Design, setting, participants & measurements: A retrospective review was conducted of all 62 adult, hyponatremic patients who were treated with hypertonic saline during 5 yr at a 528-bed, acute care, teaching hospital.

Results: Median infusion rate was 0.38 ml/kg per h, increasing serum sodium concentration by 0.47 ± 0.05 mEq/L per h, 7.1 ± 0.6 mEq/L per 24 h, and 11.3 ± 0.7 mEq/L per 48 h. In 11.3% of cases, the increase was >12 mEq/L per 24 h and in 9.7% was >18 mEq/L per 48 h. No patient's rate was corrected by >25 mEq/L per 48 h. Among patients with serum sodium <120 mEq/L, the observed increase in sodium exceeded the rise predicted by the Adrogué-Madias formula in 74.2%; the average correction in overcorrectors was 2.4 times the predicted. Inadvertent overcorrection was due to documented water diuresis in 40% of cases.

Conclusions: The Adrogué-Madias formula underestimates increase in sodium concentration after hypertonic saline therapy. Unrecognized hypovolemia and other reversible causes of water retention pose a risk for inadvertent overcorrection. Hypertonic saline should be infused at rates lower than those predicted by formulas with close monitoring of serum sodium and urine output.