Abdominal Pain

Key considerations: Ruptured AAA, Mesenteric ischemia, Ectopic pregnancy

Cannot miss

Ruptured AAA
Mesenteric ischemia
Ectopic pregnancy
Appendicitis (atypical)
Bowel obstruction with strangulation
Perforated viscus
Acute pancreatitis (necrotizing)

Likely diagnoses

Gastroenteritis
Constipation
Gastritis / GERD
Urinary tract infection
Musculoskeletal pain
Functional abdominal pain / IBS
Biliary colic / Cholecystitis

Red flags

Age >50 with new-onset abdominal pain
Rigid abdomen / peritoneal signs
Hemodynamic instability
Pain out of proportion to exam (mesenteric ischemia)
Abdominal pain with syncope (ruptured AAA)
Fever with peritoneal signs
Immunocompromised patient
Post-operative abdominal pain

Workup

history: Location, onset, quality, severity, radiation; Associated: nausea, vomiting, diarrhea, constipation, bloody stool; Last menstrual period — pregnancy test in all women of reproductive age; Surgical history: prior abdominal surgeries (adhesion risk); Medications: NSAIDs (ulcer), anticoagulants, steroids (mask peritonitis); Diet: alcohol, fatty foods (biliary), timing of onset; exam: Vital signs: tachycardia and fever suggest surgical abdomen; Inspection: distension, scars, visible peristalsis; Auscultation: high-pitched (obstruction), absent (ileus); Palpation: tenderness location, guarding, rebound, rigidity, Murphy sign; Rectal: blood, masses, tenderness; Pelvic exam if GYN pathology suspected; CVA tenderness (pyelonephritis, renal colic); labs: CBC: WBC, Hgb (bleeding); BMP: BUN/Cr, electrolytes (dehydration); Lipase (pancreatitis — lipase alone is sufficient, no need for amylase); Liver function tests: AST, ALT, Alk Phos, Bilirubin (biliary/hepatic); Urinalysis: UTI, kidney stone; HCG: every woman of reproductive age with abdominal pain; Lactate: mesenteric ischemia, sepsis; imaging: CT abdomen/pelvis with IV contrast: most comprehensive ED study for undifferentiated abdominal pain; RUQ ultrasound: biliary pathology — cholecystitis, cholelithiasis, CBD dilation; Pelvic ultrasound: ectopic pregnancy, ovarian pathology; KUB: obstruction (air-fluid levels), free air (upright); CT angiography: mesenteric ischemia (if high suspicion); bedside: Point-of-care ultrasound: free fluid (FAST), AAA screening (>3cm abnormal, >5cm urgent), gallbladder, hydronephrosis; Pregnancy test

Management

immediate: IV access, fluid resuscitation if dehydrated or hemodynamically unstable; Pain control: do NOT withhold analgesia — pain management does not mask surgical findings; Pregnancy test before imaging; NPO if surgical cause suspected; general: Broad differential — location-based approach helps narrow; RUQ: biliary, hepatic, pneumonia. LUQ: splenic, pancreatitis, gastric. RLQ: appendicitis, ovarian, hernia. LLQ: diverticulitis, ovarian, hernia; Epigastric: gastritis, pancreatitis, ACS, AAA. Diffuse: obstruction, mesenteric ischemia, peritonitis; specific: diagnosis: Appendicitis; steps: Surgery consult for appendectomy; NPO, IV antibiotics (ceftriaxone + metronidazole); IV fluids and pain control; CT with IV contrast confirms diagnosis (sensitivity >95%); diagnosis: Cholecystitis; steps: NPO, IV fluids, pain control; IV antibiotics if febrile or septic (piperacillin-tazobactam); Surgery consult for cholecystectomy within 72 hours; MRCP or ERCP if CBD dilation or elevated bilirubin (choledocholithiasis); diagnosis: Small Bowel Obstruction; steps: NPO, nasogastric tube for decompression; IV fluid resuscitation; Surgery consult — urgent if strangulation suspected (fever, tachycardia, peritoneal signs); CT abdomen with IV contrast: transition point, closed loop, pneumatosis (ischemia); diagnosis: Ruptured AAA; steps: Emergent vascular surgery consult — OR immediately; Activate MTP if hemodynamically unstable; Bedside ultrasound: AAA >5cm = urgent; Do NOT delay for CT if clinical diagnosis and unstable

Disposition

admit: Surgical abdomen (appendicitis, cholecystitis, obstruction, perforation); Pancreatitis unable to tolerate PO; Mesenteric ischemia; Hemodynamic instability; Intractable pain or vomiting; discharge: Benign exam with clear etiology (gastroenteritis, constipation, biliary colic); Able to tolerate PO and pain controlled; Reliable follow-up; Return precautions given (worsening pain, fever, bloody stool, inability to eat/drink); consults: General surgery: appendicitis, cholecystitis, obstruction, perforation; Vascular surgery: AAA, mesenteric ischemia; GI: GI bleeding, pancreatitis complications, ERCP; OB/GYN: ectopic pregnancy, ovarian torsion

Clinical pearls

Pain out of proportion to exam = mesenteric ischemia until proven otherwise — the classic presentation has a high mortality if missed
Elderly patients with abdominal pain have higher rates of surgical pathology and atypical presentations — have a low threshold for CT
Lipase alone is sufficient for pancreatitis diagnosis — amylase adds no value and has lower specificity
A normal WBC does not rule out appendicitis — 20% of appendicitis cases have a normal WBC
Every woman of reproductive age with abdominal pain needs a pregnancy test — ectopic pregnancy kills

Source and review

ACR Appropriateness Criteria, Eastern Association for Surgery of Trauma (EAST) Guidelines, ACS Emergency General Surgery. Last reviewed: 2024-11-01