Application of the sodium dilution principle to calculate extracellular fluid volume changes in horses during dehydration and rehydration.

The research focused on applying the sodium dilution principle to measure changes in the extracellular fluid volume (ECFV) and intracellular fluid volume (ICFV) during periods of dehydration and rehydration in horses.

Research Methodology

• The study was conducted on a group of eight healthy horses of various breeds.
• The horses were subjected to a period of dehydration for four hours, achieved by withholding water and administering furosemide, a diuretic which promotes urine production.
• This was followed by rehydration over the next two hours via intravenous (IV) administration of a saline solution (0.9% NaCl) at a rate of 20 mL/kg/hour, totalling 40 mL/kg.
• The horses were further monitored for an additional hour after the administration of the IV fluid.

Initial Measurements and Subsequent Monitoring

• The initial ECFV was determined using multifrequency bioelectrical impedance analysis, a common method for estimating body fluid composition.
• Total ECFV sodium content was computed using the serum sodium concentration data collected.
• Changes in sodium and fluid volume were monitored and calculated throughout the study, which were then used to estimate shifts in ECFV and ICFV during the fluid balance alterations.

Research Findings

• Most changes occurred within the ECFV during both dehydration and rehydration processes.
• The sodium dilution principle estimated a greater expansion of the ECFV beyond the volume of fluid that was administered. This suggests a minor contraction of the ICFV in response to fluid administration.
• Recorded serum and urinary electrolyte changes were consistent with previous research studies.

Conclusions and Recommendations

• The sodium dilution principle provided an efficient method to estimate changes in ECFV and ICFV during fluid administration. It observed an overexpansion of the ECFV in response to the administration of the IV saline solution.
• However, these findings require further validation in both healthy and clinically ill horses to solidify their applicability within practical scenarios.

Overall, the study recommends additional research to confirm the reliability and applicability of the sodium dilution principle for monitoring and managing fluid balances in horses, with potential clinical applications mirroring those in other species.