Incidence and prognosis of dysnatraemia in critically ill patients: analysis of a large prevalence study

BACKGROUND: The objective of this study is to assess the impact of dysnatraemia on mortality among intensive care unit (ICU) patients in a large, international cohort. MATERIAL AND METHODS: Analysis of the Extended Prevalence of Infection in Intensive Care (EPIC II) study, a 1-day (8 May 2007) worldwide multicenter, prospective point prevalence study. Hyponatraemia was categorized as mild (130-134 mM/L), moderate (125-129 mM/L) or severe (< 125 mM/L). Hypernatraemia was also categorized as mild (146-150 mM/L), moderate (151-155 mM/L) or severe (> 155 mM/L). Patients with normal serum sodium (135-145 mM/L) constituted the reference group. The main outcome was hospital mortality. Analysis was conducted separately for patients admitted on the study day (25.8%) and those already present on the ICU (74.2%). RESULTS: Serum sodium was measured in 13 276 of the 13 796 patients (96.2%). A total of 3815 patients (28.7%) had dysnatraemia: 12.9% with hyponatraemia and 15.8% with hypernatraemia. The prevalence of dysnatraemia was significantly greater in patients already present on the ICU prior to the study day than for those just admitted (13.1% vs. 12.3% for hyponatraemia and 17.1% vs. 12.1% for hypernatraemia, both P < 0.001). Hospital mortality rates were higher in patients with dysnatraemia than in those with normal sodium levels and were directly related to the severity of hypo- and hypernatraemia. This association between dysnatraemia and mortality was similar in infected and noninfected patients (P = 0.061). CONCLUSIONS: Dysnatraemia is more frequent during the ICU stay than on the day of admission. Dysnatraemia in the ICU - even mild - is an independent predictor of increased hospital mortality.