Incidence and prognosis of dysnatremias present on ICU admission

Dysnatremias are common in patients admitted to the intensive care unit (ICU). Whether the presence of disorders of sodium balance on ICU admission is independently associated with excess mortality is unknown. We hypothesized that dysnatremias at the time of ICU admission are independent risk factors for increased mortality in critically ill patients. We conducted a retrospective study in 77 medical, surgical, and mixed ICUs in Austria, with a database of 151,486 adults admitted consecutively over a period of 10 years (1998-2007). Most patients (114,170, 75.4%) had normal sodium levels (135 a parts per thousand currency sign Na a parts per thousand currency sign 145 mmol/L) on ICU admission. The frequencies of borderline (130 a parts per thousand currency sign Na < 135 mmol/L), mild (125 a parts per thousand currency sign Na < 130 mmol/L), and severe hyponatremia (Na < 125 mmol/L) were 13.8%, 2.7%, and 1.2%, respectively. The frequencies of borderline (145 < Na a parts per thousand currency sign 150 mmol/L), mild (150 < Na a parts per thousand currency sign 155 mmol/L), and severe hypernatremia (Na > 155 mmol/L) were 5.1%, 1.2%, and 0.6%, respectively. All types and grades of dysnatremia were associated with increased raw and risk-adjusted hospital mortality ratios. Multiple logistic regression analysis showed an independent mortality risk rising with increasing severity of both hyponatremia and hypernatremia. Odds ratios and 95% confidence interval (CI) for borderline, mild, and severe hyponatremia were 1.32 (1.25-1.39), 1.89 (1.71-2.09), and 1.81 (1.56-2.10), respectively. Odds ratios and 95% CI for borderline, mild, and severe hypernatremia were 1.48 (1.36-1.61), 2.32 (1.98-2.73), and 3.64 (2.88-4.61), respectively. Our results suggest that both hypo- and hypernatremia present on admission to the ICU are independent risk factors for poor prognosis.