Association of potassium concentration and variability with mortality among patients requiring continuous renal replacement therapy in intensive care units: a hospital-based retrospective cohort study

Background: Serum potassium between 3.5 to 5.0 mmol/L is known to be a safe range for patients. The optimal serum potassium level for critically-ill patients with acute kidney injury undergoing continuous renal replacement therapy (CRRT) remains uncertain. This retrospective analysis investigated the association between ICU mortality and potassium concentrations and variability. Methods: ICU patients aged 20 or older, with a minimum of two serum potassium values during received CRRT, treated in ICU in a tertiary hospital in central Taiwan between 1 January 2010 and 30 April 2021 were eligible for inclusion. Patients were categorized into groups of mean potassium: <3.0, 3.0 to <3.5, 3.5 to <4.0, 4.0 to <4.5, 4.5 to <5.0, and ³5.0 mmol/L; potassium variability was divided by quartiles of the average real variation. We analyzed the association between potassium concentration and variability with mortality and performed Cox’s proportional hazard models. Results: We studied 1991 CRRT patients with 9891 serum potassium values within 24 hours after receiving CRRT. There was a J-shaped association between serum potassium and mortality, with the lowest mortality observed in patients with mean potassium concentrations between 3.0 and 4.0 mmol/L. The risk of in-hospital death was also significantly increased in those with the highest variability [HR and 95% CI=1.31(1.03-1.65) for in-hospital mortality; 1.39(1.06-1.82) for 28-day mortality and 1.43(1.11-1.83) for 90-day mortality, respectively]. Conclusions: Patients receiving CRRT may benefit from a lower and tighter serum potassium control. During CRRT, progressively increased mortality was noted in patients with higher potassium variability. Thus, careful and timely correction of dyskalemia among these patients is particularly important.