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

Partial pressure of end-tidal carbon dioxide (P_ETCO ) monitoring in children is important to detect apnea or hypopnea early to intervene before hypoxemia develops. Monitoring P_ETCO in children without a tracheal tube is challenging. To improve P_ETCO measurement accuracy in a commercially available mask with a mainstream CO₂ detector, we implemented design changes with deform-and-hold shaping technology and anterior-posterior adjustment of the expiratory gas flow cup.

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 CO₂. 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.

Bench testing revealed a P_ETCO difference of 3.4 ± 1.5 mm Hg between a measured P_ETCO by the redesigned mask and CO₂ concentration at trachea, as compared with 6.7 ± 6.2 mm Hg between P_ETCO 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).

P_ETCO measurement by a redesigned open-system face mask with a mainstream CO₂ 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.