Figure 40.1. Location and differential diagnosis of acute abdominal pain.
Diagnosis and evaluation
- History and physical characteristics
- A thorough history will generally narrow the differential diagnosis.
- Past medical and surgical histories and medication usage may harbor clues (e.g., prior abdominal surgery may suggest adhesions as an etiology for bowel obstruction) or rule out potential diagnoses (e.g., prior cholecystectomy in the setting of right upper quadrant pain).
- Always note the location and characterization of the pain to help with the differential diagnosis (see Figure 40.1).
- Duration of symptoms, mode of onset (gradual and insidious versus sudden), and associated symptoms (nausea, vomiting, anorexia, fatigue, rash) should be noted.
- Change over time should be noted: the temporal transition from poorly described vague abdominal pain to persistent sharp discomfort specific to an area of the abdomen, such as occurs in appendicitis, often signifies the worsening of an intra-abdominal process and might need surgical intervention.
- A thorough history will generally narrow the differential diagnosis.
- Physical examination
- Assess the patient overall, including vital signs (derangement of vital signs signifies more serious underlying illness) and demeanor.
- A focused examination should include not only the gastrointestinal system but also the cardiovascular and respiratory systems.
- Abdominal examination:
- Begin the abdominal examination away from the area that is most painful.
- Inspect the abdomen for surgical scars, bulges, pulsations, and other abnormalities (skin discoloration, petechiae).
- Observe the respiratory movement of the abdomen – in cases of peritonitis the abdominal wall will barely move due to muscle rigidity, which can be localized or generalized.
- Auscultate for bowel sounds, bruits and abnormal pulsations.
- Begin the palpation portion of the examination gently, progressing slowly to deeper palpation (remember that the stethoscope can be used to distract and palpate simultaneously). Ask the patient to point with one finger to the area that is most painful, and begin palpating the abdomen far away from that point.
- Involuntary guarding (physiological contraction of the abdominal wall) denotes an underlying inflammatory process (i.e., peritonitis), which can be localized or generalized.
- Gentle percussion combined with palpation is more specific than testing for rebound.
- Muscular rigidity, the extreme of involuntary guarding, can be absent in cases of chronic deconditioning, the severely decompensated patient, or the elderly.
- Begin the abdominal examination away from the area that is most painful.
- Rectal and pelvic examinations should be performed in appropriate patients.
- Assess the patient overall, including vital signs (derangement of vital signs signifies more serious underlying illness) and demeanor.
- Laboratory testing
- Results of a selected test should be anticipated to alter the management plan; otherwise that test should not be ordered.
- Initial bloodwork including a hematocrit and electrolytes can guide initial fluid resuscitation.
- The white blood cell count (WBC), while useful, is fairly nonspecific as WBCs can be elevated in a variety of nonsurgical conditions, and normal or low in surgical conditions.
- In the unstable patient, an arterial blood gas and/or base deficit may provide more information than blood chemistries and better guide resuscitation.
- Coagulation studies and a type and screen are generally necessary tests for the patient with acute abdominal pain of suspected surgical etiology. Cross-matched blood should be requested in select patients.
- Females of child-bearing age should have a urine pregnancy test.
- Results of a selected test should be anticipated to alter the management plan; otherwise that test should not be ordered.
- Radiological testing
- Abdominal plain films are rarely diagnostic, although they may identify air–fluid levels (suggestive of a bowel obstruction or ileus), renal or ureteral calculi, and occasionally free intraperitoneal air.
- The test of choice to identify free intraperitoneal air is the upright chest radiograph. For patients who cannot sit upright, consider a lateral decubitus radiograph.
- Ultrasound should be considered for suspected biliary (acute cholecystitis) and gynecological etiologies of acute abdominal pain (tubo-ovarian abscess, ectopic pregnancy).
- Computed tomography (CT) has largely supplanted plain film radiology in many centers, but concerns of cost and the risk of ionizing radiation require judicious use of this modality.
- When considering abdominal and pelvic CT, the suspected diagnosis should guide the use of IV and oral contrast. Many emergency departments have established protocols to guide the use of contrast.
- Water-soluble oral contrast should be used in cases of suspected obstruction or perforation.
- The interpretation of findings on CT (or any test) should match the story painted by the history and physical examination. Otherwise, reevaluate the patient.
- When considering abdominal and pelvic CT, the suspected diagnosis should guide the use of IV and oral contrast. Many emergency departments have established protocols to guide the use of contrast.
- Abdominal plain films are rarely diagnostic, although they may identify air–fluid levels (suggestive of a bowel obstruction or ileus), renal or ureteral calculi, and occasionally free intraperitoneal air.
Critical management
- The unstable patient
- As with the stable patient, a well-formulated differential diagnosis based on careful history and physical examination will guide the plan of care far better than a “shotgun” approach of imaging and laboratory tests.
- Resuscitation must begin concurrently with the diagnostic modalities.
- Intubation may be necessary for airway protection.
- Large-bore intravenous access should be secured and electrolyte abnormalities corrected.
- Nasogastric decompression is beneficial in patients with generalized ileus.
- A Foley catheter can be placed to monitor fluid status and guide resuscitation.
- Hypothermia should be corrected with warming blankets and heated fluids.
- Frequent reassessment of hemodynamics and acid–base status is necessary.
- An unstable patient should never be transported to the radiology suite without a supervising physician.
- Intubation may be necessary for airway protection.
- Pain control
- Early and judicious opioid administration is recommended.
- Historically, some clinicians have cautioned against the use of analgesia in the patient with an “acute abdomen” out of concern that opioids would mask presenting symptoms and confound timely diagnosis. Over the past decade, multiple prospective, randomized, controlled trials have failed to show that early analgesia administration impairs diagnostic accuracy.
- Early and judicious opioid administration is recommended.
- Preparation for the OR
- The amount of time allowed for preoperative resuscitation should be balanced with the degree to which the underlying disease process is likely to progress.
- Patients with an acute abdomen requiring surgical correction should be treated in similar fashion as the unstable patient.
- Appropriate fluid resuscitation should be given (via large-bore intravenous access), and electrolyte abnormalities should be corrected.
- In addition to a type and screen, cross-matched blood should be available for the operating suite in cases in which the degree of operative intervention is unknown (i.e., the patient with large amounts of free intraperitoneal air, as opposed to the stable patient with early appendicitis).
- The amount of time allowed for preoperative resuscitation should be balanced with the degree to which the underlying disease process is likely to progress.
Special circumstances
- Special populations
- A higher index of suspicion for abdominal catastrophe is necessary in situations in which the history is compromised or in which the physical examination is altered or unreliable.
- Some patients, including children, developmentally delayed, or obtunded individuals (from illness or drugs) cannot give a reliable history.
- Patients with spinal cord injuries and impaired sensation often present in a delayed fashion.
- Pregnancy displaces the abdominal viscera and alters the presentation of common illnesses.
- The elderly or immunosuppressed may not experience symptoms in the same way as most adults.
- Morbid obesity hinders physical examination.
- A higher index of suspicion for abdominal catastrophe is necessary in situations in which the history is compromised or in which the physical examination is altered or unreliable.
References
Ameloot K, Gillebert C, Desie N, Malbrain ML. Hypoperfusion, shock states, and abdominal compartment syndrome (ACS). Surg Clin North Am. 2012; 92(2): 207–20, vii.
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