Acute respiratory distress syndrome (ARDS) is a clinical syndrome of severe dyspnea of rapid onset, hypoxemia, and diffuse pulmonary infiltrates leading to respiratory failure. ARDS is caused by diffuse lung injury from many underlying medical and surgical disorders. The lung injury may be direct, as occurs in toxic inhalation, or indirect, as occurs in sepsis (Table 294-1). The clinical features of ARDS are listed in Table 294-2. By expert consensus, ARDS is defined by three categories based on the degrees of hypoxemia (Table 294-2). These stages of mild, moderate, and severe ARDS are associated with mortality risk and with the duration of mechanical ventilation in survivors.
Table 294-1Clinical Disorders Commonly Associated with ARDS ||Download (.pdf) Table 294-1 Clinical Disorders Commonly Associated with ARDS
|Direct Lung Injury ||Indirect Lung Injury |
|Pneumonia ||Sepsis |
|Aspiration of gastric contents ||Severe trauma |
|Pulmonary contusion || Multiple bone fractures |
|Near-drowning || Flail chest |
|Toxic inhalation injury || Head trauma |
| || Burns |
| ||Multiple transfusions |
| ||Drug overdose |
| ||Pancreatitis |
| ||Postcardiopulmonary bypass |
TABLE 294-2Diagnostic Criteria for ARDS ||Download (.pdf) TABLE 294-2 Diagnostic Criteria for ARDS
|Severity: Oxygenationa ||Onset ||Chest Radiograph ||Absence of Left Atrial Hypertension |
Mild: 200 mmHg < PaO2/FIO2 ≤ 300 mmHg
Moderate: 100 mmHg < PaO2/FIO2 ≤ 200 mmHg
Severe: PaO2/FIO2 ≤ 100 mmHg
|Acute: Within 1 week of a clinical insult or new or worsening respiratory symptoms. ||Bilateral opacities consistent with pulmonary edema not fully explained by effusions, lobar/lung collapse, or nodules ||Hydrostatic edema is not the primary cause of respiratory failure. If no ARDS risk factor is present, then some objective evaluation is required (e.g., echocardiography) to rule out hydrostatic edema |
The annual incidence of ARDS is estimated to be as high as 60 cases/100,000 population. Approximately 10% of all intensive care unit (ICU) admissions involve patients with ARDS.
While many medical and surgical illnesses have been associated with the development of ARDS, most cases (>80%) are caused by a relatively small number of clinical disorders: pneumonia and sepsis (~40–60%), followed in incidence by aspiration of gastric contents, trauma, multiple transfusions, and drug overdose. Among patients with trauma, the most frequently reported surgical conditions in ARDS are pulmonary contusion, multiple bone fractures, and chest wall trauma/flail chest, whereas head trauma, near-drowning, toxic inhalation, and burns are rare causes. The risks of developing ARDS are increased in patients with more than one predisposing medical or surgical condition.