title: Modelling thirty-day mortality in the Acute Respiratory Distress Syndrome (ARDS) in an adult ICU.
abstract: Variables predicting thirty-day outcome from Acute Respiratory Distress Syndrome (ARDS) were analysed using Cox regression structured for time-varying covariates. Over a three-year period, 1996-1998, consecutive patients with ARDS (bilateral chest X-ray opacities, PaO2/FiO2 ratio of <200 and an acute precipitating event) were identified using a prospective computerized data base in a university teaching hospital ICU. The cohort, 106 mechanically ventilated patients, was of mean (SD) age 63.5 (15.5) years and 37% were female. Primary lung injury occurred in 45% and 24% were postoperative. ICU-admission day APACHE II score was 25 (8); ARDS onset time from ICU admission was 1 day (median: range 0-16) and 30 day mortality was 41% (95% CI: 33%-51%). At ARDS onset, PaO2/FiO2 ratio was 92 (31), 81% had four-quadrant chest X-ray opacification and lung injury score was 2.75 (0.45). Average mechanical ventilator tidal volume was 10.3 ml/predicted kg weight. Cox model mortality predictors (hazard ratio, 95% CI) were: APACHE II score, 1.15 (1.09-1.21); ARDS lag time (days), 0.72 (0.58-0.89); direct versus indirect injury, 2.89 (1.45-5.76); PaO2/FiO2 ratio, 0.98 (0.97-0.99); operative versus non-operative category, 0.24 (0.09-0.63). Time-varying effects were evident for PaO2/FiO2 ratio, operative versus non-operative category and ventilator tidal volume assessed as a categorical predictor with a cut-point of 8 ml/kg predicted weight (mean tidal volumes, 7.1 (1.9) vs 10.7 (1.6) ml/kg predicted weight). Thirty-day survival was improved for patients ventilated with lower tidal volumes. Survival predictors in ARDS were multifactorial and related to patient-injury-time interaction and level of mechanical ventilator tidal volume.
authors.affiliation: Department of Intensive Care Medicine, The Queen Elizabeth Hospital Adelaide, South Australia.
authors.forename: J L
authors.initials: JL
authors.lastname: Moran
authors.forename: P J
authors.initials: PJ
authors.lastname: Solomon
authors.forename: V
authors.initials: V
authors.lastname: Fox
authors.forename: M
authors.initials: M
authors.lastname: Salagaras
authors.forename: P J
authors.initials: PJ
authors.lastname: Williams
authors.forename: K
authors.initials: K
authors.lastname: Quinlan
authors.forename: A D
authors.initials: AD
authors.lastname: Bersten
mesh_terms: D018806:APACHE; D000328:Adult; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011859:Radiography; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000401:mortality* / Q000628:therapy; D015996:Survival Rate