Table 2 Comparison of gas exchange and mechanical properties of the respiratory system in different phases of the study
|  | Supine | Supine + weight | Prone | Prone + weight | p value |
|---|---|---|---|---|---|
pH | 7.36 ± 0.03 | 7.36 ± 0.02 | 7.37 ± 0.03 | 7.37 ± 0.02 | 0.2470 |
PaO2 (mmHg) | 68.9 ± 4.6 | 67.8 ± 8.3 | 101 ± 15°* | 92.4 ± 12.4°*§ |  < 0.0001 |
PaCO2 (mmHg) | 48.8 ± 8.0 | 48.7 ± 7.0 | 47.8 ± 7.5 | 48.1 ± 6.8 | 0.9070 |
PaO2/FiO2 (mmHg) | 121 ± 18 | 118 ± 15 | 177 ± 41°* | 161 ± 27°*§ |  < 0.0001 |
EtCO2 (mmHg) | 39.1 ± 3.4 | 39.3 ± 3.8 | 39.5 ± 3.98 | 39.6 ± 4.34 | 0.9465 |
Ventilatory ratio | 1.72 ± 0.42 | 1.71 + 0.38 | 1.68 ± 0.40 | 1.69 ± 0.37 | 0.9701 |
Alveolar dead space (%) | 19.0 ± 6.76 | 18.9 ± 4.6 | 16.6 ± 5.64 | 17.4 ± 4.4 | 0.1364 |
Airway plateau pressure (cmH2O) | 21.3 ± 5.0 | 21.8 ± 2.1 | 19.5 ± 3.5* | 20.5 ± 2.1 | 0.0193 |
Airway driving pressure (cmH2O) | 11.9 ± 4.32 | 12.4 ± 2.06 | 10.1 ± 3.02* | 11.1 ± 2.28 | 0.0063 |
Respiratory system compliance (ml/cmH2O) | 48.5 ± 21.8 | 40.4 ± 9.4 | 53.8 ± 21.0* | 45.2 ± 9.4 | 0.0041 |
Mean arterial pressure (mmHg) | 78.4 ± 5.5 | 78.5 ± 5.5 | 79.6 ± 5.7 | 79.6 ± 5.5 | 0.6341 |
Heart rate (1/min) | 77.1 ± 8.1 | 77.5 ± 8.3 | 78.3 ± 7.6 | 78.4 ± 7.8 | 0.8861 |