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Table 3 Changes in respiratory mechanics, blood gas analysis and VDalv in PaO2 responders (n = 7) and PaO2 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 value
PaO2/FiO2, mmHg R 51 (48 to 69) 91 (86 to 112) 94 (83 to 142) 97 (86 to 126) 98 (93 to 142) 108 (99 to 142) 0.0003
  NR 77 (76 to 81) 91 (82 to 99) 79 (73 to 88) 84 (82 to 99) 84 (82 to 87) 89 (82 to 97)  
VDalv/VT R 0.43 (0.41 to 0.47) 0.35 (0.31 to 0.46) 0.35 (0.29 to 0.41) 0.38 (0.23 to 0.42) 0.40 (0.31 to 0.40) 0.41 (0.32 to 0.45) 0.31
  NR 0.42 (0.36 to 0.50) 0.35 (0.28 to 0.47) 0.31 (0.22 to 0.43) 0.32 (0.27 to 0.44) 0.36 (0.28 to 0.51) 0.35 (0.27 to 0.53)  
PaCO2, mmHg R 58 (54 to 60) 52 (51 to 58) 51 (47 to 57) 49 (48 to 53) 54 (48 to 55) 51 (47 to 55) 0.14
  NR 55 (52 to 60) 56 (51 to 62) 57 (48 to 62) 55 (48 to 60) 54 (48 to 63) 53 (48 to 58)  
Pplat, cmH2O R 27 (27 to 30) 25 (22 to 26) 24 (23 to 26) 24 (23 to 26) 24 (22 to 26) 24 (24 to 25) 0.27
  NR 27 (24 to 28) 25 (24 to 28) 25 (22 to 26) 25 (23 to 27) 26 (22 to 26) 26 (25 to 26)  
Crs, mL/cmH2O R 16 (13 to 28) 19 (16 to 37) 18 (16 to 38) 18 (16 to 35) 20 (17 to 35) 19 (17 to 33) 0.023
  NR 19 (14 to 31) 21 (14 to 33) 21 (14 to 36) 21 (14 to 34) 19 (15 to 34) 19 (15 to 34)  
  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 values represent 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 PaO2/FiO2 increased > 20 mmHg after 15 hours of PP.