Lindner G et al. (2007) Hypernatremia in the critically ill is an independent risk factor for mortality. Am J Kidney Dis 50: 952–957

Lindner et al. have screened the database of a Viennese intensive care unit (ICU) to determine the prevalence of hypernatremia, its impact on mortality, and whether it affects length of stay.

Hypernatremia (defined as a serum sodium level >149 mmol/l) occurred in 90 (9%) of 981 patients admitted to the ICU during the 35-month study period; 69 (7%) cases developed during the ICU stay. Hypernatremia lasted on average for 2 days (range 1–10 days). ICU-acquired hypernatremia was shown to be an independent risk factor for 28-day mortality in multivariable analysis (relative risk 1.8, 95% CI 1.1–2.9; P = 0.03). Mortality was 43% and 39% respectively for the patients who had hypernatremia on admission or developed hypernatremia during their ICU stay, compared with 24% in patients without hypernatremia (P <0.01). The most common causes of death in patients with hypernatremia were multiorgan failure, circulatory failure, and septic shock. Development of hypernatremia during the ICU stay was also significantly associated with increased length of ICU stay; mean length of stay was 20 ± 16 days in these patients, compared with only 8 ± 10 days in those without hypernatremia (P <0.001). A positive sodium balance and defects in renal concentration were largely responsible for the development of the condition.

Assessment of renal electrolyte loss is not standard practice in many ICUs. The authors highlight the importance of evaluation of fluid and electrolyte balance so that hypernatremia can be avoided, or rigorously treated as early as possible.