| Patient characteristics | Retrospective derivation cohort# | Prospective validation cohort¶ |
| Demographics | ||
| Age yrs | 68.0 (57.0–78.0) | 68.0 (51–84) |
| Female | 186 (45) | 243 (52) |
| Predisposing conditions | ||
| Sepsis | 47 (11) | 257 (55) |
| Trauma | 18 (4) | 27 (6) |
| Shock | 164 (40) | 135 (29) |
| Pneumonia | 55 (13) | 214 (46) |
| Aspiration | 19 (5) | 44 (9) |
| Pancreatitis | 4 (1) | 41 (9) |
| High-risk surgery | ||
| None | 308 (75) | 419 (90) |
| Elective | 31 (8) | 16 (3) |
| Emergent | 70 (17) | 32 (7) |
| Risk modifiers | ||
| Alcohol | 26 (6) | 36 (8) |
| Smoking | 175 (43) | 198 (42) |
| Hypoalbuminaemia | 13 (3) | 58 (12) |
| Diabetes | 87 (21) | 116 (25) |
| Chemotherapy | 2 (0) | 31 (7) |
| Oxygen supplementation >0.35 FI,O2+ | 194 (47) | 126 (27) |
| Tachypnoea§ | 51 (12) | 47 (10) |
Data are presented as mean (interquartile range) or n (%). Missing data: smoking (83% complete), alcohol (93% complete) and serum albumin (7% complete). Missing data were considered as negative. FI,O2: inspiratory oxygen fraction. #: intensive care unit, n = 409; ¶: hospital, n = 467; +: >4 L·min−1 nasal cannula; §: respiratory rate, 30 breaths·min−1.