Cohort characteristics
| N | 590 |
| Age, mean (SD) | 68.5 (16.3) years |
| Sex, male (%) | 297 (50.3%) |
| Country of birth, n (%) | |
| Australia | 265 (45%) |
| Other | 324 (55%) |
| Not recorded | 1 (<0.01%) |
| Arterial blood gas values, median (IQR) | |
| pH | 7.34 (7.28–7.38) |
| pCO2 | 53 (48–61) |
| pO2 | 76 (60–113) |
| Bicarbonate | 29 (26–32) |
| Potential underlying cause for hypercapnia, n (%) | |
| Chronic obstructive pulmonary disease | 353 (60%) |
| Congestive cardiac failure | 289 (49%) |
| Sleep disordered breathing | 121 (21%) |
| Opioid use | 108 (18%) |
| Neuromuscular disease | 15 (2.5%) |
| Charlson Comorbidity Index, median (IQR) | 7 (4–9) |