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Published on: January 29, 2011
Spontaneous effort causes occult pendelluft during mechanical ventilation.
Takeshi Yoshida1, Vinicius Torsani, Susimeire Gomes
11 Laboratório de Pneumologia LIM-09, Disciplina de Pneumologia, Heart Institute (Incor) Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil.
Spontaneous breathing during mechanical ventilation causes pendelluft, moving air to dependent lung regions. This can lead to overstretch and lung damage, even without increasing tidal volume.
Area of Science:
- Respiratory Physiology
- Critical Care Medicine
- Pulmonary Mechanics
Background:
- In healthy lungs, pleural pressure changes are uniform.
- Lung injury can cause localized pleural pressure changes and air movement (pendelluft) during spontaneous breathing.
- Electrical impedance tomography (EIT) can visualize these phenomena.
Purpose of the Study:
- To test if negative pleural pressure from diaphragm contraction has localized effects in injured lungs.
- To determine if these localized pressure changes cause pendelluft.
- To investigate the impact of spontaneous breathing on regional lung inflation during mechanical ventilation.
Main Methods:
- Utilized EIT and dynamic computed tomography (CT) in anesthetized pigs with lung injury.
- Measured local pleural pressure in dependent and nondependent lung regions via intrabronchial balloon catheters.
- Estimated airway pressure for comparable lung inflation during paralysis versus spontaneous breathing.
Main Results:
- Spontaneous breathing induced pendelluft during early inflation in all animals.
- Dependent lung regions experienced more negative local pleural pressure (-13.0 ± 4.0 cm H2O) compared to nondependent regions (-6.4 ± 3.8 cm H2O).
- Dynamic CT confirmed pendelluft, occurring with tidal volumes < 6 ml/kg; spontaneous breathing required less driving pressure for dependent lung inflation than paralysis.
Conclusions:
- Spontaneous breathing effort during mechanical ventilation can cause overstretch of dependent lung regions.
- Reciprocal deflation of nondependent lung regions occurs simultaneously.
- Significant spontaneous effort may increase lung injury risk, even without increasing tidal volume.
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