Table 1.

Physiological effects of COT, HFNC and CPAP/NIV.

	Conventional oxygen therapy (COT)	High-flow nasal cannula (HFNC)	Continuous positive airway pressure (CPAP) / Non-invasive ventilation (NIV)
Deliver fixed concentrations of oxygen and other gasses	+	+++	++
Generate positive end-expiratory pressure	=	+	+++
Reduce work of breathing	=	++	+++
Anatomic dead space washout	=	+++	+
Reduce inspiratory resistance	=	+	+++
Gas conditioning	=	+++	+
Improve mucociliary clearance	=	+++	=

=, no effect; +, low effect; ++, medium effect; +++, high effect.