Effect of resuscitative mild hypothermia and oxygen concentration on the survival time during lethal uncontrolled haemorrhagic shock in mechanically ventilated rats

Objective: To test the hypothesis that resuscitative mild hypothermia (MH) (34 degrees C) or breathing fractional inspired oxygen (FIo(2)) of 1.0 would prolong survival time during lethal uncontrolled haemorrhagic shock (UHS) in mechanically ventilated rats. Methods: Forty Wistar rats were anaesthetized with halothane, nitrous oxide and oxygen (70/30%), intubated and mechanically ventilated. UHS was induced by volume-controlled blood withdrawal of 3 ml/100 g over 15 min, followed by 75% tail amputation of its length. The animals were randomly divided into four UHS treatment groups (10 rats in each group): group 1 was maintained on an FIo(2) of 0.21 and rectal temperature of 37.5 degrees C. Group 2 was maintained on an FIo(2) of 0.21 and induced MH. Group 3 was maintained on an FIo(2) of 1.0 and 37.5 degrees C. Group 4 was maintained on an FIo(2) of 1.0 and MH. Rats were observed otherwise untreated until death. Results: During the initial blood withdrawal, mean arterial pressure (MAP) decreased to 40 mmHg, and the heart rate (HR) increased up to 400 beats/min. The induction of MH increased MAP to 60mmHg and increased survival time. Moreover, it reduced the HR to 300 beats/min but did not increase bleeding. Ventilation with an FIo(2) of 1.0 did not influence MAP, blood loss or survival time, but increased arterial oxygen tension. The mean survival time was 62, 202, 68 and 209 min in groups 1, 2, 3 and 4, respectively. Blood loss from the tail was 1.0, 1.2, 0.9 and 0.7 ml, respectively, in groups 1, 2, 3 and 4. Conclusion: MH prolonged the survival time during UHS in mechanically ventilated rats. However, an FIo(2) of 1.0 did not influence the survival time or blood loss from the tail. (C) 2004 Lippincott Williams & Wilkins