Pulmonary embolus is defined as a condition in which a foreign material travels to the lung blood vessels and lodges there. In a vast majority of cases, the material is a blood clot (thrombus) that originates in the deep leg veins (DVT). The blood clot travels through the circulatory system to the lungs where it lodges in the pulmonary arteries. This is referred to as pulmonary thromboembolism, or PE. There are estimated to be 150,000 cases diagnosed each year.
While the extent and amount of clot blockage of the pulmonary arteries may vary, PE generally leads to inadequate transfer of oxygen to the blood and sudden loss of cardiac output. Furthermore, although pulmonary embolism is usually secondary to blot clots, other causes of embolism include:
- Air – usually introduced during removal of a indwelling vascular catheter.
- Fat – originating from bone marrow following fractures, or after liposuction.
- Rare cases of cancer.
- Amniotic fluid following delivery.
- Foreign body migration, for example vascular stents.
Presentation
The presentation of pulmonary embolism may be obvious or may be subtle. It is often asymptomatic (30%+), however signs and symptoms of PE include:
- Dyspnea, or shortness of breath, during activity or during exercise (acute).
- Hemoptysis (coughing blood).
- Chest pain during breathing (pleurisy).
- Leg swelling and calf pain.
- Sudden collapse and shock.
- Sudden unexpected cardiac arrest and or death.
- Incidental Post mortem findings.
Diagnosis
The diagnosis of pulmonary embolism requires a high degree of clinical suspicion based on history and presenting complaints.
- Examination – tachypnea (rapid breathing), DVT, lung findings.
- Low oxy-hemoglobin saturation or Aa gradient. These measurements indicate inefficient oxygen transfer due to blocked pulmonary arteries, but may be seen in many other conditions affecting the lungs and / or the heart.
- EKG changes – These are usually subtle, unless the pulmonary embolus is extensive and strains the heart.
- Blood tests – d dimer, troponin (sensitive but not specific).
- Pulmonary angiogram (negative predictive value 99%). Pulmonary angiogram is now the test of choice when pulmonary embolus is suspected.
- Doppler ultrasound (for DVT) – This is easily performed in the emergency room, but requires training for accurate interpretation.
- Ventilation Perfusion scans. These are less popular now, and more difficult to interpret, but they are indicated in some situations where the administration of dye is contraindicated.
Several diagnosis scoring systems have been developed to measure the likelihood of PE and help physicians order testing appropriately. The Wells composite score is the best for ED and hospital settings.
Wells Score – Scores greater than 6 indicate a high probability of PE
- Symptoms of DVT (3pts).
- No alternative diagnosis better explains the illness (3pts).
- Tachycardia pulse >100/min (1.5 points).
- Immobilization (> 3days) or surgery in the previous 4 weeks (1.5pts).
- Prior history of DVT or PE (1.5pts).
- Hemoptysis (1.5pts).
- Presence of malignancy (1.5pts).
After clinical evaluation, D-dimer testing in combination with probability scores can guide further diagnostic testing. The sensitive D-dimer blood test measures a small protein released after the blood clots:
- For patients in whom PE is unlikely and the D-dimer level is <500 ng/mL, no further testing is required.
- For patients in whom PE is unlikely and the D-dimer is ≥500 ng/mL, diagnostic imaging should be performed.
- A normal D-dimer is not sufficient to confirm or exclude a PE.
However, in practice the diagnosis can still be difficult. Pulmonary embolus is confirmed on only 10-20% of patients in whom the diagnosis is suspected. The initial clinical impression by physicians has a sensitivity of 85%, but a specificity of only 50%. Diagnostic studies are not perfect:
- False negative ventilation perfusion scans – these studies will not pick up small emboli.
- False positive CT angiograms – usually occurs with inexperienced readers and or with poor quality studies.
- Other common diagnoses in a patient complaining of shortness of breath include heart failure, pulmonary diseases and anxiety.
Predispositions to pulmonary embolus include:
- DVT – may be silent or present with leg swelling and pain. Common after hip and knee surgery.
- Chronic illness e.g. heart disease, lung disease, or cancer. Associated with immobility.
- Pregnancy, oral contraceptives.
- Post-operative – associated with immobility and/or inadequate ineffective DVT prophylaxis.
- Cancer – especially involving the GI tract and prostate.
- Medications – some plasma protein derivatives.
- Inactivity –couch potato syndrome, prolonged airline or car travel.
- Inherited abnormalities of clotting e.g. Factor V Leiden, anti-thrombin III deficiency. Work up for these conditions may be undertaken in those without a known predisposition to DVT or PE.
Treatment
Advantages – reduces the risk of recurrent pulmonary embolus by preventing clot extension. Disadvantages – increases the risk of major bleeding.
- Acute blood thinning.
- Weight based IV heparin.
- Weight based twice daily low molecular weight heparin (enoxaparin).
- Oral rivaroxaban.
- Fibrinolysis – e.g. IV tissue plasminogen activator –indicated in life threatening massive pulmonary embolism with shock but is contraindicated where the risk of bleeding is very high.
- Chronic blood thinning – e.g. warfarin, rivaroxaban. Usually treatment is for 3 months in unprovoked DVT/PE
- Surgical or catheter embolectomy in massive life-threatening pulmonary embolism.
Prevention
- Early mobilization and / or rehabilitation, especially after surgery.
- Sequential compression device – second line therapy when blood thinners are contraindicated.
- Low dose or unfractionated heparin – daily. Adjust dose depending on PE risk. May require continuation following discharge.
- IVC filters are devices deployed into the inferior vena cava and designed to prevent clots travelling from leg veins to the pulmonary vessels. Their use is controversial, but may be indicated in certain circumstances such as extensive DVT and / or absolute contraindication to anticoagulants. Complications include filter migration and chronic leg swelling. Pulmonary embolism may still occur.
Prognosis
- Underlying condition (especially heart disease and cancer). Pulmonary embolus may be a presenting sign of poor prognosis.
- Extent of clot- more clot in the veins and pulmonary arteries the more complications such as post-phlebitic syndrome a condition of chronic leg swelling, pain and ulceration. Chronic thromboembolic pulmonary hypertension leads to heart failure and occurs rarely after pulmonary embolus.
- Massive versus Sub-massive- defined by the presence or absence of shock. High risk of death in massive PE (at least 15%). The pulmonary CT angiogram in massive and sub-massive PE may show blood clot blocking both major pulmonary arteries (‘the saddle’ embolus)
Special Situations
- Orthopedic surgery – prophylaxis may be continued after certain types of surgery.
- Neuro-surgery – routine anticoagulation may be contraindicated in certain circumstances.
- Obstetrics and Gynecology – special considerations for diagnosis and treatment. Requires a coordinated team approach.
Litigation
Cases are filed when there is an unexpected and devastating adverse event, Often following routine medical management. The basis for asserting a failure to provide an expected standard of care in my experience falls into three main categories.
Failure to Diagnose
- Transient symptoms such a dizziness, shortness of breath with full recovery.
- Non-specific symptoms – such as uncharacteristic chest pain, feeling faint.
- Occurs without leg swelling – DVT may be silent.
- Failure to obtain a history of symptoms pointing to the possibility.
- Failure to appreciate underlying risk factors for thromboembolism.
- Difficulties in differentiating other causes of symptoms e.g. heart disease, lung disease.
Failure to prevent
- Unclear or absent documentation of the relative or absolute contra-indication to anticoagulation.
- Poor compliance with hospital or published guidelines.
- Poor patient compliance due to lack of communication and understanding.
- Risk factors for PE/DVT are underestimated or not recognized.
Failure to treat and manage complications adequately
- Guidelines not followed resulting in inadequate dosing or time of treatment.
- Transition from IV or injectable heparin to oral agents.
- Inadequate monitoring of warfarin with either over or under treatment.
In summary Pulmonary embolus is a common condition and its diagnosis and management provides diagnostic and therapeutic challenges for physicians.
