ABSTRACT
I. Introduction The acute respiratory distress syndrome (ARDS) is characterized by increased permeability of the alveolar-capillary membrane, diffuse alveolar damage, the accumulation of proteinaceous interstitial and intra-alveolar edema, and the presence of hyaline membranes. These pathological changes are accompanied by physiological alterations including severe hypoxemia, an increase in the mean pulmonary dead-space fraction, and a decrease in pulmonary compliance. ARDS is a relatively common diagnosis in patients who require mechanical ventilation for greater than 24 hours. In a population-based cohort study of 21 hospitals over a 16-month period of time, 21% of patients who required mechanical ventilation for more than 24 hours met established criteria for ARDS (1). A European survey of 132 intensive care units similarly demonstrated that 18% of mechanically ventilated patients had ARDS (2). Economically, ARDS patients account for a disproportionately higher amount of hospital resources due to their prolonged intensive care unit and hospital length of stays. In one observational study, ARDS patients who required mechanical ventilation for at least seven days represented only 6% of intensive care unit (ICU) admissions yet comprised 33% of all ICU patient days and 24% of all hospital charges among ICU patients (3).
