Bloodstream Infections and Sepsis

Bloodstream Infections and Sepsis

Bloodstream Infections and Sepsis

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Definitions & Criteria - Sepsis Starter Pack

  • SIRS (Systemic Inflammatory Response Syndrome): ≥2 criteria:
    • Temperature >38°C or <36°C
    • Heart Rate >90/min
    • Respiratory Rate >20/min or PaCO2 <32 mmHg
    • WBC >12,000/mm³ or <4,000/mm³ or >10% immature bands
  • Sepsis (Sepsis-3): Suspected infection + life-threatening organ dysfunction (SOFA score ↑ by ≥2 points).
  • qSOFA (quick SOFA - bedside prompt for sepsis outside ICU, ≥2 criteria):
    • Respiratory rate ≥22/min
    • Altered mentation (GCS <15)
    • Systolic BP ≤100 mmHg
  • Septic Shock: Sepsis + persisting hypotension requiring vasopressors to maintain MAP ≥65 mmHg AND serum lactate >2 mmol/L despite adequate fluid resuscitation.

⭐ Sepsis-3 definition de-emphasized SIRS, focusing on organ dysfunction (SOFA score) for sepsis diagnosis.

Infection, Sepsis, Septic Shock, and MODS Progression

Pathophysiology of Sepsis - Cascade of Chaos

  • Trigger: Pathogen-Associated Molecular Patterns (PAMPs, e.g., LPS from Gram-neg bacteria) or host-derived Damage-Associated Molecular Patterns (DAMPs) activate Pattern Recognition Receptors (PRRs, e.g., TLRs) on immune cells.
  • Inflammatory Cascade: Leads to a "Cytokine Storm" - massive release of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6).
    • Activates complement & coagulation cascades (→ risk of Disseminated Intravascular Coagulation - DIC).
  • Endothelial Dysfunction: Causes ↑vascular permeability, widespread vasodilation, and microthrombi formation.
  • Cellular & Organ Damage: Results in tissue hypoperfusion, cellular hypoxia, and mitochondrial dysfunction, ultimately leading to Multiple Organ Dysfunction Syndrome (MODS).
  • Immune Dysregulation: A simultaneous Compensatory Anti-inflammatory Response Syndrome (CARS), involving cytokines like IL-10, can occur, potentially leading to immunosuppression and susceptibility to secondary infections.

⭐ TNF-α is a key early mediator in sepsis, largely responsible for fever, hypotension, and initiating widespread inflammation leading to tissue injury.

Etiology & Microbiology - Bug Lineup

  • Gram-Positive Cocci (GPC):
    • Staphylococcus aureus (MSSA/MRSA): Skin, catheters, endocarditis.
    • Streptococcus pneumoniae: Pneumonia, meningitis.
    • Coagulase-Negative Staphylococci (CoNS): Catheters, implants.
    • Enterococci (E. faecalis, E. faecium): UTI, intra-abdominal, biliary.
  • Gram-Negative Rods (GNR):
    • Escherichia coli: UTI (commonest source), intra-abdominal.
    • Klebsiella pneumoniae: Pneumonia, liver abscess, UTI.
    • Pseudomonas aeruginosa: HAP/VAP, burns, neutropenia.
    • Acinetobacter spp.: Ventilators, ICUs.
  • Anaerobes: Bacteroides fragilis (intra-abdominal).
  • Fungi: Candida spp. (e.g., C. albicans): Immunocompromised, CVCs, TPN. E. durans and E. faecalis culture and Gram stain

Staphylococcus aureus is the leading cause of infective endocarditis in many regions and a frequent cause of catheter-related bloodstream infections (CRBSI).

Clinical Presentation & Diagnosis - Spotting Sepsis Signs

  • Red Flags (Think Sepsis!):

    • Temp >38°C or <36°C; HR >90/min; RR >20/min
    • Altered mental status; Hypotension (SBP <90 mmHg)
  • qSOFA Score (Bedside, ≥2 points = High Risk): 📌 HAT

    • Hypotension (SBP ≤100 mmHg) - 1 pt
    • Altered Mentation (GCS <15) - 1 pt
    • Tachypnoea (RR ≥22/min) - 1 pt
  • Key Labs:

    • Blood cultures (PRIORITY, pre-antibiotics!)
    • Lactate (↑ = hypoperfusion)
    • Procalcitonin, CRP
    • CBC, Coags, LFTs, RFTs Old and New Definitions of Sepsis

⭐ Septic shock: Sepsis + persisting hypotension requiring vasopressors to maintain MAP ≥65 mmHg AND serum lactate >2 mmol/L despite adequate fluid resuscitation.

Sepsis Management - Rescue Mission

Rapidly implement Hour-1 Bundle (SSC):

  • Lactate: Measure; remeasure if initial > 2 mmol/L.
  • Cultures: Blood cultures before antibiotics.
  • Antibiotics: Broad-spectrum IV within 1 hour.
  • Fluids: 30 mL/kg IV crystalloid for hypotension or lactate ≥ 4 mmol/L.
  • Vasopressors: If hypotensive post-fluids, for MAP ≥ 65 mmHg (Norepi 1st line).

⭐ Early administration of appropriate antibiotics (within 1 hour of recognition) is critical for improving survival in sepsis and septic shock.

High‑Yield Points - ⚡ Biggest Takeaways

  • Sepsis: life-threatening organ dysfunction from dysregulated infection response; use qSOFA (≥2) or SOFA (↑≥2).
  • Septic shock: sepsis + hypotension (MAP <65 mmHg despite fluids, needs vasopressors) + lactate >2 mmol/L.
  • Common pathogens: S. aureus (GPC), E. coli, Klebsiella (GNB); Candida in immunocompromised.
  • Key management: Early fluids (30mL/kg in 3h), antibiotics (<1hr), source control.
  • Procalcitonin is a key biomarker for bacterial sepsis, aiding antibiotic de-escalation.

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