Abstract
Background: Measuring the fraction of inspired oxygen (FiO2) is challenging in spontaneously breathing patients with impaired respiratory mechanics during low-flow nasal cannula. Our study investigates the FiO2 with varied tidal volume (VT) and respiratory rate (RR) among different lung mechanics and provides equations to estimate the FiO2. 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 VT (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 FiO2 was measured at the carina. Results: The lowest and highest FiO2 were evident during high (700 mL) and low VT (300 mL), respectively, among normal, restrictive, and obstructive lung models. As RR increases, this decreases the FiO2. However, we found that VT and oxygen flow rate are the principal factors influencing measured FiO2 by multiple linear regression analysis. Conclusions: Our data suggest that the actual FiO2 is never as high in spontaneously breathing patients as that estimated. VT and oxygen flow rate had a substantial impact on the FiO2.
Highlights
Supplemental oxygen is one of the most commonly prescribed treatments to treat spontaneously breathing patients in general units, and for long-term oxygen therapy in the home care setting [1,2,3]
Restrictive, and obstructive lung models, we found no obvious effect of respiratory rate (RR) on measured FiO2, but these appeared statistically significantly affected by the VT and oxygen flow rate
Our experiment demonstrated that the variation of oxygen flow rate, VT, and RR with a low-flow nasal cannula influenced the delivery of oxygen concentrations in the normal, restrictive, and obstructive lung models
Summary
Supplemental oxygen is one of the most commonly prescribed treatments to treat spontaneously breathing patients in general units, and for long-term oxygen therapy in the home care setting [1,2,3]. Rule of thumb suggests that every liter per minute increases the fraction of inspired oxygen (FiO2) by approximately 4% for normal rate and depth of breathing [12,13,14]. Measuring the fraction of inspired oxygen (FiO2) is challenging in spontaneously breathing patients with impaired respiratory mechanics during low-flow nasal cannula. Our study investigates the FiO2 with varied tidal volume (VT) and respiratory rate (RR) among different lung mechanics and provides equations to estimate the FiO2. The flow rate of the nasal cannula was set to 1, 3, and 5 L per minute (LPM), and the FiO2 was measured at the carina. Conclusions: Our data suggest that the actual FiO2 is never as high in spontaneously breathing patients as that estimated. VT and oxygen flow rate had a substantial impact on the FiO2
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