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 (FetOe), the end-tidal fraction of oxygen (FetO2) 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 FetOe by analyzing expired oxygen as oxygen washes out of the lung. The method for estimating FetOe 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 FetOe/FetO2 measurements. After the method was evaluated, it was implemented to compare the FetOe obtained when administering oxygen using two different techniques (pulsed and continuous flow). A total of eighteen breath washout conditions were evaluated on the bench. FetOe estimates and tracheal FetO2 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 FetO2 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 FetOe 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 FetO2 enhanced by administering supplemental oxygen with clinically insignificant differences. This paper has also shown that PFO can obtain FetO2 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 FetO2 enhanced by supplemental oxygen administration.