OBJECTIVE: Oxygen therapy for infants and small children in developing countries is often not available. Entrainment devices may provide an accurate and precise concentration of oxygen when used at the flow rates appropriate for infants and small children. METHODS: A continuously adjustable entrainment device was tested to determine the concentrations and flows of oxygen delivered by using low inlet flow rates suitable for therapy for infants and small children and 3 distinct oxygen delivery systems that varied in their resistive load. RESULTS: The use of long and large bore, low resistance tubing (similar to a mask) resulted in the delivery of oxygen concentrations that tracked closely (accurate and precise) to values indicated by the entrainment device. The directly connected system with lower resistance (similar to a hood) produced a similar profile of concentrations and flow rates to the large bore tubing but with even greater accuracy. The use of a long and narrow tubing with higher resistance (similar to a cannula) did not deliver accurate oxygen concentrations. In fact, this high-resistance system failed to work as intended, and instead of entraining air, a large proportion (sometimes >50%) of the oxygen delivered to the entrainment device was ejected through its vents. CONCLUSIONS: Entrainment devices can deliver accurate oxygen concentrations at low flow rates if used with low resistance delivery systems; however, entrainment devices are not suitable for use with high resistance delivery systems such as a standard nasal cannula. Copyright © 2011 by the American Academy of Pediatrics.