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

Background: Measuring the fraction of inspired oxygen (FiO(2)) is challenging in spontaneously breathing patients with impaired respiratory mechanics during low-flow nasal cannula. Our study investigates the FiO(2) with varied tidal volume (V(T)) and respiratory rate (RR) among different lung mechanics and provides equations to estimate the FiO(2). 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(T) (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(2) was measured at the carina. Results: The lowest and highest FiO(2) were evident during high (700 mL) and low V(T) (300 mL), respectively, among normal, restrictive, and obstructive lung models. As RR increases, this decreases the FiO(2). However, we found that V(T) and oxygen flow rate are the principal factors influencing measured FiO(2) by multiple linear regression analysis. Conclusions: Our data suggest that the actual FiO(2) is never as high in spontaneously breathing patients as that estimated. V(T) and oxygen flow rate had a substantial impact on the FiO(2).