Combination of mild hypothermia and delayed fluid resuscitation improved the survival rate after uncontrolled hemorrhagic shock in rats

Objective

To evaluate the effect of mild hypothermia combined with delayed fluid resuscitation on the survival rate in mechanically ventilated rats.

Methods

An initial blood withdrawal of 3 ml/100 g over 15 min of time followed by 75% tail amputation of its length and observed during an additional 45 min to induce phase I. Homeostasis of the tail wound and maintaining the mean arterial pressure (MAP) of 100 mmHg during resuscitation phase II from 60 to 120 min. Phase III is an observational phase up to 72 hours. Forty-eight male rats were anaesthetised, mechanically ventilated and were randomised into four groups (12 in each group). Group 1 received immediate fluid resuscitation and normothermia; group 2 received immediate fluid resuscitation and mild hypothermia. Both these groups were allowed to normalize the MAP by giving Ringer's solution. Group 3 received limited Ringer's solutions to maintain a MAP of 40 mmHg and normothermia. In group 4, the rats also received limited Ringer's solution to maintain a MAP of 40 mmHg but were subjected to mild hypothermia. During phase II, all rats were allowed to normalize the MAP by giving shed blood. At the end of the observational phase III, the rats were killed, and the brain was fixed and histologically analysed.

Results

The blood loss from the tail during phase I was significantly higher in groups where immediate fluid resuscitation was performed (groups 1 and 2). Group 4 required the lowest fluid resuscitation. The survival rate was 33.3%, 83.3%, 58.3% and 91.7%, respectively, in group 1, group 2, group 3 and group 4. In all surviving rats no brain histological damage was observed.

Conclusions

Mild hypothermia or limited (hypotensive) fluid resuscitation increases the survival rate. However, when mild hypothermia and limited fluid resuscitation were combined during phase I, the survival rate was the highest.