Table 3 Variables and diagnostic accuracy (for HFNC outcomes) at different time points during HFNC therapy initiated for acute respiratory failure

ROX index

Before initiation

54

4.23 (3.50–5.13)

45

3.80 (3.12–5.37)

0.280

0.564 (0.447–0.680)

1 h

54

5.36 (4.17–7.35)

44

4.62 (2.61–5.85)

0.032

0.625 (0.515–0.736)

2 h

54

6.81 (5.03–8.33)

44

4.80 (3.96–6.66)

0.001

0.705 (0.602–0.809)

4 h

53

6.26 (4.93–8.77)

40

5.23 (4.14–6.81)

0.016

0.649 (0.535–0.762)

6 h

52

7.19 (5.47–8.58)

36

5.44 (4.42–6.66)

0.001

0.709 (0.595–0.822)

8 h

50

7.78 (5.59–10.22)

32

6.13 (4.41–7.41)

0.013

0.667 (0.547–0.786)

10 h

49

7.90 (5.91–9.16)

29

5.48 (4.40–7.52)

0.001

0.723 (0.605–0.840)

12 h

49

8.25 (6.20–11.11)

27

5.66 (4.78–8.58)

0.008

0.684 (0.559–0.809)

18 h

44

7.92 (6.56–9.98)

21

6.32 (4.65–7.51)

0.005

0.723 (0.584–0.862)

24 h

37

8.77 (6.92–11.27)

13

5.33 (3.76–6.42)

< 0.001

0.866 (0.758–0.974)

48 h

23

8.30 (6.53–12.83)

8

5.45 (4.50–6.55)

0.005

0.860 (0.706–1.000)

Before termination*

NA

9.76 (8.01–12.94)

NA

4.25 (3.38–5.50)

< 0.001

NA

Heart rate (beats/min)

Before initiation

54

94 (78–110)

45

102 (88–111)

0.162

0.582 (0.486–0.696)

1 h

54

90 (76–98)

44

100 (87–112)

0.003

0.675 (0.566–0.783)

2 h

54

90 (77–102)

44

95 (89–112)

0.016

0.643 (0.531–0.755)

4 h

53

89 (76–98)

40

94 (84–112)

0.011

0.658 (0.541–0.774)

6 h

52

88 (75–96)

36

91 (78–103)

0.238

0.575 (0.449–0.702)

8 h

50

87 (73–97)

32

89 (79–105)

0.126

0.602 (0.474–0.731)

10 h

49

85 (72–99)

29

99 (81–109)

0.010

0.678 (0.548–0.808)

12 h

49

83 (70–97)

27

96 (77–117)

0.041

0.642 (0.504–0.779)

18 h

44

87 (74–100)

21

96 (71–116)

0.084

0.638 (0.469–0.806)

24 h

37

84 (77–99)

13

103 (75–116)

0.075

0.666 (0.471–0.860)

48 h

23

84 (72–93)

8

97 (83–111)

0.120

0.698 (0.435–0.961)

Before termination*

NA

86 (77–95)

NA

110 (88–127)

< 0.001

NA

ROX-HR index

Before initiation

54

4.49 (3.36–6.95)

45

4.05 (2.98–5.97)

0.181

0.579 (0.464–0.693)

1 h

54

5.97 (4.59–8.37)

44

4.76 (6.73–3.40)

0.005

0.664 (0.557–0.771)

2 h

54

7.14 (5.58–10.75)

44

5.16 (4.02–6.97)

< 0.001

0.727 (0.627–0.828)

4 h

53

6.85 (5.47–11.67)

40

5.83 (4.10–7.94)

0.007

0.667 (0.554–0.779)

6 h

52

7.84 (6.51–11.36)

36

6.40 (4.55–8.50)

0.003

0.693 (0.579–0.807)

8 h

50

8.59 (6.14–13.08)

32

7.15 (5.06–9.57)

0.011

0.670 (0.552–0.788)

10 h

49

8.24 (7.00–12.51)

29

6.57 (4.32–8.40)

0.001

0.739 (0.626–0.853)

12 h

49

10.44 (6.26-14.22)

27

6.38 (3.82–11.00)

0.008

0.685 (0.558–0.813)

18 h

44

9.24 (7.74-12.17)

21

6.05 (4.38–11.40)

0.016

0.691 (0.531–0.852)

24 h

37

10.20 (7.39-14.03)

13

6.08 (3.46–7.87)

< 0.001

0.831 (0.706–0.957)

48 h

23

11.79 (7.07-17.53)

8

5.23 (4.81–8.69)

0.003

0.864 (0.704–1.000)

Before termination*

NA

10.81 (8.62-15.93)

NA

4.30 (3.19–5.27)

< 0.001

NA