Research
Spontaneous breathing with airway pressure release ventilation favors ventilation in dependent lung regions and counters cyclic alveolar collapse in oleic-acid-induced lung injury: a randomized controlled computed tomography trial
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* Corresponding author: Hermann Wrigge Hermann.Wrigge@ukb.uni-bonn.de
1 Assistant Professor, Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, Sigmund-Freud-Strasse 25, D-53105 Bonn, Germany and Research Fellow, Department of Clinical Physiology, University of Uppsala, University Hospital, SE-751 85 Uppsala, Sweden
2 Physicist and Research Associate, Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, Sigmund-Freud-Strasse 25, D-53105 Bonn, Germany
3 Assistant Professor, Department of Anaesthesiology and Intensive Care Medicine, University of Göttingen, Robert Koch Strasse 40, D-37075 Göttingen, Germany
4 Resident, Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, Sigmund-Freud-Strasse 25, D-53105 Bonn, Germany
5 Professor of Radiology, Department of Radiology, University of Uppsala, University Hospital, SE-751 85 Uppsala, Sweden
6 Professor of Anaesthesiology and Intensive Care Medicine, Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, Sigmund-Freud-Strasse 25, D-53105 Bonn, Germany
7 Professor of Clinical Physiology, Department of Clinical Physiology, University of Uppsala, University Hospital, SE-751 85 Uppsala, Sweden
Critical Care 2005, 9:R780-R789 doi:10.1186/cc3908
See related commentary http://ccforum.com/content/10/1/102
Published: 16 November 2005Abstract
Introduction
Experimental and clinical studies have shown a reduction in intrapulmonary shunt with spontaneous breathing during airway pressure release ventilation (APRV) in acute lung injury. This reduction was related to reduced atelectasis and increased aeration. We hypothesized that spontaneous breathing will result in better ventilation and aeration of dependent lung areas and in less cyclic collapse during the tidal breath.
Methods
In this randomized controlled experimental trial, 22 pigs with oleic-acid-induced lung injury were randomly assigned to receive APRV with or without spontaneous breathing at comparable airway pressures. Four hours after randomization, dynamic computed tomography scans of the lung were obtained in an apical slice and in a juxtadiaphragmatic transverse slice. Analyses of regional attenuation were performed separately in nondependent and dependent halves of the lungs on end-expiratory scans and end-inspiratory scans. Tidal changes were assessed as differences between inspiration and expiration of the mechanical breaths.
Results
Whereas no differences were observed in the apical slices, spontaneous breathing resulted in improved tidal ventilation of dependent lung regions (P < 0.05) and less cyclic collapse (P < 0.05) in the juxtadiaphragmatic slices. In addition, with spontaneous breathing, the end-expiratory aeration increased and nonaerated tissue decreased in dependent lung regions close to the diaphragm (P < 0.05 for the interaction ventilator mode and lung region).
Conclusion
Spontaneous breathing during APRV redistributes ventilation and aeration to dependent, usually well-perfused, lung regions close to the diaphragm, and may thereby contribute to improved arterial oxygenation. Spontaneous breathing also counters cyclic collapse, which is a risk factor for ventilation-associated lung injury.