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Updated: Dec 24 2024

Pulmonary Embolism

Images
https://upload.medbullets.com/topic/120673/images/pe.jpg
  • Snapshot
    • A 36-year-old woman presents to the emergency department with worsening shortness of breath and pleuritic chest pain. She recently returned to the United States from a business meeting overseas. She takes an oral contraceptive. Her temperature is 98.6°F (37°C), blood pressure is 135/82 mmHg, pulse is 112/min, respirations are 24/min, and oxygen saturation is 89% on room air. A CT angiogram demonstrates a filling defect in the pulmonary vasculature. She is started on supplemental oxygen and heparin.
  • Summary
    • Pulmonary embolism is mechanical obstruction of the pulmonary vasculature secondary to a blood clot
      • it is a common cause of chest pain and dyspnea in the general population
    • Diagnosis is made
      • with a CTA of the chest (preferred in most patients)
      • with a V/Q scan in patients who cannot undergo a CTA of the chest
      • with angiography (most accurate test but rarely used)
    • Treatment is usually
      • Blood thinners in stable patients (heparin, enoxaparin, warfarin, apixaban, etc.)
      • Thrombolytics (in hemodynamically unstable/peri-arrest patients)
      • Mechanical thrombectomy (for massive/submassive PEs and in patients with unstable hemodynamics
  • Epidemiology
    • Risk factors
      • prolonged immobilization
      • malignancy
      • thrombophilia / hypercoagulability (factor V Leiden, antithrombin III deficiency, protein C/S deficiency)
      • high estrogen states (pregnancy, hormonal contraceptives, obesity)
      • autoimmune conditions (lupus)
      • nephrotic syndrome (including HIV which can cause a nephrotic syndrome)
      • trauma
      • smoking
  • Etiology
    • DVT (most common)
      • from the veins of the proximal thigh (iliac, femoral, or popliteal)
    • Phlegmasia cerulea dolens
      • a progression from a DVT
      • massive thrombus that can embolize from the proximal ileofemoral vein
      • enlarged, blue, and tender lower extremity
    • Septic embolism from right-heart endocarditis
    • Fat embolism
    • Amniotic fluid embolism
    • Cement embolism from kyphoplasty
    • Pathophysiology
      • occlusion of the pulmonary vasculature commonly from a dislodge DVT results in hypoxemia and subsequent pulmonary vasoconstriction
        • the increased pulmonary constriction causes an increase in pulmonary vascular resistance, which decreases right ventricular stroke volume leading to 
          • increased ventricular oxygen demand
          • right ventricular dilatation
          • decreased left ventricular preload
          • poor blood flow to the lung, leading to a ventilation-perfusion mismatch
      • hypoxemia leads to compensatory tachypnea, hyperventilation, and a respiratory alkalosis
  • Presentation
    • Symptoms
      • dysnea (most common)
      • chest pain
      • palpitations
      • hemoptysis
      • extremity swelling (suggestive of DVT)
      • syncope in cases of a large PE
    • Physical exam
      • tachypnea
      • tachycardia
      • loud P2
      • findings of DVT
      • fever
      • hemodynamic instability and syncope in cases of a large PE
  • Imaging
    • CT angiography of the chest
      • indication
        • most appropriate confirmatory test
        • indicated if moderate/high risk via Wells' score or if D-dimer is positive
    • Chest radiography (typically normal and neither sensitive nor specific)
      • pleural effusions
      • Hampton hump (wedged-shaped infarct)
      • Westermark sign (avascularity distal to the PE)
    • V/Q scan
      • indication
        • performed if patient cannot undergo a CT angiogram
      • interpretation (not a specific test)
        • normal = rules out PE
        • high-probability with a positive V/Q scan = treat with blood thinners
        • low or intermediate probability = consider angiography vs empiric treatment
    • Venous duplex ultrasound of the lower extremities
      • indication
        • to evaluate if there are DVTs (if positive, can start anticoagulation)
        • useful in pregnancy to avoid radiation exposure
    • Echocardiography
      • larger PEs may cause right ventricular dysfunction and dilatation
  • Studies
    • ECG
      • findings
        • sinus tachycardia (most common) 
        • tachydysrhythmias
        • right ventricular strain
        • S1Q3T3 (neither sensitive nor specific)
          • presence of S wave in lead I and Q wave and inverted T wave in lead III
        • T-wave inversions in V1-V4
    • Arterial blood gas 
      • findings
        • hypoxemia
        • hypocapnia
        • respiratory alkalosis
        • alveolar-arterial gradient may be elevated
    • D-dimer
      • has a high sensitivity but poor specificity for PE
        • used to rule-out PE if there is a low pre-test probability via Wells' score
          • a positive D-dimer in a low risk patient must be followed by a confirmatory study (CTA chest)
  • Differential
    • Acute coronary syndrome
      • differentiating factors
        • ST elevation in a vascular distribution in a STEMI
        • troponin elevation in STEMI or NSTEMI (but can also be elevated in PE)
    • Costochondritis
      • differentiating factors
        • pain with palpation or movement of the arms
    • Aortic dissection
      • differentiating factors
        • sudden tearing pain that radiates to the chest, back, and/or abdomen
        • CTA can differentiate between these diagnoses
  • Treatment
    • Medical
      • anticoagulation
        • indication
          • initial therapy in patients with PE in order to prevent further clot formation
        • medication options (best initial step in high risk patient with obvious PE)
          • low-molecular weight heparin
            • avoid in renal failure
          • unfractionated heparin
            • dose by monitoring aPTT
            • preferred in kidney injury/failure
          • direct Xa inhibitors (apixaban, rivaroxaban)
            • easy dosing, no need to monitor INR
        • warfarin
          • must monitor INR and ensure stable vitamin K consumption (diets high in vegetables may alter INR)
          • typically need to bridge to warfarin until INR is therapeutic (goal = 2-3)
      • thrombolytic therapy
        • indication
          • performed in patients with PE who are hemodynamically unstable or in cardiac arrest from a PE
    • Operative
      • embolectomy
        • indication
          • performed in patients with massive/sub-massive PE
      • IVC filter
        • indication
          • performed in patients with PE who have a contraindication or failure of anticoagulation
  • Prognosis
    • High mortality without treatment
    • PERC - if meet all criteria in a low-risk patient can avoid further workup for PE
      • Age < 50 years
      • Heart rate < 100/min
      • Oxygen saturation 95% or greater on room air
      • Absence of hemoptysis
      • No recent trauma or surgery
      • No history of thromboembolism
      • No signs or symptoms of DVT
      • No estrogen use or medications that cause hypercoagulability
    • Wells Criteria
      • used to assess for risk of pulmonary embolism
        • signs and symptoms of DVT +3
        • pulmonary embolism (PE) is the most likely diagnosis +3
        • pulse is 100/min or greater +1.5
        • surgery within the past 4 weeks or immobilization for the past 3 days + 1.5
        • previously diagnosed PE or DVT + 1.5
        • hemoptysis +1
        • malignancy with treatment in the past 6 months
      • < 2 points
        • low risk
        • consider using D-dimer
      • 2-6 points
        • moderate risk
        • consider D-dimer or CTA
      • > 6 points
        • high risk
        • imaging required
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