Hyponatremia: an overlooked risk factor associated with adverse outcomes after cardiac surgery.

BACKGROUND: Hyponatremia is an unrecognized risk factor for adverse outcomes after cardiac surgery. We sought to study the prevalence of preoperative hyponatremia and its impact in short-term and long-term outcomes after cardiac surgery.

METHODS: Patients who had CABG, valve, or CABG and valve procedures from 2000 to 2016 and available preoperative serum sodium within 30 days of the index procedure were included in the study. The effect of preoperative sodium on short and long-term outcomes was analyzed as a continuous and as a binary (hyponatremia (Na+<135mEq/L) vs. no hyponatremia) predictor variable in multivariable regression models.

RESULTS: Preoperative hyponatremia was present in 9.9% of 16,238 patients with available sodium levels. Comorbidities were more common in patients with hyponatremia. Hyponatremia was independently associated with operative mortality (OR 1.80, 95% CI 1.38 - 2.34, p<0.001), long term mortality (HR 1.31, 95% CI 1.21 - 1.40, p<0.001), longer post-operative length of stay (HR 1.35, 95% CI 1.28 - 1.43, p<0.001), renal failure (OR 1.52, 95% CI 1.20- 1.93, p<0.001), prolonged ventilation (OR 1.52, 95% CI 1.30 - 1.78, p<0.001), and stroke or TIA (OR 1.48, 95% CI 1.09 - 2.02, p=0.013). Severity of hyponatremia, as measured by sodium level, was similarly associated with increased risk of death and post-operative complications.

CONCLUSIONS: Preoperative hyponatremia is relatively common and is associated with adverse short- and long-term outcomes after cardiac surgery. Preoperative hyponatremia can be used independently from standard risk factors to identify high risk patients for cardiac surgery.