Chapter 11 Intensive Care Unit

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SECTION 1 • Techniques and Methods in Critical Care

Intra-aortic Balloon The intra-aortic balloon (IAB) is an inflatable device placed in the proximal aorta to assist the failing ven- tricle. Diastolic inflation of the balloon produces a distinct, rounded lucency within the aortic shadow, but in systole, the deflated balloon is not visible (whereas the supporting catheter is). Ideal posi- tioning places the catheter tip just distal to the left subclavian artery. Placed too cephalad, the IAB may occlude the carotid or left subclavian artery. Placed too caudally, the IAB may occlude the lumbar or mesenteric arteries and produce less-effective coun- terpulsation. Daily radiographic assessment is pru- dent to detect catheter migration or a change of the aortic contour suggestive of IAB-induced dissection. Gastric Access Tubes Whether inserted through the nose (NG) or mouth (OG), it is usually prudent to obtain a CXR to con- firm gastric tube position before administration of medication, fluid, or feeding, even when clinical evaluation indicates proper positioning. Even in intubated patients, a small number of tubes intended for the stomach do end up in the lung (usually the right mainstem bronchus). Vigorous insertion tech- nique can force the gastric tube through the lung into the pleural space. Inadvertent airway entry is most likely to occur when using a small-bore-stylet- stiffened tube, especially when inserted in comatose or deeply sedated patients. When inserted via the esophagus, the side holes of the enteral tube should be fully advanced past the lower esophageal sphinc- ter to minimize reflux. Following similar safety pre- cautions, an abdominal film should be obtained after placement of a percutaneous endoscopic gastric (PEG) tube to search for common complications, such as extragastric migration or peritoneal leakage. As already mentioned the outset of this discussion, it must be recognized that the chest CT offers far greater diagnostic precision than the bedside radio- graph. Yet, for many purposes, the humble bed- side chest radiograph remains indispensible, being cheaper and quicker to obtain, presenting less expo- sure to ionizing radiation, and sparing the patient the hazards associated with transport from the ICU environment. Specific Applications of Chest Radiography

Atelectasis Atelectasis is a frequent cause of infiltration on ICU CXRs. The wide spectrum of findings ranges from invisible microatelectasis, through plate, segmental, and lobar atelectasis, to collapse of an entire lung. Differentiating between segmental atelectasis and segmental pneumonia is often difficult, because these conditions often coexist. However, marked volume loss, rapid onset, and quick reversal are more characteristic of acute collapse. Atelectasis tends to develop in dependent regions and, more commonly, in the left rather than the right lower lobe by a 2:1 margin. Radiographic findings of atelectasis include hemidiaphragm elevation, parenchymal density, vascular crowding (especially in the retrocardiac area), deviation of hilar vessels, ipsilateral mediastinal shift, and loss of the lateral border of the descending aorta or heart. Each lobe has a characteristic pattern of atelecta- sis. With right upper lobe collapse, apical density increases as the minor fissure rotates superior medi- ally producing an easily recognizable curvilinear arch extending to the mediastinum. Because the left lung does not have a middle lobe or minor fissure, upper lobe collapse occurs anteriorly, producing a diffuse haziness of the hemithorax and loss of the upper left cardiac border. In both cases, the main pulmonary artery shadow moves cephalad. On lat- eral CXR, right middle lobe atelectasis appears as a prominent wedge with its apex directed toward the hilum, as the minor fissure and major fissure move toward each other. Unfortunately, on frontal films, the findings are typically more subtle, often mani- fest only as obscuration of the right heart border. A lordotic film increases the density and sharpens the definition of the airless but thin right middle lobe. Partial collapse of either the right or left lower lobe produce similar patterns of diaphragmatic “silhou- etting.” When lower lobe volume loss is extensive, a triangular posteromedial density can be seen with its base resting on the diaphragm. Contrary to popu- lar belief, the “silhouette sign” is not always reliable on portable films, particularly in the presence of an enlarged heart or when the film was obtained in a lordotic or rotated projection. Air bronchograms extending into an atelectatic area suggest that col- lapse continues without total occlusion of the cen- tral airway and that attempts at airway clearance by bronchoscopy or aggressive suctioning, therefore, are likely to fail.