• Rachael L Parke, Andreas Bloch, and Shay P McGuinness.
• Cardiothoracic and Vascular Intensive Care Unit, Auckland City Hospital, Auckland, New Zealand. Australian and New Zealand Intensive Care Research Centre, Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Victoria, Australia and the Medical Research Institute of New Zealand, Wellington, New Zealand. rparke@adhb.govt.nz.
• Respir Care. 2015 Oct 1; 60 (10): 139714031397-403.

BackgroundPrevious research has demonstrated a positive linear correlation between flow delivered and airway pressure generated by high-flow nasal therapy. Current practice is to use flows over a range of 30-60 L/min; however, it is technically possible to apply higher flows. In this study, airway pressure measurements and electrical impedance tomography were used to assess the relationship between flows of up to 100 L/min and changes in lung physiology.MethodsFifteen healthy volunteers were enrolled into this study. A high-flow nasal system capable of delivering a flow of 100 L/min was purpose-built using 2 Optiflow systems. Airway pressure was measured via the nasopharynx, and cumulative changes in end-expiratory lung impedance were recorded using the PulmoVista 500 system at gas flows of 30-100 L/min in increments of 10 L/min.ResultsThe mean age of study participants was 31 (range 22-44) y, the mean ± SD height was 171.8 ± 7.5 cm, the mean ± SD weight was 69.7 ± 10 kg, and 47% were males. Flows ranged from 30 to 100 L/min with resulting mean ± SD airway pressures of 2.7 ± 0.7 to 11.9 ± 2.7 cm H2O. A cumulative and linear increase in end-expiratory lung impedance was observed with increasing flows, as well as a decrease in breathing frequency.ConclusionsMeasured airway pressure and lung impedance increased linearly with increased gas flow. Observed airway pressures were in the range used clinically with face-mask noninvasive ventilation. Developments in delivery systems may result in this therapy being an acceptable alternative to face-mask noninvasive ventilation.Copyright © 2015 by Daedalus Enterprises.

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