Objective: To determine the incidence, clinical characteristics, and outcome for general medical-surgical hospital patients with hypernatremia.
Design: A prospective cohort study.
Setting: A 942-bed urban university hospital.
Patients: All patients who developed a serum sodium concentration of 150 mmol/L or greater during a 3-month observation period.
Measurements: Daily fluid balance, mental status, and serum and urine electrolytes and osmolality.
Results: 103 patients were identified. Eighteen patients were hypernatremic on hospital admission, and 85 developed hypernatremia during hospitalization. Patients who developed hypernatremia during hospitalization were younger than patients who developed hypernatremia before hospital admission (mean age ±SD, 58.9 ± 19.2 years compared with 76.6 ± 16.6 years; P < 0.01) but did not differ in age from the patients of the general hospitalized population. Eighty-nine percent of patients who developed hypernatremia during hospitalization had urine concentrating defects, primarily as the result of the use of diuretics or of solute diuresis, whereas only 50% of patients who were hypernatremic on admission could be shown to have concentrating defects (P < 0.01). Fifty-five percent of all hypernatremic patients had increased insensible water losses, and 35% had increased enteral water losses. Eighty-six percent of patients with hospital-acquired hypernatremia lacked free access to water, 74% had enteral water intake of less than 1 L/d, and 94% received less than 1 L of intravenous electrolyte-free water per day during the development of hypernatremia. No supplemental electrolyte-free water was prescribed during the first 24 hours of hypernatremia in 49% of patients. The duration of hypernatremia was shorter in patients who were hypernatremic on admission (median duration, 3 days) than in patients with hospital-acquired hypernatremia (median duration, 5 days; P < 0.05). Mortality was 41% for all patients, but hypernatremia was judged to have contributed to mortality in only 16% of patients.
Conclusions: Although the development of hypernatremia before hospital admission occurs primarily in geriatric patients, hospital-acquired hypernatremia was more common in our cohort and had an age distribution similar to that of the general hospitalized population. Hospital-acquired hypernatremia was primarily iatrogenic, resulting from inadequate and inappropriate prescription of fluids to patients with predictably increased water losses and impaired thirst or restricted free water intake or both. Treatment of hypernatremia is often inadequate or delayed. Efforts to manage hypernatremia better and altogether avoid hospital-acquired hypernatremia should focus on both physician education and the development of hospital systems to prevent errors in fluid prescription.