Effect of Different Interfaces on F_IO2 and CO₂ Rebreathing During Noninvasive Ventilation

BACKGROUND: Improving F_IO2 and reducing CO₂ rebreathing (V̇_ICO2) are the key means to improve the therapeutic efficacy of noninvasive ventilation (NIV). This study aimed to investigate the impact of interface design on F_IO2 and V̇_ICO2 during NIV.

METHODS: A simulated lung model was established to analyze 17 different interfaces. CO₂ was injected into the outlet of the simulated lung, and the noninvasive ventilator was connected to the simulated lung to simulate the application of NIV in patients with COPD with hypercapnia. F_IO2 and V̇_ICO2 were calculated by mathematical integration of synchronously collected data pertaining to real-time pressure, flow, oxygen concentration, and CO₂ concentration in the breathing circuit. Comparisons were performed between different types (nasal vs oronasal) and models of interfaces as well as between interfaces with different leak positions. Correlation of F_IO2 and V̇_ICO2 with inner volume and leakage, respectively, and the correlation between F_IO2 and V̇_ICO2 were analyzed.

RESULTS: F_IO2 levels were significantly different with a nasal or an oronasal mask (0.45 ± 0.05% vs 0.41 ± 0.08%, respectively; P < .001). F_IO2 levels associated with different models of interfaces varied significantly (all P < .001); V̇_ICO2 did not differ significantly among the different interfaces (P = .19). Leak position significantly affected F_IO2 and V̇_ICO2 (all P < .001). Both inner volume and leakage significantly correlated with F_IO2 (r = −0.23, P < .001; r = −0.08, P = .02). There was a significant correlation between F_IO2 and V̇_ICO2 (r = 0.43, P < .01); the general linear equation was y = 0.17 + 0.02x (r = 0.43, R² = 0.19).

CONCLUSIONS: The design of the interface had a significant impact on F_IO2 and V̇_ICO2 during NIV. F_IO2 and V̇_ICO2 showed a significant positive correlation, although the effect size of correlation was moderate.