Pulmonary embolism

Question 1

Define pulmonary embolus

Answer 1

Pulmonary embolus (PE) refers to obstruction of the pulmonary artery or one of its branches by material (eg, thrombus, tumor, air, or fat) that originated elsewhere in the body.

Pulmonary embolism - a condition in which there is sudden blockage of one more pulmonary arteries.

Question 2

From where do almost all pulmonary thromboemboli originate?

Answer 2

More than 95% of pulmonary thromboemboli arise from the deep veins of the lower extremity: the popliteal, femoral, and iliac veins

May also sometimes originate from he upper extremity, esp in people who have upper extremity central venous catheters

Question 3

What hemodynamic changes are brought about by significant pulmonary thromboemboli?

Answer 3

Pulmonary emboli cause mechanical obstruction of the pulmonary circulation
As the obstruction of pulmonary circulation increases, pulmonary artery pressures rise, ultimately leading to right ventricular strain
In severe pulmonary embolism, occlusion of the pulmonary outflow tract may occur, severely reducing cardiac output and even causing death

Question 4

What changes in ventilation/perfusion relationships are brought about by significant pulmonary thromboemboli?

Answer 4

Pulmonary embolism decreases perfusion distal to the site of the occlusion
This increases V̇/Q̇ mismatching, with a shift in the proportion of lung segments with high V̇/Q̇ ratios (alveolar dead space or wasted ventilation)
A shift toward high V̇/Q̇ ratios impairs the excretion of carbon dioxide with minimal effect on oxygenation initially
The patient initially compensates for this wasted ventilation by increasing total minute ventilation
Eventually, local hypoperfusion reduces surfactant production, causing edema, alveolar collapse, and atelectasis, creating lung units with little or no ventilation
Depending on the level of perfusion to these segments, there will be an increased number of lung units with low V̇/Q̇ ratios, including some areas of true shunting. These, in turn, contribute to an increased A-a ΔPO2 and arterial hypoxemia

Question 5

What are the risk factors for pulmonary thromboemboli?

Answer 5

Risk factors include:
— Venous stasis: bed rest, immobilization of the limb, obesity, incompetent venous valves, low cardiac output, pregnancy, hyperviscosity, central venous catheters, increasing age
— Increased coagulability: tissue injury from surgery or trauma, malignancy, nephrotic syndrome, a lupus anticoagulant, oral contraceptives, genetic coagulation disorders

Family history 
Surgery esp orthopedic surgery in leg
Immobilization 
Cancer
Estrogen use
Age
Inherited/Acquired thrombophilia

Question 6

Symptoms of PE

Answer 6

Pleuritic chest pain
Hemoptysis
Pulmonary infiltrate (which can be seen radiographically)

Question 7

Pulmonary circulation

Answer 7

the system of transportation that shunts de-oxygenated blood from the heart to the lungs to be re-saturated with oxygen before being dispersed into systemic circulation.
Deoxygenated blood from the lower half of the body enters the heart from the inferior vena cava while deoxygenated blood from the upper body is delivered to the heart via the superior vena cava. Both the superior vena cava and inferior vena cava empty blood into the right atrium. Blood flows through the tricuspid valve into the right ventricle. It then flows through the pulmonic valve into the pulmonary artery before being delivered to the lungs. While in the lungs, blood diverges into the numerous pulmonary capillaries where it releases carbon dioxide and is replenished with oxygen. Once fully saturated with oxygen, the blood is transported via the pulmonary vein into the left atrium which pumps blood through the mitral valve and into the left ventricle. With a powerful contraction, the left ventricle expels oxygen-rich blood through the aortic valve and into the aorta: This is the beginning of systemic circulation