Abstract
BACKGROUND: The nasal cannula is widely regarded as a safe and effective means of administering low- and high-flow oxygen to patients irrespective of their age. However, variability in delivered oxygen concentration (F(DO(2)) F(DO(2)) ) via nasal cannula has the potential to pose health risks. The present study aimed to evaluate predictive equations for F(DO(2)) over a large parameter space, including variation in breathing, oxygen flow, and upper-airway geometry representative of both young children and adults. METHODS: Realistic nasal airway geometries were previously collected from medical scans of adults, infants, and neonates. Nasal airway replicas based on these geometries were used to measure the F(DO(2)) for low-flow oxygen delivery during simulated spontaneous breathing. The present study extends previously published data sets to include higher oxygen flows. The extended data sets included nasal cannula oxygen flows that ranged from 6 to 65 L/min for the adult replicas, and from 0.5 to 6 L/min for the infant replicas. For both age groups, F(DO(2)) was measured over a range of breathing frequencies, inspiratory to expiratory time ratios, and tidal volumes. Measured F(DO(2)) values were compared with values predicted by using a previously derived flow-weighted equation. RESULTS: For both age groups, F(DO(2)) was observed to increase nonlinearly with the ratio between oxygen flow supplied to the nasal cannula and the average inhalation flow. The previously derived flow-weighted equation over-predicted F(DO(2)) at higher oxygen flows. A new empirical equation, therefore, was proposed to predict F(DO(2)) for either age group as a function of nasal cannula flow, tidal volume, and inspiratory time. Predicted F(DO(2)) values matched measured values, with average relative errors of 2.4% for infants and 4.3% for adults. CONCLUSIONS: A new predictive equation for F(DO(2)) was obtained that accurately matched measured data in both adult and infant airway replicas for low- and high-flow regimens.