Background: Despite widespread use of HME devices with oxygen ports in tracheostomised patients, the impact of supplemental oxygen on humidification performance remains poorly understood, with no published data. Inadequate humidification may lead to mucosal damage, thickened secretions and airway obstruction.1,2 We hypothesised that increasing oxygen flow via the HME port reduces the absolute humidity provided. This study aimed to assess this effect using a simulated tracheostomised airway.

Methods: Expired tracheal airflow was simulated with a Bellavista 1000 ventilator (Zoll Medical, USA), MR850 Humidifier (Fisher & Paykel, NZ), AirSim Combo anatomical dummy (TruCorp, NI) and BlueSelect size 9 tracheostomy tube (ICU-Medical, UK). Three HME devices (Atos-Freevent, Atos-Trachphone, ICU-Medical Thermovent) were tested across five supplemental oxygen flow rates (0, 1, 2, 4, 10 L/min). Each condition was tested in triplicate. Absolute humidity was measured within the HME devices using a Sensirion SHT85 temperature and humidity detector (Sensirion, CH). Data was analysed in SPSS-30.0 using the Kruskal-Wallis test with post-hoc pairwise comparisons (p < 0.05).

Results: Statistically significant but small differences in absolute humidity were observed across oxygen flow rates for all three devices, with all maintaining humidity above 26 g H2O/m3. Only two devices met the ISO 9360 standard of delivering 30 g/m3 (compared with 44 g/m3 in the human trachea).

Conclusions: Although the hypothesis was not consistently supported, these results provide quantitative evidence that entraining oxygen into tracheostomy HMEs causes variable changes in humidity, which may increase the clinical risk of dried secretions and tube blockage.