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pressors should be available for immediate administration(70).The sampling area should be chosen based on the location ofthe infiltrate on chest X ray or CT scan. This typically corre-sponds to the bronchial segment with purulent secretionsand/or where endobronchial abnormalities are maximal, whichcan be clues in the setting of diffuse pulmonary infiltrates orminimal changes in a previously abnormal chest X ray (137).When in doubt, sample the posterior right lower lobe, sinceautopsy studies have indicated that VAP frequently involvesthis area (61, 92, 130, 173). Multiple specimens are no moreaccurate than single specimens (136).As with nonquantitative and semiquantitative cultures, onlyadequate specimens should be processed. The presence ofmore than 1% epithelial cells or 10 epithelial cells per low-power field (magnification,100) in bronchoscopic or “blind”BAL, PSB, PTC, or bronchial sampling suggests heavy oropha-ryngeal colonization. Returns of10% of the instilled BALfluid are probably not representative of the lower respiratorytract (70). Since interpretation of such specimens is unreliable,they should not be cultured. For QEAs, the same criteriamentioned above for nonquantitative and semiquantitative cul-tures of an ETA should be utilized.For each of the quantitative culturing methods, thresholdvalues have been derived and are expressed in CFU per mil-liliter. If the number of CFU/ml is equal to or exceeds thethreshold values for the particular technique, a diagnosis ofpneumonia is made. Threshold values often employed for di-agnosing pneumonia by quantitative cultures are105to 106,104, and103CFU/ml for QEA, bronchoscopic BAL, andPSB, respectively, with105CFU/ml being the most widelyaccepted value for QEA (12, 30). For “blind” distal sampling,the thresholds are103CFU/ml for PSB and mini-BAL and104CFU/ml for cultures obtained with BBS and unprotectedBAL (Table 1) (30).These “cutoff” values for diagnosing VAP are based in parton the findings of quantitative cultures obtained from infectedlung tissue and the volume and dilution of the respiratorysecretions retrieved by the technique. For instance, BAL col-lects approximately 1 ml of secretions in 10 to 100 ml of effluent.This corresponds to a dilution factor of 1/10 to 1/100. Severalinvestigators have confirmed that with pneumonia, pathogens arepresent in lower respiratory tract inflammatory secretions at con-centrations of at least 105to 106CFU/ml; contaminants are gen-erally present at less than 104CFU/ml. Consequently, for BAL,the threshold value of 104CFU/ml corresponds to 105to 106CFU/ml in the pneumonia (30).Numerous factors can influence the results of quantitativecultures, including the timing of the pneumonia, the skill andexperience of the operator, the adequacy of the specimen,technical aspects such as appropriate processing and delays intransport to the laboratory, special populations such as thosewith chronic obstructive pulmonary disease (who may have

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Term
Summer
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Tags
The Hours, ventilator associated pneumonia, Positive predictive value

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