Test dose of desmopressin: 0.3 micrograms per kg in 50 mL normal saline infused intravenously over 30 minutes.
The time to the maximum plasma concentration of Factor VIII and von Willebrand factor is about 1 hour.
Assuming a first order elimination:
concentration at time t in IU/mL=
= (maximum concentration in IU/mL) * EXP((-1) * (elimination rate constant) * (hours since peak reached))
where:
• The assumption is that the plasma concentrations of Factor VIII and vWF are low.
• If the plasma levels are higher, then the elimination equation needs to be adjusted for the baseline concentration, with increase from desmopressin = (measured value) - (baseline value).
If the concentration is measured at t hours (often about 4 hours later):
elimination rate constant =
= LN((maximum concentration) / (concentration at time t)) / (time in hours)
half life in hours =
= 0.693 / (elimination rate constant)
Interpretation:
• The half-life is normally 5 to 8 hours.
• Peak levels of 0.4 to 0.6 IU/mL for both Factor VIII and vWF is sufficient for minor surgery.
• Peak levels of > 1.0 IU/mL may be needed for major surgery.
• The response of Factor VIII and von Willebrand factor differs depending on the type of von Willebrand's disease that the patient has.
|
Type of vWD
|
Factor VIII Response
|
vWF Response
|
|
Type 1
|
very high peak but short half-life
|
very high peak but short half-life
|
|
Type 2N
|
poor
|
normal
|
|
Type 2A
|
normal
|
poor
|
