Pulmonary thromboembolism is a clinically significant obstruction of a part or the whole of the pulmonary arterial tree usually by thrombus that becomes detached from its sites of formation outside the lung.
The emboli is swept downstream until it is arrested at points of intrapulmonary vascular narrowing.
Predisposing factors for pulmonary thromboembolism
The virchow’s triad:
- Relative venous statis
- Injury to the wall of a vein
- Increased coagulability of blood itself.
Pulmonary thromboembolism most
commonly results from deep vein thrombosis (a blood clot in the deep veins of the legs or pelvis) that breaks off and migrate to the lung – i.e. Venous thromboembolism (VTE).
Sources of non-thrombotic emboli: Air, fat, amniotic fluid, bone marrow.
Factors that contribute to venous thromboembolism
- Heart disease
- Oestrogen therapy
Other risk factors include: obesity, chronic bronchitis, emphysema, diabetes mellitus, homocyteinuria and polycythaemia.
Massive pulmonary thromboembolism is a medical emergency.
Symptoms and clinical features of pulmonary thromboembolism
- Sudden onset of breathlessness
- Chest pain
- Sudden death.
Signs of pulmonary thromboembolism
- Varying degrees of dyspnea
- Pleuritic pain on inspiration
- Pleural rub
- Gallop rhythm
- Accentuated pulmonary component of the second heart sound.
- Jugular venous engorgement
- Clinical signs of deep venous thrombosis (DVT)
- Acute coronary syndrome
- Acute respiratory distress syndrome.
- Anxiety disorder
- Atrial fibrillation
- Cardiogenic shock
- Pulmonary hypertension
- CT pulmonary angiography
- Ventilation / perfusion scan
- Chest x-ray.
- Arterial blood gases.
- D-dimer level
Pulmonary embolism can be predicted using the wells score.
- Clinically suspected DVT-3.0 points
- Alternative diagnosis is less likely than P.E – 3 points
- Tachycardia (H.R > 100) – 1.5 points
- Immobilization ≥ 3days or surgery in previous four weeks – 1.5 points
- History of DVT – 1.5 points
- Hemoptysis – 1.0 points.
- Malignancy (with treatment within 6 months) or palliative – 1.0 points
- Score > 6 – High (probability 59% based on pooled data)
- Score 2.0 to 6.0 moderate (probability 29% based on pooled data).
- Score < 2.0 – Low (probability 15% based on pooled data).
- Score > 4 – PE likely
- Score 4 or less – PE unlikely
Complications of pulmonary thromboembolism
- Sudden cardiac death.
- Obstructive shock
- Pulseless electrical activity
- Atrial or ventricular arrhythmias
- Severe hypoxemia
- Paradoxical embolism
- Enoxaparin (LMWH e.g. lovenox)
1mg/kg SC q12hr or 1.5mg/kg SC qDay
- Warfarin (e.g. Coumadin, Jantoven)
initial dose: 2-5mg PO qDay (overlap warfarin and parenteral anticoagulant for at least 5days then discontinue parenteral therapy)
- The INR is maintained 2.0-3.0
- Side effect is spontaneous bleeding
2. Thrombolysis-with fibrinolytic therapy
- Streptokinase rarely used because of anaphylaxis
- Alteplase (e.g. Activase, TPA,) 100mg iv infused over 2 hours; 10mg bolus followed by 90mg over 2hr followed
immediately with heparin therapy when PTT returns to < 2 times normal.
- Side effects is spontaneous bleeding.
3. Inferior vena cava filters
- Used when anticoagulant therapy is contraindicated
- Pulmonary embolectomy
5. Prophylaxis for pulmonary embolism
- Low-dose heparin e.g. levonox 40mg SC qDay
- Antiplatelets e.g. Asprin 75- 81mg PO every day
Notable adverse drug reactions, caution and contraindications
- Thrombocytopaenia and haemorrhage
- Pathologic fractures
- May cause hyperkalaemia (inhibition of aldosterone secretion)
- Contraindicated after recent surgery or trauma, in haemophilia and other bleeding disorders, peptic ulcer, severe liver disease, acute bacterial endocarditis
- May cause hyperkalemia (inhibition of aldosterone secretion)
- Skin necrosis
- Avoid during pregnancy
- Recombinant tissue plasminogen activator
- Intracranial haemorrhage
How to Prevent pulmonary thromboembolism
- Prophylactic warfarin or heparin in patients at risk.
- Inferior vena cava filters, when
anticoagulation cannot be undertaken because of active bleeding.