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British Journal of Anaesthesia, 2002, Vol. 89, No. 4 541-545
© 2002 The Board of Management and Trustees of the British Journal of Anaesthesia

Clinical Investigations

Comparison of two techniques for measuring penetration of sodium chloride particles through breathing system filters

A. R. Wilkes{dagger}

Department of Anaesthetics and Intensive Care Medicine, University of Wales College of Medicine, Heath Park, Cardiff CF14 4XN, UK

{dagger}Declaration of interest. The author is funded by the Medical Devices Agency. Manufacturers of some of the devices tested in this article have provided travel and subsistence expenses to visit their factories. The Department of Anaesthetics and Intensive Care Medicine, University of Wales College of Medicine, undertakes commercial testing of some of these products.

Background. The filtration performance of breathing system filters can be determined by measuring the penetration of sodium chloride particles through the filter media.

Method. The penetration of sodium chloride particles through 12 breathing system filters was measured by two different techniques (using either forward light-scattering laser photometers or a neutral hydrogen flame photometer).

Results. The geometric means of the penetration values for the 12 filters varied from 0.0039% to 22.6% and from 0.0004% to 20.6% for the two techniques, respectively. For 10 of the 12 filters, with penetration values greater than 0.03%, the penetration values measured by, and the repeatability of, the two techniques were similar. The ratio of the penetration values measured by the two techniques (calculated from the mean difference in log10(penetration) between the two techniques for these 10 filters) was 0.93 (95% confidence interval 0.38 to 2.30). There is therefore only a small difference (at most a factor of about two either way) between the two techniques compared with the thousand-fold range in penetration values of the breathing system filters. For the remaining two filters, penetration values obtained using the flame photometer were less, and were close to or below the detection threshold of the laser photometer.

Conclusion. The neutral hydrogen flame photometer provides similar results to the forward light-scattering laser photometer technique.

Br J Anaesth 2002; 89: 541–5


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