Vibrating mesh nebuliser positioning during helmet CPAP: A thermo-hygrometric bench-top study

Aerosol therapy during helmet continuous positive airway pressure (CPAP) is clinically relevant but technically challenging. Evidence regarding the optimal nebuliser position during helmet CPAP is lacking. This bench study assessed thermo-hygrometric changes at the distal end of a simulated trachea across different vibrating mesh nebuliser positions during helmet CPAP, using these changes as indirect indicators of aerosol reaching the airway model.

A bench-top study was performed using an ASL 5000 lung simulator connected to a simulated trachea and head model. The aerosol was generated using a vibrating mesh nebuliser. Five configurations were tested: standard oxygen mask as reference, oxygen mask positioned under helmet CPAP, nebuliser at the helmet gas inlet, and nebuliser on the front left or front right helmet port. The relative humidity and temperature were recorded at the distal end of the simulated trachea.

Compared with the reference mask setup, the mask-nebuliser system maintained under the helmet showed the greatest increase in delta absolute humidity (+4.23 ± 3.12 mg/L; p < 0.001), followed by front-left port placement (+2.74 ± 2.85 mg/L; p = 0.001). Gas inlet placement resulted in a significant decrease in delta absolute humidity (-3.98 ± 1.82 mg/L; p < 0.001).

In this bench model, the mask-nebuliser system placed under the helmet showed the most favourable thermo-hygrometric profile. However, among external helmet configurations, front-left port placement showed the most promising performance, particularly for absolute humidity, while preserving the helmet CPAP interface. Further studies using direct aerosol dose measurements are needed.

These findings may support critical care nurses in interpreting how different aerosol delivery positions during helmet CPAP can affect thermo-hygrometric behaviour in a simulated airway model. Although direct aerosol deposition was not measured, this evidence may contribute to more informed nursing decisions when administering aerosol therapy without interrupting helmet CPAP support.