Carbon dioxide rebreathing in non-invasive ventilation. Analysis of masks, expiratory ports and ventilatory modes
Carbon dioxide (CO2) rebreathing is a complication of non-invasive ventilation (NIV). Our objectives were to evaluate the ability of masks with exhaust vents (EV) to avoid rebreathing while using positive pressure (PP) NIV with different levels of expiratory pressure (EPAP). Concerning volume-cycled NIV, we aimed to determine whether cylindrical spacers located in the circuit generate rebreathing. 5 healthy volunteers were evaluated. Bi-level PP was used with 3 nasal and 2 facial masks with and without EV. Spacers of increasing volume attached to nasal hermetic masks were evaluated with volume NIV. Inspired CO2 fraction was analyzed. Rebreathing was zero with all nasal masks and EPAP levels. Using facial masks 1 volunteer showed rebreathing. There was no rebreathing while using all the spacers. In healthy volunteers, nasal and facial masks with EV prevent rebreathing. In addition, the use of spacers did not generate this undesirable phenomenon.