Mild hypothermia protects the spinal cord from ischemic injury in a chronic porcine model.
OBJECTIVE
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-clamped in 30 juvenile pigs (20-22 kg) for different intervals at normothermia (36.5 degrees C), and during mild hypothermia (32.0 degrees C). Three pigs 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, animals 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 degrees C should be encouraged during surgery which may compromise spinal cord blood supply. An ischemic insult of borderline severity may result in delayed paraplegia.
Strauch
Justus T
JT
Department of Cardiothoracic Surgery, Mount Sinai School of Medicine/New York University, One Gustave L. Levy Place, P.O. Box 1028, New York, NY 10029, USA. ju.strauch@gmx.de
Lauten
Alexander
A
Spielvogel
David
D
Rinke
Sindy
S
Zhang
Ning
N
Weisz
Donald
D
Bodian
Carol A
CA
Griepp
Randall B
RB
D000818:Animals; D001013:Aorta, Thoracic / Q000601:surgery*; D004195:Disease Models, Animal; D019054:Evoked Potentials, Motor; D005260:Female; D007036:Hypothermia, Induced / Q000379:methods*; D007427:Intracranial Pressure; D007430:Intraoperative Care / Q000379:methods; D019344:Lactic Acid / Q000097:blood; D016343:Monitoring, Intraoperative / Q000379:methods; D010264:Paraplegia / Q000517:prevention & control*; D011183:Postoperative Complications / Q000517:prevention & control*; D020760:Spinal Cord Ischemia / Q000517:prevention & control*; D013552:Swine
D019344:Lactic Acid