TABLE 2.
Main Physiologic Variables During the Semirecumbent and Prone Periods
| Variables, Units | Semirecumbent Position | Prone Position | ||||||
|---|---|---|---|---|---|---|---|---|
| Base | End | Absolute Difference | Relative Difference | Base | End | Absolute Difference | Relative Difference | |
| Gas exchange | ||||||||
| Arterial pH | 7.45 (7.44–7.48) | 7.47 (7.44–7.49) | 0.01 (–0.01 to 0.01) | 0.1 (–0.1 to 0.1) | 7.46 (7.44–7.49) | 7.44 (7.43–7.48) | –0.01 (–0.02 to 0.01) | –0.1 (–0.3 to 0.1) |
| Pao2, torr | 79 (64–90) | 64 (56–82) | –6 (–19 to 4) | –8 (–22 to 3) | 70 (61–96) | 130 (103–180)a | 37 (16–96)b | 34 (16–147)c |
| Fio2, torr | 0.8 (0.7–0.9) | 0.8 (0.7–0.95) | 0 (0–0) | 0 (0–0) | 0.8 (0.7–0.95) | 0.8 (0.7–1) | 0 (0–0) | 0 (0–0) |
| Pao2/Fio2, torr | 95 (73–135) | 91 (64–120) | –8 (–26 to 4) | –8 (–22 to 3) | 84 (61–137) | 208 (114–226)a | 41 (20–124)b | 34 (12–147)c |
| Paco2, torr | 32 (30–35) | 31 (28–34) | 0 (–3 to 1.4) | 0 (–9 to 5) | 32 (29–34) | 33 (30–35) | 1.2 (–1 to 2) | 4 (–3 to 7) |
| End-tidal CO2 tension, torr | 30 (27–31) | 28 (26–32) | 0.1 (–1.3 to 0.8) | 0.5 (–4 to 3) | 29 (26–31) | 31 (29–33) | 2.8 (0–3.7)b | 9 (0–14)c |
| Physiologic dead space to tidal volume ratio | 0.51 (0.48–0.58) | 0.52 (0.5–0.56) | 0 (–0.03 to 0.02) | –0.8 (–5.5 to 3.8) | 0.54 (0.48–0.57) | 0.49 (0.45–0.52) | –0.03 (–0.06 to –0.02)b | –5 (–11.5 to –3.7)c |
| Respiratory mechanics | ||||||||
| Respiratory rate, breaths/min | 26 (21–32) | 28 (20–33) | 0 (–4 to 2) | 0 (–14 to 8) | 26 (21–30) | 21 (19–22)a | –5 (–9 to 1)b | –17 (–29 to 6)c |
| Delta of the esophageal pressure between the end-expiratory and end-inspiratory values, cm H2O | 11.3 (8.1–14.7) | 11.6 (9–16.9) | 0.2 (–0.8 to 4.1) | 1 (–9 to 31) | 10.6 (7.4–17.7) | 9.7 (7.5–13.1) | –1.5 (–3.5 to 1.2) | –11 (–19 to 14) |
| Delta of the transpulmonary pressure (airway minus esophageal) between the end-inspiratory and end-expiratory values, cm H2O | 11.3 (8–14.7) | 11.6 (9–16.9) | 0.2 (–0.8 to 4.2) | 1 (–9 to 30) | 10.6 (6.8–17.7) | 9.7 (7.5–13.1) | –1.5 (–3.5 to 1.2) | –11 (–19 to 14) |
| sPTPES/breath, cm H2O.s | 6.1 (4.8–10.8) | 6.6 (4.9–12.1) | 0.1 (–0.3 to 1.1) | 1 (–4 to 13) | 7 (5.1–11.2) | 8.2 (5.2–10.3) | –0.6 (–1.9 to 1.5) | –6 (–23 to 26) |
| sPTPES/min, cm H2O.s.min-1 | 213 (161–267) | 217 (161–331) | 20 (7–50) | 10 (3–20) | 225 (176–332) | 174 (161–254) | –29 (–54 to 7)b | –10 (–22 to 2)c |
| Self-assessed symptoms | ||||||||
| Dyspnea, VAS | 29 (20–45) | 20 (13–40) | –5 (–12 to 0) | –24 (–38 to 0) | 30 (8–40) | 20 (0–40) | 0 (–10 to 5) | –9 (–80 to 18) |
| Discomfort, VAS | 30 20–34) | 20 (18–40) | 0 (–17 to 5) | 0 (–34 to 18) | 30 (15–42) | 31 (25–62) | 0 (–5 to 25)a | 5 (–17 to 75) |
| Pain, VAS | 0 (0–15) | 0 (0–20) | 0 (0–0) | 0 (0–0) | 10 (0–20) | 15 (0–20) | 5 (0–17) | 0 (0–0) |
| Hemodynamics | ||||||||
| Heart rate, beats/min | 72 (65–84) | 75 (68–88) | –1 (–2 to 3) | –1 (–2 to 4) | 77 (71–84) | 78 (64–84) | –1 (–10 to 6) | –1 (–14 to 8) |
| Mean arterial pressure, mm Hg | 91 (85–97) | 91 (89–98) | 0 (–2 to 3) | 0 (–2 to 7) | 91 (88–93) | 93 (83–95) | –2 (–4 to 9) | –2 (–4 to 10) |
sPTPES = simplified esophageal pressure time product, VAS = Visual Analog Scales with values ranging from 0 (minimal) to 100 (maximal).
p < 0.05 vs the end value of the semirecumbent position (SRP).
p < 0.05 vs the absolute difference of the SRP.
p < 0.05 vs the relative difference of the SRP.
The absolute difference corresponds to the crude difference between the values at the end of the period minus the baseline. The relative difference is calculated as ([end value–baseline value]/baseline value) × 100 and is expressed as a percentage. Between-group comparisons (prone position vs SRP) were performed by a mixed model analysis. Data are expressed as the median (interquartile range 25–75%) unless otherwise specified.