The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts

COMPARISON OF ACCURACY OF FLOW AND OXYGEN CONCENTRATION IN FOUR OXYGEN BLENDERS.

Gary R. Lowe1, Shirley Holt3, Tracy Thurman3, Mark Heulitt2,3; 1Respiratory Care Services, Arkansas Children's Hospital, Little Rock, AR; 2Dept. of Pediatrics, Critical Care Medicine, University of Arkansas for Medical Sciences, Little Rock, AR; 3Arkansas Children's Hospital Research Institute, Little Rock, AR

Background: Respiratory therapists use oxygen blenders on a daily basis. Our institution utilizes both high-flow blenders (HFB) and low-flow blenders (LFB). HFB guarantee accuracy of FIO2 +/- 3% for flow 2-100 LPM. LFB guarantee accuracy of FIO2 +/- 3% for flow 0-30 LPM. We compared delivered flow rates and FIO2 of four blender types, and hypothesized that there would be no significant difference for flow and FIO2 between the HFB and LFB utilizing low liter flow ranges. Methods: A bench study was performed comparing set flow rates and FIO2 to delivered flow rates and FIO2 on five randomly selected blenders of the four blender types (three HFB and one LFB) in our institution. Flow rates were set at 0.25, 0.50, 0.75, 1.00, 1.50, and 2.00 LPM. FIO2 was set at 0.21, 0.50, and 1.00. Flow measurements were acquired using the Biopac MP-100 System and a 0-10 LPM calibrated pneumotachograph. Volume measurements were obtained through a computer by integrating the flow signal. Volume was verified with a calibrated syringe. All output signals were routed via an analog channel box into the Biopac MP-100 data acquisition unit converting them into digital signals that could then be processed by a computer. Signals were obtained at a rate of 1000 samples per second. Flow was measured and averaged over a 60 second period for each delivered flow rate. FIO2 was measured on two oxygen monitors within the system (mean of the two = delivered FIO2). One minute of equilibration time was allowed for each change in flow or FIO2. Percent error between set vs. delivered values were utilized for analysis. A t-test with significance (p < 0.05) was used to compare mean % error between the LFB and the HFB group. Results: There was a < 1% error in set vs. delivered FIO2 for all blender types. The mean % error for set vs. measured flow rates was less for the LFB (-4% +/- 15 %) compared to the HFB group (-11% +/- 19%), (p=0.001). Conclusion: There was < 1% error in delivered FIO2 for all blender types. This is within the manufacturer's guaranteed accuracy. However, the LFB system delivered set flows more accurately (< 10% error) when compared to the HFB systems (< 15% error). These results suggest that when using low flows a LFB system should be employed. This was a limited study, and further research needs to be completed on blender systems to ensure the accuracy of the flow rates.
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