Answer
Desmopressin (DDAVP) is a vasopressin analogue that releases vWf from endothelial cells.
Most patients with type I von Willebrand disease can be treated with DDAVP for minor surgeries and dental procedures. The usual dose is 0.3 μg/kg infused slowly approximately 30 minutes before an operative procedure. This dose can be repeated once a day for 2-3 days, after which it is ineffective because of tachyphylaxis. Other adverse effects occasionally include a hypertensive response and hyponatremia.
An intranasal preparation of DDAVP has been made available for individuals with von Willebrand disease and is administered at a dose of 150 μg or 300 μg (ie, 150 μg per nostril). The more diluted preparation is used in patients with diabetes insipidus and does not increase vWf levels.
DDAVP does not usually increase factor VIII levels in patients with type IIA and can induce thrombocytopenia in patients with type IIB or pseudo von Willebrand disease.
Replacement therapy is used for more extensive surgeries or trauma and for patients with type II and type III disease. The treatment of choice is vWf concentrates. Purified plasma-derived concentrates of vWF/FVIII (Humate-P or Alphanate) are heat-treated, and the solvent is extracted; therefore, they are considered safe from viral contamination. Recombinant von Willebrand factor (Vonvendi) was approved by the US Food and Drug Administration (FDA) in December 2015. [32]
The dose of vWf concentrate is calculated based on ristocetin cofactor units (usual dose is 50-100 U/kg). The factor VIII level often rises following the infusion of von Willebrand protein concentrate, and it remains elevated for at least for 40 hours, reflecting the half-life of von Willebrand protein rather than that of factor VIII. The need for further doses is often assessed based on clinical criteria rather than blood test results.
Cryoprecipitate has approximately 100 U of factor VIII per bag and has all multimeric forms of vWf. Despite screening tests, patients have a small risk developing viral infections.
Highly purified preparations of factor VIII or recombinant factor VIII should not be administered to patients with von Willebrand disease, because these preparations have very little von Willebrand factor.
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Normal hemostasis.
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Purpuric spots.
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Spurious thrombocytopenia. Peripheral smear of a patient reported to have platelet counts of 10,000-150,000/μL on various occasions. The smear shows clumping of the platelets and satellitism involving neutrophils and platelets.
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Examination of the peripheral smears in immune thrombocytopenic purpura often shows giant platelets. These platelets reflect the increased megakaryocytic mass in the marrow.
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Peripheral smear of a patient with Bernard-Soulier syndrome showing giant platelets. These platelets are not counted as platelets in most particle counters.
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Examination of the peripheral smear shows red blood cell fragments, basophilic cells, in addition to thrombocytopenia in thrombotic thrombocytopenic purpura.
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Bone marrow in immune thrombocytopenic purpura. Bone marrow examination reveals an increased number of megakaryocytes.
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Vasculitis in childhood.
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Schistocytes (thrombotic thrombocytopenic purpura).
