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Br J Anaesth. 2009 Dec;103(6):886-90. doi: 10.1093/bja/aep280. Epub 2009 Oct 20.

Nasal high-flow therapy delivers low level positive airway pressure.

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Cardiothoracic and Vascular Intensive Care Unit, Level 4, Building 32, Auckland City Hospital, Private Bag 92024, Auckland, New Zealand.



The aim of this prospective study was to determine whether a level of positive airway pressure was generated in participants receiving nasal high flow (NHF) delivered by the Optiflow system (Fisher and Paykel Healthcare Ltd, Auckland, New Zealand) in a cardiothoracic and vascular intensive care unit (ICU).


Nasopharyngeal airway pressure was measured in 15 postoperative cardiac surgery adult patients who received both NHF and standard facemask therapy at a flow rate of 35 litre min(-1). Measurements were repeated in the open mouth and closed mouth positions. Mean airway pressure was determined by averaging the pressures at the peak of inspiration of each breath within a 1 min period, allowing the entire pressure profile of each breath to be included within the calculation.


Low level positive pressure was demonstrated with NHF at 35 litre min(-1) with mouth closed when compared with a facemask. NHF generated a mean nasopharyngeal airway pressure of mean (SD) 2.7 (1.04) cm H(2)O with the mouth closed. Airway pressure was significantly higher when breathing with mouth closed compared with mouth open (P<or=0.0001).


This study demonstrated that a low level of positive pressure was generated with NHF at 35 litre min(-1) of gas flow. This is consistent with results obtained in healthy volunteers. Australian Clinical Trials Registry ACTRN012606000139572.

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