Effects on respiratory mechanics of bronchoalveolar lavage in mechanically ventilated patients

Inconsistent findings have been reported about the effects of bronchoalveolar lavage (BAL) on respiratory mechanics. The aims of this study were to study the effects of BAL on respiratory mechanics in mechanically ventilated patients with suspected pneumonia and to find out whether these effects are related to the extension of radiographic infiltrate and preceding respiratory mechanics measurements.

Bronchoscopy BAL was performed with 150 mL of sterile isotonic saline in 3 aliquots of 50 mL. Respiratory mechanics parameters were measured by the rapid airway occlusion technique, immediately before and after BAL and 90 minutes later. Patients were classified according to unilateral or bilateral radiological infiltrate occurrence.

Fifty critically ill patients undergoing mechanical ventilation were included. Respiratory system compliance (Crs) decreased from 43.32±13.17 mL/cm H2O to 33.02±9.56 mL/cm H2O (P<0.01) and airway resistance increased from 15.16±7.04 cm H2O/L/s to 17.54±9.40 cm H2O/L/s (P<0.05) immediately after BAL; 90 minutes later both the parameters returned to the pre-BAL values. Patients who showed a greater than 20% decrease in Crs had a higher pre-BAL Crs than patients with a less severe decrease (49.85±10.7 mL/cm H2O vs. 35.65±11.67 mL/cm H2O; P<0.01). However, neither pre-BAL airway resistance nor the extension of the radiographic infiltrates was related to the changes in respiratory mechanics.

BAL in mechanically ventilated patients can lead to a significant, although transitory, deterioration in pulmonary mechanics, characterized by a decrease in Crs and by an increase in airway resistance. Patients with better initial Crs showed the most severe affectation.