Document Detail

The effects of apparatus dead space on P(aCO2) in patients receiving lung-protective ventilation.
MedLine Citation:
PMID:  17005059     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: Lung-protective ventilation using tidal volume (V(T)) of 4-6 mL/kg (predicted body weight) reduces mortality (compared with traditional V(T)) in patients with acute respiratory distress syndrome and acute lung injury. Standardized use of lower V(T) can result in respiratory acidosis and has raised new concerns about the appropriate configuration of the ventilator circuit, especially in regard to the dead space (V(D)) of the apparatus. We hypothesized that, with a patient receiving lung-protective ventilation, the removal of all apparatus dead space from the circuit would reduce P(aCO2) and allow a reduction in minute ventilation. METHODS: All the studied patients met the American-European consensus-conference criteria for acute respiratory distress syndrome/acute lung injury, were receiving a lung-protective ventilation strategy, were > 18 years of age, and were hemodynamically stable. We prospectively tested 3 different ventilator-circuit configurations, in random sequence, for 15 min each: (1) standard hygroscopic heat-and-moisture exchanger (HME) with 15-cm flexible tubing, (2) 15-cm flexible tubing only, (3) no HME or flexible tubing. V(T), respiratory rate, positive end-expiratory pressure, and fraction of inspired oxygen were maintained constant throughout the study, and exhaled CO2 was measured continuously. Physiologic dead space (V(D)/V(T)) was calculated using the Enghoff modification of the Bohr equation. RESULTS: Seven patients were studied. Removal of the HME from the circuit significantly decreased V(D)/V(T) (by approximately 6%) and P(aCO2) (by approximately 5 mm Hg). Removal of both the HME and flexible tubing from the circuit reduced V(D)/V(T) by an additional 5%, and P(aCO2) by an additional 6 mm Hg. With both circuit-configuration changes, minute ventilation fell from a mean of 11.51 L/min to 10.35 L/min, and pH increased from 7.30 to 7.38. Carbon-dioxide production did not change significantly. CONCLUSION: In patients receiving lower-V(T) ventilation, removing all the apparatus V(D) from the ventilator circuit reduces P(aCO2) and increases pH, at a lower minute ventilation. This information will help guide ventilator-circuit configuration for patients receiving lung-protective ventilation.
Carl R Hinkson; Michael S Benson; Lauri M Stephens; Steven Deem
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Publication Detail:
Type:  Journal Article; Randomized Controlled Trial    
Journal Detail:
Title:  Respiratory care     Volume:  51     ISSN:  0020-1324     ISO Abbreviation:  Respir Care     Publication Date:  2006 Oct 
Date Detail:
Created Date:  2006-09-28     Completed Date:  2007-01-30     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  7510357     Medline TA:  Respir Care     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1140-4     Citation Subset:  IM    
Department of Respiratory Care, Harborview Medical Center, Mail Stop 359761, 325 9th Avenue, Seattle, WA 98104, USA.
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MeSH Terms
Carbon Dioxide
Hydrogen-Ion Concentration
Lung Injury
Middle Aged
Positive-Pressure Respiration / instrumentation*,  methods*
Pulmonary Gas Exchange
Respiratory Distress Syndrome, Adult / therapy*
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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