Reappraisal of distal diagnostic testing in the diagnosis of ICU-acquired pneumonia.

BACKGROUND

The thresholds of the diagnostic procedures performed to diagnose ICU-acquired pneumonia (IAP) are either speculated or incompletely tested.

PURPOSE

To evaluate the best threshold of protected specimen brush (PSB), plugged telescoping catheter (PTC), BAL culture (BAL C), and direct examination of cytocentrifugated lavage fluid (BAL D) to diagnose IAP. Each mechanically ventilated patient with suspected IAP underwent bronchoscopy successively with PSB, PTC, and BAL in the lung segment identified radiographically.

POPULATION

One hundred twenty-two episodes of suspected IAP (occurring in 26% of all mechanically ventilated patients) were studied. Forty-five patients had definite IAP, and 58 had no IAP. Diagnosis was uncertain in 19 cases.

RESULTS

Using the classic thresholds, sensitivity was 67% for PSB, 54% for PTC, 59% for BAL D, and 77% for BAL C. Specificity was 88% for PSB, 77% for PTC, 98% for BAL D, and 77% for BAL C. We used receiver operating characteristics methods to reappraise thresholds. Decreasing the thresholds to 500 cfu/mL for PSB, 10(2) cfu/mL for PTC, 2% cells containing bacteria for BAL D, 4 x 10(3) cfu/mL for BAL C increased the sensitivities (plus 14%, 23%, 25%, 10%, respectively) and moderately decreased the specificities (minus 4%, 9%, 2%, 4%, respectively) of the four examinations. The association of PSB with a 500 cfu/mL threshold and BAL D with a 2% threshold recovered all but one episode of pneumonia (SE 96 +/- 4%) with a 84 +/- 10% specificity. For a similar ICU population, these "best" thresholds increased negative predictive value with a minimal decrease of positive predictive value. They need to be confirmed in multiple ICU settings in prospective fashion.