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Summary of Key Points

Individualized care
  • Fluid therapy must be individualized and tailored to each patient.
  • Therapy is constantly re-evaluated and reformulated according to changes in patient status.
  • Fluid selection is dictated by the patient’s needs, including volume, rate and fluid composition required, and location the fluid is needed (interstitial versus intravascular).
  • The appropriate route of fluid administration depends on the patient’s condition.
    • Use oral fluids for patients with a functioning gastrointestinal system and no significant fluid imbalance.
    • Use subcutaneous fluids to prevent losses. This route is not adequate for replacement therapy in anything other than very mild dehydration.
    • Use intravenous or intra-osseous fluids for patients undergoing anesthesia; for hospitalized patients not eating or drinking normally; and to treat dehydration, shock, hyperthermia or hypotension.

Fluids during anesthesia

  • The decision about whether to provide fluids during anesthesia, and the type and volume used, depends on the patient’s signalment, physical condition, and the length and type of procedure.
  • Current recommendations are for less than 10 mL/kg/hr to avoid adverse effects of hypervolemia. Consider starting the anesthetic procedure at 3 mL/kg/hr in cats and 5 mL/kg/hr in dogs.

Maintenance fluid rates

  • Cat: Formula = 80 x body weight (kg)0.75 per 24 hr Rule of thumb 2–3 mL/kg/hr
  • Dog: Formula = 132 x body weight (kg)0.75 per 24 hr Rule of thumb 2–6 mL/kg/hr

Fluids for the sick patient


Assess for three types of fluid disturbances.

  1. Changes in volume (e.g., dehydration, blood loss, heart disease)
    1. Fluid deficit calculation for dehydration: body weight (kg) x % dehydration = volume in liters to correct. See section on dehydration for more details on determining timeframe for replacement of deficit.
    2. Treatment for hypervolemia includes correcting underlying disease (e.g., chronic renal disease, heart disease) decreasing or stopping fluid administration, and possibly use of diuretics.
  2. Changes in content (e.g., hyperkalemia, diabetes or renal disease)
    1. In general, the choice of fluid is less important than the fact that it is isotonic. Volume benefits the patient much more than exact fluid composition. Isotonic fluids will begin to bring the body’s fluid composition closer to normal, pending laboratory results that will guide more specific fluid therapy.
  3. Changes in distribution (e.g., pleural effusion, edema)
    1. For pulmonary edema or pleural/abdominal effusions, stop fluid administration.

Staffing and monitoring

  1. Provide staff training on assessment of patient fluid status, catheter placement and maintenance, use and maintenance of equipment related to fluid administration, benefits and risks of fluid therapy, and drug/fluid incompatibility.
  2. Use equipment and supplies that enhance patient safety, such as fluid pumps, small fluid bags, Luer-lock connections and Elizabethan collars.
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