Epidural regional hypothermia for prevention of paraplegia after aortic occlusion: Experimental evaluation in a rabbit model

Purpose: The efficacy of epidural regonal hypothermia in the prevention of acute and delayed-onset paraplegia, as well as possible complications and limitations of this technique to a clinically acceptable form, were evaluated in 49 New Zealand white rabbits.Methods: A modified rabbit spinal cord ischemia model of infrarenal aortic occlusion for 30 minutes was employed. The study was performed in two phases. In phase I (n=20), regional hypothermia induced by epidural perfusion of iced normal saline solution (4°C) was tested versus control in 10 rabbits each (groups A and B). In phase II (n=29) the animals were subdivided into three groups to study the kinetics of absorption and distribution of methylene blue (group C; n=10), radiographic contrast material (group D; n=9), and measurement of cerebrospinal pressure while an epidural iced solution was or was not infused (group E; n=10).Results: At 24 and 48 hours, all of the normothermic animals showed irreversible paraplegia (Tarlov score 0). In contrast, at 24 hours none of the rabbits undergoing epidural cold infusion were paraplegic, although at 48 hours one animal had weakness of a hindlimb (Tarlov score 3). Plasma concentration-time profiles of a continuous epidural perfusion with methylene blue showed that the spinal canal is a highly compliant space. Epidurographs showed that epidural perfusion tends to spread more in a cephalic than caudal direction and the main uptake is by the vascular compartment. Despite the large volumes infused (78.75 ml/hr; range, 50 to 100 ml), we observed only a modest transient increase in cerebrospinal fluid pressure (from 2.5±0.3 mm Hg to 5.4±0.1 mm Hg), although some animals had intracranial hypertension.Conclusions: Regional hypothermia induced by epidural cold perfusion has a highly protective effect against the ischemic spinal cord damage. However, this method probably does not avoid the risk of delayed-onset paraplegia. An important limitation of this technique is the difficulty of controlling the intrathecal pressures