The studies were carried out to investigate the phygiological changes in deep hypothermia in rabbits. Sixty rabbits were continuously cooled with femoral arterio-venous bypass circulation to rectal temperatures of 34.0±0.3℃(mild hypothermia), 30.0±0.3℃(moderate hypothermia), and 25.0±0.3℃(deep hypothermia).
The results obtained in these experiments were summarized as follows : In mild, moderate, and deep hypothermia, MAP, HR, RR, pH, pCO₂, pO₂, Na^+, K^+, HCT, PLT, glucose, L-lactate, BUN, and creatinine were analyzed. During hypothermia, a statistically significant decrease of MAP occurred between 30℃ and early 25℃ (Start) of rectal temperature while significant increases occurred between baseline(38.7℃) and 30℃. Significant decreases of HR and RR were observed in the rabbits, particularly those changes appeared to similar patterns in proportion to hypothermia. Significant decreases of pH occurred between 34℃ and 25℃, and significant increases of pO₂ and pCO₂ were observed continuously in the hypothermic rabbits. The hypothermia had no significant effect on blood Na^+ and serum creatinine. Blood K^+ significantly decreased from 3.1±0.5(baseline) to 2.6±0.6mmol/l(34℃) with the hypothermia for about 30 minutes, and significantly increased from 2.4±0.6(25℃(S)) to 2.7±0.5mmol/l(25℃(E)) with the hypothermia for 2 hrs. HCT significantly increased to 34℃, thereafter, continuously increased to 25℃(Start, End). PLT increased to 34℃, thereafter, continuously decreased to 25℃(Start, End). Also PLT decreased significantly from 414.3(30℃) to 308.8 x 103/mm³(25℃, Start). Significant increases of blood glucose and L-lactate occurred between 30℃ and 25℃ (Start, End). Slight increase of serum BUN continuously appeared with the hypothermia.
These results, such as characteristic changes of the significant decrease of pH and PLT at 34℃, the significant decrease of MAP at 30℃, and the significant increase of glucose and l-lactate at 30℃, suggest that homeostasis of rabbits to hypothermia rapidly decreases at 34∼30℃ of rectal temperature. Therefore, we suggest that, during the period with the rapidly decreased homeostasis, the very carefully control and treatment need to recover hypothermic animals under the circumstances of the various hypothermic experiments and emergency medicine.
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