Performance Evaluation of Nasal Prong Interface for CPAP Delivery on a Critical Care Ventilator: A Bench Experiment.

BACKGROUND: The RAM cannula (Neotech, Valencia, CA) has become a commonly used interface for CPAP in neonatal intensive care. Performance characteristics of this interface used with a critical care ventilator are not well described. METHODS: This was a bench study utilizing a lung simulator configured as an actively breathing infant (weights of 800 g, 1.5 kg, and 3 kg) with moderate lung disease and a critical care ventilator in CPAP mode with leak compensation on. Three sizes of the RAM cannulae (preemie, newborn, and infant) were compared to 3 BabyFlow nasal prongs (Drager Medical, Lubeck, Germany) (medium, large, and extra-large). Fabricated nasal models produced a 70% occlusive fit for the RAM cannula and an occlusive fit with the Drager prongs. Delivered flow and pressure levels were recorded at 9 CPAP levels between 5 and 20 cm H2O. RESULTS: The Drager prongs produced a mean airway pressure ( P ¯ aw ) within 0.20 cm H2O (range –0.10 to 0.35) of the set CPAP across all evaluated prong sizes and CPAP levels. In contrast, the RAM cannula produced P ¯ aw values that averaged 8.5 cm H2O (range –15 to –3.5) below the set CPAP levels. The deficit in delivered versus target CPAP level for the RAM cannula increased with greater set CPAP. Set CPAP of 5 cm H2O delivered P ¯ aw values that ranged from 0.6 to 1.5 cm H2O (difference of 3.5–4.4 cm H2O). Set CPAP of 20 cm H2O delivered P ¯ aw values that ranged from 5.0 to 8.4 cm H2O (difference of 11.7–15 cm H2O). Inspiratory flow required to achieve set CPAP levels did not differ between interfaces, suggesting high resistance in the RAM cannula device masks the delivered CPAP levels. CONCLUSIONS: Use of the RAM cannula with a 30% leak on a critical care ventilator delivered P ¯ aw values lower than set CPAP. This may be clinically meaningful and should be considered when choosing a nasal interface.