Table 1 Patients’ characteristics according to PEEP-absorber behaviors, classified as in the primary and secondary analyses

Number of patients (%)

33 (33 %)

67 (67 %)

–

21 (21 %)

46 (46 %)

–

Total PEEP at ZEEP (cmH₂O)

8 ± 3

6 ± 2

<0.001

8 ± 3

5 ± 1*^,#

<0.001

Applied PEEP (cmH₂O)

7 ± 2

5 ± 2

0.001

7 ± 2

4 ± 0*^,#

<0.001

Total PEEP with PEEP (cmH₂O)

9 ± 3

9 ± 2

0.65

10 ± 3

8 ± 1^#

0.001

Female, n (%)

18 (55 %)

24 (36 %)

0.12

5 (24 %)

19 (41 %)

0.08

Age (years)

74 ± 8

70 ± 11

0.07

71 ± 10

69 ± 12

0.18

Body mass index (kg/m²)

30 ± 7

28 ± 6

0.05

31 ± 7

26 ± 5*^,#

0.002

Respiratory rate (1/min)

16 ± 3

22 ± 4

< 0.001

20 ± 3

22 ± 4*

<0.001

Expiratory time (s)

2.7 ± 0.7

1.5 ± 0.5

< 0.001

1.7 ± 0.5

1.4 ± 0.5*

<0.001

Minute ventilation (l/min)

7.1 ± 1.4

10.5 ± 2

< 0.001

10 ± 2

11.1 ± 2.1*

<0.001

Tidal volume (ml/IBW)

8 ± 1

8 ± 1

0.94

8 ± 1.5

8 ± 1.2

0.29

Resistance (cmH₂O∙l⁻¹∙s)

21 ± 5

18 ± 7

0.05

20 ± 9

18 ± 6*

0.03

Elastance (cmH₂O/l)

20 ± 5

19 ± 6

0.25

19 ± 6

18 ± 6

0.47

Flow limitation, n (%)

32 (97 %)

29 (47.8 %)

<0.001

19 (90 %)

10 (22 %)*^,#

<0.001

Chronic pulmonary disease, n (%)

25 (76 %)

22 (33 %)

<0.001

12 (57 %)

10 (22 %)*^,#

<0.001

History of smoking, n (%)

24 (75 %)

24 (38 %)

<0.001

9 (45 %)

15 (34 %) *

0.002

Acute pulmonary disease, n (%)

27 (84 %)

25 (37 %)

<0.001

12 (57 %)

13 (28 %)*

<0.001

PaO₂/F_IO₂ (mmHg)

203 ± 82

275 ± 132

0.01

205 ± 89

306 ± 137*^,#

<0.001

Supine position, n (%)

21 (64 %)

31 (46 %)

0.16

10 (48 %)

21 (46 %)

0.26