What composes pulmonary emboli that can injure blood vessels and cause ARDS?

Pulmonary emboli that can injure blood vessels and lead to Acute Respiratory Distress Syndrome (ARDS) are often composed of fat. This is particularly the case with fat embolism syndrome, where fat globules enter the bloodstream, commonly after a fracture of long bones or trauma.

When fat globules travel to the pulmonary circulation, they can obstruct blood vessels, causing an inflammatory response. This response can trigger ARDS, characterized by increased permeability of the alveolar-capillary membrane, resulting in pulmonary edema and impaired gas exchange.

Other potential substances, such as air or fluid, while capable of causing different types of embolic events or conditions, do not typically lead to the same inflammatory cascade and direct vascular injury associated with fat emboli. Bone marrow can also enter circulation after trauma (known as bone marrow embolism), but it's less common than fat embolism in the context of ARDS.