Table 3 Comparison of the low O/R ratio group and the high O/R group

Age (years)

57 (45–75)

66 (55–74)

APACHE II score

16 (14–21)

21 (15–26)

High-risk ARDS

5/14

5/14

Mild ARDS

3/14

5/16

Moderate ARDS

4/14

5/16

Severe ARDS

2/14

1/16

FiO₂ (%)

40 (30–60)

40 (30–50)

PEEP at baseline (cmH₂O)

8 (5–10)

6 (5–8)

PaO₂/FiO₂ at baseline

208 (112–355)

233 (187–331)

Vt at baseline (ml)

410 (400–463)

450 (380–503)

28-day mortality

3/14

4/16

 ZEEP

91 (81–114)

99 (82–105)

 High PEEP

91 (80–112)

97 (83–105)

 ZEEP

86 (82–95)

87 (79–89)

 High PEEP

86 (80–89)

84 (76–97)

 ZEEP

95 (90–99)

97 (91–97)

 High PEEP

99 (96–99)^¶

97 (94–99)

ΔSpO₂ (%)

3 (0–8)

0 (− 1 to 5)

 ZEEP

26 (16–42)

15 (9–24)

 High PEEP

11 (5–21)^¶

16 (9–19)

ΔShunt_%

− 12 (− 23 to − 5)

− 2 (− 7 to 6)

 ZEEP

20 (11–28)

17 (8–25)

 High PEEP

13 (3–18)^¶

13 (5–19)

ΔDeadSpace_%

− 6 (− 16 to − 1)

− 4 (− 8 to 3)

 ZEEP

47 (45–61)

68 (59–75)

 High PEEP

74 (67–80)^¶

73 (60–78)

ΔVQMatch_%

29.7 (22.5–34.4)

3.6 (− 0.3 to 11)

 ZEEP

0.427 (0.379–0.504)

0.411 (0.365–0.505)

 High PEEP

0.360 (0.335–0.381)^¶

0.425 (0.389–0.478)

ΔGI

− 0.071 (− 0.121 to − 0.028)

0.015 (− 0.044 to 0.095)

 ZEEP

1500 (964–1850)

1250 (1000–1775)

 High PEEP

6450 (4400–8325)^¶

7850 (5450–13,000)^¶

ΔEELI (AU)

5000 (3125–6850)

6550 (3650–11,025)

 Total

188 (107–260)

94 (63–145)

 Ventral

99 (28–146)

22 (4–43)

 Dorsal

102 (36–146)

72 (58–105)

 Total

0 (0–17)

110 (93–149)

 Ventral

0 (0–17)

107 (91–147)

 Dorsal

0 (0–0)

0 (0–4)

O/R pixels ratio

0 (0–0.12)

1.0 (0.58–2.20)