Numerical simulation of aerosolised medicine delivery through tracheostomy airways

The administration of inhaled antibiotics to patients with upper or lower respiratory infections is sometimes conducted via a tracheostomy airway. However, precise dosing via this route remains uncertain, especially in spontaneously breathing paediatric patients. This study uses computational fluid dynamics (CFD) to explore the delivery of aerosolised medicine through an idealised tracheostomy tube, focussing on how droplet size distribution (polydispersity) and breathing flow conditions affect drug delivery efficiency. Unlike previous studies that incorporate elongated inlet and outlet sections to minimise flow disturbances, this work considers the compact geometry of tracheostomy tubes, demonstrating an earlier vortex formation around the inlet, resulting in an increased droplet deposition along the outer wall, closer to the inlet. As a result, the transfer efficiency, $\eta$ (i.e. mass percentage of particles exiting the tracheostomy tube relative to the inlet rate), which decreases with increasing velocity, is found to be lower than those shown in other studies of 90° pipes. This efficiency further decreases with increased polydispersity of the inlet particles. The proportion of respirable droplets in the outlet stream is strongly influenced by the Mass Median Diameter (MMD) of the inlet. When the inlet MMD is 3.5 μm, the net transfer efficiency of respirable droplets, ${\eta }_{respirable}$, is 50.3 %, with minimal variation across flow conditions. A lower inlet MMD of 2.2 μm yields higher ${\eta }_{respirable}$ values (64.9–87.7 %), although with greater sensitivity to flow and polydispersity. These findings offer new insights into optimising aerosol drug delivery through tracheostomy airways.