PS-376 Non-invasive Ventilation In Neonates: Effect Of Nasal Cannula Size, Insertion Depth And Nares Diameter On Mean Airway Pressure - An In-vitro Study

Abstract

Background Increased neonatal Non-Invasive Ventilation (NIV) use, such as nCPAP and high flow nasal cannula (HFNC) prompted re-evaluation of nasal interface devices - specifically short bi-nasal prongs, and their size and fit relative to the nares. Objective To quantify the effect of nasal prong size and insertion depth on generated mean airway pressure (MAP) during NIV. Design/methods A Drager traditional nCPAP interface, three sizes of RAM cannulae (Neotech, Valencia, CA, USA) and two Fisher and Paykel (FP) (Auckland, NZ) HFNC cannulae were tested with 8 simulated nares sizes. A simulated nasal airway was connected to an active lung model set at: Vt 8-10 ml, 60 b/m, Ti 0.35-0.40 s. A Drager Evita XL ventilator delivered 4,5,6,7 and 8 cmH2O to the RAM and the Drager nCPAP cannulae and a FP HFNC system delivered 1-6 L/m flows. MAP was measured for open and closed-mouth conditions. Results MAP decreased progressively as the percent nares occlusion (%Occl) decreased. At one-half insertion and closed-mouth conditions, close fitting prongs with high% Occl yielded MAP's of one-half of set CPAP levels. Delivered MAP's were significantly lower during open-mouth condition using either HFNC or CPAP cannulae. MAP increased with both flowrate and%Occl. A rapid rise in pressure was associated with% Occl's >74%. Complete nares occlusions generated the highest pressures. Simulated closed-mouth produced 12 +/- 7 SD higher MAP's than open-mouth over all%Occl's at HFNC flows >1 L/m. Conclusion RAM 'CPAP' does not deliver MAP as effectively as standard nasal prong CPAP. Optimum delivered airway pressure is dependent on appropriate %Occl, insertion depth and NIV settings.