Acute Abdomen

The acute abdomen is a clinical syndrome of sudden onset abdominal pain, generally lasting under 7 days (usually under 24 to 48 hours), with signs of peritoneal irritation or systemic disturbance suggesting an intra abdominal disease that needs urgent assessment and often surgery. It is a presentation, not a diagnosis. Abdominal pain accounts for 5 to 10% of emergency department visits, and 20 to 30% of those patients need surgery or intervention.

Pain mechanisms:

• Visceral pain: stretch or ischaemia of hollow viscera; poorly localised, dull or cramping, felt in the midline by embryological origin (foregut epigastrium, midgut periumbilical, hindgut hypogastrium)
• Parietal (somatic) pain: irritation of the parietal peritoneum; sharp, well localised, worse with movement and coughing
• Referred pain: shoulder tip (diaphragmatic irritation), scapula (biliary), testis (renal colic), back (pancreatic, aortic)

Major causes:

• Inflammatory and infective: appendicitis, cholecystitis, cholangitis, diverticulitis, pancreatitis, perforated peptic ulcer, pelvic inflammatory disease, abscess, infective colitis
• Obstruction: small bowel obstruction (adhesions, hernia, tumour), large bowel obstruction, volvulus, biliary or ureteric colic
• Vascular: mesenteric ischaemia, ruptured aortic aneurysm, ischaemic colitis, splenic infarct, ovarian torsion
• Haemorrhage and perforation: ruptured ectopic pregnancy, ruptured ovarian cyst, ruptured spleen or liver lesion, trauma
• Medical mimics: diabetic ketoacidosis, inferior myocardial infarction, lower lobe pneumonia, porphyria, adrenal crisis, sickle cell crisis, lead poisoning, herpes zoster
• Special groups: elderly, immunosuppressed, pregnant and steroid treated patients have blunted signs; up to 40% of elderly patients present atypically, with mortality of 10 to 20% in those over 65

History: onset (sudden suggests perforation, torsion or rupture), site and radiation, character (colicky versus constant), aggravating factors, vomiting (bilious or faeculent), bowel habit, urinary symptoms, fever, menstrual history and contraception, medication (NSAIDs, steroids, anticoagulants, opioids), previous surgery, cardiovascular disease and atrial fibrillation (embolic mesenteric ischaemia), alcohol, diabetes.

Examination:

• General: appearance (lies still in peritonitis, writhes in colic), pallor, jaundice, temperature, pulse, blood pressure, respiratory rate, hydration, shock
• Abdomen: distension, scars, hernias (examine all orifices), visible peristalsis, tenderness, guarding, rigidity (board like in perforation), rebound, percussion tenderness, Murphy sign, Rovsing sign, psoas and obturator signs, masses, pulsatile mass, bowel sounds (absent in ileus and peritonitis, high pitched and tinkling in obstruction)
• Rectal and pelvic examination when indicated; testes and hernial orifices

Peritonitis: stillness, guarding, rigidity, rebound and absent bowel sounds. Pain out of proportion to findings suggests mesenteric ischaemia.

Initial tests: full blood count, urea, electrolytes, creatinine, glucose, C-reactive protein, liver function, amylase or lipase, lactate and blood gas, coagulation, group and save, urinalysis, urine or serum beta-hCG in women of reproductive age, ECG, and troponin when indicated. Blood cultures if febrile or septic. Lactate above 2 mmol/L suggests ischaemia or sepsis, though a normal lactate does not exclude mesenteric ischaemia.

Imaging:

• Erect chest radiograph: free subdiaphragmatic gas in 70 to 80% of perforated viscus. Plain abdominal films help in obstruction but are otherwise of limited value
• Ultrasound: first line for biliary disease, gynaecological disease, ectopic pregnancy, appendicitis in children and thin patients, and free fluid. Bedside ultrasound for aortic aneurysm and free fluid
• CT abdomen and pelvis with IV contrast: most accurate for most causes, with sensitivity of 90 to 95% for appendicitis, diverticulitis and obstruction. CT angiography for mesenteric ischaemia and aneurysm
• MRI: pregnancy (after ultrasound) and selected biliary or pelvic problems
• Diagnostic laparoscopy when imaging is inconclusive in an unwell patient

Resuscitation, concurrent with assessment.

1. Airway, breathing, circulation; oxygen to keep saturation 94 to 98%
2. Two large bore cannulae and blood tests
3. Balanced crystalloid (Hartmann or Ringer lactate) 500 mL to 1 L boluses with reassessment after each; urinary catheter in unstable patients with a target of 0.5 mL/kg/hour
4. Nil by mouth; nasogastric tube for vomiting or obstruction
5. Analgesia: titrated IV opioid (morphine 2.5 to 5 mg or fentanyl 25 to 50 micrograms) does not mask the diagnosis and should not be withheld; paracetamol 1 g IV; ondansetron 4 mg IV
6. Antibiotics within 1 hour for sepsis, peritonitis or perforation: piperacillin tazobactam 4.5 g IV every 6 to 8 hours, or ceftriaxone 2 g daily with metronidazole 500 mg every 8 hours; meropenem 1 g every 8 hours for severe sepsis or resistant organisms
7. Correct coagulopathy and electrolytes; reverse anticoagulants when needed
8. Early senior surgical review and anaesthetic assessment

Indications for urgent laparotomy or laparoscopy. Generalised peritonitis, perforation with free gas, haemodynamic instability with intra abdominal bleeding (ruptured aneurysm, ectopic pregnancy), strangulated bowel or hernia, mesenteric ischaemia with bowel necrosis, volvulus, closed loop obstruction, abdominal compartment syndrome, and failure of non-operative treatment in a deteriorating patient.

Selected non-operative management. Stable patients with localised peritonitis: uncomplicated diverticulitis, early adhesive small bowel obstruction (water soluble contrast study; operate if contrast has not reached the colon by 24 hours), pancreatitis, a sealed perforated ulcer, or abscess treated by percutaneous drainage.

Common surgical emergencies in outline.

• Perforated peptic ulcer: omental patch repair (laparoscopic or open), IV pantoprazole 40 mg twice daily, and Helicobacter pylori eradication
• Mesenteric ischaemia: heparin infusion (80 units/kg bolus, then 18 units/kg/hour), revascularisation (embolectomy, stenting or bypass), resection of non-viable bowel, and a second look operation at 24 to 48 hours
• Appendicitis: antibiotics and appendicectomy
• Strangulated hernia or volvulus: urgent operation
• Obstruction: nasogastric decompression, fluids, and operation for strangulation or failure to resolve

Special groups. Pregnancy: ultrasound then MRI, and do not delay necessary surgery. Elderly: lower threshold for CT, expect atypical presentations. Immunosuppressed: perforation may occur with minimal signs. Children and infants: the differential is age dependent, with intussusception, malrotation with volvulus, appendicitis and torsion the surgical emergencies to exclude first.

Reassessment and disposition. Frequent reassessment, hourly early on, by the same clinician where possible, is the most valuable test in undifferentiated pain; repeat bloods and imaging as needed. Discharge only when pain is controlled, the patient tolerates fluids and the examination is benign, with clear return advice.