Fluid Therapy

Question 1

Describe the clinical signs of a dehydrated/hypovolemic horse.

Answer 1

Dehydration - loss of total body water
Dry-tacky oral mucous membranes
Decreased urine production
Lethargy
Weakness
Sunken eyes

Hypovolemia - decreased intravascular fluid volume
Decreased jugular distensibility
Prolonged CRT >2 sec
Cold extremities
Tachycardia

Question 2

Develop a rational fluid therapy plan for a horse with ongoing losses (diarrhea, reflux).

Answer 2

1. Resuscitation to treat hypovolemia: Hypertonic saline 4-6 mL/kg (1L) bolus IV
2. Rehydration to treat dehydration: (BW kg)(% dehydrated) = L
3. Ongoing losses: estimate L

Maintenance = 50 mL/kg/d

Total fluids L/day = deficit + ongoing losses + maintenance (- shock dose)
Divide by 24 for L/hr

Monitor HR, PCV, and CRT to re-evaluate and adjust

Question 3

Explain when, why, and how you would administer hypertonic saline to a horse.

Answer 3

When - transporting a sick, dehydrated horse to a hospital for 2-4 hour ride
Why - to rapidly restore circulating vascular volume, improve cardiac output, and enhance tissue perfusion
How - bolus at 4 mg/kg IV

This is a short-term fix and must be followed within a few hours with appropriate volumes of isotonic fluids.

Question 4

List the causes, clinical signs, and treatment options for increases/decreases in plasma potassium, calcium, or bicarbonate concentrations in horses.

Answer 4

Hypokalemia
Causes: Anorexia, diarrhea, reflux, exercise
Clinical signs: weakness, ileus
Tx: KCl 20 mEq/L fluids IV; 15g q8 h PO

Hyperkalemia
Causes: RF, hyperkalemic periodic paralysis (HYPP), ruptured bladder, rhabdomyolysis
Clinical signs: weakness, collapse, death
Tx: Dextrose IV (insulin); Ca Gluconate IV

Hypocalcemia - common
Causes: anorexia, exercise, cantharidin tox, etc.
Clinical signs: ileus, tremors, muscle fasciulations, etc.
Tx: Ca gluconate to crystalloids

Hypercalcemia - rarer
Causes: neoplasia, CRF, vitamin D tox
Clinical signs: Anorexia, arrhythmias, lethargy, soft tissue calcification
Tx: NaCl to expand ECF; furosemide to enhance urinary calcium excretion

Low bicarbonate - Metabolic acidosis
Causes: lactic acid accumulation secondary to dehydration and decreased tissue perfusion
Clinical signs:
Tx: eliminate underlying cause; restore circulating volume with maintenance fluid containing lactate (LRS); if severe consider bicarb therapy

High bicarbonate - Metabolic alkalosis
Causes: severe nasogastric reflux, diuretics, sweat loss/exhaustion
Clinical signs:
Tx: restore extracellular volume, chloride replacement, potassium replacement