Therapeutic hypothermia limited to the resuscitation period does not prolong survival after severe hemorrhagic shock in rats

Abstract

Objective: Controlled hypothermia induced during hemorrhagic shock (HS) has been shown previously to improve survival in HS rat outcome models. We hypothesized that hypothermia (34 °C) induced immediately with reperfusion would also improve survival. Methods: Twenty-four rats were lightly anesthetized with halothane and maintained spontaneous breathing. The rats underwent: an HS phase I of 75 min, with an initial blood withdrawal of 2.5 mL/100 g over 15 min, followed by either additional blood withdrawal or re-infusion in order to maintain a mean arterial pressure (MAP) of 30 mmHg over 60 min; a resuscitation phase II of 60 min with return of shed blood and infusion of lactated Ringer's solution to maintain a MAP of 75 mmHg; and an observation phase III without anesthesia for 72 h. Five minutes before the start of phase II, 12 rats were randomized into either a normothermia (38 °C) group or hypothermia (34 °C) group. The rectal temperature in each group was carefully maintained during the 60-min period of phase II. Survival at 72 h, as well as gut damage were assessed. Results: All 24 rats survived beyond phases I and II. At 72 h, 8 of 12 rats survived in the hypothermia group, while and 6 of 12 survived in the normothermia group ( p = 0.64). Intestines of the 72 h survivors were macroscopically normal. In rats that died during phase III, total gut scores did not differ statistically between the groups (1.2 ± 0.6 versus 1.0 ± 0.9). Conclusion: Brief resuscitative hypothermia of 60 min duration induced immediately with reperfusion after HS did not improve survival in this model.