TECHNIQUE OF SELECTIVE SPINAL-CORD COOLING IN RAT - METHODOLOGY AND APPLICATION

In a number of interventions, it is desirable to be able to produce a rapid but readily reversible change in spinal cord temperature (SCT) w ithout altering general body temperature and to maintain this selectiv e spinal cord hypothermia stable for an extended interval. To accompli sh this, we developed a technique of subcutaneous perfusion cooling in rat. This was accomplished by constructing a copper heat exchanger wh ich was readily implanted into subcutaneous space overlying the upper thoracic to upper sacral spinal segments. The heat exchanger was then perfused with fluid from an external temperature bath maintained at (8 degrees C) at a perfusion rate of 100 ml/min. The temperature of the heat exchanger was controlled by regulating the pump with a feed back controller driven by a thermocouple placed percutaneously into the par aspinal musculature. A series of studies were performed to demonstrate the characteristics and utility of this cooling technique. Lowering t he pump set point to 24 degrees C resulted in a fall in the intratheca l temperature (ITT) to 27 +/- 0.3 degrees C within 15 min with no sign ificant changes observed in rectal temperature (37.5- > 37.2 degrees C ). Change in intrathecal temperature showed a highly significant corre lation with changes in paravertebral muscle temperature (r = 0.977). T he hypothermic state could be readily maintained for extended interval s up to 5 h and an underbody heating pad was used to maintain rectal t emperature between 35-36.5 degrees C. Lowering the ITT from 37 degrees C-27 degrees C evoked a temperature-dependent increase in the latency of precooling spinal somatosensory evoked potentials (SSEPs) with the highest sensitivity observed in postsynaptic components. Returning th e set point temperature back to 37 degrees C produced a rapid recovery of the SSEPs latencies. Consistent with previously published data, se lective spinal cord hypothermia (27 degrees C) provided complete prote ction against otherwise injurious interval of normothermic ischemia pr oduced by balloon occlusion of the descending aorta. This technique pr ovides a simple, relatively non-invasive and reliable experimental too l for studying the effect of selective, acute and/or prolonged spinal cord hypothermia. (C) 1997 Elsevier Science B.V.