• R Parke, S McGuinness, and M Eccleston.
• Cardiothoracic and Vascular Intensive Care Unit, Level 4, Building 32, Auckland City Hospital, Private Bag 92024, Auckland, New Zealand. rparke@adhb.govt.nz
• Br J Anaesth. 2009 Dec 1;103(6):886-90.

BackgroundThe 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).MethodsNasopharyngeal 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.ResultsLow 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 (PConclusionsThis 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 www.actr.org.au ACTRN012606000139572.

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