Pro/con clinical debate: the use of a protected specimen brush in the diagnosis of ventilator associated pneumonia.

Pro/con clinical debate: the use of a protected specimen brush in the diagnosis of ventilator associated pneumonia. Crit Care 2002;6:117–20. Heyland D, Ewig S, Torres A. Queen's University, Kingston, Ontario, Canada; Medizinische Universitäts–Poliklinik, Bonn, Germany; Servei de Pneumologia i Allergia Respiratoria, Universitat de Barcelona, Spain. Comments: This publication is a debate among the three participants who weigh the pros and cons of protected specimen brush (PSB) in the diagnosis of ventilator-associated pneumonia (VAP). VAP is a common complication in patients admitted to the intensive care unit for mechanical ventilation necessitated by respiratory insufficiency or failure. The detection of the etiology of VAP is a constant challenge to the physicians who manage these patients. At many medical centers, empiric antibiotic therapy is begun as soon as the patient is considered clinically to have VAP. Often, the antibiotic therapy is begun while the results of cultures of respiratory secretions are pending. The excellent diagnostic yield for bacterial cultures from either PSB or bronchoalveolar lavage (BAL) is well established. However, the role of bronchoscopy and BAL/PSB in the diagnosis of VAP remains unclear and thus is not used on a routine basis. The discussants in this debate consider the case of a 50-year-old man in the intensive care unit for 10 days. He was admitted initially with respiratory failure secondary to congestive heart failure. Since admission he has been intubated and ventilated mechanically. His progress in the intensive care unit has been relatively slow as a result of a variety of minor setbacks. Finally, his condition seems to be improving and the weaning process has begun. The patient now develops fever, and purulent secretions are being suctioned from his endotracheal tube. The chest radiograph shows a new infiltrate. VAP is suspected. The question is whether to perform a bronchoscopy to make a diagnosis and to guide future antibiotic choice. Discussant D.H. concedes the absence of a true “gold standard” to diagnose VAP and states that several studies have documented that patients with a suspicion of VAP who receive inadequate empiric antibiotic therapy are more likely to die or experience complications. The pro-PSB discussant infers that the potential advantage of using invasive techniques is that antibiotic therapy may be tailored to the results of diagnostic tests, and this may reduce unnecessary broad-spectrum antibiotics, which could have important clinical implications, such as minimizing the emergence of resistant microorganisms in the intensive care unit and reducing antibiotic costs. The con-PSB discussants (S.E., A.T.) question whether independent microbiologic criteria are able to correct for the bias arising from clinical judgment. They concede that PSB has been studied most extensively and, theoretically, the double catheter and the distal plug design should preserve a very high specificity but limited sensitivity. They indicate that the results of clinical studies evaluating the PSB technique have in fact been conflicting, with wide variations of operative indices being a striking feature, and they quote several references that have reported overall, false-negative, and false-positive results in 10 to 40% of cases. Reasons for false-positive results include contamination of the sample during bronchoscopy or in the processing laboratory, colonization rather than infection, and bronchiolitis. They argue that it is unlikely that PSB (and/or BAL) could have an advantage over noninvasive tools in terms of clinical outcomes. The discussants ask the question: What, therefore, is the role of PSB in clinical practice? They argue that currently available data do not support a regular bronchoscopic approach to the diagnosis of suspected VAP. The pro-PSB discussant in his rebuttal indicates that he does not suggest that we “rely on microbiologic data [from bronchoscopic specimens] as an independent reference standard,” and that microbiologic data, from whatever source, need to be incorporated as a variable in a complex equation that considers other patient characteristics to determine the likelihood of pneumonia. He concludes that sufficient evidence exists to infer that bronchoscopy can help clinicians manage the use of broad-spectrum antibiotics more appropriately, and whether bronchoscopy influences patient outcomes remains to be determined. The con-PSB group responds by stating that given the failure of any diagnostic tool to establish independently the presence of VAP, no tool is helpful in reducing “unnecessary” broad-spectrum antimicrobial treatment, and that treatment decisions must still be based on both clinical and microbiologic data. They also argue that given the comparable yield of quantitative PSB/BAL and tracheobronchial aspirates in the detection of potentially pathogenic microorganisms, antimicrobial treatment may be tailored satisfactorily according to general microbial and susceptibility patterns prevalent in a given institution and to the results of quantitative tracheobronchial aspirates in the individual patient. This discussion is selected for this section of the Journal because of the variations in clinical practice in the management of patients with VAP. At the medical center where I work, there are also similar discussions about the role of bronchoscopy and BAL/PSB in the diagnosis of VAP. The number of bronchoscopies for BAL/PSB in patients with VAP has diminished markedly during the past 5 to 6 years. With newer antibiotics and other drugs becoming available for the treatment of VAP, the role for bronchoscopy and BAL/PSB is likely to diminish in the management of VAP.

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