Pulmonary Embolism (PE) Flashcards
What is venous thromboembolism?
Venous thromboembolism (VTE) is a term used to describe both deep vein thrombosis (DVT) and pulmonary embolism (PE)- disorders caused by thrombus formation.
Briefly describe Virchow’s triad
The formation of a thrombus in a patient is dependent on any one of Virchow’s Triad being present:
- Abnormal blood flow-usually due to recent immobility, such as a long-distance flight or being bed-bound in hospital
- This is the most common underlying cause of a DVT
- Abnormal blood components- can be caused by multiple factors, such as smoking, sepsis, malignancy, or even inherited blood disorders (e.g. Factor V Leiden)
- Abnormal vessel wall- can be from atheroma formation, inflammatory response, or direct trauma
What are the risk factors for VTE?
The main risk factors for developing a venous thromboembolism include:
- Increasing age
- Previous VTE
- Smoking
- Pregnancy or recently post-partum
- Recent surgery (especially abdominal surgery, pelvic surgery, or hip or knee replacements)
- Prolonged immobility (> 3 days)
- Hormone replacement therapy or the combined oral contraceptive pill
- Current active malignancy
- Obesity
- Known thrombophilia disorder (e.g. antiphospholipid syndrome or Factor V Leidin)
What are thrombophilias? And give examples
Thrombophilias are conditions that predispose patients to develop blood clots. There are a large number of these:
- Antiphospholipid syndrome (this is the one to remember for your exams)
- Antithrombin deficiency
- Protein C or S deficiency
- Factor V Leiden
What is a pulmonary embolism (PE)?
A pulmonary embolism (PE) refers to a blockage of the pulmonary artery by a substance that has travelled there in the bloodstream.
Give examples of causes of PE
Most commonly, this blockage is a thrombosis that has broken off and migrated (such as from a DVT).
Other causes include a right-sided mural thrombus (e.g. post-MI), atrial fibrillation (AF), neoplastic cells, or from fat cells (e.g. following tibial fracture).
How does a PE present?
The key clinical features of a PE are sudden onset dyspnoea, pleuritic chest pain, cough, or (rarely) haemoptysis.
Clinically, a patient may have tachycardia, tachypnoea, pyrexia, a raised JVP (rare), or pleural rub or pleural effusion (rare). Remember to examine for any signs of DVT in any patient with suspected PE.
What parameters are assessed when investigating Well’s Score for PE?
- Clinical signs and symptoms of DVT (minimum of leg swelling and pain with palpation of the deep veins)
- An alternative diagnosis is less likely than PE
- Heart rate more than 100 beats per minute
- Immobilisation for more than 3 days or surgery in previous 4 weeks
- Previous DVT/PE
- Haemoptysis
- Malignancy (on treatment, treated in the last 6 months, or palliative)
How does a Wells score dictate further investigations?
If pulmonary embolism is suspected in a patient, the PE Wells’ Score should be calculated:
- Score less than or equal to 4: PE clinically unlikely, requires a further D-dimer test to exclude
- Score greater than 4: PE clinically likely and a PE diagnosis should be confirmed with a CT Pulmonary Angiography (CTPA) scan (or V/Q scan in those with poor renal function).
What are other causes of raised D-dimers?
A D-dimer test is sensitive but not specific; a D-dimer may also be raised following recent surgery or trauma, with ongoing infection or inflammation, concurrent liver disease, or pregnancy, and indeed in any patient with a prolonged hospital stay.
What tests are used to diagnose PE?
Pulmonary embolism can be diagnosed with a CT pulmonary angiogram or ventilation–perfusion (VQ) scan.
How may a PE present on and ECG?
Less commonly, a PE may present on ECG with a:
- Right bundle branch block (RBBB)
- RV strain (inverted T waves in V1-V4 and / or leads AvF-III)
- Rare S1Q3T3 (deep S wave in Lead I, pathological Q wave in Lead III, and inverted T wave in Lead III)
Briefly describe CT pulmonary angiogram (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.
Briefly describe ventilation-perfusion (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.
How does a PE present on an ABG?
Patients with a pulmonary embolism often have a respiratory alkalosis when an ABG is performed.
