ACCURACY OF OXYGEN DELIVERY BY LIQUID-OXYGEN CANISTERS

The oxygen how rate delivered by liquid oxygen canisters mag be less t han intended, owing to inaccuracies of the set flow rates and/or as a result of the outflow resistance caused by the humidifer, oxygen tubin g, delivery or conserving device. The aim of this study was to investi gate the accuracy of oxygen delivery by liquid oxygen canisters at dif ferent flaw rates and levels of outflow resistance. Four stationary an d 18 portable liquid oxygen canisters from three manufacturers were te sted. All Rows were measured using a Timemeter RT 200 Calibration Anal yser. An adjustable obstruction was used to calculate the effect of th e outflow resistance on the delivered flow rate. The measured and set Row rates of both stationary and portable canisters were strongly corr elated, Expressed as a percentage of the set Row rate, the measured Bo w rate of the canisters varied from 36-128%, with the lowest values at Row rates <1 L . min(-1). Sixty-two (26%) of the measured flow rates differed greater than or equal to 10% from the set flow rate. A differ ence of 05-1.0 L . min(-1) occurred in 16 (7%) of the measurements, bu t only at set Bow rates >2 L , min(-1), Irrespective of the set flow r ate, the measured flow rate was hardly affected by the outflow resista nce. We conclude that the accuracy of oxygen delivery by liquid oxygen canisters depends on the inaccuracy of the set Row rates rather than on the outflow resistance, even at high Row rates. Although the differ ences between the measured and set Bow rates were mostly small, they m ay have clinical significance, particularly in patients with chronic o bstructive pulmonary disease. To prevent inaccuracy, monthly checks of the canisters by the oxygen provider at the patient's home are more i mportant than yearly maintenance.