Factors Affecting FiO₂ And PEEP During High-flow Nasal Cannula Oxygen Therapy: A Bench Study

Objectives: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.Methods:A lung simulation model was used to study the factors that might affect FiO₂and PEEP during HFNC therapy in vitro.These factors included set-flow?20,40,60,80and 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:Regression formula were:?a?actual-FiO2 as the dependent variable:actual FiO₂=2.71+0.15×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?.conclusion: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.