The potential danger in treating Hypothermia-induced Hypokalemia

The post from Veeraish earlier this week reminded me of this patient who demonstrated an important learning point regarding hypokalemia in hypothermic patients. A 75 year old woman was found unconscious in her unheated home with overnight temperatures of -1⁰C. On arrival at the Emergency Department, her core rectal temperature was a staggering 21⁰C, blood pressure 90/50 and pulse was 28 beats per minute. EKG was classic, demonstrating slow atrial fibrillation, wide T wave inversion and the characteristic J waves of hypothermia (see Figure; note that the depth of the J wave inflection correlates with the degree of hypothermia). Laboratory values included  serum potassium of 1.1 mmol/L, phosphorous <1 mg/dl, pH 6.95, lactate 8.5 mmol/L, glucose 522 mg/dl. Her renal function was normal. After some initial warming, repeat potassium was 1.6 mmol/L and her heart rate improved. When she had been warmed to 26⁰C, the serum potassium corrected to 5.1 mmol/L before settling at 3.6 mmol/L (with no potassium supplementation). Her serum phosphorous level and blood sugars normalized when her body temperature rose above 30⁰C. She also spontaneously converted to sinus rhythm. 

This case illustrates the profound metabolic complications which can arise in the context of extreme hypothermia. Hypokalemia is well recognized in hypothermia, however, the drop in serum potassium levels is usually mild. Most reported cases involve intentional body cooling in treatment of severe head injury or post-cardiac arrest. The mechanism of hypokalemia is thought to be redistribution of potassium back into the cell. As mentioned by Veeraish, a case has been bravely described of a patient developing hypothermia-associated hypokalemia while being intentionally cooled after head injury. Treatment with potassium supplementation and re-warming occurred concurrently and the patient then suffered a fatal arrhythmia. As the serum potassium will correct itself with rewarming, we should be extremely cautious about administering potassium to hypothermic patients due to the risk of severe rebound hyperkalemia.