Acute respiratory distress syndrome or ARDS is a life threatening complication of disease or injury to the lungs. It starts as inflammation which eventually leads to the inability of the lungs to exchange gases with the blood. The blood starts to be deprived of oxygen, which leads to multiple organ failure. It is a medical emergency which requires treatment in an intensive care unit.
ARDS was first described in 1967, but the definition of the condition remained vague, leading to conflict over just what patients had the syndrome and what the mortality rate was. It was finally defined as a combination of a ratio between arterial blood gases and the percentage of oxygen in the gases being breathed by the patient in excess of 300mm of mercury, combined with bilateral infiltrates on a lung x-ray. For example, in a normal patient, arterial blood oxygen should be close to 100% in an normal atmosphere of 21% oxygen. If the amount of oxygen in the breathing air goes up while the arterial blood oxygen remains low, ARDS should be suspected and then confirmed with an x-ray.
Many diseases and injuries can lead to ARDS, including pneumonia, sepsis and trauma. This causes the inflammation, which leads to enough pulmonary edema to interfere with the passage of air between the lungs and the bloodstream. Once the reaction starts, it tends to keep getting worse until the underlying cause is treated.
First treatment is to put the patient on a ventilator, although care should be taken as this can lead to further lung damage and a worsening of the condition. After that, he underlying cause should be treated. Fluids should be restricted as they can make the edema worse. Nitric oxide can often act as a vasodilator. Experimental therapies include steroids and surfactants.