Table 2.
Respiratory mechanics, gas exchange, CT scan variables and outcome of the patients divided according to lower or higher airway driving pressure at PEEP 5 cmH2O
| Variable | Overall population (N = 150) | Lower airway driving pressure (<15 cmH2O) (N = 108) | Higher airway driving pressure (≥15 cmH2O) (N = 42) | p value |
|---|---|---|---|---|
| Airway driving pressure (cmH2O) | 12.6 [10.3–15.2] | 11.6 [10.0–13.1] | 16.9 [15.7–18.9] | <0.001 |
| Transpulmonary driving pressure (cmH2O) | 9.0 [7.3–11.7] | 8.1 [6.5–9.8] | 13.6 [11.7–15.1] | <0.001a |
| End-inspiratory airway plateau pressure (cmH2O) | 18.2 [16.2–20.9] | 17.2 [15.6–18.7] | 22.5 [20.9–24.0] | <0.001 |
| Lung stress (cmH2O) | 13.5 [10.7–16.0] | 11.8 [10.0–14.0] | 17.5 [15.4–18.9] | <0.001a |
| Respiratory system elastance (cmH2O/L) | 25.2 [19.8–30.5] | 22.1 [18.7–26.7] | 33.6 [29.6–40.4] | <0.001 |
| Lung elastance (cmH2O/L) | 17.5 [13.9–23.2] | 15.4 [12.7–19.9] | 27.4 [21.9–31.6] | <0.001 |
| Chest wall elastance (cmH2O/L) | 6.3 [4.3–9.0] | 5.9 [4.3–8.7] | 7.8 [4.6–10.4] | 0.054 |
| PaCO2 (mmHg)b | 44.2 [39.9–50.5] | 43.9 [39.2–50.5] | 47.6 [41.3–50.7] | 0.117a |
| PaO2/FiO2 ratiob | 143 [98–177] | 145 [104–178] | 132 [81–176] | 0.404 |
| Lung total gas (mL)c | 1058 [721–1662] | 1234 [879–1827] | 694 [562–903] | <0.001 |
| Total lung tissue weight (g)b | 1394 [1145–1684] | 1369 [1173–1742] | 1457 [1050–1682] | 0.787 |
| • Non-aerated lung tissue (%)b | 45.2 [34.0–56.9] | 44.9 [36.6–53.6] | 50.4 [30.7–61.1] | 0.419a |
| • Poorly aerated lung tissue (%)b | 28.1 [20.2–39.2] | 27.1 [20.1–36.1] | 34.1 [20.3–43.0] | 0.067 |
| • Well-aerated lung tissue (%)b | 23.9 [14.2–33.9] | 28.2 [17.2–34.6] | 16.5 [8.2–26.7] | 0.006 |
| • Over-aerated lung tissue (%)b | 0.01 [0.00–0.17] | 0.03 [0.00–0.29] | 0.00 [0.00–0.02] | 0.002 |
| Lung recruitability (%)b | 15.6 [7.9–23.7] | 12.5 [7.5–22.1] | 18.5 [9.7–26.4] | 0.110 |
| ICU mortality N (%) | 48 (32.0) | 29 (26.9) | 19 (45.2) | 0.049 |
Lung mechanics, gas exchange, CT-related variables and lung total gas were determined at PEEP 5 cmH2O. Statistical analysis: Student’s t testa, Mann-Whitney rank sum test, chi-square, as appropriate
Abbreviations: CT computed tomography, PEEP positive end-expiratory pressure, PaCO 2 arterial partial pressure of carbon dioxide, PaO 2 arterial partial pressure of oxygen, FiO 2 inspired fraction of oxygen, ICU intensive care unit
bData available for 91 patients (59 in the “lower airway driving pressure” group and 32 in the “higher airway driving pressure” group)
cTotal gas was computed either by CT scan analysis (in 59 and 32 patients, respectively), or by helium dilution technique (in 48 and ten patients, respectively)