Optiflow™ high flow mechanisms of action

The mechanisms of action of Optiflow nasal high flow (NHF) therapy differs from those of conventional therapies, as do the resulting physiological effects and clinical outcomes.
The Optiflow NHF therapy mechanisms of action are:
Note: the above mechanisms apply to delivery via an Optiflow nasal cannula interface. The mechanisms of action differ when high flow is delivered through a tracheostomy or mask interface adapter.


Reduction of dead space

Clearance of expired air in the upper airways reduces rebreathing of gas high in CO2 and depleted O2, increasing alveolar ventilation.

Dynamic, positive airway pressure

NHF creates breath and flow-dependent pressure, making inspiration
easier and promoting slow, deep breathing on expiration,
thereby increasing alveolar ventilation.

Airway hydration/heated humidification

Humidity enables the comfortable delivery of high flows of gas.  
Optimized humidity emulates the natural balance of heat and moisture in healthy lungs and may promote physiological stability in compromised airways.  

Patient comfort

Respiratory support delivered via a mask poses challenges for clinicians and patients.
NHF delivered via a cannula promotes patient comfort and may improve compliance.

Supplemental oxygen (if required)

Oxygen delivered via conventional oxygen therapy (COT) is 'bone' dry. Delivering oxygen via NHF therapy allows for oxygen to be optimally humidified eliminating the issues associated with exposure of the vulnerable upper airway to dry gas. 
Additionally delivering oxygen via NHF gives you confidence in the accurate delivery of blended oxygen. 


How does NHF compare with COT?

Although an NHF device can deliver high oxygen levels (up to 100% FiO2), it’s not specifically an oxygen delivery device. NHF can be, and is, often used without supplemental oxygen, i.e., with room air – 0.21 FiO2.

Conventional oxygen therapy via a low-flow cannula and most styles of oxygen face masks are limited to lower flow rates (up to 10 L/min) partly because the gas is cold and dry, making tolerability a significant issue.

These lower flow rates also limit FiO2 delivery and accuracy and aren’t high enough to offer the benefits of dead-space washout and positive airway pressure.

Typically, “high flow” refers to flow rates above 15 L/min of a fully humidified air and oxygen mix. These higher flow rates enable mechanisms that cold, dry oxygen alone cannot provide.

See the table below for a comparison of standard COT devices and NHF.