Document Detail

Concentration and second gas effects: can the accepted explanation be improved?
MedLine Citation:
PMID:  9175984     Owner:  NLM     Status:  MEDLINE    
During induction with high inspired concentrations of nitrous oxide, net uptake of gas produces a contraction in volume and a concentrating effect. In turn, this results in concentration and second gas effects. Most explanations of these effects are based on the common "rectangle" diagram devised by Stoelting and Eger and contain several inconsistencies which are explored here in order to produce a more accurate description. It is shown that in the standard diagram gas uptake is incomplete, there is ambiguity over functional residual capacity (FRC), equilibration with blood is inadequately represented and there is no representation of recirculation of anaesthetic. Compensation for loss of volume may be by means of an increased inspired ventilation, decreased expired ventilation or reduction in lung volume. Numerous accounts in the literature (including those based on the standard diagram) focus on the former mechanism at constant FRC. This has produced an unbalanced picture in which it is often implied that extra gas is routinely drawn into the lungs to replace that taken up. Significant compensation by this means cannot occur, for example when a constant volume ventilator is used. In discussing concentration and second gas effects, it is necessary to give a balanced view of the alternative mechanisms of compensation or to revert, as above, to a simple statement of the principle of conservation of volume.
B Korman; W W Mapleson
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Publication Detail:
Type:  Journal Article; Review    
Journal Detail:
Title:  British journal of anaesthesia     Volume:  78     ISSN:  0007-0912     ISO Abbreviation:  Br J Anaesth     Publication Date:  1997 May 
Date Detail:
Created Date:  1997-06-19     Completed Date:  1997-06-19     Revised Date:  2004-11-17    
Medline Journal Info:
Nlm Unique ID:  0372541     Medline TA:  Br J Anaesth     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  618-25     Citation Subset:  IM    
Department of Anaesthesia, Royal Perth Hospital, Western Australia.
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MeSH Terms
Anesthetics, Inhalation / pharmacokinetics*
Functional Residual Capacity
Lung / metabolism*
Models, Biological*
Nitrous Oxide / pharmacokinetics*
Pulmonary Gas Exchange
Reg. No./Substance:
0/Anesthetics, Inhalation; 10024-97-2/Nitrous Oxide
Erratum In:
Br J Anaesth 1997 Aug;79(2):268

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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