Equine Fluid Therapy

Introduction to Fluid Therapy in Horses

  • Objectives of fluid therapy for adult horses focused on colic-related issues:

    • Develop a fluid therapy plan including fluid replacement needs.

    • Identify electrolyte and acid-base imbalances.

    • Know sources for fluid loss and methods for replenishment.

    • Estimate fluid losses based on physical exam findings.

Case Example: Shadow

  • Patient: Shadow, an 18-year-old Quarter Horse mare with mild colic symptoms.

  • Symptoms: Kicking at the belly, pawing, occasionally lying down.

  • Physical Exam Findings:

    • Normal temperature.

    • Slightly elevated heart rate.

    • Pink but tacky mucous membranes.

    • Capillary refill time 2 seconds.

    • Decreased gut motility.

    • Delayed skin tenting over shoulder indicating mild dehydration.

Estimating Dehydration

  • A horse showing clinical signs of dehydration usually presents with:

    • Delay in skin tenting and tacky mucous membranes.

    • Estimated dehydration for slight signs: 5% deemed appropriate for Shadow.

Fluid Loss Calculation

  • Fluid Loss for 5% Dehydration in a 500 kg Horse:

    • 5% of 500 kg = 25 liters (or kg since 1 liter = 1 kg).

  • Importance of recognizing substantial fluid loss in horses to inform fluid therapy planning.

Key Fluid Loss Areas

  • Fluid Sources:

    • Fluid intake through drinking and feeding.

    • Fluid administered during veterinary care.

  • Fluid Loss Areas:

    • Pre-existing dehydration.

    • Maintenance requirements (sensible and insensible losses).

    • Ongoing losses from conditions like diarrhea or reflux.

Maintenance Fluid Requirements

  • Typical daily maintenance fluid requirement for adult horses:

    • 50 to 60 ml/kg/day (approximately 1 liter/hour).

    • This figure varies with dietary water content and environmental factors (heat, humidity).

Maintenance Changes

  • Factors affecting maintenance requirements include:

    • Anorexia (reduces requirements to about 16% of daily needs).

    • High-protein or high-calcium diets (increase urine production).

Continued Case Management of Shadow

  • Palpation Results: Moderate impaction palpated in the pelvic flexure.

  • Fluid Therapy Plan Considerations:

    • Initial fluid deficit: 25 liters for 5% dehydration.

    • Maintenance needs for the first 12 hours calculated from 50-60 ml/kg/day:

      • Approximation: 12 liters over 12 hours.

    • Ongoing losses may be estimated at 1 liter/hour due to colic.

  • Total Estimated Fluid Therapy Needs in 12 Hours:

    • Approximately 49 liters (including deficit, maintenance, and ongoing losses).

Purpose of Fluid Therapy

  • Key purposes of fluid therapy include:

    • Resolve the impaction.

    • Rehydrate effectively without electrolyte disruption.

    • Counteract dehydration without further electrolyte imbalances.

Fluid Delivery Methods

  1. Enteral Fluid Therapy:

    • Use of balanced electrolyte solutions, administered via a nasogastric tube.

    • Intermittent boluses (5-10 liters, ideally given every 1-2 hours until impaction resolves).

  2. Rectal Fluid Therapy:

    • Tap Water: Can run 2-2.5 liters/hour via rectum if enteral administration is challenging.

    • Effective at improving hydration and reducing PCV without major electrolyte disturbances.

  3. IV Fluids:

  • Often used in combination with enteral fluids in more severe cases or in referral settings.

Case Study: Lily

  • Patient: 500 kg Thoroughbred mare with diarrhea and decreased appetite for 2 days.

  • Observations: Severe tachycardia, tacky mucous membranes, prolonged capillary refill.

Estimating Dehydration in Lily

  • Dehydration estimated at 10%, aligns with acute fluid loss due to severe diarrhea.

  • Potential fluid losses approximated at 50 liters due to dehydration, plus maintenance and ongoing losses estimated around 23 liters in the first 24 hours.

Summary of Key Points

  1. **Dehydration vs. Hypovolemia:

    • Dehydration:** Total body water loss. Clinical signs include tacky membranes, delayed CRT.

    • Hypovolemia: Reduced blood volume causing different clinical signs (cold extremities, tachycardia).

  2. Fluid Therapy Considerations:

    • Key to calculate hydration status, maintenance needs, and ongoing losses.

    • Frequently reassess fluid therapy efficacy through physical exams and laboratory tests (PCV, electrolytes, lactate levels).

  3. Closing Thoughts:

    • Monitor kidney health and avoid nephrotoxic drugs not to exacerbate dehydration consequences (i.e. NSAIDs).

    • Recognize the importance of teamwork and resources in successfully addressing fluid therapy needs in equine medicine.