Chest
Volume 108, Issue 6, December 1995, Pages 1632-1639
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Clinical Investigations in Critical Care
Reappraisal of Distal Diagnostic Testing in the Diagnosis of ICU-Acquired Pneumonia

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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, 102 cfu/mL for PTC, 2% cells containing bacteria for BAL D, 4×103 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.

Section snippets

Methods

Between March 1990 and December 1992, we performed serially PSB, PTC, BAL D, and BAL C on consecutive patients with suspected IAP and evaluated the diagnostic value of each procedure and its best threshold.

Patients

During the study period, 663 patients were admitted to the ICU. Four hundred eighteen patients (63%) were mechanically ventilated for more than 2 days. IAP was suspected in 122 patients who were enrolled into the study. Reasons for ICU admission are summarized in Table 1. Patients had been receiving mechanical ventilation for 13.2±10 days prior to suspicion of IAP. Forty-nine (40%) of these patients fulfilled criteria for diagnosis of ARDS and 39 (32%) patients had a history of preexisting

Discussion

Our ICU patient population was quite similar to those previously studied.3,4 The high ratio of patients with COPD,20 with ABDS,20, 21, 22 and with previous antibiotic therapy during the ICU stay1,4,23, 24 was presumed to decrease the diagnostic value of bacteriologic samples and partly explains modest sensitivity and specificity results using classic thresholds. However, the diagnostic value of each procedure is similar to those previously reported.1–3,0,0,9,23,24 The best results were obtained

Acknowledgment

We thank J.Y. Fagon (Paris) and W.G. Johanson (Newark) for their advice and review of the manuscript; Melanie Christensen for her technical help in writing this manuscript; and Eric Roupie, MD, André Cabie, MD, and Bertrand Renaud for active participation in the study.

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