No clear recommendation exists concerning humidification during non-invasive ventilation (NIV) and high flow CPAP, and few hygrometric data are available.Methods
We measured hygrometry during NIV delivered to healthy subjects with different humidification strategies: heated humidifier (HH), heat and moisture exchanger, (HME) or no humidification (NoH). For each strategy, a turbine and an ICU ventilator were used with different FiO2 settings, with and without leaks. During CPAP, two different HH and NoH were tested. Inspired gases hygrometry was measured, and comfort was assessed. On a bench, we also assessed the impact of ambient air temperature, ventilator temperature and minute ventilation on HH performances (with NIV settings).Results
During NIV, with NoH, gas humidity was very low when an ICU ventilator was used (5 mgH2O/l), but equivalent to ambient air hygrometry with a turbine ventilator at minimal FiO2 (13 mgH2O/l). HME and HH had comparable performances (25–30 mgH2O/l), but HME's effectiveness was reduced with leaks (15 mgH2O/l). HH performances were reduced by elevated ambient air and ventilator output temperatures. During CPAP, dry gases (5 mgH2O/l) were less tolerated than humidified gases. Gases humidified at 15 or 30 mgH2O/l were equally tolerated.Conclusion
This study provides data on the level of humidity delivered with different humidification strategies during NIV and CPAP. HH and HME provide gas with the highest water content. Comfort data suggest that levels above 15 mgH2O/l are well tolerated. In favorable conditions, HH and HMEs are capable of providing such values, even in the presence of leaks.