Peritonitis

Inflammation of the peritoneum.

Nomenclature

• Intra-abdominal infection: intraperitoneal presence of micro-organisms, and the inflammatory response

• Peritoneal contamination: micro-organisms, but no inflammatory response

• Abdominal sepsis: not a very descriptive term, but implies systemic host response to intra-abdominal infection

Aetiology

• Generally caused by bacterial inoculation

Pathophysiology

• Primary peritonitis: originates from a source outside the abdomen, including dialysis catheters
  • Extremely rare without a known predisposing factor
  • Typically single organism
    • Streptococcus through genital tract in young girls
    • E coli in spontaneous bacterial peritonitis affective pre-existing ascites from cirrhosis
    • Staphylococcus through a peritoneal dialysis catheter
  • Seen on presentation as an acute abdomen with free fluid on CT but no obvious source
  • Diagnosis via paracentesis (polymorphonuclear count in ascitic fluid > 250 cells per cubic mm
  • Avoid diagnostic exploratory laparoscopy or laparotomy because of its prohibitive mortality
• Secondary peritonitis: caused by a breach in the anatomical integrity of a hollow viscus
  • Usually aerobic and anaerobic polymicrobial inoculation, reflecting GIT flora
• Tertiary peritonitis: the end stage of high-risk intra-abdominal infection
  • Becoming less-frequently described and less useful as a clinical descriptor
  • Seen in an ICU patient with multi-organ dysfunction, who has survived peritonitis through aggressive source control but has an open abdomen, and now the peritoneal cavity contains a thin, cloudy, poorly walled-off exudate which grows opportunistic micro-organisms
  • An outcome of unsuccessful treatment of bacterial peritonitis
  • Frequently fatal outcomes

Management

• Approach
  • Risk classification: assess premorbid reserves, current physiological compromise and virulence of infection
  • Adjunctive measures
  • Source control
  • Peritoneal toilet
• Risk classification
  • High risk: hospital-acquired infections; post-operative infections; critically ill or immunocompromised
    • Needs tailored antibiotics
    • Source control can be very hard
    • Poor prognosis
  • Low risk: community-acquired (perforated appendicitis or diverticulitis etc); not physiologically compromised; pre-morbidly healthy
    • Standard broad-spectrum antibiotics
    • Source control will be easy
    • Good prognosis
• Adjunctive measures
  • Resuscitation
  • Monitoring
  • Antibiotics
    • Empirical is ok - don't need peritoneal cultures in patients with community-acquired, low-risk peritonitis; but should be obtained in the following situations:
      • High-risk peritonitis
      • Already been on antibiotics
      • Previous resistant organism
      • Suspected primary peritonitis
      • Tertiary peritonitis
• Source control
  • Doesn't necessarily mean an operation - match the intervention to the individual patient
  • Use the least invasive approach that can achieve source control
  • Temporisation if there is major physiological compromise, but otherwise as soon as possible
• Peritoneal toilet (if operating)
  • Remove liquid contaminants and infected exudates
  • Irrigate with warm crystalloids
  • Rationalise use of drains - evacuate established abscesses, allow escape of potential secretions, or establish a controlled intestinal fistula
• Recognise treatment failure
  • Ongoing or increasing sepsis for more than 24-48 hours suggests that the initial source control was inadequate