Acute abdomen

Acute abdomen refers to severe abdominal pain lasting for hours to a few days. The underlying pathology may be intraabdominal, thoracic, or systemic and may require urgent surgical intervention. The initial approach to acute abdomen should be to assess for immediately life-threatening causes (e.g., ruptured abdominal aortic aneurysm, bowel perforation) by checking vital signs, performing a quick physical examination, and immediately conducting the appropriate focused diagnostic tests (e.g., abdominal ultrasound, abdominal x-ray). Once emergency causes have been ruled out, a thorough history and physical examination should be performed to narrow the differential diagnoses and guide further diagnostic workup and therapy. Causes of chronic abdominal pain are not addressed in this article.

See “Blunt abdominal trauma” and “Penetrating abdominal trauma” for details on traumatic causes of abdominal pain.

Patient acuity and high-risk demographics for certain acute abdominal conditions determine the urgency of the approach. Critically ill patients need to be stabilized and evaluated concurrently.

Initial management ^[1]

• ABCDE survey
  • Hemodynamic support
    • IV access with two large-bore peripheral IVs
    • IV fluid resuscitation
    • If hemorrhagic shock is suspected in unstable patients with abdominal pain, order type and crossmatched blood immediately.
  • Respiratory support, e.g., oxygen therapy as needed
• Establish NPO status.
• Perform a focused history and physical examination.
• Perform targeted diagnostics (see “Diagnostic workup of acute abdomen”).
• Immediate or urgent specialty consult as needed; examples include: (see also “Disposition.”)
  • Vascular surgery for a ruptured or symptomatic AAA
  • General surgery for hemodynamically unstable patients with a rigid abdomen
  • Urology for testicular torsion
  • OB/GYN for a ruptured ectopic pregnancy
• Administer supportive care as needed.
  • Parenteral analgesics
  • Empiric antibiotics for intraabdominal infections
  • Antiemetics
  • NG tube placement
  • Urinary catheter placement (e.g., Foley catheter)
• Identify and treat the underlying cause.

To avoid misdiagnosis, remember to consider gynecological causes of abdominal pain such as PID and pregnancy-related conditions in sexually active female patients and those of childbearing age. ^[2]

Red flags for abdominal pain

The following red flags highlight conditions that can put patients at high risk for life-threatening causes of abdominal pain or misdiagnosis.

• Risk Factors
  • Age > 50 years
  • Immunocompromise ^[3]
  • Previous abdominal surgery ^[4]
  • History of CAD and/or atrial fibrillation
• Unstable vital signs: hypotension, tachycardia
• Pain characteristics
  • Sudden onset of severe pain
  • Pain that interrupts sleep
  • Pain out of proportion to abdominal findings
• Accompanying symptoms
  • Bilious vomiting
  • Hematemesis, hematochezia
  • Jaundice
• Findings on examination
  • Possible peritoneal signs
    • Guarding and/or rigidity (focal or diffused)
    • Rebound tenderness (focal or diffused)
  • Absent or tinkling bowel sounds
  • Gross abdominal distention
  • Irreducible, tender bulge on abdomen or groin

Abdominal pain accompanied by hemodynamic instability may indicate internal bleeding, perforated viscus, necrotic bowel, or sepsis.

Maintain a high index of suspicion in immunocompromised and older patients, as they may present without fever, leukocytosis, or localized abdominal tenderness despite having an underlying life-threatening disease. ^[3][5]

Immediately life-threatening diagnoses

• Ruptured abdominal aortic aneurysm
• Aortic dissection
• Myocardial infarction
• Bowel perforation
• Mechanical bowel obstruction
• Acute mesenteric ischemia
• Acute pancreatitis
• Acute cholangitis
• Ruptured ectopic pregnancy

Delays in treatment of serious intraabdominal causes of acute abdominal pain can result in bowel necrosis, sepsis, fistula formation, and death.

Disposition ^[6][7]

• Hemodynamically unstable patients: Consider direct transfer to OR for patients needing emergency surgery or ICU admission.
• Underlying surgical pathology, intractable nausea and vomiting, and/or unremitting pain: inpatient admission
• Stable patients with inconclusive or negative diagnostic workup
  • Extended observation in the ED with serial abdominal examination
  • OR consider discharge with instructions and follow-up if the following criteria are met: :
    • Resolution of pain and nausea
    • Ability to tolerate oral intake
    • Reassuring general appearance and physical examination
    • Ability to adhere to discharge instructions.

The diagnostic workup should be guided by the pretest probability of the diagnoses under consideration. The following list includes some commonly used diagnostic tools that can help to diagnose or rule out possible etiologies in a patient with acute abdominal pain.

Laboratory studies

• Blood gas analysis
• Lactate
• Troponin
• Serum glucose
• CBC
• Coagulation studies (e.g., INR, PT)
• BMP
• LFTs
• Lipase, amylase
• Blood type and screen
• ESR/CRP
• Urinalysis
• β-hCG urine test
• Cultures

Strongly consider a urine pregnancy test in sexually active female patients of reproductive age, irrespective of current contraception use.
Patients with obvious signs of diffuse peritonitis or sepsis may require immediate surgical management without further diagnostic imaging.

Imaging ^{[8][9][10][11][12][13][14]}

Approach

• The initial imaging modality should be guided by the working diagnosis, as based on the patient history, vital signs, and examination.
• The following recommendations apply to nonpregnant adults.
• In pregnant women with acute abdominal pain, ultrasound and/or MRI of the abdomen and/or pelvis without contrast are the preferred initial imaging modalities.

By suspected diagnosis ^[11]

By location of the pain

Maintain a low threshold for obtaining diagnostic imaging in older patients, for whom abdominal pain is associated with higher morbidity and mortality as well as lower initial diagnostic accuracy. ^[24]

Consider diagnostic laparoscopy in hemodynamically stable patients in which the diagnosis is still unclear after complete physical examination and imaging. For patients with hemodynamic instability or severe abdominal distention, proceed to diagnostic laparotomy. ^[25]

In pregnant patients, regardless of the site of pain, ultrasound and MRI are the preferred initial imaging modalities.

Approach

• Determine if the infection is community-acquired or healthcare-associated and how severe it is.
• Consider organisms commonly implicated in intraabdominal infection (e.g., E. coli).
• Consider local resistance patterns.
• See also empiric antibiotic therapy for acute biliary infection.

Community-acquired infections ^[89][90][91]

• Coverage of the following organisms should be considered:
  • Enteric gram-positive streptococci
  • Enteric gram-negative aerobic and facultative bacilli
  • Fluoroquinolone-resistant E. coli
• Enterococcal coverage is not usually necessary for mild to moderate community-acquired infection but is recommended for severe infection.
• Fluoroquinolones are only recommended as a single-agent regimen if the hospital antibiogram indicates > 90% susceptibility of E. coli. ^[89]

Metronidazole is contraindicated in the first trimester of pregnancy.

Healthcare-associated infections ^{[71][89][90][91]}

Healthcare-associated infections are more likely to be antibiotic-resistant and both institutional and individual patient antibiograms should be considered when choosing an empiric regimen!

• Coverage of the following organisms should be considered:
  • Enteric gram-positive streptococci
  • Enteric gram-negative aerobic and anaerobic bacilli (including Pseudomonas aeruginosa)
  • Enterococci
  • MRSA
• Agents to avoid as empiric therapy:
  • Cephalosporins as a single-agent regimen
  • Fluoroquinolones as a single-agent regimen
  • Ampicillin-sulbactam

Obtain cultures, if necessary, before the administration of empirical IV antibiotics.

For patients with a beta-lactam or carbapenem allergy, consider vancomycin with aztreonam and metronidazole.

The differential diagnoses listed here are not exhaustive.