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

Abstract

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 120L/min), PIF (40, 80 and 120L/min), tidal volume (400 and 600mL), 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.