Invasive Methods for the Diagnosis of Ventilator-Associated Pneumonia: Is their Value Overestimated?

Abstract

The diagnosis of ventilator-associated pneumonia (VAP) is a difficult one, and controversy persists about the appropriate approach to this clinical problem. Clinical features of pneumonia are not specific, and many patients who are given the diagnosis have other processes to explain the presence of new lung infiltrates and fever [1, 2]. To address this problem, investigators have developed methods to collect quantitative bacterial cultures of respiratory secretions in order to establish whether invasive lung infection is present. These cultures can be collected bronchoscopically or blindly, and thresholds for defining the presence of pneumonia have been identified for each method [3]. Proponents of these methods point to the inaccuracy of the clinical diagnosis of VAP, and state that invasive methods provide a more accurate estimate of the presence of pneumonia. Invasive methods have been advocated for the routine care of patients with suspected VAP, as a means for defining when therapy is needed [4–6]. It has also been suggested that quantitative cultures can be used to tell which of the many organisms present in a patient’s tracheobronchial secretions are causing infection and which are simply serving as colonizing bacteria. In addition to these therapeutic applications, advocates of invasive methods have suggested that studies of pneumonia epidemiology and therapy are not adequate unless they involve a microbiologic diagnosis of VAP [5].