| Days 1–2 | Days 5–7 | Days 14–17 | Days 18–21 | |
| Paco2 (mm Hg) | 44.0 (5.4) | 46.3 (5.2) | 53.9 (6.8)* | 53.9 (6.2)* |
| VT, set (ml/kg) | 5.12 (0.70) | 5.05 (0.80) | 5.21 (0.98)† | 5.62 (1.17)* |
| VT, measured (ml/kg) | 5.15 (0.62) | 5.24 (0.71) | 5.63 (1.0)* | 6.07 (1.4)* |
| MV (ml/kg/min) | 287 (46) | 279 (46) | 318 (60)* | 337 (67)† |
| PIP limit (cm H2O) | 21.8 (3.8) | 21.4 (3.1) | 26.3 (5.8)‡ | 26.6 (5.6)‡ |
| Working PIP (cm H2O) | 17.7 (4.5) | 17.8 (4.1) | 21.7 (6.4) | 20.5 (5.4) |
Values are expressed as mean (SD).
*p<0.01, †p<0.05, ‡p<0.001 compared with days 1–2.
MV, minute ventilation; Paco2, partial pressure of arterial carbon dioxide; PIP, peak inspiratory pressure; VT, tidal volume.