Intra Abdominal Abscess

An intra abdominal abscess is a localised collection of infected fluid or pus within the peritoneal cavity, retroperitoneum or an abdominal organ.

It commonly follows gastrointestinal perforation, appendicitis, diverticulitis, pancreatitis, trauma or abdominal surgery. A postoperative abscess should prompt consideration of an ongoing source such as an anastomotic leak, bowel injury or infected haematoma.

Antibiotics penetrate poorly into large established collections.

Effective management therefore depends primarily on source control.

Presentation may be obvious or subtle. Persistent fever, abdominal pain, focal tenderness, anorexia and ileus are typical.

Postoperative clues include failure to recover as expected, persistent tachycardia, recurrent fever after initial improvement, prolonged ileus, increasing inflammatory markers or new organ dysfunction.

Deep pelvic or subphrenic collections may produce minimal abdominal findings.

Septic shock indicates uncontrolled infection until proven otherwise.

• Check full blood count, renal function, electrolytes and C reactive protein. Measure lactate when systemic illness or hypoperfusion is present.
• Blood cultures are particularly appropriate when fever is accompanied by hypotension, tachypnoea or delirium, or when resistant organisms are a concern.
• CT abdomen and pelvis with IV contrast: investigation of choice in nonpregnant adults; confirm the collection and determine whether a safe percutaneous drainage route exists. IV contrast improves visualisation of the abscess wall.

There is no universal abscess diameter that independently determines drainage. Size must be interpreted with accessibility, loculation, clinical condition and response to antibiotics.

1. Source control is the central treatment.

2. A small collection in a stable patient may occasionally resolve with antibiotics alone, particularly when drainage would be difficult and there is no ongoing leak. A mature accessible collection causing systemic or persistent local infection should generally undergo image guided percutaneous drainage.

3. Send aspirated or operative fluid for bacterial culture when source control is performed.

4. A practical adult antimicrobial regimen for stable community acquired infection is: Ceftriaxone 2 g IV every 24 hours plus metronidazole 500 mg IV every 12 hours.

5. For severe sepsis, healthcare associated infection or substantial resistant Gram negative risk: Piperacillin tazobactam 4.5 g IV loading dose followed by 4.5 g IV every 8 hours by extended infusion, adjusted for renal impairment.

Operate when there is:

• Generalised peritonitis

• An uncontrolled perforation or anastomotic leak requiring repair

• Bowel ischaemia or necrosis

• A collection not amenable to percutaneous drainage with ongoing sepsis

• Failed percutaneous drainage

• Persistent physiological deterioration despite appropriate treatment

The operative objective is not merely drainage. Any continuing source of contamination must also be controlled.

After adequate percutaneous or operative source control, antibiotic treatment should generally be limited to 4 days, including higher risk patients with sepsis.

Persistent fever, leukocytosis or organ dysfunction after source control should trigger reassessment for inadequate drainage, another collection, fistula, retained foreign material or continued gastrointestinal leakage rather than automatic prolongation of antibiotics.