AKT · Gastroenterology/Acute abdomen & surgicallow yield

Peritonitis

Inflammation of the peritoneum (localised/generalised; primary [SBP] or secondary)

Overview

Inflammation of the peritoneal cavity — secondary (commonest, from a perforated/inflamed/ischaemic viscus or contamination) or primary/spontaneous (SBP — infection of ascitic fluid in cirrhosis, without a perforation). Localised peritonitis gives focal guarding; generalised peritonitis gives a rigid abdomen and sepsis. Treat the cause (often surgery) for secondary; antibiotics for SBP.

Recognise

Abdominal pain worse on movement/coughing, guarding, rebound/percussion tenderness, lies still; generalised = rigid 'board-like' abdomen, ileus, sepsis
Secondary: a surgical source (perforation, appendicitis, diverticulitis, ischaemia, anastomotic leak)
Primary/SBP: cirrhotic with ascites + fever/abdominal pain/encephalopathy — ascitic neutrophils ≥250/mm³

Red flags

Generalised peritonitis + sepsis → emergency
SBP in a decompensating cirrhotic → diagnostic ascitic tap + antibiotics

Differentials & how to tell them apart

Secondary peritonitis (perforation/appendicitis/diverticulitis)a surgical cause on imaging — needs source control/surgery

Spontaneous bacterial peritonitiscirrhosis + ascites, no perforation, ascitic neutrophils ≥250 — antibiotics, not surgery

Medical mimicsDKA, lower-lobe pneumonia, MI — can present with abdominal pain

Investigations

FBC/CRP/U&Es/lactate, blood cultures; erect CXR/CT for a surgical source; ASCITIC TAP (neutrophils ≥250 = SBP) in cirrhotics. Amylase/lipase.

Management

Resuscitate + antibiotics; surgery (secondary) or antibiotics-only (SBP)

1Resuscitate and give broad-spectrum antibiotics. Determine secondary (surgical source → CT) vs primary (SBP — ascitic tap in a cirrhotic).Gate: SBP (cirrhosis + ascites, ascitic neutrophils ≥250) is treated with ANTIBIOTICS, NOT surgery — whereas secondary peritonitis needs SOURCE CONTROL (surgery); the ascitic tap and imaging distinguish them
2Secondary → laparotomy/source control; SBP → IV antibiotics + albumin + secondary antibiotic prophylaxis; critical care for sepsis.

Resuscitation + broad-spectrum antibiotics — sepsis management

Source control (surgery) for secondary peritonitis — treat the perforation/inflamed organ

IV antibiotics (e.g. cefotaxime) for SBP — primary peritonitis — no surgery; secondary prophylaxis after

Key points

Rigid abdomen + sepsis = peritonitis. Secondary (a surgical source → operate) vs SBP (cirrhotic ascites, neutrophils ≥250 → antibiotics, don't operate). The ascitic tap is the splitter in a cirrhotic.

Monitor & prognosis

Sepsis; ascitic response in SBP.

Depends on cause; SBP signals poor liver prognosis.

Source: RCS; EASL (SBP)