Pulmonary Embolism Flashcards
What is the most common cause of a pulmonary embolism?
it is most commonly a complication of venous thromboembolism (VTE) from another source
e.g. clot in the legs (DVT) becomes dislodged and flows via the bloodstream, through the right side of the heart, and becomes lodged in the pulmonary circulation
Other than a clot, what other things can cause a pulmonary embolism?
- fat
- air
- amniotic fluid
for fat and amniotic fluid, these often resolve themselves with supportive care
air is often an iatrogenic cause
What is the mortality like for a PE caused by venous thromboembolism?
- <5% if there is no haemodynamic instability
- 30% if shock is present
- 70% with cardiac arrest (in hospital)
What lifestyle factors act as risk factors for VTE pulmonary embolism?
-
immobility
- bed rest > 24 hours
- immobiity > 48 hours
- plaster of paris (POP) over limb
- smoking
- dehydration
- obesity
- trauma / surgery (especially pelvic & orthopaedic)
- pregnancy (oestrogen)
What other medical conditions can increase the risk for VTE pulmonary embolism?
- malignancy
- infection
- previous DVT / embolism
- recent MI
- congestive heart failure
- varicose veins
- antithrombin deficiency
- protein C deficiency
- inherited clotting deficiencies (thrombophilia , factor V Leiden)
What are other risk factors for VTE pulmonary embolism?
- age
- family history
-
oestrogen therapy
- HRT or OCP
- only the combined pill, not the progesterone only one
How do clinical features for PE vary?
What question is it important to always ask about?
symptoms can be wide ranging from none at all to sudden death
symptoms are usually correlated to severity
it is important to always ask about a family history of thrombosis
What are the clinical signs of pulmonary embolism?
- pyrexia
- cyanosis
- tachypnoea
- 90% of patients have RR > 16
- tachycardia
- hypotension
- raised JVP
- pleural rub
- pleural effusion
What are the typical symptoms of pulmonary embolism?
- pleuritic chest pain (pain worse on inspiration)
- breathlessness
- cough
- haemoptysis (as a result of pulmonary infarct)
- dizziness / pre-syncope
- syncope (loss of consciousness / fainting)
- non-pleuritic chest pain
What is usually the first symptom of PE that presents?
Shortness of breath typically occurs within seconds to minutes of onset
pain then develops later
What symptom of PE is it important to pay special attention to?
patients with unexplained syncope
around 25% of patients admitted to hospital with unexplained syncope have PE
What are the 2 tools to use to help define the risk of the probability of PE?
-
PERC score
- pulmonary embolism rule-out criteria
- Well’s score
When is the PERC score used to rule out PE?
This is used to rule out PE in low-risk patients
if the patient’s score is 0, then there is a <2% chance of PE
in the absence of convincing clinical signs, you can usually safely exclude PE as a differential
What are the factors that are measured in the PERC score?
- age > 50
- heart rate > 100
- SaO2 on room air <95%
- unilateral leg swelling
- haemoptysis
- recent surgery or trauma
- previous PE or DVT
- exogenous oestrogen
- oral contraceptives, hormone replacement or other oestrogen hormones
How is the PERC score calculated?
What does it mean if someone scores more than 0?
Each factor gives a score of 1 if present
If the patient scores 0, and in the absence of convincing clinical signs, you can usually safely exclude PE
If the patient scores 1 or more, the PERC criteria CANNOT be used to safely rule out PE and the Well’s score is used
What is the purpose of calculating the Well’s score?
it will stratify patients as low or high risk
in high risk patients, you should proceed straight to imaging
in a low risk patient, you should consider a D-dimer test
How is the Well’s score calculated?
What is each factor worth?
Factors that score 3 points:
- clinically suspected DVT
- PE is the most likely diagnosis
Factors that score 1.5 points:
- tachycardia > 100 bpm
- immobilisation > 3 days or surgery in past 4 weeks
- history of DVT or PE
Factors that score 1 point:
- haemoptysis
- malignancy
How is the Well’s score interpreted?
- Score > 6.0 means high probability of PE
- Score 2.0 - 6.0 means moderate probability of PE
- Score < 2.0 means low probability of PE
What is D-dimer?
Why is it useful when there is a suspected PE?
D-dimer is a fibrin degradation product
Levels of D-dimer are raised by the presence of a blood clot in the circulation
D-dimer can be useful to RULE OUT a PE or DVT as a differential
Why can D-Dimer alone not be diagnostic of a PE?
There are many factors that can cause a positive D-Dimer
having a raised D-dimer does not necessarily mean there is a clot
a positive D-dimer usually indicates the need for further investigation
When should D-dimer be used in practice?
it should only be used as a “rule-out” test in low probability cases (based on Well’s score)
A negative D-dimer + a low Well’s score means that PE or DVT is extremely unlikely
What is important to remember about another reason why D-dimer might be raised before requesting this test?
almost any factor that causes inflammation will also result in raised D-dimer
Even if the patient has a low Well’s score, D-dimer may not be the best option if they have had a recent cellulitis / infection
When is D-dimer not necessary?
In cases with a high probability of PE, as based on the Well’s score
D-dimer should be skipped and imaging performed straight away
How does D-dimer change with age?
How do new reference ranges reflect this?
D-dimer rises with age
normal range of D-dimer is < 0.50 for anyone aged < 50
for anyone aged >50, normal range is <0.50 plus 0.1 for every decade of life over the age of 50
e.g. age 60 - normal < 0.60
age 70 - normal < 0.70
What are other factors known to cause an increased D-dimer?
- liver disease
- high rheumatoid factor
- malignancy
- trauma
- pregnancy
- recent surgery
Why is a chest X-ray performed as part of an investigation into PE?
CXR will often be normal in PE
the main reason to perform a CXR is to exclude other causes
What signs may be present on a CXR for pulmonary embolism?
- may show pulmonary oedema signs such as raised hemidiaphragm
- may show atelectasis - little areas of collapsed lung
- this occurs because there is loss of blood to some areas of the lungs, resulting in collapse fo these areas
What results from CXR will raise the suspicion of pulmonary embolism?
- if CXR is normal but the patient is breathless
- if CXR has bilateral changes but the patient only has unilateral pain
these both raise the suspicion of PE
What ECG changes can occur in PE?
ECG changes are common but often non-specific
the most common findings are T wave inversion and sinus tachycardia
(ECG shows T wave inversion)
What “classic sign” is present on ECG in <20% of cases of PE?
Why does it happen?
larger emboli can cause right heart strain, which results in the “classical” S1Q3T3 pattern of ECG changes
- S waves present in lead I
- Q waves present in lead III
- T wave inversion in lead III
What is a CTPA?
What are the benefits and downfalls of using this?
CT-pulmonary angiogram
it is a CT with contrast that assesses the pulmonary blood vessels
it’s main use is in the diagnosis of PE as it is much more sensitive and specific than a VQ scan
In what groups might a VQ scan be considered over a CTPA and why?
VQ is considered in young females and pregnant females
this is because CTPA uses a high dose of radiation
What is shown in this CTPA image?
this CTPA shows a saddle PE
the red arrows are indicative of thrombus and show lack of contrast in the pulmonary vessels
When is a VQ scan used?
They are used to assess for PE in patients who are at risk from higher radiation doses
e.g. pregnant women and young women
they use much less radiation than a CTPA
What is the downfall of using a VQ scan?
How are they interpreted?
they are much less accurate at diagnosing a PE and need to be interpreted carefully by a radiologist
a negative VQ scan has a very high negative predictive value, but positive scans are less useful
the result of a VQ scan is given as a risk probability - high, intermediate or low risk
What is shown in images A and B of VQ scans?
Image A:
- inhaled radioactive element (usually Xenon gas) showing normal perfusion throughout the bronchial tree
Image B:
- this image follows injection of technetium
- patchy update in different regions of the lungs indicates multiple areas of reduced blood flow, likely due to PE
What patients are not suitable for VQ scans?
VQ is only suitable for patients who have been previously well and not those with chronic disease
any CXR abnormalities are likely to cause abnormalities on VQ
What might an ABG show for someone with PE?
- O2 may often be low
- CO2 may often be normal or low
- the patient may be hyperventilating, hence the low CO2
What condition is seen on ABG in someone with a massive PE?
Can it be used for diagnosis?
metabolic acidosis is commonly seen in patients with a massive PE and cardiovascular collapse
A PE CANNOT be excluded with an arterial blood gas
Why might troponin be raised in PE?
What is higher troponin associated with?
troponin is raised in 20-40% of patients with PE as a result of the extra stress and stretch placed on the right ventricle
this is due to increased pulmonary arterial pressure
higher troponin is associated with worse prognosis
When might an Echocardiogram be used to look at PE?
What can this scan predict?
it 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
What is the initial treatment for PE?
- anticoagulate with low molecular weight heparin (LMWH) - e.g. dalteparin 200u / kg / 24hrs
the maximum dose is 18,000u
- at the same time start oral warfarin 10mg
When should heparin and warfarin be stopped in the treatment of PE?
- heparin is stopped when INR > 2
- warfarin is continued for a minimum of 3 months, aiming for an INR of 2 - 3
What treatment can be given to patients who continue to develop thrombi despite anticoagulation?
a vena cava filter can be placed in patients who continue to develop thrombi despite anticoagulation
BUT implanting a filter without adequate anticoagulation will increase the risk of thrombus
When can thrombolysis be used as a treatment for PE?
What dose is given?
thrombolysis can be used if the PE is deemed “massive” as long as there are no contraindications
50mg of alteplase is used
How long should warfarin be continued at the very minimum?
How about for those with idiopathic disease and risk factors?
- Warfarin should be continued for 6 weeks at the very minimum
- it should be continued for 3 months in those with an identifiable & reversible risk factor
- it should be continued for 6 months in those with idiopathic disease
What is a paradoxical embolism?
an embolism that goes through a defect in the heart and goes on to cause a stroke
the clot passes from a vein to an artery, through some sort of “fistula” (usually a cardiac defect such as patent foramen ovale)
How could a paradoxical embolism result from a DVT?
- DVT embolises and travels to the heart
- it enters the right atrium via the vena cava
- this would usually end up travelling to the lungs and causing a PE
- it travels from the right side of the heart to the left side via a defect in the heart
- the embolism misses out the pulmonary circulation and is free to travel in the arterial circulation
- it travels until it reaches an artery that is so small it cannot travel down it, and causes an ischaemic blockage
What are the potential differential diagnoses for pulmonary embolism?
- acute coronary syndrome
- pleuritic chest pain - pneumonia
- pericarditis
- musculoskeletal back pain
- embolus of other cause (fat, amniotic fluid, air)
- dissecting aortic aneurysm
- anxiety
- exacerbation of COPD
- syncope of another cause
