Small Bowel Necrosis

Generalised peritonitis is diffuse inflammation of the peritoneal cavity involving multiple abdominal regions. In surgical practice, the critical form is secondary peritonitis, produced by loss of gastrointestinal integrity from perforation, ischaemic bowel, anastomotic failure, complicated appendicitis, perforated diverticulitis, perforated peptic ulcer or another contaminated intra abdominal source.

Primary peritonitis occurs without gastrointestinal perforation, classically in cirrhosis with ascites, and is generally managed medically. Persistent or recurrent peritoneal infection after failed treatment and source control is often termed tertiary peritonitis.

Secondary generalised peritonitis is a surgical emergency because outcome is determined largely by how quickly and adequately the source of contamination is controlled.

Pain is usually severe and diffuse. Patients often avoid movement because motion worsens parietal peritoneal irritation.

Typical findings include:

• Diffuse abdominal tenderness
• Involuntary guarding and rigidity
• Percussion tenderness
• Reduced or absent bowel sounds from ileus
• Abdominal distension
• Fever and tachycardia

Advanced disease produces sepsis and organ dysfunction. Look specifically for hypotension, prolonged capillary refill, cool or mottled extremities, altered mentation, oliguria, hypoxaemia and increasing respiratory effort.

An elderly, immunocompromised or severely septic patient may have surprisingly little rigidity. A quiet abdomen does not exclude catastrophic pathology.

The cause may sometimes be suggested clinically. Sudden severe epigastric pain suggests gastroduodenal perforation. Previous colorectal surgery raises concern for anastomotic leakage. Atrial fibrillation with pain out of proportion raises concern for mesenteric ischaemia. Right lower quadrant symptoms progressing to diffuse pain may indicate perforated appendicitis.

Diagnosis begins with recognition of the surgical syndrome, not with imaging.

Immediately obtain:

• Full blood count
• Renal function and electrolytes
• Liver profile
• Coagulation profile
• Venous or arterial blood gas
• Serum lactate
• Blood glucose
• Group and crossmatch

Blood cultures should be obtained promptly in probable sepsis or septic shock, ideally before antimicrobial therapy, provided this does not delay antibiotics.

Contrast enhanced CT of the abdomen and pelvis is the investigation of choice in a haemodynamically stable patient when the source is uncertain.

Important findings include free intraperitoneal gas, focal bowel wall defect, extraluminal contrast, bowel ischaemia, abscess, abnormal bowel enhancement, free fluid and inflammatory change.

A normal erect chest radiograph does not exclude perforation. CT is substantially more sensitive for small amounts of free air.

An unstable patient with convincing generalised peritonitis and an obvious need for laparotomy should proceed to source control without waiting for CT.

Resuscitation, antimicrobial treatment and source control must occur in parallel.

Establish large bore IV access, continuous physiological monitoring and urinary output measurement in significant sepsis or shock.

Balanced crystalloids are preferred for initial resuscitation. Current 2026 Surviving Sepsis Campaign guidance suggests at least 30 mL/kg within the first 3 hours for sepsis induced hypoperfusion or septic shock, but emphasises frequent reassessment and individualisation to avoid fluid overload. Dynamic assessment of fluid responsiveness is preferred when available.

Do not continue giving crystalloid simply because hypotension persists.

If hypotension continues despite appropriate intravascular volume restoration, start norepinephrine as first line vasopressor and target an initial mean arterial pressure around 65 mm Hg. Vasopressors may be started through an appropriate peripheral IV while definitive access is obtained rather than delaying treatment.

Insert a nasogastric tube when there is vomiting, significant distension or ileus. Correct potassium, magnesium, acid base disturbance, glucose abnormality, hypothermia and clinically relevant coagulopathy.

Antimicrobial therapy should be given immediately, ideally within one hour in septic shock or probable sepsis.

For stable community acquired secondary peritonitis without major resistant organism risk:

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 using extended infusion.

Empirical MRSA, enterococcal or antifungal therapy is not required for every patient. Broaden treatment according to healthcare exposure, prior microbiology, immunosuppression, recurrent perforation, prolonged antibiotic exposure and local resistance.

The 2026 sepsis guideline specifically advises against unnecessary empirical MDR or antifungal coverage in patients without relevant risk factors.

Definitive source control may require:

• Closure of a perforation
• Resection of nonviable bowel
• Anastomosis or faecal diversion
• Removal of an infected organ
• Drainage of pus
• Debridement of necrotic tissue
• Percutaneous drainage in selected anatomically suitable collections

Source control should occur as soon as medically and logistically possible. The 2026 Surviving Sepsis Campaign suggests that sepsis requiring source control should ideally receive intervention within approximately 6 hours of diagnosis.

In severe physiological derangement, prolonged definitive reconstruction can be dangerous. Damage control laparotomy with rapid contamination control, resection without immediate anastomosis where appropriate, temporary abdominal closure and planned relook may be preferable when the patient has profound shock, severe acidosis, hypothermia, major coagulopathy, uncertain bowel viability or inability to close safely. Surgical Infection Society guidance supports abbreviated laparotomy when physiology is severely compromised or planned re exploration is required.

Obtain intra abdominal cultures during source control for complicated infection. Narrow antimicrobials when susceptibility data become available.

After adequate source control, antibiotics should generally be limited to 4 days. Persistent systemic inflammation should prompt investigation for failed source control rather than routine extension of therapy.