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Peritonitis, Acute

BASICS

  • Definition: Inflammation of the peritoneum.
  • Classification:
  • Aseptic: Chemical/systemic inflammation (not infection).
  • Bacterial: Infection of peritoneal fluid.
    • Primary (SBP): Infection of ascitic fluid, no intraabdominal source.
    • Secondary: Infection from detectable intra-abdominal source (perforation/nonperforation).
    • Tertiary: >48 hours of infection despite source control.
    • PD-associated: In peritoneal dialysis patients.

EPIDEMIOLOGY

  • SBP: Incidence ≈1/3 per year in hospitalized cirrhotics.
  • Secondary: Most common surgical ICU sepsis.
  • PD peritonitis: Complication of peritoneal dialysis.

ETIOLOGY & PATHOPHYSIOLOGY

  • SBP:
  • Bacterial translocation, typically with advanced cirrhosis + ascites.
  • Monomicrobial; E. coli, Klebsiella, Streptococcus, Staphylococcus.
  • Risk: SIBO, immune dysfunction, low protein ascites.
  • Secondary: From intra-abdominal pathology (perforation, ischemia, IBD, pancreatitis, trauma).
  • Organism: Gram-negative (lower GI); Gram-positive (upper GI); anaerobes.
  • PD peritonitis: Skin flora contamination during exchange (S. epidermidis, S. aureus).

RISK FACTORS

  • SBP: Advanced cirrhosis + ascites, malnutrition, prior SBP, variceal bleed, acid suppression, low ascitic protein (<1 g/dL).
  • Secondary: Peptic ulcer, vascular disease, pancreatitis, trauma, IBD.
  • PD peritonitis: Nonsterile technique, recent instrumentation.

PREVENTION

  • SBP:
  • Primary prophylaxis (norfloxacin, ciprofloxacin, TMP-SMX) for high-risk patients (ascitic protein <1.5 g/dL + renal/liver dysfunction).
  • Limit PPI use.
  • PD: Strict sterile technique; antibiotic prophylaxis for select procedures.

ASSOCIATED CONDITIONS

  • Decompensated cirrhosis (almost always in SBP)
  • Peritonitis = high risk for sepsis, organ failure

DIAGNOSIS

History

  • SBP: Cirrhosis/ascites + fever, chills, abdominal pain (may be mild), mental status changes, GI symptoms.
  • Secondary: May be indistinguishable; consider recent surgery, abscess, or perforation.
  • Tertiary: Persistent infection after treatment.
  • PD peritonitis: Cloudy effluent.

Physical Exam

  • Tachycardia, hypotension, altered mental status
  • Abdominal pain/distension, ascites, rebound, hypoactive/absent bowel sounds
  • No rigidity (ascites separates peritoneal layers)

Differential Diagnosis

  • Liver disease, intra-abdominal abscess, ileus, volvulus, malignancy, PID, UTI, pneumonia, SLE, MI, TB

Diagnostics

  • CBC: Leukocytosis, anemia, thrombocytopenia
  • BMP: Acidosis, azotemia
  • LFTs/coag: Often abnormal
  • CRP >60 mg/L: Highly specific for SBP if cirrhosis present
  • Abdominal imaging: For suspected secondary peritonitis (free air, abscess, etc.)
  • Paracentesis (gold standard):
  • SBP: Ascitic PMN >250/mm³, monomicrobial culture
  • Secondary: PMN >250/mm³, polymicrobial culture and/or Runyon criteria: protein >1 g/dL, glucose <50, LDH >serum ULN
  • PD peritonitis: 2/3: Positive culture, clinical symptoms, peritoneal WBC >100/mm³ with PMN >50%

TREATMENT

General

  • Hospitalization; aggressive volume resuscitation if shock.
  • Control ascites (salt restriction, diuretics, albumin).
  • Discontinue nephrotoxins, β-blockers (if hypotension/AKI).
  • Early empiric antibiotics; hold until after paracentesis if possible.

SBP

  • First line: IV 3rd-gen cephalosporin (cefotaxime).
  • If no prior quinolone, non-severe, may use PO fluoroquinolones.
  • Add IV albumin for renal/liver dysfunction.
  • Monitor: Repeat paracentesis after 48 hours (PMN drop >25% expected).
  • Broad coverage if no response or if MDRO likely.

Secondary Peritonitis

  • Empiric broad-spectrum antibiotics: IV cephalosporin + metronidazole.
  • Surgery: Required for perforated viscus/source control.

Tertiary

  • Continue broad-spectrum therapy; add antifungals if needed; avoid surgery if possible unless source control required.

PD Peritonitis

  • Preferred: Intraperitoneal antibiotics (vancomycin or cefazolin + ceftazidime/cefepime/aminoglycoside/carbapenem).
  • Remove catheter if: fungal/mycobacterial infection, refractory, recurrent, or nonresolving peritonitis.

SURGERY

  • SBP: Avoid surgery; high mortality.
  • Secondary: Emergent laparotomy for source control.
  • Tertiary: Only if source not controlled medically.

ONGOING CARE

  • Monitor vitals, leukocytosis, PMN count in ascites
  • NPO, TPN if ileus/obstruction (secondary)
  • Resume oral/enteral diet as tolerated
  • Sodium restriction to reduce future ascites

PROGNOSIS

  • SBP: Good if treated early; renal dysfunction = poor prognosis.
  • Secondary: Higher mortality, especially with perforation.
  • PD peritonitis: 2–6% mortality; 5–20% transition to hemodialysis if chronic.

COMPLICATIONS

  • Renal/liver failure, encephalopathy, coagulopathy
  • Abscess, fistula, compartment syndrome
  • Sepsis/shock, ARDS, adrenal insufficiency
  • Complications of paracentesis (bleeding, infection)

ICD-10 CODES

  • K65.0 Generalized (acute) peritonitis
  • K65.2 Spontaneous bacterial peritonitis
  • K65.8 Other peritonitis

CLINICAL PEARLS

  • High suspicion for SBP in cirrhotics with ascites—even if asymptomatic.
  • Early paracentesis and empiric antibiotics reduce mortality.
  • E. coli is the most common SBP pathogen; 3rd-gen cephalosporins are first-line.
  • Renal function is a key prognostic factor.
  • Always consider secondary causes if polymicrobial or poor response to therapy.