title: Carbon dioxide rebreathing with the anaesthetic conserving device, AnaConDa®.
abstract: BACKGROUND
  The anaesthetic conserving device (ACD) AnaConDa(®) was developed to allow the reduced use of inhaled agents by conserving exhaled agent and allowing rebreathing. Elevated has been observed in patients when using this ACD, despite tidal volume compensation for the larger apparatus dead space. The aim of the present study was to determine whether CO(2), like inhaled anaesthetics, adsorbs to the ACD during expiration and returns to a test lung during the following inspiration.
  
  
  METHODS
  The ACD was attached to an experimental test lung. Apparent dead space by the single-breath test for CO(2) and the amount of CO(2) adsorbed to the carbon filter of the ACD was measured with infrared spectrometry.
  
  
  RESULTS
  Apparent dead space was 230 ml larger using the ACD compared with a conventional heat and moisture exchanger (internal volumes 100 and 50 ml, respectively). Varying CO(2) flux to the test lung (85-375 ml min(-1)) did not change the measured dead space nor did varying respiratory rate (12-24 bpm). The ACD contained 3.3 times more CO(2) than the predicted amount present in its internal volume of 100 ml.
  
  
  CONCLUSIONS
  Our measurements show a CO(2) reservoir effect of 180 ml in excess of the ACD internal volume. This is due to adsorption of CO(2) in the ACD during expiration and return of CO(2) during the following inspiration.
authors.affiliation: Section of Anaesthesiology and Intensive Care, Lund Universityand Skane University Hospital Lund, Sweden. louise.walther_sturesson@med.lu.se
authors.forename: L W
authors.initials: LW
authors.lastname: Sturesson
authors.forename: G
authors.initials: G
authors.lastname: Malmkvist
authors.forename: M
authors.initials: M
authors.lastname: Bodelsson
authors.forename: L
authors.initials: L
authors.lastname: Niklason
authors.forename: B
authors.initials: B
authors.lastname: Jonson
mesh_terms: D000769:Anesthesia, Inhalation / Q000295:instrumentation*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage; D002245:Carbon Dioxide / Q000032:analysis*; D015920:Gas Scavengers; D006801:Humans; D001239:Inhalation / Q000502:physiology; D008953:Models, Anatomic; D012126:Respiratory Dead Space / Q000502:physiology; D056152:Respiratory Rate / Q000502:physiology; D013990:Tidal Volume / Q000502:physiology
chemical_list: D018685:Anesthetics, Inhalation; D002245:Carbon Dioxide