Chapter 11 Intensive Care Unit

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SECTION 1 • Techniques and Methods in Critical Care

FIGURE 11-17. Options for MRI display (normal brain, axial view). T1-weighted brightness corresponds to fat content, and details the anatomy particularly well. T2 weighting tends to highlight pathology associated with higher water content, such as cerebral edema or inflammation. The Flair image attenuates the CSF brightness of the T2 image and therefore is particularly helpful in distinguishing details of pathology. Diffusion-weighted images (DWI, not shown) are the best option for distinguishing well perfused from ischemic tissues, as in early stroke.

ABDOMINAL RADIOGRAPHY Abdominal CT and Screening Films (KUB) Because plain abdominal X-rays have largely been replaced by the abdominal CT scan, it is prudent for the acute care practitioner to become familiar with its essential elements (Fig. 11-18). The use of abdomi- nal US and CT scanning is discussed in detail, as it relates to specific disease entities in Chapter 36. The standard examination of the abdomen, consist- ing of supine kidney–ureter–bladder (KUB) or “flat plate” and upright views, can still be useful and does not require a trip outside the ICU. If an upright film cannot be taken, a lateral decubitus view may be substituted. Systematic review of the KUB may fur- nish important information, especially after trauma. Fractures of the lower ribs on the left suggest the possibility of a ruptured spleen or lacerated kidney as does medial displacement of the gastric bubble. Breaks in lower ribs on the right suggest the possibil- ity of renal or hepatic damage. Fractures of the lum- bar spine, pelvis, and hips may be seen as “incidental” findings on plain abdominal radiographs in trauma patients. A ground-glass appearance, displacement of the retroperitoneal fat stripe, or centralization of gas shadows suggests ascites or hemoperitoneum. Free air usually indicates a ruptured viscus, gas-producing infection, barotrauma-induced pneumoperitoneum,

fever or with a persistent pneumothorax, the chest CT is invaluable to evaluate the location and effec- tiveness of thoracic drainage tubes. From a scien- tific standpoint, CT scanning has added greatly to our understanding of the distribution and positional kinetics of acute lung injury (ARDS). CT scanning also demonstrates the severity and distribution of regional barotrauma, offering insight into the poten- tial deleterious effects of excessive airway pressure. Normal-appearing lung is seen immediately juxta- posed with densely infiltrated lung. These normal- appearing and presumably normally compliant lung units are likely to be overdistended or overstrained by elevated positive pressure, whereas densely infil- trated lung is likely to remain atelectatic. The physi- ologic result is shunting of blood past atelectatic alveoli and overdistention of other alveoli, predis- posing them to rupture or VILI. In summary, the chest CT represents one of the most useful diagnostic tests available to inten- sive care practitioners. A short list of indications for chest CT scanning include (1) evaluation of tho- racic trauma, (2) searching for occult or persistent sources of fever (empyema, lung, or mediastinal abscess), (3) guiding placement of drainage tubes for loculated or persistent pneumothorax or pleu- ral effusions, (4) detecting mediastinal pathology (especially in the presence of parenchymal infil- trate), and (5) searching for pulmonary emboli.