Mean Airway Pressure Generated by HHFNC at Varying Flows and Naris Occlusions

Gerald Moody, Respiratory Care Practitioner, Children’s Medical Center, Dallas, TX


Gerald Moody, RRT

The use of Heated High Flow Nasal Cannula (HHFNC) in our institution has increased over the past few years but the mechanism of action is not fully understood. In addition, we have not fully grasped how much support, in terms of pressure, is being delivered to the patient. We also use two different HHFNC delivery devices in our practice and each manufacturer has different recommendations for nasal cannula size. The aim of our research was to determine how much mean airway pressure (MAP), if any, was generated throughout the respiratory cycle at varying flows and naris occlusions with each HHFNC delivery device.

To measure MAPs we used the ASL 5000™ Adult/Neonatal Breathing Simulator with the Pediatric Patient Model.

Adapter made of PVC pipe to simulate nare diameter


Adapters made of PVC pipe were used to simulate different naris diameters for each nasal cannula to represent 50%, 75%, and 90% occlusion of the nares. Each adapter was connected to the ASL 5000 and the MAP was measured at flows of 3, 5, 7, 9, 11, 13, and 15 liters per minute.

The results of our research indicated there was no significant difference between the HHFNC delivery devices, but occlusion of nares by the nasal cannula greatly influences MAP and significant pressures can be generated when occlusion is greater than 75%. An abstract of our research, “Comparison of Mean Airway Pressure Generated by Two Heated High Flow Nasal Cannula Devices and Nasal Noninvasive Ventilation in a Simulated Pediatric Lung Model” has been accepted for presentation at the 2015 AARC Congress.

“Having the ASL 5000 at our disposal has enabled us to gain a better understanding of our use of HHFNC and the amount of support we are potentially delivering to patients when considering cannula size, nares occlusion, and flow.”Gerald Moody, Respiratory Care Practitioner, Children’s Medical Center, Dallas, TX

Our research determined that we grossly under-estimated support in some instances and over-estimated in others. The results of this research and supporting information will be used to educate staff and providers so we have more objective data when assessing patients and making recommendations on therapy.