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.


OBJECTIVE
In the absence of hypertonic saline, hypertonic mannitol will shrink the cell volume. Because mannitol is excreted rapidly, our aim was to ensure that it would be excreted with electrolyte-free water (EFW) and to evaluate the renal mechanisms responsible for EFW excretion.


METHODS
A randomized, prospective, placebo-controlled study in rats was carried out in a research laboratory.


METHODS
Adult male Wistar rats.


METHODS
The control group of rats (n = 6) was administered hypotonic saline, a loop diuretic, vasopressin, and glucose by the intraperitoneal route; in the experimental group (n = 6), glucose was replaced with mannitol. Plasma electrolytes were measured at 0 and 210 mins, and balances for water, sodium, and potassium were obtained from 0 to 90 mins and from 90 to 210 mins.


RESULTS
Virtually 100% of the administered mannitol was excreted within 210 mins, and half was excreted in the first 90 mins. The urine contained EFW only in the mannitol group because of a larger volume in the first 90 mins (EFW, 3.7 mL) and to a lower excretion of NaCl in the next 120 mins (EFW, 3.5 mL).


CONCLUSIONS
The combined use of mannitol and a loop diuretic caused the excretion of a predictable volume of EFW because the urine was iso-osmotic to plasma and contained all the administered mannitol. The calculated decrease in intracellular fluid volume was equivalent when mannitol was retained or excreted.
Porzio
P
P
Department of Veterinary Internal Medicine, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada.
Halberthal
M
M
Bohn
D
D
Halperin
M L
ML
D000208:Acute Disease; D000818:Animals; D004232:Diuretics / Q000008:administration & dosage; D004573:Electrolytes / Q000008:administration & dosage*; D007010:Hyponatremia / Q000628:therapy* / Q000652:urine*; D008297:Male; D008353:Mannitol / Q000008:administration & dosage; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D012996:Solutions / Q000008:administration & dosage
D004232:Diuretics; D004573:Electrolytes; D012996:Solutions; D008353:Mannitol