Computational Fluid Dynamics Modeling of Extrathoracic Airway Flush: Evaluation of High Flow Nasal Cannula Design Elements

Abstract

Objective: High flow nasal cannula (HFNC) is an evolving respiratory therapy whereby high flow rates of conditioned breathing gas are delivered into the nasal cavity to purge anatomical dead space of CO 2 rich expired gas. The aim of this project was to create a computational fluid dynamics (CFD) model to evaluate the fluid patterns in the human nasal and pharyngeal cavities with HFNC application, and quantify time to purge for two cannula configurations.Methods: Three-dimensional geometry of the human airway was used to define the extrathoracic dead space and the two cannula designs tested incorporate large vs small bore nasal prong configurations (Vapotherm, Exeter, NH, USA). The fluid flow simulations were performed using FLOW-3D software, set up for a cannula flow rate of 20 L•min -1 and run until steady state.Results: Basic flow patterns were similar between cannulae, creating vortices around a central inward flow path. Flow velocity around the vortices was greater with the small prong cannula, resulting in a lower pressure in each region of the nasal and nasopharyngeal space. The calculation of purge time revealed that the small prong nasal cannula was able to clear the nasal, pharyngeal and oral cavities in 2.2 seconds, whereas the large bore cannula required 3.6 seconds (64% longer). Conclusion:The current CFD data validate that a smaller bore nasal prong facilitates the purge action, which is related to velocity and dynamic energy induced by the tighter prong nozzle as opposed to the lesser occlusion of the nares.

Effect of High-Flow Nasal Cannula on Expiratory Pressure and Ventilation in Infant, Pediatric, and Adult Models

“…Optiflow cannulae have independent flow channels to each prong and wider bore tubing, whereas the Precision Flow cannulae have a common flow channel and narrower tubing. Three-dimensional computational fluid dynamic models have shown that smaller bore cannulae may produce a higher flow velocity, 37 and we speculate that a similar phenomenon occurs with the Precision Flow cannulae. Improved CO 2 clearance with HFNC helps explain reported clinical reductions in breathing frequency, arterial CO 2 , and work of breathing in patients treated with HFNC.…”

High-Flow Oxygen Therapy Application in Chronic Obstructive Pulmonary Disease Patients With Acute Hypercapnic Respiratory Failure: A Multicenter Study

“…HVNI administration employs a small-bore nasal cannula prong, imparting greater velocity to the gas flow. This has been demonstrated to provide a mechanistic advantage to flush the accessible deadspace in the upper airway, likely through creation of increased turbulent kinetic energy ( 37 – 39 ).…”

Pharyngeal pressure due to high‐flow nasal cannula devices in preterm infants

“…A high-flow nasal cannula (HFNC) is widely used in preterm infants to provide tolerable and comfortable respiratory support. 1 The benefits of an HFNC include a secure oxygen supply, 2 heat humidification of the airway, 3,4 CO 2 washout in the anatomical dead space, 5,6 and mild positive pressure. 6,7 Studies have reported significant correlations between flow rate and airway pressure generated by an HFNC in preterm infants.…”