Table 1.
Respiratory mechanics and gas exchange. Values are given as mean and standard deviation. Effects of Injury on variables were tested with paired t-test (Baseline vs Injury, P<0.05). Differences between and within groups (Group effect; Time × Group effect) were tested with general linear model statistics with BASELINE2 as a covariate. Global statistical significance was accepted at P<0.05. VT, tidal volume; CV VT, coefficient of variation of tidal volume; VF, ventilatory frequency; MV, minute ventilation; Pplat, plateau airway pressure averaged over 100 single breaths; Pmean, mean airway pressure averaged over 100 single breaths; Ppeak, peak airway pressure averaged over 100 single breaths; ERS, elastance of the respiratory system; RRS resistance of the respiratory system; VV, variable ventilation; NV, nonvariable ventilation; Pao2/FIo2, arterial partial oxygen pressure divided by inspiratory oxygen fraction; Pao2; arterial partial oxygen pressure; Paco2, arterial partial carbon dioxide pressure; pH, arterial pH value
| Variable | Group | Baseline1 | Injury | Baseline2 | Time1 | Time2 | Time3 | Time4 | Group effect P-value | Time × Group effect P-value |
|---|---|---|---|---|---|---|---|---|---|---|
| VT (ml kg−1) | VV | 6.5 (0) | 6.5 (0.1) | 6.5 (0) | 6.2 (0.5) | 6.2 (0.5) | 6.2 (0.6) | 6.1 (0.5) | 0.931 | 0.20 |
| NV | 6.6 (0.2) | 6.6 (0.2) | 6.9 (1.0) | 6.5 (0.3) | 6.4 (0.5) | 6.5 (0.4) | 6.6 (0.2) | |||
| CV VT (%) | VV | 0.6 (0.1) | 0.6 (0.2) | 0.5 (0.2) | 28 (2.4) | 26.6 (6.8) | 27.6 (4.3) | 27.4 (4) | ≤0.001 | 0.843 |
| NV | 0.7 (0.3) | 0.6 (0.2) | 0.6 (0.4) | 0.5 (0.2) | 0.4 (0.1) | 0.5 (0.2) | 0.5 (0.1) | |||
| VF (min−1) | VV | 33.6 (2.5) | 33.6 (2.5) | 35.1 (0.1) | 28.3 (7.2) | 27.5 (8.1) | 25.3 (8.6) | 26 (9.3) | 0.522 | 0.162 |
| NV | 33.6 (2.5) | 33.6 (2.5) | 35.1 (0.0) | 32.9 (2.7) | 29.3 (6.1) | 27.9 (5.7) | 26.4 (5.6) | |||
| MV (L min−1) | VV | 7.9 (0.6) | 7.9 (0.6) | 8.3 (0.7) | 6.2 (1.4) | 6.0 (1.6) | 5.4 (1.5) | 5.5 (1.5) | 0.333 | 0.349 |
| NV | 7.6 (0.7) | 7.6 (0.6) | 8.2 (0.9) | 7.3 (0.6) | 6.4 (0.8) | 6.1 (1) | 6 (1.4) | |||
| ERS (cm H2O L−1) | VV | 24.1 (2.7) | 81.2 (7) | 69.2 (12) | 74.6 (22) | 74.1 (24) | 71.3 (23) | 70.1 (23) | 0.746 | 0.647 |
| NV | 23.6 (4.3) | 67.7 (9.8) | 69.1 (8.8) | 79.3 (14) | 78 (14) | 74.6 (11) | 71 (10) | |||
| RRS (cm H2O L−1 s) | VV | 7.3 (0.6) | 10.7 (2) | 7.4 (0.3) | 8.2 (0.6) | 9.1 (1.1) | 9.8 (2.1) | 10.7 (4.2) | 0.479 | 0.101 |
| NV | 7.6 (1.1) | 10 (1.6) | 8.5 (1.9) | 7.9 (0.6) | 8.4 (2.1) | 9.4 (2.2) | 9.6 (2.4) | |||
| Ppeak (cm H2O) | VV | 21 (0.7) | 34.4 (2.4) | 27.6 (4.2) | 27.1 (5.2) | 27.6 (6) | 26.8 (5) | 27.2 (4.7) | 0.713 | 0.152 |
| NV | 20.9 (0.7) | 31.1 (2.6) | 30.5 (3.6) | 29.1 (3.9) | 28.1 (2.3) | 28 (2.5) | 26.6 (2.4) | |||
| Pplat (cm H2O) | VV | 17.4 (0.7) | 30.8 (2.3) | 25.6 (4.3) | 24.6 (5.2) | 24.7 (7) | 23.5 (6.1) | 23.4 (6.2) | 0.608 | 0.188 |
| NV | 17.3 (0.6) | 27 (2.3) | 27.8 (4.8) | 27.1 (4.2) | 25.7 (3.4) | 25.2 (3.1) | 23.6 (3) | |||
| Pmean (cm H2O) | VV | 14 (0.2) | 19.2 (0.8) | 15.5 (3.2) | 14.2 (2.7) | 14.4 (3.5) | 13.8 (3.1) | 14 (3.2) | 0.479 | 0.101 |
| NV | 14 (0.3) | 17.9 (0.9) | 17.6 (3.1) | 15.9 (2.8) | 15.3 (2.2) | 15.2 (2.1) | 13.9 (1.7) | |||
| PEEP (cm H2O) | VV | 10 (0.0) | 9.8 (0.2) | 7.7 (2.9) | 6.2 (1.5) | 6.3 (2) | 5.8 (1.9) | 6.2 (2) | 0.519 | 0.088 |
| NV | 10 (0.0) | 9.8 (0.2) | 9.7 (2.8) | 7.6 (2) | 6.9 (1.9) | 6.7 (1.9) | 5.6 (1.5) | |||
| Pao2/Fio2 (kPa) | VV | 80.1 (80.3) | 9.2 (2.1) | 27.1 (10.9) | 28.5 (10.5) | 29.3 (10.3) | 29.7 (9.9) | 30.4 (11.5) | 0.990 | 0.530 |
| NV | 80 (8) | 8.5 (2) | 21.1 (5.6) | 22 (4.3) | 25.2 (5.9) | 26.4 (6.4) | 25.3 (5.6) | |||
| Pao2 (kPa) | VV | 80.1 (80.3) | 9.2 (2.1) | 11.6 (1.7) | 11.1 (2.4) | 11 (2.1) | 11.1 (1.9) | 11.7 (2.4) | 0.349 | 0.483 |
| NV | 80 (8) | 8.5 (2) | 10.8 (0.8) | 10.1 (1.5) | 9.9 (1.3) | 10.3 (1.4) | 9.9 (1.2) | |||
| Paco2 (kPa) | VV | 6.4 (0.8) | 11.9 (1.4) | 11.7 (2.4) | 11.2 (1.5) | 10.9 (1.0) | 12.2 (1.4) | 12.8 (2.1) | 0.237 | 0.587 |
| NV | 6.8 (0.8) | 11.8 (3.7) | 11.9 (2.7) | 10.7 (2.0) | 10.7 (2.1) | 11.6 (2.6) | 11.2 (1.4) | |||
| pH | VV | 7.38 (0.04) | 7.23 (0.06) | 7.26 (0.08) | 7.30 (0.06) | 7.33 (0.06) | 7.32 (0.06) | 7.30 (0.07) | 0.188 | 0.401 |
| NV | 7.38 (0.04) | 7.25 (0.11) | 7.22 (0.08) | 7.30 (0.05) | 7.32 (0.04) | 7.34 (0.05) | 7.35 (0.05) |