Chapter 134. Acute Respiratory Distress Syndrome

1. What are the predisposing diseases/conditions that lead to acute respiratory distress syndrome (ARDS)?

2. How can ARDS be differentiated from other causes of hypoxemic respiratory failure?

3. What is the correct strategy in the management of mechanical ventilation in ARDS?

4. What adjunctive therapies may be beneficial in ARDS management?

5. What is the expected morbidity for patients who survive ARDS to hospital discharge?

The acute respiratory distress syndrome (ARDS) describes a common disorder encountered in the critical care unit that remains a significant cause of morbidity and mortality since its initial description in 1967. Standardization of ventilator strategies and overall improvement in critical care management, however, has resulted in significant improvements in outcomes in the last decade. Early recognition is essential in order to admit and/or transfer the patient to a higher level of care, when indicated.

Since the publication of the American-European Consensus Conference (AECC) (see Diagnosis) definitions for acute lung injury (ALI) and ARDS, the incidence has been identified in several studies. Without differentiating between ALI and ARDS, the incidence may range from 20 to 50 cases per 100,000 person-years. When rigorous screening for ALI and ARDS was applied in King County, Washington in 2000, investigators reported an incidence of 78.9 cases/100,000 person-years and 58.7 cases/100,000 person-years, respectively. Methodological differences may explain the disparity in incidence, as some reports retrospectively review prior ARDS studies while others prospectively identify patients admitted to an intensive care unit (ICU) or among those requiring mechanical ventilation. Inaccuracies in true incidence are magnified by a nonspecific case definition—the AECC ARDS criteria—and the relative lack of validation studies for said criteria (see Diagnosis).

Patients presenting with acute lung injury or impending ARDS may be difficult to differentiate initially from other causes of hypoxemic respiratory failure. A predisposing cause of ALI/ARDS should be present, with pulmonary and non-pulmonary sepsis most common (Table 134-1). Knowledge of the common etiologies of ARDS is important as early vigilance in regards to moving the patient to a higher level of care (eg, transferring to the ICU) and initiation of appropriate ICU interventions can minimize morbidity and mortality. Furthermore, identification of an underlying cause or inciting event is important in differentiating ARDS from other lung diseases or syndromes that may be misidentified as ARDS. Early and efficient identification of predisposing syndromes may prevent progression to ALI or ARDS. The evolution from inciting cause to ARDS typically occurs within 3 to 5 days, giving the clinician a window of suspicion for ARDS to develop.