Epidemiology

Since the 1960s, U.S. mortality rates of 9.5% to 12.7% for civilian gunshot wounds and up to 3.6% for stab wounds have been reported. Most deaths caused by penetrating trauma take place in the first 24 hours; about 70% occur in the first 6 hours of the patient’s course, most commonly in the emergency department (ED), followed by the operating room. Most of these patients tend to have vascular injuries and succumb to exsanguination or refractory hemorrhagic shock.¹ If patients survive the first 24 hours, later deaths tend to cluster after 72 hours and are related mainly to acute systemic complications such as multiple system organ failure, acute respiratory distress syndrome, pulmonary embolism, and pneumonia.^2,³

Management of penetrating abdominal trauma has undergone many changes over the last 20 years. Major transformations include rapid transport to trauma centers, “scoop and run” protocols in the field, damage control surgery, increased use of interventional radiologic techniques, and recognition and treatment of abdominal compartment syndrome. Better diagnostic studies, including rational use of computed tomography (CT) and ultrasonography, as well as expanded use of laparoscopy, have also improved morbidity rates, but no marked change in mortality has occurred.¹ Although management of patients with obvious peritonitis or hypovolemic shock remains essentially unchanged from the perspective of the emergency physician (EP), a patient without obvious intraperitoneal injury still presents a diagnostic dilemma. The benefits of nonoperative management, when performed appropriately, include lower hospital costs, less morbidity, and shorter hospital stays.^4,⁵

Pathophysiology

Physiologic evaluation of patients with penetrating abdominal trauma concentrates on two major findings related to the pathophysiologic basis of the injury—peritonitis and hemodynamic instability. Peritonitis develops when the peritoneal envelope and the posterior aspect of the anterior abdominal wall are inflamed by enteric contents. Intraperitoneal or retroperitoneal blood and organ contents inflame the deeper nerve endings (visceral afferent pain fibers), thereby resulting in poorly defined and localized pain. Direct contact of the parietal peritoneum with blood or bowel contents can cause inflammation, which may be manifested as tenderness on palpation of the abdomen, as well as involuntary guarding of the abdominal wall musculature. Patients may also have referred pain. Because of the afferent, embryologically related pain fibers that ascend during development, a back or shoulder distribution of pain may provide a clue to the damaged organ (e.g., left shoulder pain from splenic rupture with subphrenic blood). Even though penetrating trauma is associated with multiple specific mechanisms, for most purposes it is divided into low- and high-energy injury; in general, these categories correlate with stab wounds or gunshot wounds. Gunshot wounds may be further divided into low- and high-velocity injuries, although both have the ability to cause secondary injury by energy transfer, fragmentation, and secondary missiles such as bone fragments. Handguns and lower-caliber rifles such as .22 gauge tend to have lower energy transfer than do military rifles and hunting rifles. Shotgun injuries, despite having lower velocity, often cause massive tissue damage if the wound is sustained at close range (i.e., less than 3 feet).

Presenting Signs and Symptoms

The anterior part of the abdomen is the region between the anterior axillary lines from the anterior costal margins to the groin. The thoracoabdominal area is the region in which an injury can enter the chest, abdomen, or both. In addition to the anterior abdominal boundaries, it includes the lower part of the chest bordered by the nipple line or the fourth intercostal space anteriorly, the sixth intercostal space laterally, and the inferior scapular tip posteriorly because the diaphragm may extend to this level with expiration. The flank is the area between the anterior and posterior axillary lines bilaterally and ranges from the sixth intercostal space to the iliac crest. The back is bordered by the posterior axillary lines, with the inferior scapular tip located superiorly and the iliac crest inferiorly. In addition, depending on the type of penetrating object, simultaneous abdominal and thoracic penetration may be present. Within the abdominal cavity, both the intraperitoneal and retroperitoneal organs may be injured. The intraperitoneal organs include the liver, spleen, small bowel, transverse colon, gallbladder, and bladder. The retroperitoneal structures include the duodenum, pancreas, kidneys, ureters, bladder, ascending and descending colon, aorta and branching vessels, and rectum.⁶

Classic teaching is that the majority (about 90%) of gunshot wounds to the abdomen penetrate the peritoneum.⁷ However, recent studies looking at nonoperative management show that a larger number of nontangential wounds do not penetrate. If a patient is initially stable and peritoneal signs are absent, the rate is probably closer to about 40%; however, abdominal gunshot wounds associated with peritonitis or instability have penetrated the peritoneum.^8,⁹ The majority of wounds that penetrate the peritoneum require laparotomy for repair. The most commonly injured organs are the small bowel, colon, and liver, followed by vascular structures, the stomach, and the kidneys (Box 80.1).

Box 80.1 Approximate Percentage of Organs Injured with Penetrating Trauma

Stab Wounds

Gunshot Wounds

Small bowel (50%)

Colon (40%)

Liver (30%)

Abdominal vasculature (25%)

Stab wounds, as opposed to gunshot wounds, tend to follow the track of the wound and have more predictability. Approximately one fourth to one third of anterior abdominal stab wounds penetrate the peritoneum. Of those that do penetrate, about one third cause intraabdominal injury that requires operative repair. In addition to wounds involving the abdominal cavity, injuries to the thoracic cavity must also be considered in patients with thoracoabdominal stab wounds or any gunshot wound.

Physical examination often plays a major role in the management of patients with penetrating abdominal trauma, especially those who are hemodynamically stable. Serial examinations are a common and time-tested management strategy for low-velocity wounds. Studies show that it is an effective approach and that delay in diagnosis, if less than 24 hours, does not lead to a significant increase in complications. Furthermore, the decrease in morbidity and cost of nontherapeutic laparotomy is considerable.¹⁰^–¹² In fact, in some centers, even patients with evisceration (especially omentum alone) without peritonitis are observed successfully after replacement of the eviscerated peritoneal contents, although such management remains controversial.¹³^–¹⁵

Differential Diagnosis and Medical Decision Making

Examination may be used as a sole modality or in conjunction with other modalities. In patients with an anterior stab wound, local wound exploration can be a valuable diagnostic aid and should shorten a prolonged evaluation or observation if the results are negative. Its utility is dependent on the wound’s mechanism and location. Stab wounds involving the anterior aspect of the abdomen are well suited for local wound exploration because many do not penetrate the fascia and can easily be visualized. Back, flank, and thoracoabdominal wounds do not allow clear delineation of the wound track and extent and are not candidates for this procedure. Likewise, this is a poor option for gunshot wounds or wounds from a sharp pinpoint instrument (e.g., ice pick).

Over the last decade, patients with gunshot wounds have also been managed by serial observation, though generally in conjunction with some other modality, usually CT. The length of observation varies by institution. Standard practice is usually a 24-hour observation period, but recent data suggest that all important injuries will become apparent within a 12-hour period.¹⁶ Until more data are available or a clear institutional protocol has been established, approximately 24 hours of observation seems appropriate.

Diagnostic Modalities

Plain Radiography

Although plain abdominal radiography rarely adds to the evaluation of patients with blunt abdominal trauma, in cases of penetrating trauma with projectiles or retained foreign bodies it allows one to account for bullets, shrapnel, and foreign bodies. If all foreign bodies are not accounted for, one must consider the possibility that the foreign body is intraluminal or intravascular and a potential source of emboli. In patients with stab wounds or injuries without a foreign body, radiography’s utility lies in ruling out a broken instrument in the abdomen or in evaluating a large amount of free air consistent with a hollow viscus injury.

In thoracoabdominal trauma, chest radiography can identify the presence of hemothorax, pneumothorax, and possibly diaphragmatic injury. Unfortunately, its sensitivity for pneumothorax is variable, and at least two separate radiographs 4 to 6 hours apart must be taken to exclude clinically significant pneumothorax. Diaphragmatic injuries are seen clearly on plain radiographs only about 30% of the time. They cannot be excluded on the basis of normal radiographic findings.

Ultrasonography

Focused abdominal sonography for trauma (FAST) is a useful test if positive (i.e., free fluid is found during the examination). Several authors have shown specificity and positive predictive values in the low 90th percentile for therapeutic laparotomy if ultrasound reveals free fluid. A positive ultrasound finding after penetrating abdominal trauma should lead to exploration by either laparotomy or laparoscopy. Unfortunately, although its specificity is very high, its sensitivity ranges from 21% to 70%, which is not acceptable to rule out an injury requiring laparotomy.¹⁷^–²¹ Therefore, FAST findings negative for free fluid should be considered indeterminate, and further observation or testing is required. FAST should be able, in trained hands, to rule out significant pericardial effusion after thoracoabdominal trauma.

Computed Tomography

The expanded use of CT is a major change in the initial evaluation of patients with penetrating trauma in the past decade. In the past, use of CT had been limited in patients with penetrating abdominal trauma because of the high incidence of bowel injury and its lack of sensitivity in diagnosing bowel and mesenteric injuries, as well as rents in the diaphragm. The newest-generation CT scanners (i.e., multidetector scanners), as well as increased familiarity with their use, have markedly improved resolution and diagnostic capabilities. It is generally agreed that CT scanning of stab wounds in stable patients without the need for immediate laparotomy is a useful approach and can obviate admission when the wound is found to be superficial. In addition, it may reveal the path of a knife, identify or rule out peritoneal violation, and show with increasing sensitivity signs of hollow viscus perforation (free intraperitoneal air, unexplained free fluid, or bowel edema). These signs remain excellent in diagnosing solid organ injury. In addition, CT may show a “contrast blush,” a sign of active bleeding or false aneurysms in patients with solid organ injuries, and may establish whether early laparotomy or angiographic intervention is warranted.²² Although the negative predictive value of the need for operative intervention is high, patients with peritoneal penetration and no other clear operative requirements still merit an overnight observation period. In the case of gunshot wounds the literature is a bit less clear, but it generally shows that for tangential wounds in a stable patient, CT is excellent for ruling out abdominal penetration.

Even though it has not been shown to have high enough sensitivity to rule out diaphragmatic injuries, CT has improved and may one day be useful for this role.²¹ CT is now accepted for use in stable patients with penetrating flank trauma. “Triple-contrast” (intravenous, oral, rectal) CT has been found to be highly sensitive in diagnosing injuries to retroperitoneal structures, including bowel and renal injuries. At this time, however, its sensitivity is too low to fully exclude a bowel injury, and a negative CT scan should be followed by a period of observation, usually 24 hours. The one caveat is that it should be clear on CT that the wound track is superficial and that no intraperitoneal or retroperitoneal penetration has occurred.