A scanographic assessment of alveolar recruitment and overinflation during high frequence ventilation : preliminary results in three patients

BACKGROUND AND OBJECTIVES: High-frequency ventilation (HFV) may offer an attractive alternative to conventional strategies in the ventilation of the acute respiratory distress syndrome (ARDS) or acute lung injury (ALI) because it can minimize lung injury. Maintaining ventilation between lower and upper inflection points, it can warrant alveolar recruitment with probably reduced level of overinflation. The goal of this study was to compare alveolar recruitment and overinflation induced by HFV versus conventional mechanical ventilation with positive-end expiratory pressure (PEEP), in three patients with ALI/ARDS. METHODS: This was a prospective study in an Intensive Care Unit of a University Hospital, evaluating three ALI/ARDS patients. Scanographic measurements were done, using special software (Lungview), during HFV and conventional ventilation with or without PEEP, in a randomised order. In HFV and PEEP mean airway pressure was kept constant. Lung density histograms were plotted. Alveolar recruitment was calculated as the percentages of air that entering in sick lung areas. Overinflation was calculated as lung volume under –900 Hounsfield units. RESULTS: Lung density histograms were similar in both conditions. Alveolar recruitment was 49 ± 35% versus 48 ± 27% and overinflation was15 ± 5 ml (0.4 ± 0.1 %) and 2 ± 2 ml (0.1 ± 0.1%) in HFV and PEEP, respectively. CONCLUSIONS: In the three patients evaluated application of HFV and conventional mechanical ventilation with PEEP showed, for the same mean airway pressure, similar lung density histograms as well as similar level of alveolar recruitment and lung overinflation