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

Background: Measuring the fraction of inspired oxygen (FiO) is challenging in spontaneously breathing patients with impaired respiratory mechanics during low-flow nasal cannula. Our study investigates the FiO with varied tidal volume (V) and respiratory rate (RR) among different lung mechanics and provides equations to estimate the FiO.

Methods: Two training and test lungs were used in this study, and the three lung mechanics (normal (R5/C60), restrictive (R20/C80), obstructive (R5/C40)) were designed. Spontaneous breathing with V (300, 500, and 700 mL) and RR (10, 20, and 30 breaths/min) was simulated. The flow rate of the nasal cannula was set to 1, 3, and 5 L per minute (LPM), and the FiO was measured at the carina.

Results: The lowest and highest FiO were evident during high (700 mL) and low V (300 mL), respectively, among normal, restrictive, and obstructive lung models. As RR increases, this decreases the FiO. However, we found that V and oxygen flow rate are the principal factors influencing measured FiO by multiple linear regression analysis.

Conclusions: Our data suggest that the actual FiO is never as high in spontaneously breathing patients as that estimated. V and oxygen flow rate had a substantial impact on the FiO.