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.