Pos Operatorias

Jonathan L. Meakins, M.D., D.Sc., F.A.C.S., and Byron J. Masterson, M.D., F.A.C.S.

1 PREVENTION OF POSTOPERATIVEINFECTION

Epidemiology of Surgical Site Infection

Historically, the control of wound infection depended on anti-septic and aseptic techniques directed at coping with the infectingorganism. In the 19th century and the early part of the 20th cen-tury, wound infections had devastating consequences and a mea-surable mortality. Even in the 1960s, before the correct use ofantibiotics and the advent of modern preoperative and postopera-tive care, as much as one quarter of a surgical ward might havebeen occupied by patients with wound complications. As a result,wound management, in itself, became an important component ofward care and of medical education. It is fortunate that many fac-tors have intervened so that the so-called wound rounds havebecome a practice of the past.The epidemiology of wound infec-tion has changed as surgeons have learned to control bacteria andthe inoculum as well as to focus increasingly on the patient (thehost) for measures that will continue to provide improved results.

The following three factors are the determinants of any infec-tious process:

1. The infecting organism (in surgical patients, usually bacteria).2. The environment in which the infection takes place (the local

response).3. The host defense mechanisms, which deal systemically with the

infectious process.1

Wounds are particularly appropriate for analysis of infectionwith respect to these three determinants. Because many compo-nents of the bacterial contribution to wound infection now areclearly understood and measures to control bacteria have beenimplemented, the host factors become more apparent. In addi-tion, interactions between the three determinants play a criticalrole, and with limited exceptions (e.g., massive contamination),few infections will be the result of only one factor [see Figure 1].

Definition of Surgical Site Infection

Wound infections have traditionally been thought of as infec-tions in a surgical wound occurring between the skin and the deepsoft tissuesa view that fails to consider the operative site as awhole. As prevention of these wound infections has become moreeffective, it has become apparent that definitions of operation-related infection must take the entire operative field into account;obvious examples include sternal and mediastinal infections, vas-cular graft infections, and infections associated with implants (ifoccurring within 1 year of the procedure and apparently related toit). Accordingly, the Centers for Disease Control and Preventioncurrently prefers to use the term surgical site infection (SSI). SSIscan be classified into three categories: superficial incisional SSIs(involving only skin and subcutaneous tissue), deep incisionalSSIs (involving deep soft tissue), and organ/space SSIs (involvinganatomic areas other than the incision itself that are opened ormanipulated in the course of the procedure) [see Figure 2].2,3

Standardization in reporting will permit more effective sur-veillance and improve results, as well as offer a painless way ofachieving quality assurance.The natural tendency to deny that asurgical site has become infected contributes to the difficulty ofdefining SSI in a way that is both accurate and acceptable to sur-geons. The surgical view of SSI recalls one judges (probablyapocryphal) remark about pornography: It is hard to define, butI know it when I see it. SSIs are usually easy to identify.Nevertheless, there is a critical need for definitions of SSI thatcan be applied in different institutions for use as performanceindicators.4The criteria on which such definitions must be basedare more detailed than the simple apocryphal remark just cited;they are outlined more fully elsewhere [see 1:8 Preparation of theOperating Room].

STRATIFICATION OF RISK FOR SSI

The National Academy of SciencesNational Research Councilclassification of wounds [see Table 1], published in 1964, was alandmark in the field.5 This report provided incontrovertible datato show that wounds could be classified as a function of probabil-ity of bacterial contamination (usually endogenous) in a consistentmanner. Thus, wound infection rates could be validly comparedfrom month to month, between services, and between hospitals.As surgery became more complex in the following decades, how-ever, antibiotic use became more standardized and other risk vari-ables began to assume greater prominence. In the early 1980s, theStudy on the Efficacy of Nosocomial Infection Control (SENIC)study identified three risk factors in addition to wound class: loca-tion of operation (abdomen or chest), duration of operation, and

BACTERIA

SURGICAL SITE

HOST DEFENSE

MECHANISMS

Figure 1 In a homeostatic, normal state, the determinants ofany infectious processbacteria, the surgical site, and hostdefense mechanisms (represented by three circles)intersect at apoint indicating zero probability of sepsis.

2005 WebMD, Inc. All rights reserved.I BASIC SURGICAL AND PERIOPERATIVE CONSIDERATIONS

ACS Surgery: Principles and Practice1 PREVENTION OF POSTOPERATIVE INFECTION 1



Skin Bowel

Is the operation Clean Clean- contaminated Contaminated Dirty or infected

Varies indifferentclinicalsituations.

Operatingteamrelated

Surveillance and quality assurance

Epidemiology of Surgical Site Infection

Surgical site infection is caused by exogenous or endogenous bacteria; infection is influenced not only by the source of the infecting inoculum but also by the bacterial characteristics.

Ensure that prophylactic antibiotics, if indicated, are present in tissue in adequate concentrations at beginning of operation.

Postpone elective operation if possible.Treat remote infectionappropriately.

Remote sites of infection

Endogenous factors or sources of bacteria

Bacterial characteristics of importance(virulence and antibiotic resistance)

Exogenous factors or sources of bacteria

Size of inoculum required toproduceinfection

Nature and siteof operation

Comportment Use of impermeable drapes and gowns Surgical scrub

Traffic control Cleaning Air

Operatingroomrelated

Preventive measures to control bacteria

Decontamination of patient's skin [see Sidebar Preoperative Preparation of the Operative Site] Additional antibiotics if indicated, depending on likelihood of contamination and on bacterial inoculum and properties [see Sidebar Antibiotic Prophylaxis of Infection]





Patient-related factors include

HOSTDEFENSE

MECHANISMS

Factors contributing to dysfunction of host defense mechanismscan be related to surgical disease, to events surrounding the operation, to the patients underlying disease, and to anesthetic management.

BACTERIA

SURGICAL SITE

Local factors influence the susceptibility of the wound environment by affecting the size of the inoculum required to produce infection.

Operating teamrelated

Factors influenced by the surgeon and operating team include Duration of operation Maintenance of hemostasis and perfusion Avoidance of seroma, hematoma, necrotic tissue, wound drains Tissue handling Cautery use

Patient-related

Age PaO2 Abdominal procedure Tissue perfusion Presence of foreign body Barrier function Diabetes

Surgeon-related

Factors influenced by thesurgeon include Preoperative decisions Timing of operation Surgical technique Transfusion Blood loss Duration and extent of operation Glucose control Tissue oxygenation (mask)

Patient-related factorsinclude Presence of 3 concomitant diagnoses Underlying disease Age Drug use Preoperative nutritional status Smoking

Patient-related

Normothermia Normovolemia Pain control Tissue oxygenation Glucose control Sterility of drugs

Anesthesiologist-related



patient clinical status (three or more diagnoses on discharge).6The National Nosocomial Infection Surveillance (NNIS) studyreduced these four risk factors to three: wound classification,duration of operation, and American Society of Anesthesiologists(ASA) class III, IV or V.7,8 Both risk assessments integrate thethree determinants of infection: bacteria (wound class), local envi-ronment (duration), and systemic host defenses (one definition ofpatient health status), and they have been shown to be applicableoutside the United States.9 However, the SENIC and NNISassessments do not integrate other known risk variables, such assmoking, tissue oxygen tension, glucose control, shock, and main-tenance of normothermia, all of which are relevant for clinicians(though often hard to monitor and to fit into a manageable riskassessment).

Bacteria

Clearly, without aninfecting agent, no infectionwill result. Accordingly,most of what is knownabout bacteria is put to usein major efforts directed atreducing their numbers by means of asepsis and antisepsis. Theprincipal concept is based on the size of the bacterial inoculum.

Wounds are traditionally classified according to whether thewound inoculum of bacteria is likely to be large enough to over-whelm local and systemic host defense mechanisms and producean infection [see Table 1]. One study showed that the most impor-tant factor in the development of a wound infection was the num-ber of bacteria present in the wound at the end of an operativeprocedure.10 Another study quantitated this relation and providedinsight into how local environmental factors might be integratedinto an understanding of the problem [see Figure 3].11 In the yearsbefore prophylactic antibiotics, as well as during the early phasesof their use, there was a very clear relation between the classifica-tion of the operation (which is related to the probability of a sig-nificant inoculum) and the rate of wound infection.5,12 This rela-tion is now less dominant than it once was; therefore, other fac-tors have come to play a significant role.6,13

CONTROL OF SOURCES OF

BACTERIA

Endogenous bacteria area more important cause ofSSI than exogenous bacte-ria. In clean-contaminated,contaminated, and dirty-infected operations, thesource and the amount of bacteria are functions of the patientsdisease and the specific organs being operated on.

Operations classified as infected are those in which infected tis-sue and pus are removed or drained, providing a guaranteedinoculum to the surgical site.The inoculum may be as high as 1010bacteria/ml, some of which may already be producing an infec-tion. In addition, some bacteria could be in the growth phaserather than the dormant or the lag phase and thus could be morepathogenic.The heavily contaminated wound is best managed bydelayed primary closure. This type of management ensures thatthe wound is not closed over a bacterial inoculum that is almostcertain to cause a wound infection, with attendant early and lateconsequences.

Patients should not have elective surgery in the presence ofremote infection, which is associated with an increased incidenceof wound infection.5 In patients with urinary tract infections,wounds frequently become infected with the same organism.Remote infections should be treated appropriately, and the oper-ation should proceed only under the best conditions possible. Ifoperation cannot be appropriately delayed, the use of prophylac-tic and therapeutic antibiotics should be considered [see SidebarAntibiotic Prophylaxis of Infection and Tables 2 through 4].

Preoperative techniques of reducing patient flora, especiallyendogenous bacteria, are of great concern. Bowel preparation,antimicrobial showers or baths, and preoperative skin decontami-

Skin

SubcutaneousTissue

Deep Soft Tissue(Fascia and Muscle)

Organ/Space

Superficial Incisional

SSI

Deep IncisionalSSI

Organ/SpaceSSI

Table 1 National Research CouncilClassification of Operative Wounds5

NontraumaticNo inflammation encounteredNo break in techniqueRespiratory, alimentary, or genitourinary tract not

entered

Gastrointestinal or respiratory tract entered without significant spillage

AppendectomyOropharynx enteredVagina enteredGenitourinary tract entered in absence of infected urineBiliary tract entered in absence of infected bileMinor break in technique

Major break in techniqueGross spillage from gastrointestinal tractTraumatic wound, freshEntrance of genitourinary or biliary tracts in presence

of infected urine or bile

Acute bacterial inflammation encountered, without pusTransection of clean tissue for the purpose of surgical

access to a collection of pusTraumatic wound with retained devitalized tissue, for-

eign bodies, fecal contamination, or delayed treat-ment, or all of these; or from dirty source

Clean (class I)

Clean-contaminated(class II)

Contaminated(class III)

Dirty and infected(class IV)

Figure 2 Surgical site infections are classified into three cate-gories, depending on which anatomic areas are affected.3



nation have been proposed frequently.These techniques, particu-larly preoperative skin decontamination [see Sidebar PreoperativePreparation of the Operative Site], may have specific roles inselected patients during epidemics or in units with high infectionrates. As a routine for all patients, however, these techniques areunnecessary, time-consuming, and costly in institutions or unitswhere infection rates are low.

The preoperative shave is a technique in need of reassessment.It is now clear that shaving the evening before an operation is asso-ciated with an increased wound infection rate.This increase is sec-

ondary to the trauma of the shave and the inevitable small areas ofinflammation and infection. If hair removal is required,14,15 clip-ping is preferable and should be done in the OR or the prepara-tion room just before the operative procedure. Shaving, if ever per-formed, should not be done the night before operation.

In the past few years, the role of the classic bowel preparation [seeTable 5] has been questioned [see Discussion, Infection Preventionin Bowel Surgery, below].16-20 The suggestion has been made thatselective gut decontamination (SGD) may be useful in major elec-tive procedures involving the upper GI tract and perhaps in othersettings.At present, SGD for prevention of infection cannot be rec-ommended in either the preoperative or the postoperative period.

When infection develops after clean operations, particularlythose in which foreign bodies were implanted, endogenous infect-ing organisms are involved but the skin is the primary source of theinfecting bacteria. The air in the operating room and other ORsources occasionally become significant in clean cases; the degreeof endogenous contamination can be surpassed by that of exoge-nous contamination. Thus, both the operating teamsurgeon,assistants, nurses, and anesthetistsand OR air have been report-ed as significant sources of bacteria [see 1:8 Preparation of theOperating Room]. In fact, personnel are the most important sourceof exogenous bacteria.21-23 In the classic 1964 study by the NationalAcademy of SciencesNational Research Council, ultraviolet light(UVL) was efficacious only in the limited situations of clean andultraclean cases.5 There were minimal numbers of endogenousbacteria, and UVL controlled one of the exogenous sources.

Clean air systems have very strong advocates, but they also haveequally vociferous critics. It is possible to obtain excellent resultsin clean cases with implants without using these systems.However, clean air systems are here to stay. Nevertheless, the pres-ence of a clean air system does not mean that basic principles ofasepsis and antisepsis should be abandoned, because endogenousbacteria must still be controlled.

The use of impermeable drapes and gowns has received con-siderable attention. If bacteria can penetrate gown and drapes,they can gain access to the wound.The use of impermeable drapesmay therefore be of clinical importance.24,25 When wet, drapes of140-thread-count cotton are permeable to bacteria. It is clear thatsome operations are wetter than others, but generally, much canbe done to make drapes and gowns impermeable to bacteria. Forexample, drapes of 270-thread-count cotton that have been water-

0 1 2 3 4 5 6

50

40

30

20

10

0

Dry Wound; Cephaloridine > 10 g/ml

Dry Wound; Placebo

Wet Wound;Wound Fluid Hematocrit > 8%; Placebo

Clin

ical

Wou

nd In

fect

ion

Rat

e (%

)

Leg Wound Bacteria

Figure 3 The wound infection rate is shown here as a function ofbacterial inoculum in three different situations: a dry wound withan adequate concentration of antibiotic (cephaloridine > 10 g/ml),a dry wound with no antibiotic (placebo), and a wet wound with noantibiotic (placebo, wound fluid hematocrit > 8%).11

Table 2 Parenteral Antibiotics Recommended for Prophylaxis of Surgical Site Infection

For coverage against aerobic gram-positive and gram-negative organisms

If patient is allergic to cephalosporins or if methicillin-resistant organisms are present

Combination regimens for coverage against gram-negative aerobes and anaerobes

For single-agent coverage against gram-negative aerobes and anaerobes

Dose

1 g

1 g

600 mg

500 mg

1.5 mg/kg

12 g12 g

Route of Administration

I.V. or I.M. (I.V. preferred)

I.V.

I.V.

I.V.

I.V. or I.M. (I.V. preferred for first dose)

I.V.I.V.

Antibiotic

Cefazolin

Vancomycin

Clindamycinor

Metronidazoleplus

Tobramycin (or equivalentaminoglycoside)

CefoxitinCefotetan



proofed are impermeable, but they can be washed only 75 times.Economics plays a role in the choice of drape fabric becauseentirely disposable drapes are expensive. Local institutional factorsmay be significant in the role of a specific type of drape in the pre-vention of SSI.

PROBABILITY OF CONTAMINATION

The probability of contamination is largely defined by thenature of the operation [see Table 1]. However, other factors con-tribute to the probability of contamination; the most obvious is theexpected duration of the operative procedure, which, wheneverexamined, has been significantly correlated with the wound infec-tion rate.6,10,12 The longer the procedure lasts, the more bacteriaaccumulate in a wound; the sources of bacteria include thepatient, the operating team (gowns, gloves with holes, wet drapes),the OR, and the equipment. In addition, the patient undergoing alonger operation is likely to be older, to have other diseases, and tohave cancer ofor to be undergoing operation ona structure

with possible contamination. A longer duration, even of a cleanoperation, represents increased time at risk for contamination.These points, in addition to pharmacologic considerations, sug-gest that the surgeon should be alert to the need for a second doseof prophylactic antibiotics [see Sidebar Antibiotic Prophylaxis ofInfection].

Abdominal operation is another risk factor not found in theNNIS risk assessment.6,8 Significant disease and age are addition-al factors that play a role in outcome; however, because the majorconcentrations of endogenous bacteria are located in theabdomen, abdominal operations are more likely to involve bacter-ial contamination.

For some years, postoperative contamination of the wound hasbeen considered unlikely. However, one report of SSI in sternalincisions cleaned and redressed 4 hours postoperatively clearlyshows that wounds can be contaminated and become infected inthe postoperative period.26 Accordingly, use of a dry dressing for24 hours seems prudent.

SelectionSpectrum. The antibiotic chosen should be active against the most

likely pathogens. Single-agent therapy is almost always effective ex-cept in colorectal operations, small-bowel procedures with stasis,emergency abdominal operations in the presence of polymicrobial flo-ra, and penetrating trauma; in such cases, a combination of antibioticsis usually used because anaerobic coverage is required.

Pharmacokinetics. The half-life of the antibiotic selected must be longenough to maintain adequate tissue levels throughout the operation.

AdministrationDosage, route, and timing. A single preoperative dose that is of the

same strength as a full therapeutic dose is adequate in most instanc-es. The single dose should be given I.V. immediately before skin inci-sion. Administration by the anesthetist is most effective and efficient.

Duration. A second dose is warranted if the duration of the operationexceeds either 3 hours or twice the half-life of the antibiotic. No addi-tional benefit has been demonstrated in continuing prophylaxis beyondthe day of the operation, and mounting data suggest that the preopera-tive dose is sufficient. When massive hemorrhage has occurred (i.e.,blood loss equal to or greater than blood volume), a second dose iswarranted. Even in emergency or trauma cases, prolonged courses ofantibiotics are not justified unless they are therapeutic.77,108

IndicationsCLEAN CASES

Prophylactic antibiotics are not indicated in clean operations if thepatient has no host risk factors or if the operation does not involveplacement of prosthetic materials. Open heart operation and opera-tions involving the aorta of the vessels in the groin require prophylaxis.

Patients in whom host factors suggest the need for prophylaxis in-clude those who have more than three concomitant diagnoses, thosewhose operations are expected to last longer than 2 hours, and thosewhose operations are abdominal.6 A patient who meets any two ofthese criteria is highly likely to benefit from prophylaxis. When host fac-tors suggest that the probability of a surgical site infection is signifi-cant, administration of cefazolin at induction of anesthesia is appropri-ate prophylaxis. Vancomycin should be substituted in patients who areallergic to cephalosporins or who are susceptible to major immediatehypersensitivity reactions to penicillin.

When certain prostheses (e.g., heart valves, vascular grafts, andorthopedic hardware) are used, prophylaxis is justified when viewedin the light of the cost of a surgical site infection to the patients health.Prophylaxis with either cefazolin or vancomycin is appropriate for car-

diac, vascular, or orthopedic patients who receive prostheses.Catheters for dialysis or nutrition, pacemakers, and shunts of vari-

ous sorts are prone to infection mostly for technical reasons, and pro-phylaxis is not usually required. Meta-analysis indicates, however, thatantimicrobial prophylaxis reduces the infection rate in CSF shunts by50%.109 Beneficial results may also be achievable for other perma-nently implanted shunts (e.g., peritoneovenous) and devices (e.g.,long-term venous access catheters and pacemakers); however, thestudies needed to confirm this possibility will never be done, becausethe infection rates are low and the sample sizes would have to be pro-hibitively large. The placement of such foreign bodies is a clean oper-ation, and the use of antibiotics should be based on local experience.

CLEAN-CONTAMINATED CASES

Abdominal procedures. In biliary tract procedures (open or laparo-scopic), prophylaxis is required only for patients at high risk: thosewhose common bile duct is likely to be explored (because of jaundice,bile duct obstruction, stones in the common bile duct, or a reoperativebiliary procedure); those with acute cholecystitis; and those older than70 years. A single dose of cefazolin is adequate. In hepatobiliary andpancreatic procedures, antibiotic prophylaxis is always warranted be-cause these operations are clean-contaminated, because they are long,because they are abdominal, or for all of these reasons. Prophylaxis isalso warranted for therapeutic endoscopic retrograde cholangiopancre-atography. In gastroduodenal procedures, patients whose gastric acidi-ty is normal or high and in whom bleeding, cancer, gastric ulcer, and ob-struction are absent are at low risk for infection and require noprophylaxis; all other patients are at high risk and require prophylaxis.Patients undergoing operation for morbid obesity should receive doublethe usual prophylactic dose110; cefazolin is an effective agent.

Operations on the head and neck (including the esophagus). Pa-tients whose operation is of significance (i.e., involve entry into the oralcavity, the pharynx, or the esophagus) require prophylaxis.

Gynecologic procedures. Patients whose operation is either high-risk cesarean section, abortion, or vaginal or abdominal hysterectomywill benefit from cefazolin. Aqueous penicillin G or doxycycline may bepreferable for first-trimester abortions in patients with a history of pelvicinflammatory disease. In patients with cephalosporin allergy, doxycy-cline is effective for those having hysterectomies and metronidazole forthose having cesarean sections. Women delivering by cesarean sec-tion should be given the antibiotic immediately after cord clamping.

Urologic procedures. In principle, antibiotics are not required in pa-tients with sterile urine. Patients with positive cultures should be treat-ed. If an operative procedure is performed, a single dose of the appro-priate antibiotic will suffice.

Antibiotic Prophylaxis of Infection

(continued )



BACTERIAL PROPERTIES

Not only is the size of thebacterial inoculum impor-tant; the bacterial proper-ties of virulence and patho-genicity are also significant.The most obvious patho-genic bacteria in surgical patients are gram-positive cocci (e.g.,Staphylococcus aureus and streptococci). With modern hygienicpractice, it would be expected that S. aureus would be foundmostly in clean cases, with a wound infection incidence of 1% to2%; however, it is in fact an increasingly common pathogen inSSIs. Surveillance can be very useful in identifying either wardsor surgeons with increased rates. Operative procedures in infect-ed areas have an increased infection rate because of the highinoculum with actively pathogenic bacteria.

The preoperative hospital stay has frequently been found tomake an important contribution to wound infection rates.12 Theusual explanation is that during this stay, either more endogenousbacteria are present or commensal flora is replaced by hospitalflora. More likely, the patients clinical picture is a complex one,often entailing exhaustive workup of more than one organ system,

various complications, and a degree of illness that radicallychanges the hosts ability to deal with an inoculum, however small.Therefore, multiple factors combine to transform the hospitalizedpreoperative patient into a susceptible host. Same-day admissionshould eliminate any bacterial impact associated with the preop-erative hospital stay.

Bacteria with multiple antibiotic resistance (e.g., methi-cillin-resistant S. aureus [MRSA], S. epidermidis, and van-comycin-resistant enterococci [VRE]) can be associated withsignificant SSI problems. In particular, staphylococci, withtheir natural virulence, present an important hazard if inap-propriate prophylaxis is used.

Many surgeons consider it inappropriate or unnecessary toobtain good culture and sensitivity data on SSIs; instead of con-ducting sensitivity testing, they simply drain infected wounds,believing that the wounds will heal. However, there have been anumber of reports of SSIs caused by unusual organisms23,26,27;these findings underscore the usefulness of culturing pus orfluid when an infection is being drained. SSIs caused by antibi-otic-resistant organisms or unusual pathogens call for specificprophylaxis, perhaps other infection control efforts, and, if theproblem persists, a search for a possible carrier or a commonsource.21-23,26,27

CONTAMINATED CASES

Abdominal procedures. In colorectal procedures, antibiotics activeagainst both aerobes and anaerobes are recommended. In appen-dectomy, SSI prophylaxis requires an agent or combination of agentsactive against both aerobes and anaerobes; a single dose of cefoxitin,2 g I.V., or, in patients who are allergic to -lactam antibiotics, metroni-dazole, 500 mg I.V., is effective. A combination of an aminoglycosideand clindamycin is effective if the appendix is perforated; a therapeu-tic course of 3 to 5 days is appropriate but does not seem warrantedunless the patient is particularly ill. A laparotomy without a precise di-agnosis is usually an emergency procedure and demands preopera-tive prophylaxis. If the preoperative diagnosis is a ruptured viscus(e.g., the colon or the small bowel), both an agent active against aer-obes and an agent active against anaerobes are required. Dependingon operative findings, prophylaxis may be sufficient or may have to besupplemented with postoperative antibiotic therapy.

Trauma. The proper duration of antibiotic prophylaxis for trauma pa-tients is a confusing issue24 hours or less of prophylaxis is probablyadequate, and more than 48 hours is certainly unwarranted. When la-parotomy is performed for nonpenetrating injuries, prophylaxis shouldbe administered. Coverage of both aerobes and anaerobes is manda-tory. The duration of prophylaxis should be less than 24 hours. In cas-es of penetrating abdominal injury, prophylaxis with either cefoxitin ora combination of agents active against anaerobic and aerobic organ-isms is required. The duration of prophylaxis should be less than 24hours, and in many cases, perioperative doses will be adequate. Foropen fractures, management should proceed as if a therapeuticcourse were required. For grade I or II injuries, a first-generationcephalosporin will suffice, whereas for grade III injuries, combinationtherapy is warranted; duration may vary. For operative repair of frac-tures, a single dose of cefazolin may be given preoperatively, with asecond dose added if the procedure is long. Patients with major softtissue injury with a danger of spreading infection will benefit from cefa-zolin, 1 g I.V. every 8 hours for 1 to 3 days.

DIRTY OR INFECTED CASES

Infected cases require therapeutic courses of antibiotics; prophylax-is is not appropriate in this context. In dirty cases, particularly those re-

sulting from trauma, contamination and tissue destruction are usuallyso extensive that the wounds must be left open for delayed primary orsecondary closure. Appropriate timing of wound closure is judged atthe time of debridement. Antibiotics should be administered as part ofresuscitation. Administration of antibiotics for 24 hours is probably ad-equate if infection is absent at the outset. However, a therapeuticcourse of antibiotics is warranted if infection is present from the outsetor if more than 6 hours elapsed before treatment of the wounds wasinitiated.

Prophylaxis of Endocarditis

Studies of the incidence of endocarditis associated with dentalprocedures, endoscopy, or operations that may result in transientbacteremia are lacking. Nevertheless, the consensus is that patientswith specific cardiac and vascular conditions are at risk for endo-carditis or vascular prosthetic infection when undergoing certain pro-cedures; these patients should receive prophylactic antibiotics.111-113A variety of organisms are dangerous, but viridans streptococci aremost common after dental or oral procedures, and enterococci aremost common if the portal of entry is the GU or GI tract. Oral amoxi-cillin now replaces penicillin V or ampicillin because of superior ab-sorption and better serum levels. In penicillin-allergic patients, clin-damycin is recommended; alternatives include cephalexin, cef-adroxil, azithromycin, and clarithromycin. When there is a risk of ex-posure to bowel flora or enterococci, oral amoxicillin may be given. Ifan I.V. regimen is indicated, ampicillin may be given, with gentamicinadded if the patient is at high risk for endocarditis. In patients allergicto penicillin, vancomycin is appropriate, with gentamicin added inhigh-risk patients. These parenteral regimens should be reserved forhigh-risk patients undergoing procedures with a significant probabili-ty of bacteremia.

In patients receiving penicillin-based prophylaxis because of ahistory of rheumatic fever, erythromycin rather than amoxicillinshould be used to protect against endocarditis.111 There is consen-sus concerning prophylaxis for orthopedic prostheses and acquiredinfection after transient bacteremia. In major procedures, where therisk of bacteremia is significant, the above recommendations arepertinent.

Antibiotic Prophylaxis of Infection (continued )

SURGEONS AND BACTERIA

The surgeons periopera-tive rituals are designed toreduce or eliminate bacteriafrom the operative field.Many old habits are obso-lete [see 1:8 Preparation ofthe Operating Room andDiscussion, Hand Washing, below]. Nonetheless, it is clear that sur-geons can influence SSI rates.13 The refusal to use delayed prima-ry closure or secondary closure is an example. Careful attention tothe concepts of asepsis and antisepsis in the preparation and con-duct of the operation is important. Although no single step in theritual of preparing a patient for the operative procedure is indis-pensable, it is likely that certain critical standards of behavior mustbe maintained to achieve good results.

The measurement and publication of data about individuals orhospitals with high SSI rates have been associated with a diminu-tion of those rates [see Table 6].12,13,28 It is uncertain by whatprocess the diffusion of these data relates to the observed improve-ments. Although surveillance has unpleasant connotations, it pro-vides objective data that individual surgeons are often too busy toacquire but that can contribute to improved patient care. For

example, such data can be useful in identifying problems (e.g., thepresence of MRSA, a high SSI incidence, or clusters), maintain-ing quality assurance, and allowing comparison with acceptedstandards.

Environment: LocalFactors

Local factors influenceSSI development becausethey affect the size of thebacterial inoculum that isrequired to produce aninfection: in a susceptiblewound, a smaller inoculum produces infection [see Figure 2].

THE SURGEONS INFLUENCE

Most of the local factors that make a surgical site favorable tobacteria are under the control of the surgeon. Although Halstedusually receives, deservedly so, the credit for having established theimportance of technical excellence in the OR in preventing infec-tion, individual surgeons in the distant past achieved remarkableresults by careful attention to cleanliness and technique.29 TheHalstedian principles dealt with hemostasis, sharp dissection, finesutures, anatomic dissection, and the gentle handling of tissues.Mass ligatures, large or braided nonabsorbable sutures, necrotictissue, and the creation of hematomas or seromas must be avoid-ed, and foreign materials must be judiciously used because thesetechniques and materials change the size of the inoculum requiredto initiate an infectious process. Logarithmically fewer bacteria arerequired to produce infection in the presence of a foreign body(e.g., suture, graft, metal, or pacemaker) or necrotic tissue (e.g.,that caused by gross hemostasis or injudicious use of electro-cautery devices).

The differences in inoculum required to produce wound infec-tions can be seen in a model in which the two variables are thewound hematocrit and the presence of antibiotic [see Figure 3]. Inthe absence of an antibiotic and in the presence of wound fluidwith a hematocrit of more than 8%, 10 bacteria yield a woundinfection rate of 20%. In a technically good wound with no antibi-otic, however, 1,000 bacteria produce a wound infection rate of20%.11 In the presence of an antibiotic, 105 to 106 bacteria arerequired.

Drains

The use of drains varies widely and is very subjective. All sur-geons are certain that they understand when to use a drain.However, certain points are worth noting. It is now recognizedthat a simple Penrose drain may function as a drainage route butis also an access route by which pathogens can reach the patient.30It is important that the operative site not be drained through thewound.The use of a closed suction drain reduces the potential forcontamination and infection.

Many operations on the GI tract can be performed safely with-out employing prophylactic drainage.31 A review and meta-analy-sis from 2004 concluded that (1) after hepatic, colonic, or rectalresection with primary anastomosis and after appendectomy forany stage of appendicitis, drains should be omitted (recommenda-tion grade A), and (2) after esophageal resection and total gas-trectomy, drains should be used (recommendation grade D).Additional randomized, controlled trials will be required to deter-mine the value of prophylactic drainage for other GI procedures,especially those involving the upper GI tract.



Table 3 Conditions and ProceduresThat Require Antibiotic Prophylaxis

against Endocarditis111,112

CONDITIONSCardiac

Prosthetic cardiac valves (including biosynthetic valves)Most congenital cardiac malformationsSurgically constructed systemic-pulmonary shuntsRheumatic and other acquired valvular dysfunctionIdiopathic hypertrophic subaortic stenosisHistory of bacterial endocarditisMitral valve prolapse causing mitral insufficiencySurgically repaired intracardiac lesions with residual hemodynamic

abnormality or < 6 mo after operation

VascularSynthetic vascular grafts

PROCEDURESDental or oropharyngeal

Procedures that may induce bleedingProcedures that involve incision of the mucosa

RespiratoryRigid bronchoscopy

Incision and drainage or debridement of sites of infectionUrologic

Cystoscopy with urethral dilatationUrinary tract proceduresCatheterization in the presence of infected urine

GynecologicVaginal hysterectomyVaginal delivery in the presence of infection

GastrointestinalProcedures that involve incision or resection of mucosaEndoscopy that involves manipulation (e.g., biopsy, dilatation,

or sclerotherapy) or ERCP



Duration of Operation

In most studies,6,10,12 contamination certainly increases withtime (see above).Wound edges can dry out, become macerated, orin other ways be made more susceptible to infection (i.e., requir-ing fewer bacteria for development of infection). Speed and poortechnique are not suitable approaches; expeditious operation isappropriate.

Electrocautery

The use of electrocautery devices has been clearly associatedwith an increase in the incidence of superficial SSIs. However,when such devices are properly used to provide pinpoint coagu-lation (for which the bleeding vessels are best held by fine for-ceps) or to divide tissues under tension, there is minimal tissuedestruction, no charring, and no change in the wound infectionrate.30

PATIENT FACTORS

Local Blood Flow

Local perfusion cangreatly influence the devel-opment of infection, as isseen most easily in the ten-dency of the patient withperipheral vascular disease to acquire infection of an extremity. Asa local problem, inadequate perfusion reduces the number of bac-teria required for infection, in part because inadequate perfusionleads to decreased tissue levels of oxygen. Shock, by reducing localperfusion, also greatly enhances susceptibility to infection. Fewerorganisms are required to produce infection during or immediate-ly after shock [see Figure 4].

To counter these effects, the arterial oxygen tension (PaO2) mustbe translated into an adequate subcutaneous oxygen level (deter-mined by measuring transcutaneous oxygen tension)32; this,together with adequate perfusion, will provide local protection byincreasing the number of bacteria required to produce infection.Provision of supplemental oxygen in the perioperative period may

lead to a reduced SSI rate, probably as a consequence of increasedtissue oxygen tension,33 though the value of this practice has beenquestioned.34 If the patient is not intubated, a mask, not nasalprongs, is required.35

Barrier Function

Inadequate perfusion may also affect the function of otherorgans, and the resulting dysfunction will, in turn, influence thepatients susceptibility to infection. For example, ischemia-reper-fusion injury to the intestinal tract is a frequent consequence ofhypovolemic shock and bloodstream infection. Inadequate perfu-sion of the GI tract may also occur during states of fluid and elec-trolyte imbalance or when cardiac output is marginal. In experi-mental studies, altered blood flow has been found to be associat-ed with the breakdown of bowel barrier functionthat is, theinability of the intestinal tract to prevent bacteria, their toxins, orboth from moving from the gut lumen into tissue at a rate too fast to permit clearance by the usual protective mechanisms. Avariety of experimental approaches aimed at enhancing bowelbarrier function have been studied; at present, however, the mostclinically applicable method of bowel protection is initiation ofenteral feeding (even if the quantity of nutrients provided doesnot satisfy all the nutrient requirements) and administration ofthe amino acid glutamine [see 8:22 Nutritional Support].Glutamine is a specific fuel for enterocytes and colonocytes andhas been found to aid recovery of damaged intestinal mucosa andenhance barrier function when administered either enterally orparenterally.

Advanced Age

Aging is associated with structural and functional changes thatrender the skin and subcutaneous tissues more susceptible toinfection. These changes are immutable; however, they must beevaluated in advance and addressed by excellent surgical tech-nique and, on occasion, prophylactic antibiotics [see SidebarAntibiotic Prophylaxis of Infection]. SSI rates increase with aginguntil the age of 65 years, after which point the incidence appearsto decline.36

Table 4 Antibiotics for Prevention of Endocarditis55,111

Prophylactic Regimen*Manipulative Procedure

Dental procedures likely to causegingival bleeding; operations or instrumentation of the upperrespiratory tract

Gastrointestinal or genitourinaryoperation; abscess drainage

Usual

OralAmoxicillin, 2.0 g 1 hr before procedure

ParenteralAmpicillin, 2.0 g I.M. or I.V. 30 min before procedure

OralAmoxicillin, 2.0 g 1 hr before procedure

ParenteralAmpicillin, 2.0 g I.M. or I.V. within 30 min before proce-

dure; if risk of endocarditis is considered high, addgentamicin, 1.5 mg/kg (to maximum of 120 mg) I.M. or I.V. 30 min before procedure

In Patients with Penicillin Allergy

OralClindamycin, 600 mg 1 hr before procedure

orCephalexin or cefadroxil, 2.0 g 1 hr before procedure

orAzithromycin or clarithromycin, 500 mg 1 hr before procedure

ParenteralClindamycin, 600 mg I.V. within 30 min before procedure

orCefazolin, 1.0 g I.M. or I.V. within 30 min before procedure

Vancomycin, 1.0 g I.V. infused slowly over 1 hr, beginning 1 hrbefore procedure; if risk of endocarditis is considered high,add gentamicin, 1.5 mg/kg (to maximum of 120 mg) I.M. orI.V. 30 min before procedure

*Pediatric dosages are as follows: oral amoxicillin, 50 mg/kg; oral or parenteral clindamycin, 20 mg/kg; oral cephalexin or cefadroxil, 50 mg/kg; oral azithromycin or clarithromycin, 15 mg/kg;parenteral ampicillin, 50 mg/kg; parenteral cefazolin, 25 mg/kg; parenteral gentamicin, 2 mg/kg; parenteral vancomycin, 20 mg/kg. Total pediatric dose should not exceed total adult dose.Patients with a history of immediate-type sensitivity to penicillin should not receive these agents.High-risk patients should also receive ampicillin, 1.0 g I.M. or I.V., or amoxicillin, 1.0 g p.o., 6 hr after procedure.



Host DefenseMechanisms

The systemic response isdesigned to control anderadicate infection. Manyfactors can inhibit systemichost defense mechanisms;some are related to the sur-gical disease, others to the patients underlying disease or diseasesand the events surrounding the operation.

SURGEON-RELATED FACTORS

There are a limited number of ways in which the surgeon canimprove a patients systemic responses to surgery. Nevertheless,

when appropriate, attempts should be made to modify the host.The surgeon and the operation are both capable of reducingimmunologic efficacy; hence, the operative procedure should becarried out in as judicious a manner as possible. Minimal bloodloss, avoidance of shock, and maintenance of blood volume, tissueperfusion, and tissue oxygenation all will minimize trauma and willreduce the secondary, unintended immunologic effects of majorprocedures.

Diabetes has long been recognized as a risk factor for infectionand for SSI in particular. Three studies from the past decadedemonstrated the importance of glucose control for reducing SSIrates in both diabetic and nondiabetic patients who underwentoperation,37,38 as well as in critically ill ICU patients.39 Glucosecontrol is required throughout the entire perioperative period.Thebeneficial effect appears to lie in the enhancement of host defens-es. The surgical team must also ensure maintenance of adequatetissue oxygen tension32,33 and maintenance of normothermia.40

When abnormalities in host defenses are secondary to surgicaldisease, the timing of the operation is crucial to outcome. Withacute and subacute inflammatory processes, early operation helpsrestore normal immune function. Deferral of definitive therapyfrequently compounds problems.

PATIENT FACTORS

Surgeons have alwaysknown that the patient is asignificant variable in theoutcome of operation.Various clinical states areassociated with alteredresistance to infection. In allpatients, but particularly those at high risk, SSI creates not onlywound complications but also significant morbidity (e.g., reoper-ation, incisional hernia, secondary infection, impaired mobility,increased hospitalization, delayed rehabilitation, or permanentdisability) and occasional mortality.22 SENIC has proposed thatthe risk of wound infection be assessed not only in terms of prob-

The sole reason for preparing the patient's skin before an opera-tion is to reduce the risk of wound infection. A preoperative anti-septic bath is not necessary for most surgical patients, but theirpersonal hygiene must be assessed and preoperative cleanlinessestablished. Multiple preoperative baths may prevent postopera-tive infection in selected patient groups, such as those who carryStaphylococcus aureus on their skin or who have infectious le-sions. Chlorhexidine gluconate is the recommended agent forsuch baths.114

Hair should not be removed from the operative site unless itphysically interferes with accurate anatomic approximation of thewound edges.115 If hair must be removed, it should be clipped inthe OR.14 Shaving hair from the operative site, particularly on theevening before operation or immediately before wound incision inthe OR, increases the risk of wound infection. Depilatories are notrecommended, because they cause serious irritation and rashes ina significant number of patients, especially when used near theeyes and the genitalia.116

In emergency procedures, obvious dirt, grime, and dried bloodshould be mechanically cleansed from the operative site by usingsufficient friction. In one study, cleansing of contaminated woundsby means of ultrasound debridement was compared with high-pressure irrigation and soaking. The experimental wounds werecontaminated with a colloidal clay that potentiates infection 1,000-fold. The investigators irrigated wounds at pressures of 8 to 10 psi,a level obtained by using a 30 ml syringe with a 1.5 in. long 19-gauge needle and 300 ml of 0.85% sterile saline solution. High-pressure irrigation removed slightly more particulate matter (59%)than ultrasound debridement (48%), and both of these methodsremoved more matter than soaking (26%).117 Both ultrasound de-bridement and high-pressure irrigation were also effective in re-ducing the wound infection rate in experimental wounds contami-nated with a subinfective dose of S. aureus.

For nonemergency procedures, the necessary reduction in mi-croorganisms can be achieved by using povidone-iodine (10%available povidone-iodine and 1% available iodine) or chlorhexi-dine gluconate both for mechanical cleansing of the intertriginousfolds and the umbilicus and for painting the operative site. Whichskin antiseptic is optimal is unclear. The best option appears to bechlorhexidine gluconate or an iodophor.118 The patient should beassessed for evidence of sensitivity to the antiseptic (particularly ifthe agent contains iodine) to minimize the risk of an allergic reac-tion. What some patients report as iodine allergies are actually io-dine burns. Iodine in alcohol or in water is associated with an in-creased risk of skin irritation,90 particularly at the edges of theoperative field, where the iodine concentrates as the alcohol evap-orates. Iodine should therefore be removed after sufficient contacttime with the skin, especially at the edges. Iodophors do not irritatethe skin and thus need not be removed.

Preoperative Preparation of the Operative Site

Table 5 Parenteral Antibiotics CommonlyUsed for Broad-Spectrum Coverage of

Colonic MicrofloraCOMBINATION THERAPY OR PROPHYLAXIS

Aerobic Coverage(to be combined with a drug having anaerobic activity)

Amikacin CiprofloxacinAztreonam GentamicinCeftriaxone Tobramycin

Anaerobic Coverage(to be combined with a drug having aerobic activity)

Chloramphenicol MetronidazoleClindamycin

SINGLE-DRUG THERAPY OR PROPHYLAXISAerobic-Anaerobic Coverage

Ampicillin-sulbactam Imipenem-cilastatin*Cefotetan Piperacillin-tazobactamCefoxitin Ticarcillin-clavulanateCeftizoxime

*This agent should be used only for therapeutic purposes; it should not be usedfor prophylaxis.

ability of contamination but also in relation to host factors.6,7,9According to this study, patients most clearly at risk for woundinfection are those with three or more concomitant diagnoses;other patients who are clearly at risk are those undergoing a clean-contaminated or contaminated abdominal procedure and thoseundergoing any procedure expected to last longer than 2 hours.These last two risk groups are affected by a bacterial component,but all those patients who are undergoing major abdominal pro-cedures or lengthy operations generally have a significant prima-ry pathologic condition and are usually older, with an increasedfrequency of concomitant conditions. The NNIS system usesmost of the same concepts but expresses them differently. In theNNIS study, host factors in the large study are evaluated in termsof the ASA score. Duration of operation is measured differentlyas well, with a lengthy operation being defined by the NNIS asone that is at or above the 75th percentile for operating time.Bacterial contamination remains a risk factor, but operative site iseliminated.8

Shock has an influence on the incidence of wound infection [seeFigure 4]. This influence is most obvious in cases of trauma, butthere are significant implications for all patients in regard to main-tenance of blood volume, hemostasis, and oxygen-carrying capac-ity. The effect of shock on the risk of infection appears to be notonly immediate (i.e., its effect on local perfusion) but also latebecause systemic responses are blunted as local factors return tonormal.

Advanced age, transfusion, and the use of steroids and otherimmunosuppressive drugs, including chemotherapeutic agents,are associated with an increased risk of SSI.41,42 Often, these fac-tors cannot be altered; however, the proper choice of operation,the appropriate use of prophylaxis, and meticulous surgical tech-nique can reduce the risk of such infection by maintaining patienthomeostasis, reducing the size of any infecting microbial inocu-lum, and creating a wound that is likely to heal primarily.

Smoking is associated with a striking increase in SSI incidence.As little as 1 week of abstinence from smoking will make a posi-tive difference.43

Pharmacologic therapy can affect host response as well.Nonsteroidal anti-inflammatory drugs that attenuate the pro-duction of certain eicosanoids can greatly alter the adverseeffects of infection by modifying fever and cardiovascular effects.Operative procedures involving inhalational anesthetics result inan immediate rise in plasma cortisol concentrations.The steroidresponse and the associated immunomodulation can be modi-fied by using high epidural anesthesia as the method of choice;pituitary adrenal activation will be greatly attenuated. Somedrugs that inhibit steroid elaboration (e.g., etomidate) have alsobeen shown to be capable of modifying perioperative immuneresponses.



Table 6 Effect of Surveillance and Feedbackon Wound Infection Rates in Two Hospitals28

Period 2*

1,4473.7%

1,9393.7%

Hospital A

Hospital B

Period 1

1,5008.4%

1,7465.7%

Number of woundsWound infection rate

Number of woundsWound infection rate

*Periods 1 and 2 were separated by an interval during which feedback on wound infectionrates was analyzed.

Control 1 Hr Day 1 3 5 Control 1 Hr Day 1 3 5

Wou

nd In

fect

ion

Rat

e (%

)

100

80

60

40

20

0

No Antibiotic Antibiotic

Time of Inoculation

108 Bacteria/ml 107 Bacteria/ml 106 Bacteria/ml

Figure 4 Animals exposed to hemorrhagic shock followed by resuscitation show an earlydecreased resistance to wound infection. There is also a persistent influence of shock on thedevelopment of wound infection at different times of inoculation after shock. The impor-tance of inoculum size (106/ml to 108/ml) and the effect of antibiotic on infection rates areevident at all times of inoculation.103

ANESTHESIOLOGIST-

RELATED FACTORS

A 2000 commentary inThe Lancet by Donal Buggyconsidered the question ofwhether anesthetic manage-ment could influence surgi-cal wound healing.44 Inaddition to the surgeon- and patient-related factors already dis-cussed (see above), Buggy cogently identified a number of anes-thesiologist-related factors that could contribute to better woundhealing and reduced wound infection. Some of these factors (e.g.,pain control, epidural anesthesia, and autologous transfusion) areunproven but nonetheless make sense and should certainly be test-ed. Others (e.g., tissue perfusion, intravascular volume, andsig-nificantlymaintenance of normal perioperative body tempera-ture) have undergone formal evaluation. Very good studies haveshown that dramatic reductions in SSI rates can be achievedthrough careful avoidance of hypothermia.40,45 Patient-controlledanalgesia pumps are known to be associated with increased SSIrates, through a mechanism that is currently unknown.46 Infectioncontrol practices are required of all practitioners; contamination ofanesthetic drugs by bacteria has resulted in numerous small out-breaks of SSI.47,48

As modern surgical practice has evolved and the variable of bac-

terial contamination has come to be generally well managed, theimportance of all members of the surgical team in the preventionof SSI has become increasingly apparent. The crux of Buggyscommentary may be expressed as follows: details make a differ-ence, and all of the participants in a patients surgical journey cancontribute to a continuing decrease in SSI. It is a systems issue.

INTEGRATION OF DETERMINANTS

As operative infection rates slowly fall, despite the performanceof increasingly complex operations in patients at greater risk, sur-geons are approaching the control of infection with a broader viewthan simply that of asepsis and antisepsis. This new, broader viewmust take into account many variables, of which some have no re-lation to bacteria but all play a role in SSI [see Table 7 and Figure 1].

To estimate risk, one must integrate the various determinants ofinfection in such a way that they can be applied to patient care.Much of this exercise is vague. In reality, the day-to-day practice ofsurgery includes a risk assessment that is essentially a form of logis-tic regression, though not recognized as such. Each surgeonsassessment of the probability of whether an SSI will occur takesinto account the determining variables:

Probability of SSI =x + a (bacteria) + b (environment: local factors)+ c (host defense mechanisms: systemic factors)



Antibiotic Prophylaxis of Surgical Site Infection

It is difficult to understand why antibiotics have not always pre-vented SSI successfully. Certainly, surgeons were quick to appreci-ate the possibilities of antibiotics; nevertheless, the efficacy ofantibiotic prophylaxis was not proved until the late 1960s.11Studies before then had major design flawsprincipally, theadministration of the antibiotic some time after the start of theoperation, often in the recovery room. The failure of studies todemonstrate efficacy and the occasional finding that prophylacticantibiotics worsened rather than improved outcome led in the late

1950s to profound skepticism about prophylactic antibiotic use inany operation.

The principal reason for the apparent inefficacy was inadequateunderstanding of the biology of SSIs. Fruitful study of antibioticsand how they should be used began after physiologic ground-work established the importance of local blood flow, maintenanceof local immune defenses, adjuvants, and local and systemic perfusion.49

The key antibiotic study, which was conducted in guinea pigs,unequivocally proved the following about antibiotics:

Table 7 Determinants of Infection and Factors That Influence Wound Infection Rates

WoundEnvironment

(Local Factors)

BBB

B

BBB

Variable

Bacterial numbers in wound10

Potential contamination6,10,12

Preoperative shave12

Presence of 3 or more diagnoses6

Age10,12

Duration of operation6,10,12

Abdominal operation6

ASA class III, IV, or V8

O2 tension32

Glucose control37,38

Normothermia40

Shock103

Smoking43

Bacteria

AAA

AA

Host DefenseMechanisms

(Systemic Factors)

CCCCC

CCCC

Determinant of Infection

Discussion

1. They are most effective when given before inoculation of bacte-ria.

2. They are ineffective if given 3 hours after inoculation.3. They are of intermediate effectiveness when given in between

these times [see Figure 5].50

Although efficacy with a complicated regimen was demonstrat-ed in 1964,51 the correct approach was not defined until 1969.11Established by these studies are the philosophical and practicalbases of the principles of antibiotic prophylaxis of SSI in all surgi-cal arenas11,50: that prophylactic antibiotics must be given preoper-atively within 2 hours of the incision, in full dosage, paren-terally, and for a very limited period. These principles remainessentially unchanged despite minor modifications from innumer-able subsequent studies.52-56 Prophylaxis for colorectal operationsis discussed elsewhere [see Infection Prevention in Bowel Surgery,below].

PRINCIPLES OF PATIENT SELECTION

Patients must be selected for prophylaxis on the basis of eithertheir risk for SSI or the cost to their health if an SSI develops (e.g.,after implantation of a cardiac valve or another prosthesis). Themost important criterion is the degree of bacterial contaminationexpected to occur during the operation.The traditional classifica-tion of such contamination was defined in 1964 by the historicNational Academy of SciencesNational Research Council study.5The important features of the classification are its simplicity, easeof understanding, ease of coding, and reliability. Classification isdependent on only one variablethe bacterial inoculumand theeffects of this variable are now controllable by antimicrobial pro-phylaxis. Advances in operative technique, general care, antibiotic

use, anesthesia, and surveillance have reduced SSI rates in all cat-egories that were established by this classification [see Table8].6,12,13,51

In 1960, after years of negative studies, it was said, Nearly allsurgeons now agree that the routine use of prophylaxis in cleanoperations is unnecessary and undesirable.57 Since then, muchhas changed: there are now many clean operations for which nocompetent surgeon would omit the use of prophylactic antibiotics,particularly as procedures become increasingly complex and pros-thetic materials are used in patients who are older, sicker, orimmunocompromised.

A separate risk assessment that integrates host and bacterialvariables (i.e., whether the operation is dirty or contaminated, islonger than 2 hours, or is an abdominal procedure and whether thepatient has three or more concomitant diagnoses) segregates moreeffectively those patients who are prone to an increased incidenceof SSI [see Integration of Determinants of Infection, below]. Thisapproach enables the surgeon to identify those patients who arelikely to require preventive measures, particularly in clean cases, inwhich antibiotics would normally not be used.6

The prototypical clean operation is an inguinal hernia repair.Technical approaches have changed dramatically over the past 10years, and most primary and recurrent hernias are now treatedwith a tension-free mesh-based repair. The use of antibiotics hasbecome controversial. In the era of repairs under tension, there wassome evidence to suggest that a perioperative antibiotic (in a sin-gle preoperative dose) was beneficial.58 Current studies, however,do not support antibiotic use in tension-free mesh-based inguinalhernia repairs.59,60 On the other hand, if surveillance indicates thatthere is a local or regional problem61 with SSI after hernia surgery,antibiotic prophylaxis (again in the form of single preoperativedose) is appropriate. Without significantly more supportive data,prophylaxis for clean cases cannot be recommended unless specif-ic risk factors are present.

Data suggest that prophylactic use of antibiotics may contributeto secondary Clostridium difficile disease; accordingly, cautionshould be exercised when widening the indications for prophylax-is is under consideration.62 If local results are poor, surgical prac-tice should be reassessed before antibiotics are prescribed.

ANTIBIOTIC SELECTION AND ADMINISTRATION

When antibiotics are given more than 2 hours before operation,the risk of infection is increased.52,54 I.V. administration in the ORor the preanesthetic room guarantees appropriate levels at the timeof incision.The organisms likely to be present dictate the choice ofantibiotic for prophylaxis.The cephalosporins are ideally suited toprophylaxis: their features include a broad spectrum of activity, anexcellent ratio of therapeutic to toxic dosages, a low rate of allergicresponses, ease of administration, and attractive cost advantages.Mild allergic reactions to penicillin are not contraindications forthe use of a cephalosporin.

Physicians like new drugs and often tend to prescribe newer,more expensive antibiotics for simple tasks. First-generationcephalosporins (e.g., cefazolin) are ideal agents for prophylaxis.Third-generation cephalosporins are not: they cost more, are notmore effective, and promote emergence of resistant strains.63,64

The most important first-generation cephalosporin for surgicalpatients continues to be cefazolin. Administered I.V. in the OR atthe time of skin incision, it provides adequate tissue levels through-out most of the operation. A second dose administered in the ORafter 3 hours will be beneficial if the procedure lasts longer thanthat. Data on all operative site infections are imprecise, but SSIs



5

Mea

n 24

-Hou

r Les

ion

Dia

met

er (m

m)

Lesion Age at Time of Penicillin Injection (hr)

1 0 1 2 3 4 5 6

10

Staphylococcal Lesions

Staphylococcal Lesions + Antibiotic

Killed Staphylococcal Lesions

Figure 5 In a pioneer study of antibiotic prophylaxis,50 the diam-eter of lesions induced by staphylococcal inoculation 24 hours ear-lier was observed to be critically affected by the timing of peni-cillin administration with respect to bacterial inoculation.

can clearly be reduced by this regimen. No data suggest that fur-ther doses are required for prophylaxis.

Fortunately, cefazolin is effective against both gram-positiveand gram-negative bacteria of importance, unless significantanaerobic organisms are encountered.The significance of anaero-bic flora has been disputed, but for elective colorectal surgery,65abdominal trauma,66,67 appendicitis,68 or other circumstances inwhich penicillin-resistant anaerobic bacteria are likely to beencountered, coverage against both aerobic and anaerobic gram-negative organisms is strongly recommended and supported bythe data.

Despite several decades of studies, prophylaxis is not alwaysproperly implemented.52,54,68,69 Unfortunately, didactic educationis not always the best way to change behavior. Preprinted orderforms70 and a reminder sticker from the pharmacy71 have provedto be effective methods of ensuring correct utilization.

The commonly heard decision This case was tough, lets givean antibiotic for 3 to 5 days has no data to support it and shouldbe abandoned. Differentiation between prophylaxis and therapeu-sis is important. A therapeutic course for perforated diverticulitisor other types of peritoneal infection is appropriate. Data on casu-al contamination associated with trauma or with operative proce-dures suggest that 24 hours of prophylaxis or less is quite ade-quate.72-74 Mounting evidence suggests that a single preoperativedose is good care and that additional doses are not required.

Trauma Patients

The efficacy of antibiotic administration on arrival in the emer-gency department as an integral part of resuscitation has beenclearly demonstrated.66 The most common regimens have been(1) a combination of an aminoglycoside and clindamycin and (2)cefoxitin alone. These two regimens or variations thereof havebeen compared in a number of studies.40,67,75 They appear to beequally effective, and either regimen can be recommended withconfidence. For prophylaxis, there appears to be a trend towardusing a single drug: cefoxitin or cefotetan.55 If therapy is requiredbecause of either a delay in surgery, terrible injury, or prolongedshock, the combination of an agent that is effective against anaer-obes with an aminoglycoside seems to be favored. Because amino-glycosides are nephrotoxic, they must be used with care in thepresence of shock.

In many of the trauma studies just cited, antibiotic prophylaxislasted for 48 hours or longer. Subsequent studies, however, indi-cated that prophylaxis lasting less than 24 hours is appropri-ate.73,74,76 Single-dose prophylaxis is appropriate for patients withclosed fractures.77

COMPLICATIONS

Complications of antibiotic prophylaxis are few. Although datalinking prophylaxis to the development of resistant organisms are

meager, resistant microbes have developed in every other situationin which antibiotics have been utilized, and it is reasonable toexpect that prophylaxis in any ecosystem will have the same result,particularly if selection of patients is poor, if prophylaxis lasts toolong, or if too many late-generation agents are used.

A rare but important complication of antibiotic use ispseudomembranous enterocolitis, which is induced most com-monly by clindamycin, the cephalosporins, and ampicillin [see 8:16Nosocomial Infection].62 The common denominator among differ-ent cases of pseudomembranous enterocolitis is hard to identify.Diarrhea and fever can develop after administration of single dosesof prophylactic antibiotics. The condition is rare, but difficultiesoccur because of failure to make a rapid diagnosis.

CURRENT ISSUES

The most significant questions concerning prophylaxis of SSIsalready have been answered. An important remaining issue is theproper duration of prophylaxis in complicated cases, in the settingof trauma, and in the presence of foreign bodies. No change in thecriteria for antibiotic prophylaxis is required in laparoscopic pro-cedures; the risk of infection is lower in such cases.78,79 Cost fac-tors are important and may justify the endless succession of stud-ies that compare new drugs in competition for appropriate clinicalniches.

Further advances in patient selection may take place but willrequire analysis of data from large numbers of patients and a dis-tinction between approaches to infection of the wound, which isonly a part of the operative field, and approaches to infectionsdirectly related to the operative site. These developments willdefine more clearly the prophylaxis requirements of patientswhose operations are clean but whose risk of wound or operativesite infection is increased.

A current issue of some concern is potential loss of infectionsurveillance capability. Infection control units have been shown tooffer a number of benefits in the institutional setting, such as thefollowing:

1. Identifying epidemics caused by common or uncommon organisms.23,26,56

2. Establishing correct use of prophylaxis (timing, dose, duration,and choice).52,55,72

3. Documenting costs, risk factors, and readmission rates.80,814. Monitoring postdischarge infections and secondary conse-

quences of infections.82-845. Ensuring patient safety.856. Managing MRSA and VRE.86

S. aureusin particular, MRSAis a major cause of SSI.86Cross-infection problems are a concern, in a manner reminiscentof the preantibiotic era. Hand washing (see below) is coming backinto fashion, consistent with the professional behavior toward



Table 8 Historical Rates of Wound Infection

Infection Rate (%)Wound

Classification

CleanClean-contaminatedContaminatedDirty-infected

Overall

1960196251(15,613 patients)

5.110.816.328.0

7.4

1967197712(62,937 patients)

1.57.7

15.240.0

4.7

19821986107(20,703 patients)

1.32.57.1

2.2

1977198113(20,193 patients)

1.82.99.9

2.8

197519766(59,353 patients)

2.93.98.5

12.6

4.1

cross-infection characteristic of that era. At present, hard evidenceis lacking, but clinical observation suggests that S. aureus SSIs areespecially troublesome and destructive of local tissue and requirea longer time to heal than other SSIs do. When S. aureus SSIsoccur after cardiac surgery, thoracotomy, or joint replacement,their consequences are significant. Prevention in these settings isimportant. When nasal carriage of S. aureus has been identified,mupirocin may be administered intranasally to reduce the inci-dence of S. aureus SSIs.87

The benefits of infection surveillance notwithstanding, as thebusiness of hospital care has become more expensive and finan-cial control more rigid, the infection control unit is a hospital com-ponent that many administrators have come to consider a luxuryand therefore expendable. Consequently, surveillance as a qualitycontrol and patient safety mechanism has been diminished.

It is apparent that SSIs have huge clinical and financial impli-cations. Patients with infections tend to be sicker and to undergomore complex operations.Therefore, higher infection rates trans-late into higher morbidity and mortality as well as higher cost tothe hospital, the patient, and society as a whole.With increasinglyearly discharge becoming the norm, delayed diagnosis of postdis-charge SSI and the complications thereof is a growing prob-lem.82-84 Effective use of institutional databases may contributegreatly to identification of this problem.83

Clearly, the development of effective mechanisms for identify-ing and controlling SSIs is in the interests of all associated with thedelivery of health care.85 The identification of problems by meansof surveillance and feedback can make a substantial contributionto reducing SSI rates [see Table 6].12,85

Hand Washing

The purpose of cleansing the surgeons hands is to reduce thenumbers of resident flora and transient contaminants, therebydecreasing the risk of transmitting infection. Although the properduration of the hand scrub is still subject to debate, evidence sug-gests that a 120-second scrub is sufficient, provided that a brushis used to remove the bacteria residing in the skin folds around thenails.88 The nail folds, the nails, and the fingertips should receivethe most attention because most bacteria are located around thenail folds and most glove punctures occur at the fingertips.Friction is required to remove resident microorganisms which areattached by adhesion or adsorption, whereas transient bacteria areeasily removed by simple hand washing.

Solutions containing either chlorhexidine gluconate or one ofthe iodophors are the most effective surgical scrub preparationsand have the fewest problems with stability, contamination, andtoxicity.89 Alcohols applied to the skin are among the safest knownantiseptics, and they produce the greatest and most rapid reduc-

tion in bacterial counts on clean skin.90 All variables considered,chlorhexidine gluconate followed by an iodophor appears to bethe best option [see Table 9].

The purpose of washing the hands after surgery is to removemicroorganisms that are resident, that flourished in the warm, wetenvironment created by wearing gloves, or that reached the handsby entering through puncture holes in the gloves. On the ward,even minimal contact with colonized patients has been demon-strated to transfer microorganisms.91 As many as 1,000 organismswere transferred by simply touching the patients hand, taking apulse, or lifting the patient.The organisms survived for 20 to 150minutes, making their transfer to the next patient clearly possible.

A return to the ancient practice of washing hands between eachpatient contact is warranted. Nosocomial spread of numerousorganismsincluding C. difficile; MRSA, VRE, and other antibi-otic-resistant bacteria; and virusesis a constant threat.

Hand washing on the ward is complicated by the fact that over-washing may actually increase bacterial counts. Dry, damagedskin harbors many more bacteria than healthy skin and is almostimpossible to render even close to bacteria free. Although little isknown about the physiologic changes in skin that result from fre-quent washings, the bacterial flora is certainly modified by alter-ations in the lipid or water content of the skin.The so-called dryhand syndrome was the impetus behind the development of thealcohol-based gels now available.These preparations make it easyfor surgeons to clean their hands after every patient encounterwith minimal damage to their skin.

Infection Prevention in Bowel Surgery

At present, the best method of preventing SSIs after bowelsurgery is, once again, a subject of debate.There have been threeprincipal approaches to this issue, involving mechanical bowelpreparation in conjunction with one of the following three antibi-otic regimens55,92-97:1. Oral antibiotics (usually neomycin and erythromycin),20,962. Intravenous antibiotics covering aerobic and anaerobic bowel

flora,16,20,55,94,95 or3. A combination of regimens 1 and 2 (meta-analysis suggests that

the combination of oral and parenteral antibiotics is best).97

The present controversy, triggered by a clinical trial,16 areview,20 and three meta-analyses, relates to the need for mechan-ical bowel preparation,17-19 which has been a surgical dogma sincethe early 1970s.The increased SSI and leak rates noted have beenattributed to the complications associated with vigorous bowelpreparation, leading to dehydration, overhydration, or electrolyteabnormalities.

An observational study reported a 26% SSI rate in colorectal



Table 9 Characteristics of Three Topical Antimicrobial Agents Effective against Both Gram-Positive and Gram-Negative Bacteria90

Agent

Chlorhexidine

Iodine/iodophors

Alcohols

Comments

Poor activity against tuberculosis-causing organisms; cancause ototoxicity and eye irritation

Broad antibacterial spectrum; minimal skin residual activi-ty; possible absorption toxicity and skin irritation

Rapid action but little residual activity; flammable

Mode of Action

Cell wall disruption

Oxidation and substitution by free iodine

Denaturation of protein

AntifungalActivity

Fair

Good

Good

surgery patients.98 Intraoperative hypotension and body massindex were the only independent predictive variables. All patientsunderwent mechanical bowel preparation the day before operationand received oral antibiotics and perioperative I.V. antibiotics. Halfof the SSIs were discovered after discharge. Most would agree thatthe protocol was standard.These and other results suggest that afresh look at the infectious complications of surgeryand of bowelsurgery in particularis required.

The recommended antibiotic regimen for bowel surgery con-sists of oral plus systemic agents (see above).55 The approach tomechanical bowel preparation, however, is open. Intuition wouldsuggest that the presence of less liquid and stool in the colon mightbe beneficial and perhaps that a preoperative phosphate enemawith 24 hours of fluid might make sense. It is hard to throw out30 years of apparent evidence on the basis of these three meta-analyses. These studies do, however, present data that cannot beignored. Protocols for bowel surgery in the modern era of same-day admission, fast track surgery, and rapid discharge will requirefurther study and clinical trials.

Integration of Determinants of Infection

The significant advances in the control of wound infection dur-ing the past several decades are linked to a better understanding ofthe biology of wound infection, and this link has permitted theadvance to the concept of SSI.2 In all tissues at any time, there willbe a critical inoculum of bacteria that would cause an infectiousprocess [see Figure 3].The standard definition of infection in urineand sputum has been 105 organisms/ml. In a clean dry wound, 105bacteria produce a wound infection rate of 50% [see Figure 3].11Effective use of antibiotics reduces the infection rate to 10% withthe same number of bacteria and thereby permits the wound totolerate a much larger number of bacteria.

All of the clinical activities described are intended either toreduce the inoculum or to permit the host to manage the numberof bacteria that would otherwise be pathologic. One study inguinea pigs showed how manipulation of local blood flow, shock,the local immune response, and foreign material can enhance thedevelopment of infection.99 This study and two others defined anearly decisive period of host antimicrobial activity that lasts for 3to 6 hours after contamination.50,99,100 Bacteria that remain afterthis period are the infecting inoculum. Processes that interferewith this early response (e.g., shock, altered perfusion, adjuvants,or foreign material) or support it (e.g., antibiotics or total care)

have a major influence on outcome.One investigation demonstrated that silk sutures decrease the

number of bacteria required for infection.101 Other investigatorsused a suture as the key adjuvant in studies of host manipula-tion,102 whereas a separate study demonstrated persistent suscep-tibility to wound infection days after shock.103 The common vari-able is the number of bacteria. This relation may be termed theinoculum effect, and it has great relevance in all aspects of infec-tion control. Applying knowledge of this effect in practical termsinvolves the following three steps:

1. Keeping the bacterial contamination as low as possible via asep-sis and antisepsis, preoperative preparation of patient and sur-geon, and antibiotic prophylaxis.

2. Maintaining local factors in such a way that they can preventthe lodgment of bacteria and thereby provide a locally unrecep-tive environment.

3. Maintaining systemic responses at such a level that they cancontrol the bacteria that become established.

These three steps are related to the determinants of infectionand their applicability to daily practice.Year-by-year reductions inwound infection rates, when closely followed, indicate that it ispossible for surgeons to continue improving results by attention toquality of clinical care and surgical technique, despite increasinglycomplex operations.5,13,28-30 In particular, the measures involved inthe first step (control of bacteria) have been progressively refinedand are now well established.

The integration of determinants has significant effects [see Figures3 and 4].When wound closure was effected with a wound hemat-ocrit of 8% or more, the inoculum required to produce a woundinfection rate of 40% was 100 bacteria [see Figure 3].Ten bacteriaproduced a wound infection rate of 20%.The shift in the numberof organisms required to produce clinical infection is significant. Itis obvious that this inoculum effect can be changed dramatically by good surgical technique and further altered by use of prophylac-tic antibiotics. If the inoculum is always slightly smaller than thenumber of organisms required to produce infection in any given set-ting, results are excellent. There is clearly a relation between thenumber of bacteria and the local environment.The local effect canalso be seen secondary to systemic physiologic change, specificallyshock. One study showed the low local perfusion in shock to beimportant in the development of an infection.99,100

One investigation has shown that shock can alter infection ratesimmediately after its occurrence [see Figure 4].103 Furthermore, if



Table 10 Comparison of WoundClassification Systems6

HighRisk

Traditional WoundClassification System

Clean

Clean-contaminated

Contaminated

Dirty-infected

All from SENIC index

LowRisk

0

1.1

0.6

1.0

All fromTraditional

Classification

2.9

3.9

8.5

12.6

4.1

Simplified Risk Index

MediumRisk

1

3.9

2.8

4.5

6.7

3.6

2

8.4

8.4

8.3

10.9

8.9

4

23.9

27.4

27.0

3

15.8

17.7

11.0

18.8

17.2

SENICStudy of the Efficacy of Nosocomial Infection Control

the inoculum is large enough, antibiotics will not control bacteria.In addition, there is a late augmentation of infection lasting up to3 days after restoration of blood volume. These early and lateeffects indicate that systemic determinants come into play afterlocal effects are resolved.These observations call for further study,but obviously, it is the combined abnormalities that alter outcome.

Systemic host responses are important for the control of infec-tion. The patient has been clearly implicated as one of the fourcritical variables in the development of wound infection.6 In addi-tion, the bacterial inoculum, the location of the procedure and itsduration, and the coexistence of three or more diagnoses werefound to give a more accurate prediction of the risk of woundinfection. The spread of risk is defined better with the SENICindex (1% to 27%) than it is with the traditional classification(2.9% to 12.6%) [see Table 10].The importance of the number ofbacteria is lessened if the other factors are considered in additionto inoculum. The inoculum effect has to be considered withrespect to both the number of organisms and the local and sys-temic host factors that are in play. Certain variables were found tobe significantly related to the risk of wound infection in threeimportant prospective studies [see Table 10].6,10,12 It is apparentthat the problem of SSI cannot be examined only with respect tothe management of bacteria. Host factors have become muchmore significant now that the bacterial inoculum can be main-tained at low levels by means of asepsis, antisepsis, technique, andprophylactic antibiotics.104

Important host variables include the maintenance of normalhomeostasis (physiology) and immune response. Maintenance of

normal homeostasis in patients at risk is one of the great advancesof surgical critical care.104 The clearest improvements in thisregard have come in maintenance of blood volume, oxygenation,and oxygen delivery.

One group demonstrated the importance of oxygen delivery,tissue perfusion, and PaO2 in the development of wound infec-tion.105 Oxygen can have as powerful a negative influence on thedevelopment of SSI as antibiotics can.106 The influence is verysimilar to that seen in other investigations.Whereas a PaO2 equiv-alent to a true fractional concentration of oxygen in inspired gas(FIO2) of 45% is not feasible, maintenance, when appropriate, ofan increased FIO2 in the postoperative period may prove an ele-mentary and effective tool in managing the inoculum effect.

Modern surgical practice has reduced the rate of wound infec-tion significantly. Consequently, it is more useful to think in termsof SSI, which is not limited to the incision but may occur any-where in the operative field; this concept provides a global objec-tive for control of infections associated with a surgical procedure.Surveillance is of great importance for quality assurance. Reportsof recognized pathogens (e.g., S. epidermidis and group A strepto-cocci) as well as unusual organisms (e.g., Rhodococcus [Gordona]bronchialis, Mycoplasma hominis, and Legionella dumoffii) in SSIshighlight the importance of infection control and epidemiology forquality assurance in surgical departments.21-23,26,27 (

Pos Operatorias

Documents

Transcript of Pos Operatorias