Pulmonary thromboembolism Flashcards
What is a pulmonary thromboembolism?
A condition in which one (or more) blood clots (thrombi), typically from the deep veins of the legs, travel to the lung and obstruct pulmonary arteries.
Name the key signs and symptoms of a pulmonary thromboembolism (8)
- Dyspnea (SOB)
- Pleuritic chest pain
- Tachycardia
- Hypotension
- Signs of deep vein thrombosis (swelling and pain in the leg)
- Hemoptysis
- Palpitations
- Syncope
What is one of the main causes of pulmonary thromboembolism
Deep vein thrombosis (usually in the leg): about 95% of pulmonary thromboembolism results from DVT
What are some risk factors for pulmonary thromboembolism? (10)
- Surgery
- Pregnancy
- COPD
- Congestive heart failure
- Varicose veins
- Fractures
- Malignant disease
- Age
- Immobility
- Thrombotic disorders
Describe the Virchow’s triad, i.e. the 3 primary risk factors for thrombosis
- Hypercoagulability
- Abnormal blood flow (stasis and turbulence)
- Endothelial injury/dysfunction
What are some risk factors for endothelial injury? (3)
- Trauma
- Surgery (post-operative injury)
- Previous venous thromboembolism
What are some risk factors for blood stasis? (2 main ones)
Immobility:
* Post-operative (surgery)
* Medical illness (congestive heart failure, stroke)
* Travel (economy flight syndrome)
Obstruction to venous flow:
* Pregnancy
* Previous venous thromboembolism
* Malignancy
* “May Thurner” syndrome (anatomic)
What are some risk factors for hypercoagulability (5)?
- Hormones (pregnancy, contraceptive pill)
- Malignancy
- Medications
- Medical illness
- Congenital mutations of factors involved in the coagulation cascade
How does a pulmonary thromboembolism disrupt the pressures in the vasculature and what are the 2 consequences of the cardiovascular system?
- Pulmonary artery blockage results in an increase in pulmonary vascular pressure
- Increase in vascular pressure leads to the back flow of blood to the right side of the heart
- Back flow leads to increase in the right ventricular pressure: right ventricle becomes dilated and weakened
- Dilation of the right ventricle can cause right-sided heart failure
- Right-sided heart failure results in a decreased stroke volume, decreased cardiac output and overall decreased blood pressure
Net Result
Hypotension (low BP) Tachycardia (compensatory mechanism for low CO)
A pulmonary thromboembolism will cause abnormal gas exchange because the obstruction of pulmonary vessels causes… (2)
V-Q mismatch (ventilation-perfusion mismatch) and inflammation
During a PTE, how does inflammation in the lung result in hyperventilation?
Inflammation stimulates bronchoconstriction by the release of various cytokines. This leads to a decrease in oxygen (hypoxemia), which will stimulate hyperventilation.
Note that hyperventilation during a PTE is also a compensatory mechanism for increased dead space due to decreased perfusion
What is the consequence of hyperventilation during a PTE?
Hypocapnia (decrease in carbon dioxide)
Hyperventilation and inflammation during a PTE ultimately result in….
- Hypocapnia (decrease in blood CO2)
- Hypoxemia (decrease in blood O2)
Together, these conditions result in RESPIRATORY ALKALOSIS
As you know, PTE causes hyperventilation, but the blood vessels are unperfused (V/Q>1). This leads to…
an increased alveolar dead space.
Unusual case:
A patient has a pulmonary thromboembolism. However, their minute ventilation is fixed, because they are unconscious and anesthetized, and their ventilation is controlled by a mechanical ventilator. How might their PCO2 be affected?
Decreased perfusion without hyperventilation will still lead to an increase in alveolar dead space. However, in this case, the patient may develop hypercapnia (high CO2 in blood) and hypoxemia because fewer areas of the lungs can participate in gas exchange.
Respiratory acidosis
