Pulmonary Embolism

Question 1

What is a pulmonary embolism?

Answer 1

A consequence of thrombus formation within a deep vein of the body, most frequently in the lower extremities. Approximately 51% of deep venous thrombi will embolise to the pulmonary vasculature, resulting in a PE.

Question 2

What is Virchow’s triad?

Answer 2

Triad of factors that predispose to thrombus formation in the venous system:

1. Venous stasis
2. Trauma
3. Hypercoagulability

Question 3

What are the risk factors for pulmonary embolism?

Answer 3

• Increasing age
• Diagnosis of deep vein thrombosis
• Surgery within the last 2 months
• Bed rest > 5 days
• Previous thromboembolic event
• Active malignancy
• Pregnancy
• Combined oral contraception (COCP)

Question 4

What are the symptoms of PE?

Answer 4

• Dyspnoea
• Tachypnoea
• Chest pain
• Cough and haemoptysis

Question 5

What are the signs of PE?

Answer 5

• Tachycardia
• Hypotension
• Hypoxaemia
• Signs of DVT (e.g. typically pain and swelling in one leg)

Question 6

Describe the chest pain experienced in a pulmonary embolism

Answer 6

Acute pleuritic chest pain worse on inspiration. The pain is normally localised to one side of the chest.

Question 7

What investigations should be ordered for a PE?

Answer 7

• Computed tomographic pulmonary angiography (CTPA)
• Echocardiography
• D-dimer
• FBC
• ECG
• Urea and electrolytes
• Coagulation studies
• LFTs
• VQ scan
• ABG

Question 8

What is the definitive investigation used to diagnose a PE?

Answer 8

Computed tomographic pulmonary angiography (CTPA)

Question 9

Why investigate computed tomographic pulmonary angiography (CTPA)? And what may this show?

Answer 9

• Preferred investigation for definitive confirmation of PE.
• PE is confirmed by direct visualisation of thrombus in a pulmonary artery; appears as a partial or complete intraluminal filling defect.

Question 10

Why investigate echocardiography? And what may this show?

Answer 10

• Use echocardiography for haemodynamically unstable patients who cannot have CTPA.
• The presence of any signs of right ventricular (RV) dysfunction is sufficiently suggestive of PE to confirm the diagnosis and justify urgent reperfusion treatment (usually thrombolysis).

Question 11

Why investigate D-dimer? And what may this show?

Answer 11

• Use a clinical probability score to determine whether a patient needs D-dimer testing.
  Request D-dimer testing in any haemodynamically stable patient whose Wells (or Geneva) score categorises them as ‘PE unlikely’.
• Elevated (typically >500 ng/mL).

Question 12

Why investigate FBC? And what may this show?

Answer 12

• May indicate thrombocytopenia or anaemia. These patients are at an increased risk of complications from bleeding when taking an anticoagulant.
• Baseline values.

Question 13

Why investigate ECG? And what may this show?

Answer 13

• An ECG is not diagnostic of PE but can be useful to support the diagnosis of PE or rule out other causes.
• Various presentations:
  
  • Normal sinus rhythm
  • Sinus tachycardia
  • New right bundle branch block (complete or incomplete)
  • QR pattern in V1
  • S1Q3T3 pattern
  • T wave inversion in V1-V4

Question 14

Why investigate urea and electrolytes? And what may this show?

Answer 14

• Check baseline renal function. Doses of some anticoagulants (e.g., low molecular weight heparin, fondaparinux, apixaban, rivaroxaban, dabigatran, edoxaban) may need to be adjusted in patients with renal impairment.
• Baseline values.

Question 15

Why investigate coagulation studies? What may this show?

Answer 15

• Order international normalised ratio (INR), prothrombin time (PT), and activated partial thromboplastin time (aPTT). These are needed to establish baseline values before starting anticoagulation.
• Baseline values.

Question 16

Why investigate LFTs? And what may this show?

Answer 16

• Abnormal LFTs can influence the choice of anticoagulation.
• Baseline values.

Question 17

Briefly describe the use of a ventilation-perfusion (VQ) scan

Answer 17

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.

Question 18

How does PE affect an ABG? And why?

Answer 18

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.

Question 19

What scoring system is used to identify PE?

Answer 19

Wells Score

Question 20

Briefly describe the Wells Score

Answer 20

Assessing the clinical probability of a PE:

• Clinical signs of DVT (3)
• HR >100 BPM (1.5)
• Surgery or immobilisation within 4 weeks (1.5)
• Previous PE or DVT (1.5)
• Haemoptysis (1)
• Active cancer (1)
• Alternative diagnosis less likely than PE (3)

Interpretation:

• Score >4→ immediate CTPA or treat empirically
• Score <4→ do D-dimer

Question 21

What scoring system is used to assess bleeding in PE?

Answer 21

HAS-BLED

Question 22

Briefly describe the treatment for PE

Answer 22

• Anti-coagulation
• Thrombolysis

Question 23

What anti-coagulants are used in an acute PE?

Answer 23

Start LMWH or unfractionated heparin (UFH) prior to thrombolysis. Continue anticoagulation with UFH for several hours after the end of thrombolysis before switching to apixaban or rivaroxaban.

Question 24

Briefly describe thrombolysis

When is it used?

Answer 24

Thrombolysis involves injecting a fibrinolytic medication (they break down fibrin) that rapidly dissolves clots. There is a significant risk of bleeding which can make it dangerous.

Where there is a massive PE with haemodynamic compromise there is a treatment option called thrombolysis. It is only used in patients with a massive PE where the benefits outweigh the risks.

Question 25

What drugs are used as thrombolytics in PE?

Answer 25

* Alteplase * Streptokinase * Urokinase

Question 26

If thrombolysis is contra-indicated, what are the other treatment options for PE?

Answer 26

Surgical embolectomy or percutaneous catheter-directed therapy.

Question 27

Give exampls of low-molecular weight heparins (LMWH)

Answer 27

Enoxaparin and dalteparin

Question 28

Briefly describe the long-term management of PE

Answer 28

Continue anticoagulation for at least **3 months** for all patients with PE. **DOACs** have emerged as an equally effective and safer option than heparin/warfarin.

Question 29

How long is anti-coagulation required for following a PE?

Answer 29

3 months if there is an obvious reversible cause (then review). Beyond 3 months if the cause is unclear, there is recurrent VTE or there is an irreversible underlying cause such as thrombophilia. This is often 6 months in practice. 6 months in active cancer (then review).

Question 30

What are the 2 different ways in which thrombolysis can be performed?

Answer 30

There are two ways thrombolysis can be performed: 1. Intravenously using a peripheral cannula 2. Directly into the pulmonary arteries using a central catheter (this is called catheter-directed thrombolysis)

Question 31

Briefly describe catheter-directed thrombolysis

Answer 31

In catheter-directed thrombolysis a **catheter is inserted into the venous system**, through the right side of the heart and **in to the pulmonary arteries**. The operator can then administer the thrombolytic agent directly into the location of the thrombus. Special equipment can also be used to physically break down the thrombus and aspirate it. There is a risk of damaging the pulmonary arteries doing this.

Question 32

What are the complications of PE?

Answer 32

* Acute bleeding during event * Pulmonary infarction * Cardiac arrest/ death * Recurrent venous thromboembolic event

Question 33

What differentials should be considered for PE?

Answer 33

1. Unstable angina 2. STEMI 3. NSTEMI 4. Pneumonia

Question 34

How does PE and unstable angina differ?

Answer 34

Differentiating signs and symptoms: * Typical cardiac chest pain is described as a retrosternal pressure or heaviness radiating to the jaw, arm, or neck * Pain may be intermittent or persistent * Differentiating risk factors include long-standing hypertension, diabetes, or hypercholesterolaemia * Can be difficult to differentiate from PE on the basis of signs and symptoms alone Differentiating investigations: * ST segment depression in contiguous leads on ECG * Normal troponin I or T. These tests may be elevated in PE. Negative diagnostic imaging study for PE * Critical stenosis of a coronary artery on coronary angiography

Question 35

How does PE and NSTEMI differ?

Answer 35

Differentiaing signs and symptoms: * Presents with central chest pain that is classically heavy in nature, like a sensation of pressure or squeezing * Examination findings are variable and range from normal to a critically ill patient in cardiogenic shock * Often difficult to differentiate from PE in acute setting Differentiating investigations: * ECG does not show ST-elevation but serum levels of cardiac biomarkers are raised * ECG may show non-specific ischaemic changes such as ST depression or T wave inversion * May see bilateral increased pulmonary vascular congestion on chest radiograph consistent with congestive heart failure (CHF) * Elevated troponin I or T (note: these may also be elevated in the setting of PE) * Regional wall motion abnormality of the left ventricle on echocardiography

Question 36

How does PE and STEMI differ?

Answer 36

Differentiating signs and symptoms: * Presents with central chest pain that is classically heavy in nature, like a sensation of pressure or squeezing * Examination findings are variable and range from normal to a critically ill patient in cardiogenic shock * Often difficult to differentiate from PE in acute setting Differentiating investigations: * STEMI is diagnosed by persistent ST segment elevation in 2 or more anatomically contiguous ECG leads in a patient with a consistent clinical history * Elevated troponin I or T (note: can also be elevated in PE) * Regional wall motion abnormality of the left ventricle on echocardiography * Critical stenosis of a coronary artery on coronary angiography

Question 37

How does PE and pneumonia differ? Note: community acquired

Answer 37

Differentiating signs and symptoms: * May be difficult to differentiate on the basis of signs and symptoms * Cough productive of purulent sputum * Fever above 39.0°C; generally higher than in PE Differentiating investigations: * White blood cell (WBC) count normally \>11 x 10⁹/L (\>11,000/microlitre) * Chest x-ray (CXR) may show a focal opacity and other features of pneumonic consolidation (note: this can also be seen with PE) * Sputum culture grows an organism known to cause pneumonia * Negative diagnostic imaging study for PE