Application of the sodium dilution principle to calculate extracellular fluid volume changes in horses during dehydration and rehydration.
OBJECTIVE
To apply the principle of sodium dilution to calculate the changes in the extracellular fluid (ECF) volume (ECFV) and intracellular fluid volume (ICFV) that occur during dehydration and rehydration in horses.


METHODS
8 healthy horses of various breeds.


METHODS
Horses were dehydrated over 4 hours by withholding water and administering furosemide. Saline (0.9% NaCl) solution was administered IV during the next 2 hours (20 mL/kg/h; total 40 mL/kg). Horses were monitored for an additional hour following IV fluid administration. Initial ECFV was determined by use of multifrequency bioelectrical impedance analysis, and serum sodium concentration was used to calculate total ECF sodium content. Sodium and fluid volume losses were monitored and calculated throughout the study and used to estimate changes in ECFV and ICFV during fluid balance alterations.


RESULTS
Changes during dehydration and rehydration primarily occurred in the ECFV. The sodium dilution principle estimated an overexpansion of the ECFV beyond the volume of fluid administered, indicating a small contraction of the ICFV in response to fluid administration. Serum and urinary electrolyte changes were recorded and were consistent with those of previous reports.


CONCLUSIONS
The sodium dilution principle provided a simple method that can be used to estimate the changes in ECFV and ICFV that occur during fluid administration. Results suggested an overexpansion of the ECFV in response to IV saline solution administration. The sodium dilution principle requires further validation in healthy and clinically ill horses, which could provide clinical applications similar to those in other species.
Fielding
C Langdon
CL
Loomis Basin Equine Medical Center, Loomis, CA 95650, USA.
Magdesian
K Gary
KG
Carlson
Gary P
GP
Rhodes
Diane M
DM
Ruby
Rebecca E
RE
D000818:Animals; D003681:Dehydration / Q000378:metabolism / Q000628:therapy / Q000662:veterinary*; D004573:Electrolytes / Q000097:blood / Q000652:urine; D045604:Extracellular Fluid / Q000378:metabolism*; D005440:Fluid Therapy / Q000662:veterinary*; D006734:Horse Diseases / Q000378:metabolism* / Q000628:therapy; D006736:Horses; D007201:Indicator Dilution Techniques / Q000662:veterinary; D012964:Sodium
D004573:Electrolytes; D012964:Sodium