Table 2.
Comparison between HFNC 1 and CPAP
| Variable | HFNC 1 | CPAP | Adjusted p-value |
|---|---|---|---|
| FiO2 (%) | 70 (50–100) | 70 (50–100) | NA |
| Flow (L.min− 1) | 50 (50–60) | NA | NA |
| Respiratory rate (.min− 1) | 24 (19–28) | 24 (20–30) | 0.09 |
| Tidal volume (mL) | 453 (353–578) | 629 (551–686) | < 0.001 |
| Tidal volume/PBW (mL.kg− 1 PBW) | 6.6 (5.9–8.7) | 9.4 (8.3–11) | < 0.001 |
| Minute ventilation (L.min− 1) | 10.6 (7.9–13.8) | 15.8 (12.5–17.5) | < 0.001 |
| Tidal impedance variation pixel−level (arbitrary units) | 37.9 (29.3–50.6) | 46.9 (38.9–65.7) | < 0.001 |
| Pendelluft (%) | 12.1 (8.3–18.5) | 9.8 (6.3–14.1) | 0.002 |
| EELV variation (mL) | 0 | 170 (43–399) | < 0.001 |
| EELV variation/PBW (mL.kg− 1 PBW) | 0 | 2.5 (0.6–5.4) | < 0.001 |
| Anterior EELV variation/PBW (mL.kg− 1 PBW) | 0 | 1.1 (0.2–3.1) | < 0.001 |
| Posterior EELV variation/PBW (mL.kg− 1 PBW) | 0 | 1.1 (0.1–2.7) | < 0.001 |
| Thoraco-abdominal phase angle (°) (N = 20) | 15 (9–34) | 10 (7–21) | 0.51 |
| SpO2 (%) | 96 (95–99) | 99 (97–100) | < 0.001 |
| Dyspnea (n = 23) | 0 | 0 (-1-1) | 0.15 |
| Discomfort (n = 23) | 0 | 1 (0–1) | 0.02 |
| ROX | 5.7 (4.2–8.2) | 5.5 (4.1–8.5) | 0.55 |
| Anterior distribution (%) | 46 (41–54) | 41 (37–50) | 0.01 |
| Global inhomogeneity index | 0.56 (0.53–0.60) | 0.58 (0.53–0.60) | 0.78 |
| Ventilated pixels (n) | 327 (292–356) | 358 (341–394) | < 0.001 |
| Hemodynamic parameters | |||
| Heart rate (beat.min− 1) | 87 (72–97) | 87 (71–103) | 0.09 |
| SAP (mm Hg) | 123 (117–139) | 134 (115–146) | < 0.01 |
| DAP (mm Hg) | 69 (57–75) | 74 (61–78) | < 0.01 |
| PP (mm Hg) | 55 (49–68) | 58 (48–77) | 0.28 |
| Arterial blood gases ( n = 12) | |||
| PaO2/FiO2 (mm Hg) | 109 (77–160) | 153 (109–194) | < 0.01 |
| PaCO2 (mm Hg) | 33 (31–35) | 35 (34–37) | < 0.001 |
| pH | 7.48 (7.44–7.5) | 7.45 (7.41–7.48) | < 0.001 |
| [HCO3−] (mmol.L− 1) | 24.6 (24-26.5) | 25.6 (23.6–26.8) | 0.11 |
| Corrected minute ventilation (L.min− 1) | 8.5 (7.4–11.3) | 14.6 (11.4–15.8) | < 0.001 |
| Ventilatory ratio | 1.39 (1.11–1.67) | 2.15 (1.91–2.6) | 0.001 |
Adjusted p-values were computed by the mean of Wilcoxon paired tests with Benjamini-Hochberg correction
Tidal impedance variation pixel−level refers to the sum of the tidal impedance variations of every pixel, with the breath cycle defined for each pixel, thus considering the Pendelluft. End-expiratory lung volume during CPAP is expressed as difference from HFNC1. The change in discomfort and dyspnea between HFNC 1 and CPAP was assessed using a 5-point Likert scale ranging from − 2 (much less discomfort or dyspnea to + 2: much more discomfort or dyspnea)
HFNC: High Flow Nasal Cannula; CPAP: Continuous Positive Airway Pressure; FiO2: inspired fraction of oxygen; PBW: predicted body weight; EELV: end-expiratory lung volume; SpO2: oxygen saturation by pulse oximeter; SAP: systolic arterial pressure; DAP: diastolic arterial pressure; PP: pulse pressure; PaO2: arterial oxygen pressure; FiO2: inspired fraction of oxygen; PaCO2: arterial carbon dioxide pressure