The Science Journal of the American Association for Respiratory Care

2002 OPEN FORUM Abstracts

Low-Flow FLowmeters Are Not Accurate in Delivering Therapy at Flows Less Than 1L/Min

Tinaglia A, Batt S, Banzon J, Marion K, Davis K, Schumacher D, Opdahl G, Witzke M, Whard J, RRT, Helmholz H, Jr, MD, Plevak D, MD. Rochester community & Technical College/Mayo Foundation, Rochester, MN

Background: Perinatal/pediatric and chronic obstructive pulmonary disease (COPD) patients may require supplemental oxygen administered at low flows. Industry notes a standard of ±10%. Clinical use, storage, and handling may effect performance. This investigation was performed to determine if the low-flow devices at our institution are accurate according to industry standards at flows ranging from 0.25-1.5 L/min.

Methods: Twenty-four oxygen flowmeters (16 Ohmeda-Madison, WI; 4 Timeter-St. Louis, MO; and 4 Dwyer-Michigan City, IN) currently in clinical uses were tested at three flows: 0.25, 1.0, 1.5 L/min. the flowmeters were all in working order and ranged from brand-new to “many” years old. Flow settings were made visually be the same person and verified by three observers; the Porter Calibration Flowmeter (Baily-Fischer & Porter, Warminster, Pennsylvania). Each glowmeter was tested 3 times at every flow for accuracy and three indicated values were averaged. The oxygen regulator was calibrated to 50 psi using a Timeter RT 200 Calibration Analyzer (Allied Healthcare Products, Inc., St. Louis, MO). The accuracy of the Fischer-Porter was confirmed at three flow,s 0.25, 1.0, and 1.5L/min, using a Tissot water-sealed spirometer and a stopwatch. Bland-Altman plots were used to analyze the data. Statistical agreement between the flow-meter’s indicator ball and the calibration flowmeter measurements would have been confirmed if 95% of the datapoints (two standard deviations) were contained within a 10% margin of error for each flow level.


Flow 0.25 L/min 1.5 L/min 1.5 L/min
Mean ±SD 0.32±0.05 1.05±0.05 1.52±0.06
Mean Diff from expected ±SD of diff 0.07±0.05 0.05±0.05 0.02±0.06

Figure 1 displays a Bland-altman plot of 0.25 L/min flows.

Conclusions: Low-flow flowmeters are not accurate and tend to administer more oxygen than indicated at flows less than 1 L/min. This could be problematic in perinatal, pediatric, and COPD patients.


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