Microbiological diagnosis of ventilator-associated pneumonia: to direct or not to direct samplings?

Non-bronchoscopic bronchoalveolar lavage in the microbiological diagnosis of pneumonia in mechanically ventilated patients

A prospective study comparing standardized non-bronchoscopic bronchoalveolar lavage (sNB-BAL) and non-specific endotracheal aspirate (NsETA) in the microbiological diagnosis of pneumonia in mechanically ventilated patients is described. One hundred episodes in 82 mechanically ventilated patients with or without radiological and clinical diagnostic criteria of pneumonia were studied. NsETA and sNB-BAL was performed on the day of study. Fifty-one patients had pneumonia (21 ventilator-associated, 12 hospital-acquired, 18 community-acquired) and 49 had no pneumonia as defined by widely accepted clinico-radiological criteria. The sNB-BAL was found to be significantly more specific (0. 73) compared to NsETA (0.35) for the microbiological diagnosis of pneumonia. Colonization rates with NsETA were significantly higher compared to sNB-BAL (P value <0.0001). No patient had complications attributable to the sNB-BAL procedure. We conlude that sNB-BAL is a safe, effective, sensitive, specific and inexpensive procedure for the serial evaluation of pneumonia in mechanically ventilated patients.

Evaluation of the invasive techniques for diagnosing bacterial respiratory infections

Bacterial community-acquired respiratory infections are usually sustained by strains highly responsive to antibiotic therapy. Thus, the clinical approach is based on an empirical treatment and does not require the isolation of the causative pathogen and the determination of the bacterial susceptibility to antibiotics. On the other hand, Gram-negative bacteria, most commonly multidrug resistant, frequently affect immunocompromised and nosocomial patients and their identification in cultures is absolutely necessary for proper antibacterial treatment. To this aim, two conventional methods are used, i.e. the blood culture, which is positive only in 20% of pneumonia cases, and the sputum culture, which is not invasive but easily contaminated by oropharyngeal flora. Consequently, invasive techniques for sampling the pathologic specimen, such as the BAL and the PSB, performed with the help of fiberoptic bronchoscope, are needed. The diagnostic power and the limits of both these techniques are analyzed. Moreover, the opportunity to obtain quantitative cultures, which may discriminate between contamination and infection is considered.

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