Pulmonary Embolism

Pathogenesis:

• Most emboli -> proximal DVT of lower extremities above the knee (MC: ileofemoral DVT)
• DVT dislodges -> vena cava -> right heart -> pulmonary circulation -> obstruct part of the pulmonary artery -> ↑ alveolar dead space (hypoxemia + hypercarbia -> tachypnea) -> vascular constriction -> pulmonary hypertension
• When 50% of lung vasculature is involved -> ↑ RV workload -> right-sided HF
• Massive PE: when > 2\3 of one lung is involved

 

High risk:

• Age (>60), obesity
• Recent surgery (esp orthopedic)
• Cancer history
• Immobile pts (esp hospitalized), travelling
• Acquired thrombophilia: lupus anticoagulant, nephrotic (loss of antithrombin III), oral contraceptives
• Inherited thrombophilia: factor V Leiden mutation, protein C and S def, antithrombin III def
• Pregnancy: risk continues until 2 months after delivery

 

Clinical presentation:

• Sudden onset of dyspnea and tachypnea
• Cough
• Pleuritic chest pain
• Hemoptysis (only w\ infarction; rare bc of lung’s dual circulation ‘bronchial + pulmonary’)
• Thigh or calf swelling
• Syncope in large PE
• PE: rales tachycardia, S₄, shock in massive PE, low-grade fever, ↓ BS, dull percussion

 

 Investigations:

» If high clinical suspicion -> start anti-coagulant (don’t wait for test results)

ABG: hypoxemia, ↑ A-a gradient, respiratory alkalosis

D-dimer: most sensitive for thromboembolic ds. Useful as an adjunct test in a low-risk pts. Little value if pretest probability is high

CXR:

• Normal, atelectasis, pleural effusion, hemi diaphragm elevation
• Westermark sign: lack of vascular markings (oligemia) distal to PE
• Hampton bump: wedge-shaped infiltrate due to pulmonary infarct

CT angio: initial test for PE

• Positive -> 100% treat PE
• Negative -> consider peripheral PE

Pulmonary angiogram: gold standard -> filling defect

• Negative angiogram excludes clinically relevant PE

Duplex US: for DVT

V\Q scan: in PE; perfusion defect w\ normal ventilation.

• Normal -> rule out PE
• High-probability -> treat w\ heparin
• Low\intermediate-probability -> go with the clinical suspicion
• Low clinical suspicion -> rule out PE
• High clinical suspicion -> do duplex US
• Positive duplex -> treat DVT (same as PE)
• Negative\uncertain duplex -> do pulmonary angio

  

ECG: most commonly sinus tachycardia, or evidence of right heart strain (due to pulmonary HTN) -> large S wave in lead I,  deep Q wave in lead III, T wave inversion in lead III “S₁, Q_3, T₃”

 

 

Treatment:

» Heparin (LMWH or unfractionated) + warfarin for 5-7 days (or until therapeutic INR) -> then continue on warfarin for 6 mo

• A pt w\ recurrent PE or DVT despite heparin treatment? Consider Heparin-induced thrombocytopenia (which, paradoxically, is associated with thromboembolic events after giving heparin for 5-7 days) (occurs in both unfractionated and LWMH ‘but less’)
• What to do? Monitor plt while on heparin and stop it if plt ↓ by < 50% -> give new anti-coagulants (Argatroban or Lepirudin)
• In pts w\ preexisting protein C deficiency -> warfarin skin necrosis (bc protein C has a shorter half-life than factors 1972 -> “transient hypercoagulable state”

 

• Contraindication: eye\neurosurgery -> use IVC filter (placed below the renal veins to prevent renal V thrombosis)

 

» If massive PE: defined as hemodynamically unstable by either:

1. Hypotension (systolic <90)
2. A drop in BP > 40 mmHg persisting for > 15 mins

• Treatment: give thrombolytics (tPA, streptokinase)

 

» Intermediate PE: defined as hemodynamically stable + either or both of:

1. Right heart strain by echo
2. Positive cardiac enzymes

 

• To prevent chronic swelling w\ DVT (post-thrombotic \postphlebitic syndrome)? Compression stockings
• Fat embolism (3 days after long bone fracture; acute dyspnea, petchiae in neck + axilla, confusion) -> supportive treatment (no anticoagulation)
• Duration of treatment: minimum of 3 mo -> then asses risk of bleeding -> if none; continue for another 3 mo
• The risk of recurrence if unprovoked: in 1 yr is 10%, in 5 yrs is 30%, in 10 yrs is 50%

 

 

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Download the PDF version: here

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References:

• Toronto notes
• The Johns Hopkins Internal Medicine Board Review
• Master the boards
• Step up to medicine