Clinical meaning
A pulmonary embolism (PE) occurs when a thrombus (most commonly from deep veins in the legs or pelvis) dislodges and travels to the pulmonary vasculature, occluding one or more pulmonary arteries. This creates a ventilation-perfusion mismatch: the affected lung segments are ventilated but not perfused, resulting in hypoxemia. Other embolic sources include fat (from long bone fractures), air (from IV line disconnection), or amniotic fluid (peripartum). Massive PE can cause obstructive shock and right heart failure. The nurse must recognize acute respiratory distress, monitor vital signs, and report changes immediately.