Effect of hypothermia on survival time and ECG in rats with acute blood loss

The effects of hypothermia on survival time and ECGs were investigated in hemorrhagic-shocked rats. Acute blood loss corresponding to LD84 was achieved within 1 min through cannulation of the carotid artery. Immediately following the hemorrhagic episode, extracorporeal cooling was performed by placing the animals, with ice packs attached to their lateral sides, in a cold water bath. Rewarming was achieved by removing the ice packs and resetting the temperature of the water bath to 37 degrees C. With this system, the survival time of the hemorrhagic rats was lengthened from 40 to 60 min without rewarming and to 123 min with rewarming. ECGs showed sinus bradycardia, prolonged PR and QRS intervals, AV block, and finally ventricular fibrillation in both the control and hemorrhagic groups during extracorporeal cooling. During rewarming, the above ECG changes returned to normal in the control group as did body temperature. In contrast, animals in the hemorrhagic group did not survive. Body temperature in this group began to rise toward normal, and above ECG changes showed slight but not complete improvement. It is concluded that extracorporeal cooling can lengthen the survival time of hemorrhagic-shocked rats and that recovery of the disturbed conduction system is a prerequisite for survival from severe hypothermia.