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Infection in Surgical Patients
Defense Barriers
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Physical
Chemical
Immunologic
Host defense
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Barrier
Microbial flora
Humoral
Cellular
cytokine
Microbial flora
Humoral defenses
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Immunoglobulin
Complement
Immunoglobulin
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All Ig classes (IgM, G, A, E, D and igG
subclasses are composed of one type
(M,G,A,E,D) of heavy (H) and one type of
light (L) protein.
Each L chain is linked to an H chain, and H
chains are interlinked.
H chain activate complement or bind to
receptors of either macrophages or PMN
leucocytes
The amino terminus of the H and L chains
together forms antigen-binding site
Immunoglobulin
Complement system
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Series of serum proteins that may
became activated via either classic or
alternative pathway
Cellular defense
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Macrophage
PMN leucocytes
cytokines
Surgical Site Infection ( SSI )
Clinical criteria ( CDC )
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A purulent exudate draining from the
surgical site
A positive fluid culture obtained from a
surgical site that was closed primarily
The surgeon’s diagnosis of infection
A surgical site that requires reopening
FACTS
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One out of every 24 patients who have
inpatient surgery in the United States
has a postoperative SSI
The cost of SSIs are substantial: an
increased total cost of more than 300%
SSIs increase the post operative length
of hospital stay by 10-14 days
Definition
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SSI is a difficult term to define
accurately because it has a wide
spectrum of possible clinical features
“It’s hard to define, but I know it when
I see it.”
SSI are classified into three categories,
depending of which anatomic areas are
affected
Definitions of SSI
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Superficial incisional SSI: Infection involves only
skin and subcutaneous tissue of incision.
Deep incisional SSI: Infection involves deep
tissues, such as fascial and muscle layers. This
also includes infection involving both superficial
and deep incision sites and organ/space SSI
draining through incision.
Organ/space SSI: Infection involves any part of
the anatomy in organs and spaces other than the
incision, which was opened or manipulated during
operation.
Causes
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Table 1. Pathogens
Commonly Associated
with Wound Infections
and Frequency of
Occurrence*
Pathogen Frequency
(%) *NNIS System (CDC,
1996)
Staphylococcu 20
s aureus
Coagulasenegative
staphylococci
enterococci
14
Escherichia coli
Pseudomonas
enterobacter
Proteus
Mirabilis
Klebsiella pn.
Bact. fragilis
8
8
7
3
12
3
2
Risk factors
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Decreased host resistance can be due to systemic factors affecting the
patient's healing response, local wound characteristics, or operative
characteristics.
Systemic factors include age, malnutrition, hypovolemia, poor tissue
perfusion, obesity, diabetes, steroids, and other immunosuppressants.
Wound characteristics include nonviable tissue in wound; hematoma;
foreign material, including drains and sutures; dead space; poor skin
preparation, including shaving; and preexistent sepsis (local or distant).
Operative characteristics include poor surgical technique; lengthy
operation (>2 h); intraoperative contamination, including infected
theater staff and instruments and inadequate theater ventilation;
prolonged preoperative stay in the hospital; and hypothermia
The type of procedure is a risk factor too
Antimicrobial agents
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Prophylaxis
Empiric therapy
Directed therapy
Classes of Antimicrobial Agents
 Penicillins, Cephalosporins,
carbapenems inhibit cell wall synthesis,
resulting in bacteriolysis
 Tetracyclins, chloramphenicol, and
macrolides inhibit bacterial ribosomal
activities and thus overall protein
synthesis
 Vanco inhibits assembly of peptido
glycan polymers
 Quinolones inhibit bacterial DNA
synthesis
Prophylactic Antibiotics
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General agreement exists that prophylactic antibiotics
are indicated for clean-contaminated and
contaminated wounds
Antibiotics for dirty wounds are part of the treatment
because infection is established already.
Clean procedures might be an issue of debate. No
doubt exists regarding the use of prophylactic
antibiotics in clean procedures in which prosthetic
devices are inserted because infection in these cases
would be disastrous for the patient.
Systemic preventive antibiotics
should be used in the following cases
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A high risk of infection is associated
with the procedure (eg, colon
resection).
Consequences of infection are unusually
severe (eg, total joint replacement).
The patient has a high NNIS risk index.
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The antibiotic should be administered
preoperatively but as close to the time of the
incision as is clinically practical. Antibiotics
should be administered before induction of
anesthesia in most situations.
The antibiotic selected should have activity
against the pathogens likely to be
encountered in the procedure.
Postoperative administration of preventive
systemic antibiotics beyond 24 hours has not
been demonstrated to reduce the risk of SSIs
Intraoperative re-dosing
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Operation is prolong
If massive blood loss occurs
The patient is obese
Colorectal Surgery
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Recommended oral prophylaxis consist
of Neomycin plus erythromycin or
Neomycin plus Flagyl, along with
administration of mechanical bowel
preparation
Intravenous cefoxitin or cefazolin
preoperatively and continued 2 doses or
24 hrs postoperatively
Intraabdominal Infection
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Usually polymicrobial
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There is synergism between aerobic and anaerobic
organisms
Peritonitis vs abscesses formation
Abscesses
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Determined by gravity and the physiologic
drainage basins of the abdomen
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Subphrenic space, pelvic space, subhepatic space,
paracolic gutter, lesser sac, subfascial area
Primary Peritonitis
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Microorganisms lodge in the peritoneal
cavity without a fundamental intraabd.
Process
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Previously occurred in miliary TB, but now
commonly occurs in ascites
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Most common organism in ascties is S.
pneumoniae
Secondary peritonitis
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Usually begins with perforation of the GI tract
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One major factor in determining severity is the size of
the bacterial inoculum
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Perforated appendix has 106 to 107 bacteria per g
Sigmoid colon has 1010 to 1011 bacteria per g
 Anaerobes exceed aerobes 1,000-fold
Adjuvant factors are also important
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From inflammatory or neoplastic process
Food, fiber, exfoliated cells, blood, dead tissue
Bacteria that are eliminated are either phagocytized
or removed into the lymphatic system
Tertiary Peritonitis
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recurrent intra-abdominal infection after
initial surgical and antimicrobial therapy
of secondary bacterial peritonitis.
Nosocomial Pneumonia
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Comes from atelectasis,
aspiration, and
contamination from
ventilation
Most common bacteria
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Pseudomonas, Klebsiella,
Staph, E. coli, Proteus,
Enterobacter,
Pneumococcus, Serratia,
group A Strep, H. flu
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Host defenses
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Glottis
Cilia
Mucus
Secretory IgA and IgG
Surfactant
Transferrin
Alveolar macrophages
Urinary Tract Infections
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Foley catheterization is usually the culprit
Host defenses
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Urine flow, antireflux, epithelium, mucus, IgA,
urethral length
Common organisms
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E. coli, Klebsiella, Pseudomonas, Proteus,
Enterobacter, Enterococcus, Serratia, Citrobacter,
Staph epidermidis
Catheter and Prosthetic Device
Infection
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The trauma of the catheter
placement, the foreign body itself,
and the contaminating bacteria
lead to an inflammatory response
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Eradication cannot be achieved
because of the persistence of the
foreign body
Intimal vein disruption and clot
formation also lead to bacterial
proliferation
Removal should never be delayed
nor should antimicrobial agents be
withheld
Other Specific Site Infection
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Parotitis
Sinusitis
Pseudomembranous colitis