Intensive care-acquired hypernatremia after major cardiothoracic surgery is associated with increased mortality

Hypernatremia is common in the medical Intensive Care Unit (ICU) and has been described as an independent risk factor for mortality. Hypernatremia has not yet been studied in a collection of ICU patients after cardiothoracic surgery. Therefore, we wanted to determine the incidence of hypernatremia in a surgical ICU and its association with outcomes of critically ill surgical patients.

In this retrospective cohort study performed at a surgical ICU of a university hospital in Vienna, patients were admitted to the ICU after major cardiothoracic surgery between May 1999 and October 2007. Data on serum sodium in the ICU, ICU mortality, hospital mortality, and length of ICU stay were collected prospectively.

2,699 patients underwent surgery during the study period, and 2,314 patients were included in the study. Two hundred twenty-one (10%) patients acquired hypernatremia during their ICU stay. Median onset of hypernatremia was on day 4 (2-7). Patients with ICU-acquired hypernatremia had a higher ICU mortality (19%) compared to patients without hypernatremia (8%; p < 0.01). Length of ICU stay was increased in patients with hypernatremia (17 vs. 3 days; p < 0.01). In a multivariate Cox regression, ICU-acquired hypernatremia was an independent risk factor for ICU mortality within 28 days.

Hypernatremia is a common event early in the course of critical illness after major cardiothoracic surgery and is independently associated with ICU mortality within 28 days. Future research should focus on the impact of hypernatremia on physiological functions as well as adequate and safe treatment of the electrolyte disorder.