Source identification and control

Common Sources - The Usual Suspects

📌 Mnemonic: LUCAS → Lungs, Urine, Catheters, Abdomen, Skin.

• Lungs (~50%):
  • Pneumonia, empyema.
  • Action: Chest X-ray, sputum culture.
• Intra-abdominal (~20%):
  • Peritonitis, cholangitis, abscess.
  • Action: CT Abdomen/Pelvis.
• Urinary Tract (~15%):
  • UTI/Pyelonephritis, often catheter-related.
  • Action: Urinalysis, urine culture.
• Catheter-Related (CRBSI):
  • Central or peripheral lines.
  • Action: Paired blood cultures (line + peripheral).
• Skin/Soft Tissue:
  • Cellulitis, fasciitis, infected ulcers.

⭐ Occult abscesses (e.g., intra-abdominal, pelvic) are a classic cause of persistent fever and non-resolving sepsis despite appropriate antibiotic therapy.

Diagnostic Imaging - Seeing the Source

• Goal: Rapidly confirm & localize suspected infection to guide source control.
• Chest X-ray (CXR): First-line for suspected pneumonia. Look for infiltrates, consolidation. Portable CXR is key for unstable patients.
• CT Scan (IV contrast): Gold standard for deep-seated infections.
  • Abdomen/Pelvis: Abscesses, collections, pyelonephritis.
  • Soft Tissue: Necrotizing fasciitis (look for gas).
• Ultrasound (US): Rapid, bedside assessment.
  • RUSH exam: Screens for effusions, hydronephrosis.
  • Excellent for cholecystitis, DVT, and guiding procedures.
• Echocardiogram (TTE/TEE): Essential for suspected infective endocarditis to visualize vegetations.

⭐ A CT scan with IV contrast is the diagnostic test of choice for most suspected deep space infections or intra-abdominal abscesses, providing a roadmap for intervention.

Labs & Cultures - The Bug Hunt

• Core Blood Work:

  • Blood Cultures: 2 sets from different venipuncture sites, drawn before starting antibiotics. Use aerobic & anaerobic bottles.
  • Lactate: Key diagnostic and prognostic marker. Re-measure if initial is > 2 mmol/L to guide resuscitation.
  • CBC with differential: Look for leukocytosis (WBC > 12,000), leukopenia (WBC < 4,000), or >10% bands (left shift).
  • CMP: Assesses for end-organ damage (e.g., ↑ creatinine, ↑ LFTs).
  • Coagulation studies: PT, PTT, INR, fibrinogen to screen for DIC.

• Targeted Investigations:

  • Source-specific cultures: Urine, sputum, wound, or CSF based on clinical suspicion.

⭐ Procalcitonin (PCT) rises more rapidly and is more specific for bacterial sepsis than C-reactive protein (CRP). It's a key biomarker for guiding antibiotic therapy duration.

Source Control - The Fix-It Plan

• Goal: Eradicate the source of infection. Intervene as soon as sepsis is identified and initial resuscitation is underway, ideally within 6-12 hours.
• Core Principles (The "4 D's"):
  • Drainage: Purulent collections (e.g., abscess, empyema).
  • Debridement: Infected, necrotic tissue (e.g., necrotizing fasciitis).
  • Device Removal: Infected lines, catheters, or prosthetics.
  • Definitive Management: Correcting anatomical derangements to stop ongoing contamination (e.g., bowel perforation repair).

⭐ High-Yield: For severe intra-abdominal infections, definitive source control is critical. Delays beyond 12 hours are associated with significantly increased mortality. This often requires emergent surgical or percutaneous procedures.

High‑Yield Points - ⚡ Biggest Takeaways

• Promptly identify and control the source of infection, ideally within 6-12 hours of presentation.
• Early imaging (e.g., CT abdomen/pelvis) is crucial for diagnosing occult intra-abdominal or deep space infections.
• The most common sources are lungs, abdomen, urinary tract, and skin/soft tissue.
• Remove infected intravascular catheters and other devices after establishing alternative access.
• Urgent surgical or percutaneous drainage is critical for abscesses, empyema, or obstructive cholangitis.