InfusionFox
Calculator · Transfusion medicine

Transfusion calculator

Volume and rate planning for blood-product transfusion in dogs and cats. Handles packed red blood cells, whole blood, and fresh frozen plasma. Outputs the volume to deliver and the safe infusion rate, accounting for the slow reaction-monitoring window at the start.

  • Cats: blood type and crossmatch before every transfusion. Cats have naturally occurring alloantibodies. A type B cat receiving type A blood can have a fatal reaction on first exposure with no prior sensitization.
  • Dogs: blood type before first transfusion; crossmatch before any subsequent transfusion. Dogs do not have clinically significant naturally occurring alloantibodies, so first transfusion is generally safe even without crossmatching, but DEA 1.1 typing is still recommended.
  • 4-hour limit. Sterility window for blood products at room temperature. Transfusion not completed within 4 hours of starting must be discarded.
  • Diphenhydramine doesn't prevent acute hemolytic reactions. It is given for prophylaxis of mild allergic / urticarial reactions only. Do not let premedication delay treatment.
Patient
Product
PCV targets (pRBC / whole blood)

Aim for clinical stability rather than reference-range PCV. Target 25–30% is usually sufficient.

Leave 0 to use defaults: pRBC ~80%, whole blood ~60%.

FFP dose (if FFP selected)

Standard 10–20 mL/kg. Use 10 for general factor replacement, 15–20 for active bleeding or DIC.

Awaiting input

Enter a patient weight to see the result.

Reference

Formula

For pRBC and whole blood, the volume needed to raise PCV from current to target is calculated from the patient's total blood volume and the donor PCV:

$$V_{\text{transfuse}} = \frac{\text{PCV}_{\text{target}} - \text{PCV}_{\text{current}}}{\text{PCV}_{\text{donor}}} \times \text{BV}_{\text{recipient}}$$

Recipient blood volume is 90 mL/kg in dogs, 60 mL/kg in cats. Default donor PCV is 80% for pRBC and 60% for whole blood (overridable on the form). FFP uses a simpler weight-based dose: 10-20 mL/kg.

Worked example with current inputs

Enter a patient weight to see the worked example.

Reference

Monitoring schedule

Baseline TPR, mucous membrane color, PCV/TS recorded immediately before transfusion. Then:

  • Every 5–15 min during the first 30 min (slow trial period). Watch for acute reactions: vomiting, urticaria, facial swelling, fever, tachycardia, dyspnea, weakness, hemoglobinemia/hemoglobinuria.
  • Every 30 min thereafter until completion. Continue TPR.
  • 15 min, 1 hr, 12 hr, and 24 hr post-transfusion: TPR and PCV/TS for delayed reactions.
  • Recheck PCV at 1 hr post-transfusion to confirm expected rise. Each unit of pRBC should raise PCV by ~5–10% in a typical 25-kg dog.
Reference

Transfusion reactions

Reactions are categorized by mechanism and timing. Stop the transfusion immediately for any reaction; many are reversible if caught early.

Acute hemolytic (immediate, life-threatening)

Fever, vomiting, collapse, hemoglobinemia, hemoglobinuria, DIC. Most often from blood-type incompatibility. STOP transfusion. IV crystalloids, supportive care. Diphenhydramine and steroids do not treat this.

Allergic / urticarial (mild, common)

Facial swelling, urticaria, pruritus, mild fever. Pause transfusion, give diphenhydramine 1–2 mg/kg IM, resume at slower rate once signs resolve. Premedication helps prevent recurrence in patients with prior reactions.

Volume overload (TACO)

Tachypnea, dyspnea, pulmonary crackles. More common in cats and patients with cardiac disease. Slow or stop transfusion, furosemide, oxygen.

Delayed hemolytic (3–14 days post)

Falling PCV without overt signs. Confirms anti-RBC antibody response. Future transfusions require crossmatching.

Sources

  • Davidow B. Transfusion medicine in small animals. Vet Clin North Am Small Anim Pract 2013;43:735–756.
  • Plumb DC. Plumb's Veterinary Drugs: Blood products. Volume calculations for pRBC, whole blood, and fresh frozen plasma.
  • Garden OA, Kidd L, Mexas AM, et al. ACVIM consensus statement on the diagnosis of immune-mediated hemolytic anemia in dogs and cats. J Vet Intern Med 2019;33:313–334. (Transfusion section.)