Microbial investigation in ventilator-associated pneumonia

Abstract

Ventilator-associated pneumonia (VAP) is a serious infectious condition in intensive care unit (ICU) patients, currently related to a high mortality rate. Therefore, this complication of mechanical ventilation requires a prompt diagnosis and adequate antibiotic treatment. The detection of the causative organism is imperative for guiding an appropriate therapy as there is strong evidence of the adverse effect of inadequate empirical treatment on outcome. The major difficulty of the microbial investigation is to obtain the sample from the lower respiratory tract, mainly because of the potential contamination with upper airways flora, which may result in a misinterpretation of the cultures.Microbial investigation in VAP is based on the culture of samples obtained from lower respiratory tract by noninvasive or invasive methods. The most common techniques of sampling are the endotracheal aspirate (ETA), which is considered a noninvasive method, the protected specimen brush (PSB) and the bronchoalveolar lavage (BAL), both being invasive methods of investigation. The latter were designed as an attempt to avoid the colonizing flora of the upper airways. The best of these diagnostic approaches is still controversial. In terms of outcome, there is strong evidence that the impact of both invasive and noninvasive methods seems to be similar. In terms of cost, however, the endotracheal aspirate is less expensive compared to BAL or PSB. On the other hand, invasive methods could be particularly beneficial in patients who are not responding to the initial empirical antibiotic treatment.The rationale for the quantitative culture of the respiratory samples is to differentiate between infection and colonization of lower airways, because the bacterial colonization is a frequent event in mechanically ventilated patients. The thresholds currently employed for the diagnosis of the pneumonia are the following: ETA samples, ≥105–106colony forming units (cfu)·mL−1; PSB samples, ≥103cfu·mL−1; and BAL samples, ≥104 cfu·mL−1.Intending to provide a practical approach to the issue, the present manuscript reviews the available noninvasive (blood culture, endotracheal aspirate) and invasive (protected specimen brush, bronchoalveolar lavage, blinded methods and lung biopsy) techniques used for the diagnosis of ventilator-associated pneumonia.

Neumonia Nosocomial

“…En los últimos años se han desarrollado técnicas más específicas para el diagnóstico microbiológico como: broncoscopia, lavado bronquio-alveolar, cepillos endoscópicos protegidos y biopsia transbronquial (26). Estos métodos están orientados a obtener muestras dístales de secreciones bronquiales, consideradas más apropiadas para su cultivo y cuantificación, presentan diferente sensibilidad y especificidad y disminuyen la posibilidad de contaminación de la muestra (27,28).…”

Ventilatör İlişkili Pnömoni

“…Başta pnömoni olmak üzere eşlik eden önemli patolojiler nedeniyle mortalite ve morbidite riski söz konusudur. Komplikasyon oranı %4-19 arasındadır ve en sık komplikasyon pnömoto-rakstır (14). Steril teknikler kullanılmalı, alınan örnekler steril koşullarla hem mikrobiyolojik hem de patolojik inceleme için gönderilmelidir (17).…”

“…Bu yöntemlerde tanı için anlamlı eşik değer PSB için 10 3 cfu/mL BAL için10 4 cfu/mL olarak bilinmektedir (13). PSB'nin özgünlüğü %50-100, duyarlılığı %33-100 olup BAL'ın özgünlüğü %45-100 duyarlılığı %42-93'dür (14). Bronkoskopik yöntemlerle ilgili komplikasyonları ve maliyeti azaltmak için mini BAL ve kör PSB yöntemleri geliştirilmiştir.…”

Comparative study of incidence, risk factors, etiological agents and outcome of early and late ventilator associated pneumonia in paediatric intensive care unit at a tertiary care centre

“…8 Moreover, pathogens can reach the lung from exogenous sources such as hands of healthcare workers, ventilator circuits, and the biofilm of endotracheal tube. 17 As children differ greatly from adults in their anatomy, physiology and underlying disease, specific aetiology for VAP in them is described. In neonates and paediatric patients, microbial diagnosis of VAP is based on the culture of samples obtained from the lower respiratory tract by tracheal aspirate, which is considered a less invasive method and may have an acceptable diagnostic accuracy.…”

“…12 Due to a strong evidence of the adverse effects of inadequate empirical antibiotic treatment on outcome, the detection of the causative organism in VAP becomes imperative in guiding appropriate therapy. 17,18 Early, aggressive, empirical therapy with broad spectrum agents targeted at likely pathogens followed by a regimen driven by microbiological documentation is an effective strategy for the management of VAP and other serious infections. 19 However, inappropriate use and overuse of antibiotics can lead to increased hospital expenditures and could potentially promote antibiotic resistance.…”