• David E Whitelock and David A H de Beer.
• Department of Anaesthesia, Great Ormond Street Hospital for Children, Great Ormond Street, London WC1N 3JH, UK.
• Respir Care Clin N Am. 2006 Jun 1;12(2):307-20.

AbstractThe use of breathing system filters may be particularly beneficial in small infants, compared with older children and adults, because of their greater need for warming and humidification of inspired gases as well as their increased susceptibility to lower respiratory tract contamination. The only evidence available regarding the safety and efficacy of breathing system filters in small infants comes from a few small studies conducted on intensive care patients, however. These studies have suggested that the use of HME filters may be effective in preserving body temperature and airway humidity while decreasing fluid build-up in the breathing system and therefore reducing breathing system contamination. Nonetheless, the use of filters has not been shown to decrease the incidence of VAP in small infants. In contrast,their use in adult intensive care patients, particularly those requiring prolonged ventilation, has been associated with a decrease in the infection rate. The use of breathing system filters is not associated with a statistically significant increase in the rate of complications, despite the potentially greater hazards associated with their use in small infants compared with older children and adults. In practice the use of breathing system filters, even in small infants, rarely causes any major clinical problems that cannot be prevented with a high degree of vigilance and appropriate monitoring. This vigilance is particularly important to prevent the serious morbidity and even mortality that may result from filter occlusion; when subjected to excessive loading, smaller filters are more prone to obstruction than are their larger counterparts. The increased resistance provided by smaller filters should not translate into a clinically significant increase in the work of breathing during general anesthesia, because it is common practice to ventilate small infants for all but the shortest of surgical procedures. An increase in the work of breathing may, however, become more significant when spontaneous ventilation is established at the end of a surgical case. It remains unclear whether the use of filters allows the safe reuse of breathing systems in small infants. None of the breathing system filters tested by the MHRA had a zero-percent penetrance to sodium chloride particles, and pediatric filters generally had a higher penetrance than their adult counterparts. This finding suggests that there is a potential, albeit small, risk of cross-contamination. The exact risk depends on the type of filter used and on the particular patient undergoing anesthesia or ventilation in the ICU. Although no evidence has been published showing cross-infection occurring when any filter has been used in the anesthesia breathing system for adults or small infants, the level of filtration performance required to allow the safe reuse of anesthesia breathing systems in small infants remains unanswered. Because the incidence of lower respiratory tract colonization is low in unselected small infants, a study with sufficient power to answer accurately the questions regarding the safety of breathing system reuse in small infants would be very difficult to conduct. The effect of filters on post operative infection rates may in fact be of less significance than the adoption of adequate standards of hygiene (eg, hand washing and the use of gloves).Further research is needed to determine if the variations in filtration efficiency demonstrated by the MHRA have any effects on patient outcome. This research might allow setting an effective minimal level of filtration performance for breathing system filters for use in small infants. On a practical note, the publication of the MHRA assessments of breathing system filters provides a useful tool for objective comparison of the different filters available for use in small infants, even though the relevance of the flow used to test pediatric filters has been criticized. Individual institutions will need to formulate policies for the use of breathing system filters for clinical reasons as well as for cost containment or logistical reasons. These policies should be within the frameworks set out by their regulatory agencies. Any problems arising from policies that are in breach of these frame works will remain the responsibility of the individual clinicians caring for these small infants.

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