How is dehydration deficit calculated in veterinary fluid therapy?

Dehydration deficit (mL) is calculated as: percentage dehydration × body weight (kg) × 10. For example, a 10 kg dog that is 8% dehydrated has a deficit of 10 × 8 × 10 = 800 mL.

What is the maintenance fluid requirement for dogs and cats?

Maintenance fluid needs are estimated using allometric scaling: dogs receive approximately 132 × kg^0.75 mL/day, and cats receive approximately 70 × kg^0.75 mL/day. These values replace older linear formulas and better reflect metabolic body mass.

When should hypertonic saline be used in veterinary patients?

Hypertonic saline (7.5%) is reserved for severe hypovolemia or shock when rapid intravascular volume expansion is needed. It is typically followed by isotonic crystalloids and is contraindicated in dehydration without hypovolemia or in patients with uncontrolled bleeding.

What is the standard shock dose for dogs and cats?

The standard isotonic crystalloid shock dose is 90 mL/kg/hr for dogs and 45–60 mL/kg/hr for cats. Hypertonic saline can be used at 4–7 mL/kg for rapid intravascular expansion, followed by crystalloids.

Fluid Therapy Wizard | Dog & Cat

Safety checks

This tool supports calculation and education only.
It does not diagnose, prescribe, or replace current clinical references.
Verify patient-specific decisions with current fluid therapy guidelines, hospital protocols, and veterinarian judgment.
Patients with cardiac disease, renal failure, or electrolyte disorders may require modified fluid plans.
Monitor closely for signs of fluid overload, especially in cats and small patients.

Basis and limits

Dehydration deficit: % dehydration × body weight (kg) × 10 = mL deficit. This is a clinical estimate; actual deficit varies with body composition and concurrent disease.
Maintenance: Allometric scaling (132 × kg^0.75 for dogs; 70 × kg^0.75 for cats) replaces older linear formulas and aligns with current RECOVER and AAHA guidance.
Replacement phase: 50% of deficit over 4–6 hours is a common starting point; adjust based on patient tolerance and comorbidities.
Shock dose: 90 mL/kg/hr dogs, 45–60 mL/kg/hr cats for isotonic crystalloids. Hypertonic saline 4–7 mL/kg may be used for rapid intravascular expansion.
Drip rate: Calculated using macrodrip 20 gtt/mL. Microdrip (60 gtt/mL) yields 3× slower drop rate for the same mL/hr.
Scope: This tool guides planning. It does not replace physical examination, diagnostics, or specialist consultation.

Formula audit trail

1. Convert weight to kg if entered in lb (lb ÷ 2.205).

2. Dehydration deficit (mL) = % dehydration × kg × 10.

3. Maintenance (mL/day) = 132 × kg^0.75 (dog) or 70 × kg^0.75 (cat).

4. Ongoing losses (mL) = sum of entered vomiting, polyuria, drainage, and other losses.

5. Total 24h plan (mL) = deficit + maintenance + ongoing losses.

6. Replacement rate (mL/hr) = 50% deficit ÷ 4 hours (or 6 hours).

7. Maintenance phase volume (mL) = remaining 50% deficit + maintenance + ongoing losses.

8. Maintenance phase rate (mL/hr) = phase volume ÷ 18 hours (or 20 hours).

9. Drops/sec (macro) = (mL/hr × 20) ÷ 3600.

Calculation steps will appear here as you complete the wizard.

Related tools

Last reviewed: May 2026

Sources: Merck Veterinary Manual; RECOVER Guidelines; AAHA Fluid Therapy Guidelines

Fluid Therapy Wizard

Step 1: Patient Assessment

Step 2: Fluid Needs Assessment

Step 3: Fluid Selection

Step 4: Rate Calculation

Fluid Rate Plan

Replacement Phase (first 4–6 hours)

Maintenance Phase (remaining 18–20 hours)

Shock Bolus Protocol

Continuous Infusion (CRI) Rates

Step 5: Monitoring Plan

Monitoring Checklist

🚩 Red Flags — Reassess Immediately

When to Taper Fluids

📋 Fluid Plan Summary