Journal Article

Anaesthetic conserving device AnaConDa<sup>®</sup>: dead space effect and significance for lung protective ventilation

L. W. Sturesson, M. Bodelsson, B. Jonson and G. Malmkvist

Edited by A. R. Absalom

in BJA: British Journal of Anaesthesia

Published on behalf of the British Journal of Anaesthesia

Volume 113, issue 3, pages 508-514
Published in print September 2014 | ISSN: 0007-0912
Published online May 2014 | e-ISSN: 1471-6771 | DOI: https://dx.doi.org/10.1093/bja/aeu102
Anaesthetic conserving device AnaConDa®: dead space effect and significance for lung protective ventilation

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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.

Clinical trial registration

Clinical Trials NCT01699802.

Keywords: airway; anaesthetic techniques; carbon dioxide; dead space; inhalation; rebreathing

Journal Article.  4228 words.  Illustrated.

Subjects: Anaesthetics

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