Abdominal Pain

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Chapter 27

Abdominal Pain

Perspective

Abdominal pain is a common emergency department (ED) complaint but for many reasons is often diagnostically challenging. The nature and quality of abdominal pain may be difficult for the patient to convey. Physical examination findings are variable and can be misleading. The location and severity of the pain may change over time. Initially benign symptoms and presentations may evolve into life-threatening conditions. Conversely, patients with severe symptoms may carry a relatively benign diagnosis. All of these factors make evaluation of patients with acute abdominal pain challenging in the ED setting.

Epidemiology

Abdominal pain accounts for up to 10% of all ED visits. Some of the most common causes of acute abdominal pain are listed in Table 27-1. Many patients have pain and other symptoms that are not typical of any specific disease process. Even after ED workup, a diagnosis may not be found in some patients. In addition, several adult groups deserve special consideration: elders (those older than 65 years of age), the immunocompromised, and women of reproductive age.

Elders with acute abdominal pain are more likely to have a life-threatening process as the cause of their pain. Conditions such as diverticulitis, ruptured abdominal aneurysm, or mesenteric ischemia may manifest atypically and be rapidly progressive. Decreased diagnostic accuracy, coupled with increased probability of severe disease, results in increased mortality in elderly patients with abdominal pain.

Increasingly, emergency physicians are seeing patients in immunocompromised states secondary to human immunodeficiency virus and acquired immunodeficiency syndrome (HIV/AIDS), uncontrolled diabetes, chronic liver disease, chemotherapy, and immunosuppressive drugs. For many reasons, these patients also prove challenging. Their clinical presentation can be misleading owing to atypical physical and laboratory findings, such as lack of fever. The white blood cell (WBC) count, which is unreliable in all cases of abdominal pain, may be frankly misleading in such patients, such as in those with persistent elevations. With regard to infection, the scope of the differential diagnosis also should be broader than usual.1,2 Presentations in the immunocompromised patient may be highly variable and subtle and are discussed in Chapter 183.

The evaluation of abdominal pain in women involves a differential diagnosis of considerable extent and often requires a more in-depth physical examination and further diagnostic testing. Pelvic organs may be the source of significant pathology in both the pregnant and the nonpregnant patient. The possibility of ectopic pregnancy in women of reproductive age greatly increases the risk of serious disease with a high potential for misdiagnosis. During pregnancy the uterus becomes an abdominal rather than a pelvic organ and may displace the normal intraperitoneal contents, adding complexity to the evaluation of these patients. Nonpregnant patients require evaluation for various ovarian and uterine pathologic states.

Pathophysiology

Pathology in the gastrointestinal and genitourinary tracts remains the most common source of pain perceived in the abdomen. Also, pain can arise from a multitude of other intra-abdominal and extra-abdominal locations (Box 27-1). Abdominal pain is derived from one or more of three distinct pain pathways: visceral, somatic, and referred.

Visceral pain results from stimulation of autonomic nerves invested in the visceral peritoneum surrounding internal organs. It is often the earliest manifestation of a particular disease process. Distention of hollow organs by fluid or gas and capsular stretching of solid organs from edema, blood, cysts, or abscesses are the most common stimuli. This discomfort is poorly characterized and difficult to localize. If the involved organ is affected by peristalsis, the pain often is described as intermittent, crampy, or colicky. In general, visceral pain is perceived from the abdominal region that correlates with the embryonic somatic segment, as follows:

Visceral pain can be perceived in a location remote from the actual disease process. Localization occurs with the extension of the disease process beyond the viscera. A classic example is that of the early periumbilical pain of appendicitis (midgut). When the parietal peritoneum becomes involved, the pain localizes to the right lower quadrant of the abdomen, the usual location of the appendix.

Somatic pain occurs with irritation of the parietal peritoneum. This is usually caused by infection, chemical irritation, or another inflammatory process. Sensations are conducted by the peripheral nerves and are better localized than the visceral pain component. Figure 27-1 illustrates some more typical pain locations corresponding to specific disease entities. Somatic pain is often described as intense and constant. As disease processes evolve to peritoneal irritation with inflammation, better localization of the pain to the area of pathology generally occurs.

Referred pain is defined as pain felt at a distance from its source because peripheral afferent nerve fibers from many internal organs enter the spinal cord through nerve roots that also carry nociceptive fibers from other locations, as illustrated in Figure 27-2. This makes interpretation of the location of noxious stimuli difficult for the brain. Both visceral pain and somatic pain can manifest as referred pain. Two examples of referred pain are the epigastric pain associated with an inferior myocardial infarction and the shoulder pain associated with blood in the peritoneal cavity irritating the diaphragm. It is common for a patient to interpret pain originating from the hips as pelvic pain, especially in the very young or elderly. Lower lobe pneumonias can cause referred abdominal pain secondary to diaphragmatic irritation. Finally, some metabolic disorders and toxidromes may manifest with abdominal pain.

Gynecologic and obstetric presentations are discussed in other chapters. Notably, abdominal pain in a female may represent referred pain from pelvic structures or an extension of a pelvic process, as in the case of perihepatic inflammation with pelvic inflammatory disease.

Diagnostic Approach

The clinical approach should focus on early stabilization, history, physical examination, and any ancillary tests collectively facilitating appropriate management and disposition plans.

Differential Considerations

Classically, potential diagnoses are divided into intra-abdominopelvic (intraperitoneal, retroperitoneal, and pelvic) causes (e.g., appendicitis, cholecystitis, pancreatitis) and extra-abdominopelvic processes (e.g., pneumonia, myocardial infarction, ketoacidosis, toxicologic).

Although significant morbidity and mortality can result from many disorders causing abdominal pain, a few processes warrant careful consideration in the ED. Table 27-2 lists important potentially life-threatening nontraumatic causes of abdominal pain. This group represents the major causative disorders likely to be associated with hemodynamic compromise and for which early therapeutic intervention is critical.

Rapid Assessment and Stabilization

As with any complaint, triage is the first critical step in management. Most patients with abdominal pain do not have hemodynamic instability, although a small proportion of these stable-appearing patients may have a life-threatening process. This percentage is higher in elders and immunocompromised patients.

Physiologically compromised patients should be brought to a treatment area immediately, and resuscitation initiated. Sepsis or protracted severe volume loss (emesis, diarrhea) can lead to shock; prompt resuscitation is required.

Extreme conditions, such as ruptured abdominal aortic aneurysm, massive gastrointestinal hemorrhage, ruptured ectopic pregnancy, ruptured spleen, and hemorrhagic pancreatitis, may necessitate blood or blood product replacement. Bedside ultrasonography can be used to quickly evaluate patients for free intraperitoneal fluid, volume status, and presence of aortic pathology. Ultrasound assessment should be part of the initial physical examination and can be invaluable in guiding treatment and disposition. Because any of the immediately life-threatening entities may necessitate surgical intervention or management, early surgical consultation is indicated.