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(Chest. 2001;120:702-704.)
© 2001 American College of Chest Physicians

Ventilator-Associated Pneumonia

Science and Hocus-Pocus

Paul E. Marik, MD, FCCP (Pittsburgh, PA ).

Joseph Varon, MD, FCCP (Houston, TX ).

Dr. Marik is affiliated with the Trauma Life Support Center, Mercy Hospital of Pittsburgh. Dr. Varon is Associate Professor of Medicine, Pulmonary and Critical Care Section, Baylor College of Medicine and Research Director, Department of Emergency Services, The Methodist Hospital.

Correspondence to: Joseph Varon, MD, FCCP, 2219 Dorrington, Houston, TX 77030; e-mail: jvaron{at}bcm.tmc.edu

Ventilator-associated pneumonia (VAP) is the most important infectious complication occurring in critically ill patients, increasing ICU length of stay and mortality.1 2 3 In the last 2 decades, intensive scientific enquiry has improved our understanding of the pathogenesis and treatment of VAP. Yet, despite this information, myths and misconceptions ("hocus-pocus") continue to dominate the management of patients with suspected VAP. The article "International Conference for the Development of a Consensus on the Diagnosis and Treatment of Ventilator-Associated Pneumonia," which appears in this issue of CHEST (see page 955), goes a long way toward dispelling many of the myths associated with the management of VAP. Dr. Jordi Rello, the conference chairperson, used an interesting and rather unique format to explore this controversial topic. He presented 12 international authorities with a set of highly pertinent questions regarding the diagnosis and management of VAP. For each question, he provided the scientific background and then the responses of the expert panel, followed by a consensus statement. Although agreement was not reached on all questions, the responses of the expert panel provide insight into the range of acceptable approaches to this complex problem.

The most important and controversial question pertains to the diagnosis of VAP. The importance of this question lies in the fact that clinical criteria alone are notoriously unreliable in the diagnosis of VAP and, consequently, that many patients without pneumonia are needlessly treated with broad-spectrum antibiotics.4 5 6 This is a significant factor leading to the emergence and persistence of multiresistant bacteria in the ICU.7 Interventions that limit the reckless use of antibiotics in the ICU lower the incidence of resistant organisms and, surprisingly, the risk of infections.8 9 10 11 Unfortunately, a "gold standard" for the diagnosis of VAP does not exist. However, the expert panel recommended obtaining lower respiratory tract samples as soon as the diagnosis of VAP is suspected, because this approach "provides results with a high specificity and positive predictive value and is, therefore, better in differentiating colonization or contamination from infection." An alternative approach would be a decision-tree approach based on the likelihood of VAP, as proposed by Singh and colleagues.9 The use of Gram’s stain and culture of sputum samples (endotracheal aspirates) to diagnose VAP is to be seriously discouraged. Surprisingly, endotracheal aspirates are commonly requested in ICU patients, even in those patients without a pulmonary infiltrate. These patients are frequently treated with antibiotics based on the results of the sputum culture. However, as emphasized by Rello and colleagues, the use of sputum culture to diagnose VAP is plagued by both high false-positive and false-negative results.

It has been well-established that the most important factor affecting the outcome of patients with confirmed VAP is the early institution of appropriate antibiotic therapy.12 13 14 15 Based on these data, it has been suggested that lower respiratory tract sampling does not change outcome and, therefore, has a limited role in the management of patients with VAP.16 17 This reasoning is flawed for a number of reasons. First, lower respiratory tract sampling and quantitative culturing safely allow for the discontinuation of antibiotic therapy in patients with negative results of quantitative cultures.1 11 14 Second, in ICUs where resistant organisms are common, the initial empirical therapy may have to be extremely broad and may require dual antipseudomonal therapy along with an agent directed at methicillin-resistant Staphylococcus aureus.18 This regimen can be narrowed based on the results of lower respiratory tract sampling. Third, such an approach may actually reduce the mortality rate of patients with suspected VAP.19 Furthermore, this approach provides useful epidemiologic data on which to base empiric antimicrobial therapy.

Bronchoscopic lower respiratory tract sampling, however, has a number of limitations. It is important that the sampling be performed prior to the initiation of a new course of antibiotics, as the diagnostic accuracy falls significantly if it is performed after antibiotic therapy has been commenced.20 21 22 23 Furthermore, bronchoscopy is expensive, time-consuming, and not readily available in many ICUs. These limitations may be overcome by nonbronchoscopic sampling techniques. A number of studies14 24 25 26 27 28 29 30 have found the results obtained from blind protected-specimen brush (BPSB) sampling and mini-BAL to be comparable to those obtained by bronchoscopy. Importantly, these blind techniques require little preparation and equipment, and can be rapidly and safely performed by adequately trained respiratory therapists.11 31 Since BPSB is generally recognized to have operating characteristics that are similar to bronchoscopic sampling, we believe that BPSB is a cost-effective alternative to invasive diagnostic testing.

Other myths dispelled by Rello and colleagues include the use of once-daily vancomycin dosing in patients with normal renal function, the practice of treating Candida spp in respiratory tract secretions with antifungal agents, the use of antibiotics with anaerobic activity, the use of guidelines that ignore local epidemiologic variables, and prolonged courses of antibiotics for the treatment of patients with VAP.

References

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