Although multiple diagnostic modalities exist to detect intra-abdominal injuries, no study is fail proof. Therefore, a combination of careful physical exam, attention to the mechanisms and circumstances of injury, and judicious selection of diagnostic studies is used for diagnosis. Hemodynamic instability may limit the utilization of some diagnostic testing before definitive treatment is initiated (such as laparotomy or transfer to a trauma center).
Not every patient with multisystem or isolated abdominal trauma will need a diagnostic evaluation beyond a physical exam. However, because the consequences of a missed intra-abdominal injury may be significant, augment an initial exam with laboratory analysis, imaging study, or repeat examination in several conditions (Table 263-1).
TABLE 263-1Abdominal Injuries That Need Expanded Evaluation ||Download (.pdf) TABLE 263-1 Abdominal Injuries That Need Expanded Evaluation
Presence of abdominal pain, tenderness, distention, or external signs of trauma
Mechanism of injury with a high likelihood of causing an abdominal injury
Suspicious lower chest, back, or pelvic injury
Inability to tolerate a delayed diagnosis (e.g., patients who are elderly, on anticoagulants, or have liver cirrhosis/portal hypertension)
Presence of distracting injuries
Altered consciousness/sensorium (e.g., CNS injury, intoxicating substances)
The focused assessment with sonography for trauma (FAST) examination is a widely accepted primary diagnostic study. The underlying premise of the FAST exam is that many clinically significant injuries will be associated with free intraperitoneal fluid (Figure 263-1). The greatest benefit of FAST is the rapid identification of free intraperitoneal fluid in the hypotensive patient with blunt abdominal trauma.
Hemoperitoneum. The abdominal IV contrast CT. A. A fractured spleen with surrounding hematoma is demonstrated, but a small stripe of fluid is also present above the right kidney in Morrison's pouch. B. A right intercostal oblique US view from the same patient reveals a thin stripe of fluid in Morrison's pouch. [Reproduced with permission from Ma OJ, Mateer JR, eds: Ma and Mateer's Emergency Ultrasound, 3rd ed. © 2014, McGraw-Hill, Inc. New York.]
Advantages of the FAST examination are that it is accurate, rapid, noninvasive, repeatable, and portable, and involves no nephrotoxic contrast material or ionizing radiation exposure to the patient. There is limited risk for patients who are pregnant, coagulopathic, or have had previous abdominal surgery. The average time to perform a complete FAST examination of the thoracic and abdominal cavities is 4 minutes or less.9 Massive hemoperitoneum is quickly detected with a single view of Morrison's pouch in 82% to 90% of hypotensive patients,10,11 and this maneuver required an average of only 19 seconds in one study.10 One major advantage of the FAST examination compared to diagnostic peritoneal lavage (DPL) is the ability of FAST to also evaluate for free pericardial or pleural fluid and for pneumothorax.
The main disadvantage of US compared to CT is the inability to identify the exact source of free intraperitoneal fluid. This limitation may change with the adoption of contrast-enhanced US for the identification and treatment of solid organ injuries.12,13 Other potential disadvantages of the FAST examination are the operator-dependent nature of the examination, the difficulty in interpreting the images in patients who are obese or have subcutaneous air or excessive bowel gas, and the difficulty in distinguishing intraperitoneal hemorrhage from ascites. The FAST examination also cannot evaluate the retroperitoneum as well as CT. Therefore, US and CT are complementary rather than competing technologies when time permits and the potential benefits of CT outweigh the risks.
US has other useful applications in the trauma bay. For example, US may guide the placement of a suprapubic catheter when indicated. The inferior vena cava diameter of trauma patients, as measured on initial CT imaging, is a marker of intravascular volume and a predictor of mortality.14,15 Although the best modality to measure inferior vena cava diameter is debated,16 US can be a clinically helpful tool for trauma resuscitation.
Because the FAST examination can reliably detect small amounts of free intraperitoneal fluid and can estimate the rate of hemorrhage through serial examinations, US has essentially replaced DPL for blunt abdominal trauma in the majority of North American trauma centers. A positive DPL in isolation is no longer an absolute indication for exploratory laparotomy; the amount of hemorrhage and the hemodynamic status of the patient are important factors for determining further management steps.
Abdominopelvic CT with IV contrast is the noninvasive gold standard study for the diagnosis of abdominal injury (unless the patient has allergy to iodinated contrast). The addition of PO contrast can result in aspiration and is too time-consuming to be practical in trauma management. Although most institutions use IV contrast CT for trauma assessment, there are still some institutions that use noncontrast CT or add PO contrast in the evaluation of trauma.17 The major advantage of IV contrast CT over other diagnostic modalities is that the precise location(s) and grade of injury can be identified (Figure 263-1). CT can quantify and differentiate the amount and type of free fluid in the abdomen. Because CT can evaluate for retroperitoneal injuries, it is the ideal study for assessment of the duodenum and pancreas. The use of multiphasic CT (arterial, portal, and equilibrium phases) accurately identifies life-threatening mesenteric hemorrhage and transmural bowel injuries.5 CT evidence of a flat inferior vena cava suggests hypovolemia.
Some patients with free intraperitoneal fluid seen on CT with IV contrast but without an obvious solid visceral injury may have a very small liver or splenic injury that is missed by CT, although mesenteric or small bowel injuries must also be considered. Often the safest course is surgical exploration to avoid late diagnosis of GI perforation or ischemia. Careful observation and repeat CT with the addition of oral contrast is also an option.
Two distinct disadvantages of CT are the ionizing radiation burden and the need to leave the trauma bay to obtain imaging. Radiation is of great concern in children and young adults. Although CT is the most sensitive modality, use it judiciously based on the clinical circumstances. Furthermore, limit the practice of repeat CT imaging following transfer to another facility whenever possible. Outcomes and time to definitive care are not significantly improved when imaging is repeated at the accepting trauma center.18
DIAGNOSTIC PERITONEAL LAVAGE
Despite the reproducibility and prospectively validated sensitivity of DPL to diagnose intraperitoneal injury, the advent and acceptance of other diagnostic modalities have reduced the frequency of DPL.19 DPL can be performed using a closed (Figure 263-2) or open technique. However, the open DPL technique requires advanced training and expertise. Some advocate the use of DPL in the hemodynamically unsTable patient with concern for intra-abdominal injury when the FAST exam is negative.19 Table 263-2 lists criteria for laparotomy based on DPL results.20
TABLE 263-2Criteria for Positive Diagnostic Peritoneal Lavage ||Download (.pdf) TABLE 263-2 Criteria for Positive Diagnostic Peritoneal Lavage
>10 mL free flowing blood immediately on aspiration
>15,000 RBC/mm3 in abdominal wounds or >25,000 RBC/mm3 in lower chest wounds
Closed diagnostic peritoneal lavage. Drain the urinary bladder. Infiltrate the area just below the umbilicus with lidocaine and epinephrine. Insert the needle two fingerbreadths below the umbilicus. Aspirate directly with a syringe attached to the needle, or insert a guidewire into the abdomen and place the peritoneal lavage catheter over the guidewire. Instill 1 L of normal saline through the catheter, and then aspirate.
DIAGNOSIS IN PENETRATING TRAUMA
The same diagnostic tools are available for evaluation of intraperitoneal injury in the patient with penetrating trauma (CT, US, and DPL). Mandatory exploration for patients sustaining a stab wound to the abdomen has yielded unacceptably high rates of nontherapeutic laparotomy,21 yet physical exam alone can miss important intra-abdominal injuries. Locally explore anterior abdominal stab wounds (Figure 263-3) to assess for violation of the peritoneum. Patients with transabdominal gunshot wounds almost always have intra-abdominal injuries. In the hemodynamically sTable patient with penetrating trauma, CT can help guide the surgeon for operative versus nonoperative management.22
Local abdominal wound exploration for anterior abdominal stab wounds. This is a surgical procedure requiring expertise, proper instrumentation, and lights. Use only for anterior abdominal stab wounds. Widen the stab wound and explore down to the level of the fascia to determine if the anterior fascia and/or posterior fascia have been violated.