Troubleshooting Acute Abdominal Pain

Two emergency physicians provide a neurologic map of the abdomen, identify temporal clues and telltale signs, explain what to look for during the physical assessment, and describe the judicious use of diagnostic tests for patients with sudden, severe pain anywhere from sternum to pubis.

By Michael J. White, MD, and Francis L. Counselman, MD

Dr. White is a second-year emergency medicine resident and Dr. Counselman is the distinguished professor of emergency medicine and chairman and program director in the department of emergency medicine, at Eastern Virginia Medical School in Norfolk, Virginia.

The diagnosis of acute abdominal pain continues to be one of medicine's most daunting tasks. The abdomen might be thought of as an incredibly intricate biological "black box" in which it can be extremely difficult to pinpoint the source of distress. This article attempts to simplify the natural complexity of the abdomen and offer a means of appropriately evaluating and diagnosing pain in the area from sternum to pubis.

One of the main obstacles to the diagnostic process in patients with acute abdominal pain is the physician's own personal bias. Too often a presumptive diagnosis is reached before the data is fully collected; such hastiness leads to inefficient use of time, overuse of tests, and delay in making the correct diagnosis. To counter that tendency, physicians must keep in mind that many of the axioms commonly applied to abdominal pain are misguided‹for example, "Left lower quadrant pain is not clinically significant," or "Pain of acute onset, which is progressive and continuous with a duration of less than six hours, is surgical," or "Non-severe pain that is intermittent and has lasted longer than six hours is not surgical."

As outlined in Cope's Manual on acute abdominal pain, the patient's history is fundamental to making an expedient and correct diagnosis. Certain features of the history are key. Simple knowledge of age, sex, previous episodes of pain, family history, current medications, travel and social history, and medical and surgical history can significantly aid diagnosis. Finer features of the history are also important. The clinician should explore the nature, duration, location, radiation, and temporal characteristics of the pain; noted associations such as exacerbating and ameliorating factors; and any alterations in dietary, urinary, and bowel habits. In the evaluation of a female patient, knowledge of her obstetric and gynecologic history, including her menstrual cycle, is also fundamental.

Acute abdominal pain represents 5% to 10% of all emergency department visits. Challenging as it is, a careful history-taking, thorough evaluation of symptoms, head-to-toe physical examination, and judicious use of laboratory tests can simplify the evaluation of this complaint.

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Neurologic Underpinnings

The location of pain is critical to aiding in making the correct diagnosis, and a physician must be versed in its interpretation (see tables). This requires a fundamental understanding of the three basic forms of pain: visceral, somatic, and referred.

In broad terms, the autonomic nervous system innervates visceral structures such as involuntary muscles, the heart, and glands. With respect to the abdomen, general visceral afferent nerves work through stretch receptors, which are extremely important for sensation in tubular structures, as well as in solid organs. Visceral pain is poorly localized, frequently colicky, intermittent, and recurring. The archetypal example of visceral pain is a child attempting to localize abdominal pain; everything feels periumbilical in nature. Another example is pelvic inflammatory disease, which by irritating tubular structures produces what is generally described as a diffuse suprapubic or hypogastric discomfort. However, true visceral pain often is difficult to independently discern because a somatic component confounds the clinical picture.

The abdominal somatic nervous system innervates structures such as skeletal muscles and skin. General somatic afferent nerves are responsible for sensory function from somatic tissues and utilize pain and temperature receptors. A classic example of somatic pain is advanced appendicitis with irritation of the psoas muscle.

Finally, the vagus and phrenic nerves carry both afferent and efferent fibers, and are both somatic and visceral. Due to their dual nature, these nerves may manifest irritation either away from or within the abdominal cavity. For example, vertigo and labyrinthitis, both distant from the abdomen, frequently manifest with a sense of nausea and abdominal discomfort. Conversely, irritation of the vagus nerve has been known to stimulate the phrenic nerve and manifest as hiccups. Clearly, these nerves can cloud the clinical picture because of their dual nature. One way to simplify the picture is with some generalizations about nerve involvement in abdominal pain (see table below).

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Temporal Characteristics of Pain

Pain can present in various ways. Major vascular events, such as embolic occlusion or rupture of an abdominal aortic aneurysm (AAA), have a stereotypical picture highlighted by exquisite pain‹sudden, severe, and intense. Acute myocardial infarction and rupture of a viscous organ also fall into that category, but myocardial pain when sensed in the abdomen tends to be crampy and diffuse.

Pain that rapidly matures from intermediate to severe frequently represents an intraparenchymal or intraluminal process, such as acute pancreatitis, acute appendicitis, or acute cholecystitis. Colic, on the other hand, is often relative and can be linked to peristaltic movement of smooth muscle and subsequent muscle spasm and pain. Examples of colicky pain include the passage of renal calculi, gallstones, and intestinal obstruction.

Abdominal pain tends to "mature" over time. Initially it may be poorly localized, but will narrow as somatic structures become involved. The astute clinician will use the temporal progression to assist in diagnosis by noting the time of onset, character, and severity, and recording changes over time. For example, appendicitis initially irritates visceral tissue and causes periumbilical pain. Eventually, parietal peritoneum and skeletal muscles are irritated and the pain localizes to the right lower quadrant (McBurney's point).

Certain disease processes tend to have a classic, temporal picture (see table below). Acute pancreatitis and pending rupture of an ectopic pregnancy are apt to steadily worsen, whereas the pain associated with embolism to the superior mesenteric artery typically is intense at first and then waxes and wanes until ultimately appearing to have resolved.

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Telltale Signs of Specific Conditions

Beyond the initial description of the abdominal pain, other symptoms help bring the clinical picture into focus. Some symptoms, such as obstipation, are usually cited by the patient, while others, such as anorexia, are more likely to be overlooked and should always be specifically inquired about. Many associations are considered typical of certain disease processes; for example, gastric ulcer pain worsens after the patient eats, while duodenal ulcer pain tends to subside temporarily. Along similar lines, gastroesophageal reflux disease is linked to the intake of alcohol, caffeine or chocolate or to lying flat, and almost any food has the potential to cause intestinal angina. Also, certain behaviors are suggestive of certain diagnoses, such as retching and the lacerations associated with Mallory-Weiss syndrome, writhing in pain and renal calculi, or lying morbidly quiet and peritonitis.

It is important to beware of pain as a possible confounding factor in the interpretation of symptoms. Pain and consequent anxiety can cause some signs and symptoms that are not directly related to the issue at hand, such as elevated blood pressure or vomiting. Meanwhile, pain in certain locations is especially subject to presumptive misdiagnosis; for example, AAA, with its associated flank pain, is frequently mistaken for renal colic or lumbar muscle spasm.

Nonetheless, when evaluated properly, pain and associated symptoms can be helpful. Certain features such as nausea, vomiting, and decreased appetite prior to pain suggest a non-surgical abdomen, and conversely, the absence of such features should raise suspicion of a surgical problem. Moreover, there are symptoms that tend to reflect an ominous picture in certain groups. Severe pain, vomiting, or obstipation in an elderly patient nearly always represents significant pathology. And, of course, the toxic patient who lies perfectly still so as to avoid further peritoneal irritation has a surgical abdomen.

Certain associations tend to be reassuring. For example, a clinical picture of crampy abdominal pain, vomiting, and diarrhea is typical of gastroenteritis. Similarly, the young adult patient with flank pain radiating to the groin who twists and turns and is consistently unable to obtain a position of comfort most often is experiencing renal colic.

Finally, some causes of abdominal pain do not localize well, including sickle cell crisis, mesenteric ischemia, intestinal obstruction, and diabetes mellitus. The pain triggered by these acute conditions has no classic profile.

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How to Examine the Patient

In the evaluation of abdominal pain, a complete and thorough physical examination must be performed. The examination should be undertaken in a systematic fashion so as not to overlook important aspects. The first things to review and record are the patient's gender and race, any available nursing notes, and vital signs. This information is not only important when initially interviewing the patient but should be part of the reassessment of every patient. Tachypnea may indicate apprehension, acidosis, or subdiaphragmatic irritation. Elevated blood pressure, with an increased pulse rate, can imply either anxiety or pain or both. Hypotension, of course, may imply a medical or surgical emergency.

Before initiating examination, the physician should talk to the patient and outline his approach. A defensive patient is much more difficult to examine than one who anticipates the physician's next move. It is also important to perform the examination from the point of least discomfort to the point of greatest pain. Starting at the wrong place will cause pain, limit and confound the examination, and diminish patient trust.

The physician's entrance into the examining room is an opportunity to make an overall inspection of the patient from a distance. This baseline impression should be compared with each subsequent impression of the patient. As discussed above, changes in the condition of the patient, including vital signs and appearance, are key to risk stratification and appropriate diagnosis.

The abdomen should be auscultated prior to palpation, with close attention paid to the presence and tone of bowel sounds. It is necessary to listen for at least one minute over various parts of the abdomen before concluding that bowel sounds are absent. The absence of bowel sounds suggests peritonitis, profound ileus, mesenteric thrombosis, hypokalemia, or narcotic overdose. Hypoperistalsis suggests inflammation, bowel ischemia, or hypokalemia. Hyperperistalsis with diarrhea suggests gastroenteritis.

It is helpful to talk to the patient throughout the examination, which serves to relax and distract him or her and thus allows more accurate findings. While palpating the abdomen, the physician should carefully note the area of greatest tenderness, judging either by indications of discomfort or the patient's subjective impression. Of course, any signs such as guarding, rigidity, or rebound tenderness should be noted. Guarding is either voluntary or involuntary. Voluntary guarding is the conscious contraction of the abdominal musculature. Involuntary guarding (or rigidity) is a reflex contraction of the abdominal musculature, usually due to underlying peritoneal inflammation. Unilateral abdominal wall muscle spasm is always involuntary. Rebound tenderness refers to the pain following abrupt cessation of palpation, and traditionally indicates peritonitis. However, this sign should not be considered specific or sensitive for peritonitis.

The areas of highest probability of hernia must be evaluated as appropriate to the patient's gender. Unilateral splinting should be carefully noted, as well as any scars. The act of percussion must not be overlooked, as it can help identify ascites or hepatosplenomegaly (if performed carefully) and define more precisely the area of maximal discomfort. Ascites can be determined by percussing areas of dullness and noting whether those areas shift with changes in patient position. This phase of the examination must also include percussion of the flanks for costovertebral angle tenderness, which suggests pyelonephritis.

More invasive procedures such as rectal and vaginal examinations should be undertaken in most patients. The rectal examination, although it is sometimes misleading, allows for detection of gastrointestinal bleeding, masses, and tenderness and may help redirect and redefine a differential diagnosis. A painful rectal examination is particularly relevant in a patient with hypogastric pain, because it may indicate retrocecal appendicitis or prostatitis. The presence of hemorrhoids, the size of the prostate, and any fecal impaction should be noted. The pelvic examination, of course, can yield a tremendous amount of information from intravaginal inspection as well as from palpation of the cervix, uterus, bladder, and adnexal structures. Similarly, in males, the genitalia should be examined, looking specifically for testicular tenderness and swelling indicative of hernia, epididymitis, or testicular torsion.

There are certain distinct physical examination findings, signs, and maneuvers that can help narrow the differential diagnosis. Although not 100% sensitive (or specific), knowledge of these signs can aid in the evaluation of a patient with abdominal pain (see table below).

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Judicious Use of Tests

The shotgun approach to abdominal pain, although tempting and frequently reassuring, should be avoided. The role of laboratory studies is to complement, not supplant, the clinical impression, and the physician ordering a wide array of tests to answer a question should always stop to consider whether the answer he seeks might be found at the patient's bedside instead.

Beyond the overzealous use of labs, studies are only as good as the physician who interprets the results. Regrettably, a coincidental finding is too often accepted as the answer while the true abdominal emergency goes unrecognized. Fear of litigation seemingly drives many physicians to order a barrage of tests, but the best course is a tempered approach with judicious use of studies, a candid discussion with the patient, and adequate follow-up. Laboratory studies should be ordered after the differential diagnosis has been formed and, generally, should serve to confirm or exclude items on the differential.

A complete blood count is probably the most frequently ordered test for patients with abdominal pain. The important point for the clinician to remember is that an elevated white blood cell (WBC) count is not specific and not 100% sensitive. It can be elevated in conditions ranging from gastroenteritis to appendicitis to extraperitoneal causes of pain, including lower lobe pneumonia and diabetic ketoacidosis. Even more important, the WBC count may be normal in patients with a surgical abdomen. Therefore, the clinician should not rely too much on the results of the WBC count; the clinical impression is of much greater importance.

The hemoglobin and hematocrit may be helpful in evaluating patients with suspected gastrointestinal bleeding (as in peptic ulcer disease). A urinalysis should be ordered for patients with suspected urinary infection or renal calculi, keeping in mind, however, that in approximately 10% of patients with documented kidney stones, there will be no red blood cells in the urine. For patients with significant vomiting or diarrhea, or who appear dehydrated, a basic metabolic panel (sodium, chloride, potassium, carbon dioxide, blood urea nitrogen, glucose, creatinine) should be ordered. Patients with suspected liver, pancreas, or gallbladder disease should have liver function studies and a serum lipase ordered. An acute abdominal x-ray series can be helpful for patients with suspected bowel obstruction, perforated viscous organ, or lower lobe pneumonia. While these x-rays are frequently ordered for abdominal pain, they are rarely helpful, unless one of the above is suspected. In the majority of cases, only nonspecific findings are present.

Specialized imaging studies can be quite helpful in selected cases. Ultrasonography is excellent in evaluating the gallbladder and abdominal aorta and for detecting pelvic pathology such as ectopic pregnancy or tubo-ovarian abscess. Computerized axial scanning of the abdomen and pelvis (with contrast) can be very sensitive in identifying appendicitis, bowel obstruction, diverticulitis, and AAA. Again, the history and physical examination should guide the selection of laboratory studies to be performed.

Next month, part 2 of this article will focus on several common etiologies of abdominal pain, detailing their history, symptoms, classic associated physical findings, and the tests that best facilitate their diagnosis.

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