Reduced mortality in association with the acute respiratory distress syndrome (ARDS)

Abstract

Background - A study was undertaken to investigate possible reductions in mortality and/or changes in outcome predictive factors in patients with the acute respiratory distress syndrome (ARDS) managed in a single centre. Methods - The study was a prospective observational cohort study of two patient populations with ARDS. Group 1 comprised 41 patients enrolled between May 1990 and April 1993, and group 2 consisted of 78 patients enrolled between June 1993 and March 1997. The end points of the study were mortality and various factors predictive of death. Results - There was a marked reduction in mortality between groups 1 and 2 (66% versus 34%; relative risk 1.77; CI 1.23 to 2.55). There were no significant differences between the groups in terms of age (40.6 (3.3) versus 45.5 (2.2) years), APACHE score (14.5 (0.72) versus 13.6 (0.1)), lung injury score (2.95 (0.07) versus 2.8 (0.1)), incidence of multi-organ failure (29% versus 32%), incidence of sepsis (31% versus 39%), or Pao2/FIO2 (kPa) ratio (11.8 (0.67) versus 12.0 (0.6)). There was a significantly lower proportion of men in group 1 (51% versus 74%). The case mix of the two groups was closely matched: following elective surgery 48% versus 48%, trauma 17% versus 16%, primary lung injury 12% versus 24%. Patients in group 1 were supported using several ventilatory and other modes (volume preset, non-inverse ratio ventilation, n = 15; pressure controlled inverse ratio Ventilation (PC-IRV), n = 11; ultra high frequency jet ventilation (UHFJV), n = 13; an intravascular oxygenation device (IVOX) and extracorporeal gas exchange (ECGE), n = 2). Within group 1 no significant difference in mortality was observed between the patients on volume controlled ventilation and the remainder. In group 2 all Patients received PC-IRV (n = 78) but, in addition, some received other support techniques (UHFJV n = 4, ECGE n = 2). In group 1 only sepsis on admission (21% (survivors) versus 56% (non-survivors)) predicted death. In group 2 age of survivors and non-survivors (41.2 (2.6) versus 52.6 (3.5)), APACHE score (12.2 (0.6) versus 15.8 (0.9)), and Pao2/FIO2 (12.8 (0.86) versus 10.5 (0.72)) predicted survival but not the incidence of sepsis or multi-organ failure. Conclusions - In recent years a highly significant reduction in mortality associated with ARDS has been observed between two groups of patients well matched for disease severity and case mix. Changes in ICU organisation rather than specific interventions may account for this reduction, although different ventilatory and other management strategies used in the two groups may also be relevant.