Factors affecting FiO₂ and PEEP during high-flow nasal cannula oxygen therapy: A bench study

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.

To investigate the effects of set-FiO₂ , set-flow, PIF and tidal volume on the actual-FiO₂ and PEEP during HFNC oxygen therapy.

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.

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.