The Effect of Graded Postischemic Spinal Cord Hypothermia on Neurological Outcome and Histopathology after Transient Spinal Ischemia in Rat

Background: Previous data have shown that postischemic brain hypothermia is protective. The authors evaluated the effect of postischemic spinal hypothermia on neurologic function and spinal histopathologic indices after aortic occlusion in the rat.

Methods: Spinal ischemia was induced by aortic occlusion lasting 10 min. After ischemia, spinal hypothermia was induced using a subcutaneous heat exchanger. Three studies were conducted. In the first study, the intrathecal temperature was decreased to 34, 30, or 27 [degree sign]C for 2 h beginning with initial reperfusion. In the second study, hypothermia (target intrathecal temperature 27 [degree sign]C) was initiated with reflow and maintained for 15 or 120 min. In the third study, the intrathecal temperature was decreased to 27 [degree sign]C for 2 h starting 5, 60, or 120 min after normothermic reperfusion. Animals survived for 2 or 3 days, at which time they were examined and perfusion fixed with 4% paraformaldehyde.

Results: Normothermic ischemia followed by normothermic reflow resulted in spastic paraplegia and spinal neuronal degeneration. Immediate postischemic hypothermia (27 [degree sign]C for 2 h) resulted in decreasing motor dysfunction. Incomplete protection was noted at 34 [degree sign]C. Fifteen minutes of immediate cooling (27 [degree sign]C) also provided significant protection. Delay of onset of post-reflow hypothermia (27 [degree sign]C) by 5 min or more failed to provide protection. Histopathologic analysis revealed temperature-dependent suppression of spinal neurodegeneration, with no effect of delayed cooling.