Diagnostic options widen for vent-related pneumonia
Bronchoscopy not only diagnostic tool
Synopsis: Quantitative culture of bronchoscopic specimens from patients clinically suspected of having ventilator-associated pneumonia, as compared to culture of endotracheal aspirates, led to more frequent changes of antibiotic coverage, but had no effect on clinical outcome.
Source: Sanchez-Nieto JM, et al. Am J Respir Crit Care Med 1998; 157:371-376.
In 51 patients requiring mechanical ventilation for more than 72 hours and who were clinically suspected of having ventilator-associated pneumonia, Sanchez-Nieto and associates compared the effects of two different strategies for pursuing the diagnosis. By random allocation, 24 patients (Group A) underwent noninvasive investigation (quantitative endotracheal aspirates, QEA) and bronchoscopy with both bronchoalveolar lavage (BAL) and protected specimen brush (PSB); 27 other patients (Group B) underwent only QEA cultures. In keeping with previous studies, diagnostic thresholds for positive cultures were 105 colony-forming units for QEA, 104 for BAL, and 103 for PSB. Empiric antibiotic treatment was given according to each patient's attending physician who had access to BAL and PSB results in Group A and to QEA results in Group B.
Quantitative culture results were positive from 67% of QEA samples, 67% of BAL samples, and 58% of PSB samples in Group A, and from 74% of the QEA samples in Group B. All patients with positive BAL or PSB cultures had positive QEA cultures. All three cultures agreed in 71% of Group A patients; QEA results coincided with either BAL or PSB results in 21%; in only 8% (2 patients) did QEA culture results not coincide with those from either BAL or PSB. Initial antibiotic therapy selected by the patients' attending physicians was modified in 42% of Group A patients and in 16% of Group B patients (P < 0.05). There were no significant differences in either crude mortality rates (46% in Group A, 26% in Group B) or mortality rates adjusted for initial prognostic assessment (29% and 10%, respectively).
Comment by David J. Pierson, MD, FACP, FCCP, medical director for respiratory care, Harborview Medical Center, Seattle.
In this study, there was no difference in mortality among patients clinically suspected of having ventilator-associated pneumonia, regardless of whether bronchoscopic techniques were used to gather specimens for bacteriologic study. When BAL and PSB were used, as compared with blind nonbronchoscopic endotracheal aspiration, there were more subsequent changes in the initial empirical antibiotic therapy, but the outcomes were the same.
Does this paper settle the issue, and can we now abandon bronchoscopic techniques in investigating suspected ventilator-associated pneumonia? As Sanchez-Nieto, et al point out, the sample sizes in this study limit the confidence with which conclusions about mortality can be drawn, and there is no question that this hotly contested matter has not yet been settled. However, the results probably do indicate that, based on presently available knowledge, it would be clinically acceptable to approach the problem with either of the diagnostic methods used in this study.
There are problems, however, with acting on this conclusion in everyday clinical practice. Sanchez-Nieto, et al did not study bronchoscopic vs. nonbronchoscopic diagnosis as usually carried out, at least in the United States. They used both BAL and PSB, and they did quantitative cultures on everything, including the specimens obtained by aspiration through the endotracheal tube. Quantitative cultures are seldom done on routine suction specimens and are not even available from many clinical laboratories. This study did not evaluate the value of non-quantitative sputum culture results, the data most likely to be available to practicing clinicians, which previous studies have found to have much less value than the techniques used by these investigators.
Although Sanchez-Nieto, et al did not address costs (and, in fact, few studies of the diagnosis of ventilator-associated pneumonia have done so), there is no question that the diagnostic regimen described is expensive, at least in the United States. When professional fees are added to the others associated with bronchoscopy, specimen handling, and quantitative cultures, the invasive pursuit of a diagnosis of ventilator-associated pneumonia is a pretty expensive activity, especially if, as suggested by this study, it has no effect on the clinical outcome.
>More studies are clearly needed, and I hope they will address not only diagnostic sensitivity and specificity in ventilator-associated pneumonia, but also the effects of different diagnostic and therapeutic strategies on mortality, morbidity, and costs-as done at least in part by Sanchez-Nieto, et al in this commendable first step.
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