Mild or moderate hypothermia but not increased oxygen breathing prolongs survival during lethal uncontrolled hemorrhagic shock in rats, with monitoring of visceral dysoxia

Objective: To test the hypotheses that during lethal uncontrolled hemorrhag ic shock (UHS) in rats compared with normothermia and room air breathing: a ) mild hypothermia would prolong survival time as well as moderate hypother mia; b) oxygen breathing would prolong survival further; and c) hypothermia and oxygen would mitigate visceral ischemia (dysoxia) during UHS. Design: Prospective, randomized, controlled laboratory animal study. Setting: Animal research facility. Subjects: Male Sprague-Dawley rats. Intervention: Fifty-four rats were lightly anesthetized with halothane duri ng spontaneous breathing, UHS was induced by blood withdrawal of 3 mL/100 g over 15 mins, followed by 75% tail amputation with topical application of heparin, Five minutes after tail cut, rats were randomly divided into nine groups (6 rats each) with three rectal temperature levels (38 degrees C [10 0.4 degrees F; normothermia] vs. 34 degrees C [93.2 degrees F; mild hypothe rmia] vs. 30 degrees C [86 degrees F; moderate hypothermia]) by surface coo ling; each with 3 FIO2 levels (0.25 vs. 0.5 vs. 1.0). Rats were observed wi thout fluid resuscitation until death (apnea and pulselessness). Visceral i schemia was monitored by observing liver and gut surface PCO2. Measurements and Main Results: Mean survival time, which was 51 mins in the control group with normothermia and FIO2 of 0.25, was more than doubled wi th hypothermia, to 119 mins in the combined mild hypothermia groups (p < .0 5) and to 132 mins in the combined moderate hypothermia groups (p < .05; NS for moderate vs. mild hypothermia), FIO2 had no statistically significant effect on survival time. Increases in visceral surface PCO2 correlated with hypotension (r(2) = .22 for intestine and .40 for liver). Transiently, inc reased FIO2, not hypothermia, mitigated visceral ischemia. Conclusions: Both mild and moderate hypothermia prolonged survival time dur ing untreated, lethal UHS in rats. Increased FIO2 had no effect on survival . The effects of hypothermia and increased FIO2 during UHS on viscera, the ability to be resuscitated, and outcome should be explored further.