Mild hypothermia prolongs the survival time during uncontrolled hemorrhagic shock in rats

Objective: To test our hypothesis that during lethal uncontrolled hemorrhagic shock (UHS) in rats, mild hypothermia of either 36 or 34 degreesC would prolong the survival time in comparison with normotherma of 38 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 C), and mild hypothermic Groups 2 (36 C) and 3 (34 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 degreesC in 5 and 10 min, respectively. The mean survival time, which was 76 +/- 26 min in the control group (38 degreesC), was nearly doubled by mild hypothermia, 178 +/- 65 min for Group 2 (36 degreesC) (P < 0.01 vs. control) and 144 +/- 54 min for Group 3 (34 degreesC) (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 degreesC prolongs the survival time during lethal UHS in rats. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.