Objective: To test our hypothesis that during lethal uncontrolled hemorrhagic shock (UHS) in rats, mild hypothermia of either 36 or 34 degrees C would prolong the survival time in comparison with normotherma of 38 degrees C.
Methods: Twenty-four rats were lightly anesthetized with halothane and maintained spontaneous breathing. UHS was induced by blood withdrawal of 2.5 ml/100 g over 15 min, followed by 75% tail amputation. Immediately after the tail cut, the rats were randomly divided into three groups (eight rats for each); normothermic Group 1 (control, rectal temperature 38 degrees C), and mild hypothermic Groups 2 (36 degrees C) and 3 (34 degrees C). Hypothermia was induced and maintained by body surface cooling. The rats were then observed without fluid resuscitation until their death (apnea and no pulse) or for a period of 240 min maximum.
Results: The rectal temperature was cooled down to 36 and 34 degrees C in 5 and 10 min, respectively. The mean survival time, which was 76+/-26 min in the control group (38 degrees C), was nearly doubled by mild hypothermia, 178+/-65 min for Group 2 (36 degrees C) (P<0.01 vs. control) and 144+/-54 min for Group 3 (34 degrees C) (P<0.05 vs. control) (no significant difference between Group 2 and 3). Additional blood losses from tail stumps were not significantly different among the three groups.
Conclusion: Mild hypothermia of either 36 or 34 degrees C prolongs the survival time during lethal UHS in rats.