FiO 2 prediction formula during low flow oxygen therapy in an adult model: a bench study

During low-flow oxygen therapy, the true value of inspired oxygen fraction (FiO 2 ) is generally unknown. Knowledge of delivered FiO 2 values may be useful as well as to adjust oxygen therapy, as well as to predict patient deterioration. This study proposes a New FiO 2 Prediction Formula (NFiO 2 ) for low-flow oxygenation and compares its predictive value to precedent formulas. In a bench study, the O 2 Flow rate was delivered through a T-piece connected to a dual-compartment artificial lung controlled by a mechanical ventilator. To test the NFiO 2 formula, a set of ventilatory parameters were tested: Tidal Volume was set from 400 to 600 ml, Respiratory Rate (RR) was set from 18 to 30 CPM, Ti/Ttot was set at 0.33 and 0.25, and O 2 flow rates from 3 to 10 L/min. A data acquisition system measured all parameters. To quantify the accuracy of the NFiO 2 compared to other FiO 2 prediction formulas, Bland and Altman agreement analyses were performed. To make use of the Duprez Formula 2018 in clinical practice, we simplified the formula to estimate the FiO 2 during oxygenation at low flow. This NFiO 2 formula makes use of only O 2 Flow Rate and RR. Bias and limits of agreement between predicted FiO 2 and benchtop FiO 2 highlighted consistent differences between different FiO 2 prediction formulas. The NFiO 2 and the Duprez Formula 2018 seemed to be the most accurate formulas, followed by the Vincent Formula, and lastly the Shapiro Formula. A New FiO 2 Prediction Formula was developed using clinical readily available variables (RR and O 2 Flow rate) which showed good accuracy in predicting FiO 2 during oxygenation at low flow.