Surgical Site Infection ( SSI )

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Clinical criteria ( CDC )
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

Definition
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
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.

Risk factors
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

Prophylactic Antibiotics
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
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.

Intraoperative re-dosing
Operation is prolong
If massive blood loss occurs
The patient is obese

Intraabdominal Infection
Usually polymicrobial
There is synergism between aerobic and anaerobic organisms
Abscesses
 Determined by gravity and the physiologic drainage basins of the abdomen
  Subphrenic space, pelvic space, subhepatic space, paracolic gutter, lesser sac, subfascial area

Primary Peritonitis
Microorganisms lodge in the peritoneal cavity without a fundamental intraabd. Process
 Previously occurred in miliary TB, but now commonly occurs in ascites
  Most common organism in ascties is S. pneumoniae

Secondary peritonitis
Usually begins with perforation of the GI tract
 From inflammatory or neoplastic process
One major factor in determining severity is the size of the bacterial inoculum
 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
 Food, fiber, exfoliated cells, blood, dead tissue
Bacteria that are eliminated are either phagocytized or removed into the lymphatic system

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