Acute respiratory distress syndrome (ARDS) is characterized by the development of sudden breathlessness within hours to days of an inciting event. Inciting events include:
- 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%, but mortality increases with advancing age.
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
- Transfusion of multiple units of blood
- Acute pancreatitis
- Drug overdose
- Viral pneumonias
- Bacterial and fungal pneumonias
- Near drowning
- Toxic inhalations
- Severe difficulty in breathing
When to Seek Medical Care for ARDS
Because ARDS is an urgent medical condition that typically follows a significant illness or injury the patient is usually already hospitalized when ARDS develops. Anyone developing severe shortness of breath should see a health care provider immediately.
Exams and Tests for ARDS
- 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 will 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 a 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 for ARDS
- 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 ARDS or if the patient is in shock, but their use is controversial.
Medications for ARDS
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
- Anti-anxiety drugs to relieve anxiety
- Inhaled drugs administered by respiratory therapists to open up the airways (bronchodilators)
Patients with ARDS may require a prolonged period of rehabilitation for both respiratory problems and muscle weakness. After discharge from the hospital, the person should follow-up with his or her healthcare provider for a lung function assessment.
Prevention of ARDS
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 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, some of them may have residual lung impairment or persistent muscle weakness. 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.