title: Humidification performance of humidifying devices for tracheostomized patients with spontaneous breathing: a bench study.
abstract: BACKGROUND
  Heat and moisture exchangers (HMEs) are commonly used for humidifying respiratory gases administered to mechanically ventilated patients. While they are also applied to tracheostomized patients with spontaneous breathing, their performance in this role has not yet been clarified. We carried out a bench study to investigate the effects of spontaneous breathing parameters and oxygen flow on the humidification performance of 11 HMEs.
  
  
  METHODS
  We evaluated the humidification provided by 11 HMEs for tracheostomized patients, and also by a system delivering high-flow CPAP, and an oxygen mask with nebulizer heater. Spontaneous breathing was simulated with a mechanical ventilator, lung model, and servo-controlled heated humidifier at tidal volumes of 300, 500, and 700 mL, and breathing frequencies of 10 and 20 breaths/min. Expired gas was warmed to 37°C. The high-flow CPAP system was set to deliver 15, 30, and 45 L/min. With the 8 HMEs that were equipped with ports to deliver oxygen, and with the high-flow CPAP system, measurements were taken when delivering 0 and 3 L/min of dry oxygen. After stabilization we measured the absolute humidity (AH) of inspired gas with a hygrometer.
  
  
  RESULTS
  AH differed among HMEs applied to tracheostomized patients with spontaneous breathing. For all the HMEs, as tidal volume increased, AH decreased. At 20 breaths/min, AH was higher than at 10 breaths/min. For all the HMEs, when oxygen was delivered, AH decreased to below 30 mg/L. With an oxygen mask and high-flow CPAP, at all settings, AH exceeded 30 mg/L.
  
  
  CONCLUSIONS
  None of the HMEs provided adequate humidification when supplemental oxygen was added. In the ICU, caution is required when applying HME to tracheostomized patients with spontaneous breathing, especially when supplemental oxygen is required.
authors: Department of Emergency and Critical Care Medicine, The University of Tokushima Graduate School, Tokushima, Japan.
authors: Yusuke
authors: Y
authors: Chikata
authors: Jun
authors: J
authors: Oto
authors: Mutsuo
authors: M
authors: Onodera
authors: Masaji
authors: M
authors: Nishimura
mesh_terms: D045422:Continuous Positive Airway Pressure; D006361:Heating; D006801:Humans; D006813:Humidity; D010102:Oxygen Inhalation Therapy; D012138:Respiratory Therapy / Q000295:instrumentation*; D013990:Tidal Volume; D014139:Tracheostomy
keywords: CPAP; HME; heat and moisture exchanger; humidification; mechanical ventilation; respiratory; spontaneous breathing; supplemental oxygen; tracheostomy