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Acute Abdominal Pain

by Parswa Ansari, MD

Abdominal pain is common and often inconsequential. Acute and severe abdominal pain, however, is almost always a symptom of intra-abdominal disease. It may be the sole indicator of the need for surgery and must be attended to swiftly: Gangrene and perforation of the gut can occur < 6 h from onset of symptoms in certain conditions (eg, interruption of the intestinal blood supply due to a strangulating obstruction or an arterial embolus). Abdominal pain is of particular concern in patients who are very young or very old and those who have HIV infection or are taking immunosuppressants (including corticosteroids).

Textbook descriptions of abdominal pain have limitations because people react to pain differently. Some, particularly elderly people, are stoic, whereas others exaggerate their symptoms. Infants, young children, and some elderly people may have difficulty localizing the pain.

Pathophysiology

Visceral pain comes from the abdominal viscera, which are innervated by autonomic nerve fibers and respond mainly to the sensations of distention and muscular contraction—not to cutting, tearing, or local irritation. Visceral pain is typically vague, dull, and nauseating. It is poorly localized and tends to be referred to areas corresponding to the embryonic origin of the affected structure. Foregut structures (stomach, duodenum, liver, and pancreas) cause upper abdominal pain. Midgut structures (small bowel, proximal colon, and appendix) cause periumbilical pain. Hindgut structures (distal colon and GU tract) cause lower abdominal pain.

Somatic pain comes from the parietal peritoneum, which is innervated by somatic nerves, which respond to irritation from infectious, chemical, or other inflammatory processes. Somatic pain is sharp and well localized.

Referred pain is pain perceived distant from its source and results from convergence of nerve fibers at the spinal cord. Common examples of referred pain are scapular pain due to biliary colic, groin pain due to renal colic, and shoulder pain due to blood or infection irritating the diaphragm.

Peritonitis

Peritonitis is inflammation of the peritoneal cavity. The most serious cause is perforation of the GI tract (see Acute Perforation), which causes immediate chemical inflammation followed shortly by infection from intestinal organisms. Peritonitis can also result from any abdominal condition that causes marked inflammation (eg, appendicitis [see Appendicitis], diverticulitis [see Diverticulitis], strangulating intestinal obstruction [see Intestinal Obstruction], pancreatitis [see Pancreatitis], pelvic inflammatory disease [see Pelvic Inflammatory Disease (PID)], mesenteric ischemia [see Acute Mesenteric Ischemia]). Intraperitoneal blood from any source (eg, ruptured aneurysm, trauma, surgery, ectopic pregnancy [see Ectopic Pregnancy]) is irritating and results in peritonitis. Barium causes severe caking and peritonitis and should never be given to a patient with suspected GI tract perforation. However, water-soluble contrast agents can be safely used. Peritoneosystemic shunts, drains, and dialysis catheters in the peritoneal cavity predispose a patient to infectious peritonitis, as does ascitic fluid. Rarely, spontaneous bacterial peritonitis occurs, in which the peritoneal cavity is infected by bloodborne bacteria.

Peritonitis causes fluid to shift into the peritoneal cavity and bowel, leading to severe dehydration and electrolyte disturbances. Adult respiratory distress syndrome can develop rapidly. Kidney failure, liver failure, and disseminated intravascular coagulation follow. The patient’s face becomes drawn into the masklike appearance typical of hippocratic facies. Death occurs within days.


Etiology

Many intra-abdominal disorders cause abdominal pain (see Figure: Location of abdominal pain and possible causes.); some are trivial but some are immediately life threatening, requiring rapid diagnosis and surgery. These include ruptured abdominal aortic aneurysm (AAA—see Abdominal Aortic Aneurysms (AAA)), perforated viscus, mesenteric ischemia, and ruptured ectopic pregnancy. Others (eg, intestinal obstruction, appendicitis, severe acute pancreatitis) are also serious and nearly as urgent. Several extra-abdominal disorders also cause abdominal pain (see Extra-Abdominal Causes of Abdominal Pain).

Location of abdominal pain and possible causes.

Extra-Abdominal Causes of Abdominal Pain

Abdominal wall

Rectus muscle hematoma

GU

Testicular torsion

Infectious

Herpes zoster

Metabolic

Alcoholic ketoacidosis

Corticosteroid insufficiency

Diabetic ketoacidosis

Hypercalcemia

Porphyria

Sickle cell disease

Thoracic

Costochondritis

Myocardial infarction

Pneumonia

Pulmonary embolism

Radiculitis

Toxic

Black widow spider bite

Heavy metal poisoning

Methanol poisoning

Opioid withdrawal

Scorpion sting

Abdominal pain in neonates, infants, and young children has numerous causes not encountered in adults. These causes include necrotizing enterocolitis, meconium peritonitis, pyloric stenosis (see Hypertrophic Pyloric Stenosis), volvulus of a gut with intestinal malrotation (see Malrotation of the Bowel), imperforate anus (see Anal Atresia), intussusception (see Intussusception), and intestinal obstruction caused by atresia (see Jejunoileal Atresia).

Evaluation

Evaluation of mild and severe pain follows the same process, although with severe abdominal pain, therapy sometimes proceeds simultaneously and involves early consultation with a surgeon. History and physical examination usually exclude all but a few possible causes, with final diagnosis confirmed by judicious use of laboratory and imaging tests. Life-threatening causes should always be ruled out before focusing on less serious diagnoses. In seriously ill patients with severe abdominal pain, the most important diagnostic measure may be expeditious surgical exploration. In mildly ill patients, watchful waiting and a diagnostic evaluation may be best.

History

A thorough history usually suggests the diagnosis (see History in Patients with Acute Abdominal Pain). Of particular importance are pain location (see Figure: Location of abdominal pain and possible causes.) and characteristics, history of similar symptoms, and associated symptoms. Concomitant symptoms such as gastroesophageal reflux, nausea, vomiting, diarrhea, constipation, jaundice, melena, hematuria, hematemesis, weight loss, and mucus or blood in the stool help direct subsequent evaluation. A drug history should include details concerning prescription and illicit drug use as well as alcohol. Many drugs cause GI upset. Prednisone or immunosuppressants may inhibit the inflammatory response to perforation or peritonitis and result in less pain, tenderness, or leukocytosis than might otherwise be expected. Anticoagulants can increase the chances of bleeding and hematoma formation. Alcohol predisposes to pancreatitis.

History in Patients with Acute Abdominal Pain

Question

Potential Responses and Indications

Where is the pain?

What is the pain like?

Acute waves of sharp constricting pain that “take the breath away” (renal or biliary colic)

Waves of dull pain with vomiting (intestinal obstruction)

Colicky pain that becomes steady (appendicitis, strangulating intestinal obstruction, mesenteric ischemia)

Sharp, constant pain, worsened by movement (peritonitis)

Tearing pain (dissecting aneurysm)

Dull ache (appendicitis, diverticulitis, pyelonephritis)

Have you had it before?

Yes suggests recurrent problems such as ulcer disease, gallstone colic, diverticulitis, or mittelschmerz

Was the onset sudden?

Sudden: “Like a light switching on” (perforated ulcer, renal stone, ruptured ectopic pregnancy, torsion of ovary or testis, some ruptured aneurysms)

Less sudden: Most other causes

How severe is the pain?

Severe pain (perforated viscus, kidney stone, peritonitis, pancreatitis)

Pain out of proportion to physical findings (mesenteric ischemia)

Does the pain travel to any other part of the body?

Right scapula (gallbladder pain)

Left shoulder region (ruptured spleen, pancreatitis)

Pubis or vagina (renal pain)

Back (ruptured aortic aneurysm, pancreatitis, sometimes perforated ulcer)

What relieves the pain?

Antacids (peptic ulcer disease)

Lying as quietly as possible (peritonitis)

What other symptoms occur with the pain?

Vomiting precedes pain and is followed by diarrhea (gastroenteritis)

Delayed vomiting, absent bowel movement and flatus (acute intestinal obstruction; the delay increases with a lower site of obstruction)

Severe vomiting precedes intense epigastric, left chest, or shoulder pain (emetic perforation of the intra-abdominal esophagus)

Known medical conditions and previous abdominal surgeries are important to ascertain. Women should be asked whether they are pregnant.


Physical examination

The general appearance is important. A happy, comfortable-appearing patient rarely has a serious problem, unlike one who is anxious, pale, diaphoretic, or in obvious pain. BP, pulse, state of consciousness, and other signs of peripheral perfusion must be evaluated. However, the focus of the examination is the abdomen, beginning with inspection and auscultation, followed by palpation and percussion. Rectal examination and pelvic examination (for women) to locate tenderness, masses, and blood are essential.

Palpation begins gently, away from the area of greatest pain, detecting areas of particular tenderness, as well as the presence of guarding, rigidity, and rebound (all suggesting peritoneal irritation) and any masses. Guarding is an involuntary contraction of the abdominal muscles that is slightly slower and more sustained than the rapid, voluntary flinch exhibited by sensitive or anxious patients. Rebound is a distinct flinch upon brisk withdrawal of the examiner’s hand. The inguinal area and all surgical scars should be palpated for hernias.


Red flags

Certain findings raise suspicion of a more serious etiology:

  • Severe pain

  • Signs of shock (eg, tachycardia, hypotension, diaphoresis, confusion)

  • Signs of peritonitis

  • Abdominal distention


Interpretation of findings

Distention, especially when surgical scars, tympany to percussion, and high-pitched peristalsis or borborygmi in rushes are present, strongly suggests bowel obstruction. Severe pain in a patient with a silent abdomen who is lying as still as possible suggests peritonitis; location of tenderness suggests etiology (eg, right upper quadrant suggests cholecystitis, right lower quadrant suggests appendicitis) but may not be diagnostic. Back pain with shock suggests ruptured AAA, particularly if there is a tender, pulsatile mass. Shock and vaginal bleeding in a pregnant woman suggest ruptured ectopic pregnancy. Ecchymoses of the costovertebral angles (Grey Turner sign) or around the umbilicus (Cullen sign) suggest hemorrhagic pancreatitis but are not very sensitive for this disorder.

History is often suggestive (see History in Patients with Acute Abdominal Pain). Mild to moderate pain in the presence of active peristalsis of normal pitch suggests a nonsurgical disease (eg, gastroenteritis) but may also be the early manifestations of a more serious disorder. A patient who is writhing around trying to get comfortable is more likely to have an obstructive mechanism (eg, renal or biliary colic).

Previous abdominal surgery makes obstruction caused by adhesions more likely. Generalized atherosclerosis increases the possibility of MI, AAA, and mesenteric ischemia. HIV infection makes infectious causes more likely.


Testing

Tests are selected based on clinical suspicion.

  • Urine pregnancy test for all women of childbearing age

  • Selected imaging tests based on suspected diagnosis

Standard tests (eg, CBC, chemistries, urinalysis) are often done but are of little value due to poor specificity; patients with significant disease may have normal results. Abnormal results do not provide a specific diagnosis (the urinalysis in particular may show pyuria or hematuria in a wide variety of conditions), and they can also occur in the absence of significant disease. An exception is serum lipase, which strongly suggests a diagnosis of acute pancreatitis. A bedside urine pregnancy test should be done for all women of childbearing age because a negative result effectively excludes ruptured ectopic pregnancy.

An abdominal series, consisting of flat and upright abdominal x-rays and upright chest x-rays (left lateral recumbent abdomen and anteroposterior chest x-ray for patients unable to stand), should be done when perforation or obstruction is suspected. However, these plain x-rays are seldom diagnostic for other conditions and need not be otherwise automatically done. Ultrasound should be done for suspected biliary tract disease or ectopic pregnancy (transvaginal probe) and for suspected appendicitis in children. Ultrasound can also detect AAA but cannot reliably identify rupture. Noncontrast helical CT is the modality of choice for suspected renal stones. CT with oral and IV contrast is diagnostic in about 95% of patients with significant abdominal pain and has markedly lowered the negative laparotomy rate. However, advanced imaging must not be allowed to delay surgery in patients with definitive symptoms and signs.


Treatment

Some clinicians feel that providing pain relief before a diagnosis is made interferes with their ability to evaluate. However, moderate doses of IV analgesics (eg, fentanyl 50 to 100 mcg, morphine 4 to 6 mg) do not mask peritoneal signs and, by diminishing anxiety and discomfort, often make examination easier.

Key Points

  • Look for life-threatening causes first.

  • Rule out pregnancy in women of childbearing age.

  • Seek signs of peritonitis, shock, and obstruction.

  • Blood tests are of minimal value.

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  • DURAMORPH PF, MS CONTIN
  • ACTIQ, DURAGESIC, SUBLIMAZE

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