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Pulmonary Shunt Is Independent of Decrease in Cardiac Output during Unsupported Spontaneous Breathing in the Pig.
MedLine Citation:
PMID:  23334665     Owner:  NLM     Status:  Publisher    
BACKGROUND:: During mechanical ventilation (MV), pulmonary shunt is cardiac output (CO) dependent; however, whether this relationship is valid during unsupported spontaneous breathing (SB) is unknown. The CO dependency of the calculated venous admixture was investigated, with both minor and major shunt, during unsupported SB, MV, and SB with continuous positive airway pressure (CPAP). METHODS:: In seven anesthetized supine piglets breathing 100% oxygen, unsupported SB, MV (with tidal volume and respiratory rate corresponding to SB), and 8 cm H2O CPAP (airway pressure corresponding to MV) were applied at random. Venous return and CO were reduced by partial balloon occlusion of the inferior vena cava. Measurements were repeated with the left main bronchus blocked, creating a nonrecruitable pulmonary shunt. RESULTS:: CO decreased from 4.2 l/min (95% CI, 3.9-4.5) to 2.5 l/min (95% CI, 2.2-2.7) with partially occluded venous return. Irrespective of whether shunt was minor or major, during unsupported SB, venous admixture was independent of CO (slope: minor shunt, 0.5; major shunt, 1.1%·min·l) and mixed venous oxygen tension. During both MV and CPAP, venous admixture was dependent on CO (slope MV: minor shunt, 1.9; major shunt, 3.5; CPAP: minor shunt, 1.3; major shunt, 2.9%·min·l) and mixed-venous oxygen tension (coefficient of determination, 0.61-0.86 for all regressions). CONCLUSIONS:: In contrast to MV and CPAP, venous admixture was independent of CO during unsupported SB, and was unaffected by mixed-venous oxygen tension, casting doubt on the role of hypoxic pulmonary vasoconstriction in pulmonary blood flow redistribution during unsupported SB.
Laszlo Vimlati; Anders Larsson; Goran Hedenstierna; Michael Lichtwarck-Aschoff
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2013-1-17
Journal Detail:
Title:  Anesthesiology     Volume:  -     ISSN:  1528-1175     ISO Abbreviation:  Anesthesiology     Publication Date:  2013 Jan 
Date Detail:
Created Date:  2013-1-21     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  1300217     Medline TA:  Anesthesiology     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
* Department of Surgical Sciences, Anesthesiology and Critical Care, Uppsala University, Uppsala, Sweden; Consultant, Uppsala Cancer Clinic, Uppsala, Sweden. † Professor, § Associate Professor, Department of Surgical Sciences, Anesthesiology and Critical Care, Uppsala University, Uppsala, Sweden. ‡ Professor, Department of Medical Sciences, Clinical Physiology, Uppsala University, Uppsala, Sweden.
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