Intra-abdominal Infections

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IAI: Overview - Gut Gone Wrong

  • Intra-abdominal Infection (IAI): Inflammation within peritoneal cavity due to microorganisms.
  • Types:
    • Primary Peritonitis (Spontaneous Bacterial Peritonitis - SBP): No evident intra-abdominal source. Common in liver cirrhosis.
    • Secondary Peritonitis: Due to perforation/inflammation of GI tract (e.g., appendicitis, diverticulitis, PUD). Most common type.
    • Tertiary Peritonitis: Persistent/recurrent infection after initial treatment, often with resistant organisms.
  • Classification:
    • Uncomplicated IAI: Infection confined to a single organ.
    • Complicated IAI (cIAI): Infection extends beyond organ into peritoneal space; associated with abscess or peritonitis.
  • Common Origins: Appendix, colon, stomach/duodenum, biliary tract.

⭐ Most common cause of secondary peritonitis is perforated appendicitis.

IAI: Pathogens & Process - Belly's Bad Bugs

  • Key Pathogens (Often Polymicrobial):
    • Aerobes:
      • Escherichia coli (most frequent Gram-negative)
      • Klebsiella spp.
      • Enterococcus spp. (Gram-positive cocci)
    • Anaerobes:
      • Bacteroides fragilis (most frequent anaerobe)
      • Clostridium spp.
      • Peptostreptococcus
    • Fungi (e.g., Candida): Consider in immunocompromised, prolonged antibiotics, or recurrent IAI.
    • 📌 Mnemonic: "BECK" - Bacteroides, E.coli, Clostridium, Klebsiella.
  • Pathogenesis Cascade:
    • Source of microbes:
      • Perforation (e.g., appendicitis, diverticulitis, Peptic Ulcer Disease)
      • Ischemia/Necrosis (e.g., mesenteric ischemia, strangulated bowel)
      • Translocation (e.g., severe pancreatitis, shock states)
    • Peritoneal contamination → Inflammation (Peritonitis).
    • Host defense: Opsonization, phagocytosis, fibrin deposition (walling-off → phlegmon/abscess).

Escherichia coli is the most common aerobic pathogen, and Bacteroides fragilis is the most common anaerobic pathogen in Intra-abdominal Infections (IAIs).

IAI: Diagnosis - Spotting Sepsis Signs

  • Clinical:
    • Local: Abdominal pain, tenderness, guarding, rigidity.
    • Systemic: Fever, tachycardia, hypotension.
  • Labs:
    • ↑WBC (left shift), ↑CRP.
    • ↑Serum Lactate (>2 mmol/L = hypoperfusion).
    • ↑Procalcitonin. Blood cultures (pre-antibiotics).
  • Imaging:
    • X-Ray (erect): Free air (perforation), air-fluid levels.
    • USG: Fluid, abscesses, organ-specific (e.g., appendicitis, cholecystitis).
    • CT (Contrast): Gold standard for source, extent, complications. CT scan showing intra-abdominal abscess
  • Sepsis (qSOFA ≥2):
    • Respiratory Rate ≥22/min
    • Altered Mentation (GCS <15)
    • Systolic BP ≤100 mmHg 📌 Mnemonic: HAT (Hypotension, Altered Mental Status, Tachypnea).

⭐ Serum lactate >2 mmol/L is a key indicator of tissue hypoperfusion and adverse outcomes in sepsis. Early qSOFA assessment is vital for timely intervention in IAI cases.

IAI: Treatment - Quelling the Chaos

  • Core Principles (Time-Sensitive):

    • Resuscitation: ABCs, IV crystalloids, O2. Target UO > 0.5 ml/kg/hr.
    • Early Empiric Antibiotics: Broad-spectrum IV within 1 hour of sepsis/septic shock diagnosis.
    • Definitive Source Control: Within 6-12 hours. Critical for outcomes.
  • Antimicrobial Strategy:

    • CA-IAI (Community-Acquired):
      • Mild-Moderate (e.g., uncomplicated appendicitis, diverticulitis): Ertapenem OR (Ceftriaxone/Cefotaxime + Metronidazole).
      • Severe/High-Risk (e.g., diffuse peritonitis): Piperacillin-Tazobactam OR Carbapenem (Imipenem, Meropenem).
    • HA-IAI (Hospital/Healthcare-associated):
      • Broader coverage for MDROs (Pseudomonas, ESBL): Piperacillin-Tazobactam, Carbapenems. Add Vancomycin/Linezolid if MRSA suspected.
    • Duration: Typically 4-7 days after adequate source control.
  • Source Control Modalities:

    • Surgical: Laparotomy/laparoscopy (e.g., appendectomy, resection, repair of perforation).
    • Percutaneous Drainage (PCD): For localized abscesses.

    ⭐ In complicated IAI (e.g., perforated diverticulitis with abscess), achieving source control within 6 hours is associated with significantly improved survival.

  • Supportive Measures:

    • Nutritional support (enteral preferred), DVT & stress ulcer prophylaxis.

Surgical team performing laparoscopy

High‑Yield Points - ⚡ Biggest Takeaways

  • Secondary peritonitis: E. coli (aerobic) & B. fragilis (anaerobic) are most common.
  • Tertiary peritonitis: Persistent infection, often resistant organisms or fungi.
  • Hinchey classification guides diverticulitis management; Stages III & IV often need surgery.
  • Appendicitis: Primarily clinical diagnosis; Alvarado score aids, imaging for equivocal cases.
  • Source control (drainage/repair/resection) is key, with antibiotics.
  • Empirical antibiotics: Must cover gram-negative bacilli & anaerobes.
  • Intra-abdominal abscess: Percutaneous drainage (USG/CT guided) is often treatment.

Practice Questions: Intra-abdominal Infections

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Which of the following statements is true regarding intra-abdominal compartment syndrome?

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Flashcards: Intra-abdominal Infections

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In Fournier's gangrene, the _____ are spared due to the intra-abdominal origin of their blood supply

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In Fournier's gangrene, the _____ are spared due to the intra-abdominal origin of their blood supply

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