Charcoal as an airway isoflurane reflection filter

Research output: Contribution to journalArticle


The isoflurane-saving and CO2-retaining effects of a charcoal filter were compared with a Siemens standard heat and moisture (HME) exchanger and an emptied specimen (dummy). Isoflurane was delivered during the inspiratory phase and consumption investigated at 10, 15 and 25 cycles min-1. The investigation was performed by ventilation with humidified air with a constant end-tidal CO2 and temperature. For a comparison, isoflurane was delivered in a conventional manner via the ventilator. The arrangement with a charcoal filter reduced the isoflurane consumption by a factor of 2.0-2.6, depending on ventilatory rate. Most of the saving was a result of the method of isoflurane delivery (factor 1.4-2.0), while adding the reflector gave a further reduction (factor 1.3-1.5). One circumstance that reduced the net efficiency of the charcoal filter was that it also reflected CO2; consequently, total minute ventilation had to be increased to maintain constant end-tidal CO2.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Anesthesiology and Intensive Care


  • anaesthetic, volatile, isoflurane, equipment, charcoal filter, physics, gas adsorption
Original languageEnglish
Pages (from-to)230-233
JournalEuropean Journal of Anaesthesiology
Issue number2
Publication statusPublished - 1998
Publication categoryResearch