The effect of resuscitative mild hypothermia and oxygen concentration on the survival time during lethal uncontrolled hemorrhagic shock in mechanically ventilated rats
KeywordsOxygen Public Health Blood Pressure Heart Rate Treatment Group
To test the hypothesis that resuscitative mild hypothermia (MH) (34°C) or breathing FiO2 of 1.0 would prolong survival time during lethal uncontrolled hemorrhagic shock (UHS) in mechanically ventilated rats.
Forty Wistar rats were anaesthetised with halothane, N2O and O2 (70/30%), intubated and mechanically ventilated. UHS was induced by volume-controlled blood withdraw of 3 ml/100 g over 15 min, followed by 75% tail amputation of its length. The animals were randomised into four UHS treatment groups (10 rats in each group): group 1 was maintained on FiO2 of 0.21 and rectal temperature of 37.5°C. Group 2 was maintained on FiO2 of 0.21 and induced MH. Group 3 was maintained on FiO2 of 1.0 and 37.5°C. Group 4 was maintained on FiO2 of 1.0 and MH. Rats were observed otherwise untreated until death (pulseless and mean arterial blood pressure [MAP] less than 10 mmHg, and without fluctuation).
During the initial blood withdraw, MAP decreased to an average of 40 mmHg, and the heart rate (HR) increased to an average of 400 beats/min. Induction of MH increased the MAP to 60 mmHg, and the survival time moreover, it reduced the HR to 300 beats/min but did not increase bleeding. Ventilation with FiO2 of 1.0 did not influence the MAP, the blood loss or the survival time, but increased the PaO2. The mean survival time was 62 min, 202 min, 68 min and 209 min in group 1, group 2, group 3 and group 4, respectively. Blood loss from the tail was 1.0 ml, 1.2 ml, 0.9 ml and 0.7 ml, respectively, in group 1, group 2, group 3 and group 4 (not significant).
MH prolonged the survival time during UHS in mechanically ventilated rats. However, a FiO2 of 1.0 did not influence the survival time or the blood loss from the tail.