Precision and Accuracy of Oxygen Flowmeters: A Systematic Review with Meta-Analysis

Introduction: Oxygen therapy is a ubiquitous pharmacological therapy, whose efficacy and safety critically depend on the accuracy of the delivery device. However, the accuracy of conventional oxygen flowmeters is often questioned. Objective: To conduct an in-depth systematic review with meta-analysis to quantify the precision and accuracy of oxygen flowmeters, identify the drivers of inaccuracy, and outline the implications for clinical practice and health policy. Methods: A systematic search of the PubMed, EMBASE, Cochrane Library, and LILACS databases was conducted for studies published between 1980 and 2025 that evaluated the accuracy of oxygen flowmeters against a gold standard. The meta-analysis was conducted using a random-effects model to calculate the weighted mean difference (WMD) of the percentage deviation. Subgroup analyses were performed by technology (analog vs. digital), flow range, and presence of pressure compensation. Results: Fifteen studies were included, totaling 1,847 flowmeters and over 15,000 measurements. The global meta-analysis revealed a weighted mean deviation of 8.7% (95% CI: 5.2-12.1%), with extreme heterogeneity (I² = 89%). Individual deviations varied dramatically, from -52% to +85% of the nominal value. Analog flowmeters exhibited a linear deterioration in accuracy, with median deviations increasing from 2% at 1 L/min to over 30% at 15 L/min. In contrast, digital flowmeters maintained a consistently low deviation (<1.5%) across the entire operating range (p < 0.001). Inaccuracy was significantly higher at low flows (<3 L/min) and in devices without pressure compensation. Conclusion: The evidence conclusively demonstrates that analog oxygen flowmeters lack the precision necessary for safe therapy.