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.