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

Abstract

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 (Dräger Medical, Lübeck, Germany) (medium, large, and extra-large). Fabricated nasal models produced a 70% occlusive fit for the RAM cannula and an occlusive fit with the Dräger prongs. Delivered flow and pressure levels were recorded at 9 CPAP levels between 5 and 20 cm H₂O.

RESULTS:

The Dräger prongs produced a mean airway pressure ( ${\overline{P}}_{\mathbf{\text{aw}}}$ ) 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 ${\overline{P}}_{\mathbf{\text{aw}}}$ 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 ${\overline{P}}_{\mathbf{\text{aw}}}$ 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 ${\overline{P}}_{\mathbf{\text{aw}}}$ 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 ${\overline{P}}_{\mathbf{\text{aw}}}$ values lower than set CPAP. This may be clinically meaningful and should be considered when choosing a nasal interface.