The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

IN VITRO AND IN VIVO EVALUATION OF A NEONATAL HIGH-FLOW NASAL CANNULA SYSTEM.

IN VITRO AND IN VIVO EVALUATION OF A NEONATAL HIGH-FLOW NASAL CANNULA SYSTEM.

B. J. Plumm1, P. Meyers1, C. Worwa1, A. Lampland 1, 2, M. Mammel 1, 2

Background: Humidified high flow nasal cannulae (HHNC) are used in NICUs to deliver oxygen and continuous positive airway pressure. Little data exists regarding these systems. We analyzed pressures delivered by the Fisher & Paykel RT329 HHNC system using an RT091 Premature cannula and RT092 Neonate cannula at varying gas flows both in vitro with these two cannula sizes with varying air leaks and in vivo in newborn piglets.

Methods:
In vitro: Pressure and flow at various points in the RT329 system were measured with a flow analyzer (Fluke Biomedical, Everett, WA) with 0%, 30% and 50% leaks. Fixed variables included initial flow (0.5-6 lpm) and cannula size. In vivo: We measured esophageal pressures (Pes) generated at flow levels ranging from 1-6 lpm in 7 newborn piglets.

Results: In vitro: The pop-off valve (40 cmH2O) limited pressure delivery. Flow delivery was preserved to the point of nasal cannula insertion. Pressure and flow delivery at the cannula end was limited at >2 lpm. With all cannula sizes, introduction of a 30% and 50% leak resulted in >96% and >98% decrease in delivered pressure respectively. With all cannulae, removal of the pop-off valve resulted in a direct increase in pressure delivery as the flow was increased: 2 lpm >80 cmH2O, 3 lpm >140 cmH2O, 4 lpm >210 cmH2O, 5 lpm >220 cmH2O, and 6 lpm >280 cmH2O. In vivo: As HHNC flow was increased from 1 lpm to 6 lpm, mean Pes increased, but extreme variation suggests a variable leak (figure- values are mean ± SD).

Conclusion:
In vitro using the RT329 system with no leak, we saw high pressures, However, they were limited by the pop-off valve at flows >2 lpm. Addition of a 30-50% leak at the cannula end dramatically reduced delivered pressures to <2 cmH2O, regardless of initial flow. In vivo, we saw variable, but generally increasing Pes as flow increased. With any leaks, cannula size, and patient variation, it may be impossible to predict pressure delivery during HHNC use without direct measurement.


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IN VITRO AND IN VIVO EVALUATION OF A NEONATAL HIGH-FLOW NASAL CANNULA SYSTEM.