What is the recommended management for a peritoneal abscess, including imaging, source control, and antimicrobial therapy?

Management of Peritoneal Abscess

For peritoneal abscesses, immediate source control via percutaneous drainage (for localized collections) or surgical intervention (for diffuse peritonitis) combined with broad-spectrum antibiotics is essential, with delays beyond 24 hours significantly increasing mortality. 1, 2

Imaging and Diagnosis

• Contrast-enhanced CT scan is the gold standard for confirming peritoneal abscess location, size, complexity, and planning drainage approach 2, 3
• Plain abdominal X-ray may show free air indicating perforation but has lower sensitivity 1, 2
• Ultrasound is useful as a first-line tool in resource-limited settings to identify free fluid, though CT provides superior characterization 1, 2
• Obtain blood cultures and diagnostic aspiration (when safe) for Gram stain, culture, and susceptibility testing before starting antibiotics 2, 3

Source Control: The Critical Determinant

The timing and adequacy of source control are the most important factors determining survival—incomplete or delayed procedures beyond 24 hours dramatically worsen outcomes. 1, 2

Localized Peritoneal Abscesses (No Diffuse Peritonitis)

• Percutaneous catheter drainage (PCD) is first-line for well-defined, accessible abscesses >3-5 cm combined with antibiotics 1, 2, 3
• Success rates for PCD range from 74-100% for unilocular abscesses with accessible approach 3, 4
• PCD failure occurs in 15-36% of cases, most commonly due to multiloculated collections, high-viscosity contents, or fistulization 3
• If drainage output is ≤25 mL/day or abscess enlarges despite catheter, upsize the catheter or place additional drains 3
• Consider intracavitary alteplase (tissue plasminogen activator) for multiloculated collections refractory to standard drainage—72% success rate versus 22% with saline in randomized trial 3

Diffuse Peritonitis or Hemodynamic Instability

• Immediate surgical exploration (laparotomy or laparoscopy) is mandatory for patients with diffuse peritonitis, hemodynamic instability, or signs of ongoing sepsis 1, 2
• Surgical objectives include: draining collections, debriding necrotic tissue, controlling contamination source (resection/repair of perforated viscus), and restoring anatomy 1
• Operating room delays ≥60 hours independently predict need for relaparotomy and death 2
• Damage control surgery with open abdomen may be necessary for physiologically deranged patients with ongoing sepsis 2

Post-operative Peritoneal Abscesses

• Localized post-operative abscesses without diffuse peritonitis can be managed with antibiotics plus PCD 1, 4
• Prompt surgical re-exploration is required for post-operative diffuse peritonitis—delays beyond 24 hours result in higher mortality 1
• The inability to control the septic source is associated with intolerably high mortality 1, 4

Antimicrobial Therapy

Empiric Regimens (Community-Acquired)

Start broad-spectrum antibiotics within 1 hour of sepsis recognition, covering Gram-negative Enterobacteriaceae, anaerobes, and Gram-positive cocci. 1, 2

First-line options for immunocompetent, non-critically ill patients:

• Ceftriaxone 2g IV every 24h PLUS metronidazole 500mg IV every 8h 2, 3
• Piperacillin-tazobactam 4g/0.5g IV every 6h 2, 3
• Ertapenem 1g IV every 24h 2, 5

For critically ill or septic shock patients:

• Meropenem 1g IV every 6-8h (extended infusion preferred) 3
• Imipenem-cilastatin 500mg IV every 6h 3

For β-lactam allergy:

• Eravacycline 1mg/kg IV every 12h 2, 3
• Tigecycline 100mg IV loading dose, then 50mg IV every 12h 3

Hospital-Acquired/Nosocomial Peritonitis

Use broader-spectrum regimens with anti-ESBL and anti-Pseudomonal coverage due to higher risk of multidrug-resistant organisms. 2, 6, 7

• Piperacillin-tazobactam 4g/0.5g IV every 6h OR 16g/2g continuous infusion 2, 4
• For high ESBL risk or piperacillin-tazobactam failure: Ertapenem 1g IV daily 2, 3
• For carbapenem-resistant organisms: Meropenem 1g IV every 6h plus amikacin 5
• Add empirical antifungal therapy (fluconazole or echinocandin) for hospital-acquired peritonitis due to high Candida risk 2, 5

Duration of Therapy

• Limit antibiotics to 3-5 days post-operatively in patients with adequate source control 2
• No post-operative antibiotics needed for uncomplicated appendicitis or cholecystitis with definitive source control 2
• If signs of infection persist beyond 5-7 days, investigate for inadequate source control rather than simply continuing antibiotics 2, 3, 4
• Median time to defervescence in complicated cases is 5-7 days 3

Monitoring and Reassessment

• Serial physical examinations monitoring vital signs, temperature trends, white blood cell count, C-reactive protein, and procalcitonin 2, 3
• If fever persists 72-96 hours despite adequate drainage, broaden coverage to piperacillin-tazobactam 2, 3
• Repeat contrast-enhanced CT and reassess drainage adequacy if infection persists beyond 7 days 2, 3, 4
• Consider repeat diagnostic aspiration to check for antibiotic resistance if no response by 48-72 hours 3

Critical Pitfalls to Avoid

• Do not delay source control in septic patients—mortality increases dramatically with delays beyond 24 hours 1, 2
• Do not use narrow-spectrum antibiotics in hospital-acquired peritonitis—resistance patterns demand broader coverage 2, 6
• Do not continue antibiotics beyond 5 days without investigating for inadequate source control (undrained collection, ongoing leak, resistant organisms) 2, 3
• Do not rely on antibiotics alone for abscesses >4-5 cm—failure rate is unacceptably high without drainage 3
• For multiloculated or complex abscesses, do not persist with failed PCD—surgical drainage (laparoscopic preferred) is indicated 3
• Adjust antibiotic dosing based on renal function and pharmacokinetic parameters in critically ill patients 2