A New Formula for Predicting the Fraction of Delivered Oxygen During Low-Flow Oxygen Therapy.

BACKGROUND: During O2 therapy at low flow in patients who breathe spontaneously, the fraction of delivered O2 (...) is unknown. In recent years, ... prediction formulas have been proposed. However, they do not take into account the effect of inspiratory flow (VI) on the .... The aim of this study was to validate a new ... prediction formula, which takes into account the VI and compares it with other ... prediction formulas. METHODS: During a bench study, spontaneous breathing was generated with a mechanical test lung connected to a mechanical ventilator set to volume control mode. O2 flow from a wall-mounted tube was delivered through a heat-and-moisture exchanger filter. A flow sensor recorded each breath of the VI in ambient temperature and barometric pressure conditions. Three parameters [O2 flow at 2, 3, 4, 5, 6 L/min; minute ventilation at 5, 10, 15, 20 L/min; and ratio of the inspiratory time (TI) to the total breathing cycle time (Ttot) (TI/Ttot) of 0.33 (TI/Ttot value) and 0.50 (TI/Ttot value)] were modified to generate many ventilatory patterns. An O2 analyzer continuously examined the .... RESULTS: When the O2 flow and/or TI/Ttot increased, the ... increased. When the minute ventilation increased, the ... decreased. The results of the Bland-Altman method for the ..., calculated by using our mathematical model and the measured ..., showed that the mean ± SD bias value was equal to 1.49 ± 0.84%, and the limits of agreement ranged from -0.17% to 3.14%. The intraclass correlation coefficients were 0.991 for TI/Ttot = 0.33 and 0.994 for TI/Ttot = 0.50, and the coefficient of variation was 2.1% for TI/Ttot = 0.33 and 1.3% for TI/Ttot = 0.50. The results of the Bland-Altman method for the ... calculated by using the Shapiro formula and the ... measured on the bench indicated that the bias value was 0.075 ± 8.66% and the limits of agreement ranged from -16.89% to 17.04%. For the Vincent formula, the bias value was 3.08% ± 8.56% and the limits of agreement ranged from -13.69% to 19.84%. CONCLUSIONS: The VI has a major impact on ... during O2 therapy at low flow. ... comparisons between frequently used prediction formulas and ... measured on the bench indicated greater differences. Uncritical use of these formulas should be used cautiously to predict .... In this study, our prediction formula indicated a good accuracy for predicting ... during supplemental oxygenation through a heat-and-moisture exchanger in patients who breathe spontaneously.