• Katie R Nielsen, Laura E Ellington, Alan J Gray, Larissa I Stanberry, Lincoln S Smith, and Robert M DiBlasi.
• Division of Critical Care Medicine, Department of Pediatrics, University of Washington, Seattle, Washington.
• Respir Care. 2018 Feb 1; 63 (2): 147-157.

BackgroundHeated and humidified high-flow nasal cannula (HFNC) is a widely used form of respiratory support; however, data regarding optimal flows for a given patient size or disease state are lacking. A comprehensive study of the physiologic effects of HFNC is needed to better understand the mechanisms of action. The objective of the current study was to quantify the effect of HFNC settings in age-specific, anatomically correct nasal airways and spontaneously breathing lung models. We hypothesized that there is an effect of flow on pressure and ventilation.MethodsThree-dimensionally printed upper airway models of a preterm neonate, term neonate, toddler, small child, and adult were affixed to the ASL 5000 test lung to simulate spontaneous breathing with age-appropriate normal ventilation parameters. CO2 was introduced to simulate profound hypercapneic respiratory failure with an end-tidal partial pressure of carbon dioxide (PETCO2 ) of 90 ± 1 mm Hg. Two commercially available HFNC systems were applied to the airway models, and PEEP, inspired CO2, and exhaled CO2 (PETCO2 ) were recorded for 6 min across a range of flow.ResultsIncreasing HFNC flow provided a non-linear increase in PEEP in closed-mouth models, with maximum tested flows generating 6 cm H2O in the preterm neonate to 20 cm H2O in the small child. Importantly, PEEP decreased by approximately 50% in open-mouth models. Increasing HFNC flow improved expiratory CO2 elimination to a certain point, above which continued increases in flow had minimal additional effect. This change point ranged from 4 L/min in the preterm neonate to 10 L/min in the small child.ConclusionsThese findings may help clinicians understand the effects of HFNC at different settings and may inform management guidelines for patients with respiratory failure.Copyright © 2018 by Daedalus Enterprises.

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