Document Detail

Anatomic dead space cannot be predicted by body weight.
MedLine Citation:
PMID:  18593489     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: Anatomic dead space (also called airway or tracheal dead space) is the part of the tidal volume that does not participate in gas exchange. Some contemporary ventilation protocols, such as the Acute Respiratory Distress Syndrome Network protocol, call for smaller tidal volumes than were traditionally delivered. With smaller tidal volumes, the percentage of each delivered breath that is wasted in the anatomic dead space is greater than it is with larger tidal volumes. Many respiratory and medical textbooks state that anatomic dead space can be estimated from the patient's weight by assuming there is approximately 1 mL of dead space for every pound of body weight. With a volumetric capnography monitor that measures on-airway flow and CO2, the anatomic dead space can be automatically and directly measured with the Fowler method, in which dead space equals the exhaled volume up to the point when CO2 rises above a threshold. METHODS: We analyzed data from 58 patients (43 male, 15 female) to assess the accuracy of 5 anatomic dead space estimation methods. Anatomic dead space was measured during the first 10 min of monitoring and compared to the estimates. RESULTS: The coefficient of determination (r2) between the anatomic dead space estimate based on body weight and the measured anatomic dead space was r2 = 0.0002. The mean +/- SD error between the body weight estimate and the measured dead space was 60 +/- 54 mL. CONCLUSIONS: It appears that the anatomic dead space estimate methods were sufficient when used (as originally intended) together with other assumptions to identify a starting point in a ventilation algorithm, but the poor agreement between an individual patient's measured and estimated anatomic dead space contradicts the assumption that dead space can be predicted from actual or ideal weight alone.
Lara M Brewer; Joseph A Orr; Nathan L Pace
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Respiratory care     Volume:  53     ISSN:  0020-1324     ISO Abbreviation:  Respir Care     Publication Date:  2008 Jul 
Date Detail:
Created Date:  2008-07-02     Completed Date:  2008-11-18     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7510357     Medline TA:  Respir Care     Country:  United States    
Other Details:
Languages:  eng     Pagination:  885-91     Citation Subset:  IM    
Department of Anesthesiology, University of Utah Health Sciences Center, Salt Lake City, Utah, USA.
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MeSH Terms
Aged, 80 and over
Body Weight / physiology*
Middle Aged
Respiration, Artificial / methods,  standards
Respiratory Dead Space / physiology*
Respiratory Distress Syndrome, Adult / diagnosis,  physiopathology*,  therapy
Severity of Illness Index
Comment In:
Respir Care. 2008 Jul;53(7):860-1   [PMID:  18593486 ]

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