Synonyms

Adult respiratory distress syndrome; Respiratory distress syndrome

Definition

Acute respiratory distress syndrome (ARDS) is the presence of pulmonary edema in the absence of volume overload or depressed left ventricular function and is characterized by the development of sudden breathlessness within hours to days of an inciting event. ARDS is not a specific disease; instead, it is a type of severe, acute lung dysfunction that is associated with a variety of diseases and trauma.

Historical Background

In the past, ARDS signified adult respiratory distress syndrome to separate this from infant respiratory distress syndrome seen in premature infants. However, this type of pulmonary edema can also occur in children, so ARDS has gradually evolved to mean acute rather than adult.

Current Knowledge

ARDS typically develops within 12–48 h 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.

The 1994 American-European Consensus Committee defines ARDS as the acute onset of bilateral infiltrates on chest radiography, a partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (FIO2) ratio of less than 200 mmHg and a pulmonary artery occlusion pressure of less than 18, or the absence of clinical evidence of left arterial hypertension. Revised definition in 2012 (JAMA) describes criteria for mild, moderate, and severe ARDS based on PaO2 and FIO2. Mortality rate is approximately 27% for mild, 32% for moderate, and 45% for severe. Death usually results from multisystem organ failure rather than lung failure alone.

Causes: A number of clinical conditions are associated with the development of ARDS.

  • Sepsis and the systemic inflammatory response syndrome (SIRS) are the most common conditions associated with the development of ARDS.

  • Severe traumatic injury (especially multiple fractures), severe head injury, and pulmonary contusion are strongly associated with the development of ARDS. In traumatic injury, factures of the long bones can cause ARDS through fat embolism. In severe brain injury, ARDS is thought to develop owing to a sudden discharge of the sympathetic nervous system, which then leads to acute pulmonary hypertension and injury to the pulmonary capillary bed. In pulmonary contusions, ARDS develops through direct trauma to the lung.

  • Multiple blood transfusions are an independent risk factor for ARDS. The risk is independent of the reason for the transfusion or the coexistence of trauma. The incidence of ARDS increases with the number of units of blood transfused. If the patient has preexisting abnormal liver functioning or a coagulation abnormality, the risk is further increased.

  • Near drowning can be another cause of ARDS. Development of ARDS is slightly more common with saltwater than with freshwater. Aspiration leads to an osmotic gradient that favors movement of water into air spaces of the lung. Aspiration may be visible with chest radiography, although the chest radiograph may be normal early in the course of the disease.

  • Smoke inhalation is another possible cause of ARDS. Smoke inhalation causes lung tissue damage from direct heat, toxic chemicals, and particulate matter carried into the lung. Patients with smoke inhalation initially may be asymptomatic, but patients with airway burns, exposure to toxic fumes, or exposure to carbon monoxide should be monitored closely for the development of ARDS, even if the symptoms are initially absent.

  • Overdoses of narcotics, tricyclic antidepressants, and other sedatives have been associated with the development of ARDS. Overdoses of tricyclic antidepressants are the most common. This risk is independent of the risk from concurrent aspiration.

Medical treatment for ARDS:

  • People with ARDS require hospitalization and treatment in an intensive care unit.

  • There is no specific treatment for ARDS, but, rather, treatment is primarily supportive using a mechanical respirator and supplemental oxygen.

  • Diuretics can be given to eliminate fluid from the lungs. However, fluids are often given via IV to provide nutrition and prevent dehydration, but fluids must be carefully monitored to avoid fluid accumulation in the lungs.

  • Antibiotic therapy may be administered to treat infection, which is often the underlying cause of ARDS.

  • Corticosteroids may sometimes be given late in the process of ARDS or if the patient is in shock. If the patient is in shock, drugs to counteract low blood pressure caused by shock may be administered.

  • If the patient is experiencing anxiety, this can be treated with antianxiety medications.

Respiratory therapists may see these patients to provide inhaled drugs to decrease inflammation and provide respiratory comfort.

Because of the acute and medically serious nature of ARDS, it would be unlikely for neuropsychological exam to be requested when a person is acutely ill with ARDS. Mortality with ARDS is 30–40%, and the person would typically be treated in an intensive care unit. If the person survives, outpatient neuropsychological evaluation could be requested, and results may show memory deficits related to the hypoxia as well as neuropsychological deficits related to the underlying medical cause for ARDS (e.g., severe TBI, near drowning, sepsis, medication overdose).

Cross-References