Patients with tracheostomies are unable to produce sputum in the normal fashion, but lower respiratory tract secretions can easily be collected in a Lukens trap (Figure 53-2). Tracheostomy aspirates or tracheostomy
suction specimens should be treated as sputum by the laboratory. Patients with tracheostomies rapidly become colonized with gram-negative bacilli and other nosocomial pathogens. Such colonization per se is not clinically relevant, but these organisms may be aspirated into the lungs and cause pneumonia. Thus, there can be a great deal of confusion for microbiologists and dinidans trying to ascertain the etiologjc agent of pneumonia in these patients.
Bronchoscopy. The diagnosis of pneumonia, particularly in HTV- infected and other immunocompromised patients, often necessitates the use of more invasive procedures. Fiberoptic bronchoscopy has dramatically affected the evaluation and management of these infections. With this method, the bronchial mucosa can be direcdy visualized and collected for biopsy, and the lung tissue can be sent for transbronchial biopsy to evaluate lung cancer and other lung diseases. Although transbronchial biopsy is important, the procedure is often associated with significant complications such as bleeding.
During bronchoscopy, physidans can obtain bronchial washings or aspirates, bronchoalveolar lavage (BAL) samples, protected bronchial brush samples, or specimens for transbronchial biopsy. Bronchial washings or aspirates are obtained by instilling a small amount of sterile physiologic saline into the bronchial tree and withdrawing the fluid when purulent secretions are not visualized. Such specimens will still be contaminated with upper respiratory trad flora such as viridans strep-tococd and Neisseria spp. Recovery of potentially pathogenic organisms from bronchial washings should be attempted, because such specimens may be more diag-nostically relevant than sputa.
A deeper sampling of desquamated host cells and secretions can also be obtained via bronchoscopy by BAL. Lavages are especially suitable for detecting Pneumocystis cysts and fungal elements.5-" During this procedure, a high volume of saline (100 to 300 mL) is infused into a lung segment through the bronchoscope to obtain cells and protein of the pulmonary interstitium and alveolar spaces. It is estimated that more than 1 million alveoli are sampled during this process. The value of this technique in conjunction with quantitative culture for the diagnosis of most major respiratory tract pathogens, including bacterial pneumonia, has been documented.6-11 Scientists have found significant correlation between acute bacterial pneumonia and greater than 10* to 10" bacterial colonies per milliliter of BAL fluid. BAL has been shown to be a safe and practical method for diagnosing opportunistic pulmonary infections in immunosuppressed patients. Recently, a bedside, nonbronchoscopic "mini BAL" using a Metras catheter has been introduced; typically 20 mL or less of saline is instilled.29
Another type of respiratory specimen is obtained via a protected catheter bronchial brush as part of a bronchoscopy examination.4 Specimens obtained by this moderately invasive collection procedure are best suited for microbiologic studies, particularly in aspiration pneumonia. Protected specimen brush bristles collect from 0.001 to 0.01 mL of material. An overview of the collection process is shown in Figure 53-3. Upon receipt contents of the bronchial brush may be suspended in 1 mL of broth solution with vigorous vor-texing and then inoculated onto culture media using a 0.01 mL calibrated inoculating loop. Some researchers have stated that specimens obtained via double-lumen-protected catheters are suitable for both anaerobic and aerobic cultures. Colony counts of greater than or equal to 1000 organisms per milliliter in the broth diluent (or 104/mL in the original specimen) have been considered to correlate with infection. All facets of the bronchoscope: procedure, such as order of sampling, use of anesthetic, and rapidity of plating, should be rigorously standardized.4-25
Transtracheal Aspirates. Percutaneous transtracheal aspirates (TTA) are obtained by inserting a small plastic catheter into the trachea via a needle previously inserted through the skin and cricothyroid membrane. This invasive procedure, although somewhat uncomfortable for the patient and not suitable for all patients (it cannot be used in uncooperative patients, in patients with bleeding tendency, or in patients with poor oxygenation), reduces the likelihood that a specimen will be contaminated by upper respiratory tract flora and diluted by added fluids, provided that care is taken to keep the catheter from being coughed back up into the pharynx- Although this technique is rarely used anymore, anaerobes, such as Actinomyces and those associated with aspiration pneumonia, can be isolated from TTA specimens.
Other Invasive Procedures. When pleural empyema is present, thoracentesis may be used to obtain infected fluid for direct examination and culture. This constitutes an excellent specimen that accurately reflects the bacteriology of an associated pneumonia. Laboratory examination of such material is discussed in Chapter 61. Blood cultures, of course, should always be obtained from patients with pneumonia, because they will be positive in about 20% of patients requiring hospitalization.
For patients with pneumonia, a thin needle aspiration of material from the involved area of the lung may be performed percutaneously. If no material is withdrawn into the syringe after the first try, approximately 3 mL of sterile saline can be injected and then withdrawn into the syringe. Patients with emphysema, uremia, thrombocytopenia, or pulmonary hypertension may be at increased risk of complication (primarily pneumothorax [air in the pleural space] or bleeding) from this procedure, The specimens obtained are very small in volume, and protection from aeration is usually impossible. This technique is more frequently used in children than in adults.
The most invasive procedure for obtaining respiratory tract specimens is the open lung biopsy. Performed by surgeons, this method is used to procure a wedge of lung tissue. Biopsy specimens are extremely helpful for diagnosing severe viral infections, such as herpes simplex pneumonia, for rapid diagnosis of Pneumocystis pneumonia, and for other hard-to-diagnose or life-threatening pneumonias. Ramifications of this and all other specimen collection techniques are discussed in Cumitech 7B, titled, "Laboratory Diagnosis of Lower Respiratory Tract Infections.'29
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