Acute Abdominal Pain

Introduction

Acute abdominal pain is a cornerstone topic for the MCCQE1 and a frequent presentation in Canadian emergency departments. As a candidate, you must demonstrate the CanMEDS Medical Expert role by differentiating between self-limiting conditions and life-threatening surgical emergencies (the “Acute Abdomen”).

For MCCQE1 preparation, focus on the “undifferentiated patient.” You are expected to efficiently gather data, formulate a differential diagnosis based on anatomy and epidemiology, and select high-value investigations in line with Choosing Wisely Canada.

Clinical Approach: History and Physical

History taking

A thorough history is the most powerful tool in your arsenal. Utilize the SOCRATES mnemonic to characterize the pain.

Physical Examination

The physical exam should be systematic. Avoid the rookie mistake of palpating the painful area first.

Differential Diagnosis by Quadrant

For the MCCQE1, categorizing differentials by anatomy is the most efficient strategy.

Red Flags for Surgical Abdomen

Identify these immediately.

Investigations

Investigations must be targeted. In the Canadian context, resource stewardship is vital.

Laboratory Studies

Imaging Guidelines (Canadian Context)

The choice of imaging depends on the differential and patient stability.

1. Abdominal X-ray (AXR):

   • Indications: Suspected obstruction (air-fluid levels), perforation (free air under diaphragm), foreign body.
   • Limitation: Low sensitivity for most other pathologies.

2. Ultrasound (US):

   • First line: Biliary pathology (RUQ), Pelvic pathology (Gyn), Appendicitis (in children/pregnant patients).
   • Point of Care US (POCUS): Essential in ER for detecting AAA or free fluid (FAST).

3. CT Abdomen/Pelvis:

   • Gold Standard: Appendicitis (adults), Diverticulitis, Ischemia, Pancreatitis, Obstruction.
   • Note: Use IV contrast for most abdominal pain unless looking for stones (CT KUB).

Management Principles

Initial Stabilization

Follow the ABCDE protocol.

• IV Access: 2 large-bore IVs if unstable.
• Fluids: Ringer’s Lactate or Normal Saline.
• NPO: Keep patient “Nil Per Os” until surgical decision is made.

Analgesia

Myth Buster: Administering analgesia (e.g., Morphine, Fentanyl) does not mask peritoneal signs or delay diagnosis. Early analgesia is the standard of care in Canada.

Specific Management

• Surgical Consult: For appendicitis, cholecystitis, perforation, obstruction, ischemia.
• Antibiotics: Broad-spectrum (e.g., Cefazolin + Metronidazole or Pip/Tazo) if sepsis or perforation is suspected.

Key Points to Remember for MCCQE1

• Ectopic Pregnancy: Always the first rule-out in a female of reproductive age with abdominal pain.
• The Elderly: Often present atypically. They may have a “silent abdomen” (no guarding) even with severe pathology like perforation. Have a low threshold for CT.
• Mesenteric Ischemia: Suspect in patients with Atrial Fibrillation or vascular disease presenting with severe pain but a “benign” exam.
• DKA: Can present with diffuse abdominal pain and vomiting, mimicking an acute abdomen (especially in children). Check glucose/ketones.
• Referred Pain: Remember that MI (Inferior) and Pneumonia (Lower lobe) can present as abdominal pain.

Sample Question

Case Presentation

A 26-year-old female presents to the Emergency Department with a 12-hour history of abdominal pain. The pain began periumbilically and has now migrated to the right lower quadrant. She reports associated nausea and anorexia but no vomiting. Her last menstrual period was 4 weeks ago. She is sexually active and uses condoms intermittently.

On examination, she is afebrile (37.2°C), HR 88 bpm, BP 118/76 mmHg. There is tenderness at McBurney’s point with voluntary guarding.

Question

Which one of the following is the most appropriate initial diagnostic investigation?

• A. Computed tomography (CT) of the abdomen and pelvis
• B. Abdominal ultrasound
• C. Urine Beta-hCG test
• D. Diagnostic laparoscopy
• E. Plain abdominal radiograph

Explanation

The correct answer is:

• C. Urine Beta-hCG test

Detailed Explanation: In any female of reproductive age presenting with abdominal pain, the most critical initial step is to rule out pregnancy to exclude an ectopic pregnancy, which is a life-threatening emergency. Even though the clinical picture is classic for appendicitis (migratory pain, anorexia, RLQ tenderness), an ectopic pregnancy can mimic these symptoms perfectly. Furthermore, the pregnancy status dictates imaging choices (avoiding radiation/CT if pregnant).

• Option A (CT): While CT is highly sensitive for appendicitis, it involves radiation and is contraindicated until pregnancy is ruled out.
• Option B (Ultrasound): This would be the imaging modality of choice after pregnancy status is established or if the patient is pregnant/pediatric. However, the beta-hCG is the initial screening test required.
• Option D (Laparoscopy): This is invasive and reserved for treatment or when diagnosis remains unclear after imaging.
• Option E (X-ray): Low yield for appendicitis or ectopic pregnancy.

Canadian Guidelines & Resources

1. Choosing Wisely Canada: Guidelines on imaging for appendicitis and lower back pain.
2. Canadian Association of Gastroenterology (CAG): Clinical practice guidelines for management of various GI conditions.
3. SOGC Guidelines: For management of ectopic pregnancy and acute pelvic pain.

References

1. Medical Council of Canada. (n.d.). Objectives for the Qualifying Examination Part I. Retrieved from mcc.ca 
2. Choosing Wisely Canada. (2023). Emergency Medicine: Ten Things Physicians and Patients Should Question.
3. Dubin, J., et al. (2022). Diagnosis and Management of Acute Appendicitis. Canadian Journal of Emergency Medicine.
4. Tintinalli, J. E., et al. (2020). Tintinalli’s Emergency Medicine: A Comprehensive Study Guide (9th ed.). McGraw-Hill Education.