Hyponatremia Predicts Poor Outcomes in Patients With Chronic Kidney Disease Undergoing Heart Operation

Preoperative hyponatremia adversely affects outcomes of cardiothoracic operation. However, in patients with chronic kidney disease, the association of sodium levels on postoperative events has never been evaluated. We investigated the impact of preoperative hyponatremia on outcomes after cardiac operation in patients with non-dialysis-dependent chronic kidney disease. Primary end points were operative mortality and acute kidney injury that required dialysis. Secondary end points were major infection and long-term survival.

The study is observational and includes all patients with stage III to IV chronic kidney disease (non-dialysis) undergoing cardiac operation between February 2000 and January 2016. Patients were stratified into two groups by preoperative sodium levels: sodium less than 135 mEq/L and sodium of 135 mEq/L or more.

There were 1,008 patients (mean estimated glomerular filtration rate [GFR]: 43 ± 14 mL • min^-1 • 1.73 m^-2) with 92 patients (9%) in the low-sodium group. Patients with low sodium had higher operative mortality (p = 0.0004), need for new dialysis (p = 0.0008), and infection (p = 0.002). Predictors of operative mortality were European System for Cardiac Operative Risk Evaluation (EuroSCORE) (hazard ratio [HR] 1.03. 95% confidence interval [CI]: 1.02 to 1.05, p < 0.0001), decreasing values of sodium (HR 1.14. 95% CI: 1.07 to 1.2, p = 0.0002), and decreasing values of GFR (HR 1.01, 95% CI: 1.003 to 1.03, p = 0.007). Sodium less than 135 mEq/L was independently associated with increased need for dialysis (HR 1.3, 95% CI: 1.1 to 1.7, p = 0.0008). By linear regression, decreasing values of preoperative sodium were proportionate to the incidence of operative mortality (p < 0.0001) and need for dialysis (p < 0.0001).

Preoperative hyponatremia is a predictor of increased mortality and other adverse events in patients with non-dialysis-dependent chronic kidney disease undergoing cardiac operation. These findings are similar to those in hyponatremic patients without kidney disease.