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Evaluation of Breathing System Filters
This review is based on the assessment published by
United Kingdom's Medicines and Healthcare Products Regulatory Agency in
March 2004
Edited by Maija Numerla, M. Sc., Project Leader
GE Healthcare, Technologies, Clinical Systems
The article also available in 
PDF:
98KB
Clinician's viewpoint In our present clinical environment, infections of various origins are an increasing burden, particularly in intensive care, where resistance to antibiotics is increasingly an everyday reality. Simultaneously, we need to be aware of the unexpected spread of infections, which may be facilitated by international travel. Hence, we need standardized routines to protect patients and staff, and to avoid the contamination of our facilities. Breathing system filters have been suggested to reduce bacterial and viral contamination in ventilated patients. Up until now, there has been only limited evidence-based information on the performance of the filters. Manufacturers may have reported a high of 99.99...% -type filtration ratios in their brochures. Without knowing facts behind the numbers, however, such data do not necessarily indicate economical feasibility or clinical performance. Clearly, there has been a need for objective comparison of the performances of the filters, to increase knowledge and to aid clinicians in their choice. The comparison made by the Regulatory Agency in UK is important, as it is a standardized and an objective approach to this matter. Ilkka Kalli M.D., Ph.D. |
Introduction
In March 2004, the United Kingdom's Medicines and Healthcare Products Regulatory Agency (MHRA) published an assessment of 104 different breathing-system filters currently available on the UK market [1]. The MHRA also published an alert notice that highlights the problems of making comparisons among filters from different manufacturers when different test protocols for their assessment have been used. Comparing results from the various studies is difficult because of the use of different test methods and micro-organisms. In 2001, a new standard was published: Breathing system filters for anesthetic and respiratory use [2]. Describing a salt test method to assess filtration performance, this standard allows an objective comparison to be made among filters supplied by different manufacturers. In the referred MHRA evaluation, filtration performance was measured in accordance with this standard.
There are two types of filters available, pleated (sometimes called mechanical) and electrostatic. The MHRA evaluation focused primarily on electrostatic filters. Of the 104 filters tested in the MHRA evaluation, 78 were electrostatic filters provided by 14 different manufacturers. GE Healthcare had 4 different filters and 3 different Heat and Moisture exchangers (HMEF) included in the MHRA evaluation.
Filtration efficiency was not the only feature compared in the MHRA evaluation. Humidification and filtration devices are selected based on several different features such as the intended duration of use, patient's previous respiratory health, type of airway secretions, moisture output, resistance, dead space (compared to patients tidal volume) and cost. In addition to filtration efficiency, the MHRA evaluation also compared pressure drop, moisture output, weight, dimensions, internal volume, connectors, tidal volume range and price. The results below are based on a selected comparison of certain features and are not meant to be an exhaustive comparison. We encourage the reader to review the full report for definitions of terms and detailed results.
Results from the MHRA evaluation
We have collected the results of the MHRA evaluation on certain features and prepared comparisons based on those features to show how GE Healthcare electrostatic filters compared to other filters on the market.
The comparison presented in Chart 1 is based on the results of the MHRA evaluation on filtration efficiency and list price of 78 different electrostatic filters from 13 manufacturers. Due to the large number of filters evaluated, we have, for the purposes of the comparison only, calculated the average of the results from each manufacturer's products. Thus the comparison does not reflect the actual results produced by any individual products, but rather gives an indication of how various manufacturers ranked based on the average filtration efficiency and list price of their products. This chart shows that the average list price of the GE Healthcare electrostatic filters (HMEF 1000, HMEF 500, HMEF Mini, Uni-Filter/S, Uni-Filter Junior and Mini-Filter/S) ranked among the lowest average list prices of all the manufacturers participating in the evaluation even though they produced an average filtration efficiency which was among the highest of the averages of all the manufacturers participating in the evaluation.
Chart 2 illustrates the results of the MHRA evaluation on filtration efficiency and pressure drop of 12 different pediatric electrostatic filters from 12 different manufacturers. This chart shows that the GE Healthcare Uni-Filter Junior had the highest filtration efficiency and the lowest breathing resistance after three hours use. High filtration efficiency and low breathing resistance are two important features of filters used in pediatric applications.
Chart 3 illustrates the results of the MHRA evaluation on moisture output and pressure drop of 10 different pediatric electrostatic Heat and Moisture exchangers with filters (HMEFs) by 9 different manufacturers. This chart shows that the GE Healthcare HMEF 500 and HMEF Mini had some of the highest moisture outputs while still maintaining a very low breathing resistance after 3 hours use.
Chart 4 illustrates the results of the MHRA evaluation on filtration efficiency and internal volume of 19 different adult electrostatic filters from 14 different manufacturers. This chart shows that the GE Healthcare Uni-Filter Junior and Uni-Filter/S are among the smallest and most efficient filters on the market. Small size filters are better suitable for small children. The small internal volume of the filter means less dead-space, an important benefit during pediatric mechanical ventilation.
Charts (Click to enlarge)
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Conclusion
GE Healthcare (Datex-Ohmeda) has more than 25 years experience in the development of breathing system filters and HMEFs. All of GE Healthcare's knowledge of ventilation, humidification and work of breathing has been applied to the design of the HMEFs and filters included in the MHRA evaluation. This independent evaluation of 104 different breathing-system filters supports the statement that GE Healthcare HMEFs and filters are among the best products on the market.
References
- "Breathing-System Filters: An Assessment of 104 Different Breathing-System Filters," Evaluation 04005, MHRA, London (2004).
- Breathing system filters for anesthetic and respiratory use. Part 1: Salt test method to assess filtration performance. BS EN 13328-1:2001.
Last updated: 21 March 2005Created |
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