Document Detail

Carbon dioxide spirogram (but not capnogram) detects leaking inspiratory valve in a circle circuit.
MedLine Citation:
PMID:  9390611     Owner:  NLM     Status:  MEDLINE    
Expiratory valve incompetence in the circle circuit is diagnosed by using capnography (PCO2 versus time) when significant CO2 is present throughout inspiration. However, inspiratory valve incompetence will allow CO2-containing expirate to reverse flow into the inspiratory limb. CO2 rebreathing occurs early during the next inspiration, generating a short extension of the alveolar plateau and decreased inspiratory downslope of the capnogram, which may be indistinguishable from normal. We hypothesized that CO2 spirography (PCO2 versus volume) would correctly measure inspired CO2 volume (VCO2) during inspiratory valve leak. Accordingly, a metabolic chamber (alcohol combustion) was connected to a lung simulator, which was mechanically ventilated through a standard anesthesia circle circuit. By multiplying and integrating airway flow and PCO2, overall, expired, and inspired VCO2 (VCO2,br = VCO2,E - VCO2,I) were measured. When the inspiratory valve was compromised (by placing a wire between the valve seat and diaphragm), VCO2,I increased from 2.7 +/- 1.7 to 5.7 +/- 0.2 mL (P < 0.05), as measured by using CO2 spirography. In contrast, the capnogram demonstrated only an imperceptible lengthening of the alveolar plateau and did not measure VCO2,I. To maintain effective alveolar ventilation and CO2 elimination, increased VCO2,I requires a larger tidal volume, which could result in pulmonary barotrauma, decreased cardiac output, and increased intracranial pressure. Implications: Circle circuit inspiratory valve leak will allow CO2-containing expirate to reverse flow into the inspiratory limb, with subsequent rebreathing during the next inspiration. This CO2 rebreathing causes imperceptible lengthening of the alveolar plateau of the capnogram and is detected only by using the CO2 spirogram (PCO2 versus volume).
P H Breen; B P Jacobsen
Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Anesthesia and analgesia     Volume:  85     ISSN:  0003-2999     ISO Abbreviation:  Anesth. Analg.     Publication Date:  1997 Dec 
Date Detail:
Created Date:  1997-12-19     Completed Date:  1997-12-19     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  1310650     Medline TA:  Anesth Analg     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1372-6     Citation Subset:  AIM; IM    
Department of Anesthesiology, University of California-Irvine Medical Center, Orange 92868, USA.
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MeSH Terms
Anesthesia, Closed-Circuit*
Carbon Dioxide / analysis*
Equipment Failure
Lung / physiology
Models, Structural
Grant Support
Reg. No./Substance:
124-38-9/Carbon Dioxide

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

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