Fluid Therapy in Veterinary Medicine

Objectives of Fluid Therapy in Veterinary Medicine

  • Fluid Calculation Objectives:

    1. Calculate fluid rates and requirements for various animals including:

    • Small animals

    • Equine (horses)

    • Food animals

    1. List clinical signs and clinical pathologic differences between dehydration and hypovolemia.

    2. Develop a complete fluid therapy plan tailored to a specific patient’s disease.

    3. List different types of available fluids for therapy.

    4. Describe clinical signs observed during successful rehydration and volume resuscitation, as well as signs of fluid overload.

    5. Describe indications for fluid therapy and when it should be applied.

Commonly Available Fluids

Table 129-1: Composition of Commonly Available Crystalloids Used in Dogs and Cats

Isotonic Crystalloids/Replacement

  • Examples:

    • 0.9% Sodium Chloride

    • Normosol-R

    • Plasma-Lyte

Fluid Composition for Common Isotonic Crystalloids

  • 0.9% NaCl:

    • Na+: 154 mEq/L

    • Cl-: 154 mEq/L

    • K+: 0 mEq/L

    • Ca2+: 0 mEq/L

    • Mg2+: 0 mEq/L

    • Glucose: 0 g/L

    • pH: 5.0

    • Osmolarity: 308 mOsm/L

  • Normosol-R:

    • Na+: 140 mEq/L

    • Cl-: 98 mEq/L

    • K+: 5 mEq/L

    • Ca2+: 0 mEq/L

    • Mg2+: 3 mEq/L

    • Glucose: 0 g/L

    • pH: 6.4

    • Osmolarity: 296 mOsm/L

Table 129-2: Common Commercially Available Fluids for Dogs and Cats

Types of Fluids

  • Hypotonic Crystalloids/Maintenance

  • Hypertonic Saline

  • Colloids:

    • Examples include Hydroxyethyl starches (e.g., Hespan, VetStarch)

    • Human Serum Albumin (HSA) or Canine Serum Albumin (CSA) for hypoproteinemia

Differences Between Hypovolemia and Dehydration

Definitions

  • Hydration Status:

    • It is a measure of interstitial fluid content.

    • Assessed through:

      • Skin turgor

      • Mucous membrane moisture

      • Possible enophthalmos

  • Volume Status:

    • Measures tissue perfusion.

    • Assessed through:

    • Heart rate (HR)

    • Capillary refill time (CRT)

    • Mucous membrane (MM) color

    • Blood pressure (BP)

    • Note: In cats, HR may be normal or show bradycardia as opposed to dogs.

  • Important Distinction:

    • Dehydration does not equal hypovolemia and they may coexist.

    • Hypovolemia Treatment:

      • Must prioritize treatment for hypovolemia before addressing dehydration.

      • Treatment typically requires completion within 1-2 hours:

      • Cats: 40-50 ml/kg

      • Dogs: 60-90 ml/kg

      • Start with ¼ of calculated volume.

Fluid Therapy Objectives

Key Considerations

  1. Resuscitation

  2. Replacement

  3. Maintenance

Clinical Questions

  • Is the patient hypovolemic?

  • Is the patient dehydrated?

  • Are there ongoing fluid losses?

  • What are the patient's daily physiologic fluid requirements?

Physiology of Shock

  • Types of Shock:

    • Cardiogenic

    • Hypovolemic

    • Distributive

    • Hypoxic

    • Metabolic

Mechanisms

  • Receptors/Monitors

  • Effectors/Hormones/Responses

Stages of Shock

1. Compensated Stage

  • Normal blood pressure maintained through:

    • Arterial baroreceptors

    • Renin-angiotensin-aldosterone system (RAAS)

    • Antidiuretic hormone

  • Symptoms include:

    • Tachycardia

    • Increased heart contractility

    • Vasoconstriction

    • Reduced urine output

    • Sodium (Na) and water (H2O) retention

  • Potential Progression:

    • If untreated, the condition may lead to the next stage.

2. Progressive Stage

  • Symptoms include:

    • Decreased tissue perfusion

    • Cellular hypoxia and organ dysfunction

    • Treatments may or may not reverse issues.

3. Irreversible Stage

  • Consequence of:

    • Cellular hypoxia leading to cellular injury

    • Failure of vascular smooth muscle, myocardium, and endothelial cells

    • Loss of vascular tone resulting in leaky vessels, causing effusion and edema

    • Blood stasis leading to thrombosis and disseminated intravascular coagulation (DIC)

    • Mucosal compromise due to ischemia may lead to bacterial translocation, resulting in sepsis/systemic inflammatory response syndrome (SIRS).

Endpoints of Resuscitation

  • Important parameters to restore (not limited to death):

    • Normal vital signs

    • Normalization of mentation

    • Restoration of blood pressure

    • Return lactate levels to normal

    • Central venous oxygen saturation >70%

    • Packed cell volume (PCV) > 25% (note: dehydration does not treat anemia)

    • Urine output (UOP) > 1 ml/kg/h

    • Oxygen saturation (SpO2) > 93%

    • Central venous pressure (CVP) = 5-10 cm H20

Fluid Resuscitation Guidelines

  1. Hypovolemia:

    • Crystalloid administration:

      • Dogs: 20-90 ml/kg

      • Cats: 10-50 ml/kg

    • Colloid administration:

      • Dogs: 5 ml/kg up to 20 ml/kg

      • Cats: 2-5 ml/kg up to 10 ml/kg

    • Assess end-of-resuscitation (EoR) after each bolus.

  2. Dehydration Calculation:

    • Formula:

      • % Dehydration x Body Weight (kg) x 10 = mL to administer

      • Decimal percent x Body Weight (kg) = L to administer

      • Decimal percent x Body Weight (kg) x 1000 = mL to administer

    • Example Calculation for 20 kg Patient at 5% Dehydration:

      • 5 x 20 kg x 10 = 1000 mL

      • 0.05 x 20 kg = 1 L

  3. Maintenance Needs:

    • Formula: 50 ml/kg/day.

Case Studies in Fluid Therapy

Case 1: 3-Year-Old FS GSHP (30 kg)

  • Presentation: 3 days history of vomiting and diarrhea; signs of increased skin turgor, CRT of 2 seconds, and tacky mucous membranes. Pulses appear fair.

  • Fluid therapy considerations: 5% dehydration estimation.

  • Fluid Administered:

    • Maintenance: 150 ml/kg/day = 1500 ml/day

    • Replacement: 5 x 30 kg x 10 = 1500 mL, considering ongoing losses.

    • Administered Cerenia for treatment of vomiting.

Case 2: 6-Year-Old MC DSH (5 kg)

  • Symptoms: Neurologic signs; laboratory findings indicate sodium 171 mEq/L (normal range 147-158).

  • Fluid Needs:

    • Administer hypertonic saline and NaCl; monitor sodium closely.

Case 3: 9-Year-Old FS Sheltie (10 kg)

  • Symptoms: History of diabetes mellitus with vomiting and diarrhea; 5% dehydration noted during PE.

  • Fluid Therapy Requirements: Replacement fluids and ongoing losses to be addressed; check electrolytes, BUN, creatinine levels with fluid therapy.

Case 4: 12-Year-Old FS DSH

  • Conditions: Renal failure with 7-8% dehydration and azotemia; hypokalemia noted.

  • Treatment Plan: Start IV fluids for diuresis; consider additives based on patient need.

Fluid Monitoring and Reassessment

  • Additional Monitoring Needs: Evaluate potassium levels for potential supplementation within fluids; reassess hydration status, CRT, skin turgor, and overall vital signs after bolus administration in critical situations.