EPIDURAL REGIONAL HYPOTHERMIA FOR PREVENTION OF PARAPLEGIA AFTER AORTIC OCCLUSION - EXPERIMENTAL EVALUATION IN A RABBIT MODEL

Purpose: The efficacy of epidural regional hypothermia in the preventi on of acute and delayed-onset paraplegia, as well as possible complica tions and limitations of this technique to a clinically acceptable for m, 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 pha se I (n = 20), regional hypothermia induced by epidural perfusion of i ced normal saline solution (4 degrees C) was tested versus control in 10 rabbits each (groups A and B). In phase II (n = 29) the animals wer e subdivided into three groups to study the kinetics of absorption and distribution of methylene blue (group C; n = 10), radiographic contra st material (group D; n = 9), and measurement of cerebrospinal pressur e 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 sho wed 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 s core 3). Plasma concentration-time profiles of a continuous epidural p erfusion 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 i s by the vascular compartment. Despite the large volumes infused (78.7 5 ml/hr; range, 50 to 100 ml), we observed only a modest transient inc rease in cerebrospinal fluid pressure (from 2.5 +/- 0.3 mm Hg to 5.4 /- 0.1 mm Hg), although some animals had intracranial hypertension. Co nclusions: Regional hypothermia induced by epidural cold perfusion has a highly protective effect against the ischemic spinal cord damage. H owever, this method probably does not avoid the risk of delayed-onset paraplegia. An important limitation of this technique is the difficult y of controlling the intrathecal pressures.