A great improvement in sampling cells from the lower respiratory tract occurred with the development of the flexible bronchoscope in the late 1960s. The complications of bronchoscopy, including laryngospasm, bronchospasm, disturbances of cardiac conduction and sepsis, are very rare. Bronchoscopic methods are particularly good for diagnosing central lesions, on which a biopsy and a brush for cytology can be directly performed.
Bronchial aspirations and washings
Bronchial secretions can be aspirated directly from the lower respiratory tract through the bronchoscope. However, a more common method is to obtain bronchial washings by instilling 3-10 ml of saline and aspirating the fluid, which is then centrifugated. The concentrated cellular material is used for smears, thinlayer preparations, or cell blocks (very useful if special stains are needed).
Fiberoptic bronchoscopy allows direct visualization and sampling of the tracheobronchial tree. A brush is applied to an endobronchial lesion and the cells are smeared on a glass side.
Bronchioloalveolar lavage (BAL)
In BAL the bronchoscope is wedged into position as far as it will go and distal airways are flushed with several aliquots of sterile saline. The first one is more representative of the cellular material from larger airways, whereas the other ones reflect the alveolar compartment.
BAL is very useful for the diagnosis of opportunistic infections in immunocompromised patients, as well as for the diagnosis of malignancy (particularly helpful when peripherally located) and the investigation of interstitial lung diseases, granulomatous disease, including sarcoid, hypersensitivity pneumonia, drug-induced pulmonary toxicity, asbestosis, pulmonary hemorrhage.
Pulmonary capillary blood samples obtained by using a catheter in the wedge position are useful in the diagnosis of disorder of the pulmonary microvasculature (such as lymphangitic spread of carcinoma and amniotic fluid or fat embolism). Blood is collected in a heparinized tube to prevent clotting and cells are then concentrated using a Ficolle-Hypaque gradient. Megacaryocytes, normally present in the pulmonary capillaries, confirm the proper site and are useful to determine specimen adequacy.