Laboratory Studies
A complete blood count (CBC) may reveal parameters suggestive of infection (eg, leukocytosis), though leukocytosis may be absent in elderly patients. Elevated packed blood cell volume suggests a shift of intravascular fluid. Blood culture for aerobic and anaerobic organisms is indicated. Findings from liver function and renal function tests may be within reference ranges (or nearly so) if no preexisting disorder is present.
Imaging Studies
Radiography
Erect radiographs of the chest are recognized as the most appropriate first-line investigation when a perforated peptic ulcer is considered likely. [15] However, in approximately 30% of patients, no free gas can be identified. Thus, an erect posteroanterior chest radiograph is not sufficiently sensitive to rule out pneumoperitoneum in patients presenting with upper abdominal pain.
Plain supine and erect radiographs of the abdomen are the most common first steps in the diagnostic imaging evaluation of patients presenting with medical history and/or clinical signs suggestive of bowel perforation. Findings suggestive of perforation include the following:
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Free air trapped in the subdiaphragmatic locations - If the quantity of free air is great enough, its presence can be visualized on the supine radiograph of the abdomen, allowing clear definition of the inner and outer surface of the wall of the bowel
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Visible falciform ligament - The ligament may appear as an oblique structure extending from the right upper quadrant toward the umbilicus, particularly when large quantities of gas are present on either side of the ligament
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Air-fluid level - This is indicated by the presence of hydropneumoperitoneum or pyopneumoperitoneum on erect radiographs of the abdomen
Water-soluble radiologic contrast media administered orally or through a nasogastric tube can be used as an adjunct diagnostic tool to detect any intraperitoneal leak.
The perforation has sealed at presentation in approximately 50% of patients. For those who favor a nonoperative approach, contrast radiology is routine in the management of these patients.
Ultrasonography
Localized gas collection related to bowel perforation may be detectable on ultrasonography (US), particularly if it is associated with other visible abnormalities (eg, thickened bowel loop). The site of bowel perforation can be detected by US (eg, gastric vs duodenal perforation, perforated appendicitis vs perforated diverticulitis). Ultrasonograms of the abdomen can also provide rapid evaluation of the liver, spleen, pancreas, kidneys, ovaries, adrenals, and uterus.
Computed tomography
Computed tomography (CT) of the abdomen can be a valuable investigative tool, providing differential morphologic information not obtainable with plain radiography or ultrasonography.
CT scans may provide evidence of localized perforation (eg, perforated duodenal ulcer) with leakage in the area of the gallbladder and right flank with or without free air being apparent. They may show inflammatory changes in the pericolonic soft tissues and focal abscess due to diverticulitis (may mimic perforated colonic carcinoma). CT scans may not provide definitive radiographic evidence of perforated Meckel diverticulitis.
Procedures
Laparoscopy may significantly improve surgical decision making in patients with acute abdominal pain, particularly when the need for operation is uncertain.
Peritoneal diagnostic tap may be useful in determining the presence of intra-abdominal blood, fluid, and pus.
Peritoneal lavage is more valuable in the presence of a history of blunt abdominal trauma. The presence of blood or purulent material or the detection of bacteria on Gram stain suggests the need for early surgical exploration. Alkaline phosphatase concentration in the peritoneal lavage is a helpful and sensitive test that may be used to detect occult blunt intestinal injuries. A concentration greater than 10 IU/L has been shown to be a sensitive and reliable test in the detection of occult small bowel injuries.
Fine-catheter peritoneal cytology involves the insertion of a venous cannula into the peritoneal cavity, through which a fine umbilical catheter is inserted while the patient is under local anesthesia. Peritoneal fluid is aspirated, placed on a slide, and stained for examination under a light microscope for percentage of polymorphonuclear cells. A value greater than 50% suggests a significant underlying inflammatory process. This test, however, provides no clue as to the exact cause of inflammation.
