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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Acute abdomen is a clinical syndrome: severe abdominal pain with concern for surgical or life-threatening disease.
- Red flags: peritonitis, shock, persistent vomiting, GI bleeding, pregnancy, severe pain out of proportion, pulsatile mass, immunosuppression, or older age.
- Pregnancy test is mandatory in reproductive-age patients with abdominal pain.
- Unstable patient with peritonitis or ruptured AAA concern needs immediate surgical/vascular consultation, resuscitation, and often OR rather than prolonged imaging.
- Pain out of proportion to exam suggests mesenteric ischemia until proven otherwise.
Overview
Emergency approach to severe abdominal pain focused on recognizing peritonitis, ischemia, perforation, obstruction, hemorrhage, ectopic pregnancy, and need for urgent surgery. Emergency management focuses on early recognition, stabilization, targeted investigation, and prompt definitive therapy while avoiding common pitfalls tested on USMLE Step 2 CK.
Epidemiology
This presentation is encountered in emergency and acute care settings. Risk varies by exposure, comorbidity, age, mechanism, and timeliness of treatment. Morbidity and mortality increase when recognition is delayed or when airway, breathing, circulation, antidotal therapy, or definitive source control is postponed.
Clinical Features
Symptoms
Sudden severe pain suggests perforation, ischemia, ruptured aneurysm, stone, torsion, or hemorrhage
Pain out of proportion to exam suggests mesenteric ischemia
Migratory periumbilical to RLQ pain suggests appendicitis
Bilious vomiting, distension, obstipation suggest bowel obstruction
Syncope, shoulder-tip pain, vaginal bleeding, or pregnancy risk suggests ectopic pregnancy/hemoperitoneum
Back/flank pain with hypotension or pulsatile mass suggests ruptured AAA
Signs
Peritonitis: rebound, guarding, rigidity, pain with movement/cough
Shock, fever, altered mental status, or toxic appearance
Incarcerated hernia, scrotal/testicular tenderness, adnexal tenderness, or pelvic mass
Jaundice with fever/RUQ pain suggests cholangitis
Distension, high-pitched bowel sounds early obstruction, absent sounds late ileus/peritonitis
Investigations
First-line
Pregnancy testRequired in all reproductive-age patients with abdominal pain; ectopic pregnancy must be considered until excluded.
CBC, CMP, lipase, urinalysisEvaluate infection, anemia, renal/hepatic disease, pancreatitis, UTI/stone, electrolyte derangement.
Lactate and blood gasConcerning for mesenteric ischemia, shock, sepsis, or perforation; normal lactate does not fully exclude early ischemia.
Type and screen/crossmatchIf bleeding, ruptured AAA, ectopic pregnancy, trauma, or likely surgery.
Second-line
CT abdomen/pelvis with IV contrastWorkhorse for stable adults with undifferentiated acute abdomen.
RUQ ultrasoundFirst-line for suspected gallstones/cholecystitis and useful for biliary obstruction.
Pelvic ultrasoundEvaluate ectopic pregnancy, ovarian torsion, tubo-ovarian abscess, and pelvic pathology.
CTA abdomen/pelvisFor suspected mesenteric ischemia, aortic pathology, or active bleeding.
Specialist
Diagnostic/therapeutic interventionSurgery, vascular surgery, OB/GYN, GI, urology, or interventional radiology depending on suspected diagnosis and instability.
1
Initial stabilization
- ABCs, IV access, monitor, NPO status, IV fluids if dehydrated/shocked.
- Give adequate analgesia and antiemetics; analgesia does not prevent accurate diagnosis.
- Early broad-spectrum antibiotics for sepsis, peritonitis, perforation, cholangitis, ischemic bowel, or complicated intra-abdominal infection.
- Correct hypoglycemia/electrolytes and treat shock while diagnosis is pursued.
2
When to call surgery immediately
- Peritonitis, free air, unstable GI bleed, ruptured AAA, ischemic bowel, strangulated obstruction/hernia, abdominal compartment syndrome.
- Unstable patient with suspected surgical abdomen should not wait for exhaustive diagnostic testing.
- Early consultation for high-risk older adults with concerning exam or persistent severe pain.
3
Condition-specific emergencies
- Ruptured AAA: permissive resuscitation, blood products, vascular surgery/OR, avoid delays.
- Mesenteric ischemia: CTA if stable, broad antibiotics, anticoagulation if arterial/venous thrombotic cause and no contraindication, urgent surgery/vascular.
- Bowel obstruction: NPO, NG tube if significant vomiting/distension, IV fluids, electrolyte correction, surgery if strangulation/peritonitis/closed-loop.
- Ectopic pregnancy: OB/GYN; unstable or ruptured = surgical management and resuscitation.
- Ovarian/testicular torsion: urgent surgical detorsion; imaging should not delay if high suspicion.
4
Disposition
- Admit for peritonitis, obstruction, ischemia, sepsis, uncontrolled pain/vomiting, high-risk imaging findings, or uncertain diagnosis with concerning features.
- Discharge only when dangerous causes are reasonably excluded and return precautions are clear.
Complications
- Sepsis and septic shock: Perforation, cholangitis, appendicitis, diverticulitis, or ischemic bowel can progress rapidly
- Bowel necrosis: From strangulated obstruction, hernia, volvulus, or mesenteric ischemia
- Hemorrhagic shock: Ruptured AAA, ectopic pregnancy, splenic rupture, GI bleed
- Infertility/organ loss: Ovarian or testicular torsion if detorsion delayed
- Missed diagnosis: Older, pregnant, immunosuppressed, and diabetic patients may present atypically
USMLE Step 2 CK Exam Tips
- 1Pain out of proportion = mesenteric ischemia; best test in stable patient is CTA.
- 2Reproductive-age abdominal pain = pregnancy test first.
- 3Peritonitis + free air = perforated viscus; surgery and antibiotics.
- 4Unstable older patient with back/abdominal pain and pulsatile mass = ruptured AAA; OR/vascular now.
- 5Analgesia is appropriate and should not be withheld.
- 6RUQ pain/fever/jaundice = cholangitis; antibiotics and urgent ERCP.
- 7Obstruction with fever, leukocytosis, continuous pain, peritonitis, or lactic acidosis suggests strangulation.
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