title: Anaesthetic conserving device AnaConDa: dead space effect and significance for lung protective ventilation.
abstract: BACKGROUND
  The anaesthetic conserving device AnaConDa (ACD) reflects exhaled anaesthetic agents thereby facilitating the use of inhaled anaesthetic agents outside operating theatres. Expired CO₂ is, however, also reflected causing a dead space effect in excess of the ACD internal volume. CO₂ reflection from the ACD is attenuated by humidity. This study tests the hypothesis that sevoflurane further attenuates reflection of CO₂. An analysis of clinical implications of our findings was performed.
  
  
  METHODS
  Twelve postoperative patients received mechanical ventilation using a conventional heat and moisture exchanger (HME, internal volume 50 ml) and an ACD (100 ml), the latter with or without administration of sevoflurane. The ACD was also studied with a test lung at high sevoflurane concentrations. Reflection of CO₂ and dead space effects were evaluated with the single-breath test for CO2.
  
  
  RESULTS
  Sevoflurane reduced but did not abolish CO₂ reflection. In patients, the mean dead space effect with 0.8% sevoflurane was 88 ml larger using the ACD compared with the HME (P<0.001), of which 38 ml was due to CO₂ reflection. Our calculations show that with the use of the ACD, normocapnia cannot be achieved with tidal volume <6 ml kg(-1) even when respiratory rate is increased.
  
  
  CONCLUSIONS
  An ACD causes a dead space effect larger than its internal volume due to reflection of CO₂, which is attenuated but not abolished by sevoflurane administration. CO₂ reflection from the ACD limits its use with low tidal volume ventilation, such as with lung protection ventilation strategies.
  
  
  BACKGROUND
  Clinical Trials NCT01699802.
authors.affiliation: Section of Anaesthesiology and Intensive Care, Lund University and Skane University Hospital, SE-221 85 Lund, Sweden louise.walther_sturesson@med.lu.se.
authors.forename: L W
authors.initials: LW
authors.lastname: Sturesson
authors.affiliation: Section of Anaesthesiology and Intensive Care, Lund University and Skane University Hospital, SE-221 85 Lund, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Bodelsson
authors.affiliation: Section of Clinical Physiology, Department of Clinical Sciences Lund, Lund University and Skane University Hospital, SE-221 85 Lund, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Jonson
authors.affiliation: Section of Anaesthesiology and Intensive Care, Lund University and Skane University Hospital, SE-221 85 Lund, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Malmkvist
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000769:Anesthesia, Inhalation / Q000295:instrumentation* / Q000379:methods*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D002245:Carbon Dioxide / Q000032:analysis; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage; D008875:Middle Aged; D011182:Postoperative Care / Q000379:methods; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D012121:Respiration, Artificial / Q000379:methods*; D012126:Respiratory Dead Space / Q000187:drug effects*; D000077149:Sevoflurane; D013990:Tidal Volume / Q000187:drug effects
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D002245:Carbon Dioxide; D000077149:Sevoflurane
keywords: airway; anaesthetic techniques; carbon dioxide; dead space; inhalation; rebreathing