Chapter 11 Intensive Care Unit

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SECTION 1 • Techniques and Methods in Critical Care

areas of ileus over the pancreas, such as the “colon cut-off sign” and the “sentinel loop,” may also help in the diagnosis of pancreatic inflammation. Stomach and Bowel The stomach normally contains some fluid and air, but massive gastric dilation suggests gastric outlet obstruction, gastroparesis, or esophageal intubation. By contrast, the small bowel normally contains little air; gaseous distention indicates ileus or small bowel obstruction. Air–fluid levels of different heights within the same loop of small bowel on an upright film usually indicate mechanical small bowel obstruction and imply residual peristaltic activity. Fluid levels at the same height in a loop of bowel do not necessarily indicate mechanical obstruc- tion. Absence of colonic or rectal gas in patients with small bowel air–fluid levels strongly suggests complete obstruction of the small bowel with distal clearing of gas. Conversely, the presence of gas in the colon (except for small amounts of rectal gas) all but excludes the diagnosis of complete small bowel obstruction. (Incomplete obstruction may be pres- ent, however.) Colonic obstruction because of a sigmoid vol- vulus may be diagnosed via a KUB view that shows massive sigmoid dilation; the sigmoid forms an inverted “U” whose limbs rise out of the pelvis. Apposition of the medial walls of these bowel seg- ments produces a midline soft tissue density whose inferior extent approximates the site of torsion. A variety of conditions leading to ICU admission may produce colonic pseudo-obstruction (Ogilvie syn- drome) in which massive colonic dilation occurs due to diminished parasympathetic activity (see Chapter 36). Radiographically, the CT demon- strates the absence of a distinct transition point, and unlike the frequently encountered adynamic ileus, affects the small bowel to a lesser degree. Although usually managed conservatively, cecal dilatation to greater than 12 cm suggests the possi- bility of impending perforation and prompts decom- pressive interventions. The frequently observed sign of “thumb print- ing” is a useful, highly significant but nonspecific sign of large bowel wall thickening that is most closely associated with ischemia. These nodular indentations appear at regular intervals along the bowel wall and may originate from bowel inflam- mation (Crohn disease or ischemic colitis, C. dif- ficile or pseudomembranous colitis, diverticulitis)

or more chronically in such noninflammatory con- ditions as lymphoma and amyloid. When seen in conjunction with massive colonic dilation and sup- portive abnormalities of vital signs, toxic megacolon is highly likely. Peritoneal Cavity On the supine abdominal radiograph, ascites is demonstrated by diffuse haze, indistinctness of the iliopsoas stripes, centralization of small bowel seg- ments, and abnormal separation of bowel loops. Increased pelvic density characterizes ascites on the upright film. Abnormal gas collections are recognized by their nonanatomic location. Therefore, all gas densities on supine and erect films require explanation. Each must be assigned to an anatomic segment of bowel. Gas may collect under the diaphragm or overlie the liver on erect or lateral decubitus films, respectively. Free air also allows visualization of both sides of the walls of gas-filled bowel. “Bubbly,” curvilinear, or tri- angular gas collections between segments of bowel suggest abdominal abscess. Bowel ischemia may produce a characteristic pattern known as pneuma- tosis cystoides that represents gas within the bowel wall. Rarely, pneumatosis may rupture to produce free intraperitoneal air, simulating a perforated vis- cus. Bowel ischemia is more confidently diagnosed when thumb printing is observed. ACUTE CARE ULTRASOUND Few areas of critical care practice have been adopted as quickly or impacted care as profoundly as the bedside application of US imaging by the clinician. Although its full potential for diagnosis and moni- toring continue to be actively explored, dramatic advantages have become apparent for settings as diverse as cardiopulmonary arrest to weaning from mechanical ventilation. Its major benefits include portability, lack of radiation hazard, speed of data acquisition, low cost, serial repeatability, and ability to interrogate dynamic properties of the lungs and heart by two-dimensional and time-based (M-mode) imaging displays. Development and deployment have been especially rapid in the general diagnostic categories of acute dyspnea, trauma, and shock. US has proven itself to be an invaluable aid in vascular cannula insertion (venous and arterial) as well other bedside procedures, both facilitating those other- wise time-consuming interventions and preventing