The correct answer is B. The pulmonary artery, and would prevent blood from entering the lungs for gas exchange.

When a deep vein thrombosis (DVT) dislodges, it becomes an embolus and travels through the venous system to the right side of the heart and then into the pulmonary arteries. This results in a pulmonary embolism (PE).

The embolus will lodge in the pulmonary artery or its branches, not the pulmonary veins. The pulmonary veins carry oxygenated blood away from the lungs to the heart, so a clot from the venous system cannot reach them directly.

The primary problem caused by a pulmonary embolism is:

Obstruction of blood flow to portions of the lung

Impaired perfusion for gas exchange

This leads to a mismatch where air may still reach the alveoli, but blood cannot, preventing effective oxygenation.

According to NREMT-aligned EMT educational material:

“A pulmonary embolism blocks blood flow in the pulmonary circulation.”

“This prevents adequate gas exchange in the affected portions of the lung.”

Why the other options are incorrect:

A: While respiratory distress can occur, the key pathology is blocked perfusion, not simply a decrease in respirations.

C & D: Incorrect because emboli from DVT travel to the pulmonary arteries, not the pulmonary veins.

Exact Extracts:

“Pulmonary embolism occurs when a blood clot blocks a pulmonary artery.”

“This blockage prevents blood from reaching the alveoli for gas exchange.”

“Clots typically originate in the deep veins of the legs.”