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  primary survey should be conducted to rapidly screen for vascular catastrophes, abdominal sepsis, or perforated viscus.

  
  
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  Appendicitis should always be on the differential diagnosis for acute abdominal pain.

  
  
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  Females of childbearing age with abdominal pain are presumed to have an ectopic pregnancy until proven otherwise.

  
  
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  Older and immunocompromised patients may have an atypical presentation of disease.

  
  
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  The white blood cell count is an unreliable predictor of disease and should not be used in isolation to confirm or exclude a critical diagnosis.

Abdominal pain is a common presenting complaint and represents up to 10% of all emergency department (ED) visits. Although the etiology of abdominal pain frequently goes undiagnosed, the role of the emergency physician is to first identify and treat any immediate life- or organ-threatening conditions. Imminent causes of abdominal pain that need to be promptly diagnosed are those driven by a vascular event, infectious process, or perforated viscous (eg, ruptured abdominal aortic aneurysm [AAA], cholangitis, perforated gastric ulcer). Other disease processes may not pose an immediate threat to the patient but should be diagnosed before discharge, as delays in treatment can result in patient morbidity (eg, appendicitis, pelvic inflammatory disease).

Abdominal pain can be classified as visceral, parietal, or referred in origin. Depending on the disease process, pain may begin as visceral and become parietal, as in the stretching and subsequent rupture of a hollow viscus. Visceral pain occurs with the stretching of nerve fibers in the walls of hollow organs or the capsules of solid organs. The location of pain is not well localized, but often has an embryologic basis that aids in determining the diagnosis. Epigastric pain occurs in patients with stretching of foregut organs (stomach to duodenum, including biliary tree and pancreas). Periumbilical pain represents pathology of midgut organs (distal duodenum to transverse colon). Suprapubic pain is due to problems of the hindgut organs (distal transverse colon, rectum, and urogenital tract). Parietal pain is due to irritation of the parietal peritoneum. The patient is more readily able to localize the pain (eg, left lower quadrant pain in diverticulitis), but when the entire peritoneal cavity is involved, the pain is diffuse. Referred pain is defined as pain experienced at a site distant from its source. Its anatomic basis lies in afferent nerves from different locations sharing the same spinal cord segment. Abdominal pain may be referred from organs above the diaphragm (eg, myocardial infarction causing epigastric pain). Alternatively, abdominal pathology may refer pain to sites above the diaphragm (eg, splenic rupture causing shoulder pain).

Older and immunocompromised patients warrant special consideration as higher risk groups. Older patients have a greater incidence of vascular catastrophes and surgical disease, with as high as 40% of patients older than 65 years requiring operative intervention (Table 26-1). Compared with younger counterparts, older patients are more likely to have atypical presentations, have nonspecific symptoms, and present later in the disease course. In addition to being vulnerable to opportunistic pathogens, immunocompromised patients may not develop peritoneal findings despite a serious underlying infection owing to their blunted immune response. For both these populations, a low threshold must be maintained to pursue critical diagnoses.

History

A thoughtful history is important in obtaining an accurate diagnosis, but some specific historical elements can lead to the rapid development of a targeted differential. While keeping in mind that patients may have an atypical presentation of disease, the location of the pain, the nature of the pain at onset, and how the pain behaves since onset can help efficiently discriminate between different diagnostic considerations (Figure 26-1). Pain that is sudden and severe at onset is often associated with the rupture of a blood vessel or hollow viscus (eg, ruptured AAA, perforated peptic ulcer), occlusion of a blood vessel or hollow viscus (eg, acute mesenteric ischemia, ureteral colic), or gonadal torsion. In contrast, inflammatory conditions tend to have a more insidious onset, as is seen with appendicitis. Pain whose progression is colicky in nature is suggestive of peristaltic activity in the setting of an obstructed lumen (eg, ureteral, biliary, intestinal colic).

The manner in which the pain radiates can suggest a specific disease. Pain radiating to the back is often seen with pancreatitis. Pain radiating to the right infrascapular region is associated with biliary tract disorders. Pain that radiates to the groin may indicate a ruptured aortic aneurysm or nephrolithiasis.

Associated symptoms involving the gastrointestinal, genitourinary, and cardiopulmonary systems should be obtained. The clinician, however, must keep a broad differential as the same symptom can be seen across many disease processes. Nausea and vomiting are nonspecific symptoms, although it is worthwhile noting the temporal relationship between them. Surgical causes of abdominal pain classically present with pain preceding vomiting, whereas the reverse is often seen with medical etiologies. The clinician must be cautious in using diarrhea as conclusive evidence of gastroenteritis, as it can also be seen with appendicitis, diverticulitis, and partial small bowel obstruction. Irritative voiding symptoms such as dysuria and frequency are suggestive of a urinary tract infection; however, they can also be caused by appendicitis or pelvic abscess. Hematuria should raise concern for nephrolithiasis or a malignancy in the genitourinary tract. Vaginal bleeding and discharge are important to elicit in assessing for ectopic pregnancy and pelvic inflammatory disease. As pneumonia, pulmonary embolism, and acute coronary syndrome can all present with abdominal pain, the presence of cough, chest pain, and shortness of breath should be ascertained.