Physiological Effects of High Flow Nasal Cannulas Oxygen Therapy vs Continuous Positive Airway Pressure in Pediatric Acute Respiratory Failure

Non-invasive Continuous Positive Airway Pressure (nCPAP) is widely recognized as an efficient respiratory support in infants with mild to moderate Acute Hypoxemic Respiratory Failure (AHRF).

Its application results in alveolar recruitment, inflation of collapsed alveoli, and reduction of intrapulmonary shunt. nCPAP is traditionally delivered with nasal prongs, nasal/facial mask. CPAP by helmet was introduced more recently in the clinical practice.

The helmet circuit was described in details in previously published studies. From a physiological point of view the helmet circuit could be considered the best system to deliver CPAP because of the following: 1) it is characterized by the lowest amount of leaks around the interface and mouth opening 2) airways are free from potentially obstructing devices (cannula) thus the resistance is minimized and 3) theoretically the pressure is more stable minimizing the leaks 4) it is comfortable and usually sedation is not needed.

High Flow Nasal Cannula (HFNC) is increasing in use both in adults and pediatric population. HFNC could result in several clinical benefits by reducing inspiratory effort and work of breathing, increasing end-expiratory volume and CO2 wash-out for upper airways and creating a CPAP effects of 2-3 cmH2Oin the upper airways. This CPAP effect combined with an increase in CO2 wash-out and optimal airways humidification could decrease the respiratory work of breathing and improve gas exchange. However little is known about the optimal flow rate setting to improve the respiratory mechanics and gas exchange. Recent studies have reported that HFNC in nonintubated children improves oxygenation, reduces the respiratory drive and prevent reintubation in high patient risk. However all these physiological effects during HFNC therapy are only speculative.

To address the question on the more efficient devices to support the child in the early phase of mild to moderate AHRF, the Authors designed a physiological randomized crossover study aimed at measuring the physiological effects of HFNC 2 and 3 l/Kg and helmet CPAP on the work of breathing (estimated by the esophageal Pressure Time Product, PTPes) in pediatric AHRF.