The association between postoperative nadir serum potassium and mortality within 28-day after aortic valve replacement

BACKGROUND: This study aimed to investigate the association between postoperative nadir serum potassium and 28-day mortality in patients undergoing surgical aortic valve replacement (SAVR) using the Medical Information Mart for Intensive Care (MIMIC-IV) database. METHODS: A retrospective cohort study included 2,877 patients undergoing SAVR from MIMIC-IV. The independent variable was postoperative nadir serum potassium, and the primary outcome was 28-day all-cause mortality. Logistic regression models adjusted for sex, age, BMI, use of beta-blockers, antidiabetic drugs, diuretics, comorbidities (COPD, heart failure, peripheral vascular disease), and indexes of kidney (BUN, Creatinine). Restricted cubic spline (RCS) regression assessed the potential nonlinear relationship, and Kaplan-Meier survival curves compared mortality risk across different serum potassium levels. RESULTS: A U-shaped relationship was observed between postoperative nadir potassium and 28-day all-cause mortality. Higher nadir potassium levels were significantly associated with reduced mortality (odds ratio [OR] = 0.40, 95% confidence interval [CI]: 0.24-0.69, p < 0.001). The optimal threshold was 3.55 mmol/L; patients below this level had a markedly increased risk of death. CONCLUSION: Lower postoperative nadir serum potassium is independently associated with increased 28-day mortality in SAVR patients. Maintaining postoperative nadir serum potassium no lower than 3.5 mmol/L may be associated with reduced short-term mortality, although this threshold should not be interpreted as a target level to be constantly maintained. The nadir value represents only the lowest single measurement during ICU stay and does not reflect overall potassium homeostasis.