We identified a total of 516 ARDS patients with a P/F of < 105 at ARDS onset (1987 to 1990, 256 patients; 1994 to 1999, 260 patients). We identified 288 patients (1994 to 1999) with a P/F range of 106 to 173.

A total of 548 ARDS patients (260 + 288) were identified between 1994 and 1999. Mortality was lower in 1994-to-1999 patients when compared to 1987-to-1990 patients (p < 0.011). Fewer deaths occurred in the 1994-to-1999 group for P/F values of both < 105 and 106 to 173. Mortality was lower for those with higher arterial oxygenation efficiency (P/F, 106 to 173) than for those with lower arterial oxygenation efficiency (P/F, < 105). Between-group differences for age, gender, or risk factor for ARDS were not significant. Fewer total nonpulmonary organ failures were noted in 1994-to-1999 patients. Cardiovascular and CNS failure, and sepsis were significantly lower prior to ARDS onset and after ARDS onset among 1994-to-1999 patients. Hepatic failure was lower in the 1994-to-1999 patients only after ARDS onset. Patients with higher arterial oxygenation efficiency (P/F, > 105) and those with lower arterial oxygenation efficiency (P/F, < 105) in the 1994-to-1999 group had similar total nonpulmonary organ failure at ARDS onset and similar distributions of organ failures both prior to ARDS onset and after ARDS onset. In contrast, the 1987-to-1990 patients had a lower incidence of hepatic failure after ARDS onset, as ARDS evolved.

We found an inverse association between higher initial arterial oxygenation efficiency (ie, P/F) and lower mortality. This association of mortality with P/F was notably absent in the report of Zilberberg and Epstein. Their reported mortality rate was 58% both for patients with ALI and those with ARDS. However, their overall patient numbers were small, and they did not investigate mortality as a function of arterial oxygenation efficiency within the ARDS patient group. In addition, they studied only medical ICU patients, whereas we studied both medical and surgical patients.

We found an association between higher initial arterial oxygenation efficiency (ie, P/F) and specific organ failure before and after ARDS onset . The association of a greater incidence of organ failure in ARDS patients with a higher mortality is well-described and was observed in our 1994-to-1999 patients. However, the change in organ failure distribution that we observed has not been reported previously.