ARDS is a medical emergency. It can be caused by any major lung inflammation or injury. Some common causes include pneumonia, septic shock, trauma, aspiration of vomit, or chemical inhalation. ARDS develops as inflammation and injury to the lung and causes a buildup of fluid in the air sacs. This fluid inhibits the passage of oxygen from the air into the bloodstream.
The main symptom of ARDS is severe shortness of breath. This may develop within minutes or gradually over a few days.This inflammation causes fluid to leak from small blood vessels in the lungs. As a result, fluid builds up in the air sacs (alveoli) and other lung tissue. When the air sacs fill with fluid, the lungs can no longer fill properly with air and the lungs become stiff.Blood concentration of oxygen can remain dangerously low in spite of supplemental oxygen delivered by a mechanical ventilator (breathing machine) through an endotracheal tube (breathing tube).
It is characterized by inflammation of the lung parenchyma leading to impaired gas exchange with concomitant systemic release of inflammatory mediators causing inflammation, hypoxemia and frequently resulting in multiple organ failure. This condition is life threatening and often lethal. So it usually requires mechanical ventilation and admission to an intensive care unit. A less severe form is called acute lung injury (ALI).ARDS formerly most commonly signified adult respiratory distress syndrome to differentiate it from infant respiratory distress syndrome in premature infants.
The annual incidence of ARDS is between 1.5 to 13.5 people per 100,000 in the general population. Doctors refer to this as idiopathic ARDS. Known causes of ARDS include:
*Severe pneumonia
*Chemical inhalation, such as ammonia
*Near drowning
*Adverse drug reaction affecting the lungs
*Overwhelming heart failure with fluid (edema) in the lungs
*Widespread infection in the body (sepsis)
If the underlying disease or injurious factor is not removed, the amount of inflammatory mediators released by the lungs in ARDS may result in a systemic inflammatory response syndrome (or sepsis if there is lung infection). The evolution towards shock and/or multiple organ failure follows paths analogous to the pathophysiology of sepsis.The result is a critical illness in which the 'endothelial disease' of severe sepsis/SIRS is worsened by the pulmonary dysfunction, which further impairs oxygen delivery.
In most cases, the cause of ARDS can't be determined. But a simple urine test can predict the survival of patients with a severe lung injury known as acute respiratory distress syndrome (ARDS), researchers report.
Higher levels of nitric oxide in urine were associated not only with improved survival but also with less time spent on ventilators and decreased rates of organ damage, concluded a report in the issue of the American Journal of Respiratory and Critical Care Medicine.
"This is novel, because we are using urine as opposed to a blood test," added lead researcher Dr. Michael Matthay, a professor of medicine and anesthesia at the University of California, San Francisco.
An estimated 190,000 Americans each year suffer from ARDS because of complications from major infections, severe injuries or other conditions. Anywhere from 30 percent to 60 percent of them die from the lung injury.
The study included 566 patients enrolled in the U.S. National Heart, Lung, and Blood Institute's ARDS Network.
By the third day of the three-day study, 62 of the patients had died. All the survivors had significantly higher levels of nitric oxide than those who did not, the researchers found.
This relationship was not unexpected, since nitric oxide is involved in oxygen transport to tissues.
The study results, "mark a new approach to using urine testing to measure pathogenesis in lung injury," Matthay said. The urine test could eventually be used as a predictor in the treatment of ARDS patients, used in conjunction with other measurements, he said.
"We think it would be good to do additional studies in which we measured nitric oxide levels in blood and urine as well as in the airspaces of the lungs," Matthay said. "We want to assess in a new prospective study the value of this for identifying patients with a worse prognosis and a better prognosis."
An application for federal funding of such a study is being made, he said.
The nitric oxide urine test "can't function on its own, but it is a promising biomarker," Matthay said. "What we are currently testing, our group and others, is the additive value of this test to standard clinical assessments to determine the value of identifying patients' prognosis."
"The finding is pretty intriguing because of the close association with increased survival," noted Dr. Herbert P. Wiedemann, chairman of pulmonary, allergy and critical care medicine at the Cleveland Clinic. "This study is preliminary and hypothesis-generating. It provides an avenue for future investigation."
The test might not necessarily affect treatment of ARDS patients, he said, because the critical nature of the condition means that "normally we treat them all the same."
"But it could perhaps be a marker of prognosis, and that would be very helpful," Wiedemann said. "At this point, we don't have good markers of prognosis."
The test is also valuable because "it helps us understand the causes of mortality in ARDS, so it will help us investigate new therapies," he said.
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