Evaluation and application of a method for estimating nasal end-tidal O₂ fraction while administering supplemental O₂

This paper describes a method for estimating the oxygen enhanced end-tidal fraction of oxygen (F_etO_e), the end-tidal fraction of oxygen (F_etO₂) that is raised by administering supplemental oxygen. The paper has two purposes: the first is to evaluate the method’s accuracy on the bench and in volunteers; the second purpose is to demonstrate how to apply the method to compare two techniques of oxygen administration. The method estimates F_etO_e by analyzing expired oxygen as oxygen washes out of the lung. The method for estimating F_etO_e was first validated using a bench simulation in which tracheal oxygen was measured directly. Then it was evaluated in 30 healthy volunteers and compared to the bench simulation. Bland–Altman analysis compared calculated and observed F_etO_e/F_etO₂ measurements. After the method was evaluated, it was implemented to compare the F_etO_e obtained when administering oxygen using two different techniques (pulsed and continuous flow). A total of eighteen breath washout conditions were evaluated on the bench. F_etO_e estimates and tracheal F_etO₂ had a mean difference of − 0.016 FO₂ with 95% limits of agreement from − 0.048 to 0.016 FO₂. Thirteen breath washouts per volunteer were analyzed. Extrapolated and observed F_etO₂ had a mean difference of − 0.001 FO₂ with 95% limits of agreement from − 0.006 to 0.004 FO₂. Pulsed flow oxygen (PFO) achieved the same F_etO_e values as continuous flow oxygen (CFO) using 32.1% ± 2.27% (mean ± SD) of the CFO rate. This paper has demonstrated that the method estimates F_etO₂ enhanced by administering supplemental oxygen with clinically insignificant differences. This paper has also shown that PFO can obtain F_etO₂ similar to CFO using approximately one-third of the oxygen volume. After evaluating this method, we conclude that the method provides useful estimates of nasal F_etO₂ enhanced by supplemental oxygen administration.