Experimental Study on Local Hypothermia in the Spinal Cord

ABSTRACT

A study of effect of local hypothermia upon the spinal cord was performed in cats. With a cuff, a cooler, to which was attached connecting tubes to a refrigerator, the experimental technique was deviced to cool the spinal cord locally at midthoracic level. Cold liquid, saline at a temperature of +/-1.1 degrees C, was circulated in closed system through the tubing into the cuff which was snugly rested on the dorsal surface of the spinal cord as a heat exchanger. The temperatures were measured with thermocouples at various sites in the spinal cord before, during, and after the cooling every two minutes upto twenty minutes. In the cord underneath the cuff, the mean precooling temperature of 35.4 degrees C in normal control group was lowered to 11.0 degrees C during the first two minutes of cooling. After this in initial rapid drop in temperature, there was a further gradual reduction of 4.5 degrees C upto 20 minutes cooling to be 6.5 degrees C. The lowest mean temperatures recorded throughout cooling were 4.3 degrees C at dorsal surface and 6.9 degrees C at center of the cord. And the temperature lowering was nearly not noted beyond the cord 1 cm apart from an edge of cuff in rostral and caudal directions. For comparison, the temperature in the cord that had not been injured was also measured. The rate of cooling in the cord underneath the cuff seemed to be faster than in the control group of animal in which the cord was not injured. Another design of this experiment was an evaluation of the protective effect of local hypothermia with respect to cord edema and injury associated cord hemorrhage. Immediately after intravenous administrations of fluorescin the spinal cords were contused with impaction injury. These injured cords were removed ar different time intervals after trauma, and spread or distribution of fluorescin in frozen sectioned specimens was observed under ultraviolet illumination with fluorescence microscope. In all cooling groups, pathological pictures were reduced in its degree and extent more than those in the control group, and that, earlier the cooling after the injury to the cord, better the result was outcome. It would be well to say that local hypothermia might be within the margin of safety and beneficial in the management of spinal cord injury in this experiment.