Fluid therapy math — NY Wildlife Rehabilitator Exam

Fluid therapy math

Why this matters

If your animal cannot eat or drink and you only replace the deficit, it falls further behind every single day. This is the calculation that catches people out.

By the end of this lesson you will be able to

Distinguish rehydration from maintenance fluids

Calculate a full day's fluid need and divide it into safe doses

Apply the site and frequency limits for subcutaneous fluids

Two components

Rehydration replaces an existing deficit, slowly, over 24 hours. Maintenance supplies enough water to replace what the animal loses daily to urine, feces, sweating and panting. Normally an animal handles maintenance by drinking. Some species get all their water from food.

The numbers

Maintenance for mammals and birds: about 40 mL/kg per day, which is 0.04 mL/g per day
Young animals: up to 135 mL/kg per day
Deficit: body weight in grams × percent dehydration = grams of fluid = mL (1 g of fluid = 1 mL)
Wait at least 6 hours between SQ doses for absorption, so a maximum of 4 times a day
In birds, no more than 5 to 10 mL/kg per injection site
Rotate sites. Repeated use of one site traumatizes the tissue.

Common fluid types

Lactated Ringer's solution, Ringer's solution, Normosol-R, 5% Dextrose, 0.9% Sodium Chloride. Work with a veterinarian to decide which is appropriate, and when oral rather than subcutaneous fluids are called for.

Worked example: the 500 g squirrel

A squirrel with head trauma arrives. The skin tent over its shoulders is slow to collapse, its eyes appear sunken, and its gums are very pale.

Part 1: how dehydrated?Those signs put it in the 10 to 12% range. A serious condition.

Part 2: the deficitIt weighs 500 g. Assume 10%. 500 g × 0.10 = 50 g = 50 mL

Part 3: maintenanceWith head trauma it may not eat or drink today, so add maintenance. 500 g × 0.04 mL/g = 20 mL

Part 4: per doseTotal 50 + 20 = 70 mL. Given 3 times today: 70 mL ÷ 3 = 23.3 mL per dose

Worked example: the 5 kg raccoon

Deficit5 kg = 5,000 g, at 5% dehydration 5,000 g × 0.05 = 250 mL

Maintenance5 kg × 40 mL/kg = 200 mL

Per dose, 3 times a day(250 + 200) ÷ 3 = 150 mL

Raccoons are a rabies vector species. This is a calculation exercise, not an invitation.

This lesson is part of the NY Wildlife Rehabilitator Exam course. Open it in the course to answer the retrieval checks that go with it, track what you have read, and quiz the whole unit. Lessons, quizzes and the glossary are free.

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