Association between hypernatraemia acquired in the ICU and mortality: a cohort study

Background. The aim of this study is to describe the prevalence and outcomes of intensive care unit (ICU)-acquired hypernatraemia (IAH). Methods. A retrospective analysis was performed on a prospectively collected database fed by 12 ICUs. Subjects are unselected patients with ICU stay >48 h. Mild and moderate to severe hypernatraemia were defined as serum sodium >145 and >150 mmol/L, respectively. IAH was hypernatraemia occurring >= 24 h after ICU admission in patients with normal serum sodium at ICU admission. Results. Of the 8441 patients, 301 were excluded because they had hypematraemia at ICU admission. Of the remaining 8140 patients, 901 (11.1%) experienced mild hypernatraemia, and 344 (4.2%) experienced moderate to severe hypernatraemia. Factors independently associated with IAH were male gender, severity at admission as assessed by the Simplified Acute Physiology Score version II (SAPS II), and organ failure or life-supporting treatment at ICU admission. Unadjusted hospital mortality was 15.2% in patients without hypematraemia compared to 29.5% in patients with mild IAH and 46.2% in those with moderate to severe IAH (P < 0.0001). When any degree of IAH was handled as a time-dependent variable in a subdistribution hazard model, the subdistribution hazard ratio (SHR) for ICU mortality was 4.26 [95% confidence interval (CI), 3.74-4.84]. After stratification by centre and adjustment for confounders, both mild IAH and moderate to severe IAH were independently associated with mortality [SHR 2.03 (95% CI 1.73-2.39) and 2.67 (95% CI 2.19- 3.26), respectively]. Conclusion. IAH is frequent and associated with mortality after adjustment on severity at ICU admission.