Pulmonary Embolism Flashcards
What is PE?
Pulmonary embolism (PE) is a condition where a blood clot (thrombus) forms in the pulmonary arteries. This is usually the result of a deep vein thrombosis (DVT) that developed in the legs and travelled (embolised) through the venous system and the right side of the heart to the pulmonary arteries in the lungs. Once they are in the pulmonary arteries they block the blood flow to the lung tissue and create strain on the right side of the heart. DVTs and PEs are collectively known as venous thromboembolism (VTE).
What are the risk factors for PE?
There are a number of factors for developing a DVT or PE.
- Immobility
- Recent surgery
- Long haul flights
- Pregnancy
- Hormone therapy with oestrogen
- Malignancy
- Polycythaemia
- Systemic lupus erythematosus
- Thrombophilia
What can be used to reduce the risk of PE?
Prophylactic treatment with low molecular weight heparin to reduce the risk.
VTE prophylaxis
Every patient admitted to hospital should be assessed for their risk of venous thromboembolism (VTE). If they at increased risk of VTE they should receive prophylaxis with a low molecular weight heparin such as enoxaparin unless contraindicated.
Also anti-embolic compression stockings.
Contraindications of VTE?
Contraindications include active bleeding or existing anticoagulation with warfarin or a NOAC. Anti-embolic compression stockings are also used unless contraindicated. The main contraindication for compression stockings is significant peripheral arterial disease.
What is the presentation of PE?
Presenting features include:
- Shortness of breath
- Cough with or without blood (haemoptysis)
- Pleuritic chest pain
- Hypoxia
- Tachycardia
- Raised respiratory rate
- Low grade fever
- Haemodynamic instability causing hypotension
There may also be signs and symptoms of a deep vein thrombosis such as unilateral leg swelling and tenderness.
Wells score
The Wells score predicts the risk of a patient presenting with symptoms actually having a DVT or pulmonary embolism. It takes in to account risk factors such as recent surgery and clinical findings such as tachycardia (heart rate >100) and haemoptysis.
Diagnosis of PE
NICE recommend assessing for alternative causes with a:
History
Examination
Chest xray
Perform a Wells score and proceed based on the outcome:
Likely: perform a CT pulmonary angiogram
Unlikely: perform a d-dimer and if positive perform a CTPA
What are the 2 main methods of establishing a definitive diagnosis of PE?
CT pulmonary angiogram or ventilation–perfusion (VQ) scan.
CTPA
CT pulmonary angiogram (CTPA) involves a chest CT scan with an intravenous contrast that highlights the pulmonary arteries to demonstrate any blood clots. This is usually the first choice for investigating a pulmonary embolism as it tends to be more readily available, provides a more definitive assessment and gives information about alternative diagnoses such as pneumonia or malignancy.
VQ Scan
Ventilation-perfusion (VQ) scan involves using radioactive isotopes and a gamma camera to compare the ventilation with the perfusion of the lungs. They are used in patients with renal impairment, contrast allergy or at risk from radiation where a CTPA is unsuitable. First, the isotopes are inhaled to fill the lungs and a picture is taken to demonstrate ventilation. Next a contrast containing isotopes is injected and a picture is taken to demonstrate perfusion. The two pictures are then compared. With a pulmonary embolism there will be a deficit in perfusion as the thrombus blocks blood flow to the lung tissue. This area of lung tissue will be ventilated but not perfused.
D-dimer test
Sensitive but not specific. Good for excluding PE. But loads of other things that can cause a raised d-dimer such as:
- Pneumonia
- Cancer
- HF
- Recent surgery
- Pregnancy
Supportive management of PE?
- Admission to hospital
- Oxygen as required
- Analgesia if required
- Adequate monitoring for any deterioration
Initial management of PE?
The initial management is with treatment dose low molecular weight heparin (LMWH). It should be started immediately before confirming the diagnosis in patients where DVT or PE is suspected and there is a delay in getting the scan. Examples are enoxaparin and dalteparin.
ABG in PE?
Patients with a pulmonary embolism often have a respiratory alkalosis when an ABG is performed. This is because the high respiratory rate causes them to “blow off” extra CO2. As a result of the low CO2, the blood becomes alkalotic. It is one of the few causes of a respiratory alkalosis, the other main cause being hyperventilation syndrome. Patients with a PE will have a low pO2 whereas patients with hyperventilation syndrome will have a high pO2.
