# Nurse Anesthesia: VWF Dosage Calculation

Here is an example of how to calculate the dosage of von Willebrand factor (VWF) for a patient with severe von Willebrand disease (VWD). The preparation used most in the US for VWF replacement is Humate P, a fractionated human plasma product rich in VWF. The computation example may also be applied to replacement factor therapy for hemophilia A (factor VIII deficiency) or hemophilia B (factor IX deficiency). Another example appears in the VWD Part 2 module.
A patient with von Willebrand disease requires factor concentrate (Humate P) before a surgical procedure. Her weight is 132 lbs (60 kg) and her hematocrit is 30%. Compute the VWF dosage she needs to achieve an initial level of 100% (100 IU/dL). She is moderately obese, so we use 60 mL/kg as her blood volume conversion factor (70 mL/kg is normal).

First we compute her blood volume: 60 kg x 60 mL/kg = 3600 mL.

Next we compute plasma volume: 3600 mL x (100%-HCT%) = 3600 x 70% = 2520 mL total plasma volume.

We perform the VWF:RCo assay and determine she has <1% plasma VWF.

The dosage required is computed as follows: plasma volume (2520 mL) x (target level-initial level, 100 IU/dL or 1 IU/mL) = 2520 IU.

Note especially in the last calculation, though in the lab we express VWF as a percentage, or IU/dL, the actual dosage is calculated in mL. If you donâ€™t make this final conversion, the result would be an improbable 252,000 IU. An overdose of VWF exposes the patient to thrombotic risk. Geo