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"Closing volume" during high-frequency ventilation in anesthetized dogs.
T Hachenberg1, M Wendt, J Meyer
1Department of Anesthesiology and Intensive Care, Westfälische Wilhelms-Universität Münster, FRG.
Acta Anaesthesiologica Scandinavica
|February 1, 1988
Summary
High-frequency jet ventilation (HFJV) in dogs increased closing volume, impairing gas distribution to dependent lung regions. Conventional ventilation with positive end-expiratory pressure (PEEP) decreased closing volume.
Area of Science:
- Pulmonary Physiology
- Respiratory Mechanics
- Mechanical Ventilation
Background:
- Understanding airway closure and gas distribution is crucial for optimizing mechanical ventilation strategies.
- Different ventilation modes, including high-frequency jet ventilation (HFJV) and continuous positive pressure ventilation (CPPV), impact respiratory mechanics differently.
Purpose of the Study:
- To investigate the effects of intermittent positive pressure ventilation (IPPV), CPPV with positive end-expiratory pressure (PEEP), and HFJV on airway closure and gas exchange in healthy canine lungs.
- To compare closing volume (CV) measurements using foreign gas bolus (FGB) and single breath nitrogen (SBN2) techniques under various ventilation modes.
Main Methods:
- Anesthetized and paralyzed dogs with healthy lungs were subjected to IPPV, CPPV (PEEP = 0.49 kPa), and HFJV (2 and 30 Hz, I/E ratios of 30/70 and 60/40).
- Closing volume was determined using a modified technique with helium as a foreign gas (FGB-method) and single breath nitrogen dilution (SBN2-test).
- Mean airway pressure, gas exchange (PaO2, Aa-Do2, PaCO2), and regional lung volumes were monitored.
Main Results:
- CPPV with PEEP significantly decreased closing volume (P < 0.05).
- HFJV significantly increased closing volume (P < 0.01), primarily influenced by the inspiratory/expiratory (I/E) ratio and secondarily by ventilatory frequency.
- Both FGB and SBN2 methods showed proportional changes in CV, but significant differences existed between the absolute values obtained.
- Increased CV during HFJV correlated with decreased PaO2, increased Aa-Do2, and increased PaCO2, indicating hypoventilation and ventilation-perfusion mismatch.
- Mean airway pressure increased with both CPPV and HFJV, but HFJV showed dissociation between airway pressure and functional residual capacity (FRC) distribution.
Conclusions:
- Certain HFJV modes can lead to impaired distribution of inspired gas to dependent lung regions.
- The I/E ratio is a critical determinant of CV changes during HFJV.
- Despite differences in absolute values, FGB and SBN2 techniques provide comparable relative changes in CV across ventilation modes.
- HFJV may cause ventilation-perfusion mismatching and hypoventilation in healthy lungs.