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.
Animals—8 healthy horses of various breeds.
Procedures—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 and Clinical Relevance—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.
Objective—To evaluate the use of multifrequency
bioelectrical impedance analysis (MF-BIA) for estimating
total body water (TBW), extracellular fluid
volume (ECFV), and intracellular fluid volume (ICFV)
Animals—9 healthy mares.
Procedure—TBW and ECFV were measured by use
of deuterium oxide and sodium bromide dilution techniques,
respectively. Intracellular fluid volume was
calculated as the difference between TBW and ECFV.
Concurrently, MF-BIA recordings were obtained by
use of 4 anatomic electrode positions and 3 measurements
of length. Models for MF-BIA data were
created for all combinations of length and anatomic
electrode position. Models were evaluated to determine
the position-length configuration that provided
the most consistent estimates of TBW, ECFV, and
ICFV, compared with values determined by use of the
Results—Positioning electrodes over the ipsilateral
carpus and tarsus and use of height at the tuber
sacrale for length provided the closest estimate
between values for TBW, ECFV, and ICFV predicted by
use of MF-BIA and measured values obtained by dilutional
techniques. This model had the narrowest 95%
limits of agreement.
Conclusions and Clinical Relevance—MF-BIA
techniques have been used to predict changes in
TBW, ECFV, and ICFV in healthy and diseased
humans. Results reported in this study provide an
equine-specific model to serve as the basis for further
evaluation of MF-BIA in horses with altered fluid
states. The MF-BIA techniques have a number of
potential applications for use in horses, including
evaluation of exercise physiology, pharmacologic
studies, and critical-care management. ( Am J Vet Res 2004;65:320–326)
Objective—To determine daily variation in urinary
clearance and fractional excretion (FE) of electrolytes
and minerals within and between horses and to compare
volumetric and single-sample urine collection for
determining FE values of diets with a range of dietary
cation-anion balance (DCAB).
Animals—5 Thoroughbred and 6 mixed-breed mares.
Procedure—3 isocaloric diets with low, medium, and
high DCAB values (85, 190, and 380 mEq/kg of dry
matter, respectively) were each fed for 14 days. Daily
blood samples, single urine samples collected by
using a urinary catheter (5 mares), and volumetric
urine collections (6 mares) were obtained during the
last 72 hours of each diet.
Results—Urine and plasma pH values, plasma concentrations,
and FE values of sodium, chloride, potassium,
magnesium, phosphorus, and calcium were
altered by varying the DCAB. Noticeable variation in
clearance and FE values was detected within horses
from day-to-day on the same diet as well as between
horses. Fractional excretion values were not significantly
different between single-sample and volumetric
methods, except for magnesium in the high DCAB
diet. Volumetric and single-sample collections
revealed similar patterns of change in urinary FE values
with varying DCAB, except for calcium and magnesium.
Conclusions and Clinical Relevance—Substantial
variation in clearance and FE of electrolytes and minerals
are evident within horses between 24-hour periods
as well as between horses fed a specific diet.
Three daily urine samples provide similar information
regarding dietary-induced changes in clearance and
FE values (excluding calcium and magnesium) as that
obtained by volumetric urine collection. (Am J Vet Res 2003;64:284–291)
Objective—To determine whether plasma, urine,
and fecal electrolyte and mineral concentrations differ
between clinically normal horses and
Thoroughbreds with recurrent exertional rhabdomyolysis
(RER) after consumption of diets varying in
Animals—5 Thoroughbred mares with RER and 6
clinically normal mixed-breed mares.
Procedure—Each of 3 isocaloric diets designated as
low, medium, and high on the basis of dietary cationanion
balance (DCAB) values of 85, 190, and 380,
respectively, were fed to horses for 14 days. During
the last 72 hours, 3 horses with RER and 3 control
horses had daily urine and fecal samples obtained by
total 24-hour collection. Remaining horses had urine
samples collected daily by single catheterization.
Results—For each diet, no differences existed
between horses with RER and control horses in plasma
pH, electrolyte concentrations, and creatine
kinase activity or in urine pH and renal fractional
excretion (FE) values. Plasma pH, strong ion difference,
bicarbonate and total carbon dioxide concentrations,
and base excess decreased and plasma chloride
and ionized calcium concentrations increased
with decreasing DCAB. Urine pH decreased with
decreasing DCAB. The FE of chloride and phosphorus
were greatest for horses fed the low diet. The FE values
for all electrolytes exept magnesium did not differ
between urine samples obtained by single catheterization
and total 24-hour collection. Daily balance of
calcium, phosphorus, sodium, chloride, and potassium
did not differ significantly among horses fed the
Conclusions—In clinically normal horses and in horses
with RER, the DCAB strongly affects plasma and
urine pH and the FE of sodium, potassium, chloride,
and phosphorus. (Am J Vet Res 2002;63:1053–1060)