5.1 Pulmonary Embolism Flashcards
(24 cards)
Embolism
Obstruction of blood vessel by foreign substance or blood clot that travels through blood stream, lodging in blood vessel - plugging the vessel
Types of emboli
- Thrombus
- Tumour
- Air - after surgery
- Fat - after trauma
- Amniotic fluid - after labour
Pulmonary embolism
- In daily practice - refers to a thrombus emboli
- Emboli enters right side of heart and pulmonary arteries
- 90% of PE’s arise from DVT’s (most common cause)
- Most preventable and unexpected of hospital deaths
Virchow’s Triad
Increased risk of clotting:
• Endothelial injury - e.g. trauma/surgery
• Stasis/turbulence of blood flow - can cause propogation of clot
• Blood hypercoagulability
• Inflammation can act through any of the three above to predispose an individual to clotting
Hypercoagulability states
- Prior thrombosis
- Immobility
- Malignancy
- DIC
- HRT (Hormone replacement therapy - oestrogens)
- Pregnancy
- Prolonged travel
- Surgery
- Oral contraceptive pill
- Heart failure
- Thrombophilia
- Severe burns
Consequences of PE
- Hypoxaemia - due to V/Q mismatch (>1)
- Right sided heart failure - obstruction of pulmonary circulation causes right sided strain/hypertrophy/failure
- Pulmonary infarction - but rare due to collateral vessels (bronchial arteries) which maintain perfusion slightly
Fat emboli
• Normally resolve spontaneously
• Can give rise to fat embolism syndrome (FES):
- traumatic causes: fracture of femur/pelvis/tibia and or massive soft tissue injury/severe burns/bone marrow biopsy’s etc.
- non traumatic causes: acute pancreatitis / fatty liver / haemoglobinopathies etc.
• Seen as petechial rash, decreased level of consciousness and SOB
Amniotic fluid emboli
- Sudden, unexpected maternal collapse associated with hypotension/hypoxaemia/DIC
- Occurs when amniotic fluid or fetal cells/hair along with other debris enter maternal circulation
- Most cases occur during or immediately after labour
Covid-19
• Risks of venous thromboembolism (VTE) increased with covid-19 (due to severe inflammation)
Hypercoagulable disorders
- Antithrombin III deficiency
- Protein C or S deficiency
- Factor V Leiden mutation - resistance to protein C (anti-coagulation proteins) is the most common risk factor
How does PE: acute right ventricular overload
• Pulmonary artery pressure increases due to PE if >30% of artery is occluded
• Leads to acute right ventricular dilatation and strain
• + inotropes released in attempt to maintain BP:
- increase contractility of heart and constrict pulmonary arteries which worsens condition
- puts more strain on right side of heart
• In about ⅓ of PE patients have patent foramen ovale allowing for right-to-left shunting
- May lead to severe hypoxaemia and paradoxical embolisation (from vein to artery)
How does PE: respiratory failure
- Areas of V/Q mismatch (lower perfusion so V/Q>1)
- Low right ventricle output
- Shunt with patent foramen ovale
- All cause hypoperfusion to the lungs
How does PE: pulmonary infarction
- Small distal emboli may create areas of alveolar haemorrhage
- May result in haemoptysis, pleuritis and small pleural effusion
- May be visible of CXR as wedge shape
Symptoms of PE - most common to least common
- Dyspnoea - SOB
- Pleuritic chest pain - somatic - sharp/localised/acute
- Cough
- Substernal chest pain
- Haemoptysis
- Fever
- Syncope
- Unilateral leg pain
- Chest well tenderness
Signs of PE - most common to least common
- Tachypnoea - increased RR
- Decreased breath sounds
- Accentuated second heart sound (pulmonic artery sound much louder)
- Tachycardia
- Fever
- Diaphoresis (sweating)
- Lower extremity oedema
- Cardiac murmur
- Central cyanosis (due to hypoxaemia)
Investigations for PE
• ABG - may show hypoxaemia and hypocapnia (due to hyperventilation)
• CXR - common finding in PE is a normal CXR (wedge shaped infiltrate = pleural effusion)
• ECG - Sᵢ Qᵢᵢᵢ Tᵢᵢᵢ
- Deep S wave in lead I, Q wave in III and T wave in III
- T wave inversion also shown in right and inferior leads
- May also show tachycardia
- Also done to exclude MI/angina
• D dimer - normal range rules out PE
- in those who have a high likelihood of getting a PE, this investigation alone is not enough
Clinical Probability Score
- Wells’ score are used
- 2 outcomes - likely and unlikely
- If score >4 imaging is recommended
Saddle embolus
- At main bifurcation of an artery
* In PE, the saddle embolus would be straddling the pulmonary trunk
Treatment of PE
• LMW heparin - to reduce chance of heparin-induced thrombocytopenia
• Oxygen
• After initial heparin - started on oral anticoagulant (rivaroxoban now prescribed over warfarin as lower risk of bleeding)
• If anticoagulation cannot be used (due to high risk of bleeding) - can use IVC filter to filter any thrombi/emboli propagating towards lungs/heart
- temporary until collateral vessels are formed
Heparin
- Stops thrombus propagation in the pulmonary arteries and at the embolic source
- Does not lyse the embolus/thrombus itself
- Reduces frequency of further pulmonary embolism
Heparin-induced thrombocytopenia
- Body produces antibodies (platelet factor 4-heparin antibodies) to a portion of heparin
- Also recognise heparin-platelet complexes
- Binding of antibodies to platelets activates them, causing platelet clumps that lead to thrombi
- Low platelet count, but paradoxically increased risk of thrombosis
- Similar mechanism to AZ Covid-19 vaccine induced thrombocytopenia
- Treatment = immediate cessation of heparin
Upper extremity DVT
• Acute thrombosis of a brachial, axial, or subclavian vein that may be caused by:
• Effort-induced thrombosis, triggered by repetitive
strenuous activity of the upper extremities (e.g., weight-lifting)
• Thoracic outlet syndrome; or Presence of a foreign object in veins (e.g., central venous catheter, pacemaker lead)
• A rare blood-based thrombosis that may also lead to PE
Prevention of DVT/PE
• Outpatient - address risk factors
- obese woman may not be recommended to go on OCP or have HRT
• Inpatient
- DVT prophylaxis e.g. early mobilisation post-surgery/long flight
- Post-operative anticoagulation along with LMW heparin
Cerebral air emboli
- Usually iatrogenic (due to treatment/drugs) occurring especially in ICU patients
- Air entry through central venous cannula, pulmonary artery catheters or haemodialysis catheters
- Shows up as black regions between sulci/gyri of brain in CT scan
- After some time, the air may dissipate and leave, but may cause infarct to affected region
