Chapter 11 Intensive Care Unit

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SECTION 1 • Techniques and Methods in Critical Care

are both contraindicated by renal insufficiency. Angiography can be safely performed in most criti- cally ill patients, provided that: (1) care is used in transport, (2) pulmonary artery pressures are not excessive at the time of contrast administration, and (3) selective injections guided by perfusion scanning are performed. Septic PE should be considered in patients with multifocal cavitary lesions of varying size. A complete discussion of thromboembolism diagnosis is presented in Chapter 23. Although bacterial infection sometimes super- venes, gastric aspiration initially produces a sterile chemical pneumonitis. When bacterial infection complicates aspiration in the intubated patient, the time from intubation to aspiration can provide valuable clues to the etiologic organism. Events occurring within 4 days of intubation are usually associated with Staphylococcus , Streptococcus , and Haemophilus infections, whereas later episodes are usually because of gram-negative rods. Massive aspiration, although position and volume depen- dent, typically appears as bilateral diffuse alveolar and interstitial infiltrates of rapid onset. The extent of the infiltrate does not correlate with outcome, and radiographic improvement often occurs quite rapidly. Aspiration in the supine position usually affects the perihilar regions and superior and basilar segments of the lower lobes. Patients who aspirate in a decubitus position often develop unilateral infil- trates. When asymmetrical, the right lung is usually more involved. Significant atelectasis may occur when large pieces of solid food or foreign objects (e.g., teeth, dental appliances) are aspirated. On occasion, massive symmetrical aspiration and/or ARDS can be difficult to distinguish from acute pulmonary edema (Fig. 11-10). As discussed in Chapter 24, several CXR cues may help in mak- ing that distinction. Blurred hilar structures and the virtual absence of air bronchograms characterize acute pulmonary edema and fluid volume overload. Pneumonia Although the CXR is never diagnostic micro- biologically, it may give a clue to the organism pro- ducing bacterial pneumonia. Common bacterial pathogens typically produce patchy segmental or lobar involvement. Bulging fissures, although uncommon, Pneumonitis Aspiration and Acute Pulmonary Edema

suggest Klebsiella . A diffuse, patchy, “ground-glass” appearance suggests Legionella , Mycoplasma , or Pneumocystis . Small, widely scattered nodular den- sities suggest Mycobacterium tuberculosis as the etiological organism. Larger nodular densities are asso- ciated with Cryptococcus , Actinomycosis , or Nocardia. Aspergillus often gives rise to peripheral wedge-shaped infiltrates caused by vascular invasion and secondary infarction or cavitary formation. Cavitation suggests neoplasm, tuberculosis, fungal infection (e.g., his- toplasmosis, cryptococcosis, coccidioidomycosis), lung abscess, or septic PE. Pneumonitis that devel- ops in preexisting areas of bullous emphysema often produces air–fluid levels that can be confused with lung abscess or empyema. The thinner contour of the cavity wall, the more rapid pace of development and resolution, and premorbid CXRs demonstrating bul- lae help to identify this problem. Nosocomial- or ventilator-associated pneumonia affects up to 30% of patients with ARDS but is diffi- cult to detect with certainty because focal parenchy- mal densities may represent edema, atelectasis, and infarction, as well as infection. Hence, radiographic abnormalities must be interpreted in light of the clin- ical situation. A new unilateral infiltrate in a patient with a previously stable CXR is the best radiographic indicator of a superimposed infection; however, fever, increased sputum production, and progressive hypoxemia are better indicators than the CXR alone. A focal wedge-shaped infiltrate (especially occurring FIGURE 11-10. Radiographic appearance of pulmonary edema. Note the virtual absence of air bronchograms and the bilaterally indistinct hilar shadows.