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1.  Nasal high-flow therapy delivers low level positive airway pressure 
BJA: British Journal of Anaesthesia  2009;103(6):886-890.
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 H2O with the mouth closed. Airway pressure was significantly higher when breathing with mouth closed compared with mouth open (P≤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.
PMCID: PMC2777940  PMID: 19846404
airway pressure; nasal high-flow therapy; Optiflow™; oxygen

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