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Effect of frequency on lung protection during high-frequency oscillation ventilation in a sheep acute respiratory distress syndrome model
© BioMed Central Ltd 2008
- Published: 13 March 2008
- Lung Injury
- Acute Respiratory Distress Syndrome
- Conventional Mechanical Ventilation
- Lung Recruitment
- Alveolar Recruitment
The objective was to evaluate the effect of frequency on the prevention of ventilation-induced lung injury during high-frequency oscillation ventilation (HFOV) in a sheep acute respiratory distress syndrome (ARDS) model.
Twenty-four adult sheep (38.3 ± 2.3 kg) were randomly divided into four groups (n = 6): three HFOV groups (3 Hz, 6 Hz, 9 Hz) and a conventional mechanical ventilation (CMV) group. After induction of the ARDS model (PaO2 < 60 mmHg) by repeated NS lavage, step-by-step lung recruitment was performed in all groups, optimal alveolar recruitment as a PaO2 > 400 mmHg. After this recruitment procedure, the optimal mean airway pressure was selected by decreasing 2 mmHg every 5 minutes until the PaO2 decreased below 400 mmHg, and ventilation was continued for 4 hours. Hemodynamics, respiratory mechanics and gas exchange were measured throughout the experiment, and lung histopathological changes, lung wet/dry weight ratio, lung myeloperoxidase activity, lung and plasma IL-6 expression (ELISA) were determined.
The heart rate, mean arterial pressure, cardiac output, central venous pressure and pulmonary arterial wedge pressure did not differ among the four groups in experiment (P > 0.05). The mean pulmonary arterial pressure was significantly higher in the HFOV group after 4 hours than in the CMV group (P < 0.05). After lung recruitment, sustained improvements in the oxygenation index were observed in all groups. Lung compliance and the intrapulmonary shunt (Qs/Qt) were significantly improved in the 6 Hz and 9 Hz HFOV groups after 4 hours of ventilation (P < 0.05). The amplitude of alveolar pressure was significantly lower in the 9 Hz HFOV group during the experiment (P < 0.05). Histologically, the lung injury score was significantly lower in the 9 Hz HFOV group than the other groups (P < 0.05). The lung wet/dry weight ratio did no differ among the four groups (P > 0.05). The lung MPO activity and expression of IL-6 in lung tissue and blood plasma significantly reduced in the 6 Hz and 9 Hz HFOV-treated animals (P < 0.05).
Compared with CMV and low frequency in HFOV, the higher frequency in HFOV results in less lung injury. HFOV may be an optimal lung-protective strategy.
This article is published under license to BioMed Central Ltd.