Acute abdomen

Quick Overview

Acute abdomen represents a spectrum of surgical and medical emergencies requiring rapid triage and assessment. NICE NG158 provides structured guidance for early recognition of life-threatening conditions and timely surgical referral within 2 hours for high-risk presentations. Systematic evaluation using clinical examination, targeted investigations, and risk stratification prevents missed diagnoses and delays in definitive management.

Core Facts & Concepts

🚩 Red Flags for 2-Hour Surgical Referral (NICE NG158):

• Signs of peritonitis (guarding, rigidity, rebound tenderness)
• Suspected ruptured AAA (age >50, pulsatile mass, shock)
• Suspected intestinal obstruction with ischaemia
• Unexplained shock or sepsis with abdominal pain
• Evidence of free intraperitoneal gas

📊 Key Clinical Parameters:

• Bowel ischaemia: Lactate >2 mmol/L with disproportionate pain
• Perforation: Air under diaphragm on erect CXR (70-80% sensitivity)
• AAA rupture: Mortality 50% if delayed; systolic BP <90 mmHg
• Appendicitis: Alvarado score ≥7 indicates high probability

Initial Resuscitation Priorities:

• IV access (2 large-bore cannulae if shocked)
• Fluid resuscitation: 500ml crystalloid bolus if systolic <90 mmHg
• Analgesia: Do NOT withhold (does not mask peritonism)
• NBM status and NG tube if obstruction/ileus suspected
• Catheterise for fluid balance monitoring

Problem-Solving Approach

Systematic Assessment Framework:

1. Rapid triage (ABCDE approach):

   • Airway/Breathing: Assess for aspiration risk, respiratory compromise
   • Circulation: BP, HR, capillary refill (<2 seconds normal)
   • Disability: Conscious level (pain may cause agitation)
   • Exposure: Full abdominal examination

2. Focused history (<5 minutes):

   • Pain characteristics: Onset (sudden vs gradual), location, radiation
   • Associated symptoms: Vomiting (obstruction), diarrhoea, fever
   • Last menstrual period (ectopic pregnancy in women of childbearing age)
   • Previous surgery (adhesions), medications (anticoagulation)

3. Examination sequence:

   • Inspection: Distension, scars, hernias
   • Auscultation BEFORE palpation: Bowel sounds (absent/tinkling)
   • Palpation: Start away from pain; assess for peritonism
   • Percussion: Shifting dullness (ascites), tympany (obstruction)
   • Digital rectal examination: Masses, melaena, tenderness

4. Immediate investigations:
   • Bloods: FBC, U&E, LFTs, amylase, lactate, group & save
   • Imaging: Erect CXR (perforation), AXR (obstruction), USS (biliary/gynae)
   • Pregnancy test in all women of childbearing age

Analysis Framework

🎯 Key Discriminating Features:

• Peritonism = Surgical abdomen until proven otherwise
• Lactate >2 mmol/L + abdominal pain = Ischaemia until excluded
• Sudden onset = Perforation, AAA, ectopic pregnancy
• Gradual onset = Inflammation (appendicitis, cholecystitis, diverticulitis)

Visual Aid

Differential Diagnosis by Location:

Key Points Summary

✓ NICE NG158: Refer within 2 hours if peritonism, suspected ischaemia, ruptured AAA, or unexplained shock

✓ Do NOT withhold analgesia - does not mask peritoneal signs and improves examination compliance

✓ Lactate >2 mmol/L with abdominal pain = bowel ischaemia until proven otherwise; requires urgent CT angiography

✓ Ruptured AAA: If unstable (SBP <90), go directly to theatre - CT causes fatal delay

✓ Pregnancy test mandatory in all women of childbearing age (ectopic pregnancy can present atypically)

✓ Erect CXR detects 70-80% of perforations; if clinical suspicion high but CXR negative, proceed to CT with oral contrast

✓ Bowel sounds: Absent = ileus/peritonitis; High-pitched/tinkling = obstruction; Normal does NOT exclude pathology

⚠️ Warning: Elderly and immunocompromised patients may have minimal abdominal signs despite life-threatening pathology - maintain high index of suspicion