Drainage of pleural effusion improves diaphragmatic function in mechanically ventilated patients

BACKGROUND: Pleural effusion adversely affects the pressuregenerating capacity of the diaphragm. It uncouples the lung and chest wall, which may result in diaphragmatic dysfunction. Information on the effects of effusion drainage on diaphragmatic function is limited, but several studies report relief of dyspnoea after drainage, which was attributed to improved diaphragmatic mechanics, even if this issue was never formally addressed. OBJECTIVE: To investigate the effect of drainage of unilateral pleural effusion on diaphragmatic function. DESIGN, SETTING AND PATIENTS: In a prospective twostep protocol (at baseline and after drainage of effusion), we conducted a spontaneous breathing trial in fourteen critically ill, mechanically ventilated patients undergoing pressure support ventilation. MAIN OUTCOME MEASURES: We used ultrasonography of the ipsilateral hemidiaphragm to evaluate and record respiratory displacement and thickening during tidal and maximal breathing efforts. We recorded and analysed airway pressures, respiratory system compliance, vital capacity, indices of respiratory effort and arterial blood gases. RESULTS: After drainage of the effusion, the respiratory rate decreased and tidal volume increased, but haemodynamic parameters were unaffected and oxygenation levels showed a non-significant increase. Drainage was associated with significant decreases in indices of respiratory drive and the maximal pressure generated by the respiratory muscles, as well as an increased compliance of the respiratory system. Diaphragmatic displacement and thickening significantly increased after drainage. We found there was a significant correlation between the volume of the effusion drained and the increase in tidal diaphragmatic thickening. CONCLUSIONS: Drainage of a unilateral pleural effusion during weaning from mechanical ventilation improves diaphragmatic contractile activity and respiratory system performance.