Objective To evaluate oxygen flowmeters for accuracy and precision, assess the effects of cleaning and assess conformity to the American Society for Testing Materials (ASTM) standards. Study design Experimental study. Methods The flow of oxygen flowmeters from 31 anesthesia machines aged 1–45 years was measured before and after cleaning using a volumetric flow analyzer set at 0.5, 1.0, 2.0, 3.0, and 4.0 L minute−1. A general linear mixed models approach was used to assess flow accuracy and precision. Results Flowmeters 1 year of age delivered accurate mean oxygen flows at all settings regardless of cleaning status. Flowmeters ≥5 years of age underdelivered at flows of 3.0 and 4.0 L minute−1. Flowmeters ≥12 years underdelivered at flows of 2.0, 3.0 and 4.0 L minute−1 prior to cleaning. There was no evidence of any beneficial effect of cleaning on accuracy of flowmeters 5–12 years of age (p > 0.22), but the accuracy of flowmeters ≥15 years of age was improved by cleaning (p Conclusions Older flowmeters were more likely to underdeliver oxygen, especially at higher flows. Regardless of age, cleaning decreased flow variability, improving precision. However, flowmeters still may fail to meet ASTM standards, regardless of cleaning status. Clinical relevance Cleaning anesthesia machine oxygen flowmeters improved precision for all tested machines and partially corrected inaccuracies in flowmeters ≥15 years old. A notable proportion of flowmeters did not meet ASTM standards. Cleaning did not ensure that they subsequently conformed to ASTM standards. We recommend annual flow output validation to identify whether flowmeters are acceptable for continued clinical use.
