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 268-1). The clinical features of ARDS are listed in Table 268-2. Acute lung injury (ALI) is a less severe disorder but has the potential to evolve into ARDS (Table 268-2). The arterial (a) Po2 (in mmHg)/Fio2 (inspiratory O2 fraction) <200 mmHg is characteristic of ARDS, while a Pao2/Fio2 between 200 and 300 identifies patients with ALI who are likely to benefit from aggressive therapy.
Table 268–1. Clinical Disorders Commonly Associated with ARDS |Favorite Table|Download (.pdf)
Table 268–1. Clinical Disorders Commonly Associated with ARDS
|Direct Lung Injury||Indirect Lung Injury|
|Aspiration of gastric contents||Severe trauma|
|Pulmonary contusion||Multiple bone fractures|
|Toxic inhalation injury||Head trauma|
Table 268–2. Diagnostic Criteria for ALI and ARDS |Favorite Table|Download (.pdf)
Table 268–2. Diagnostic Criteria for ALI and ARDS
|Oxygenation||Onset||Chest Radiograph||Absence of Left Atrial Hypertension|
|ALI: PaO2/FIO2 ≤ 300 mmHg||Acute||Bilateral alveolar or interstitial infiltrates||PCWP ≤ 18 mmHg or no clinical evidence of increased left atrialpressure|
|ARDS: PaO2/FIO2 ≤ 200 mmHg|
The annual incidences of ALI and ARDS are estimated to be up to 80/100,000 and 60/100,000, respectively. Approximately 10% of all intensive care unit (ICU) admissions suffer from acute respiratory failure, with ˜20% of these patients meeting criteria for ALI or ARDS.
While many medical and surgical illnesses have been associated with the development of ALI and ARDS, most cases (>80%) are caused by a relatively small number of clinical disorders, namely, severe sepsis syndrome and/or bacterial pneumonia (∼40−50%), trauma, multiple transfusions, aspiration of gastric contents, and drug overdose. Among patients with trauma, pulmonary contusion, multiple bone fractures, and chest wall trauma/flail chest are the most frequently reported surgical conditions in ARDS, whereas head trauma, near-drowning, toxic inhalation, and burns are rare causes. The risks of developing ARDS are increased in patients suffering from more than one predisposing medical or surgical condition (e.g., the risk for ARDS increases from 25% in patients with severe trauma to 56% in patients with trauma and sepsis).
Several other clinical variables have been associated with the development of ARDS. These include older age, chronic alcohol abuse, metabolic acidosis, and severity of critical illness. ...