Laboratory studies have been performed to compare the CO₂ elimination of these different types of exhalation devices. The product specification leaflet from the manufacturer of the masks or exhalation ports provides information about the leak rate at different pressure levels used in treatment, an example of which is found from Philips Respironics Inc. [3]. It appears that the newly designed masks commonly have built-in exhalation ports rather than using the conventional detachable exhalation ports. As listed by the manufacturer, the intentional leak is increased with increasing level of applied pressure, and the leaks are usually similar between the different masks and are within a narrow range for different types of masks with different exhalation devices, except for a specific model (Small Child Profile Lite), which has a higher levels of leaks compared with other models (Table 12.1).

Clinical investigators have also performed studies on the performance of different exhalation devices. In a lung model study, Lofaso et al. [4] demonstrated that when the usual type of exhalation port (Whisper Swivel) was used, significant CO₂ rebreathing occurred with resident volume of expired air (RVEA) of up to 55 % of tidal volume detected at a positive end-expiratory pressure (PEEP) level of 1.3 cmH₂O and an inspiratory pressure of 9.4 cmH₂O. When a non-rebreathing valve (Sanders NRV-2 Non-Rebreathing Valve, Respironics Inc., Murrysville, PA, USA) was used to replace the usual type of exhalation port, an auto-PEEP effect was noted, raising the level of PEEP to 2.4 cmH₂O, and at the same time, the RVEA was eliminated.