see also:

• the patient with acute abdominal pain in the ED

• peritonitis is a life threatening inflammation within the peritoneal fluid - usually due to bacterial sepsis
• it may be spontaneous as in spontaneous bacterial peritonitis (SBP), or secondary to either inflammation of an intra-abdominal organ or following a penetrating wound
• it may initially be localised and then spread to become generalised peritonitis
• if associated with perforation of a hollow viscus, there may be free gas under the diaphragm on an erect CXR

• spontaneous bacterial peritonitis (SBP)
• secondary to inflammation:
  • appendicitis
  • diverticulitis
  • perforated viscus
  • pancreatitis
  • cholecystitis
  • ischaemic colitis
  • caecal volvulus
  • sigmoid volvulus
  • small bowel obstruction
• secondary to penetrating wounds
• iatrogenic

• ruptured ectopic pregnancy
• empyema
• acute urinary retention
• acute pyelonephritis
• abdominal wall conditions:
  • rectus sheath haematoma
  • calcified rectus sheath may cause rigidity
  • high abdominal wall muscle tone due to strength training
  • abdominal wall infection
  • herniae

• unlike colic pain, peritonitis pain is generally worse on movement, on walking, and on coughing
• it is usually associated with anorexia, nausea and often vomiting
• clinical examination generally reveals:
  • early signs may be minimal when only the visceral peritoneum is inflamed as this generally causes dull, poorly localized pain
  • when the parietal peritoneum becomes inflamed the pain becomes sharper, and more localized, initially with voluntary guarding and then involuntary guarding
  • when the peronitis becomes generalized, the involuntary guarding becomes generalized and then develops into * abdominal wall rigidity - this is usually a late feature (but may occur early such as in pancreatitis and perforated viscus) and generally indicates need for urgent surgery
  • patients often prefer to keep hips flexed to reduce abdominal wall tension
  • reduced or absent bowel sounds
  • may have abdominal distension
  • there is often a fever with tachycardia and dehydration (due to third space losses), and will usually eventually develop septic shock

• IV access
• FBE, U&E, LFTs, lipase, CRP, glucose, consider blood cultures, lactate and if female, HCG
• IV fluid therapy
• if known ascites or risk, consider Mx as per spontaneous bacterial peritonitis (SBP)
• erect CXR if suspect perforated viscus - eg. sudden onset rigidity
• erect/supine AXR if suspect small bowel obstruction
• contact surgery team ASAP
• consider empirical broad cover IV antibiotics according to likely cause
• consider CT abdomen (with contrast if time allows and adequate eGFR) or direct to theatre for exploratory laparatomy depending upon suspected cause and severity/urgency of theatre