Fig. 4

Gas exchange, respiratory rate (RR) and blood biomarker responses during NIV in the PP group and controls. The following parameters are represented: paO2/FiO2 ratio (A), RR (B), ventilatory ratio (VR) (C), corrected Minute Ventilation (MVcorr) (D), serum C-reactive protein (E), plasma D-dimer (latex test, F), serum LDH (G). Blood lymphocyte count (H), neutrophil-to-lymphocyte ratio (I). Patients were censored from the analysis after NIV failure or success. In the box plots, the middle line represents the median observed value, boxes represent the interquartile range (IQR), whiskers extend to the most extreme observed values with 1.5 times the interquartile range of the nearer quartile, and dots represent observed values outside that range. The connecting line connects the mean values within each box plot at different time points. The PP group had a mandatory night PP session of at least 8 h; this session could be extended though the daytime or additional daytime sessions could be delivered according to clinical status and patient compliance. All ABGs were drawn during NIV, at least 1 h after assuming PP or supine position. ABG, arterial blood gas analysis; BC, blood chemistry; LUS, lung ultrasound; PP, prone position; SUP, supine position. The timepoints are indicated as follows: sp0: supine position timepoint 0 (baseline, after NIV initiation), pp1: during the first PP session in the PP group; sp1: supine position timepoint 1 (after the initial 24 h of NIV; in the PP group this also corresponded to the resupination after the first PP session) on day 1, pp2: during the second PP session, sp2: supine position timepoint 2 (after the second day of NIV, in the PP group this also corresponded to the resupination after the second PP session on day 2. pp3 during the third PP session, sp3 supine position timepoint 3 (after the third day of NIV, in the PP group this also corresponded to the resupination after the third PP session on day 3. pp4 during the fourth PP session, sp4 supine position timepoint 4 (after the 4th day of NIV, in the PP group this also corresponded to the resupination after the fourth PP session on day 4. pp5 during the fifth PP session, sp5 supine position timepoint 5 (after the fifth day of NIV, in the PP group this also corresponded to the resupination after the fifth PP session on day 5. pp6 during the sixth PP session, sp6 supine position timepoint 6 (after the sixth day of NIV, in the PP group this also corresponded to the resupination after the sixth PP session on day 6. pp7 during the seventh PP session, sp7 supine position timepoint 7 (after the seventh day of NIV, in the PP group this also corresponded to the resupination after the seventh PP session on day 7