Acute respiratory distress syndrome, or ARDS, occurs when there is a malfunction of the lungs due to injury of the small air sacs or alveoli, and the surrounding capillaries. When this injury occurs, blood and fluid leak into the spaces between the air sacs, and eventually into the air sacs themselves, resulting in major breathing difficulties, hence the name. ARDS develops as a result of any disease that directly or indirectly injures the lungs.