Chest
Volume 104, Issue 1, July 1993, Pages 104-108
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Clinical Investigations
Is Protected Specimen Brush a Reproducible Method to Diagnose ICU-Acquired Pneumonia

https://doi.org/10.1378/chest.104.1.104Get rights and content

Protected specimen brush (PSB) is considered to be one of the standard methods for the diagnosis of ventilator-associated pneumonia, but to our knowledge, intraindividual variability in results has not been reported previously.

Purpose

To compare the results of two PSB performed in the same subsegment on patients with suspected ICU-acquired pneumonia (IAP).

Study design

Between October 1991 and April 1992, each mechanically ventilated patient with suspected IAP underwent bronchoscopy with two successive PSB in the lung segment identified as abnormal on radiographs. Results of the two PSB cultures were compared using 103 cfu/ml cutoff for a positive result. Four definite diagnoses were established during the follow up: definite pneumonia, probable pneumonia, excluded pneumonia, and uncertain pneumonia.

Population

Forty-two episodes in 26 patients were studied; 60 percent of patients received prior antibiotic therapy. Thirty-two microorganisms were isolated from 24 pairs of PSB. Definite diagnosis was definite pneumonia in 7, probable pneumonia in 8, excluded pneumonia in 17, and uncertain pneumonia in 10 cases.

Results

The PSB recovered the same microorganisms and argued for a good qualitative reproducibility. The distinction of positive and negative results on the basis of the 103 cfu/ml classic threshold was less reproducible. For 24 percent of the microorganisms recovered and in 16.7 percent of episodes of suspected IAP, the two consecutive samples gave results spread out on each side of the 103 cfu/ml cutoff. Discordance was higher when definite diagnosis was certain or probable than when diagnosis was excluded (p = 0.015). There was no statistical effect of the order of samples between the two specimens for bacterial index and microorganism concentrations.

Conclusion

These findings argue for the poor repeatability of PSB in suspected IAP and question the yield of the 103 cfu/ml threshold. In attempting to diagnose IAP, the results of PSB must be interpreted with caution considering the intraindividual variability.

Section snippets

Methods

The study was designed to compare the results of two PSB procedures performed in the same lung subsegment on mechanically ventilated patients with suspected IAP to assess the accuracy of this method for routine diagnosis in clinics.

Results

Forty-two episodes of suspected IAP in 26 patients were analyzed. Table 1 indicates the results of PSB1 and PSB2 for each patient (type and number of growing bacteria) and the final diagnosis. Before the new septic signs associated with a clinical suspicion of nosocomial pneumonia, 15 patients (24 episodes) received antibiotic therapy for other reasons (patients with COPD with bronchial superinfection [n = 7], peritonitis [n = 8], catheter infection [n = 2], antibiotic prophylaxis for digestive

Discussion

Protected specimen brush is considered to be one of the main diagnostic methods for diagnosing IAP. The exactness of the classic diagnostic threshold of 103 cfu/ml has been established comparing PSB culture results with histologic and bacteriologic lung cultures.8 Utilization, in routine practice, of this precise threshold assumes a correct in vivo reliability of the PSB culture which is demonstrated in vitro.9

Our results indicate that even with maximal care to carry out the PSB procedures with

ACKNOWLEDGMENT

We are indebted to Dr. I. Cunningham (Indianapolis) for helpful assistance in reviewing the manuscript.

References (10)

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Manuscript received August 4; revision accepted December 3.

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