The AAHA 2024 Fluid Therapy Guidelines provide evidence-based recommendations for small animal practice. Use the Fluid Therapy Calculator and CRI Calculator for IV fluid rates and constant rate infusion calculations.
Maintenance requirements account for sensible (urine, feces) and insensible (respiration, skin) losses.
Simplified maintenance: 2–3 mL/kg/hour for dogs; 2–4 mL/kg/hour for cats. The classic formula (body weight in kg × 30 + 70) per day is less accurate for very small or large patients. For a 10 kg dog: 20–30 mL/hour or 480–720 mL/day.
Clinical assessment of dehydration guides replacement fluid volume. Physical exam findings correlate roughly with deficit:
| Dehydration % | Clinical Signs | Deficit (mL/kg) |
|---|---|---|
| 5% | Subtle; mild skin tent | 50 |
| 6–8% | Skin tent, dry mucous membranes | 60–80 |
| 10–12% | Prolonged tent, sunken eyes, tachycardia | 100–120 |
| 12–15% | Shock, collapse | 120–150 |
Replacement formula: % dehydration × body weight (kg) × 10 = mL to replace. Give half over 1–2 hours, reassess, then remaining over 4–6 hours.
Warning: Do not correct severe dehydration too rapidly—cerebral edema risk. Spread replacement over 4–12 hours. Never correct in 30 minutes.
Lactated Ringer's (LRS): Most versatile crystalloid. Contains lactate (metabolized to bicarbonate), potassium, calcium. Avoid in hyperkalemia, lactic acidosis. pH 6.5.
0.9% Sodium Chloride (Normal Saline): Isotonic, no potassium. Use when hyperkalemia (e.g., urinary obstruction, hypoadrenocorticism), hyponatremia, or when LRS is contraindicated. Can cause hyperchloremic acidosis with large volumes.
Normosol-R, Plasma-Lyte: Balanced crystalloids with acetate/gluconate as buffer. More physiologic pH; may be preferred in critical illness. No calcium—compatibility with blood products.
5% Dextrose: Free water; use for hypoglycemia or as maintenance with electrolyte replacement. Do not use for volume resuscitation.
Weigh patients daily. Monitor urine output, mucous membrane moisture, skin turgor, heart rate, and blood pressure. Serial lactate, electrolytes, and blood gas when indicated. Overhydration causes pulmonary edema, serous nasal discharge, and weight gain.
- Overly rapid correction: Severe dehydration corrected in 30 minutes risks cerebral edema. Spread replacement over 4–12 hours.
- Ignoring ongoing losses: Vomiting, diarrhea, polyuria—add replacement for ongoing losses to maintenance.
- Wrong fluid for the patient: Hyperkalemic patient receiving LRS; hypoglycemic patient without dextrose supplementation.
- No reassessment: Fluid plans should be dynamic. Recheck electrolytes, hydration, and response.
Fluid therapy decisions require clinical judgment. Shock, electrolyte abnormalities, and renal failure need tailored plans. Refer to AAHA 2024 guidelines for complete recommendations.
Fluid therapy decisions require clinical judgment. This summary is for educational purposes.
- Maintenance: 2–3 mL/kg/hr (dogs); 2–4 mL/kg/hr (cats).
- Deficit: % dehydration × BW (kg) × 10 = mL to replace.
- Give half over 1–2 hrs, reassess, remaining over 4–6 hrs—avoid rapid correction.
- LRS: avoid in hyperkalemia. Normal saline: use when hyperkalemia.
- Add replacement for ongoing losses (vomiting, diarrhea, polyuria).