Volume kinetics of lactated Ringer's solution in adult horses.
Authors: Muir, Yiew, Bateman, Hahn
Journal: Equine veterinary journal
Summary
# Editorial Summary: Volume Kinetics of Lactated Ringer's Solution in Horses Fluid therapy in equine practice remains largely empirical, despite its critical role in managing systemic disease and shock. Muir and colleagues addressed this gap by characterising how lactated Ringer's solution (LRS) distributes and is eliminated from the body—data essential for optimising bolus dosing strategies. Thirteen healthy mares received intravenous LRS whilst researchers tracked plasma albumin concentrations, haemodynamic variables and urine output over four hours, using mathematical modelling to describe fluid kinetics across two distinct body compartments. The central circulatory compartment (estimated at 26.2 litres) rapidly shifted fluid to peripheral tissues, but crucially, return to the central space—and subsequent renal elimination—occurred much more slowly. LRS administration predictably elevated heart rate and systolic arterial pressure; notably, higher blood pressure correlated with reduced urine output, suggesting the cardiovascular response to fluid loading actively impedes diuresis. Splenic recruitment of red blood cells during fluid expansion further complicated haemoglobin-based analysis, highlighting how horses actively mobilise their blood reserves in response to IV therapy. These findings carry practical weight for practitioners managing dehydrated or hypovolaemic horses: rapid distribution does not equate to rapid elimination, meaning single large boluses may maintain an expanded plasma volume for longer than previously assumed. Understanding these kinetics provides a quantitative foundation for developing more precise fluid protocols tailored to individual clinical contexts—moving equine fluid therapy toward evidence-based practice rather than convention alone.
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Practical Takeaways
- •When administering IV boluses of crystalloids like LRS, expect increased heart rate and blood pressure; monitor urine output as high arterial pressure may reduce urine production
- •Fluid administered IV to horses distributes quickly to peripheral tissues but returns slowly to the central circulation, meaning fluid effects last longer than might be expected and overdosing risks fluid accumulation
- •Volume kinetics offers a more evidence-based approach to fluid therapy protocols than traditional empirical methods, potentially improving effectiveness of fluid resuscitation strategies
Key Findings
- •IV lactated Ringer's solution administration increased heart rate and systolic arterial pressure in healthy adult horses
- •Fluid disposition followed a two-volume model with central compartment estimated at 26.2L, showing rapid distribution to peripheral space but slow return to central compartment
- •High systolic arterial pressure was associated with decreased urine output, and hemoglobin recruitment indicated splenic erythrocyte mobilization during fluid administration
- •LRS elimination from the body was slow despite rapid initial distribution, suggesting prolonged volume expansion effects