterial pressures (mean 64.3 +/- 3.6 mmHg). Time to recovery of MEPs correlated with severity of injury all animals with irreversible MEP loss Suffered postoperative paraplegia. At normothermia, annuals with 20 min of aortic cross-clamping emerged with normal motor function. but those cross-clamped for 30 min suffered paraplegia. With mild hypothermia. animals tolerated 50 min of aortic cross-clamping without evidence of neurologic injury, but were all paraplegic after 70 min of ischemia. Animals appeared to recover normal motor function after 60 min of aortic cross-clamping at hypothermia initially, but exhibited delayed-onset paraplegia 36 h postoperatively. Conclusions: Our observations indicate that mild hypothermia dramatically increases the tolerance of the spinal cord to ischemia in the pig, and therefore suggests that cooling to 32.0 degreesC should be encouraged during surgery which may compromise spinal cord blood supply. An ischemic insult of borderline severity may result in delayed paraplegia. (C) 2003 Elsevier B.V. All rights reserved.