Table 2.

Main results of the study

	NoH	HME	HH34	HH37	p
Gas exchange
PaO2/FiO2 ratio, mmHg	260 [216–320]	252 [207–317]	232 [188–303]	234 [201–292]	0.73
PaCO2, mmHg	30 [28–36]	34 [30–37]	31 [29–35]	34 [29–38]	0.46
pH	7.47 [7.42–7.49]	7.44 [7.41–7.48]	7.46 [7.42–7.49]	7.47 [7.41–7.49]	0.73
Gas conditioning, self-assessed symptoms and fog effect
Absolute humidity, mgH2O/L	16 [12–19]αβγ	28 [23–31]αε	28 [24–31]βζ	33 [29–38]γζ	< 0.001
Relative humidity, %	52 [40–63]αβγ	92 [81–97]αε	96 [83–100]β	100 [93–100]γε	< 0.001
Helmet temperature, °C	29 [28–30]α	30 [29–31]ε	31 [29–32]ζ	32 [31–33]αεζ	< 0.001
Dyspnea, VAS	2 [1–5]	3 [1–5]	4 [1–5]	4 [1–7]	0.46
Discomfort, VAS	4 [2–6]γ	6 [2–7]	7 [4–8]	8 [4–10]γ	0.03
Fog effect, 1–3 scale	0 [0–0]αβγ	1 [1–3]αε	2 [1–3]βζ	3 [3–3]γζ	< 0.001
Respiratory mechanics and work of breathing indices
Patient respiratory rate, bpm	26 [22–31]	26 [22–32]	27 [21–33]	26 [22–31]	0.99
Ventilator respiratory rate, bpm	31 [27–36]	31 [25–34]	32 [24–34]	30 [23–33]	0.43
Helmet minute ventilation, L*min−1	21 [20–27]	19 [16–24]δε	27 [23–30]δ	24 [20–32]ε	0.009
ΔPES, cmH2O	7 [4–9]	9 [5–11]	6 [4–10]	7 [5–11]	0.54
ΔPL, cmH2O	21 [17–23]	17 [15–21]	20 [18–23]	21 [16–24]	0.21
PTPES per minute, cmH2O*sec*min−1	82 [40–127]	109 [32–172]	74 [34–137]	61 [39–112]	0.74
Patient–ventilator asynchronies
Asynchrony index (AI), %	19 [4–51]	7 [2–33]	18 [5–35]	16 [4–40]	0.78
Ineffective efforts, %	1 [0–2]	1 [0–2]	1 [0–5]	2 [0–6]	0.55
Proportion of AI due to ineffective efforts, %	14 [0–71]	15 [0–63]	19 [0–64]	22 [0–61]	0.99
Double cycling, %	1 [0–5]α	0 [0–1]αε	0 [0–3]	1 [0–3]ε	0.05
Proportion of AI due to double cycling, %	7 [0–30]α	0 [0–7]αε	0.3 [0–12]	11 [0–26]ε	0.07
Premature expiratory cycling, %	7 [1–40]	2 [0–19]	6 [0–16]	4 [0–14]	0.72
Proportion of AI due to premature expiratory cycling, %	42 [9–80]	24 [0–74]	22 [6–56]	21 [13–56]	0.66
Autotriggering, %	0 [0–1]βγ	0 [0–2]δ	1 [0–8]βδ	1 [0–6]γ	0.03
Proportion of AI due to autotriggering, %	0 [0–2]βγ	2 [0–30]	14 [2–28]β	16 [3–39]γ	0.01
Hemodynamics
Heart rate, bpm	83 [80–109]	90 [75–108]	90 [75–108]	90 [76–106]	0.98
Mean arterial pressure, mmHg	87 [73–104]	88 [78–106]	88 [72–101]	83 [74–103]	0.61

Data are expressed as median [interquartile range]

α indicates a p < 0.05 for paired comparisons between NoH and HME

β indicates a p < 0.05 for paired comparisons between NoH and HH34

γ indicates a p < 0.05 for paired comparisons between NoH and HH37

δ indicates a p < 0.05 for paired comparisons between HME and HH34

ε indicates a p < 0.05 for paired comparisons between HME and HH37

ζ indicates a p < 0.05 for paired comparisons between HH34 and HH37