Chapter 26 ICU Infections

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CHAPTER 26 • ICU Infections

Therapy Three basic principles apply to treating empyema: early diagnosis, appropriate antibiotic therapy, and thorough drainage. Of these, drainage is most important. Because there are no radiographic or physical examination features to distinguish an empyema from a routine pleural effusion, thoracen- tesis is required. Prompt diagnosis minimizes both early (sepsis and respiratory failure) and late compli- cations (fibrothorax and debilitation). When turbid, viscous, pleural fluid (especially if foul smelling) is obtained at thoracentesis, cultures for aerobic and anaerobic bacteria, tuberculosis, and fungi should be sent. In addition to routine cell counts and chemistry analysis, it is prudent to obtain triglycer- ide and cholesterol levels to exclude a diagnosis of chylothorax, which can have an empyema-like (tur- bid) appearance. (Effusions caused by rheumatoid disease also can have a similar appearance.) The pleural fluid should be Gram stained and sputum and blood cultures obtained. Antibiotic coverage should be chosen initially on the basis of the Gram stain and then fine-tuned by culture results. The usual etiologic suspects for pneumonia also cause empyema ( Streptococcus pneumoniae, H. influen- zae, anaerobic mouth flora); however, staphylococci also should be covered. Antibiotics alone are insuf- ficient; prompt insertion of a thoracostomy tube(s) of sufficient caliber to completely drain the pleu- ral space is almost always indicated. Several tubes may be required to fully drain the collection when the fluid is multiloculated. Chest CT guidance can be invaluable in guiding placement. Effusions that do not resolve with antibiotics, tube thoracostomy, and intrapleural thrombolytics may require explora- tion and drainage by thoracotomy or video-assisted thoracoscopy (VATS). Failure to resolve the acute process satisfactorily can require later pleural strip- ping or decortication. Relatively large collections of fluid that form after appropriate antibiotic ther- apy has been initiated can usually be managed by serial thoracentesis, rather than by indwelling chest tube. The latter becomes necessary, however, if the patient unexpectedly remains toxic appearing or the fluid loculates. Intravascular Catheter-Related Infections Intravascular catheter-related infections remain one of the top three causes of nosocomial sepsis; however, in ICUs with organized prevention plans,

may be enhanced by using ultrasound localization (see Chapter 11). Empyema is defined as an effusion with organ- isms detected by Gram stain or as “pus” in the pleu- ral space. Unfortunately, observers vary widely in their definition of pus. The diagnosis of empyema is not made by laboratory testing, and there are no specific laboratory cutoff values for what consti- tutes an empyema. Many empyemas do not have microorganisms visible on Gram stain examination, and not all empyemas grow bacteria in culture, per- haps because antibiotic therapy has already been administered or because the responsible organism is inherently difficult to isolate (e.g., anaerobes). If infected with bacteria, especially anaerobic bacteria, the odor of an empyema is memorable. Generally, accepted characteristics of an empyema are grossly cloudy or opaque appearance and thick, viscous character because of high levels of protein and leukocytes. Certainly, not all infected pleural fluids are thick. Yet, it is the physical characteristics of the fluid that make empyema important to diag- nose and treat appropriately. Intrapleural streptoki- nase can reduce the need for pleural decortication if used early in the clinical course and is often helpful later when tube drainage slows and pockets remain. Intrapleural streptokinase is associated with a low risk of either allergic reaction or systemic coagulop- athy. Several types of pleural effusions can mimic an empyema: chylothorax, rheumatoid effusion, tuber- culous effusion, and resolving hemothorax all can have the thick, turbid appearance characteristic of bacterial empyema. The clinical presentation of empyema can be subtle. It is not uncommon for elderly or debilitated patients to have empyema as the primary cause of or cocontributor to chronic wasting illness. The diag- nosis should be suspected in patients with unresolv- ing or hectic fever and pleural effusions that do not improve with antibiotic therapy. Empyema becomes more likely if the suspect fluid collection is adjacent to pneumonia. Because ICU chest films are often taken supine or semiupright, the classic “layering” of an effusion can be missed. Although decubitus views and pulmonary ultrasound enhance the like- lihood of finding an effusion, CT currently is the most definitive way to confirm a free or loculated fluid collection, especially if small or loculated. For febrile or frankly septic patients, especially those with an underlying pneumonia, the search for an empyema is reasonable.