High-flow nasal cannula therapy, factors affecting effective inspired oxygen fraction: an experimental adult bench model

Oxygenation through High Flow Delivery Systems (HFO) is described as capable of delivering accurate F(iO2). Meanwhile, peak inspiratory flow [Formula: see text] ) of patients with acute hypoxemic respiratory failure can reach up to 120 L/min, largely exceeding HFO flow. Currently, very few data on the reliability of HFO devices at these high [Formula: see text] are available. We sought to evaluate factors affecting oxygenation while using HFO systems at high [Formula: see text] in a bench study. Spontaneous breathing was generated with a mechanical test lung connected to a mechanical ventilator Servo-i®, set to volume control mode. Gas flow from a HFO device was delivered to the test lung. The influence on effective inspired oxygen fraction of three parameters (F(iO2) 0.6, 0.8, and 1, [Formula: see text] from 28 to 98.1 L/min, and HFO Gas Flows from 40 to 60 L/min) were analyzed and are reported. The present bench study demonstrates that during HFO treatment, measured F(iO2) in the lung does not equal set F(iO2) on the device. The substance of this variation (ΔF(iO2)) is tightly correlated to [Formula: see text] (Pearson’s coefficient of 0.94, p-value < 0.001). Additionally, set F(iO2) and Flow at HFO device appear to significatively affect ΔF(iO2) as well (p-values < 0.001, adjusted to [Formula: see text] ). The result of multivariate linear regression indicates predictors ([Formula: see text] , Flow and set F(iO2)) to explain 92% of the variance of delta F(iO2) through K-Fold Cross Validation. Moreover, adjunction of a dead space in the breathing circuit significantly decreased ΔF(iO2) (p < 0.01). The present bench study did expose a weakness of HFO devices in reliability of delivering accurate F(IO2) at high [Formula: see text] as well as, to a lesser extent, at [Formula: see text] below equivalent set HFO Flows. Moreover, set HFO flow and set F(IO2) did influence the variability of effective inspired oxygen fraction. The adjunction of a dead space in the experimental set-up significantly amended this variability and should thus be further studied in order to improve success rate of HFO therapy.