THE CHIEF
COMPLAINT

Gastrointestinal · Clinical algorithm

Abdominal Pain: General

Back to contents

Use the zoom controls to enlarge the algorithm, or open the full-screen view.

01The Approach And Initial Assessment

  • Is the patient crashing / unstable?
  • Hypotension, poor perfusion, altered, pale / diaphoretic, severe illness
  • Resuscitation and diagnosis occur together
    • IV / monitor / O2 as needed, fluids, blood if hemorrhage suspected, antibiotics if infection / perforation suspected
  • Bedside US early in the unstable abdominal-pain patient
    • Aorta → Aorta size, free fluid - AAA?
    • Abdomen / pelvis → free fluid - hemoperitoneum
    • Pregnancy? → free fluid - ruptured ectopic?
    • Free fluid in nontraumatic shock → hemorrhage until explained
  • Surgery / Vascular Surgery / Gyn consult
  • Are there peritoneal signs?
  • Guarding, rigidity, rebound, severe pain with movement
  • Think surgical abdomen
  • Resuscitate, antibiotics if appropriate, urgent surgery
  • Consider Bedside US
  • CT if stable enough and it will help define the process
  • Abdominal pain + red flag → which critical diagnosis moves up enough that I need to pursue it?
  • AAA → age / smoking / vascular disease / hypotension / syncope / pulsatile mass
  • Ectopic → reproductive potential / positive pregnancy test / syncope / bleeding
  • Mesenteric ischemia → AF / vascular disease / pain out of proportion / low-flow state
  • Perforation → peritoneal signs / severe onset / sepsis / procedural or GI risk
  • SBO → vomiting / distention / obstipation / prior surgery / hernia
  • The red flag determines the next step → bedside US, CT / CTA, urgent surgery, vascular, GYN, or IR
  • If no critical diagnosis is emerging → localize the pain and move into the upper / lower / pelvic abdominal-pain pathway

02Critical Condition?

Abdominal Aortic Aneurysm — AAA

Common Presentation

  • Often asymptomatic until symptomatic / ruptured
  • New abdominal, flank, or back pain
  • Expansile pulsatile abdominal mass — absence does not exclude AAA JAMA
  • Hypotension / shock if ruptured

Uncommon / Atypical Presentations

  • Syncope ± little abdominal pain
  • Renal colic mimic → flank / back pain ± hematuria JVS
  • Diverticulitis mimic → LLQ pain
  • Neurologic / compressive symptoms from retroperitoneal expansion
  • GI bleeding + known AAA / prior aortic repair → consider aortoenteric fistula PubMed

Red Flags — What Moves The Needle?

  • Unexplained abdominal / back / flank pain +
    • Hypotension / syncope
    • Ill appearing
    • Risk factors: older age, male, smoking, hypertension / vascular disease, family history
    • Known AAA / prior aortic repair SVS
    • Wide pulsatile abdominal mass
  • Multiple findings together → increase risk → lower threshold to image
  • Classic H&P findings have poor sensitivity therefore absence does not exclude rAAA Academic Emergency Medicine

Diagnosis

  • POCUS
    • Rapidly identifies AAA
    • Negative free fluid does not exclude rupture
    • Incomplete visualization ≠ negative study ACEP
  • CTA abdomen / pelvis
    • Stable / stabilized patient
    • Defines aneurysm, rupture, extent, anatomy ACC/AHA

The Algorithm

Crashing
  • Persistent hypotension / poor perfusion despite initial resuscitation
  • POCUS → AAA?
  • Immediate vascular surgery / OR
  • Do not delay for CT if rupture strongly suspected SVS
Unstable
  • Hypotensive / ill appearing but responds to initial resuscitation
  • POCUS first
  • Resuscitate
  • If able to tolerate transport → CTA
  • Early vascular surgery involvement
Stable / Symptomatic
  • New pain attributable to known / discovered AAA
  • CTA
  • Urgent vascular evaluation SVS
Incidental / Asymptomatic
  • Establish AAA is not the cause of presenting symptoms
  • Vascular follow-up / surveillance based on aneurysm characteristics SVS

Other Spontaneous Hemoperitoneum

  • Ruptured splenic artery or other visceral aneurysm
  • Spontaneous splenic rupture
  • Ruptured hepatic lesion / HCC / adenoma
  • Anticoagulation-related spontaneous intra-abdominal bleeding
  • Ruptured hemorrhagic ovarian cyst
  • Bedside US may show free fluid

In The Pit…

  • Abdominal / back pain + red flag → think AAA
  • Pain + crashing → POCUS → OR, Vascular Surgeon
  • Pain + unstable / ill appearing → POCUS → resuscitate → CTA if able / Vascular Surgery
  • Pain + major risk factors → CTA, Vascular Surgeon if positive
  • Classic findings help; their absence does not reassure Academic Emergency Medicine
  • Final common pathway in the stable / stabilized patient → CTA

Ruptured Ectopic Pregnancy

Acute Mesenteric Ischemia — AMI

Etiology

1. Arterial Embolism
  • Usually embolic source → atrial fibrillation / cardiac thrombus / valvular disease
  • Sudden onset abdominal pain
  • Pain out of proportion to exam
  • N/V/D ± GI bleeding
2. Arterial Thrombosis
  • Acute thrombosis on chronic mesenteric atherosclerosis
  • Vascular risk factors
  • May have preceding chronic mesenteric ischemia
    • Postprandial abdominal pain
    • Weight loss
    • Food avoidance
3. Mesenteric Venous Thrombosis
  • Often less abrupt / more progressive
  • VTE / hypercoagulable risk
    • Prior DVT / PE
    • Malignancy
    • Thrombophilia
    • Portal hypertension / intra-abdominal inflammation
4. Non-Occlusive Mesenteric Ischemia — NOMI
  • Low-flow / vasoconstricted state
  • Shock / heart failure / sepsis
  • Vasopressors
  • Dialysis / severe critical illness

Red Flags — What Moves The Needle?

  • Severe / unexplained abdominal pain +
    • Pain out of proportion to exam
    • Older / vascular disease or risk factors
    • Atrial fibrillation / embolic source
    • Prior postprandial pain / weight loss
    • Hypercoagulable / VTE history
    • Shock / low-flow state
  • Early abdominal exam may be relatively benign
  • Peritoneal signs → late / bowel infarction until proven otherwise
  • Labs are nonspecific but increase suspicion with lactate / metabolic acidosis / leukocytosis
    • Normal lactate does not exclude AMI
  • Multiple findings together → lower threshold for CTA Emergency Medicine Clinics 2026

Diagnosis

  • CTA abdomen / pelvis
    • Diagnostic study of choice
    • Tell radiology you are concerned for AMI
    • Evaluate arterial + venous vasculature + signs of bowel ischemia / infarction
    • Do not delay when clinical suspicion is meaningful ACR
    • Sensitivity ~92%, specificity ~98.8% in 2025 meta-analysis Scientific Reports 2025
  • Labs
    • Lactate / metabolic acidosis / leukocytosis may support concern or severity
    • No laboratory test reliably excludes AMI
  • Plain radiographs → little role in early diagnosis
  • Catheter angiography → selected diagnostic / therapeutic role rather than routine first test

Critical Actions

  • Resuscitate
  • Early surgery / vascular / IR involvement
  • Broad-spectrum antibiotics
  • Anticoagulation when appropriate, especially mesenteric venous thrombosis
  • Early revascularization for occlusive arterial AMI when bowel remains salvageable
  • Peritonitis / necrotic bowel → operative exploration / resection
  • NOMI → correct low-flow state / restore mesenteric perfusion

In The Pit…

  • Unexplained abdominal pain + AMI red flag → low threshold for CTA
  • Pain out of proportion + AF / embolic risk → CTA
  • Pain + vascular disease / prior postprandial symptoms → CTA
  • Pain + hypercoagulable / VTE risk → CTA
  • Critically ill / low-flow patient + unexplained abdominal deterioration → think NOMI
  • Final common pathway → CTA

Bowel Perforation

Red Flags — What Moves The Needle?

  • Abdominal pain +
    • Sudden / severe onset
    • Peritoneal signs → guarding / rigidity / rebound
    • Ill appearing / sepsis / shock
    • Recent GI procedure / instrumentation
    • PUD / NSAID use
    • Diverticulitis / IBD / malignancy
    • Obstruction / ischemia / trauma / foreign body
  • Contained perforation may be more subtle
  • Labs may support concern
    • Leukocytosis
    • Metabolic acidosis
    • Nonspecific → normal labs do not exclude perforation WSES

Diagnosis

  • CT A/P with IV contrast
    • Main diagnostic study in stable / stabilized patient
    • Identifies free air / fluid, wall defect, inflammatory change, abscess / phlegmon
    • Helps localize the perforation and underlying cause CT findings
  • Upright CXR
    • Quick positive free air can establish concern
    • Negative CXR does not exclude perforation WSES

The Algorithm

Crashing / Generalized Peritonitis
  • Resuscitate
  • Broad-spectrum IV antibiotics
  • Urgent surgery consultation
  • Source control / OR
  • CT only if it will not delay definitive care
Stable + Red Flags
  • CT A/P
  • Perforation identified → urgent surgery consultation AGA
  • Free perforation / peritonitis → operative source control
  • Contained perforation → management depends on location / cause / clinical status

In The Pit…

  • Abdominal pain + perforation red flag → bowel perforation?
  • Crashing + generalized peritonitis → resuscitation + antibiotics + surgery
  • Pain + shock / sepsis → free perforation?
  • Pain + peritoneal signs → perforation moves way up → CT
  • Pain + recent procedure / PUD / diverticulitis / IBD / obstruction / ischemia → lower threshold for CT
  • No peritoneal signs does not reassure if contained perforation is possible
  • Stable / stabilized + meaningful concern → CT
  • Final common pathway in the stable / stabilized patient → CT A/P

Small Bowel Obstruction — SBO

Causes

  • Adhesions → most common
  • Hernia
  • Malignancy
  • Inflammatory stricture
  • Volvulus
  • Intussusception
  • Less common → gallstone ileus / bezoar / foreign body

Clinical

  • Colicky abdominal pain
  • Abdominal distention
  • Nausea / vomiting
  • Obstipation / constipation
  • Partial obstruction may still pass stool / flatus

Red Flags — What Moves The Needle?

  • Abdominal pain + vomiting / distention / obstipation
  • Prior abdominal surgery / adhesions / prior SBO
  • Hernia / abdominal wall mass
  • Continuous or worsening pain rather than intermittent colic
  • Peritoneal signs
  • Fever / tachycardia / ill appearing
  • Leukocytosis / metabolic acidosis
  • Multiple findings together → lower threshold for CT / surgical evaluation

Diagnosis

  • CT A/P with IV contrast
    • Confirms obstruction
    • Identifies transition point / cause
    • Evaluates for bowel compromise
  • Plain abdominal films → limited / adjunctive role
    • Acute abdominal series (AAS): obstructive pattern, air/fluid (A/F) levels

The Algorithm

Need Early Surgery?
  • Peritonitis
  • Continuous / worsening pain
  • Fever / tachycardia / leukocytosis / metabolic acidosis
  • Clinical deterioration
  • Concern for strangulation / ischemia
  • Timely surgical exploration
No Surgical Red Flags
  • NPO
  • IV fluids / correct electrolytes
  • NG decompression if significant vomiting / distention
  • Surgical consultation
  • Initial nonoperative management
  • Reassess for failure / deterioration

In The Pit…

  • Abdominal pain + SBO red flags → think obstruction
  • Pain + vomiting + distention + obstipation → SBO moves up the differential
  • Prior abdominal surgery / adhesions / prior SBO → moves it up further
  • Hernia on exam → look for mechanical obstruction
  • Continuous pain / peritonitis / sick patient → worry about strangulation / ischemia → surgery early
  • Otherwise → CT to confirm obstruction and define cause
  • Final common pathway → CT A/P with IV contrast

Referred Pain

History & Exam

  • Myocardial infarction
  • Aortic dissection
  • Pneumonia — lower lobe
  • Pulmonary embolism

Critical Actions

  • EKG
  • CXR
  • Further testing as needed

03Focused Evaluation

Upper Abdominal Pain

Lower Abdominal Pain

Pelvic Pain

  • See Pelvic Pain Algorithm — Coming Soon

Cases

Level: MS3 CC: Right Lower Quadrant Abdominal Pain Open case~5 min Case 02 CC: It hurts under my ribs Open case8–10 min Case 03 CC: My belly hurts. Walking makes it worse Open case8–10 min

Pop Quiz Hotshot

Pop Quiz HotshotAbdominal Pain: GeneralTest your decisions on unstable abdominal pain, vascular emergencies, perforation, and obstruction.Start Quiz10 Questions

Must-Read References

View Full References

Additional Cited Guidance

Table of contentsAbdominal Pain: Upper

Privacy & analytics choices