The most common cause of pulmonary embolism is a thrombus, with approximately 70%-95% of cases occurring when a deep vein thrombosis dislodges and enters the pulmonary arteries and their branches via the bloodstream, leading to pulmonary embolism. Conditions such as prolonged bed rest or immobilization of the lower limbs can lead to the occurrence of deep vein thrombosis. Therefore, the primary site of origin is mainly the deep veins of the lower limbs. Additionally, other types of emboli can also cause pulmonary embolism, such as fat emboli, air emboli, amniotic fluid emboli, parasitic emboli, and bacterial emboli, as well as detachment of cardiac tumors; all these can lead to pulmonary embolism.