Repeated studies have shown that bacterial infections of the lung, as well as infections at other anatomic sites, containing 105 or more bacteria per milliliter of exudate. It is well recognized that previous antibiotic treatment affects the results of bacterial cultures and precludes the recovery of organisms at a significant concentration in respiratory secretions.
Protected specimen brushing is a bronchoscopic technique introduced by Wimberley et al in 1979 for collecting uncontaminated lower respiratory tract secretions. In an in vitro study, the double-catheter brush system with telescoping cannulas and a distal carbowax plug proved to be the most effective among seven different types of brush catheters. The brush, however, samples a limited portion of the peripheral airways and the amount of secretions collected varies from 0.01 to 0.001 ml. The brush is diluted in 1 ml of holding medium that results in a 100- to 1,000-fold dilution before plating. A colony count of ^lO cfu/ml (colony forming units per milliliter) has been established by independent investigators to be the diagnostic threshold for pneumonia and represents 10 to 10 bacteria per milliliter.
Broncboalveolar lavage of a lung subsegment refers to the sequential instillation (usually 100 to 240 ml) and aspiration of a physiologic solution into the lung through a fiberoptic bronchoscope wedged in an airway.
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