Chapter 11 Intensive Care Unit

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CHAPTER 11 • Intensive Care Unit Imaging

FIGURE 11-4. Appearance of a mobile pleural effusion in three positions. In the supine position, a “ground-glass” lateralized diffuse density (with preservation of vascular markings) may be the only sign of layered pleural fluid. A changing appearance with position confirms the diagnosis.

Pleural Effusion and Hemothorax Pleural effusions occur very commonly among ICU patients; however, their appearances vary with body positioning (Fig. 11-4). On the supine AP CXR, large effusions redistribute—potentially causing a hazy density to overlie the entire hemithorax without loss of vascular definition (Fig. 11-5). Apical pleural capping is another radiographic sign of large collec- tions of pleural fluid in the supine patient. Upright or lateral decubitus radiographs may help confirm the presence of an effusion (Fig. 11-6). If a large collec- tion of pleural fluid obscures the lung parenchyma, a contralateral decubitus film often helps visualize the ipsilateral lung. Pleural fluid is not ordinarily visible until several hundred milliliters have accumulated. On lateral decubitus films, 1 cm of layering fluid indicates a volume that can usually be tapped safely. If there is any question about the quantity or mobility of fluid, bedside ultrasonography is usually helpful.

Subpulmonic or loculated fluid may be diffi- cult to recognize. Hemidiaphragm elevation, lateral displacement of the diaphragmatic apex, abrupt transitions from lucency to solid tissue density, and increased distance from the upper left hemi- diaphragmatic margin to the gastric bubble (on an upright film) are all signs of a subpulmonic effusion (Fig. 11-7). US and chest CT are useful adjuncts in detecting the presence of such collections of pleural fluid and in guiding drainage. US has the obvious advantages of portability, repeatability, cost effi- ciency, safety, and real-time imaging for drainage. Extra-alveolar Gas/Barotrauma Extra-alveolar gas can manifest as interstitial emphysema, cyst formation, pneumothorax, pneu- momediastinum, pneumoperitoneum, or subcuta- neous emphysema (see Chapter 8). Pulmonary Interstitial Emphysema Radiographic signs of gas in the pulmonary intersti- tium include lucent streaks that do not conform to air bronchograms and new cysts at the lung periph- ery, usually at the bases. Interstitial emphysema may also generate small “target lesions” as air surrounds small peripheral pulmonary arterioles viewed en face. These signs, best seen when the parenchyma is densely infiltrated, portend the imminent (but not invariable) development of pneumothorax. Subpleural Air Cysts Subpleural air cysts, a potential sign of impending pneumothorax in mechanically ventilated patients, are small (3- to 5-cm wide) basilar rounded lucen- cies. The cysts often appear abruptly and tend to rapidly increase in size (sometimes to as large as 9 cm). Subpleural air cysts frequently progress to tension pneumothorax in the presence of contin- ued high-pressure mechanical ventilation. The role of prophylactic tube thoracostomy remains undefined; however, when subpleural air cysts are

FIGURE 11-5. Mobile right pleural effusion supine. Diffuse haziness with well-preserved outlines of the ipsilateral pulmonary arteries are characteristic.