Several high flow nasal cannula (HFNC) systems are widely used in clinical practice, yet few studies have evaluated the differences in design elements or clinical effectiveness. In 2014, Tero and colleagues published “Risks Associated With Conventional Humidifiers Adapted for High-Flow Nasal Cannula Therapy in Human Infants: Results of a Time and Motion Study”, which demonstrated HFNC using the Fisher & Paykel MR850TM was associated with greater staff workload and patient risk than with Vapotherm Precision Flow.
Recently, Miller et al., published a comparison study examining the upper airway gas dynamics for cannulae with different cannula prong sizes (Journal of Pulmonary & Respiratory Medicine titled Computational Fluid Dynamics Modeling of Extrathoracic Airway Flush: Evaluation of High Flow Nasal Cannula Design Elements). The study used advanced fluid dynamics software to characterize flow patterns and compare purge time between different cannula sizes. The model used large and small-bore prong designs and used actual human upper airway architecture (derived from CT scans). The authors conclude that the smaller cannula prongs achieved a faster purge of the extrathoracic dead space for a given flow rate than the larger prong configuration (28% faster at 20 L/min).
The Vapotherm Adult Nasal Cannula (MA-1700) uses a prong inner diameter of 2.7mm. The Fisher & Paykel OptiflowTM Adult Nasal Cannula (OPT546) uses a prong inner diameter of 5.4mm.
These findings help explain the differences between the various technologies in clinical use. Improving the ability to flush the nasal extrathoracic dead space is important for the management of signs and symptoms of respiratory distress, including not only hypoxia but also hypercapnia.