High Flow Nasal Oxygen (HFNO)

High-flow nasal oxygen was actually described in the mid-1950s and most commercially available devices deliver flow rates of up to 60 litres/minute. 

It has only become a mainstream device in the last decade as the technology has not been available to easily warm and humidify the gases at such high flow rates. High flow rates without active warming and humidification would feel particularly uncomfortable and quickly lead to the drying of secretions. 

In terms of advantages, HFNO delivers high FiO₂ that much better matches a patient’s PIFR. It has some CO₂ lowering effect by washing out pharyngeal dead space and delivers 1 cm of CPAP for every 10 litres of flow, thus decreasing atelectasis and improving V/Q matching. Patients can eat and drink and can continue to interact with relatives and healthcare professionals. They are generally well tolerated.  

There are not many disadvantages. It may be argued that it causes an undesirable delay to the institution of mechanical ventilation in some patients. Like a nasal cannula, it also cannot be used if a patient has a nasal obstruction, a base of skull fracture, or active epistaxis. 

There is some evidence to support the use of HFNO following the extubation of high-risk patients. It can be used to facilitate procedures such as bronchoscopy and awake fibreoptic intubation and used as a ceiling of care therapy when mechanical ventilation is considered to be inappropriate. These are outside the scope of this course. 

Click next to watch a short video by Professor Malcolm Sim on this topic.