Infection in Surgical Patients

August, 2006Mike Joutovsky, PGY3

Department of SurgerySt. Barnabas Hospital

Defense Barriers

Physical Chemical Immunologic

Host defense

Barrier Microbial flora Humoral Cellular cytokine

Microbial flora

Humoral defenses

Immunoglobulin Complement

Immunoglobulin 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

Series of serum proteins that may became activated via either classic or alternative pathway

Cellular defense

Macrophage PMN leucocytes cytokines

Surgical Site Infection ( SSI )

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

FACTS 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 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.

Causes Table 1. Pathogens

Commonly Associated with Wound Infections and Frequency of Occurrence*Pathogen Frequency (%) *NNIS System (CDC, 1996)

Staphylococcus aureus

20

Coagulase-negative staphylococci

14

enterococci 12

Escherichia coli

8

Pseudomonas 8

enterobacter 7

Proteus Mirabilis

3

Klebsiella pn. 3

Bact. fragilis 2

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

The type of procedure is a risk factor too

Antimicrobial agents

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 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.

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

Operation is prolong If massive blood loss occurs The patient is obese

Colorectal Surgery

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 Usually polymicrobial

There is synergism between aerobic and anaerobic organisms

Peritonitis vs abscesses formation 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

Tertiary Peritonitis

recurrent intra-abdominal infection after initial surgical and antimicrobial therapy of secondary bacterial peritonitis.

Nosocomial Pneumonia Comes from

atelectasis, aspiration, and contamination from ventilation

Most common bacteria Pseudomonas, Klebsiella,

Staph, E. coli, Proteus, Enterobacter, Pneumococcus, Serratia, group A Strep, H. flu

Host defenses Glottis Cilia Mucus Secretory IgA and IgG Surfactant Transferrin Alveolar macrophages

Urinary Tract Infections Foley catheterization is usually the

culprit Host defenses

Urine flow, antireflux, epithelium, mucus, IgA, urethral length

Common organisms E. coli, Klebsiella, Pseudomonas, Proteus,

Enterobacter, Enterococcus, Serratia, Citrobacter, Staph epidermidis

Catheter and Prosthetic Device Infection The trauma of the catheter

placement, the foreign body itself, and the contaminating bacteria lead to an inflammatory response

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

Parotitis Sinusitis Pseudomembranous colitis