Bronchoalveolar lavage

The fiber-optic bronchoscope is wedged in the segment implicated on the chest radiograph and 150 ml of sterile saline (less in those requiring a high FiO 2) is instilled. The return from the first 25 ml is discarded. The diagnostic yield can be increased by lavaging bilaterally. Complications include transient worsening of radiograph infiltrates and deterioration in oxygenation, with PaO2 falling by a mean of 1.07 kPa.

Quantitative cultures are required to discriminate pathogens from contaminants; a cut-off of 10 5 CFU/ml lavage fluid is commonly used but this is disputed. Varying volumes of instilled saline and dilution of return may account for some discrepancies. A comparison of protected brushing and bronchoalveolar lavage in eight normal volunteers showed that brushing was sterile in seven but lavage was sterile in only one, although on quantitative culture none had more than 10 4 CFU/ml. A method for 'protected' bronchoalveolar lavage has recently been reported with excellent sensitivity and specificity.

Bronchoalveolar lavage is the standard method for diagnosing pneumonia in the immunocompromised; here the sensitivity is up to 88 per cent and the specificity is nearly 100 per cent. If lavage fails, the gold standard remains open-lung biopsy.

The precision of bronchoalveolar lavage in the diagnosis of pneumonia has been compared with that of tracheal aspirates and protected brushing in mechanically ventilated animals. Of the bacterial species yielded by lung homogenates at postmortem, bronchoalveolar lavage recovered 74 per cent, brushing recovered 41 per cent, and needle aspirates 56 per cent. False-positive results were obtained in 8 per cent of bronchoalveolar lavage cultures but in 40 per cent of tracheal aspirates.

Bronchoalveolar lavage has a sensitivity of 53 to 93 per cent and a specificity of 60 to 100 per cent in the diagnosis of ventilator-associated pneumonia. The lack of consensus on a cut-off for a positive lavage and the variability in sensitivity and specificity limit the usefulness of quantitative cultures obtained using this technique. However, immediate Gram staining of lavage fluid has shown intracellular organisms in more than 7 per cent of leukocytes in 86 per cent of patients with pneumonia and only in 4 per cent of those without, with Gram staining and later cultures agreeing closely. Of those without pneumonia, 91 per cent had less than 2 per cent leukocytes with intracellular organisms (Chastre.an.d.Fagon 1994). This sensitivity is lost in those recently or currently on antibiotics.

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