InfusionFox
Fluid Therapy

Fluid therapy (rehydration + maintenance)

Builds a complete IV fluid plan for any dehydrated dog or cat. Enter weight, % dehydration, and ongoing losses; outputs shock-bolus volumes if needed, deficit replacement over a chosen 4–24 hr window, maintenance rate, and the combined active-phase and post-rehydration rates the pump should run at.

isotonic crystalloid
  • Phases for a dehydrated patient. If the patient is in shock, that is addressed FIRST with rapid bolus(es), not by running the rehydration + maintenance rate faster. Only after volume status is restored do you switch to the active-phase combined rate. Then, after the rehydration window completes, REDUCE to the post-rehydration rate. For a euhydrated patient the plan is a single maintenance rate; no phases.
  • Reassess every 2–6 hours. Fluid therapy is dynamic. Watch for over-rehydration (chemosis, respiratory crackles, peripheral edema, weight gain >10%) and reduce the rate accordingly. Watch electrolytes, hypokalemia, hypophosphatemia, and hypomagnesemia worsen with continued therapy in many conditions (see /hypokalemia, /hypophosphatemia, /hypomagnesemia).
  • Choose the right fluid. Replacement isotonic crystalloid is the default. Buffered solutions (LRS, Plasma-Lyte, Normosol-R) are usually preferred over 0.9% NaCl in non-emergent rehydration, they correct acidosis faster, reduce hyperchloremia, and contribute small amounts of K and bicarbonate precursors. Use 0.9% NaCl for documented severe hyponatremia, hypochloremia, or hypercalcemia.
Using this in DKA?

The math on this page is general-purpose for any dehydration scenario. When using it specifically for DKA management, two interactions matter:

  • Insulin runs through a SEPARATE line. See /insulin-cri-dka or /insulin-im-dka.
  • The fluid composition of this line changes with BG when an insulin CRI is also running (NaCl alone above 250 → NaCl + 2.5% dextrose at 150–250 → NaCl + 5% dextrose below 150). The RATE calculated here doesn't change with BG, only the composition does.
  • See the DKA management hub for the full workflow.
If yes, the result panel will surface the shock-bolus increments and ceilings (dogs up to 90 mL/kg total, cats up to 60 mL/kg). Shock bolus is delivered FIRST, then the rehydration+maintenance rate begins.
Published range is 4–24 hours. Shorter windows (4–6 hr) for severely dehydrated patients with intact cardiovascular function. Longer windows (12–24 hr) for cardiac, renal, or geriatric patients where fluid loading is a risk.
Published range is 2–4 mL/kg/hr. Default 3 mL/kg/hr (mid-range). Lower (2) for patients with cardiac or renal limitations; higher (4) for active ongoing demand or hypermetabolic states.
Estimate of ongoing fluid losses, vomiting, osmotic polyuria, diarrhea. Default 0. A 20 kg dog with active vomiting and severe glucosuria might easily lose 50–100 mL/hr. Re-estimate hourly and adjust as needed.
Awaiting input

Enter a patient weight to see the result.

Method

How the math works

Fluid therapy in a dehydrated patient combines four components. Three are calculated by this tool; the fourth (shock bolus) is surfaced as a separate ceiling and increment.

1. Shock bolus (if applicable)

If the patient is hypovolemic at presentation: 10–30 mL/kg isotonic crystalloid IV, reassess after each increment, up to a ceiling of 90 mL/kg in dogs or 60 mL/kg in cats. Most patients respond well before reaching the maximum. Shock bolus is delivered FIRST and is NOT additive to the rehydration+maintenance rate that follows.

2. Rehydration deficit

$$\text{deficit (mL)} = \text{weight (kg)} \times \%\text{ dehydration} \times 10$$ Replaced over the chosen rehydration window (4–24 hr). Rehydration rate = deficit ÷ window.

3. Maintenance rate

Published range is 2–4 mL/kg/hr. This is the older mL/kg/hr maintenance rule, not the allometric formula, and is the convention used by this calculator.

4. Combined rate during the active phase

$$\text{total (mL/hr)} = \text{rehydration} + \text{maintenance} + \text{ongoing losses}$$ Continue at this rate for the full rehydration window. At the end of the window, REDUCE to (maintenance + ongoing losses) until the patient is eating, drinking, and ketone-negative.

Formula

Rehydration deficit

$$\text{deficit}_{\text{mL}} = \text{weight}_{\text{kg}} \times \text{dehydration}_{\%} \times 10$$
$$\text{rehydration rate}_{\text{mL/hr}} = \frac{\text{deficit}_{\text{mL}}}{\text{window}_{\text{hr}}}$$

Maintenance

$$\text{maintenance}_{\text{mL/hr}} = \text{weight}_{\text{kg}} \times \text{rate}_{\text{mL/kg/hr}}$$

Total active phase rate

$$\text{total}_{\text{mL/hr}} = \text{rehydration}_{\text{mL/hr}} + \text{maintenance}_{\text{mL/hr}} + \text{ongoing losses}_{\text{mL/hr}}$$

Sources

  • Hoehne SN. Diabetic Ketoacidosis. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 3rd ed. St. Louis, MO: Elsevier; 2023. Chapter 73, Box 73.1 (Recommended Treatment and Monitoring Schedule for Dogs and Cats with Diabetic Ketoacidosis).
  • Dehydration physical-exam bands: standard veterinary internal-medicine assessment as described in DiBartola Fluid, Electrolyte, and Acid-Base Disorders and referenced by most major IM texts.