Abstract
Hospital-acquired pneumonia (HAP) is the second most frequent nosocomial infection
with an average crude mortality around 40%. Clinical and microbiological diagnoses
are important in order to establish an adequate antibiotic treatment. In mechanically
ventilated patients, clinical diagnosis frequently leads to false-positive and false-negative
interpretations, because entities other than pneumonia may cause fever and pulmonary
infiltrates. Microbiological diagnostic methods are divided into invasive and noninvasive
approaches. Among the former, the protected specimen brush and bronchoalveolar lavage
via fiberoptic bronchoscopy are the most popular. Sensitivities and specificities
range from 60 to 100%. False-negative results are mainly due to prior antibiotic treatment
while false-positive results are due to distal airway colonization. Blind methods
through the endotracheal tube have been as accurate as guided methods due to the anatomical
distribution of ventilator-associated pneumonia (VAP) (diffuse, bilateral, and predominantly
affecting the dependent lung zones). Transthoracic needle aspiration has been used
by some groups in nonventilated patients. Among the noninvasive methods, quantitative
culturing of endotracheal aspirates seems to offer reasonable results. Different gold
standards have been used to validate all these diagnostic methods which makes comparisons
very difficult. The only reliable gold standard is the presence of pneumonia in the
histopathological examination of the lung. There is no clear reason to initially perform
invasive testing in nonventilated patients. This is more controversial in VAP, with
arguments in favor and against. However, recent information suggests that using invasive
procedures does not modify the morbidity and mortality of patients with VAP but leads
to a greater cost. Our personal recommendation is to start empirical antibiotic treatment
according to standardized guidelines and adjust it according to quantitative cultures
of endotracheal aspirates. However, thresholds of quantitative cultures (of endotracheal
aspirates or any other technique) have to be flexible and balanced by clinical judgment.
In those cases (ventilated and nonventilated) not-responding to initial treatment,
invasive techniques may be warranted.
Key Words:
hospital-acquired pneumonia - ventilator-associated pneumonia - invasive diagnostic
methods - quantitative bacterial cultures
