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

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.

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.

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.