Diagnosis of Pneumonia: Techniques and Problems

Abstract

All diagnostic strategies in patients suspected of having pneumonia have considerable limitations. While the diagnostic strategy varies from patient to patient, an overview of one possible approach is summarized in Figures 2 and 3. The diagnosis and management of pneumonia usually poses little difficulty in the community setting, but the value of various diagnostic approaches in patients with hospital-acquired pneumonia is a subject of considerable controversy. Clinical criteria of pneumonia, including fever, purulent tracheobronchial secretions, leukocytosis, and a new infiltrate on chest radiograph are hampered by the high frequency with which these findings are observed in patients without pneumonia. Since tracheobronchial secretions are commonly contaminated by microorganisms colonizing the upper airways, routine culture of expectorated sputum, with the inevitable recovery of a potpourri of potential pathogens, can hardly be regarded as a meaningful exercise for the physician. Such cultures with subsequent extensive susceptibility testing form one of the largest workloads and expenses in microbiology laboratories. Clinical decisions based on such information may result in serious patient mismanagement with antibiotics, with the potential of superinfection and drug complication, which further add to hospital expenditures. Blood cultures are valuable when positive, but negative results are more common even in severe pneumonia. Transtracheal aspiration of tracheobronchial secretions is satisfactory in the diagnosis of community-acquired pneumonia in patients without pre-existing lung disease, but its value in the diagnosis of hospital-acquired pneumonia needs further evaluation. Transthoracic aspiration, especially with the newer finer needles, holds considerable promise but the significant risk of barotrauma deters most physicians from employing this procedure in patients requiring mechanical ventilation. Immunologic techniques of detecting microbial antigens, like countercurrentimmunoelectrophoresis and ELISA, are promising but presently inadequate to screen for a wide variety of organisms. Although it also has its limitations, fiberoptic bronchoscopy appears to be the most satisfactory technique if an invasive approach is being considered in a patient suspected of pneumonia. Samples taken with the plugged telescoping catheter technique, when properly performed, combined with quantitative cultures (and possibly antibody coating of bacteria) probably provide the least misleading information when a bacterial pathogen is being considered.(ABSTRACT TRUNCATED AT 400 WORDS)