2003 OPEN FORUM Abstracts
Comparison of Vapotherm? 2000i with a bubble
humidifier for humidifying flow
through an infant nasal cannula
Brian K. Walsh, BS, RRT-NPS, RPFT University of Virginia Department of Respiratory
Therapy
Background: Supplemental oxygen at low flows is typically delivered to an infant by nasal
cannula. The oxygen is dry at source, and thickening of airway secretions is a frequent side effect.
Bubble humidifiers are used in an attempt to limit the degree of drying. Vapotherm humidification
system (using a "low flow" cartridge) allow it to operate at flows of 1-8 liters per minute once
thought to be too high for neonates due to drying of the mucosia. This test compared the water
content of low-flow oxygen delivered by nasal cannula humidified by either a bubble humidifier
(Airlife, Cat. 002620) or the Vapotherm 2000i.
Method: A standard neonatal nasal cannula was used (Salter 1601). For testing with the bubble
humidifier, the cannula was used with its original 7-ft supply line. For testing with the
Vapotherm, the cannula was shortened to 6" and attached to the end of the 7-ft Vapotherm
delivery tube. The air source in both was regulated by a standard flowmeter. Temperature, relative
and absolute humidity were measured at flow rates of 1, 2, 3, 4 and 5 lpm. The Vapotherm was
run at temperature settings of 37ºC and 43ºC. The bubble humidifier has no controls.
Results: The Vapotherm delivered gas saturated with water vapor (100% relative humidity, RH)
at all flow rates and temperatures. RH from the bubble humidifier was well below saturation at all
flow rates. The water vapor content in mg/l was up to three times higher using the Vapotherm
than with the bubble humidifier, depending on flow and temperature setting. At a Vapotherm
setting of 43ºC and 3-5 lpm the gas from the nasal prongs is essentially saturated at body
temperature, so there is no respiratory loss of water or heat. Graph 1 Demonstrates the temperature
and graph 2 demonstrates the water content
Conclusion: The Vapotherm system allows supply of breathing gas by nasal cannula in the
neonatal flow range with no airway cooling or drying. By contrast, flow from a bubble humidifier
is well below body temperature and has a significant water deficit.
Discussion: These tests were performed at room temperature in an open environment. If the
cannula and part of the tubing were in a warmed isolette the delivered gas temperatures would be
warmer. (The water content would of course be unchanged.) However, the bubble humidifier
reservoir is at room temperature, and warming the output gas would reduce the RH still further.
Vapotherm output would still be close to saturation. The advantage of Vapotherm over a bubble
humidifier for humidifying cannula output would therefore be enhanced if the patient was in an
isolette.