Comparison of Oxygen Reservoir Tube Length and Imposed Work of Breathing with the Universal Portable Anesthesia Complete

The Universal Portable Anesthesia Complete is supplied with a 12-inch oxygen reservoir. Previous work suggested that using a longer (greater-volume) reservoir results in a greater inspired oxygen concentration. This study assessed the work of breathing imposed by lengths of reservoir tubing (18, 30, and 48 inches) during simulated spontaneous breathing of an adult anesthetized with isoflurane. Peak negative pressure (PNP) was used as a surrogate of imposed work. There were no clinically significant differences between the PNP with the supplied reservoir tubing and the three lengths of 22-mm corrugated tubing. The PNP ranged between -1.5 and -1.7 cm H2O for the anesthetized condition and between -4.3 and -4.7 cm H2O for the condition modeling emergence from general anesthesia. The morphologic features of the pressure-volume curves corroborated these findings and revealed that little imposed work was attributable to the length of reservoir tubing. These findings should help future investigators seeking to modify the Universal Portable Anesthesia Complete.