INFECTION AND SEPSIS

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INFECTION AND SEPSIS

• Surrounded by pathogens
• Infection is the exception
• Protective from infection
• Physical barriers
• Chemical barriers
• Immunological function

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Physical and ChemicalBarriers to Infection

• Skin
• stronger in hands and feet
• sebaceous secretions lower pH
• Mucous membranes
• ciliary function
• mucous barrier
• acid mileu in stomach

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Barriers breached in Surgery
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Barriers Breached in Trauma
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Immune Defense

• Humoral defense
• antibodies
• complement
• Cellular defense
• Cytokines
• potential for deleterious effects
• Interaction of mechanisms

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Breakdown of Host Defense

• Physical, chemical and immunological breakdown
  -act synergistically
• e.g. patient with
• diabetes
• immunosuppresion
• surgery
• Potential for deleterious effects

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Fourniers Gangrene
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Commensal Microbial Flora

• Important for immune development
• Occupy binding sites for pathogens
• Provide mucobacterial barrier
• Anerobic bacteria
• present in greatest quantity in GIT
• Greatest diversity
• Prevent invasion by gram neg. aerobes

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Breakdown of Host Defense- GIT Flora

• Transmigration of bacteria
• Lack of feeding
• Overuse of antibiotics
• Absence of bile
• Protein malnutrition
• Immune deficiency

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ICU patient fed enteraly To preserve GIT integrity
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Infection Manifestation

• Local signs
• pain,redness,swelling, warmth loss of function
• Systemic signs
• Fever, somnolence, confusion, ileus, hypotension
• Lab tests
• TW,polymorphs, Cultures
• Non infective- causes may manifest as infection

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Common Infections

• Wound infection
• Initial inoculum overwhelms host defense
• Occurs at 5 - 7 days post op
• Factors
• host - immune suppression, DM, renal failure
• surgeon - technique
• environment - contamination

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Common Infections

• Types of Wounds
• 1. Clean - no viscus, no sterile breach
• 2. Clean contaminated - controlled entry into
  viscus
• 3. Contaminated - emergency bowel resection,
  perforated appendix
• 4. Dirty - heavy contamination / long duration
• Antibiotics used
• type 2 as prophylaxis
• type 3,4 as treatment

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Wound Closure

• Wounds
• Closure by
• primary intention
• secondary intention
• Timing of closure
• delayed primary closure
• secondary closure

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Closure by Secondary Intention
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Intraabdominal Infection

• Defense
• Bacterial clearance - stomata between mesothelial
  cells under diaphragm lead to lymph vessels
• Phagocytosis - both resident and recruited
  phagocytes
• Sequestration - by fibrin rich inflammatory
  exudate, with omentum/viscera

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Intraabdomianal Infection

• Signs of peritonitis
• Pain
• sharp in character, well localised at first
• spreads to surrounding areas
• involuntary guarding, rigidity
• absent bowel sounds
• Posture
• lying still, rapid breathing ,no movement
• General condition
• ill, septic, dehydrated, hypotension

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Intraabdominal Infection

• Usually viscus perforation
• colon worse than upper GIT
• Isolates
• aerobic - E. Coli, klebsiella other enterobacter,
  strep, enterococci, proteus, pseudomonas
• anaerobic - bacteroides, Clostridium
• Treatment is surgical and aggressive antibiotic
  treatment

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Enterocutaneous Fistula
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Common Post Surgical Infections

• Pneumonia
• Protein malnourished
• upper abdominal wounds poor cough
• bed bound - atelectasis
• elderly
• ventilator
• Occurs from 3 days post op
• careful clinical exam,CXR
• Routine chest physiotherapy

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Common Post Surgical Infections

• Urinary Tract Infection
• catheters
• dehydration
• Remove catheters early
• Ensure hydration
• Antimicrobial therapy

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Common Post Surgical Infections

• Catheter and prosthetic devices
• I/v canulas
• central lines
• mesh
• Skin organisms- S aureus, S epidermidis
• Aseptic technique
• Remove if infected

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Less Common Post Surgical Infections

• Necrotising soft tissue infection
• Parotitis
• Sinusitis
• Tonsillitis

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Treatment of Infection

• General principles
• incise and drain pus
• antibiotics as needed
• debride dead tissue
• remove foreign bodies

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Antibiotic Therapy

• Prophylaxis
• Short course to prevent infection
• Must be on board before contamination
• Antibiotics with activity against expected
  inoculation organisms
• Avoid extended spectrum agents
• Post op benefit not proven
• Topical antibiotics - not proven

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Antibiotic Therapy

• Empirical therapy
• based on clinical information
• search for source must continue
• limit duration of empirical therapy
• use known institution pattern of infection
• multi agent vs broad agent

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Antibiotic Therapy

• Directed therapy
• target identified pathogens
• choose suitable efficacy /minimal toxicity agent
• cover aerobic and anaerobic if likelihood exist
  for both
• extended spectrum as last resort

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Multiple System Organ Failure

• AKA - Gram neg. bacterial sepsis
• 30 mortality
• Healthy and compromised host
• 3-13 cases per 1000 admissions
• Nosocomial

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Multiple System Organ Failure

• Factors
• Host compromise
• Elderly, disability
• Malnutrition
• Antimicrobial therapy
• Major surgery
• Cavity manipulation
• Immunosuppression e.g. steroids

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MSOF

• Fever
• Acidosis, hypoxemia
• Disordered oxygen and substrate use
• Hyperglycaemia
• Decreased systemic vascular resistance
• Elevated cardiac output
• Hypotension

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MSOF

• Evidence for LPS - endotoxin
• LPS
• O antigen - specific for each organism
• core LPS
• membrane lipid A

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LPS - EFFECTS

• non specific polyclonal b cell proliferation
• macrophage activation, cytokine release
• hypotension, hypoxemia
• bacterial translocation
• complement and coagulation activation
• platelet and white cell margination

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LPS - Mechanism

• Direct effect of bacteria
• Indirect (mediated) effect
• trigger macrophages to release TNFa, IL-1, IL-6,
  aIFN
• TNFa, IL-1, - primary mediators but may be
  deleterious in large amounts
• aIFN- causes continued activation of macrophages
• Permeability defects in microcirculation
• ARDS, GUT, Hepatic, renal failure

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Problem

• A 23 year old man had a perforated appendix.
  Three days post op this was his temperature
  chart. What is your interpretation.

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Problem

• What is your choice for antibiotic prophylaxis
  for
• colorectal surgery
• biliary surgery
• upper GI surgery

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Problem

• A 75 year old diabetic had an operation for
  perforated diverticular disease. His wound was
  found to be infected on the 5th POD.
• What factors may have contributed to this?

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