Diagnostics of Ventilator-associated Pneumonia

Overview

Ventilator-associated pneumonia (VAP) is defined as a pneumonia in a patient on mechanical ventilator support (byendotracheal tube or tracheostomy) for > 48 hours.VAP is the major cause of infection in critically ill patients and continuesto complicate the course of 8 to 28% of patients receiving mechanical ventilation. Mortality rate for VAP ranges from 24 to50% and can reach 76%in some specific settings or when lung infection is caused by high-risk pathogens.The predominantorganisms responsible for infection are Enterobacteriaceae, Pseudomonas aeruginosa and Staphylooccus aureus, butcausative agents widely differ according to the population of patients in an intensive care unit, duration of hospital stay,prior antimicrobial therapy and local epidemiological conditions.Since an appropriate antimicrobial treatment of patients with VAP significantly improves outcome, more rapid identificationof infected patients and accurate selection of antimicrobial agents represent important clinical goals. However, VAP isdifficult to diagnose and consensus on appropriate diagnostic, therapeutic, and preventive strategies for VAP has yet to bereached.Most often used diagnostic procedures of VAP are reviewed, including radiological diagnosis, clinical criteria, microscopicassessment, endotracheal aspiration sampling, blinded invasive procedures (blinded bronchial sampling, minimal bronchoalveolarlavage, blinded sampling with protected specimen brush) and bronchoscopic invasive procedures (bronchoalveolarlavage, protected specimen brush). Accuracy, advantages and risks of various methods are discussed. At thepresent time, it seems to be clear that endotracheal aspirate sampling is most sensitive, while bronchoscopic sampling ismost specific and exactness of mentioned quantitative procedures is influenced by previous antibiotic exposure.The authors are of the opinion that diagnosis of VAP and decision whether to initiate antibiotic therapy or not, should bebased on combination of the clinical likelihood of pneumonia (purulent tracheal secretion, pulmonary infiltrates, temperature,leukocytosis, alteration of gas exchange) with the results of examination of respiratory secretion specimens (Gramstains, qualitative and if indicated quantitative results) and the clinical severity of the systemic response to infection.

Key words:
ventilator-associated pneumonia – epidemiology – etiology – pathogenesis – diagnostic procedures