Acute abdomen

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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

Figure 1: Erect chest X-ray showing crescent of free air under right hemidiaphragm indicating bowel perforation

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

Figure 2: CT abdomen showing dilated small bowel loops with transition point and collapsed distal bowel indicating small bowel obstruction

  1. 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

ConditionKey DiscriminatorsInvestigationTimeframe
Perforated viscusSudden onset, board-like rigidity, peritonismErect CXR (free gas), CT if unclearImmediate surgery
Bowel obstructionColicky pain, distension, vomiting, tinkling bowel soundsAXR (dilated loops), CT (transition point)<2h if ischaemia suspected
Ruptured AAAAge >50, shock, pulsatile mass, back painNo CT if unstable - direct to theatreImmediate vascular surgery
Acute appendicitisRIF pain, McBurney's point tenderness, feverUSS/CT if diagnostic uncertainty6-12h surgical review
Acute pancreatitisEpigastric pain radiating to back, amylase >3× normalCT after 72h (complications), USS (gallstones)Conservative initially
Mesenteric ischaemiaPain out of proportion, AF/CVS disease, lactate ↑CT angiographyUrgent surgery (<6h)

🎯 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:

RUQEpigastricRIFLIFDiffuse
CholecystitisPancreatitisAppendicitisDiverticulitisPeritonitis
HepatitisPeptic ulcerEctopic pregnancyColitisObstruction
PneumoniaMIOvarian torsionOvarian pathologyAAA

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

Practice Questions: Acute abdomen

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Flashcards: Acute abdomen

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Managment of Left Ventricular Free Wall Rupture includes urgent _____

TAP TO REVEAL ANSWER

Managment of Left Ventricular Free Wall Rupture includes urgent _____

pericardiocentesis and thoracotomy

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