USMLE/COMLEX 2 - Pulmonary Embolism and Deep Vein Thrombosis

Here are key facts for USMLE Step 2 CK & COMLEX-USA Level 2 from the Pulmonary Embolism & Deep Vein Thrombosis tutorial, focusing on clinical management and treatment decision-making that are essential for these exams. See the tutorial notes for further details and relevant links.

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1. Pulmonary Embolism (PE): Presents with dyspnea, tachypnea, chest pain, hypoxemia, and ventilation-perfusion mismatch. 2. Respiratory Manifestations: Tachypnea, respiratory alkalosis, and hypoxemia due to V/Q mismatch. 3. Cardiovascular Manifestations: Tachycardia and potential right heart failure due to increased pulmonary vascular resistance. 4. Neurological Manifestations: Altered mental state, particularly important to recognize in elderly patients. 5. Deep Vein Thrombosis (DVT): When symptomatic, presents with unilateral leg swelling, tenderness, and signs of venous dilation; can also occur in upper body (less common). 1. PE Classification by Risk:

• Massive (High Risk): Hemodynamically unstable with hypotension
• Intermediate (Submassive): Stable but with right ventricular dysfunction
• Low Risk: Hemodynamically stable without right ventricular dysfunction

2. PE Classification by Location:

• Saddle Emboli: Located at pulmonary trunk bifurcation
• Lobar, Segmental, Subsegmental: Located in respective arterial branches

3. DVT-PE Relationship: DVT is the leading cause of pulmonary embolism; combined condition termed venous thromboembolism (VTE). 4. Clinical Probability Assessment:

• Wells Score for PE: Score ≥4 indicates PE likely; <2 low probability, 2-6 moderate, >6 high probability
• Wells Score for DVT: Based on swelling, edema, and likelihood of alternative diagnosis

5. Non-thrombotic Causes: Air, fat, amniotic fluid, bacterial (septic), foreign bodies, tumors. 1. Initial Workup:

• Clinical suspicion based on presentation and risk factors
• Clinical probability assessment using Wells criteria
• D-dimer testing (>500 ng/mL suggests possible PE, requiring further testing)

2. Imaging for PE:

• CT Angiography: Most widely used; visualizes disruption of blood flow in pulmonary arteries
• Ventilation-Perfusion Scan: Non-invasive test indicating blood clot presence
• Chest X-ray: May show atelectasis, Hampton hump (pulmonary infarction), Westermark sign (oligemic areas), or pleural effusion

3. ECG Findings:

• Sinus tachycardia
• S1Q3T3 pattern (S wave in lead I, inverted Q and T waves in lead III)

4. Imaging for DVT:

• Venous Ultrasonography with Compression: First-line imaging
• Contrast Venography: Alternative when ultrasound inconclusive

5. Laboratory Tests:

• D-dimer: Fibrin degradation product used to rule out low-probability cases
• Arterial blood gases: May show hypoxemia and respiratory alkalosis

1. Supportive Care:

• Oxygen administration
• Fluid resuscitation with saline
• Vasopressors for hemodynamic support if needed

2. Anticoagulation Therapy:

• Initial Treatment: Heparin, enoxaparin, or fondaparinux
• Long-term Treatment: Warfarin

3. Advanced Interventions:

• Embolectomy: Surgical removal of clot
• Clot Dissolution: Thrombolytic therapy to restore pulmonary artery flow

4. DVT Prophylaxis in High-Risk Patients:

• Mechanical: Sequential compression devices (SCDs) to prevent venous stasis
• Pharmacologic: Low-dose enoxaparin or heparin

5. Treatment Complications: Monitor for heparin-induced thrombocytopenia. 1. Virchow's Triad (Factors predisposing to DVT):

• Endothelial Injury: Fracture, surgery, trauma, previous DVT
• Venous Stasis: Immobility, elevated central venous pressure, heart failure, obesity
• Hypercoagulable States: Pregnancy, postpartum period, smoking, cancer, hormonal contraceptives/replacement therapies, coagulation disorders (e.g., Factor V Leiden)

2. High-Risk Populations:

• Individuals with multiple predisposing factors (e.g., pregnant women on bed rest)
• Post-surgical patients, especially orthopedic procedures
• Malignancy patients

3. Preventive Strategies:

• Early mobilization
• Mechanical prophylaxis (SCDs)
• Pharmacologic prophylaxis in selected patients

4. Patient Education: Essential component of prevention strategy. 5. Post-thrombotic Syndrome: Prevention through appropriate DVT management.

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1. When to Suspect PE: Unexplained dyspnea, tachypnea, chest pain, especially with risk factors for DVT. 2. Differential Diagnosis Considerations: Non-specific symptoms can make diagnosis challenging. 3. Risk Factor Assessment: Identifying patients with multiple predisposing factors from Virchow's Triad. 4. Wells Score Application: Using clinical decision tools appropriately to guide diagnostic workup. 5. Recognition in Special Populations: Altered presentation in elderly (mental status changes) requires high clinical suspicion. 1. D-dimer Utilization: Useful for ruling out PE in low-probability patients; levels >500 ng/mL warrant further investigation. 2. Imaging Selection Logic:

• CT angiography as first-line imaging for suspected PE
• Venous ultrasonography with compression for suspected DVT

3. Chest X-ray Findings:

• Hampton Hump: Wedge-shaped shadow indicating pulmonary infarction, typically in lower lobes
• Westermark Sign: Focal oligemia appearing as poorly perfused area

4. ECG Pattern Recognition: S1Q3T3 pattern, though not sensitive or specific, can support diagnosis. 5. Additional Test Interpretation: Recognizing lines of Zahn in premortem thrombi (layers of fibrin, RBCs, and platelets). 1. Anticoagulation Initiation: When to start therapy based on clinical suspicion and risk assessment. 2. Intervention Selection: Determining appropriate anticoagulant based on clinical context. 3. Advanced Treatment Decisions: When to consider embolectomy or thrombolysis for massive PE. 4. Prophylaxis Decision-Making: Risk stratification to determine appropriate preventive measures. 5. Management of Complications: Addressing post-thrombotic syndrome and recurrent events. 1. Recognition: Small emboli causing tissue ischemia, most often in lower lobes. 2. Radiographic Identification: Wedge-shaped "Hampton Hump" on chest X-ray. 3. Clinical Significance: Indicates tissue damage requiring appropriate management. 4. Treatment Approach: Anticoagulation and supportive care. 5. Monitoring: Follow-up imaging to assess resolution. 1. Pregnancy-Associated VTE: Higher risk during pregnancy and postpartum period. 2. Cancer-Associated Thrombosis: Requires specific management approaches. 3. Recurrent VTE Management: Long-term anticoagulation strategies. 4. Upper Extremity DVT: Less common but requires similar diagnostic approach. 5. Post-thrombotic Syndrome: Long-term complication of DVT due to venous valve damage.

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Below is information not explicitly contained within the tutorial but important for USMLE Step 2 CK & COMLEX Level 2. 1. Anticoagulation Selection: Direct oral anticoagulants (DOACs) vs. warfarin vs. low molecular weight heparin based on patient factors. 2. Thrombolytic Therapy: Specific indications, contraindications, and administration protocols. 3. Inferior Vena Cava Filters: Indications, placement considerations, and complications. 4. Extended Anticoagulation: Decision-making for duration based on risk factors and recurrence risk. 5. Managing Anticoagulation Complications: Approaching bleeding events in anticoagulated patients. 1. Pregnancy: Anticoagulation selection and monitoring during pregnancy and postpartum. 2. Renal Impairment: Dose adjustments and monitoring for anticoagulants. 3. Malignancy: Cancer-associated thrombosis management strategies. 4. Elderly: Balancing bleeding and thrombotic risks in older patients. 5. Thrombophilia: Management approaches for inherited hypercoagulable states. 1. Central Line-Associated DVT Prevention: Techniques to reduce catheter-associated thrombosis. 2. Thrombolytic Administration: Proper protocols for systemic and catheter-directed thrombolysis. 3. Ultrasonography Technique: Compression ultrasound approach for DVT diagnosis. 4. Arterial Blood Gas Interpretation: Recognizing PE-associated changes. 5. Post-PE Functional Assessment: Exercise testing and functional capacity evaluation. 1. VTE Prophylaxis Protocols: Institutional approaches to prevent hospital-acquired VTE. 2. Care Transitions: Anticoagulation management across inpatient and outpatient settings. 3. Quality Metrics: Hospital-acquired VTE rates as healthcare quality indicator. 4. Cost-Effective Diagnostic Strategies: Using clinical decision rules to guide testing. 5. Patient Education Programs: Improving compliance with prevention and treatment. 1. Risk-Adapted Treatment Duration: Individualizing anticoagulation duration based on risk assessment. 2. Subsegmental PE Management: Controversial approaches to small peripheral emboli. 3. Post-PE Syndrome: Chronic complications following PE similar to post-thrombotic syndrome. 4. Catheter-Directed Interventions: Advanced approaches for massive and submassive PE. 5. Outpatient Management: Selection criteria for ambulatory treatment of PE and DVT.