Abstract
Background:
A low-flow nasal cannula (LFNC) is a common device used in the administration of oxygen and has been traditionally used for flows up to 6 L/min. The heated high flow nasal cannula (HFNC) was designed for use with oxygen flow up to 60 L/min and heated humidifier. Recently, manufacturers have introduced a HFNC for use with a bubble humidifier up to 15 L/min. The ISO 80601-2-74:2017 standard for unheated humidification devices specifies that 12 mg/L is the minimum level of humidification for patients whose upper airways have not been bypassed. The purpose of this study was to determine if use of an unheated bubble humidifier for HFNC meets this standard.
Methods:
A HFNC (Westmed 0549) was attached to the bubble humidifier supplied with it (Westmed 0795) and experiments run at flows of run at 5, 10, and 15 L/min. The humidifier was filled with sterile water. To verify flow, a Citrix H4 flow meter was used to set a medical grade oxygen flow meter and the setup was allowed to reach steady state temperature. Then the Citrix H4 was removed the humidifier was weighed. After 5 h of continuous flow, the humidifier was weighted again. The delivered absolute humidity (mg/L) was calculated as water weight difference divided by delivered volume (flow × time). Each experiment was repeated once.
Results:
The absolute humidity decreased as flow increased (see Table). At 5 L/min the bubble humidifier met ISO standards. However, at flows of 10 and 15 L/min the humidifier did not meet the ISO standards.
Conclusions:
Humidity produced by an unheated bubble humidifier is only adequate at low flows but may not provide sufficient humidity at higher flows commonly used for HFNC.
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