Mechanical ventilation is associated with both impaired ciliary function and a weakened cough, which further impair secretion clearance. Continuous high-frequency oscillation (CHFO) is a promising technique to reduce respiratory muscle loading and facilitate secretion clearance in mechanically ventilated patients. The aim of this study was to assess the effect of CHFO on airway resistance (Raw).

This is a prospective, randomized controlled trial conducted in a 60-bed ICU between April 2023 and March 2024. Mechanically ventilated patients with excessive airway secretions (defined as the sputum volume exceeding 150 ml within the past 24 hours) were randomly assigned to either receive CHFO for 10 minutes followed by secretion aspiration (CHFO group), or to undergo secretion aspiration alone (control group). Throughout the study, only the study intervention and necessary suctioning were performed, and patient positioning and ventilator settings were kept constant. Arterial blood gases, respiratory mechanics, and the percentage of dorsal lung ventilation (assessed by electrical impedance tomography) were measured in both groups at four timepoints: pre-intervention (baseline), immediately post-intervention (T0), one-hour post-intervention (T1), and three-hours post-intervention (T3). The primary outcome was the change in Raw from baseline at each time point (ΔRaw: R _{post-intervention} - R _baseline ). Change in respiratory system compliance (Crs), and ventilation distribution were also recorded.

46 patients, with a median sputum volume of 160 ml over the last 24 hours, were enrolled. Baseline characteristics were well-balanced in the two groups. CHFO group showed a significantly larger decrease in Raw compared to control group at T1 (CHFO: -2.4 ± 1.8 vs. control: -0.1 ± 1.6 cmH₂O/L·s, p < 0.001) and T3 (CHFO: -1.8 ± 2.4 vs. control: -0.5 ± 1.9 cmH₂O/L·s, p <  0.05). Increase in Crs from baseline was greater in the CHFO group than control group at T1 (CHFO: 4.9 ± 8.8 vs. control: 0.3 ± 4.2 ml/cmH ₂ O, p  <  0.05) and T3 (CHFO: 4.3 ± 9.6 vs. control: 1.0 ± 5.8 ml/cmH ₂ O, p  <  0.05). Increase in dorsal lung ventilation from baseline was greater in the CHFO group compared to control group to T1 (p  <  0.05). No differences in oxygenation were observed between the two groups at any time point.

In mechanically ventilated patients with excessive airway secretions, the reduction in Raw from baseline was significantly greater in the CHFO group than control group at one-hour and three-hour post-intervention.