Lung Mechanics Affect Inhaled Oxygen Concentration With Low Flow Devices: An In Vitro Evaluation

Abstract

Background: Inspired oxygen fraction (FIO₂) of low-flow oxygen therapy devices is greatly affected by breathing patterns and parameters, such as tidal volume, respiratory rate and inspiratory to expiratory ratio (I:E). The impact of lung mechanics on FIO₂ delivered by low flow oxygen devices is not well explored.

Methods: A dual training/test lung (Michigan Instrument) was connected to an oxygen analyzer and then to an intubation training mannequin. Three breathing patterns were set with tidal volume 500 mL, and (1) a normal lung breath pattern with respiratory rate of 20 breaths/min, and I: E of 1:2, compliance 100 mL/cm H₂O, and airway resistance 1 cm H₂O/L/min; (2) a restrictive lung breath pattern with respiratory rate of 25 breaths/min, and I: E of 1:1.4, compliance 30 mL/cm H₂O, and airway resistance 1 cm H₂O/L/min; and (3) a obstructive lung breath pattern with respiratory rate of 14 breaths/min, and I: E of 1:4, compliance 100 mL/cm H₂O, and airway resistance 20 cm H₂O/L/min. A simple oxygen mask with oxygen flow 10 L/min, a non-rebreathing mask with oxygen flow 10 L/min, and a nasal cannula at 1-6 L/min were randomly placed on the face of the mannequin. The FIO₂ under each condition was recorded every 3 minutes for a total of 15 minutes, and measurement were repeated for 5 times (n = 5).

Results: Figure 1 shows FIO₂ measured with oxygen devices and breath patterns, and Figure 2 illustrates the comparisons of FIO₂ using a nasal cannula with different flow and lung conditions. The FIO₂ with normal lung parameters were significant lower with a simple mask and a nasal cannula at each flow. The equations from linear regression (R2 = 0.962-0.968) showed Y = 4.28X+19.79 for normal lungs, Y = 6.16X+19.4 for restrictive lung disease, and Y = 7.36X+18.27 for obstructive lung disease.

Conclusions: Lung conditions with various breathing parameters and mechanics influence FIO₂ with low flow oxygen devices.

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Comparisons of FiO₂ among devices under different lung conditions

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FiO₂ measured with nasal cannula with different oxygen flow amont various breathing parameters