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Table 4 Changes in respiratory mechanics, blood gas analysis and VDalv in PaCO2 responders (n = 7) and PaCO2 nonresponders (n = 6)a

From: PaCO2 and alveolar dead space are more relevant than PaO2/FiO2 ratio in monitoring the respiratory response to prone position in ARDS patients: a physiological study

   Supine PP H3 PP H6 PP H9 PP H12 PP H15  
Parameters   Median 1st to 3rd interquartile range Median 1st to 3rd interquartile range Median 1st to 3rd interquartile range Median 1st to 3rd interquartile range Median 1st to 3rd interquartile range Median 1st to 3rd interquartile range P values
PaCO2, mmHg) R 58 (55 to 59) 57 (51 to 57) 54 (44 to 57) 50 (46 to 53) 50 (46 to 55) 50 (47 to 52) 0.005
  NR 56 (49 to 60) 52 (49 to 60) 54 (49 to 62) 54 (49 to 60) 56 (51 to 62) 57 (49 to 59)  
VDalv/VT R 0.40 (0.37 to 0.45) 0.31 (0.29 to 0.46) 0.23 (0.31 to 0.40) 0.26 (0.26 to 0.42) 0.28 (0.24 to 0.44) 0.28 (0.23 to 0.43) 0.005
  NR 0.45 (0.42 to 0.51) 0.38 (0.32 to 0.47) 0.38 (0.35 to 0.43) 0.37 (0.33 to 0.45) 0.42 (0.39 to 0.51) 0.44 (0.39 to 0.54)  
PaO2/FiO2, mmHg R 70 (59 to 78) 103 (96 to 136) 138 (83 to 146) 111 (91 to 156) 136 (95 to 142) 139 (103 to 148) 0.0001
  NR 63 (44 to 76) 83 (80 to 89) 79 (73 to 88) 83 (74 to 88) 84 (62 to 87) 89 (70 to 97)  
Pplat, cmH2O R 27 (24 to 27) 23 (22 to 25) 23 (20 to 25) 23 (22 to 25) 21 (21 to 25) 23 (21 to 25) 0.002
  NR 28 (26 to 28) 26 (24 to 28) 26 (25 to 28) 26 (25 to 28) 26 (25 to 26) 26 (25 to 26)  
Crs, mL/cmH2O R 28 (15 to 30) 30 (18 to 36) 34 (17 to 41) 32 (18 to 38) 32 (19 to 39) 31 (18 to 39) 0.002
  NR 15 (12 to 20) 15 (13 to 24) 15 (13 to 23) 15 (13 to 23) 15 (14 to 22) 15 (14 to 22)  
  1. aCrs: compliance of the respiratory system; NR: nonresponders; PP: prone position; Pplat: plateau pressure; R: responders; VDalv/VT: ratio of alveolar dead space to tidal volume. P value represents comparison of changes between responders and nonresponders. H3, H6, H9, H12 and H15: 3, 6, 9, 12 and 15 hours of PP, respectively. Responders are defined as patients whose PaCO2 decreased > 2 mmHg after 15 hours of PP.