The effect of acute hypothermia and serum potassium concentration on potassium cardiotoxicity in anesthetized rats.

We examined the effects of hypothermia on serum K+ concentration and the interaction of body temperature and K+ load on cardiac toxicity in anesthetized rats. Serum K+ concentration significantly decreased to 2.61 +/- 0.13, 2.59 +/- 0.19 and 2.39 +/- 0.14 mmol/l at 31.0 degrees C, 28.0 degrees C and 25.0 degrees C, respectively, from the control value of 2.80 +/- 0.15 mmol/l at 37.0 degrees C. We used a 300% increase in baseline QRS duration as evidence of cardiac toxicity. Serum K+ concentrations of 4.95 +/- 0.12, 4.71 +/- 0.10, 4.45 +/- 0.14 and 4.07 +/- 0.14 mmol/l resulted in cardiac toxicity at 37.0 degrees C, 31.0 degrees C, 28.0 degrees C, and 25.0 degrees C, respectively. These data indicate that the level at which an elevation of serum K+ concentration causes cardiac toxicity diminishes with progressive hypothermia. We conclude that hypothermia induces hypokalemia, possibly through redistribution, and that the myocardium appears to be more sensitive to the toxic effects of K+ as hypothermia deepens.