Introduction
It is unknown if set‐flow, peak inspiratory flow (PIF), tidal volume and set fraction of inspired O2 (FiO2) affect actual‐FiO2 and positive end‐expiratory pressure (PEEP) during high‐flow nasal cannula (HFNC) oxygen therapy. In addition, the extent of their influence is also unknown.
Objectives
To investigate the effects of set‐FiO2, set‐flow, PIF and tidal volume on the actual‐FiO2 and PEEP during HFNC oxygen therapy.
Methods
A lung simulation model was used to study the factors that might affect FiO2 and PEEP during HFNC therapy in vitro. These factors included set‐flow (20, 40, 60, 80 and 120 L/min), PIF (40, 80 and 120 L/min), tidal volume (400 and 600 mL), and set‐FiO2 (30%, 50% and 70%). Actual‐FiO2 and PEEP were recorded for 10 consecutive breaths. Actual‐FiO2 and PEEP were compared under different conditions. Multivariate linear regressions were performed to investigate the effects of these factors on actual‐FiO2 and PEEP.
Results and conclusion
Regression formula were: (a) actual‐FiO2 as the dependent variable: actual FiO2 = 2.71 + 0.78 × set‐FiO2 + 0.17 × set‐flow − 0.09 × PIF (F test, F = 3866.62, P < 0.001, R2 = 0.94), (b) PEEP as the dependent variable: PEEP = 1.35 + 0.15 × set‐flow − 0.02 × PIF + 0.01 × tidal volume (F test, F = 4082.39, P < 0.001, R2 = 0.95). The following factors were found to affect actual‐FiO2 (in descending order): set‐FiO2, set‐flow and PIF. Tidal volume had little effect on actual‐FiO2. Factors which affected PEEP were (in descending order): set‐flow, peak inspiratory flow and tidal volume.