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Difficulty: MediumHemodynamic and Coagulation Processes

A 62-year-old man with end-stage renal disease receiving maintenance hemodialysis is evaluated prior to an elective inguinal hernia repair. He reports easy bruising and prolonged bleeding from venipuncture sites over the past month. Physical examination reveals scattered ecchymoses on his upper and lower extremities. Laboratory studies show:

Hemoglobin: 10.2 g/dL
Platelet count: 185,000/mm³
Prothrombin time (PT): 12 seconds (normal: 11-15 seconds)
Activated partial thromboplastin time (aPTT): 28 seconds (normal: 25-40 seconds)
Bleeding time: 14 minutes (normal: 2-7 minutes)

The physician decides to administer an intravenous medication to minimize the patient's periprocedural bleeding risk. Which of the following best describes the primary mechanism of action of the most appropriate pharmacologic agent for this patient?

  1. Induction of von Willebrand factor and factor VIII release from endothelial storesAnswer
  2. B
    Exogenous administration of functional donor platelets
  3. C
    Direct replenishment of vitamin K-dependent clotting factors
  4. D
    Proteolytic cleavage of abnormally large von Willebrand factor multimers
  5. E
    Irreversible inhibition of cyclooxygenase enzymes

Answer

Induction of von Willebrand factor and factor VIII release from endothelial stores
The patient's presentation of easy bruising, end-stage renal disease, normal platelet count, normal coagulation times, and a prolonged bleeding time is classic for uremic platelet dysfunction. Uremic toxins (such as guanidinosuccinic acid) interfere with platelet adhesion and aggregation by impairing the function of glycoprotein IIb/IIIa receptors and altering platelet-endothelial interactions. The first-line pharmacotherapy for rapid correction of uremic bleeding prior to an invasive procedure is desmopressin (DDAVP). DDAVP increases the endothelial release of von Willebrand factor (vWF) and factor VIII from Weibel-Palade bodies, which enhances platelet adhesion to the damaged endothelium and temporarily normalizes the bleeding time.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and laboratory results.
The patient has end-stage renal disease, easy bruising, a normal platelet count, normal PT/aPTT, but a significantly prolonged bleeding time.
Identifying the specific hemostatic abnormality is required to determine the underlying pathophysiology.
2
Diagnose the cause of the patient's bleeding diathesis.
The clinical picture is diagnostic of uremic platelet dysfunction, where uremic toxins impair platelet aggregation and adhesion.
Connecting ESRD with an isolated prolonged bleeding time points to a qualitative platelet defect rather than a quantitative disorder or coagulation cascade issue.
3
Select the most appropriate periprocedural pharmacologic therapy.
Desmopressin (DDAVP) is the first-line pharmacologic treatment to rapidly and temporarily correct uremic platelet dysfunction prior to surgery.
DDAVP is chosen for immediate preoperative prophylaxis over dialysis or ineffective platelet transfusions.
4
Identify the mechanism of action of the chosen therapy.
DDAVP works by stimulating the release of von Willebrand factor (vWF) and factor VIII from endothelial Weibel-Palade bodies, facilitating platelet adhesion.
The question specifically asks for the cellular mechanism of the best pharmacotherapy.

Key Concept

Uremic platelet dysfunction presents with an isolated prolonged bleeding time and is best treated preoperatively with desmopressin (DDAVP), which induces the release of von Willebrand factor and factor VIII from endothelial cells.
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Topics

Hemodynamic and Coagulation Processes

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