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

Abstract

BACKGROUND: During O 2 therapy at low flow in patients who breathe spontaneously, the fraction of delivered O 2 (F DO 2 ) is unknown. In recent years, F DO 2 prediction formulas have been proposed. However, they do not take into account the effect of inspiratory flow (V I ) on the F DO 2 . The aim of this study was to validate a new F DO 2 prediction formula, which takes into account the V I and compares it with other F DO 2 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. O 2 flow from a wall-mounted tube was delivered through a heat-and-moisture exchanger filter. A flow sensor recorded each breath of the V I in ambient temperature and barometric pressure conditions. Three parameters [O 2 flow at 2, 3, 4, 5, 6 L/min; minute ventilation at 5, 10, 15, 20 L/min; and ratio of the inspiratory time (T I ) to the total breathing cycle time (T tot ) (T I /T tot ) of 0.33 (T I /T tot value) and 0.50 (T I /T tot value)] were modified to generate many ventilatory patterns. An O 2 analyzer continuously examined the F DO 2 . RESULTS: When the O 2 flow and/or T I /T tot increased, the F DO 2 increased. When the minute ventilation increased, the F DO 2 decreased. The results of the Bland-Altman method for the F DO 2 , calculated by using our mathematical model and the measured F DO 2 , 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 T I /T tot ‫؍‬ 0.33 and 0.994 for T I /T tot ‫؍‬ 0.50, and the coefficient of variation was 2.1% for T I /T tot ‫؍‬ 0.33 and 1.3% for T I /T tot ‫؍‬ 0.50. The results of the Bland-Altman method for the F DO 2 calculated by using the Shapiro formula and the F DO 2 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 V I has a major impact on F DO 2 during O 2 therapy at low flow. F DO 2 comparisons between frequently used prediction formulas and F DO 2 measured on the bench indicated greater differences. Uncritical use of these formulas should be used cautiously to predict F DO 2 . In this study, our prediction formula indicated a good accuracy for predicting F DO 2 during supplemental oxygenation through a heat-and-moisture exchanger in patients who breathe spontaneously.

Inhaled Nitric Oxide: In Vitro Analysis of Continuous Flow Noninvasive Delivery via Nasal Cannula

“…A key variable in predicting the average inhaled O 2 concentration was the average inhalation flow, a function of inhaled tidal volume (V T ) and inspiratory time. This result echoes the findings of Duprez et al, 25 who also recently concluded that the average inspiratory flow has a major impact on average inhaled O 2 concentration during O 2 delivery at low flow to spontaneously breathing patients.…”

“…This indicates that the tracheal concentration of the delivered gas is strongly influenced by breathing pattern, a result corroborated by similar studies of continuous flow O 2 delivery. 24,25 Reasonably predictive estimates for the average inhaled concentration at the trachea (6 4.5 ppm NO at higher flow, 6 1.8 ppm NO at lower flow) were obtained in this study by accounting for the concentration and flow of the source-gas, as well as V T and inspiratory time of the patient (Equation 2). Measured concentrations tended to be somewhat higher than predicted, except in the sleep case.…”

Variability in low-flow oxygen delivery by nasal cannula evaluated in neonatal and infant airway replicas

“…formulation is similar to that proposed by Duprez et al . [ 36 ], who also conducted bench experiments to improve prediction of oxygen delivery to adults, and who also observed a major impact of the average inhalation flow rate on delivered oxygen concentrations. A similar set of algebraic equations was also developed earlier in the context of oxygen delivery to infants by Benaron and Benitz [ 10 ], although these authors based the formulation of their equations on inhaled volumes, rather than on average inhaled flow rates.…”

Impact of Oxygen Concentration Delivered via Nasal Cannula on Different Lung Conditions: A Bench Study

“…An experimental apparatus was constructed as shown in Figure 1 . Spontaneous breathing was generated with a mechanical ventilator (LTV 1200, CareFusion, San Diego, CA, USA) and two sets of two compartments training and test lung (TTL, Model 5600i, Michigan Instruments, Grand Rapids, Michigan) [ 26 ]. We linked the two TTLs with two rigid metal strap manually for three bellows.…”

“…Although the increasing use of continuous monitoring of oxygen saturation by pulse oximetry (SpO 2 ) provides an assessment of the adequacy of oxygenation, the risk may not be recognized since SpO 2 may remain in a satisfactory range because of hyperoxia [ 12 ]. The ideal method for determining the FiO 2 may be to sample tracheal air; however, the invasive procedure has only been performed in small numbers and may lead to changes in patterns [ 26 ].…”