Table 2.
Computed tomography-derived parameters over time.
| Study group | |||||
|---|---|---|---|---|---|
| Variables | PV n = 5 |
UPV n = 5 |
Effect of group, p | Effect of time, p | Group × time, p |
| Lung tissue weight at end-expiration, g.kg−1 BW | – | – | 0.05 | ||
| T1 | 16 [15–17] | 14 [14–16] | |||
| T2 | 22 [21–26]‡ | 18 [17–20]†,‡ | |||
| T3 | 26 [23–27]‡ | 24 [19–24]‡ | |||
| End-expiratory aerated lung volume (EELV), ml.kg−1 BW | – | – | <0.01 | ||
| T1 | 21 [19–23] | 27 [23–32] | |||
| T2 | 15 [15–16] | 22 [21–22] | |||
| T3 | 18 [18–22] | 34 [33–56]†,‡ | |||
| Gas fraction at end-expiration | – | – | 0.02 | ||
| T1 | 0.58 [0.55–0.58] | 0.63 [0.63–0.70] | |||
| T2 | 0.40 [0.40–0.43]‡ | 0.55 [0.54–0.57]†,‡ | |||
| T3 | 0.40 [0.39–0.48]‡ | 0.64 [0.64–0.70]† | |||
| End-expiratory hyperinflated volume, ml.kg−1 BW | – | – | <0.01 | ||
| T1 | 0.2 [0.2–0.2] | 0.8 [0.8–1.0] | |||
| T2 | 0.3 [0.2–0.5] | 2.0 [2.0–2.1] | |||
| T3 | 0.5 [0.4–0.6] | 6.0 [4.1–7.4]†,‡ | |||
| PEEP related increase in gas volume (VPEEP), ml.kg−1 BW | – | – | <0.01 | ||
| T1 | 6.2 [5.3–6.8] | 5.6 [5.3–5.6] | |||
| T2 | 3.4 [3.1–5.1] | 3.9 [2.6–4.2] | |||
| T3 | 5.8 [5.7–8.4] | 17.8 [14.6–23.5]†,‡ | |||
| PEEP-related alveolar recruitment, ml.kg−1 BW | – | – | 0.02 | ||
| T1 | 0.7 [0.5–0.9] | 0.3 [0.2–0.6] | |||
| T2 | 1.2 [0.6–1.6] | 0.7 [0.4–0.8] | |||
| T3 | 0.9 [0.7–1.5] | 4.0 [2.5–4.6]†,‡ | |||
| CRS at PEEP (CRS,PEEP), ml.cmH2O−1.kg−1 BW | <0.01 | <0.01 | 0.52 | ||
| T1 | 1.0 [1.0–1.2] | 1.0 [0.9–1.0] | |||
| T2 | 0.5 [0.5–0.7] | 0.5 [0.2–0.6] | * | ||
| T3 | 0.9 [0.7–0.9] | 1.1 [0.9–1.2] | * | ||
| Tidal volume (VT,CT), ml.kg−1 BW | – | – | <0.01 | ||
| T1 | 5.5 [5.1–5.9] | 6.2 [6.2–6.5] | |||
| T2 | 5.3 [4.9–6.1] | 6.3 [6.1–6.8] | |||
| T3 | 5.4 [4.1–5.8] | 1.6 [1.0–2.0]†,‡ | |||
| Tidal recruitment, ml.kg−1 BW | 0.04 | <0.01 | 0.22 | ||
| T1 | 0.2 [0.2–0.5] | 0.1 [0.1–0.3] | |||
| T2 | 0.8 [0.6–1.0] | 0.5 [0.4–0.7] | |||
| T3 | 1.5 [1.3–1.5] | 0.3 [0.2–0.7] | * | ||
| Tidal hyperinflation, ml.kg−1 BW | – | – | <0.01 | ||
| T1 | 0.1 [0.0–0.1] | 0.4 [0.3–0.6] | |||
| T2 | 0.1 [0.1–0.2] | 1.5 [1.3–1.7]†,‡ | |||
| T3 | 0.2 [0.1–0.4] | 0.6 [0.4–0.6] | |||
| Dynamic strain | – | – | 0.01 | ||
| T1 | 0.2 [0.2–0.2] | 0.2 [0.2–0.3] | |||
| T2 | 0.3 [0.2–0.3] | 0.2 [0.2–0.3] | |||
| T3 | 0.2 [0.1–0.2] | 0.0 [0.0–0.0]†,‡ | |||
| Static strain | 0.16 | <0.01 | 0.06 | ||
| T1 | 0.4 [0.3–0.4] | 0.3 [0.2–0.3] | |||
| T2 | 0.3 [0.2–0.3] | 0.2 [0.1–0.2] | * | ||
| T3 | 0.4 [0.4–0.4] | 0.5 [0.4–0.5] | * | ||
Values are median with an interquartile range. Study time points were baseline (T1, healthy lungs), after experimental ARDS onset (T2), and 4 h later (T3). Mixed effects linear regressions with study group and study time point as independent variables, and animal identification number as random effect, were used to compare variables at different study times and in the two groups. Interaction of time study with the group was systematically checked for (using bootstrap with 500 simulations). If no interaction was identified, the p-value of the group and the time study are given, respectively. In case of significant interaction, a pairwise post-hoc multiple comparison was performed to compare groups at each time point on the one side and compare T2 and T3 to T1 in each group, on the other. Multiple comparisons were adjusted for α inflation using the Benjamini and Hochberg method. In pigs 19 and 21, end-inspiratory CT at T3 were missing, and end-inspiratory measurements were not taken.*p < 0.05 compared to T1 (no interaction with study group); †p < 0.05 compared with control group at this study time; ‡p < 0.05 compared with T1 in this study group.UPV, ultra-protective ventilation; PV, protective ventilation; CRS,PEEP, respiratory system compliance at PEEP; EELV, end-expiratory lung volume; VPEEP, PEEP-related increase in gas volume; VT,CT, computerized tomography-derived tidal volume; BW, body weight.