Aim: Condensation often occurs when providing humidified respiratory support. We examined conditions conducive to excess water formation in heated, humified, high-flow nasal cannula (HHHFNC).
Methods: An HHHFNC device, at 35°C or 37°C, was attached with a nasal cannula to a reservoir and tested in five ambient conditions and flows. For Group A, tubing and collection bottle remained at room temperature (23°C). Group B, tubing and reservoir remained inside an incubator (31°C). Group C, tubing and reservoir remained at 33°C. In Group D the HHHFNC was set to 35°C, the reservoir remained at 33°C and the nasal cannula and tubing remained at 23°C. Group E, same as D, with HHHFNC at 37°C.
Results: The largest amounts of collected water were in groups A and E. Both had highest temperature differences. Median (range) was 4.9°C (4.1-6.9) and 4.0°C, collecting 38.4 (26.4-50.4) and 26.4 (19.2-50.4) ml/24hs, respectively. Smallest amounts of water were seen with lower temperature differences as in Groups B, C, and D with 2.7 (1.9-4.7), 1.6 (1.2-2.1), and 2.0°C with 8.4 (0.0-33.6), 2.4 (0.0-14.4), and 9.6 (4.8-16.8) ml/24hs, respectively.
Conclusion: HHHFNC devices may produce clinically significant amounts of water reaching the upper airways. This may be prevented with appropriate device setup.