Cox proportional hazards regression analysis of mortality within 90 days
| HR | 95% CI | P value* | |
| Pulmonary emphysema | 0.33 | 0.14 to 0.82 | 0.01 |
| PaO2/FIO2 ratio | 0.99 | 0.98 to 0.99 | 0.01 |
*Adjusted for age and sex.
PaO2/FIO2, partial pressure of arterial oxygen/fraction of inhaled oxygen.