Characteristics at inclusion and study outcomes, according to study group
| Moderate-to-severe dyspnoea (n=52) | Mild or no dyspnoea (n=57) | Adjusted mean difference (95% CI) | OR (95% CI) | p-value | |
| Demographics | |||||
| Age, years | 61 (53–70) | 65 (58–71) | 0.15 | ||
| Female sex | 9 (17) | 12 (21) | 0.64 | ||
| Male sex | 43 (83) | 45 (79) | 0.64 | ||
| Body mass index, kg·m−2 | 28 (26–30) | 27 (25–30) | 0.37 | ||
| Respiratory rate at enrolment, breaths per min | 28 (24–33) | 27 (23–30) | 0.13 | ||
| Device-related discomfort at enrolment# | 2 (0–5) | 0 (0–0) | <0.001 | ||
| Arterial blood gases at enrolment | |||||
| PaO2/FIO2 ratio, mmHg | 97 (82–117) | 110 (83–132) | 0.12 | ||
| PaO2, mmHg | 60 (54–74) | 66 (55–75) | 0.71 | ||
| pH | 7.46 (7.45–7.49) | 7.46 (7.45–7.48) | 0.95 | ||
| PaCO2, mmHg | 34 (31–37) | 34 (32–37) | 0.50 | ||
| Allocated treatment¶ | |||||
| Helmet noninvasive ventilation | 27 (52) | 27 (47) | 0.70 | ||
| High-flow oxygen | 25 (48) | 30 (53) | 0.70 | ||
| Outcomes | |||||
| Respiratory support+-free days at 28 days | 12 (0–23) | 21 (4–25) | −5 (−8– −1) | 0.008 | |
| Intubation within 28 days from enrolment | 27 (52) | 17 (30) | 3.8 (1.5–9.9) | 0.006 | |
| Invasive ventilation-free days at 28 days | 20 (4–28) | 28 (16–28) | −5 (−9– −1) | 0.02 | |
| Invasive ventilation free days at 60 days | 52 (11–60) | 60 (48–60) | −9 (−17– −1) | 0.03 | |
| 28-day mortality | 10 (19) | 8 (14) | 1.8 (0.6–5) | 0.29 | |
| 60-day mortality | 14 (27) | 11 (19) | 2 (0.8–5.5) | 0.16 | |
| Intensive care unit mortality | 15 (29) | 10 (17) | 2.8 (1–7.7) | 0.05 | |
| Hospital mortality§ | 16 (31) | 11 (19) | 2.6 (1–7) | 0.05 | |
| Length of stay in the intensive care unit, days | 12 (6–29) | 7 (4–12) | 6 (0–6) | 0.05 | |
| Length of stay in the hospital, days | 24 (16–41) | 18 (12–29) | 8 (0–15) | 0.04 |
Data are presented as median (interquartile range) or n (%), unless otherwise stated. There were no missing data among the two groups. Mean difference and odds ratio were adjusted for Simplified Acute Physiology Score II, allocated treatment (high-flow nasal oxygen or helmet noninvasive ventilation) and arterial oxygen tension (PaO2)/inspiratory oxygen fraction (FIO2) ratio on intensive care unit admission. For non-normal quantitative variables, comparison between groups was performed with Mann–Whitney test. Comparison between groups for qualitative variables were performed with the Chi-squared test or the Fisher's exact test, as appropriate in agreement with tests assumptions. All the calculations were unadjusted. PaCO2: arterial carbon dioxide tension. #: discomfort was assessed through visual analogue scales adapted for intensive care unit patients, ranging from 0 to 10; ¶: advanced respiratory support interface used in the first 48 h; +: invasive or noninvasive mechanical ventilation, high-flow nasal oxygen; §: one patient was discharged from hospital but died upon readmission.