Accuracy of new gas flowmeters.

The accuracy of five new oxygen and nitrous oxide flowmeter units was investigated using the bubble meter method. The results were compared with those previously found in flowmeters withdrawn from clinical use. New oxygen flowmeters demonstrated less inaccuracies than old flowmeters. No differences were found between the nitrous oxide flowmeters. Unacceptable errors were demonstrated at oxygen presettings less than 1 litre min-1, suggesting the grading within this range to be of no value. Marked deviations which exceeded the limits stated by the manufacturer could still be shown at presettings greater than 1 litre min-1. If an exact FIO2 is required, continuous monitoring with a high accuracy oxygen analyser is essential, even using new flowmeters.