Treatment of acute hyponatremia: Ensuring the excretion of a predictable amount of electrolyte-free water

Background: Hypertonic saline is the recommended therapy to shrink swollen brain cells in patients with acute hyponatremia accompanied by seizures. Objectives: In the absence of hypertonic saline, hypertonic mannitol will s hrink the cell volume. Because mannitol is excreted rapidly, our aim was to ensure that it would be excreted with electrolyte-free water (ERW) and to evaluate the renal mechanisms responsible for ENV excretion. Design: A randomized, prospective, placebo-controlled study in rats was car ried out in a research laboratory. Subjects: Adult male Wistar rats. Interventions: The control group of rats (n = 6) was administered hypotonic saline, a loop diuretic, vasopressin, and glucose by the intraperitoneal r oute; in the experimental group (n = 6), glucose was replaced with mannitol . Plasma electrolytes were measured at 0 and 210 mins, and balances for wat er, sodium, and potassium were obtained from 0 to 90 mins and from 90 to 21 0 mins, Measurements and Main Results: Virtually 100% of the administered mannitol was excreted within 210 mins, and half was excreted in the first 90 mins. T he urine contained ENV only in the mannitol group because of a larger volum e in the first 90 mins (EFW, 3.7 mt) and to a lower excretion of NaCl in th e next 120 mins (EFW, 3.5 mt). Conclusions: The combined use of mannitol and a loop diuretic caused the ex cretion of a predictable volume of EFW because the urine was iso-osmotic to plasma and contained all the administered mannitol, The calculated decreas e in intracellular fluid Volume was equivalent when mannitol was retained o r excreted.