Final answer:
Pulmonary shunting is responsible for hypoxemia in a patient with a pulmonary embolism.
Step-by-step explanation:
The mechanism responsible for hypoxemia in a patient with a pulmonary embolism is pulmonary shunting. Pulmonary shunting occurs when there is a blockage in the lungs, such as a blood clot, that obstructs the flow of blood through the pulmonary vessels. This results in blood bypassing the areas of the lung where gas exchange normally occurs, leading to a decrease in oxygenation of the blood.