BACKGROUND: High flow nasal cannula (HFNC) systems utilize higher gas flow rates 
than standard nasal cannulae. The use of HFNC as a respiratory support modality 
is increasing in the infant, pediatric, and adult populations as an alternative 
to non-invasive positive pressure ventilation.
OBJECTIVES: This critical review aims to: (1) appraise available evidence with 
regard to the utility of HFNC in neonatal, pediatric, and adult patients; (2) 
review the physiology of HFNC; (3) describe available HFNC systems (online 
supplement); and (4) review ongoing and planned trials studying the utility of 
HFNC in various clinical settings.
RESULTS: Clinical neonatal studies are limited to premature infants. Only a few 
pediatric studies have examined the use of HFNC, with most focusing on this 
modality for viral bronchiolitis. In critically ill adults, most studies have 
focused on acute respiratory parameters and short-term physiologic outcomes with 
limited investigations focusing on clinical outcomes such as duration of therapy 
and need for escalation of ventilatory support. Current evidence demonstrates 
that HFNC generates positive airway pressure in most circumstances; however, the 
predominant mechanism of action in relieving respiratory distress is not well 
established.
CONCLUSION: Current evidence suggests that HFNC is well tolerated and may be 
feasible in a subset of patients who require ventilatory support with 
non-invasive ventilation. However, HFNC has not been demonstrated to be 
equivalent or superior to non-invasive positive pressure ventilation, and 
further studies are needed to identify clinical indications for HFNC in patients 
with moderate to severe respiratory distress.