Penetrating Abdominal Trauma Workup

The approach to patients with penetrating abdominal trauma depends on whether the injury is a gunshot wound (GSW) or a stab wound and the patient’s hemodynamic status. GSWs are associated with a high incidence of intra-abdominal injuries and nearly always mandate laparotomy. Stab wounds are associated with a significantly lower incidence of intra-abdominal injuries; therefore, expectant management is indicated in hemodynamically stable patients.

Many protocols have been developed for determination of abdominal wall penetration of stab wounds to the torso, one of which is shown in the diagram below.

Patients with penetrating abdominal trauma generally require complete laboratory profiles in case of need for emergent operation. Many imaging modalities can be useful in the evaluation of a patient with penetrating abdominal trauma. The imaging needs of each patient differ, depending on hemodynamic stability and associated injuries.

In case of need for emergent operation, all patients with penetrating abdominal trauma should undergo certain basic laboratory testing, as follows:

• Blood type and crossmatch
• Complete blood count (CBC)
• Electrolyte levels
• Blood urea nitrogen (BUN) and serum creatinine level
• Glucose level
• Prothrombin time (PT)/activated partial thromboplastin time (aPTT)
• Venous or arterial lactate level
• Calcium, magnesium, and phosphate levels
• Arterial blood gas (ABG)
• Urinalysis
• Serum and urine toxicology screen

Patients who arrive in shock should be typed and cross-matched for 4-8 units packed red blood cells. The CBC provides a baseline value for later comparison, even though it may not reveal the extent of active bleeding. The basic chemistry profile reveals any baseline renal insufficiency or electrolyte abnormalities. Coagulation studies (PT with international normalized ratio [INR] and PTT) may indicate development of coagulopathy. The importance of early coagulopathy of trauma has recently been emphasized. Up to 30% of patients present to the ED with established coagulopathy prior to any resuscitation. Moreover, these patients have significantly increased mortality.

The ABG permits calculation of the anion gap (reference range, 8-12 mmol/L) and base deficit (reference range, ±4 mmol/L) as guides to hypoperfusion. It provides important information regarding acid-base balance and, thus, the hemodynamic stability of the patient.

Urine dipstick testing may reveal occult blood indicative of genitourinary tract injuries. Female patients should have urine pregnancy testing.

Ethanol and drug screens are also standard practice in trauma patients. Studies have shown that even brief intervention and counseling in patients at the time of admission for trauma injury has positive outcomes.

A chest radiograph is obtained on all patients because penetration of the chest cavity cannot be ruled out, even with abdominal stab wounds or even-numbered GSWs (ie, apparent entrance and exit wounds) outside the chest. Chest radiographs can reveal hemothorax or pneumothorax or irregularities of the cardiac silhouette, which can be a sign of cardiac injury or great vessel injury. Air under the diaphragm indicates peritoneal penetration. Chest radiography is relatively specific, although insensitive, for diagnosing diaphragmatic injury.

Abdominal radiographs in 2 views (ie, anterior-posterior [AP], lateral) are also obtained on all patients with GSWs to help determine missile trajectory and to account for retained missiles (ie, bullets, shrapnel, and foreign bodies) in patients with odd-numbered GSWs. If all foreign bodies are not accounted for, consider the possibility that the foreign body is intraluminal or intravascular, and thus is a potential source of emboli distant from the site of entrance.

Ultrasonography has been widely used in the assessment of patients with blunt trauma, but it has only recently been used in the assessment of patients with penetrating injuries. In these cases, the study is performed using the focused assessment with sonography for trauma (FAST). FAST has gained acceptance in the evaluation of penetrating abdominal trauma because of its speed, noninvasiveness, and reproducibility in diagnosing intraperitoneal injury that requires laparotomy.

FAST uses 4 views of the chest and the abdomen (ie, pericardial, right upper quadrant, left upper quadrant, pelvis) to evaluate for pericardial fluid indicative of cardiac injury and for free peritoneal fluid. Free fluid in the abdomen can be a sign of hemorrhage secondary to liver or splenic laceration or, less commonly, of spillage secondary to hollow viscus injury.

While FAST has been found to be 94-98% specific for abdominal injury in penetrating abdominal trauma, its sensitivity of 46-67% is not good.^{[14, 15]} That is, a positive FAST result in the setting of penetrating trauma is usually an indication for laparotomy due to the high positive predictive value for a therapeutic laparotomy. Unfortunately, a negative FAST result cannot rule out the need for laparotomy and cannot be relied on to exclude important intraperitoneal injury; these patients require further testing to rule out occult injury.^{[14, 16]}

Sonographic evaluation of penetrating wounds also has been evaluated in the detection of fascial defects resulting from anterior abdominal stab injuries, reducing the need for local wound exploration. In one prospective trial, a positive fascial sonogram result obviated invasive wound exploration because such patients were then taken to the operating room (OR). However, a negative fascial sonogram result did not rule out a penetration of the peritoneum.^{[17, 18]}

CT scanning is used in the evaluation of patients with stab wounds to the flank and the back and in the evaluation of selected patients with abdominal stab wounds and penetrating, nontangential GSWs. Abdominal CT is the most sensitive and specific study in identifying and assessing the injury severity to the liver or spleen.^[19] The presence of a contrast blush on CT or ongoing hemorrhage is an indication for laparotomy or angiography and embolization.^[20]

Triple-contrast helical CT has been evaluated as a diagnostic modality in hemodynamically stable patients with penetrating torso trauma. Oral, intravenous, and rectal contrasts are administered, and the images are reviewed for evidence of peritoneal penetration and visceral injuries.

Triple-contrast CT has been found to be 97% accurate in the evaluation of penetrating flank and back wounds. Exploration of these wounds is more difficult, less reliable, and therefore not indicated.^[21] One study of CT with IV contrast only found it useful for patients with GSW to the abdomen selected for nonoperative management.^[22]

Specific signs of peritoneal penetration on CT include the following:

• A wound tract outlined by hemorrhage, air, or bullet or bone fragments that clearly extend into the peritoneal cavity
• The presence of intraperitoneal free air, free fluid, or bullet fragments
• Obvious intraperitoneal organ injury

The diagnosis of significant penetrating injury should not be delayed by routinely obtaining CT scans of the abdomen and pelvis. Instead, patients with an appropriate history, physical examination or vital sign abnormalities, in particular with a positive FAST, should undergo expeditious exploration.^[23] There is no place for CT scanning in hemodynamically unstable patients with penetrating abdominal injury.

The primary limitation of CT is lack of sensitivity in diagnosing mesenteric, hollow visceral, and diaphragmatic injuries, all of which are common in penetrating trauma. Therefore, unless the wound is clearly superficial on CT scan, admission and serial observation is indicated, even with a negative CT result for injury.^[24]

No absolute indications exist for CT in anterior penetrating trauma. Some centers use CT as a screening tool to complement physical examination, while others perform serial examination or diagnostic peritoneal lavage (DPL).

In a prospective study of 200 patients, CT was found to be 97% sensitive and 98% specific for peritoneal violation.^[25] Laparotomy based on CT findings in 38 of these patients was considered therapeutic in 87%, nontherapeutic in 8%, and negative in 5%. These results were comparable to others obtained with the use of clinical examination, DPL plus local wound exploration, and DPL alone.^{[26, 27, 28]}

Patient selection is extremely important when considering CT as a diagnostic adjunct in patients with penetrating abdominal trauma. The availability and quality of the CT scan and the experience of the examining radiologist are also key considerations.

Other imaging studies that may be used in patients with penetrating abdominal injury include the following:

• Skeletal survey for associated fractures
• CT scan of the brain for coincident head injuries

Retrograde urethrogram or cystogram in a stable patient who has blood at the urethral meatus or evidence of urethral or bladder injury from penetration

Intravenous pyelography is most often used intraoperatively to assess contralateral renal function in a patient with kidney damage necessitating nephrectomy. Nuclear medicine studies have no role in the acutely injured abdominal trauma patient.

In patients with penetrating abdominal trauma, certain procedures that are necessary for treatment may at times provide diagnostic information.

All patients undergoing endotracheal intubation require decompression of the stomach to decrease the risk of aspiration. Blood in the nasogastric tube can indicate upper gastrointestinal injury.

Foley catheterization insertion is required to monitor the fluid resuscitation status of the patient with penetrating abdominal trauma. The presence of blood in the urine is a sign of genitourinary tract injury.

In the hemodynamically stable patient with penetrating abdominal injury, DPL can be used to identify hollow viscus or diaphragmatic injury. While very sensitive and specific, DPL requires a fair amount of time to perform, and it has been supplanted in many institutions’ protocols by FAST, CT scan, and/or laparoscopy. The primary disadvantages are invasiveness, inability to evaluate the retroperitoneum, moderate specificity for therapeutic laparotomy, and a significant false-positive rate.^[29]

DPL can be performed via either a closed or open method. The bladder and stomach must be decompressed. The closed method involves a small skin puncture with blind insertion of a catheter over a guidewire (ie, Seldinger technique). The open method involves exposure of the peritoneum through a small infraumbilical incision and insertion of catheter under direct vision (ie, mini-laparotomy). A standard DPL catheter is shown in the image below.

Aspiration of gross blood or food particles is positive for peritoneal penetration and organ injury. If aspiration is negative, 1 liter of warm normal saline or lactated Ringer solution (20 mL/kg for pediatric patients) is infused rapidly and allowed to return by placing the intravenous bag on the floor.^[29] The fluid is then sent for analysis (eg, cell count, differential, Gram stain, bilirubin, amylase, vegetable matter, fecal matter).

A positive test result varies with the mechanism of injury. A red blood cell (RBC) count of greater than 100,000/mm³ or white blood cell count of 100-500/mm³ count may be considered positive in a stab wound. However, if a diaphragmatic injury is possible, some physicians lower the value of a positive test to an RBC threshold of 5000/mm³. Because of the more serious nature of gunshot wounds, clinicians often use a similarly lower value for a positive test when there is concern a projectile has entered the peritoneal cavity.^[29]

The lower the threshold for positivity, the more sensitive the test, but the higher the nontherapeutic laparotomy rate (ie, higher rate of false-positive result).

Patients with penetrating wounds to the thoracoabdominal area may require chest tube placement. Absent or significantly decreased unilateral breath sounds necessitate immediate tube thoracostomy to relieve hemothorax/pneumothorax. In other patients, hemothorax/pneumothorax will be identified on chest radiograph.

Traditionally, large-bore (38-40F) chest tubes placed in the midaxillary line at the fifth intercostal space have been recommended for trauma indications. More recently, smaller (12F) pigtail catheters have been used for traumatic pneumothoraces and even hemothoraces. These catheters are more comfortable for the patient and easier to place. These catheters should probably be reserved for hemodynamically stable patients.

Time permitting, liberal local anesthesia is preferred in the patient who is awake. The tube is attached to 20-cm wall suction and a postprocedure chest radiograph is performed to confirm placement, adequate lung re-expansion, or complete drainage of pleural blood. A persistent pneumothorax accompanied by a large air leak may indicate a major bronchial injury requiring repair or further diagnostic evaluation with bronchoscopy. Residual clotted hemothorax is an indication for video-assisted thoracoscopic surgery (VATS) or open thoracotomy to fully evacuate the blood and clot.

In the trauma patient with an anterior stab wound, local wound exploration may be a valuable diagnostic aid, depending on the wound's mechanism and location. Stab wounds to the anterior abdomen are well suited for local wound exploration because many do not penetrate the fascia.

Exploration requires aseptic technique, good overhead lighting, and local anesthesia. The wound is enlarged as necessary so that the posterior fascia may be evaluated. If exploration either confirms that penetration has occurred or is inconclusive, the wound is considered intraperitoneal and must be evaluated further by DPL or more invasive procedures.

Gunshot wounds and those produced by thin instruments, such as an ice pick, are more difficult to explore and, accordingly, are generally considered intraperitoneal injuries.

Once the area is surgically prepared, draped, and anesthetized, the wound may be widened with gentle retraction and gently probed with a hemostat to determine whether a tract exists. If the wound is small, extending it to aid visualization is accomplished with a No. 10 blade scalpel. The rectus fibers may be separated by spreading in their direction using a hemostat or Kelly clamp. The posterior rectus sheath is easily identifiable as a white layer directly underlying the rectus musculature. If yellow fat or omentum is identified, a fascial violation is established.

Laparoscopy is a reasonably safe, effective procedure for the evaluation and treatment of hemodynamically stable patients with abdominal trauma, and it can reduce the number of nontherapeutic laparotomies performed. In thoracoabdominal stab wounds, laparoscopy aids in the diagnosis of diaphragmatic and other intra-abdominal injuries.

Patients with stab wounds to the anterior abdomen or with uncertain peritoneal penetration are also candidates for diagnostic laparoscopy. Gunshot wounds to the anterior abdomen with questionable penetration may be assessed this way.

Multiple studies have shown a reduction in unnecessary laparotomies in patients with a penetrating mechanism but no identifiable organ injury who underwent diagnostic laparoscopy. In one center with significant experience with diagnostic laparoscopy in penetrating abdominal trauma, laparoscopy was associated with decreased cost and length-of-stay when compared with open laparotomy (n=44).^[18]

A retrospective study of 44 laparoscopies in patients with penetrating abdominal trauma found that half of were negative for penetration and resulted in avoidance of laparotomy.^[30] A prospective study of 99 patients showed that diagnostic laparoscopy was negative in 62% of the patients with penetrating abdominal trauma, reducing the rate of unnecessary laparotomy from 78.9% to 16.9%.^[31]

The successful incorporation of diagnostic laparoscopy into the management of patients with penetrating abdominal trauma depends on the selection of hemodynamically stable patients, the availability and ease of use of quality laparoscopic equipment, and the experience of the surgeon in using the technique for diagnostic purposes in traumatic injuries.