Non-invasive Ventilation: Effect of Vented and Non-vented Exhalation Systems on Inspiratory CO2 and O2 Concentrations, Ventilation, and Breathing Pattern.

INTRODUCTION: To increase CO2 elimination and to reduce work of breathing in hypercapnic patients, non-invasive ventilation (NIV) can be applied via mask either with non-vented CO2 exhalation systems or with vented systems with leak port. The effect of the exhalation system on CO2 rebreathing in the mask and total gas exchange remains widely unknown. Aim of this study was to compare the exhalation systems in terms of inspiratory O2 and CO2 concentrations, breathing patterns and gas exchange.
METHODS: We prospectively examined 10 healthy subjects and 10 hypercapnic patients with both exhalation systems. O2 and CO2 were measured in the nose, in the mask, and in the ventilation circuit, and respiratory rate, tidal volume, and transcutaneous capnometry (PtcCO2) were recorded during the experiments.
RESULTS: Using the non-vented system, CO2 concentrations in the mask were significantly higher in both subject groups, and PtcCO2 values in the patient group increased up to 3.6 mmHg compared to the vented system (p = 0.011). O2 concentrations increased with higher O2 flow rates, but were significantly lower in the vented settings in both groups. No effect in breathing pattern could be demonstrated during the measurement time.
CONCLUSION: Using NIV, the chosen exhalation system influences CO2 and O2 concentrations under the mask, CO2 rebreathing from the mask and could influence the effectiveness of the ventilation support with regards to hypercapnia treatment. To compensate for relevant hypoxia, the O2 supplementation must be set up to a sufficient level under a vented system.