Chapter 26 ICU Infections

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SECTION II • Medical and Surgical Crises

defense (Table 26-1). Even when mechanical bar- riers fail, infection usually is averted by effective cellular (neutrophil and macrophage) and humoral immunity (antibody secretion). Unfortunately, both mechanical and immune defenses are jeopardized commonly in critically ill patients, even in those without a recognizable immune deficiency. Common conditions that allow proliferation of organisms leading to pneumonia are listed in Table 26-2. The organism causing pneumonia is highly dependent on where the infection was acquired and on indi- vidual patient characteristics. Diagnosis In the community, a patient with acute onset of fever, dyspnea, chest discomfort, and cough produc- tive of purulent sputum is likely to be suffering from bacterial pneumonia. Leukocytosis with a predomi- nance of neutrophils and distinct (new) infiltrate(s) on chest radiograph are strong supporting data. Lobar pneumonias often have detectable air bron- chograms in the zone of infiltration (Fig. 26-1). Sputum that demonstrates an overwhelming pro- Table 26-1.  Conditions Promoting Lung Inoculation Aspiration Depressed consciousness Swallowing disorders Nasogastric and tracheal tubes Hematogenous seeding (e.g., endocarditis)  Bacteremia  Fungemia Infected aerosols Contaminated ventilator tubing and humidifiers

portion of neutrophils, intracellular organisms, and the predominance of a single morphologic bacterial form further strengthens the case. Finally, the diag- nosis is established unequivocally by recovering the same organism from blood and sputum or pleural fluid cultures. The presentation is not always clas- sic, even with community-acquired pneumonia: fever may be mild, infiltrates may be subtle, and self-medication with antibiotics often obscures a bacteriologic diagnosis. In the ICU, making a correct clinical diagnosis of pneumonia can be difficult for several reasons. Fever and leukocytosis are nonspecific, and patients often have several potential nonpulmonary sites to explain these findings. In addition, the radiographic infiltrates that suggest pneumonia are mimicked by atelectasis, aspiration pneumonitis, pulmonary embolism and infarction, pleural effusion, and pul- monary edema (Fig. 26-2). Computed tomography Table 26-2.  Conditions Favorable to Proliferation of Microorganisms in Lung Impaired immunity Parenchymal necrosis Malnutrition Steroids/cytotoxic drugs Chronic alcohol abuse Diabetes Secretion retention Atelectasis Smoking Obstructive lung disease Neuromuscular weakness Acute respiratory distress syndrome Viral infections

FIGURE 26-1. Air bronchograms in setting of pneumonia. Air bronchograms are usually best detected by CT scanning.