Clinical characteristics of the study cohort
| All patients | HCRF patients | HRF patients | p-value | |
| Subjects | 654 | 594 | 60 | |
| Age years | 64.3 (53.4–71.9) | 55.2 (41.5–68.5) | 64.9 (55.3–73.9) | 0.79 |
| Male:female (% male) | 363:291 (55) | 317:277 (53) | 46:14 (77) | <0.001 |
| Diagnoses | ||||
| COPD | 375 (57) | 360 (61) | 15 (25) | <0.001 |
| Asthma | 35 (5) | 34 (6) | 1 (2) | 0.30 |
| Pneumonia | 117 (18) | 88 (15) | 29 (48) | <0.001 |
| LRTI | 22 (3) | 20 (3) | 2 (3) | 0.72 |
| Bronchiectasis | 27 (4) | 26 (4) | 1 (2) | 0.51 |
| Lung cancer | 25 (3) | 16 (3) | 9 (15) | <0.001 |
| Interstitial lung disease | 15 (2) | 4 (<1) | 11 (18) | <0.001 |
| Acute pulmonary oedema | 41 (6) | 35 (6) | 6 (10) | 0.33 |
| Sleep disordered breathing | 171 (26) | 158 (27) | 13 (22) | 0.50 |
| Obesity | 243 (37) | 231 (31) | 12 (20) | 0.006 |
| Motor neurone disease | 23 (4) | 21 (4) | 2 (3) | 0.77 |
| Admission gas exchange | ||||
| pH | 7.43 (7.29–7.40) | 7.34 (7.29–7.39) | 7.44 (7.39–7.47) | <0.001 |
| PaCO2 mmHg | 62.1 (53.0–75.0) | 65.0 (55.0–76.0) | 38.0 (32.5–43.0) | <0.001 |
| PaO2/FIO2 | 220.0 (180.0–258.9) | 222.7 (185.7–261.9) | 147.2 (79.0–244.5) | <0.001 |
| Mortality | 68 (10.4) | 47 (7.9) | 21 (35.0) | <0.001 |
| Patients requiring ICU | 12 (2) | 5 (<1) | 7 (12) | <0.001 |
| Subsequent mortality | 5 (42) | 1 (20) | 4 (57) | 0.30 |
| Usual WHO Functional Class | ||||
| I | 43 (7) | 32 (5) | 11 (18) | |
| II | 311 (48) | 284 (48) | 27 (45) | <0.001 |
| III | 298 (46) | 188 (32) | 10 (17) | |
| IV | 98 (15) | 86 (15) | 12 (20) |
Data are presented as n, median (interquartile range) or n (%), unless otherwise stated. HCRF: hypercapnic respiratory failure; HRF: hypoxaemic respiratory failure; COPD: chronic obstructive pulmonary disease; LRTI: lower respiratory tract infection; PaCO2: arterial carbon dioxide tension; PaO2: arterial oxygen tension; FIO2: inspiratory oxygen fraction; ICU: intensive care unit; WHO: World Health Organization. p-values refer to differences between HCRF and HRF cohorts.