Pulmonary Embolism (also known as pulmonary embolus) is most commonly a complication of venous thromboembolism from another source – e.g. a clot in the legs or pelvis (a DVT) that becomes dislodged, flows via the bloodstream through the right side of the heart and gets lodged in the pulmonary circulation.
It is not always a clot that causes a pulmonary embolism! Fat, air, amniotic fluid can all also be causes. For fat and amniotic fluid, these will normally resolve themselves with supportive care. Air is often an iatrogenic cause.
- <5% if no haemodynamic instability
- 30% if shock present
- 70% with cardiac arrest (in hospital)
- Varicose veins
- Bed rest >24 hours
- Immobility >48 hours
- POP – plaster of Paris over limb
- Pregnancy (oestrogen) – risk is highest in the 4 week after birth
- Previous DVT / embolism
- Antithrombin deficiency
- Protein C deficiency
- Oestrogen therapy (Pill, HRT) – note only the combined pill, not the progesterone only pill – only a small risk factor.
- Surgery – especially pelvic and orthopaedic
- Recent MI (10% of MI patients will have a DVT)
- Congestive heart failure
- Inherited clotting deficiencies – thrombophilia – factor V Leiden
- Tachypnoea – 90% of patients have RR >16
- Tachycardia – 45% of patients
- Hypotension – 25% of patients
- Raised JVP
- Pleural rub
- Pleural effusion
- Look for signs that could indicate a cause – e.g. DVT, recent surgery, air travel – only 33% of patient have clinical evidence of DVT
- Pleuritic chest pain (pain worse on inspiration) – 75% of patients
- Breathlessness – 85% of patients
- Cough – 50% of patients
- Haemoptysis – as a result of pulmonary infarct – 30% of patients
- Dizziness / syncope – 15% of patients
- Syncope (loss of consciousness/fainting) – 15% of patients
- Non-pleuritic chest pain – 15% of patients
Probably the most important question is should I investigate?
Defining risk of the probability of PE is important. There are two tools to help with this:
PERC stands for Pulmonary Embolism Rule-out Criteria.The PERC score is useful to rule out PE in low risk patients. If the patient’s score = 0, then there is a <2% chance of PE, and in the absence of convincing clinical signs, you can usually safely exclude PE as a differential.
Each factor below gives a score of 1. All factors must be negative for a negative PERC score. Any positive factor results in the need for further work up (move onto the Well’s Score)
- Age >50
- HR >100
- SaO2 on room air <95%
- Unilateral leg swelling
- Recent surgery or trauma
- Previous PE or DVT
- Exogenous Oestrogen – oral contraceptives, hormone resplacement or other oestrogen hormones
Well’s score for PE
This can stratify patients as low or high risk. In high risk patients, you should proceed straight to imaging. In low risk patient, you should consider a D-dimer test.
|Clinically suspected DVT||3|
|PE is most likely diagnosis||3|
|Immobilisation >3 days OR surgery – in previous 4 weeks||1.5|
|History of DVT or PE in past||1.5|
Interpretation of Well’s Score
- Score >6.0 — High (probability 59%)
- Score 2.0 to 6.0 — Moderate (probability 29%)
- Score <2.0 — Low (probability 15%)
- Score > 4 — PE likely. Consider diagnostic imaging.
- Score 4 or less — PE unlikely. Consider D-dimer to rule out PE.
D-Dimer is a fibrin degradation product – and as such, levels are raised by the presence of a blood clot in the circulation. A D-Dimer blood test can be useful to rule out PE or DVT as a differential. A negative D-Dimer means that PE or DVT is extremely unlikely. However, many factors can cause a positive D-Dimer – so having a raised D-Dimer does not necessarily mean there is a clot.
In reality it can be a tricky test to use. Even just a recent common cold can result in a raised D-Dimer! Almost any factor that causes inflammation will also result in a raised D-Dimer. Do be selective. Even if your patient has a low risk Well’s score, doing a D-Dimer might not always be practical – for example if they have recently had cellulitis or some other infection.
D-Dimer also rises with age. Other factors that caused an increased D-Dimer include liver disease, high rheumatoid factor, malignancy, trauma, pregnancy and recent surgery.
Will often be normal. The main reason CXR is performed is to exclude other causes.
- S waves present in lead I
- Q waves present in lead III
- T wave inversion in lead III
- Don’t do a VQ scan if there is an abnormal x-ray – it is a waste of time! Because the abnormalities on the x-ray are likely to cause abnormalities on VQ, and as PE doesn’t cause x-ray abnormalities, then x-ray and VQ abnormalities in these patients are likely to be unrelated to PE. Send them straight for CTPA. So VQ is for someone who has been previously well, and not for those with chronic disease
- O2 may often be low
- CO2 may often be normal or low
Troponin is raised in 20-40% of patients with PE as a result of the extras stress and stretch placed on the right ventricle in PE patients (due to increased pulmonary arterial pressure).
Higher troponin has been associated with a worse prognosis.
Is used to look for right ventricle strain and dilatation in patients with suspected massive PE. The degree of RV dysfunction can be used as a predictor of death.
- Anticoagulate with LMWH – e.g. dalteparin 200u/Kg/24hrs. The max dose is 18,000.
- At the same time start oral warfarin 10mg
- Stop the heparin when the INR is >2, and continue warfarin for a minimum of 3 months, aiming for an INR of 2-3.
- You can place a vena cava filter in patients who continue to develop thrombi despite anticoagulation – but remember that implanting a filter without adequate anticoagulation will increase the risk of thrombus.
- Thrombolysis may be used if the PE is deemed ‘Massive’ – 50mg alteplase – as long as no contraindications
- At the very minimum – 6 weeks
- Those with an identifiable and reversible risk factor – 3 months
- Those with idiopathic disease – 6 months
- There is also evidence that low-intensity warfarin (INR 1.5-2.0) not only reduces the risk of thromboembolism, but also has a low risk of bleeding.
- They will often travel to the brain, and cause a stroke.