ROX index calculation from pulse oximetry and ABG at admission
| Total population (N=895) | IMV (n=93) | Non-IMV (n=802) | P value | |
| Admission pulse oximetry, mean (SD) | ||||
| SpO2 | 88.0 (1.25) | 86.2 (10.31) | 88.2 (6.78) | 0.080 |
| FiO2 | 27.7 (11.43) | 41.1 (22.36) | 25.8 (7.27) | <0.001 |
| RR | 21.7 (6.12) | 24.8 (8.09) | 21.3 (5.62) | <0.001 |
| Oximetry ROX index | 18.0 (5.41) | 13.4 (6.41) | 18.5 (5.01) | <0.001 |
| Admission ABG, mean (SD) | ||||
| pH | 7.4 (0.14) | 7.4 (0.10) | 7.4 (0.14) | 0.001 |
| PaO2 | 60.0 (19.2) | 66.7 (29.22) | 59.0 (17.08) | 0.013 |
| PCO2 | 33.3 (8.4) | 37.8 (15.05) | 32.7 (6.86) | 0.002 |
| FiO2 | 27.8 (11.4) | 41.1 (22.36) | 26.0 (7.28) | <0.001 |
| Lactate | 2.4 (2.47) | 3.4 (3.93) | 2.1 (1.72) | 0.002 |
| PaO2:FiO2 | 231.0 (72.05) | 190.8 (95.31) | 237.4 (65.51) | <0.001 |
| ABG ROX index | 16.6 (5.51) | 11.5 (6.01) | 17.2 (5.10) | <0.001 |
ABG, arterial blood gases; FiO2, fraction of inspired oxygen; IMV, invasive mechanically ventilated patients; non-IMV, non-invasive mechanically ventilated patients; PaO2, arterial oxygen pressure; PaO2:FiO2, ratio of arterial oxygen pressure to fraction of inspired oxygen; PCO2, carbon dioxide partial pressure; ROX index, Respiratory rate-OXygenation index; RR, respiratory rate; SpO2, oxygen saturation by pulse oximetry.