DIAGNOSTIC APPROACHES AND HOSPITAL-ACQUIRED PNEUMONIA

Hospital-acquired pneumonia (HAP) is the second most frequent nosocomi al infection with an average crude mortality around 40%. Clinical and microbiological diagnoses are important in order to establish an adequ ate antibiotic treatment. In mechanically ventilated patients, clinica l diagnosis frequently leads to false-positive and false-negative inte rpretations, 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 prote cted specimen brush and bronchoalveolar lavage via fiberoptic bronchos copy 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 coloni zation. Blind methods through the endotracheal tube have been as accur ate as guided methods due to the anatomical distribution of ventilator -associated pneumonia (VAP) (diffuse, bilateral, and predominantly aff ecting the dependent lung zones). Transthoracic needle aspiration has been used by some groups in nonventilated patients. Among the noninvas ive 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 dif ficult. The only reliable gold standard is the presence of pneumonia i n the histopathological examination of the lung. There is no clear rea son to initially perform invasive testing in nonventilated patients. T his is more controversial in VAP, with arguments in favor and against. However, recent information suggests that using invasive procedures d oes not modify the morbidity and mortality of patients with VAP but le ads to a greater cost. Our personal recommendation is to start empiric al antibiotic treatment according to standardized guidelines and adjus t it according to quantitative cultures of endotracheal aspirates. How ever, thresholds of quantitative cultures (of endotracheal aspirates o r any other technique) have to be flexible and balanced by clinical ju dgment. In those cases (ventilated and nonventilated) not-responding t o initial treatment, invasive techniques may be warranted.