David M. Cline
EPIDEMIOLOGY
Data from the United States National Center for Health Statistics indicate that abdominal pain was the single most frequently mentioned reason offered by patients for visiting the ED in 2006 (6.7% of ED visits—8.04 million patient encounters).
Admission rates for abdominal pain vary markedly, ranging from 18% to 42%, with rates as high as 63% reported in patients over 65 years of age.
PATHOPHYSIOLOGY
Visceral abdominal pain is usually caused by stretching of fibers innervating the walls or capsules of hollow or solid organs, respectively. Less commonly it is caused by early ischemia or inflammation.
Foregut organs (stomach, duodenum, and biliary tract) produce pain in the epigastric region; midgut organs (most of the small bowel, and the appendix and cecum) cause periumbilical pain; and hindgut organs (most of the colon, including the sigmoid) as well as the intraperitoneal portions of the genitourinary system tend to cause pain initially in the suprapubic or hypogastric area.
Visceral pain is usually felt at the midline.
Parietal or somatic abdominal pain is caused by irritation of fibers that innervate the parietal peritoneum, usually the portion covering the anterior abdominal wall.
In contrast to visceral pain, parietal pain can be localized to the dermatome directly above the site of the painful stimulus. As the underlying disease process evolves, the symptoms of visceral pain give way to the signs of parietal pain, with tenderness and guarding. As localized peritonitis develops further, rigidity and rebound appear.
Referred pain is felt at a location distant from the diseased organ.
CLINICAL FEATURES
Consider immediate life threats that might require emergency intervention.
Elicit time of pain onset; character, severity, location of pain (Fig. 37-1), and its referral; aggravating and alleviating factors; and similar prior episodes.
FIG. 37-1. Differential diagnosis of acute abdominal pain by location. AKA = alcoholic ketoacidosis; DKA = diabetic ketoacidosis; LLL = lower left lobe; RLL = right lower lobe.
Cardiorespiratory symptoms, such as chest pain, dyspnea, and cough; genitourinary symptoms, such as urgency, dysuria, and vaginal discharge; and any history of trauma should be elicited.
In older patients it is also important to obtain a history of myocardial infarction, dysrhythmias, coagulopathies, and vasculopathies.
Past medical and surgical histories should be elicited, and a list of medications, particularly steroids, antibiotics, or nonsteroidal anti-inflammatory drugs (NSAIDs), should be noted.
A thorough gynecologic history is indicated in female patients.
The physical examination should include the patient’s general appearance. Patients with peritonitis tend to lie still.
The skin should be evaluated for pallor or jaundice.
The vital signs should be inspected for signs of hypo-volemia due to blood loss or volume depletion. Due to medications or the physiology of aging, tachycardia may not always occur in the face of hypovolemia.
A core temperature should be obtained; however, absence of fever does not rule out infection, particularly in the elderly.
The abdomen should be inspected for contour, scars, peristalsis, masses, distention, and pulsation. The presence of hyperactive or high-pitched or tinkling bowel sounds increases the likelihood of small bowel obstruction.
Palpation is the most important aspect of the physical examination.
The abdomen and genitals should be assessed for tenderness, guarding, masses, organomegaly, and hernias.
“Rebound” tenderness, often regarded as the clinical criterion standard of peritonitis, has several important limitations. In patients with peritonitis, the combination of rigidity, referred tenderness, and, especially, “cough pain” usually provides sufficient diagnostic confirmation; false-positive rebound tenderness occurs in about one patient in four without peritonitis.
The false-positive rate of rebound tenderness (up to 25%) has led some investigators to conclude that rebound tenderness, in contrast to cough pain, is of “no predictive value.”
A useful and underused test to diagnose abdominal wall pain is the sit-up test, also known as the Carnett sign. After identification of the site of maximum abdominal tenderness, the patient is asked to fold his or her arms across the chest and sit up halfway. The examiner maintains a finger on the tender area, and if palpation in the semisitting position produces the same or increased tenderness, the test is said to be positive for an abdominal wall syndrome.
Perform a pelvic examination in all postpubertal females.
During the rectal examination, the lower pelvis should be assessed for tenderness, bleeding, and masses.
Elderly patients often fail to manifest the same signs and symptoms as younger patients, with decreased pain perception and decreased febrile or muscular response to infection or inflammation.
Biliary disease, bowel obstruction, diverticulitis, cancer, and hernia are more common causes of abdominal pain in patients over 50 years old. Hypotension from volume contraction, hemorrhage, or sepsis can be missed if a normally hypertensive patient appears normotensive.
Conditions somewhat less frequent but proportionately higher in occurence among the elderly include sigmoid volvulus, diverticulitis, acute mesenteric ischemia, and abdominal aortic aneurysm.
Mesenteric ischemia should be considered in any patient older than 50 years with abdominal pain out of proportion to physical findings.
DIAGNOSIS AND DIFFERENTIAL
Suggested laboratory studies for goal-directed clinical testing are listed in Table 37-1.
TABLE 37-1 Suggested Laboratory Studies for Goal-Directed Clinical Testing in Acute Abdominal Pain
Diagnostic caveats for clinically suspected source of abdominal pain are listed in Table 37-2.
TABLE 37-2 Diagnostic Caveats for Clinically Suspected Source of Abdominal Pain
All women of childbearing age with abdominal pain or abnormal vaginal bleeding should receive a qualitative screening pregnancy test.
A complete blood count is neither sensitive nor specific to identify abdominal pathology; however, it remains the most commonly ordered test for ED patients with abdominal pain.
Plain abdominal radiographs are helpful in patients with suspected obstruction, perforation (look for free air), or to follow previously identified stones in renal colic patients.
Ultrasonography is useful for the diagnosis of cholelithiasis, choledocholithiasis, cholecystitis, biliary duct dilatation, pancreatic masses, hydroureter, intra-uterine or ectopic pregnancies, ovarian and tubal pathologies, free intraperitoneal fluid, suspected appendicitis (institution specific), and abdominal aortic aneurysm.
Computed tomography (CT) is the preferred imaging method for mesenteric ischemia, pancreatitis, biliary obstruction, aortic aneurysm, appendicitis, and urolithiasis and is superior for identifying virtually any abnormality that can be seen on plain films.
Intravenous contrast is essential to identify vascular lesions, is helpful to identify inflammatory conditions (ie, appendicitis), but is not needed for urolithiasis.
Oral contrast aids in the diagnosis of bowel obstruction, but otherwise is less useful.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Unstable patients should be resuscitated immediately, then diagnosed clinically with emergent surgical consultation.
The most common resuscitation need for abdominal pain patients is intravenous hydration with normal saline or lactated Ringer solution. During the initial evaluation, the patient should have nothing by mouth.
The judicious use of analgesics is appropriate and may facilitate the ability to obtain a better history and more accurate physical examination. Consider morphine 0.1 milligram/kg IV, which can be reversed by naloxone (0.4–2 milligrams SC/IV) if necessary. NSAIDs are useful in patients with renal colic, but their use in other conditions is controversial and they can mask peritoneal inflammation.
Antiemetics, such as ondansetron 4 milligrams IM/IV, or metoclopramide 10 milligrams IM or slow IV, also increase the patient’s comfort and facilitate assessment of the patient’s signs and symptoms.
When appropriate, antibiotic treatment (ie, gen-tamicin 1.5 milligrams/kg IV plus metronidazole 1 gram IV; or piperacillin-tazobactam, 3.375 grams IV) should be initiated, depending on the suspected source of infection. See specific chapters that follow in this section for additional guidelines.
Surgical or obstetric and gynecologic consultation should be obtained for patients with suspected acute abdominal or pelvic pathology requiring immediate intervention, including, but not limited to, abdominal aortic aneurysm, intraabdominal hemorrhage, perforated viscus, intestinal obstruction or infarction, and ectopic pregnancy. Historically, the “acute abdomen” or “surgical abdomen” has been identified by the presence of pain, guarding, and rebound as indicating a likely need for emergent surgery.
Indications for admission include toxic appearance, unclear diagnosis in elderly or immunocompromised patients, inability to reasonably exclude serious etiologies, intractable pain or vomiting, altered mental status, and inability to follow discharge or follow-up instructions. Continued observation with serial examinations is an alternative.
Many patients with nonspecific abdominal pain can be discharged safely with 24 hours of follow-up and instructions to return immediately for increased pain, vomiting, fever, or failure of symptoms to resolve.
For further reading in Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed., see Chapter 74, “Acute Abdominal Pain,” by Mary Claire O’Brien.