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Difficulty: HardMonitoring and Treatment Evaluation

A 62-year-old woman is admitted to the hospital with a 2-day history of acute right leg swelling and right-sided pleuritic chest pain. She has a history of type 2 diabetes mellitus, hypertension, and chronic kidney disease stage 4. Her home medications include amlodipine, insulin glargine, and atorvastatin. On presentation, her blood pressure is 138/85 mmHg, pulse is 105/min, and oxygen saturation is 94% on room air. Laboratory studies show a serum creatinine of 3.2 mg/dL3.2 \text{ mg/dL} (estimated glomerular filtration rate: 18 mL/min/1.73 m218 \text{ mL/min/1.73 m}^2). A computed tomography (CT) pulmonary angiogram confirms a right lower lobe segmental pulmonary embolism. A comprehensive lower extremity venous ultrasound demonstrates a proximal deep vein thrombosis in the right popliteal vein. Continuous intravenous unfractionated heparin is initiated.

Which of the following are necessary components of this patient's ongoing treatment and monitoring plan? (Select two)

  1. Serial measurement of activated partial thromboplastin time (aPTT) every 6 hours until the therapeutic target is achievedAnswer
  2. Monitoring of the platelet count every 2 to 3 days to evaluate for drug-induced complicationsAnswer
  3. C
    Measurement of Protein C, Protein S, and antithrombin levels prior to hospital discharge to determine the required duration of anticoagulation
  4. D
    Routine repetition of the CT pulmonary angiogram in 48 to 72 hours to document cessation of thrombus propagation
  5. E
    Transition to weight-based therapeutic subcutaneous enoxaparin to facilitate early hospital discharge
  6. F
    Routine monitoring of the prothrombin time (PT) and international normalized ratio (INR) to titrate the unfractionated heparin infusion

Answer

The correct monitoring parameters are the serial measurement of activated partial thromboplastin time (aPTT) to ensure therapeutic anticoagulation and regular monitoring of the platelet count to assess for heparin-induced thrombocytopenia.
The use of intravenous unfractionated heparin requires precise monitoring due to its unpredictable pharmacokinetic profile. Efficacy is monitored by checking the activated partial thromboplastin time (aPTT) every 6 hours after initiation or dose adjustments until two consecutive values are within the target therapeutic range. Furthermore, because unfractionated heparin carries a high risk of heparin-induced thrombocytopenia (HIT), patients must have their platelet counts monitored regularly (e.g., every 2 to 3 days from day 4 to 14 of therapy) to identify a precipitous drop that would necessitate immediate cessation of heparin and transition to a non-heparin anticoagulant.

Step-by-Step Solution

1
Evaluate the patient's clinical presentation, comorbidities, and current therapy.
The patient has an acute pulmonary embolism and deep vein thrombosis in the setting of severe chronic kidney disease (eGFR 18 mL/min/1.73 m218 \text{ mL/min/1.73 m}^2) and is appropriately started on intravenous unfractionated heparin (UFH).
Severe renal impairment restricts the use of low-molecular-weight heparins (like enoxaparin) and most direct oral anticoagulants due to the risk of bioaccumulation and fatal bleeding. UFH is primarily cleared by the reticuloendothelial system and is the safest initial option.
2
Identify the appropriate efficacy monitoring for intravenous unfractionated heparin.
The intrinsic and common coagulation pathways must be monitored using the activated partial thromboplastin time (aPTT).
UFH binds to antithrombin, enhancing its inactivation of thrombin (Factor IIa) and Factor Xa. The aPTT is measured every 6 hours until therapeutic (typically 1.5 to 2.5 times the control value), then daily.
3
Identify the required safety monitoring for unfractionated heparin therapy.
The patient requires regular monitoring of her platelet count.
UFH carries a significant risk of inducing heparin-induced thrombocytopenia (HIT), an immune-mediated prothrombotic state caused by antibodies against heparin-platelet factor 4 complexes.

Key Concept

Patients with acute venous thromboembolism and severe renal impairment should be treated with intravenous unfractionated heparin, which requires frequent aPTT monitoring to ensure therapeutic dosing and serial platelet count monitoring to detect heparin-induced thrombocytopenia.
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Topics

Monitoring and Treatment Evaluation

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