Evaluation of a nasal cannula in noninvasive ventilation using a lung simulator.

BACKGROUND: Nasal noninvasive ventilation (NIV) is a common form of noninvasive respiratory mode used in newborn infants. A next-generation nasal cannula (Neotech RAM cannula) has recently been used to provide nasal NIV. The impact of the Neotech RAM cannula on the delivery of pressure needs to be studied.

METHODS: In this ex vivo experimental design, a lung simulator (IngMar ASL 5000, version 3.4) was programmed to model a neonate (∼1-3 kg of body weight) with normal-to-moderately affected lungs. We used a Covidien PB840 ventilator with NIV software activated to compensate for leaks. Nasal NIV was set at peak airway pressures of 15, 20, and 25 cm H2O and PEEP of 5, 6, and 7 cm H2O. Three sizes of the Neotech RAM cannula were used (prong outer diameters of 3.0, 3.5, and 4.0 mm). The nose was designed to keep the leak of the nares by the prongs to 30%. We also created a worst case leak (58% leak) by using the largest simulated nostril diameter with the smallest diameter Neotech RAM cannula prong. The outcome measure was the difference in pressures, referred to as leak effect, measured by the lung simulator relative to the set peak airway pressure and PEEP on the ventilator.

RESULTS: For the interface with 30% leak, leak effects of peak airway pressure during simulated nasal NIV were similar with all Neotech RAM cannula sizes, with 63-75% of peak airway pressure and 70-90% of PEEP being transmitted across the nasal interface. The worst case scenario produced a 92% leak effect in peak airway pressure and PEEP.

CONCLUSIONS: When used with ≤ 30% leak, the Neotech RAM cannula interface results in clinically acceptable transmission of pressures. With > 50% leak, a clinically negligible amount of pressure is transmitted to the artificial lungs.