Acute respiratory distress syndrome, or ARDS, is a very serious lung disease with a high mortality rate. People with ARDS will have respiratory failure because the part of the lungs where oxygen leaves to enter the bloodstream becomes filled with fluid. The lungs will fail, less oxygen enters the blood and other organs in the body receive less oxygen as well.
Development of Disease
Oxygen leaves the alveoli of the lungs to enter the capillaries. The red blood cells in the capillaries exchange their carbon dioxide for the oxygen. Any injury that damages the barrier between the alveoli and the capillaries lets fluid into the alveoli, as explained by Polly Parsons, M.D., professor of medicine at the University of Vermont College of Medicine in "Current Diagnosis & Treatment in Pulmonary Medicine". The injury starts an inflammation. Neutrophils, a type of white blood cell, goes to the lungs. But the substances that they release add to the inflammation and damage the lungs even more. Pieces of cells, fluid and proteins then flood into the alveoli.
Injuries that Cause ARDS
Several injuries that can damage the lungs cause ARDS, according to Brian Gehlbach, M.D., assistant professor of medicine at the University of Chicago in "The Merck Manual for Healthcare Professionals". This list includes inhaling toxic gas or smoke, near drowning, pneumonia, sepsis, burns, drug overdose, a large number of blood transfusions, bruises on the lung and breathing in acid. Pneumonia is an infection of the lungs. Sepsis is the term for organisms in the blood and tissues. Usually due to bacteria, sepsis can lead to such low blood pressure--the lungs do not receive enough blood.
Symptoms
People may have tachypnea, or rapid breathing, and tachycardia, or a rapid heart rate. They may also have difficulty breathing and have a fever. In "Current Diagnosis & Treatment in Pulmonary Medicine," Parsons writes that although ARDS is a lung disorder, it can cause problems in other systems. People may become mentally confused due to problems in their central nervous system, or the part of the nervous system that involves the brain and spinal cord. They may have nose bleeds, spit up blood and bleed from puncture sites due to a problem in their bloodstream called disseminated intravascular coagulation.
Evaluation
The lungs will make sounds called crackles. This is because the alveoli have collapsed from the fluid inside them and they are trying to open. Gehlbach explains in "The Merck Manual for Healthcare Professionals", that physicians will do an ABG, which stands for arterial blood gas. It is a sample of the blood from the arteries. It tells how much oxygen and carbon dioxide are in the arterial blood. In ARDS, because of the fluid in the alveoli, the oxygen cannot reach the red blood cells in the capillaries. So there is less than the normal amount of oxygen in the arteries.
Prognosis
The prognosis means the most likely outcome. The mortality rate in ARDS is usually 30 percent to 40 percent, according to Mark Chesnutt, M.D., associate professor of Medicine, Pulmonary and Critical Care Medicine at the Oregon Health and Science University in "Current Medical Diagnosis & Treatment". If sepsis causes ARDS, the mortality rate can be as high as 90 percent. Most people who do survive will have lung problems. They may have difficulty breathing and frequently cough up mucus, but will usually get better with time.
References
- "Current Diagnosis & Treatment in Pulmonary Medicine"; Michael Hanley, M.D., Carolyn Welsh, M.D.; 2003
- "Current Medical Diagnosis & Treatment 2010"; Stephen McPhee, M.D., Maxine Papadakis, M.D.; 2010
- "The Merck Manual for Healthcare Professionals": Acute Hypoxemic Respiratory Failure (AHRF, ARDS)
