SISTEMA GDS

Abdominal Computed Tomography

Diagnostic Peritoneal Lavage Versus Computed Tomography Ultrasound

Therapeutic Versus Nontherapeutic Laparotomy

Diagnostic Peritoneal Lavage and Computer Tomography as Complementary Studies Ancillary Studies

Conclusion

INTRODUCTION

Trauma is the leading cause of death in Americans under the age of 45, and of these fatalities, 10% are attributed to abdominal injury ( 1). Abdominal injuries are often occult, and as many as one-third of the patients with multiple trauma who initially present with a benign abdominal examination will ultimately require emergent

laparotomy (2,3 and 4). A number of diagnostic modalities are used to evaluate the abdomen, and controversies rage over which test is “best.” Today's emergency physician must be aware of the evolution in the workup of blunt abdominal trauma. This chapter will help the physician recognize the advantages and limitations of computerized tomography (CT), diagnostic peritoneal lavage (DPL), and ultrasound in the modern workup of blunt abdominal trauma.

HISTORY AND PHYSICAL EXAMINATION

Certain factors associated with a traumatic event should raise the clinical suspicion of an intra-abdominal injury. Bicyclists and pedestrians struck by cars, victims of motorcycle crashes, and those who fall more than one story are at significant risk (5). Drugs, alcohol, head trauma, and other causes of altered mental status, as well as distracting injuries, render the physical examination less reliable (4). Overall, the initial physical examination in blunt abdominal trauma is only 65% accurate ( 6,7). While a single examination is notoriously inaccurate, serial examinations do play an important role in patient management. Hemodynamically stable patients with a clear sensorium and no significant distracting injuries may not require further diagnostic studies if serial examinations are normal. Diagnostic evaluation of the abdomen generally is indicated in the multiple trauma victim who has an altered sensorium, equivocal abdominal exam, or a history of hypotension. In particular, patients with combined head and abdominal injuries suffer catastrophe when management is guided solely by physical examination. A mortality rate as high as 56% is reported in one series (8). We believe that all unconscious, blunt trauma patients should undergo objective testing of the abdomen with either CT, DPL, or ultrasound. It is clear that normal vital signs do not rule out serious intra-abdominal injury in the comatose patient ( 9).

While many patients at high risk for abdominal injury require diagnostic studies, or at least serial examinations, certain patients need immediate operation without extensive testing. If no other sources of blood loss are present, the patient with a rigid abdomen who presents in frank shock requires only a chest x-ray and a type and crossmatch prior to laparotomy. However, this scenario is uncommon, as most blunt trauma patients have multiple potential sources of blood loss, and

appropriate diagnostics tests may prevent unnecessary laparotomy.

The physical examination begins with inspection. Abdominal distension is occasionally present, but when it occurs it is rarely secondary to hemoperitoneum. Two liters of blood in the peritoneal cavity will cause a nearly imperceptible increase in girth ( 10). The scaphoid abdomen usually represents an ileus, or rarely, a

pneumoperitoneum. Inspect the abdomen to reveal abdominal bruising. Ecchymosis in the distribution of a lap belt should always prompt aggressive investigation for occult bowel injury. While ecchymosis at the umbilicus (Cullen's sign) or the flanks (Gray-Turner's sign) indicates retroperitoneal bleeding, these rare signs take hours to develop. Begin palpation with the lower chest to detect rib fractures that may indicate hepatic or splenic injury. Splenic injury occurs in up to 20% of patients with left lower fractures, and hepatic injury in 10% of patients with right-sided fractures (3,11). Compress and distract the pelvis to determine stability, and palpate the lumbar spine for evidence of fractures. Kerr's sign, pain in the shoulder secondary to irritation of the diaphragm, is present in up to 60% of patients with splenic trauma and may be elicited by placing the patient in the Trendelenburg position. A rectal examination will determine the presence of an abnormal prostate, lack of rectal tone, and heme-positive stools. Digital exam may reveal a “high riding” (bulging outward towards the examining finger) or boggy prostate, suggesting urethral disruption. These findings or a scrotal hematoma would trigger a urethrogram prior to Foley catheterization.

PLAIN RADIOGRAPH

Plain films of the abdomen are rarely useful in blunt trauma. While the presence of free intraperitoneal air will prompt laparotomy, this unusual finding is best seen on an upright chest film and not a flat plate of the abdomen. Nonspecific signs that arise from intraperitoneal blood, such as the flank stripe sign, dog ear sign, and gastric displacement sign, are rarely obvious and are not reliable (2).

LABORATORY STUDIES

Laboratory tests play an ancillary role in the diagnosis of intra-abdominal injury. While an abnormal test helps confirm the suspicion of visceral injury, a normal test never rules it out. The initial hemoglobin or hematocrit provides a baseline for serial measurements. Changes in hematocrit are influenced by multiple factors

including preinjury level, rate of blood loss, intravenous fluids, and interstitial to intravascular fluid shifts ( 2). However, an initial hemoglobin of less than 8 g is a strong indicator of serious hemorrhage (12). Leukocytosis is a common, nonspecific finding in multiple trauma (2). Historically, many trauma centers included amylase as part of the “trauma package.” There is no data to support this practice, as serum amylase determinations are neither sensitive nor specific for pancreatic injury ( 13,14). Metabolic acidosis in the presence of blunt trauma implies occult shock. This acidosis may be measured by a variety of indicators, such as the base deficit on arterial blood gas, serum lactate, or serum bicarbonate. Measures of anaerobic metabolism such as base deficit and, in particular, lactate are more sensitive indicators of shock than blood pressure or sophisticated invasive monitoring (15,16). While a normal base deficit does not rule out abdominal injury, a deficit of £ -6 (i.e., more negative) alerts the emergency physician to the possibility of occult intra-abdominal injury.

The most important clue to significant renal injury is gross hematuria. All patients with gross hematuria require investigation of the genitourinary system. Microscopic hematuria in adults is seldom clinically significant unless the patient is in shock or has severe abdominal or flank injuries ( 17). Extensive renal evaluation is rarely necessary in adults if microscopic hematuria is the only finding.

Elevated liver function tests may accompany hepatic injury, but should not be used to rule out intraperitoneal hemorrhage ( 18,19).

DIAGNOSTIC PERITONEAL LAVAGE

The introduction of diagnostic peritoneal lavage (DPL) revolutionized the management of multiple trauma. Prior to DPL, up to 17% of patients with abdominal trauma died secondary to an undiagnosed visceral injury (20). In 1965, Root demonstrated that peritoneal lavage was remarkably accurate in detecting intra-abdominal injury and, since his first report, hundreds of studies have confirmed this finding. DPL has come to represent a gold standard in the evaluation of patients with multiple trauma. A pooled series containing over 10,000 patients demonstrates DPL to be 97.3% accurate, with 1.4% false-positive and 1.3% false-negative results, and a complication rate lower than 1% (7).

Indications and Contraindications

Diagnostic peritoneal lavage is a rapid, accurate, and safe method for assessing most patients with potential intra-abdominal injury. Table 11–3.1 shows common indications for DPL. Special techniques may be necessary in performing lavage on patients with previous abdominal surgery, those with pelvic fractures, or pregnant women. The only absolute contraindication to DPL is the need for emergency laparotomy.

Table 11–3.1. Indications for Primary Diagnostic Studies Blunt Trauma

Techniques

1. Basic approach. The three main approaches are open, semiopen, and closed. In each, a Foley catheter should be placed to decompress the bladder, and a nasogastric tube to empty the stomach prior to the lavage. DPL consists of two steps: a catheter is introduced into the peritoneal cavity and then aspirated for blood. Recovery of 10 mL of blood constitutes a positive test and the procedure may be terminated. If aspiration is negative, 1 L of normal saline is instilled through the catheter (15 mL/kg in children) and recovered by gravity drainage. While some centers consider 750 mL of return an adequate lavage, as little at 100 mL may be adequate for accurate diagnosis (21). Failure to recover fluid may be due to preperitoneal catheter placement, and obstructed catheter, or diaphragmatic/bladder injury (DPL fluid drains into Foley or chest tube). If one suspects that the lavage fluid is draining into a chest tube or Foley, methylene blue added to the lavage will confirm this.

2. Location. The default site for lavage is the midline infraumbilical area. Exceptions are the supraumbilical approach in patients with pelvic fractures, as retroperitoneal hematomas usually do not dissect above the umbilicus (22), and suprauterine in the second half of pregnancy. Some authors suggest a left lateral abdominal approach in patients with suspected midline adhesions.

3. Technique. The open technique may be best suited for patients with pelvic fractures, third trimester pregnancy, massive obesity, and those with prior abdominal surgery (23). The performance of the percutaneous Seldinger method is the least time consuming and most easily mastered approach to lavage, and has proven to be safe and accurate (24,25). A recent study showed no increase in complications when this technique was used in patients with prior abdominal surgery ( 26).

Interpretation of DPL Results

Generally accepted criteria for a positive lavage are listed in Table 11–3.2. A red blood cell count between 20,000 and 100,000 is considered indeterminate (27,28), and such patients may be reevaluated with a second DPL several hours later or by abdominal CT or serial ultrasounds.

Table 11–3.2. Standard Criteria for Positive Peritoneal Lavage

The lavage white blood cell count (WBC) is generally an insensitive and nonspecific test. In the absence of worsening physical findings, patients with elevated lavage WBC may be safely monitored without surgical exploration (29,30 and 31) if there is no strong suspicion of an intestinal disruption. An elevated lavage leukocyte count in patients with a seat-belt sign or in those who have fallen from a great height is a significant finding. Lavage enzymes, such as amylase and alkaline phosphatase, also have been used to detect bowel disruption (32,33).

Complications

While diagnostic peritoneal lavage is an invasive procedure, the complication rate is uniformly low, generally less than 2% ( 24). Complications involve perforation of the bowel, mesentery, bladder, and retroperitoneal vessels (2). Local wound problems, such as infection and dehiscence, are uncommon. Complications are more likely in the patient who had prior surgery with adhesions.

Limitations

Because the lavage fluid is confined by the peritoneum, DPL cannot detect injury to retroperitoneal structures. Pancreatic, renal, and retroperitoneal colon injuries are often missed by lavage (24). While small bowel injuries may go undetected (34), DPL is the most sensitive diagnostic procedure, short of laparotomy, for the detection of these injuries (35). Because diaphragm and bladder injuries result in minimal bleeding, disruption of these organs may also be missed by DPL (36,37).

Despite DPL's remarkable sensitivity for diagnosing solid visceral injury, on some occasions it may miss injury to the liver or spleen. Contained subcapsular or intraparenchymal hematomas produce no free blood and result in a negative DPL. Despite these limitations, it is not the false-negatives for which DPL is most often criticized. Critics argue that a positive DPL may lead to unnecessary operations, the so-called “nontherapeutic laparotomy.” This is particularly true in the presence of pelvic fractures, where 29% of lavages may be false-positive (38). In addition, DPL is not organ-specific and cannot determine the source of bleeding or the extent of parenchymal injury (39). A positive DPL in a hemodynamically stable patient does not automatically require laparotomy. In a center with adequate resources, an alert, cooperative, and stable patient with a DPL positive for blood may undergo serial physical examinations, repeat DPL, ultrasound, or abdominal CT scanning ( 40,41 and

42). Hemodynamically unstable patients who have a positive peritoneal aspirate should go directly to the operating room. DPL may be most specific in predicting the need for laparotomy when results are combined with the patient's prelavage blood pressure (43). Patients who have positive lavage and are hypotensive usually require laparotomy. Any patient with a positive lavage who is not taken to the operating room must be monitored in an intensive care unit setting with frequent serial exams (40).

Cost

The cost of lavage ranges between $60 and $150 (44,45) and is relatively inexpensive compared with computerized tomography.