Impact of high- and low-flow nebulized saline on airway hydration and mucociliary transport

Abstract

Nebulized drugs, including osmotic agents and saline, are increasingly used during non-invasive respiratory support including nasal high-flow therapy. The authors conducted an in vitro study to compare the hydration effect of nebulized isotonic 0.9% and hypertonic 7.0% saline on mucociliary transport.

In a perfused organ bath, 10 sheep tracheas were exposed to 7.5 mL nebulized 0.9% and 7.0% saline entrained into heated (38 °C) and humidified air delivered at high- and low-flow (20 and 7 L·min⁻¹, respectively). Simultaneous measurements of the airway surface liquid height, mucus transport velocity, cilia beat frequency and surface temperature were made over time. The data was presented as mean±sd.

The airway surface liquid height increased significantly with both 0.9% and 7.0% saline: at low-flow by 37.2±10.0 µm and 152.7±10.9 µm, and at high-flow by 62.3±5.6 µm and 163.4±25.4 µm (p<0.001), respectively. Mucus velocity was increased by both 0.9% and 7.0% saline from a baseline of 8.2±0.8 mm·min⁻¹ to 8.8±0.7 mm·min⁻¹ and 17.1±0.5 mm·min⁻¹ with low-flow and at high-flow to 9.8±0.02 mm·min⁻¹ (p=0.04) and 16.9±0.5 mm·min⁻¹ (p<0.05), respectively. Ciliary beating did not change with 0.9% saline but declined from 13.1±0.6 Hz to 10.2±0.6 Hz and 11.1±0.6 Hz (p<0.05) with 7.0% saline at low- and high-flow, respectively.

The findings demonstrate that nebulized isotonic 0.9% saline like hypertonic 7.0% saline significantly stimulates basal mucociliary transport and the use of high-flow delivery had no significantly different hydration effects compared with low-flow. Hypertonic 7.0% saline suppressed ciliary beating indicating an increase in airway surface liquid osmolarity, which may have negative effects on the airway surface with frequent use.