The role of directly applied hypothermia in spinal cord injury

Study Design. The effect of intense local hypothermia was evaluated in a pr ecision model of spinal canal narrowing and spinal cord injury in rats. The spinal cord injury was cooled with a custom cooling well used over the epi dural surface. Basso, Beattie, and Bresnahan (BBB) motor scores and transcr anial magnetic motor-evoked potential (tcMMEP) responses were used after in jury to accurately evaluate neurologic recovery. Objective. This study was undertaken to determine whether the prognosis for neurologic recovery in a standardized rat spinal cord injury model is alte red by the direct application of precisely controlled hypothermia to the ar ea of injury. Summary of Background Data. The role of hypothermia in the treatment of spi nal cord injuries with neurologic logic deficits remains undefined. Hypothe rmia may decrease an area of spinal cord injury and limit secondary damage, therefor improving neurologic recovery. How ever, it has been difficult to consistently apply localized cooling to an area of spinal cord injury, and the use of systemic hypothermia is fraught with complications. This fact, along with the unavailability of a precise spinal cord injury model, has re sulted in inconsistent results, both clinically and in the laboratory. In a rat model of spinal cord injury, 37 C and 19 C temperatures were used to s tudy the role of hypothermia on neurologic recovery. Methods. Male Spraque-Dawley rats (n = 52; weight, 277.7 g) were anesthetiz ed with pentobarbital and subjected to laminectomy at T10. The rats were di vided into three groups: 1) placement of a 50% spacer in the epidural space (16 rats), 2) severe (25 g/cm) spinal cord injury (16 rats), 3) 50% spacer in combination with spinal cord injury (16 rats). Eight rats in each group were tested at two temperatures: normothermic (37 C) and hypothermic (19 C ). With the use of a specially designed hypothermic pool placed directly ov er the spinal cord for 2 hours, epidural heating to 37 C, and epidural cool ing to 19 C was accomplished. Simultaneous measurements of spinalcord and b ody temperatures were performed. The rats underwent behavior testing using the BBB motor scores and serial tcMMEPs for 5 weeks. Statistical methods co nsisted of Student's t tests, one-way analysis of variance, Tukey post hoc t tests and chi(2) tests. Results. There was a significant improvement in motor scores in rats subjec ted to hypothermia compared with those that were normothermic after inserti on of a 50% spacer. This improvement was observed during the 5-week duratio n of follow-up. In the severe spinal cord (injury group and the spinal cord injury-spacer groups, no significant improvement in motor scores were obta ined when the spinal cord was exposed to hypothermia, Conclusion. The results demonstrate that there is a statistically significa nt (P < 0.05) improvement in neuro logic function in rats subjected to hypo thermia (19 C) after I insertion of a spacer that induced an ischemic spina l cord injury. This indicates that directly applied hypothermia may be bene ficial in preventing injury secondary to ischemic cellular damage. The data demonstrated minimal therapeutic benefit of hypothermia (19 C) after a sev ere spinal cord injury.