Chapter 26 ICU Infections

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SECTION II • Medical and Surgical Crises

bronchoscopic procedures should be reserved for those who are seriously ill, immunocompromised, or unresponsive to conventional therapy. The safety and ease of bronchoscopy are facilitated by the presence of an endotracheal tube. When a decision is made to perform bronchoscopy, bronchoalveo- lar lavage and protected brush sampling from the involved region are both reasonable alternatives. Of these, lavage methodology is perhaps more popular, as it is easier, and the protected brush seldom con- flicts with or adds to its accuracy. If the lavage spec- imen yields a predominance of polymorphonuclear leukocytes and more than 10 3 to 10 4 organisms/mL are isolated, infection with the recovered organism is likely. Fewer bacteria suggest an active infec- tion but also may be seen with a partially treated bacterial pneumonia. Blind suctioning, conducted with or without lavage through a wedged catheter (“mini-BAL”), can be performed proficiently by respiratory therapists or trained nurses. In the set- ting of diffuse pneumonia, this is a low-cost and generally effective sampling option. Only bron- choscopy, however, offers the directed sampling so often necessary. Performing transbronchial biopsies to obtain tissue for histologic examination and/or culture is more hazardous in mechanically ventilated patients. Moreover, empirically chosen antibiotics are usu- ally effective in addressing potential pathogens in patients who are immunocompetent. Although not often performed because of the risk of pneumotho- rax, transbronchial biopsy may be attempted when tissue recovery is essential, oxygenation can be well maintained, and coagulopathy is not present. In this setting, the only diagnostic alternatives are open or thoracoscopic lung biopsy. (The latter may not be feasible because of altered anatomy, high ventilation requirements, or refractory hypoxemia.) The risk of developing a pneumothorax while supported by the mechanical ventilator must be balanced against the potential yield and the clinician’s ability to promptly recognize and evacuate the air leak. (Note that the incidence of pneumothorax approaches 100% after open lung biopsy.) In addition, there are situations in which a diagnosis can be made only by tissue biopsy. Open lung biopsy is rarely necessary for patients with intact host defenses, and the value in even compromised hosts is arguable. Transthoracic needle aspiration often yields an adequate speci- men but exposes the patient to attendant risks of pneumothorax and bleeding.

The optimal diagnostic evaluation of a pneu- monic process for patients infected with HIV continues to evolve. For patients with normal or minimally reduced CD4 counts, mild to moderate illness, and a history and examination compatible with acute bacterial pneumonia, empiric antibacte- rial therapy after obtaining cultures is reasonable. For patients with reduced CD4 counts, progres- sive dyspnea, nonproductive cough, elevated lactic dehydrogenase (LDH), and a radiograph with an interstitial or ground-glass pattern, empiric therapy for Pneumocystis and close observation may be rea- sonable. (This is especially true in the absence of prior Pneumocystis prophylaxis.) For patients with low CD4 counts, severe hypoxemia, uncharacteris- tic chest X-ray infiltrates, or an unusual exposure history, early bronchoscopy is the most prudent option. When bronchoscopy is performed, bron- choalveolar lavage alone often is not sufficient; fun- gal infections, tuberculosis, and even Pneumocystis are missed at an unacceptable rate without trans- bronchial biopsy. Because of the wide variety of potential radiographic presentations of tuberculosis, it probably is wise for all patients with HIV symp- toms and acutely abnormal chest radiographs to be placed in respiratory isolation until a diagnosis of tuberculosis can be excluded reasonably. Treatment Nutritional, fluid, electrolyte, and oxygen support of the patient with bacterial pneumonia are not controversial and are applied universally. The initial choice of antibiotic(s) must be guided not only by the nature of the suspected organism but also by the severity of the illness and underlying patient factors. Thus, although treatment should be directed as spe- cifically as possible for patients who are only mod- erately ill, the initial therapy of a fragile patient with serious illness should include broad-spectrum cover- age. Pruning of the antibiotic regimen occurs when the specific causative organism and its likely sensitiv- ity are confirmed. It makes sense to give the chosen antibiotics as quickly as is feasible. There is little mar- gin for error in critically ill patients with pneumonia; however, one can never treat all potential pathogens. Holes in coverage always exist, and there is almost always more than one acceptable antibiotic combina- tion. The selection of antibiotic therapy represents a calculated bet against the most likely organisms. Recognizing the imprecision of the following descriptions, otherwise healthy patients with com-