Abstract Rationale Nebulized saline has been used in combination with nasal high flow (NHF) therapy to aid mucus clearance in the treatment of respiratory diseases. The absolute amounts of salt and water delivered to the lungs remain poorly characterized. This study quantified regional salt and water deposition in the adult respiratory tract during NHF-mediated delivery of isotonic (IS, 0.9% NaCl) and hypertonic (HS, 7% NaCl) saline using in vitro and in silico methods. Methods In vitro experiments were conducted at 30 L·min⁻¹ NHF using a 3D-printed nasal replica (based on averaged airway geometry across multiple adults, average age: 37) with a heated and humidified NHF system (AIRVO 3 with Optiflow Duet nasal cannula interface, Fisher 9 min for HS). The measured in vitro dose was input into a modified in silico computational model simulating hygroscopic droplet growth alongside regional airway deposition. Two saline tonicities (IS, HS), three initial particle size distributions (MMAD = 2, 4, 6 µm; GSD = 1.8), and three breathing patterns (I:E = 1:1, 1:2, 1:3; tidal volume = 0.5 L), referred to as BP 1, 2 and 3 hereafter, were simulated. Results In vitro tests found that saline delivery to the trachea ranged from 4-8% nebulized NaCl across all test conditions. Breathing pattern had no influence on extrathoracic deposition. In silico modeling revealed that the total deposited salt mass in the lungs was comparable between IS (6-10 mg) and HS (5-8 mg). However, total deposited water volume differed substantially between saline concentrations. IS deposited significantly more water (0.6 - 1.1 mL) than HS (0.2 - 0.3 mL). Furthermore, salinity dynamics varied between IS and HS as shown in Figure 1. Conclusions Compared with HS, IS nebulization delivered a similar salt mass to the airways but resulted in a 2- to 4-fold increase in delivered water volume. The longer nebulization time for IS may be well tolerated, as the droplets remain isotonic during transport and deposition in the lungs. This may have clinical relevance for maintaining continuous airway hydration during NHF. Figure 1. Salinity of deposited saline in the airways during NHF. Generations 0-14 represent the tracheobronchial airways, with higher generation numbers representing the alveolar lung region. This abstract is funded by: Fisher & Paykel Healthcare
Martin et al. (Fri,) studied this question.