Table 2 Variations in breathing pattern, gas exchange, dyspnea and comfort before and during the first 24 h of HFNC oxygen therapy (n = 123)

HFNC settings

 FiO₂ (%)

40 [35–50]

50 [40–60]*

50 [36–60]*

 < 0.001

 Temperature (°C)

[–]

34 [31–37]

34 [31–37]

[–]

 HFNC flow (L/min)

[–]

60 [50–60]

60 [50–60]

[–]

Arterial blood gases

 pH

7.47 [7.43–7.5]

7.48 [7.44–7.52]*

7.48 [7.43–7.51]

0.01

 PaO₂/FiO₂ (mmHg)

164 [130–214]

150 [118–205]

165 [129–211]

0.33

 PaO₂ (mmHg)

69 [57–81]

74 [62–90]

69 [62–84]

0.06

 PaCO₂ (mmHg)

40 [35–50]

41 [35–48]

42 [37–53]

0.07

 Lactate (mmol/L)

1.5 [1–2.1]

1.4 [1–2.1]

1.4 [1–2.1]

0.81

 HCO₃⁻ (mEq/L)

29 [25.9–33.2]

30.1 [27.05–35.7]

30.1 [26.6–34.7]*

0.09

 BE (mmol/L)

4.9 [1.8–9.1]

5.9 [2.6–12.4]

7.7 [2.6–11.6]

0.21

Clinical data

 SpO₂ (%)

95 [92–97]

96 [93–98]*

96 [93–98]

0.01

 RR (breaths/min)

25 [22–30]

22 [20–26]*

22 [18–25]*

 < 0.001

 ROX Index

8.64 [6.6–11.99]

9.13 [6.74–11.25]

9.05 [6.72–12.47]

0.50

 Borg Scale

3 [2–5]

2 [1–3]*

1 [0.5–3]*

 < 0.001

 Comfort Scale

3 [2, 3]

4 [3, 4]*

4 [3, 4]*

 < 0.001