Acute respiratory distress syndrome (ARDS) is a type of severe, acute lung dysfunction affecting all or most of both lungs that occurs as a result of illness or injury. Although it is sometimes called adult respiratory distress syndrome, it may also affect children. Major symptoms may include breathing difficulties (dyspnea), rapid breathing (tachypnea), excessively deep and rapid breathing (hyperventilation) and insufficient levels of oxygen in the circulating blood (hypoxemia). ARDS may develop in conjunction with widespread infection in the body (sepsis) or as a result of pneumonia, trauma, shock, severe burns, aspiration of food into the lung, multiple blood transfusions, and inhalation of toxic fumes, among other things. It usually develops within 24 to 48 hours after the original illness or injury and is considered a medical emergency. It may progress to involvement of other organs.
Typically, ARDS develops within 24 to 48 hours of the original illness or injury. It may become a life-threatening condition characterized by inflammation of the lungs, which may begin in one lung but eventually affects both, and resulting damage to the air sacs (alveoli) and surrounding small blood vessels. The damaged alveoli close down or fill up with fluid (lung edema), thereby losing their ability to oxygenate the blood and eliminate carbon dioxide. Patients experience increasingly severe respiratory distress, associated with decreasing oxygen levels in arterial blood and tissues.
With the fluid buildup, the lungs become heavy, stiff, and unable to expand properly. Most patients require mechanical ventilation because of respiratory failure. The disorder may also be accompanied or followed by impairment of other vital functions, including cardiovascular, renal, hepatic, hematologic, and neurologic functions. Involvement of other organs in addition to the lungs may lead to a condition sometimes called multi-organ dysfunction syndrome.
The person with ARDS may initially appear agitated as a result of breathing difficulty, but later may become lethargic and or even comatose. He may appear pale, and the hands and feet may have a bluish-gray tone because of the diminished level of oxygen in the blood.
Risk factors for developing acute respiratory distress syndrome include infection in the body (sepsis), pneumonia, extensive trauma, severe low blood pressure (shock), severe burns, aspiration of food into the lung, inflammation of the pancreas, and multiple emergency blood transfusions. The disorder may also follow a near drowning or the inhalation of toxic fumes, or gases such as chlorine, phosgene, and nitrogen dioxide. Acute respiratory distress syndrome may affect people who have previously had healthy lungs, and it may affect children. It is not the same thing as infant respiratory distress syndrome, although the two share some similarities.
Acute respiratory distress syndrome can affect persons of any age who suffer acute injury or illness affecting the lungs. The incidence is believed to be between 1.5 and 4.8 per 100,000 of the population. Men and women appear to be equally affected.
The diagnosis is based on the presence of respiratory distress accompanied by low levels of oxygen in the blood and the presence of known risk factors such as sepsis, pneumonia, or trauma. Chest x-rays will show fluid filling spaces that should be filled with air. The presence of fluid in the air sacs and the “wet” breathing sounds sometimes made by patients may suggest congestive heart failure but a medical examination will distinguish between that condition and ARDS.
Standard therapy consists of mechanical ventilation, supplemental oxygen, and a technique called positive end expiratory pressure (PEEP) to help push the fluid out of air sacs. These are combined with continuing treatment of the original illness or injury.
Because people with ARDS are less able to fight lung infections, they may develop bacterial pneumonia during the course of the illness. Antibiotics are given to fight infection. Also, supportive treatment such as intravenous fluid or food may be needed. If other organ systems become involved, measures may be needed to support those organs.
The introduction into standard practice of a recent recommendation to use smaller “tidal volumes” (the volume of each individual breath delivered by the ventilator) has resulted in improved outcomes. Earlier, ventilators were set to deliver 12 ml per kg of body weight. Now only 6 ml per kg of body weight are delivered.
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