Use of an oxygen concentrator linked to a draw-over vaporizer (anesthesia delivery system for underdeveloped nations).

The use of an oxygen concentrator linked to a draw-over vaporizer was examined. The fractional oxygen concentration from this equipment was dependent on the minute ventilation, oxygen output of the concentrator (%), and the presence of an oxygen economizer tube (OET) (a 900-mL corrugated tube). Fractional oxygen concentrations were always higher with an OET than without an OET (other variables being constant). With the OET in place, the fractional oxygen concentration was only dependent on the minute volume and independent of the pattern of ventilation (i.e., varying inspiratory and expiratory ratios and inspiratory and expiratory pauses). Without an OET, the performance of the system was considerably impaired. In this setting, the final oxygen concentration depended not only on the added flow of oxygen and minute volume but also on the pattern of ventilation. In conclusion, when using a draw-over vaporizer linked to an oxygen concentrator, an OET is essential so as to provide consistent oxygen concentrations to the patient at any given minute volume.