Reported mortality in ARDS patients varies from 30 to 50%. These values are lower than those previously reported. Zilberberg and Epstein2 reported that the lower mortality in ARDS was independent of the initial level of arterial oxygenation. The North American-European Consensus Conference redefined the criteria for ARDS. These new criteria require less severe arterial hypoxemia and may identify less severely injured patients than did previous criteria, This may explain some of the recently observed reductions in mortality from ARDS.
Longitudinal studies of ARDS at the same institution, using constant selection criteria are infrequent. During the 1990s, Milberg et al noted decreased mortality over an 11-year period using a constant definition of ARDS at a single institution. Abel et al also described a marked reduction in mortality for a small group of patients over a 7-year period during the 1990s in the United Kingdom. While these two studies reported decreased mortality, the paucity of longitudinal studies compromises conclusions about why ARDS mortality is changing. add comment
There are other reasons for the uncertainty regarding ARDS mortality. Included among these are changes in risk factor distribution for the development of ARDS, changes in physician reporting of ARDS patients or secular changes in care. In addition, patient host factors may be different due to changes in health care (ie, new drugs). All of the above changes might influence the development of organ failure during ARDS, with an effect on mortality. Noting a gap in the literature, we tested the hypotheses that organ failure during ARDS has changed, and that this change is associated with decreased mortality.
Materials and Methods
We prospectively identified ARDS patients at the LDS Hospital in Salt Lake City, UT (Table 1). From May 1987 to December 1990, we identified ARDS patients by the presence of all of the following conditions: (1) acute onset of lung injury requiring endotracheal intubation and mechanical ventilation; (2) alveolar-arterial oxygen pressure difference (P(A0a)O2) of £ 0.2; (3) pulmonary capillary wedge pressure (Pw) of £ 15 mm Hg or no evidence of left atrial hypertension; (4) total static thoracic compliance of £ 50 mol/cm H2O; (5) the presence of bilateral chest radiograph infiltrates; and (6) appropriate risk for ARDS (Table 1).
Table 1—ARDS Definition Used at LDS Hospital
|P/F||£ 105 f||£ 150||£ 173|
|Pw, mm Hg||£ 15||£ 18||£ 18|
|Cth, mL/cm H2O||£ 50||Not used||Not used|
|Chest radiograph||Bilateral infiltrates||Bilateral infiltrates||Bilateral infiltrates|
|Presence of risk factors||Required||Required||Required|