DIAGNOSTIC-TESTS FOR PNEUMONIA IN VENTILATED PATIENTS - PROSPECTIVE EVALUATION OF DIAGNOSTIC-ACCURACY USING HISTOLOGY AS A DIAGNOSTIC COLD STANDARD

The diagnostic accuracy of protected-specimen brush (PSB), bronchoalve olar lavage (BAL), and endotracheal aspirates (EA) was prospectively e valuated in a series of 28 mechanically ventilated patients (MV patien ts) who died within 3 d of the bronchoscopic procedure, using postmort em lung examination as the gold standard for establishing the diagnosi s of pneumonia. The entire fixed lungs were carefully dissected along the bronchovascular axes and each segment was cut into 5- to 10-mm thi ck sections, enabling gross examination of the lung parenchyma. Two ti ssue blocks were taken from each segment, including grossly abnormal a reas whenever present. In several cases, two peripheral (subpleural) l ung-tissue blocks were also taken from each lobe prior to systematic d issection of the lungs. Quantitative cultures (QC) and direct cytologi c and microbiologic examination (DE) was performed on respiratory samp les obtained within 72 h before death. Values of 10(3) cfu/ml of Ringe r's solution, 10(4) cfu/ml of retrieved fluid, and 10(8) cfu/ml of res piratory secretions were used as cutoff points for quantitative PSB, B AL, and EA cultures, respectively. The main findings in this study wer e that: (I) Pneumonia was present in 67% of the patients. (2) Histolog ic lesions of pneumonia were mainly bilateral and predominated in the dependent lung segments. (3) Coexistence of a variety of noninfectious processes was a common finding in patients with pneumonia. (4) In sev eral cases pneumonia was absent from peripheral lung samples while mor e central areas of the same segment displayed typical foci of pneumoni a. (5) The sensitivity of quantitative cultures was 55%, 57%, and 47% for EA, PSB, and BAL, respectively, and the specificity was 85%, 88%, and 100%, respectively. Reducing the diagnostic threshold of EA to 10( 5) cfu/ml of respiratory secretions instead of 10(6) cfu/ml resulted i n a sensitivity of 63.1% and a specificity of 75% for EA. The sensitiv ity of direct examination (DE) was 50%, 47%, and 47%, respectively, an d the specificity was 75%, 88%, and 87%. (6) The presence of intracell ular organisms (ICO) in BAL had a 36.8% sensitivity and 100% specifici ty in establishing the diagnosis of pneumonia regardless of their perc entage. (7) Although 15 patients (53%) were not on antibiotics or were off antibiotics for more than 48 h before testing, no relationship co uld be established between the patients' antibiotic status and the res ult of any diagnostic test. By using a recommended methodology for res piratory sampling techniques together with complete postmortem lung ex amination as a diagnostic ''gold standard,'' this study provides a rea listic insight into the diagnostic values of EA, PSB, and BAL in MV pa tients with suspected pneumonia.