15 SURGICAL INFECTIOUS DISEASE
Glenn W. Geelhoed M.D., M.P.H., DTMH

1. Have modern antibiotic developments controlled many, if not most, of the problems of surgical infection?

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No. In seriously ill surgical patients in intensive care unit (ICU) settings, the problems of sepsis have increased and remain among the principal causes of death in ICU patients, especially those with multiple organ failure and impairments of host defense. Antibiotic treatment may change the biographical sketch of the flora associated with patients’ deaths but cannot overcome the multiple causes of failing host resistance to infection that accompany barrier breeches to microbial invasion and the inflammatory and immunologic responses to the “usual suspects.”

2. What kinds of barrier breech allow microbial invasion that may set up surgical infection?

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The skin and mucosal linings of the body maintain a barrier between the multifloral outside world and the sterile interior milieu of the tissues and organs (even when the outside world is a tube of heavily populated flora through the middle of usually sterile body cavities, such as the gastrointestinal [GI] tract). It is easy to see the barrier breech when a knife penetrates the skin, carrying exterior flora beneath the skin, or when that knife perforates and spills the contaminated contents of the gut into the abdomen. It is less obvious when the breech is caused by a low-flow state or when inadequate nutrition or toxins impair mucosal immunoglobulins, making the “bug-body barrier” permeable. These polymicrobial communities of organisms may begin to invade through the breech in such barriers, particularly if there are further failures in the third line of defense in humoral and cellular resistance.

3. What is the difference between contamination and infection?

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The presence of microorganisms does not an infection make!
Resident communities of flora on body surfaces do little harm, and gut flora are even beneficial when contained in the gut. It is even possible for bacteria to be transiently present outside their usual commensal residences without constituting an infection in the normally intact host. For example, in vigorously brushing one’s teeth, gram-negative bacteria of various kinds that are resident in the oral cavity are introduced into the bloodstream but probably quickly were eliminated by normal defense mechanisms-unless they met lowered host resistance or seeded a prosthetic heart valve.

4. How can the enormous load of bacteria in the lower GI tract be beneficial?

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Bugs can be beautiful. These are the same bacteria that have lived with and in humans symbiotically for millennia. They synthesize vitamin K-something we literally cannot do without-or crowd out pathogenic organisms by their overwhelming numbers. They also help to metabolize bile salts and play a role in detoxifying some environmental hazards, similar to septic systems.

5. Whenever intraabdominal bowel spillage is encountered, is it mandatory to culture the fecal contamination and obtain sensitivities of all identified organisms?

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No. There is a difference between contamination and infection. Therefore, cultures of fecal spillage into the peritoneum will not provide useful information. The contaminant, just because of its change in position with reference to the bowel wall, is not likely to be sterile. When would you like the laboratory to quit? Will you be content to hear a report of Escherichia coli and bacteroides, two of the more than 800 species that even the most compulsive laboratory can hardly be competent to identify, given the exposure to air and time lapse until processing on different media? How will information from a sampling error of mixed, community-acquired contaminants change your therapy? If, for instance, no anaerobes are identified from the fecal specimen, will you be so confident that they are not present as to exclude these species from coverage?
The lesson to be learned is that culture of community-acquired contaminants is expensive, incomplete, and unedifying; the culture of invading microbes in infections, particularly hospital-acquired microbes that persist after treatment, may give critical information and is a more appropriate use of microbiologic resources.

6. What are preps (e.g., bowel preps)?

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Preps are decontamination procedures, designed to reduce resident flora before an elective invasive procedure. Preps may take the form of a simple process such as an alcohol swab smeared over the skin before a quick prick of the subcutaneous injection or may involve preparation of a larger area of the skin surface for the surgical field of incision (see question 7).
A bowel prep is similarly designed to reduce the resident flora in the gut through (1) mechanical catharsis (i.e., purge); (2) osmotic or volume dilution with large volumes of saline, other electrolyte solutions, or mannitol; or (3) oral administration of nonabsorbed antibiotics. Of these methods, the most important is clearly mechanical catharsis because it purges huge amounts of flora, which may account for up to two thirds the dry weight of colon contents. One of the most cogent reasons for the choice of certain oral antibiotics in bowel preps (see question 9) is their vigorous cathartic action.

7. How is the skin or mucosal cavities of a patient sterilized to prepare a sterile field for operative incision?

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There is one way, hardly recommended, by which patients can be “sterilized”: similar to instruments and drapes, they can be placed in an autoclave. But short of this absurd example, the skin is never sterile. Decontamination processes are never perfect, particularly in so complex a tissue with crevices and accessory skin structures in which bacteria reside. Resting gloved hands on a “sterile field” does not include the skin or mucosal surfaces.
At best, we simply reduce the flora to the low-level inoculum that can be handled by most intact host defense systems-as in the example of brushing your teeth-but living tissue surfaces are never “sterile.” A method that kills all microbial organisms from such surfaces would also devitalize mammalian cells and render them more susceptible to lower-level microbial inocula.

8. What means can be used to reduce surface resident flora without further injuring the skin or mucosa?

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* Volume lavage (for mnemonic value only: dilution is the solution to pollution)
* Defatting, which solubilizes the sebaceous oils that may trap flora
* Microbicidal killing with a bacteriostatic agent

To an amazing extent, one cheap, simple fluid that may serve as a diluent, fat solvent, and antimicrobial is alcohol. Alcohol is nearly ideal as prepping solution, with the minor disadvantages that it is dehydrating and minimally flammable. Because it vaporizes and disappears, flora may spread from interstices, outside the field, or even via aerosolized fallout onto the field, thus requiring the addition of extended-duration bacteriostasis to the alcohol prep.
Iodine also kills bacteria but with a greater hazard to sensitive mammalian cells (it oxidizes the cell walls of small plants). A lower initial concentration of iodine and a longer duration of action can be achieved by incorporation of an iodophor, a substance in nearly universal use in preps. The application of moisture- and vapor-permeable “incise drapes” or desiccation-preventing “ring drapes” may further retard repopulation of flora over the prepped (but still not sterile) field.

9. What are “pipe cleaner” antibiotics?

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Pipe cleaners are orally administered antibiotic regimens that reduce the flora in the GI tract, from which they are not well absorbed. They are an almost ideal component of bowel preps because they are potent cathartic agents and accomplish the vast majority of their “pipe cleaning” by mechanical purgative action. The most popular pipe cleaners include a neomycin or erythromycin base.

10. What is selective gut decontamination? How does it work?

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It does not work. This method used pipe cleaners in patients at high risk for the development of sepsis from multiple organ failure with the theoretic aim of reducing the risk involved in barrier breech of the GI tract and inoculation with gut flora. Good experimental evidence indicated that this method should reduce the high mortality rate in seriously ill patients at high risk of surgical sepsis. After prolonged clinical trials, however, it failed to demonstrate a benefit in patient survival. The likely reason is that whereas the laboratory studies were done in intact animal models with functioning host defense systems, failures of defense beyond the barrier breech may explain why selective gut decontamination failed to benefit seriously ill patients. Furthermore, resident hospital flora repopulated the purged gut over time, but with virulent forms of microbes selected by their resistance to the broad-spectrum antibiotics. The method still has some use in patients undergoing procedures such as high-dose chemotherapy or bone marrow transplantation and in some patients isolated in “life islands” (e.g., patients with immunodeficiency diseases or burns).