Acute Abdomen
Acute abdomen refers to sudden-onset severe abdominal pain requiring urgent surgical assessment. Causes include appendicitis, bowel obstruction, perforation, and vascular emergencies.
Key Facts
Peritonism (guarding, rebound tenderness, rigidity) indicates peritoneal irritation — surgical emergency until proven otherwise Erect CXR is essential — free air under diaphragm indicates perforation (sensitivity ~80%) CT abdomen/pelvis with IV contrast is the investigation of choice for most acute abdominal emergencies Ruptured AAA must be excluded in any patient >50 years with sudden abdominal/back pain and haemodynamic instability Resuscitation before investigation: IV access, fluids, analgesia (opioids do NOT mask peritonism), NBM, catheter, NG tube if vomiting Modified Alvarado Score: Aids clinical diagnosis of appendicitis (score ≥7 suggests appendicitis) Key differential by quadrant: RIF (appendicitis, ectopic), LIF (diverticulitis, sigmoid volvulus), RUQ (cholecystitis), epigastric (pancreatitis, perforated PU) Pregnancy test (β-hCG) is mandatory in all women of reproductive age with acute abdominal pain
Overview
Key Facts
The acute abdomen is one of the most common surgical emergencies. Systematic assessment using history, examination, and targeted investigations is essential to guide timely and appropriate management.
Epidemiology
Abdominal pain accounts for ~5-10% of ED attendances. Approximately 30-40% of acute surgical admissions are for acute abdominal pain. Most common causes: Non-specific abdominal pain (~35%), appendicitis (~17%), bowel obstruction (~15%), biliary disease (~10%).
Aetiology
By urgency:
- Immediate life-threatening: Ruptured AAA, mesenteric ischaemia, ruptured ectopic pregnancy
- Urgent surgical: Appendicitis, bowel obstruction, perforated viscus, strangulated hernia
- Medical causes: Acute pancreatitis, DKA, acute porphyria, sickle cell crisis, pneumonia
Pathophysiology
Types of abdominal pain:
- Visceral: Dull, poorly localised, midline — from hollow organ distension/ischaemia (autonomic afferents)
- Somatic/parietal: Sharp, well-localised — from peritoneal irritation (somatic afferents)
- Referred: Pain felt at a distant site sharing the same dermatome (e.g., diaphragmatic irritation → shoulder tip)
Clinical Presentation
Systematic Assessment
History:
- SOCRATES for pain
- Associated symptoms: Vomiting, bowel habit change, urinary symptoms, vaginal bleeding/discharge
- Menstrual history and pregnancy possibility
- Previous surgery (adhesions)
- Drug history (NSAIDs, anticoagulants, steroids)
Examination:
- Inspection: Distension, scars, visible peristalsis
- Palpation: Tenderness, guarding, rigidity, rebound, masses, hernial orifices
- Percussion: Peritonism, shifting dullness
- Auscultation: Bowel sounds (absent = peritonitis/ileus; tinkling/high-pitched = obstruction)
- PR examination: Mandatory in acute abdomen
Red Flags
- Peritonism (guarding + rigidity) — surgical emergency
- Haemodynamic instability (tachycardia, hypotension) — resuscitate immediately
- Absent bowel sounds with distension — consider perforation or late obstruction
- Pulsatile abdominal mass with back pain — ruptured AAA
- Positive pregnancy test with pain and PV bleeding — ectopic pregnancy
Differential Diagnosis
| Location | Common Causes | Key Investigation |
|---|---|---|
| RIF | Appendicitis, ectopic pregnancy, ovarian torsion, Meckel's | CT, β-hCG, US pelvis |
| LIF | Diverticulitis, sigmoid volvulus, IBD | CT, plain AXR |
| RUQ | Cholecystitis, biliary colic, hepatitis | US abdomen, LFTs |
| Epigastric | Pancreatitis, perforated PU, gastritis, AAA | Amylase/lipase, erect CXR, CT |
| Central | Bowel obstruction, early appendicitis, mesenteric ischaemia | CT, AXR |
| Suprapubic | UTI, urinary retention, ectopic, PID | Urine dip, β-hCG, US |
| Loin to groin | Renal colic, pyelonephritis | CT KUB, urine dip |
| Generalised | Peritonitis, bowel obstruction, DKA | CT, erect CXR, glucose |
Diagnosis / Investigation
Bedside
- Observations: NEWS2, HR, BP, temperature
- Urine: Dipstick (UTI, haematuria), β-hCG (ALL women of reproductive age)
- Blood glucose: Exclude DKA
- ECG: Exclude MI (inferior MI can present as epigastric pain)
Bloods
- FBC: WCC (infection/inflammation), Hb (haemorrhage)
- CRP: Inflammatory marker
- U&Es: Dehydration, renal function
- LFTs, amylase/lipase: Biliary disease, pancreatitis (amylase >3× upper limit = pancreatitis)
- Lactate: Mesenteric ischaemia (>2 mmol/L concerning), sepsis
- Coagulation: If bleeding or septic
- Group and save/crossmatch: If haemorrhage suspected
Imaging
- Erect CXR: Free air under diaphragm (perforation)
- AXR: Bowel obstruction (dilated loops, air-fluid levels), volvulus
- CT abdomen/pelvis with IV contrast: Investigation of choice — high sensitivity for most acute surgical pathology
- US abdomen: First-line for biliary disease, gynaecological pathology
- CT KUB: Renal colic (non-contrast)
Management
Initial Management (ABCDE Approach)
- A&B: Maintain airway, high-flow O₂ if needed
- C: IV access (2× large bore), IV crystalloid resuscitation, crossmatch if haemorrhage
- Analgesia: IV morphine 5-10mg (titrate) + IV paracetamol 1g + IV ondansetron 4mg; opioids do NOT mask peritonism
- NBM: Keep nil by mouth
- NG tube: If vomiting/obstruction
- Urinary catheter: Monitor urine output (target >0.5 mL/kg/hr)
- IV antibiotics: If peritonitis/sepsis — co-amoxiclav 1.2g IV TDS (or per local protocol)
- VTE prophylaxis: LMWH once surgical plan confirmed
Surgical Management
- Depends on cause — see specific conditions
- Perforated viscus: Laparotomy/laparoscopy for washout and repair
- Obstruction: Initially conservative (drip and suck); surgery if strangulation, perforation, or failure to resolve
- Appendicitis: Appendicectomy (laparoscopic preferred)
- Ruptured AAA: Emergency open repair or EVAR
Referral Criteria
- All patients with peritonism or haemodynamic instability — immediate surgical review
- Suspected vascular emergency — vascular surgery
- Gynaecological emergency — O&G
Prognosis
- Depends on underlying cause and time to treatment
- Perforated viscus: Mortality ~10-20% if delayed; <5% with timely management
- Ruptured AAA: Overall mortality ~80%; ~50% even with emergency surgery
- Mesenteric ischaemia: Mortality 60-80% — early CT angiography and intervention improves outcomes
- Appendicitis: <1% mortality with timely appendicectomy
- Non-specific abdominal pain: Self-limiting in most cases
Other Relevant Information
Acute Abdomen Assessment Framework
| Step | Action |
|---|---|
| 1 | ABCDE assessment and resuscitation |
| 2 | Focused history (SOCRATES) |
| 3 | Examination (inspection, palpation, percussion, auscultation, hernial orifices, PR) |
| 4 | Bedside tests (urine dip, β-hCG, glucose, ECG) |
| 5 | Bloods (FBC, CRP, U&Es, amylase, LFTs, lactate, G&S) |
| 6 | Imaging (erect CXR, CT abdomen/pelvis) |
| 7 | Definitive management |