13 SURGICAL WOUND INFECTION
Steven L. Peterson D.V.M., M.D.

1. Why should we worry about surgical wound infection?

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Approximately 30 million patients undergo surgery each year in the United States, and 20% of these patients acquire at least one nosocomial infection in the postoperative period. Infections at surgical sites are the third most common form of these infections and complicate 1-12% of all operations. The risk of death is four times higher in patients who develop wound infections, and each infection costs $12,000-30,000 to treat.

Commonly reported rates for specific operations are:

2. What comprises a surgical wound infection?

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Surgical wound infections more appropriately are called surgical site infections (SSIs) and must occur within 30 days of surgery unless a foreign body is left in situ. In the case of implanted foreign material, 1 year must elapse before surgery can be excluded as causative. SSIs are subdivided based on depth of tissue involvement into three clinically relevant categories.

1. Superficial incisional SSIs-involving only the skin and subcutaneous tissue
2. Deep incisional SSIs-involving deep soft tissue layers, such as fascial or muscle layers of the incision
3. Organ space SSIs-involving any anatomic structure opened or manipulated during the operative procedure

3. List the classic signs of superficial incisional, deep incisional, and organ space SSIs.

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Superficial and deep incisional SSIs:

* Calor (heat)
* Rubor (redness)
* Tumor (swelling)
* Dolor (pain)
* Purulent drainage

Organ space SSIs should be suspected in the presence of systemic signs and symptoms:

* Fever
* Ileus
* Shock

Definitive diagnosis of organ space SSIs may require imaging studies.

4. Why do these infections occur?

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Many factors contribute; however, the fundamental principle is that traumatic and surgical wounds violate the normal protective layer of skin. The importance of an intact integument has been shown experimentally in which it was determined that an inoculum of 8 million bacteria is required for infection of intact skin, 1 million are required for violated skin, and only 100 are required when foreign material is present.

5. Surgery always violates the skin and we often leave foreign material. How can we avoid SSIs?

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Although it is true that the basic act of surgery compromises the patients’ defenses, we can take steps to prevent wound infection. These steps involve the surgeon and the patient.

6. What can the surgeon do to decrease SSIs?

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The first step the surgeon can take is appropriate hand washing. The classic surgical scrub consists of 3 minutes of brushing with povidone-iodine or chlorhexidine gluconate. This protocol has been shown to have a high rate of noncompliance, which may contribute to SSIs. Data indicate improved compliance with comparable SSI rates using a much simpler protocol consisting of a 1-minute hand wash with nonantiseptic soap followed by hand-rubbing with a liquid aqueous alcoholic solution. Whether such simpler scrub protocols also can be applied in the future to the preparation of the patient is unknown.

7. What else can the surgeon do to control SSIs?

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The surgeon may limit the duration of surgery and follow good surgical principles by eliminating dead space, controlling hemorrhage, minimizing placement of foreign material (including excessive suture), and exhibiting gentle tissue handling. The surgeon should ensure that the patient remains warm during the perioperative period. This simple act of warming was shown in two prospective studies to decrease significantly the incidence of SSIs.

8. Can’t the surgeon predict who is going to get infected and just give them lots of antibiotics to stop infection from happening?

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To a degree SSIs can be anticipated. Factors that have been shown to have some predictive value to the surgeon are the physical status of the patient as classified by the American Society of Anesthesiologists, results of intraoperative cultures, and duration of preoperative hospital stay. Adequacy of regional blood supply also is important, as evidenced by the low infection rate in facial wounds. The classic description of wounds based on degree of gross contamination also may be of value. This scheme places wounds into one of four categories:

1. Clean wounds are atraumatic wounds in which no inflammation is encountered, no breaks in sterile technique occur, and no hollow viscus is entered.
2. Clean-contaminated wounds are identical except that a hollow viscus is entered.
3. Contaminated wounds are caused by trauma from a clean source or by minor spillage of infected materials.
4. Dirty-infected wounds are caused by trauma from a contaminated source or gross spillage of infected material into an incision.

Reported infection rates for each category are 2.1%, 3.3%, 6.4%, and 7.1%. Antibiotics can help but only when used appropriately.

9. How do I use antibiotics correctly to prevent SSIs?

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First by knowing what organism you are targeting, then choosing an appropriate antibiotic and delivering it at the appropriate time via the appropriate route. Because you usually will not have a preoperative culture to guide therapy, you need to base your choice of antibiotic on predicted organisms. Staphylococci are the most common skin organism and the most common etiologic agent in SSIs. Cefazolin, a first-generation cephalosporin, is usually the recommended antibiotic for prophylaxis in clean surgical procedures. In circumstances in which known contamination has occurred, initial antibiotics should be tailored based on the violated organ’s common flora. If the gut was entered, enterobacteriaceae and anaerobes are common; biliary tract and esophageal incisions yield these organisms plus enterococci. The urinary tract or vagina may contain group D streptococci, Pseudomonas, and Proteus spp.

10. If antibiotics are used, how and when should they be administered?

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Maximal benefit is obtained when tissue concentrations are therapeutic at the time of contamination. Efficacy is enhanced when prophylactic antibiotics are administered IV 20-30 minutes before surgical incision; late administration is similar to no administration. Multiple-dose regimens have no proven benefit over single-dose regimens. Indiscriminate antibiotic selection outside recommended hospital protocols may increase the incidence of SSIs. In special circumstances, administration routes other than IV may be indicated.

KEY POINTS: WOUND CLASSIFICATION AND INFECTION RATE (%)

1. Clean: atraumatic, no breaks in sterile technique, no entry into respiratory, alimentary, or genitourinary tract (2.1%)
2. Clean-contaminated: same as above except entry into respiratory, alimentary, or genitourinary tract (3.3%)
3. Contaminated: trauma from a clean source or minor spillage of infected materials (6.4%)
4. Dirty: trauma from a contaminated source or spillage of infected materials (7.1%)

11. Name other routes that you would use for prophylactic antibiotic administration.

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In patients with nasal carriage of Staphylococcus aureus, intranasal administration of mupirocin ointment may have some efficacy in decreasing nosocomial and surgical site infections. In elective colon surgery, a meta-analysis of published studies indicated that orally administered antibiotics combined with IV antibiotics are superior to IV antibiotics alone in preventing surgical site infections.
12. Does all that pulsatile lavage the surgeon uses in the operating room really do any good? Show answer
Yes. High-pressure pulsatile lavage has been evaluated extensively in soft tissue contamination and shown to be seven times more effective in reducing bacterial load than bulb syringe lavage. The inherent elastic recoil of the soft tissues allows particulate matter to escape between pulses of fluid. The optimal pressure and pulse frequency seems to be 50-70 lb/in.2 and 800 pulses/min. Adding antibiotics to lavage solutions, although commonly practiced, has not been shown definitively to improve outcome.

13. What can the patient do to help decrease SSIs?

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Stop smoking. Although obesity, poor nutritional status, advanced age, and diabetes are risk factors for SSIs, cigarette smoking is probably the leading preventable patient factor for SSIs just like it is the leading preventable cause of death and disability in the United States. Half of all people who smoke eventually die from a smoking-related illness. Smoking not only kills, but also more than triples that risk of incisional wound breakdown; in one study, smoking increased the incidence of SSIs in clean operative procedures sixfold, from 0.6% to 3.6%. Tobacco use results in decreased blood flow and decreased oxygen delivery to the wound. Toxic tobacco by-products also directly impede all stages of wound healing. Despite this knowledge, surgeons continue to operate electively on smokers, and most smokers continue to smoke up until the day of surgery.

14. When prevention fails, what do you do for SSIs?

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The first line of therapy in SSIs is drainage. This is established by reopening the wound or, in the case of deep space infections, using computed tomography-guided or ultrasound-guided techniques for drain placement or presurgical planning. Antibiotic therapy is used to control associated cellulitis and generalized sepsis.

15. What may happen with untreated superficial or deep incisional SSIs?

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Locally the wound breaks down, and infection dissects through the tissue planes and continues to advance. If the infection progresses rapidly, necrotizing fasciitis may develop. Finally, the strength layers of the wound closure break open (dehisce).
16. Define wound dehiscence. Show answer
The partial or total disruption of any or all layers of the operative wound.

17. Define evisceration.

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Rupture of the abdominal wall and extrusion of the abdominal viscera.

18. What factors predispose to dehiscence?

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Age > 60 years, obesity and increased intra-abdominal pressure, malnutrition, renal or hepatic insufficiency, diabetes mellitus, use of corticosteroids or cytotoxic drugs, and radiation have been implicated in wound dehiscence. Infection also plays an important role; an infective agent is identified in more than half of wounds that undergo dehiscence. Despite these excuses, the most important factor in wound dehiscence is the adequacy of closure. Fascial edges should not be devitalized. Ideally the linea alba sutures should be placed neither too laterally nor too medially. Excessive lateral placement may incorporate the variable blood supply of the rectus abdominis muscle and compromise fascial circulation. Excessive medial placement misses the point of maximal strength at the transition zone between the linea alba and rectus abdominis sheath. In addition, sutures should be tied correctly without excessive tension, and suture material of adequate tensile strength should be chosen.

19. When does wound dehiscence occur?

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It may occur at any time after surgery; however, it is most common between the 5th and 10th postoperative days, when wound strength is at a minimum.

20. What are the signs and symptoms of wound dehiscence?

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Normally a ridge of palpable thickening (healing ridge) extends about 0.5 cm on each side of the incision within 1 week. Absence of this ridge may be a strong predictor of impending wound breakdown. More commonly, leakage of serosanguineous fluid from the wound is the first sign. In some instances, sudden evisceration may be the first indication of abdominal wound dehiscence. The patient also may describe a sensation of tearing or popping associated with coughing or retching.

21. Describe the proper management of wound dehiscence.

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If the dehiscence is not associated with infection, elective reclosure may be the appropriate therapeutic course. If the condition of the patient or wound makes reclosure unacceptable, however, the wound should be allowed to heal by second intention. An unstable scar or incisional hernia may be dealt with at a later, safer time. Dehiscense of a laparotomy wound with evisceration is a surgical emergency with a reported mortality of 10-20%. Initial treatment in this instance consists of appropriate resuscitation while protecting the eviscerated organs with moist towels; the next step is prompt surgical closure. Exposed bowel or omentum should be lavaged thoroughly and returned to the abdomen; the abdominal wall should be closed; and the skin wound should be packed open. Vacuum-assisted wound closure may be valuable in select cases.

References
WEB SITE
http://www.acssurgery.com/abstracts/acs/acs0102.htm
BIBLIOGRAPHY
1. Barie PS: Modern surgical antibiotic prophylaxis and therapy: Less is more. Surg Infect 1:23-29, 2000. Full article
2. Garner GB, Ware DN, Cocanour CS, et al: Vacuum-assisted wound closure provides early fascial reapproximation in trauma patients with open abdomens. Am J Surg 182:630-638, 2001. Medline Full article
3. Kluytmans J, Voss A: Prevention of postsurgical infections: Some like it hot. Curr Opin Infect Dis 15:427-432, 2002. Medline Similar articles
4. Krueger JK, Rohrich RJ: Clearing the smoke: The scientific rationale for tobacco abstention with plastic surgery. Plast Reconstr Surg 108:1063-1073, 2001.
5. Myles PS, Iacono GA, Hunt JO, et al: Risk of respiratory complications and wound infection in patients undergoing ambulatory service. Anethesiology 97:842-847, 2002. Full article
6. Parienti JJ, Thibon P, Heller R, et al: Hand-rubbing with an aqueous alcoholic solution vs traditional sugical hand scrubbing and 30-day surgical site infection rates: A randomized equivalence study. JAMA 288:722-727, 2002. Medline Similar articles Full article
7. Perl TM, Cullen JJ, Wenzel RP, et al: Intranasal mupirocin to prevent postoperative Staphylococcus aureus infections. N Engl J Med 346:1871-1877, 2002. Medline Similar articles Full article
8. Seltzer J, McGraw K, Horsman A, Korniewicz DM: Awareness of surgical site infections for advanced practice nurses. ACCN Clin Iss 13:398-409, 2002. Full article