Measured CPAP in a Noninvasive Pediatric Airway and Lung Model

BACKGROUND: Bronchiolitis is the most common cause of admission in children < 2 y of age in the United States. The standard of care involves supportive measures, including noninvasive interventions such as CPAP. CPAP is traditionally delivered through a full face mask; however, pediatric ICUs have been exploring the use of the RAM cannula by Neotech as a mode of CPAP delivery. The level of CPAP delivered via the RAM cannula is uncertain. We performed an in vitro study to determine the level of CPAP delivered via the RAM cannula utilizing a pediatric lung model.

METHODS: Models of 7 sizes of pediatric upper airways, produced with a 3-dimensional printer, were connected to a breathing simulator. We applied each size of RAM cannula to weight-appropriate airway and lung compliance parameters, delivering pressures of 5, 7, and 10 cm H₂O using a ventilator in the CPAP mode. Leaks of 0%, 20%, 40%, and 60% were generated to emulate a complete seal, a poor fit, and open-mouth breathing. The outcome measure was the difference in CPAP, referred to as “%leak effect,” measured by the lung simulator relative to the CPAP set on the ventilator.

RESULTS: We found that set CPAP of 5–10 cm H₂O generated measured CPAP ranging from 2.6 to 9.7 cm H₂O. For the set CPAP levels of 5, 7, and 10 cm H₂O, the mean %leak effect values of measured CPAP from the set CPAP were –25%, –26%, and –25.7%, respectively. For each specific cannula-airway combination, increasing the set pressure and decreasing the air leak resulted in higher levels of CPAP delivered.

CONCLUSIONS: The RAM cannula delivered varying amounts of CPAP, with a percent loss of approximately –25% depending on the level of leak in the system. With minimal leak, it is conceivable that the RAM cannula can be used to deliver clinically meaningful CPAP.