Document Detail

Rationale of dead space measurement by volumetric capnography.
MedLine Citation:
PMID:  22383673     Owner:  NLM     Status:  MEDLINE    
Dead space is the portion of a tidal volume that does not participate in gas exchange because it does not get in contact with blood flowing through the pulmonary capillaries. It is commonly calculated using volumetric capnography, the plot of expired carbon dioxide (CO(2)) versus tidal volume, which is an easy bedside assessment of the inefficiency of a particular ventilatory setting. Today, Bohr's original dead space can be calculated in an entirely noninvasive and breath-by-breath manner as the mean alveolar partial pressure of CO(2) (Paco(2)) which can now be determined directly from the capnogram. The value derived from Enghoff's modification of Bohr's formula (using Paco(2) instead of PACO(2)) is a global index of the inefficiency of gas exchange rather than a true "dead space" because it is influenced by all causes of ventilation/perfusion mismatching, from real dead space to shunt. Therefore, the results obtained by Bohr's and Enghoff's formulas have different physiological meanings and clinicians must be conscious of such differences when interpreting patient data. In this article, we describe the rationale of dead space measurements by volumetric capnography and discuss its main clinical implications and the misconceptions surrounding it.
Gerardo Tusman; Fernando Suarez Sipmann; Stephan H Bohm
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Publication Detail:
Type:  Journal Article     Date:  2012-03-01
Journal Detail:
Title:  Anesthesia and analgesia     Volume:  114     ISSN:  1526-7598     ISO Abbreviation:  Anesth. Analg.     Publication Date:  2012 Apr 
Date Detail:
Created Date:  2012-03-21     Completed Date:  2012-05-08     Revised Date:  2013-01-15    
Medline Journal Info:
Nlm Unique ID:  1310650     Medline TA:  Anesth Analg     Country:  United States    
Other Details:
Languages:  eng     Pagination:  866-74     Citation Subset:  AIM; IM    
Department of Anesthesiology, Hospital Privado de Comunidad, Mar del Plata, Argentina.
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MeSH Terms
Capnography / methods*
Carbon Dioxide / metabolism
Positive-Pressure Respiration
Respiratory Dead Space / physiology*
Reg. No./Substance:
124-38-9/Carbon Dioxide
Comment In:
Anesth Analg. 2012 Dec;115(6):1472; author reply 1472   [PMID:  23175577 ]

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