Table 1.
Changes in hemodynamics, gas exchange, respiratory mechanics and pulmonary regional ventilation between High and Low PEEP in supine (n = 10)
| High PEEP | Low PEEP | P | |
|---|---|---|---|
| Clinical variables | |||
| Heart rate, beats.min−1 | 72 [64–95] | 76 [59–97] | 0.977 |
| Systolic arterial blood pressure, mmHg | 125 [108–138] | 129 [118–140] | 0.555 |
| Diastolic arterial blood pressure, mmHg | 63 [49–69] | 58 [48–65] | 0.158 |
| Mean arterial blood pressure, mmHg | 77 [72–89] | 77 [73–86] | > 0.999 |
| Transpulmonary thermodilution indices | |||
| Cardiac index, L.min−1.m−2 | 2.5 [2.0–3.0] | 2.6 [2.2–3.3] | 0.027 |
| Global end-diastolic volume indexed, mL.m−2 | 661 [551–870] | 668 [559–813] | 0.432 |
| Extravascular lung water, mL.kg−1 | 15 [13–18] | 14 [13–17] | 0.551 |
| Pulmonary vascular permeability index | 3.3 [2.7–3.9] | 3.3 [2.7–3.6] | 0.607 |
| Cardiac function index, min−1 | 4.4 [2.4–5.3] | 4.5 [2.8–5.8] | 0.008 |
| Gas exchanges | |||
| pH | 7.35 [7.29–7.37] | 7.35 [7.30–7.41] | 0.305 |
| PaCO2, mmHg | 45 [39–51] | 44 [40–47] | 0.191 |
| PaO2/FiO2 ratio, mmHg | 116 [99–196] | 106 [86–129] | 0.127 |
| SaO2, % | 97 [95–98] | 96 [92–97] | 0.172 |
| VD/VT | 0.34 [0.29–0.39] | 0.35 [0.30–0.39] | 0.348 |
| A–a gradient, mmHg | 374 [304–533] | 384 [275–543] | 0.139 |
| Respiratory mechanics | |||
| Respiratory rate, breaths.min−1 | 27 [23–30] | 27 [23–30] | – |
| Tidal volume, mL.kg−1 IBW | 6.0 [6.0–6.3] | 6.0 [6.0–6.3] | – |
| Positive end-expiratory pressure, cmH2O | 16 [16–16] | 8 [8–8] | 0.016 |
| Peak pressure, cmH2O | 44 [42–47] | 35 [33–36] | 0.002 |
| Plateau pressure, cmH2O | 28 [27–31] | 20 [18–21] | 0.002 |
| Driving pressure, cmH2O | 14 [11–16] | 12 [10–13] | 0.004 |
| End-expiratory transpulmonary pressure, cmH2O | 6 [4–8] | 2 [− 1–4] | 0.002 |
| End-inspiratory transpulmonary pressure, cmH2O | 14 [13–17] | 9 [6–10] | 0.002 |
| Respiratory system compliance, ml.cmH2O−1 | 29 [27–36] | 34 [30–42] | 0.012 |
| Respiratory system resistance, cmH2O.L−1.sec−1 | 0.24 [0.20–0.25] | 0.23 [0.22–0.26] | > 0.999 |
| Lung compliance, ml.cmH2O−1 | 47 [40–56] | 64 [46–82] | 0.008 |
| R/I ratio | 0.33 [0.21–0.54] | – | |
| End-expiratory lung volume, mL | 2546 [2151–3019] | 1725 [1450–2023] | 0.002 |
| Electrical impedance tomography derived indices | |||
| Dorsal fraction, % | 46 [43–54] | 35 [32–39] | 0.002 |
| Global inhomogeneity index, % | 58 [52–60] | 60 [55–66] | 0.059 |
| End-expiratory lung impedance | 251 [179–404] | 139 [83–243] | 0.008 |
| Changes in end-expiratory lung impedance, % | − 118 [− 150 to − 32] | 0.004 | |
Data are presented as median [interquartile range] or number (percentage). Wilcoxon matched-pairs signed-rank test was used to evaluate differences between the median values of paired data. PaCO2 partial pressure of arterial carbon dioxide, PaO2 partial pressure of oxygen, FiO2 fraction of inspired oxygen, SaO2 oxygen saturation, VD/VT estimated dead space fraction, A–a gradient alveolar–arterial gradient, R/I recruitment to inflation ratio. P values refer to the comparison between high and low PEEP for each patient