title: Modification of a high frequency oscillator circuit with a heated expiratory filter to prevent infectious pathogen transmission: a bench study.
abstract: BACKGROUND
  High frequency oscillation is a safe and effective treatment for patients with ARDS, but poses a patient and caregiver risk when the circuit is disconnected. We modified the circuit to include a heated expiratory filter, eliminating the need for daily filter changes due  to buildup of condensate. The purpose of the study was to determine if substitution of the filter resulted in a clinically important change in delivered tidal volume or amplitude. We additionally compared expiratory resistance and measured efficacy for the substituted filter.
  
  
  METHODS
  This  bench study measured tidal volume and amplitude using 5 of each filter type across 6 patient setting scenarios. Filter efficacy was tested through an independent laboratory, and expiratory resistance measurements were taken after prolonged use with humidification.
  
  
  RESULTS
  The clinically important  threshold value for tidal volume (defined as 5% difference) was excluded by the limits of agreement, confirming that use of the modified circuit does not result in alterations in tidal volume. The clinically important threshold for amplitude (defined as 10% difference) was the same as the  lower confidence interval on the lower limit of agreement, indicating it is possible for amplitude values to be different between the 2 filters. Filter efficacy for the substituted filter was not affected. Expiratory resistance was unchanged in the substituted filter, but nearly doubled for  the manufacturer's filter after 48 hours.
  
  
  CONCLUSIONS
  Modifying the circuit to include a heated expiratory filter does not affect tidal volume, and the filter material remains efficacious during oscillation. Amplitude varies under some conditions. Preventing the need for daily filter changes  reduces the risk of alveolar de-recruitment. This does not completely eliminate exposure to expired gases, but provides an additional layer of protection against occupational exposure and nosocomial spread of respiratory pathogens. Further testing in a clinical environment is necessary.
authors: Department of Professional Practice, Vancouver General Hospital, Canada. sharimck@gmail.com
authors: Shari I
authors: SI
authors: McKeown
authors: Nicola
authors: N
authors: Serreqi
mesh_terms: D004867:Equipment Design; D005374:Filtration / Q000295:instrumentation*; D006612:High-Frequency Ventilation / Q000295:instrumentation*; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D045169:Severe Acute Respiratory Syndrome / Q000517:prevention & control / Q000635:transmission*; D012122:Ventilators, Mechanical