Localised Peritonitis

Localised peritonitis is focal inflammation of the parietal peritoneum adjacent to a contained intra abdominal pathological process.

It is commonly produced by appendicitis, localised gastrointestinal perforation, diverticulitis, cholecystitis, pelvic infection or a contained anastomotic leak.

It should be regarded as a clinical manifestation of underlying pathology, not a final diagnosis.

The key question is whether the inflammatory process remains contained or is progressing toward uncontrolled contamination and generalised peritonitis.

Pain is confined predominantly to the anatomical region of the underlying pathology.

The most important physical finding is involuntary local guarding, reflecting parietal peritoneal irritation.

Other useful findings include:

• Focal percussion tenderness
• Pain on coughing or movement
• Local rebound tenderness
• Reduced bowel sounds near significant inflammation

The examination should establish whether peritonism is truly localised.

A patient with local right iliac fossa tenderness and guarding from appendicitis is fundamentally different from a patient whose tenderness is now extending across the lower abdomen with increasing tachycardia.

Progression is suggested by:

• Expansion of the tender area
• Development of diffuse guarding or rigidity
• Increasing pain
• Persistent tachycardia
• Fever with systemic deterioration
• Ileus or increasing distension
• Hypotension
• Rising lactate or organ dysfunction

These findings imply failure of containment and require immediate reassessment of source control.

The diagnosis of localised peritonitis is primarily clinical. Investigation is directed at identifying its cause.

Laboratory testing should be selective. Full blood count, C reactive protein, renal function and electrolytes are appropriate in most significant surgical presentations. Lactate is useful when bowel ischaemia, sepsis or impaired perfusion is suspected.

Imaging depends on the working diagnosis.

Ultrasound is useful for gallbladder disease, pelvic pathology and selected appendicitis presentations.

Contrast enhanced CT is preferred when the source is uncertain, perforation or abscess is suspected, the patient is older or the diagnosis will change operative planning.

Important CT questions are not simply whether inflammation exists, but:

• Is there a perforation?
• Is contamination contained?
• Is there an abscess?
• Is bowel viable?
• Is there obstruction?
• Can the source be managed nonoperatively?
• Is percutaneous drainage possible?

A patient with convincing peritonitis who is deteriorating should not undergo repeated investigations merely to obtain diagnostic certainty before surgical review.

Treatment is directed at the underlying cause.

Localised peritonitis alone does not automatically mandate laparotomy.

Examples include uncomplicated appendicitis suitable for appendicectomy, localised diverticulitis that may respond to nonoperative treatment, cholecystitis requiring disease specific management, and a small contained abscess that may be treated with antibiotics or drainage.

The patient should initially receive analgesia, correction of dehydration and repeated abdominal examination.

Antibiotics are indicated when a bacterial intra abdominal infection has extended beyond the organ of origin or when therapeutic antimicrobial treatment is otherwise required. Choice should match the likely source and severity.

For stable community acquired secondary intra abdominal infection:

Ceftriaxone 2 g IV every 24 hours plus metronidazole 500 mg IV or orally every 12 hours is an appropriate adult regimen.

The presence of localised peritonitis should prompt early surgical review because the trajectory matters more than one examination.

Observation is reasonable only when:

• Physiology is stable
• The source is understood
• There is no free perforation requiring intervention
• There is no bowel ischaemia
• Pain and tenderness are not progressing
• Appropriate monitoring and rapid escalation are available

Proceed to intervention when there is uncontrolled perforation, bowel necrosis, failure of conservative therapy, enlarging abscess not amenable to antibiotics alone, progressive sepsis or evolution to generalised peritonitis.

When source control is achieved for a complicated intra abdominal infection, prolonged antibiotic therapy is unnecessary. Current Surgical Infection Society guidance recommends no more than 4 days after adequate source control.