Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is characterized by the development of sudden breathlessness within hours to days of an inciting event. Inciting events include trauma, sepsis (microorganisms growing in a person's blood), drug overdose, massive transfusion of blood products, acute pancreatitis, or aspiration (fluid entering the lungs, especially stomach contents). In many cases, the initial event is obvious, but, in others (such as drug overdose) the underlying cause may not be so easy to identify. ARDS typically develops within 12-48 hours after the inciting event, although, in rare instances, it may take up to a few days. Persons developing ARDS are critically ill, often with multisystem organ failure. It is a life-threatening condition; therefore, hospitalization is required for prompt management.
 
ARDS is associated with severe and diffuse injury to the alveolar-capillary membrane (the air sacs and small blood vessels) of the lungs. Fluid accumulates in some alveoli of the lungs, while some other alveoli collapse. This alveolar damage impedes the exchange of oxygen and carbon dioxide, which leads to a reduced concentration of oxygen in the blood. Low levels of oxygen in the blood cause damage to other vital organs of the body such as the kidneys.
 
ARDS occurs in children as well as adults. The estimated annual frequency of ARDS is reported as 75 cases per 100,000 population. Mortality (death) rates have been reported to be in the range of 30-40%.

A number of risk factors are associated with the development of ARDS.

• Sepsis (presence of various pathogenic microorganisms, or their toxins, in the blood or tissues)
  
  
• Severe traumatic injury (especially multiple fractures), severe head injury, and injury to the chest
  
  
• Fracture of the long bones 
  
  
• Blood transfusion
  
  
• Acute pancreatitis
  
  
• Drug overdose

• Aspiration
  
  
• Viral pneumonias
  
  
• Bacterial and fungal pneumonias
  
  
• Near drowning
  
  
• Toxic inhalations

• Severe difficulty in breathing
  
  
• Anxiety
  
  
• Agitation
  
  
• Fever

Because ARDS is an urgent medical condition that typically follows a significant illness or injury the patient is usually under the care of a doctor. If not, the person should see a health care provider immediately.

• Arterial blood gas analysis reveals hypoxemia (reduced levels of oxygen in the blood).
  
  
• A complete blood count may be taken. The number of white blood cells is increased in sepsis.
  
  
• Chest x-ray may show the presence of fluid in the lungs.
  
  
• CT scan of the chest may be required only in some situations (routine chest x-ray is sufficient in most cases).
  
  
• Echocardiogram (an ultrasound of the heart) may help exclude any heart problems that can cause fluid build-up in the lung. 
  
  
• Monitoring with pulmonary artery catheter may be done to exclude a cardiac cause for the difficulty in breathing.
  
  
• Bronchoscopy (a procedure used to look inside the windpipe and large airways of the lung) may be considered to evaluate the possibility of lung infection.

|Medical Treatment|

• Persons with ARDS are hospitalized and require treatment in an intensive care unit.
  
  
• No specific therapy for ARDS exists.
  
  
• Treatment is primarily supportive using a mechanical respirator and supplemental oxygen.
  
  
• Intravenous fluids are given to provide nutrition and prevent dehydration, and are carefully monitored to prevent fluid from accumulating in the lungs (pulmonary edema).
  
  
• Because infection is often the underlying cause of ARDS, appropriate antibiotic therapy is administered.
  
  
• Corticosteroids may sometimes be administered in late phases of ARDS or if the patient is in shock.

|Medications|

The following drugs may be administered:

• Antibiotics to treat infection
  
  
• Anti-inflammatory drugs, such as corticosteroids, to reduce inflammation in the lungs in the late phase of ARDS or sometimes if the person is in septic shock 
  
  
• Diuretics to eliminate fluid from the lungs
  
  
• Drugs to counteract low blood pressure that may be caused by shock 
  
  
• Antianxiety drugs to relieve anxiety
  
  
• Inhaled drugs administered by respiratory therapists to decrease inflammation and provide respiratory comfort

|Follow-up|

After discharge from the hospital, the person should follow-up with his or her health care provider for a lung function assessment.  

|Prevention|

Because aspiration is a risk factor for ARDS, taking appropriate measures to prevent aspiration, such as elevation of the head of the bed, may prevent some cases of ARDS.

|Outlook|

• Outlook of persons with ARDS has improved over the last 20 years; 60-70% of persons survive.

• Persons with a poor outlook include those older than 65 years and those with sepsis as the underlying cause. The adverse effect of age may be related to the underlying health status.

• Survivors of ARDS may recover normal lung function. However, many of them may have residual lung impairment. Typically, the lung dysfunction is mild, but ARDS can lead to severe lung damage and a reduced health-related quality of life.
  
  
• Severe disease and prolonged duration of mechanical ventilation are predictors of persistent abnormalities in lung function.

|Support Groups and Counseling|

Because ARDS can be fatal, family members of people with ARDS are under extreme stress. It is important that family and friends of the person remain positive. They can seek support from ARDS survivors, family, and friends.

ARDS Support Center, Inc.
7172 Regional Street, #278
Dublin, California 94568-2324 

American Lung Association
61 Broadway, 6th Floor
New York, NY 10006
(212) 315-8700 

National Heart, Lung, and Blood Institute
Division of Lung Diseases
Two Rockledge Center, Suite 10122
6701 Rockledge Dr. MSC 7952
Bethesda, Maryland 20892-7952

|Web Links|

Acute Respiratory Distress Syndrome Support Center

American Lung Association

Media file 1: Acute respiratory distress syndrome (ARDS). Anteroposterior (AP) portable chest radiograph shows an endotracheal tube, left subclavian central venous catheter into the superior vena cava, and bilateral patchy opacities in mostly the middle and lower lung zones. The person had been in respiratory failure for 1 week with the diagnosis of ARDS.

Media type:  X-RAY

acute respiratory distress syndrome, ARDS, adult respiratory distress syndrome, severe respiratory distress, acute lung injury, ALI, diffuse alveolar damage, diffuse alveolar injury, noncardiogenic pulmonary edema, ventilator-associated lung injury, severe acute respiratory syndrome, SARS, difficulty in breathing, sepsis, blood infection

Author: Eloise M Harman, MD, Program Director, Chief, Professor, Department of Internal Medicine, Division of Pulmonary and Critical Care, University of Florida College of Medicine.

Coauthor(s): Rajat Walia, MD, Fellow in Lung and Heart-Lung Transplantation, Division of Pulmonary and Critical Care Medicine, Stanford University Medical Center.

Editors: Ryland P Byrd Jr, MD, Chief of Pulmonary Medicine, Medical Director of Respiratory Therapy, Quillen VA Medical Center; Professor, Department of Internal Medicine, Division of Pulmonary Diseases and Critical Care Medicine, James H Quillen College of Medicine, East Tennessee State University; Mary L Windle, Pharm D, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Pharmacy Editor, .com, Inc; Zab Mosenifar, MD, Director, Division of Pulmonary and Critical Care Medicine, Executive Vice Chair, Department of Medicine, Cedars Sinai Medical Center, Professor of Medicine, University of California at Los Angeles School of Medicine.