SM 169a - Pulmonary Embolism Flashcards
What is the recommended prevention strategy for PE?
Thromboprophylaxis in patients with ≥ 1 risk factor
If anticoagulation is contraindicated, use intermittent calf compression
What is a D-dimer?
A D-dimer is a product of fibrin degradation
Absence of D-dimers can help to rule out PE, but high levels of D-dimer (>500 mL) is not specific for PE
Wahat is the recommended long-term therapy for PE?
One of the following for 3 months if provoked, and at least 3 months if unprovoked or associated with malignancy
-
Vitamin K antagonists
- Warfarin
- Requires monitoring
-
LMWH (Low Molecular Weight Heparin)
- Preferred to treat cancer-associated VTE
- No monitoring, but not as reversible
-
Novel oral anticoagulants
- Dabigatran (Direct thrombin inhibitor)
- Rivaroxaban, apixapban, endoxaban (Xa inhibitors)
Cardiovascular collapse in a patient with pulmonary embolism occurs via 2 major pathways.
What are they?
- RV dilation and dsysfunction
- Leads to decreased RV cardiac output and a septal shift toward the left ventricle
- This decreases LV preload and cardiac output, leading to hypotension
- -> Decreased coronary perfusion, which contributes to…
- RV ischemia and infarction
- Caused by increased RV wall tension, which increases RV O2 demand and decreases RV O2 supply
Most PEs come from a ____________ extremity
Most PEs come from a proximal lower extremity
Ex: popliteal or femoral veins
Outline the diagnostic approach for pulmonary embolism
- Assess the patient’s risk of VTE using a validated risk score
-
Wells ≤ 4 => PE unlikely
- Run a D-dimer
- D-dimer ≤ 500 + Wells ≤ 4 => PE excluded
-
D-dimer >500 => PE cannot be excluded
- CTPA
- Run a D-dimer
-
Wells >4 => PE likely
- CTPA (skip D-dimer)
-
Wells ≤ 4 => PE unlikely
90 % of PEs are ther esult of an
90 % of PEs are ther esult of an embolized DVT
A 75 year old female presents to urgent care with dyspnea. She has a history of a provoked right femoral DVT 10 years ago following a cholecystectomy. She was treated with 3 months of warfarin. Her heart rate is 110 BPM and she is tachypnic, but her blood pressure is normal.
What is the most appropriate next step?
Administer unfractionated heparin or LMWH, then perform a CTPA
Her risk profile is very high, so you would skip the D-dimer step. In the meantime, you would want to start anticoagulation given her high risk of PE.
If your mechanically ventilated patient suddenly becomes hypercapnic, what should you be worred about?
Pulmonary Embolism
They cannot increase respiration to compensate for the increased dead space, leading to hypercapnia
List some of the physical exam findings that are associated with pulmonary embolism
Largely nonspecific
- Tachypnea
- Tachycardia
- Crackles on lung exam
- Decreased breath sounds
- Increased P2 component of S2 heart sound
- Mild hypoxia
What two general factors contribute to the impact of a PE on a patient’s hemodynamic status?
Degree of obstruction
+
Baseline health (CV comorbidities?)
If a patient with a PE has contraindications to anticoagulation, what is the recommended acute therapy?
IVC filter
If it is a massive PE, also administer systemic fibrinolytic therapy
What is the role of duplex ultrasonography in the diagnosis of PE?
Duplex ultrasonography (aka lower extremity compression ultrasound) is great for the diagnosis of DVT
However, a negative lower extremity compression ultrasound does not exclude PE - the clot may have already emoblized
What are the advantages of CTPA?
What are the disadvantages?
CTPA = CT pulmonary angiography: the go-to for PE diagnosis
- Advantages
- Fast
- Widely available
- High diagnostic accuracy esp. for large clots
- Detailed image helps to make alternative diagnoses
- Disadvantages
- Ionizing ratiation and contrast exposure
- Less accurate for sub-segmental (distal) pulmonary arteries
Are you more likley to see hypocapnia or hypercapnia in a patient with a PE?
If a patient is not mechanically ventilated, you are more likely to see hypocapnia
- PE creates dead space
- The patient hyperventilates to compensate
- Hyperventilation -> Hypocapnia
If the patient is mechanically ventilated, they are likely to be hypercapnic; they cannot compensate for the increased dead space
What is the goal of PE therapeutics?
Lower the risk of further embolization/clot formation
Allow time for intrinsic fibrinolysis to clear
What is Virchow’s triad?
Virchow’s triad = risk factors for PE
- Venous stasis
- Immobility
- Age >60
- Vascular injury
- Surgery
- Trauma
- Post-partum
- Indwelling vascular access
- History of VTE
- Changes in coagulation
- Hereditary thrombophilias
- Vactor V Leiden deficiency
- Prothrombin G2021A
- Hyperhomocysteinemia
- Estrogen Therapy
- Malignancy
- Hereditary thrombophilias
What is the recommended acute therapy for PE?
Acute therapy = first 5 days
-
Heparin
- Unfractionated or LMWH
- Start while awaiting test results if pre-test probability of PE is high.
- Use IVC filter if anticoagulation is contraindicated
-
Fibrinolytics only for patients who have a massive PE
(PE + Hemodynamic shock)
Who should recieve systemic fibrinolytic therapy acutely for PE?
Patients with a massive PE (PE + hemodnamic shock)
% of PEs are ther esult of an embolized DVT
90 % of PEs are ther esult of an embolized DVT
What is the preferred long-term therapy for VTE associated with malignancy?
LMWH
What is the difference between a massive PE and a submassive PE?
- Submassive PE = No hemodynamic collapse
- Associated with RV dysfunction and/or biomarkers of MI injury
- Massiv PE = Hemodynamic collapse
- The patient is in shock (SBP <90 mmHg)
The size of the clot is irrelevant!
Why are upper extremity DVTs becoming more common?
PICC lines (peripherally inserted central catheters)
10% of PEs come from an upper extremity
What is the role of ventilation-perfusion scanning (V̇/Q̇ scan) in the diagnosis of PE?
A V̇/Q̇ scan is helpful in the diagnosis of PE if it is very normal or very abnormal
- If it is very abnormal, it is 90% specific for patients with suspected PE
- If it is very normal, you can safely rule out PE
BUT: 80% of scans are not definitively normal or abnormal, and V̇/Q̇ scan results are even less accurate in patients with COPD or parenchymal disease. Therefore, CTPA is preferred over V̇/Q̇ scan
What is the most frequent diagnostic test performed for suspected PE?
Why?
Helical computed tomography pulmonary angiography (CTPA or PE-CT)
It is fast, widely available, and has a high diagnostic accuracy, especially for large clots.
It also provides a detailed image that would help to establish alternative diagnoses
What is the role of chest x-ray in the diagnosis of PE?
If a patient presents with signs/symptoms of PE but has a normal chest x-ray, this should increase you suspicion of PE
A patient presents to the ER with pleruitic chest pain. Lung exam reveals decreased breath sounds and tachypnea.
You suspect pulmonary embolism, and calculate a Wells score of 4.
What is your next step?
Perform a D-dimer
Wells score ≤ 4 => PE unlikely. Do a D-dimer to confirm
If D-dimer ≤ 500 ng/mL, you can safely rule out PE.
No further testing is needed
If D-dimer > 500 ng/mL, further testing is needed
Order a CTPA, V/Q scan, or angiography
What are the advantages of LMWH over unfractionated heparin?
- LMWH has a longer half life, and therefore a higher bioavailability
- Only patients at the extremes of weight or with renal insufficinecy need to have anti-Xa levels monitored
What is the difference between provoked and unprovoked PE?
How does this distinction inform the patient’s care?
- Provoked PE
- There is a clear, reversible, identifiable cause of the PE (ex: the patient was on a 17 hour flight)
- You only need to administer anticoagulation therapy for 3 months following therapy
- Unprovoked PE
- There is no clear cause of PE, or the patient also has cancer
- You need to administer anticoagulation therapy for at least 3 months, but problably longer
Long term anticoagulation: VKA antagonist (warfarin), LMWH, or novel oral anticoagulant (Dabigatran, Rivaroxaban, apixaban, endoxaban)
What is the main cause of hypoxemia in patient with a pulmonary embolism?
V̇/Q̇ mismatch
- If there is atelectasis, pulmonary infacrtion, or intracardiac shunting, a true shunt may be contributing to hypoxemia
- If it is a massive PE, decreased mixed oxyhemoglobin saturation may be contributing to hypoxemia
What are the advantages of unfractionated heparin over LMWH?
Unfractionated heparin is readily reversible
What is the role of the D-dimer test in the diagnosis of PE?
The D-dimer test is sensitive but not specifc for PE
- A low D-dimer can help to rule out PE
- However, a high D-dimer (>500 ng/mL) cannot diagnose PE definitively
- Use for patients with low pre-test probability of PE
What are the advantages of compression ultrasonography?
What are the disadvantages?
- Advantages
- Cheap
- Repeatable
- Noninvasive
- No radiation or contrast exposure
- Does not require extensive specialized training
- Great for diagnosing DVE
- Disadvantages
- A negative ultrasound does not rule out PE
Death from pulmonary embolism is usually due to __________.
Death from pulmonary embolism is usually due to cardiovascular collapse.
A patient presents to the ER with pleruitic chest pain. Lung exam reveals decreased breath sounds and tachypnea.
You suspect pulmonary embolism, and calculate a Wells score of 5.
What is your next step?
Perform a CTPA and give anticoagulation on the way
Wells score >4 => PE likely. Even a negative D-dimer would not rule out PE, so go straight to CTPA
What is the old “diagnostic gold standard” for PE?
Why isn’t it used widely for PE diagnosis?
Contrast venography and pulmonary angiography
It is invasive, exposes the patient to contrast, not highly accurate for small clots, and requires a high level of expertise to perform
CTPA (PE-CT) is used most commonly
