Emergency Medical Technician (EMT) Intermediate Practice Exam

Intrapulmonary shunting occurs when:

1. Alveoli collapse

2. Nonfunctional alveoli inhibit the diffusion of oxygen and carbon dioxide

3. Airway obstruction is present

4. There is hyperventilation of the lungs

The correct answer is: Nonfunctional alveoli inhibit the diffusion of oxygen and carbon dioxide

Intrapulmonary shunting refers to a condition in which blood that is not adequately oxygenated passes through the lungs and returns to the systemic circulation, leading to hypoxemia. This typically occurs when portions of the lung are ventilated poorly or not at all, which means that even though blood is flowing through the pulmonary capillaries, there is little to no gas exchange occurring. When nonfunctional alveoli inhibit the diffusion of oxygen and carbon dioxide, it creates a situation where blood can flow past alveoli that are not participating in gas exchange. This effectively means that the blood is shunted away from adequately ventilated areas, leading to low levels of oxygen in the blood despite adequate blood flow. In contrast, collapsing alveoli can contribute to shunting but under a different context, and airway obstruction affects ventilation rather than diffusion directly in the context of shunting. Hyperventilation, while it can lead to other issues such as respiratory alkalosis, does not directly induce intrapulmonary shunting as the lungs are still being ventilated and gas exchange is occurring. Thus, the correct identification of nonfunctional alveoli inhibiting the essential diffusion processes is key to understanding intrapulmonary shunting.