About the fresh frozen plasma dose formula
Fresh frozen plasma (FFP) is transfused to replace multiple coagulation factors at once, most often for warfarin/vitamin K antagonist reversal, dilutional coagulopathy from massive transfusion, or when specific factor concentrates are unavailable. This calculator uses the standard plasma-volume method to translate a desired increase in clotting-factor level into an estimated transfusion volume and unit count.
How the dose is calculated
Each unit of FFP is assumed to carry roughly normal (about 100%) activity of the clotting factors it contains. To raise a patient's circulating factor level by a given percentage, you need to add that percentage of the patient's own plasma volume in factor-replete plasma. The formula is:
- Plasma volume (mL) = body weight (kg) x plasma volume estimate (mL/kg, commonly about 40 mL/kg).
- Dose volume (mL) = plasma volume x (target factor level % - current factor level %) / 100.
- Units needed = dose volume divided by the volume of one FFP unit, rounded up to a whole unit since partial units are not transfused.
This reproduces the commonly cited bedside rule that about 10-15 mL/kg of FFP raises most coagulation factor levels by roughly 20-30%, since 40 mL/kg x 25% works out to about 10 mL/kg.
Interpreting the result
- The dose-per-kilogram figure is a useful sanity check: values noticeably outside the 10-15 mL/kg range for a 20-30% target increase suggest the inputs should be double-checked.
- Current and target factor levels are estimates. In practice they are inferred from coagulation testing (INR, PT, aPTT, fibrinogen) rather than measured directly for a single factor, so treat the inputs as a planning approximation.
- Larger volumes raise the risk of transfusion-associated circulatory overload (TACO), particularly in patients with cardiac or renal impairment; large calculated doses are often given in divided infusions with reassessment between them.
When to consult a professional
This tool performs the standard plasma-volume arithmetic for education and planning. It is not a transfusion order and does not replace clinical judgment. Any transfusion decision should be made by the treating clinician using current coagulation results, bleeding status, fluid tolerance, and institutional blood bank protocols.