Epidemiology
The annual incidence of ARDS is 1.5–13.5 people per 100,000 in the general population. Its incidence in the intensive care unit (ICU), mechanically ventilated population is much higher. Brun-Buisson et al. (2004) reported a prevalence of acute lung injury (ALI) (see below) of 16.1% percent in ventilated patients admitted for more than 4 hours. More than half these patients may develop ARDS.
Mechanical ventilation, sepsis, pneumonia, shock, aspiration, trauma (especially pulmonary contusion), major surgery, massive transfusions, smoke inhalation, drug reaction or overdose, fat emboli and reperfusion pulmonary edema after lung transplantation or pulmonary embolectomy may all trigger ARDS. Pneumonia and sepsis are the most common triggers, and pneumonia is present in up to 60% of patients. Pneumonia and sepsis may be either causes or complications of ARDS. Alcohol excess appears to increase the risk of ARDS. Diabetes was originally thought to decrease the risk of ARDS, but this has shown to be due to an increase in the risk of pulmonary oedema.
Elevated abdominal pressure of any cause is also probably a risk factor for the development of ARDS, particularly during mechanical ventilation.
The mortality rate varies from 30% to 85%. Usually, randomized controlled trials in the literature show lower death rates, both in control and treatment patients. This is thought to be due to stricter enrollment criteria. Observational studies generally report 50–60% mortality.
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