Redesign of an Open-System Oxygen Face Mask With Mainstream Capnometer for Children.

Background: Partial pressure of end-tidal carbon dioxide (P ) monitoring in children is important to detect apnea or hypopnea early to intervene before hypoxemia develops. Monitoring P in children without a tracheal tube is challenging. To improve P measurement accuracy in a commercially available mask with a mainstream CO detector, we implemented design changes with deform-and-hold shaping technology and anterior-posterior adjustment of the expiratory gas flow cup.

Methods: Two sizes of redesigned face masks (small for 7-20 kg, medium for 10-40 kg) were evaluated. Initial bench testing used a simulator modeling a spontaneously breathing infant and child with a natural airway. An infant/child manikin head was connected to the breathing lung simulator. A mass flow controller provided expiratory CO. Mask fit was then evaluated on healthy human subjects to identify anatomical features associated with good fit, defined as square shape capnography waveform during expiration. A 3-dimensional digital scan was used to quantify anatomical features. The gaps between face mask rims and facial surface were manually measured.

Results: Bench testing revealed a P difference of 3.4 ± 1.5 mm Hg between a measured P by the redesigned mask and CO concentration at trachea, as compared with 6.7 ± 6.2 mm Hg between P measured by nasal cannula and trachea (P < .001). In the human mask fit study, 35 children (13 ± 4 kg) with the small mask and 38 (24 ± 8 kg) with the medium mask were evaluated. Capnography tracing was successfully obtained in 86% of the small and 100% of the medium masks. In children with small-size masks, the gap between the face mask rim and the child's face was not statistically different among those with good mask fit and without (1.0 ± 1.5 mm vs 1.4 ± 1.9 mm, P = .73).

Conclusions: P measurement by a redesigned open-system face mask with a mainstream CO detector was accurate in the bench setting. The redesigned face mask can attain good mask fit and accurate capnography tracings in the majority of infants and children.