Serum Potassium Changes During Therapeutic Hypothermia After Out-of-Hospital Cardiac Arrest—Should It Be Treated?

BACKGROUND: Therapeutic hypothermia (TH) after out-of-hospital cardiac arrest (OHCA) is associated with adverse events, for example hypokalemia and arrhythmias. In the present study, we report the impact of serum potassium changes related to the rate of cardiac arrhythmias, and the advantages and disadvantages of potassium supplementation are discussed. METHODS: Fifty-four consecutive patients suffering from OHCA and treated with TH (32-34°C) for 24 hours at one University Hospital were included and followed for 48 hours. RESULTS: Serum potassium levels decreased during cooling from a median admission value of 4.0 mmol/L (quartiles 3.6-4.5 mmol/L) to a nadir of 3.6 mmol/L (3.5-3.9 mmol/L) 6 hours after target temperature (p=0.005), and 76% reached values of <3.5 mmol/L. During rewarming, serum potassium increased, with 15% reaching values of >5.5 mmol/L. Potassium supplementation was initiated at 3.5 mmol/L (quartiles 3.2-3.6 mmol/L) and stopped at 4.5 mmol/L (4.1-4.8 mmol/L). A total of 11% of patients experienced ventricular fibrillation (VF) or ventricular tachycardia (VT). Potassium levels in patients experiencing VF or VT were lower, though not significantly (p=0.119) compared to the rest of the patients. CONCLUSION: Serum potassium decreases significantly during the induction of TH (p=0.005). Potassium levels were not found to be different in patients with and without VF/VT in this study, perhaps due to the low number of patients, as a difference has been seen in other studies. It is recommended that an infusion of supplementary potassium be initiated during the early cooling phase in order to avoid severe hypokalemia (serum potassium <3.0 mmol/L) and terminated in due time before normothermia is reached during rewarming in order to avoid severe hyperkalemia (serum potassium >5.5 mmol/L), as serum potassium increases during rewarming.