HOW USEFUL ARE MICROBIAL FILTERS IN RESPIRATORY APPARATUS

Following an outbreak of hepatitis C in surgical patients in Australia , it has been suggested that transmission can take place as a result o f contaminated anaesthetic circuits. It has therefore been recommended that filters should be placed between patients and breathing systems with a new filter being used for each patient. Although nosocomial pne umonia is a major manifestation of hospital-acquired infection, it is unclear whether contamination of ventilator circuits is implicated in the aetiology of this condition. Some data suggest that bacteria canno t survive well in anaesthetic circuits and several studies have failed to demonstrate significant contamination of circuits in clinical situ ation. Several outbreaks of pneumonia related to contaminated anaesthe tic equipment have been described, but many of these were controlled b y appropriate decontamination of the respiratory equipment. Although v entilator filters are used by the majority of intensive care units and filters do have the ability to filter bacteria and viruses, there are few data suggesting that the use of filters reduce the rate of pulmon ary infections in long-term ventilated patients. Furthermore, to chang e filters between operations would have significant financial implicat ions, and there is no conclusive evidence that they would reduce cross infection. Until more data are available on the role of filters in bo th long-term ventilated patients and operations, standard hygienic mea sures such as appropriate disinfection protocols are still the most ef fective way of reducing ventilator-associated infections.