Blinded invasive diagnostic procedures in ventilator-associated pneumonia.

B ecause invasive diagnostic testing using fiberoptic bronchoscopy (FOB) is associated with inconvenience, expense, the need for operator expertise, and potential side effects, other methods have been developed for taking samples from the lower respiratory tract of patients suspected of having ventilator-associated pneumonia. As with other methods, issues of sensitivity and specificity arise because of the difficulty of accurately diagnosing pneumonia. This section reviews 15 studies evaluating the accuracy of blinded sampling methods.20,30,31,37,45,84,93,119–126 The studies were performed in patients receiving mechanical ventilation in various types of ICUs. Included are small numbers of patients with community-acquired pneumonia who require ventilator support, as well as a few immunocompromised patients. These studies investigated 654 episodes of pneumonia, most of which were thought to be pneumonia on a clinical basis. Of these 654 episodes, 321 were identified as pneumonia using a variety of different methods. The following three blinded procedures were evaluated: blinded bronchial sampling (BBS); mini-BAL; and blinded sampling with the protected-specimen brush (BPSB) technique, using several different protected brushes. Five studies investigated BBS (Tables 16, 17) using four different catheters. With BBS, the catheter was blindly wedged into a distal bronchus and aspirated secretions were recovered. No fluid was instilled during any of the procedures. Most investigators required a minimal amount of recovered secretions, usually on the order of 1 to 2 mL. Quantitative cultures were performed, and the concentration of bacteria considered significant for the diagnosis of pneumonia ranged from 10 to 10 cfu/mL. BBS was performed in 251 episodes, 141 of which were diagnosed as pneumonia. Seven studies investigated the second procedure, miniBAL. Three studies used the combicath, a single-sheathed, 50-cm, sterile, plugged, telescoping catheter,20,37,84 one study used a different telescoping catheter,121 and the remaining three studies used unprotected catheters. The amount of lavage fluid instilled varied from 20 to 150 mL. Quantitative cultures were performed, and the bacterial concentration considered significant for the diagnosis of pneumonia ranged from 10 to 10 cfu/mL, a bacterial index of $ 5, or was not stated. Of the 317 episodes using miniBAL, the diagnosis in 135 was pneumonia. The last blinded-sampling method, BPSB, was investigated in five studies. This method incorporates a sterile brush that is protected from contamination. Two studies used the accucath, a sterile, single-use, 15F apparatus containing a nylon specimen brush 16 mm long at its tip, which is protected from contamination by an everting, air-filled balloon mechanism. The other three studies used a standard protected-specimen brush (PSB) technique. Quantitative cultures were performed, and a level of 10 cfu/mL was considered significant for the diagnosis of pneumonia. BPSB was performed in 147 episodes, yielding a diagnosis of pneumonia in 70. Two studies simultaneously investigated two different types of blinded sampling procedures.20,125 Most of the reported studies are case series, although four immediate postmortem studies are described. Enrollment was prospective but rarely consecutive. The length of time of mechanical ventilation varied considerably. In most studies, the test results and reference tests were assessed by investigators who were aware of the patient’s clinical evolution. The techniques and bacteriologic methods used generally were well described. A major limitation with interpreting the data is a general lack of standardization of collection methods and of quantitative levels for significance. Although not specifically addressed in three studies, in at least 250 episodes the patients were either receiving antibiotics or had received antibiotics in the recent past. There is no universal reference or “gold standard” test, even among the four studies with extensive postmortem investigations.20,37,84,124 These four studies retrospectively diagnosed pneumonia by relying on traditional clinical, radiographic, and microbiological criteria or on the clinical pulmonary infection score.30,45,120,126 The remaining seven studies investigated blinded sampling only in patients with clinical evidence of pneumonia. No control subjects were included, or the study was designed to measure concordance.31,93,121–123,127 All of these studies enrolled patients who were clinically identified as having pneumonia. Also, an FOB procedure was performed and lower respiratory tract samples were collected using a protected brush. BAL samples were obtained in only a few of these studies. Since these seven investigations made up a significant proportion of the available studies, the results of the PSB sampling obtained by FOB was selected as the “gold standard.” Thus, the methodology is fairly standard, and was followed in all studies. Additionally, recovery of at least one similar organism in sufficient bacterial concentration by both the PSB sampling method and BPSB was required for confirmation. In five studies, histology data were available in at least some patients, and in several of these, cultures of lung tissue also were obtained. Unless otherwise stated in the article, sensitivity and specificity were determined using only the findings from the lung histology studies. The major limitations of blinded procedures were that most were nondirected and rarely was positioning verified by radiographic methods. The sensi*From the Division of Pulmonary and Critical Care Medicine, Louisiana State University Medical Center, Shreveport, LA.