Acute Abdomen

Acute abdomen is a clinical syndrome of recent onset abdominal pain in which urgent intra abdominal pathology must be identified or excluded. It is not a diagnosis.

The immediate task is to recognise pathology requiring resuscitation and source control before pursuing diagnostic completeness.

Major surgical causes include perforation, bowel obstruction with strangulation, mesenteric ischaemia, intra abdominal haemorrhage, complicated appendicitis, ruptured aneurysm and severe intra abdominal sepsis.

Pain physiology is clinically useful. Visceral pain is poorly localised and often midline. Parietal peritoneal irritation produces sharp localised pain aggravated by movement. Sudden severe pain suggests perforation, vascular catastrophe or haemorrhage. Pain disproportionate to examination should raise immediate concern for mesenteric ischaemia.

Define the pain precisely: onset, site, migration, character and progression. Ask specifically about vomiting, abdominal distension, last passage of stool or flatus, gastrointestinal bleeding, fever, urinary symptoms, previous abdominal surgery, anticoagulation and pregnancy possibility.

The examination begins with physiology rather than the abdomen.

High risk findings include:

• Hypotension, persistent tachycardia, oliguria or altered mentation
• Generalised involuntary guarding or rigidity
• Pain disproportionate to physical findings
• Severe abdominal distension with persistent vomiting
• Gastrointestinal bleeding with haemodynamic compromise
• Pulsatile abdominal mass
• Sepsis or rising lactate

Older adults, immunosuppressed patients and patients receiving corticosteroids may have major intra abdominal pathology with limited guarding or fever.

Investigations should answer a clinical question rather than generate a broad screening panel.

• Obtain full blood count, renal function, electrolytes and glucose in significant presentations. Add liver enzymes and lipase when hepatobiliary or pancreatic disease is plausible, lactate and blood gas when ischaemia, sepsis or shock is suspected, coagulation studies in bleeding or anticoagulated patients, and pregnancy testing where applicable.
• A normal lactate does not exclude early mesenteric ischaemia.
• CT abdomen and pelvis with IV contrast: preferred in haemodynamically stable adults with significant nonlocalised abdominal pain when the diagnosis remains uncertain; identify the underlying surgical pathology, perforation, obstruction, ischaemia, haemorrhage or collection.
• Ultrasound: preferred when the working diagnosis is biliary, pelvic, obstetric or selected vascular pathology.

Do not send an unstable patient with convincing generalised peritonitis through repeated imaging solely to establish a more precise diagnosis.

Resuscitation and diagnosis occur simultaneously.

Keep the patient fasting when intervention is possible. Establish IV access, correct hypovolaemia using balanced crystalloid in reassessed aliquots and obtain blood for crossmatch when bleeding or major surgery is possible.

Analgesia should not be withheld.

A practical adult regimen is:

• Paracetamol 1 g orally or IV every 6 to 8 hours, maximum 4 g in 24 hours in an adult without significant hepatic risk.
• Morphine approximately 0.05 to 0.1 mg/kg IV for severe pain, titrated to effect and respiratory status.

Insert a nasogastric tube for significant vomiting, proximal obstruction or major distension. Insert a urinary catheter when accurate urine output is required during major resuscitation.

Start antibiotics promptly when perforation, complicated intra abdominal infection or sepsis is suspected. For stable community acquired infection:

Ceftriaxone 2 g IV every 24 hours plus metronidazole 500 mg IV every 12 hours.

For severe sepsis, healthcare associated infection or substantial resistant organism risk:

Piperacillin tazobactam 4.5 g IV loading dose followed by 4.5 g IV every 8 hours by extended infusion, adjusted for renal function.

Urgent operative or procedural intervention takes priority when there is generalised peritonitis, perforated viscus, strangulated obstruction, bowel ischaemia, uncontrolled haemorrhage, ruptured aneurysm or sepsis from an uncontrolled abdominal source.

A transient improvement in pain, a normal white cell count or initially normal lactate must not overrule progressive physiological deterioration.