90-day mortality risk related to postoperative potassium levels in patients undergoing coronary bypass surgery.

Aims: While electrolyte depletion is known to occur during coronary artery bypass grafting (CABG) with extracorporeal circulation, little is known about the frequency of potassium disturbances following either on- or off-pump CABG and its association with mortality. We examined the frequency of potassium disturbances and the association of plasma potassium with mortality risk in patients following CABG. Methods and results: From Danish National Registries, we identified 6123 adult patients (≥18 years old) undergoing first-time CABG, and who had a registered potassium measurement within 14 days before and 7 days after their surgery between 1995 and 2018. Using 4.0-4.6 mmol/L as reference, potassium was stratified into five predefined intervals: <3.5, 3.5-3.9, 4.0-4.6, 4.7-5.0, and ≥5.1 mmol/L. We examined the absolute mortality risk and assessed the Cox proportional hazard model to analyze the 90-day all-cause mortality risk in relation to the first available post-operative potassium sample. Pre- and postoperative potassium disturbances were rare, while more common in patients with chronic kidney disease. The adjusted cox regression presented a trend of increased mortality only in hyperkalemia. The absolute mortality risk increased in hyperkalemia, hypokalemia and low-normokalemia, while high normokalemia presented a lesser relative risk of mortality, compared to the reference of 4.0-4.6 mmol/L. Conclusion: Although the cox regression presented a trend of increased mortality only in hyperkalemia, the absolute mortality risk supported a strategy of careful monitoring and evaluation of any potassium disturbance, including in the lower normokalemia interval.