Baseline characteristics of ARDS, AHRF, AHRF-UL and corresponding propensity matched control populations to derive attributable fraction
| Model 1 AFARDS | Model 2 AFARDS | Model 3 AFAHRF | Model 4 AFAHRF-UL | |||||
| ARDS (n=2653) | Non-AHRF (n=5306) | ARDS (n=851) | AHRF-UL (n=851) | AHRF (n=3504) | Non-AHRF (n=7008) | AHRF-UL (n=851) | Non-AHRF (n=1702) | |
| Age (years), mean (SD) | 61.5 (16.8) | 61.4 (16.8) | 63.0 (16.2) | 63.0 (16.9) | 61.8 (16.8) | 62.0 (16.8) | 63.0 (16.9) | 63.0 (16.8) |
| Sex—female n (%) | 1014 (38.2) | 2028 (38.2) | 297 (34.9) | 301 (35.4) | 1315 (37.5) | 2664 (38.0) | 301 (35.4) | 599 (35.2) |
| BMI mean (SD) | 27.4 (8.6) | – | 26.9 (7.3) | 26.7 (6.8) | 27.3 (8.2) | – | 26.7 (6.8) | – |
| Number of comorbidities n (%) | ||||||||
| 0 | 1053 (39.7) | – | 330 (38.8) | 322 (37.8) | 1375 (39.2) | – | 322 (37.8) | – |
| 1 | 937 (35.3) | – | 302 (35.5) | 302 (35.5) | 1239 (35.4) | – | 302 (35.5) | – |
| 2 or more | 663 (25.0) | – | 219 (25.7) | 227 (26.7) | 890 (25.4) | – | 227 (26.7) | – |
| Risk factor for ARDS n (%) | ||||||||
| Pneumonia | 1574 (59.3) | – | 510 (59.9) | 433 (50.9) | 2007 (57.3) | – | 433 (50.9) | – |
| Extrapulmonary sepsis | 421 (15.9) | – | 141 (16.6) | 115 (13.5) | 536 (15.3) | – | 115 (13.5) | – |
| Aspiration | 386 (14.5) | – | 114 (13.4) | 157 (18.4) | 543 (15.5) | – | 157 (18.4) | – |
| Pancreatitis | 57 (2.1) | – | 16 (1.9) | 11 (1.3) | 68 (1.9) | – | 11 (1.3) | – |
| Pulmonary vasculitis | 12 (0.5) | – | 2 (0.2) | 0 (0) | 12 (0.3) | – | 0 (0.0) | – |
| Trauma | 108 (4.1) | – | 37 (4.3) | 48 (5.6) | 156 (4.5) | – | 48 (5.6) | – |
| Inhalation | 69 (2.6) | – | 28 (3.3) | 22 (2.6) | 91 (2.6) | – | 22 (2.6) | – |
| Pulmonary contusion | 82 (3.1) | – | 28 (3.3) | 34 (4.0) | 116 (3.3) | – | 34 (4.0) | – |
| Burns | 7 (0.3) | – | 3 (0.4) | 2 (0.2) | 9 (0.3) | – | 2 (0.2) | – |
| Non-cardiogenic shock | 201 (7.6) | – | 75 (8.8) | 52 (6.1) | 253 (7.2) | – | 52 (6.1) | – |
| Drowning | 2 (0.1) | – | 1 (0.1) | 0 (0) | 2 (0.1) | – | 0 (0.0) | – |
| Drug overdose | 47 (1.8) | – | 11 (1.3) | 22 (2.6) | 69 (2.0) | – | 22 (2.6) | – |
| Transfusion-related | 107 (4.0) | – | 34 (4.0) | 27 (3.2) | 134 (3.8) | – | 27 (3.2) | – |
| Other | 67 (2.5) | – | 17 (2.0) | 45 (5.3) | 112 (3.2) | – | 45 (5.3) | – |
| No risk factor for ARDS | 229 (8.6) | – | 79 (9.3) | 0 (0) | 229 (6.5) | – | 0 (0.0) | – |
| PaO2:FiO2 ratio on day 1 mean (SD)* | 159 (67.4) | – | 161 (67.6) | 188 (63.6) | 166 (67.8) | – | 188 (63.6) | – |
| Severity of hypoxaemia on day 1 n (%) | ||||||||
| Mild (200–300) | 760 (28.6) | – | 249 (29.3) | 377 (44.3) | 1137 (32.4) | – | 377 (44.3) | – |
| Moderate (100–200) | 1263 (47.6) | – | 400 (47.0) | 380 (44.7) | 1643 (46.9) | – | 380 (44.7) | – |
| Severe (<100) | 626 (23.6) | – | 200 (23.5) | 93 (10.9) | 719 (20.5) | – | 93 (10.9) | – |
| Maximum number of quadrants involved in first 48 hours n (%)* | ||||||||
| 1 | – | – | – | 598 (70.2) | 482 (13.8) | – | 482 (70.2) | – |
| 2 | 1045 (39.4) | – | 351 (41.2) | 236 (27.7) | 1281 (36.6) | – | 236 (27.7) | – |
| 3 | 615 (23.2) | – | 214 (25.1) | – | 624 (17.8) | – | – | – |
| 4 | 993 (37.4) | – | 286 (33.6) | – | 1000 (28.5) | – | – | – |
| Subphenotype of ARDS n (%)* | ||||||||
| Hypoinflammatory | 1966 (74.1) | – | 616 (72.4) | – | – | – | – | – |
| Hyperinflammatory | 687 (25.9) | – | 235 (27.6) | – | – | – | – | – |
| SOFA score day 1 mean (SD) | 9.39 (4.08) | – | 9.55 (4.19) | 8.69 (3.97) | 9.2 (4.1) | – | 8.69 (3.97) | – |
| Non-respiratory SOFA score day 1* | 6.48 (3.96) | – | 6.65 (4.06) | 6.04 (3.87) | 6.4 (4.0) | – | 6.04 (3.87) | – |
| Ventilated on day 1 n (%) | 2151 (81.1) | – | 700 (82.3) | 698 (82.0) | 2849 (81.3) | – | 698 (82.0) | – |
| Duration of invasive mechanical ventilation mean (SD)* | 12.0 (12.9) | – | 12.2 (12.8) | 10.6 (12.6) | 11.7 (12.9) | – | 10.6 (12.6) | – |
| ICU LOS mean (SD) | 14.2 (14.0) | 6.2 (8.2) | 12.7 (13.8) | 6.2 (8.2) | 13.8 (14.0) | 6.2 (8.2) | 12.7 (13.8) | 6.2 (7.9) |
| ICU mortality n (%) | 906 (34.2) | 730 (13.8) | 293 (34.4) | 206 (24.2) | 1112 (31.7) | 1000 (14.3) | 206 (24.2) | 247 (14.5) |
| Hospital LOS mean (SD)* | 23.1 (20.8) | – | 23.6 (20.7) | 22.6 (20.7) | 22.9 (20.8) | – | 22.6 (20.7) | – |
| Hospital mortality n (%)* | 1044 (39.4) | – | 342 (40.2) | 259 (30.4) | 1303 (37.3) | – | 259 (30.4) | – |
AFARDS in model 1 was estimated by matching 2653 patients with ARDS to non-AHRF controls that were propensity score balanced on age and sex in a 1:2 ratio. AFARDS in model 2 was estimated by matching 851 patients with ARDS to AHRF-UL controls in a 1:1 ratio and propensity score balanced on age, sex, number of comorbidities and ventilation status on day 1. AFAHRF in model 3 was estimated by matching 3504 AHRF cases to non-AHRF controls that were propensity score balanced on age and sex in a 1:2 ratio. AFAHRF-UL in model 4 was estimated by matching 851 AHRF-UL cases to non-AHRF controls that were propensity score balanced on age and sex in a 1:2 ratio.
Postmatching standardised mean differences for the matching covariates in each model are shown in online supplemental eTable 4 and were all p<0.05; empirical cumulative density function plots for matching covariates were also consistent with good balance (online supplemental eFigure 2). Propensity score overlap following matching is shown for each model in online supplemental eFigure 3.
*Denotes variable with missing data. Further details of missing data are available in online supplemental eTable 2a.
AF, attributable fraction; AHRF, acute hypoxaemic respiratory failure; AHRF-UL, acute hypoxaemic respiratory failure with unilateral infiltrates only; ARDS, acute respiratory distress syndrome; BMI, body mass index; ICU, intensive care unit; LOS, length of stay; NMV, non-matched variable; PaO2:FiO2, arterial oxygen tension:inspired fraction of oxygen; SOFA, Sequential Organ Failure Assessment.