Prophylactic antibiotics are not indicated in clean general surgery cases

Rebecca Knight, M.D.*, Patrick Charbonneau, M.D., Erick Ratzer, M.D.,Francine Zeren, M.S.N., William Haun, M.D., Jeffrey Clark, M.D.

Department of Surgery Education, Exempla Saint Joseph Hospital, 1835 Franklin St., Denver, CO 80218-1191, USA

Manuscript received July 31, 2001; revised manuscript September 4, 2001

Presented at the 53rd Annual Meeting of the Southwestern Surgical Congress, Cancun, Mexico, April 29–May 2, 2001.

Abstract

Background: In assigning risk of infection, the traditional wound classification system has been replaced by the National NosocomialInfection Surveillance (NNIS) system. NNIS classification is determined by procedure length, wound cleanliness, and ASA status. To date,no prophylactic antibiotic guidelines have been proposed for the NNIS system.Methods: Clean general surgery cases were retrospectively reviewed in our hospital for infection and prophylactic antibiotic use. Thesecases were then stratified per the NNIS system.Results: One thousand twenty-three clean general surgery cases had 16 (1%) surgical site infections. The infection rate in NNIS class 0,1, and 2 cases not given prophylactic antibiotics was 1.21%, 3.03%, and 0%, respectively. The infection rate in NNIS class 0, 1, and 2 casesgiven prophylactic antibiotics was 0.94%, 2.44%, and 6.67%, respectively.Conclusions: No statistically significant decrease in infection rate was demonstrated by us using prophylactic antibiotics, regardless of theNNIS classification in clean general surgery cases. © 2002 Excerpta Medica, Inc. All rights reserved.

There are many reasons to predict who might get a woundinfection and to try to prevent them. Wound infections delayrecovery, increase suffering, and expend money, time, andhospital resources. It is also important to follow individual,hospital, and national data on rates of infection. An in-creased rate of surgical site infection above hospital ornational averages suggests a need for investigation of one’spreoperative preparation, operative technique, postoperativewound care, and operating room protocols and sterile pro-cessing. Prevention is an important part of medicine, andtaking extra measures in susceptible patients may reducetheir risk for infection.

In 1964 the National Research Council (NRC) proposedthe idea of using wound classification to predict risk forsurgical site infection [1]. All surgeons are familiar with theclean, clean/contaminated, contaminated, and dirty/infectedsystem for describing surgical sites defined by the NRC(Table 1). It is important to consider the cleanliness of thewound in relation to risk for infection; however, statisticsindicate that the traditional wound classification system

does not stratify the total risk of infection very well. Spe-cifically, the wound classification does not take into accountthe amount of time the wound is exposed to the environment(and potentially harmful microbes) or associated illnessesthat may predispose a patient with even a clean wound to asurgical site infection. In the 1970s, many researchers at-tempted to identify other risk factors for wound infection,besides the contamination level of the surgical site. Ulti-mately, the Study on the Efficacy of Nosocomial InfectionControl, or SENIC Project [4], simplified the index of fac-tors for predicting the risk for surgical site infection.

In 1970 the SENIC Project studied 58,498 randomlyselected surgical patients in 338 hospitals and identifiedmultiple factors that may increase risk for surgical siteinfection. Analysis of the data simplified the index into fourfactors, and each factor was valued at one point. The morepoints (risk factors) a patient had, the higher their risk forinfection. Having a surgical procedure on the abdomenposed the highest risk, followed by a procedure lastinglonger than 2 hours, a contaminated or dirty/infected surgi-cal site, and having three or more distinct discharge diag-noses, excluding a wound infection. To verify the predictivepower of these factors, the SENIC Project then applied theindex to another 59,352 surgical patients at the same hos-

* Corresponding author. Tel.:�1-303-837-7295; fax:�1-303-866-8044.

The American Journal of Surgery 182 (2001) 682–686

0002-9610/01/$ – see front matter © 2002 Excerpta Medica, Inc. All rights reserved.PII: S0002-9610(01)00826-6

pitals in 1975–76. By stratifying the patients by risk factors,this study showed that very low and very high risk groupscould be identified within each of the categories of thetraditional wound classification system. Patients with a riskindex of 0 (no risk factors) were considered at “ low risk” fora wound infection, with an overall rate of 1.0%. Patients at“medium risk” for a surgical site infection had only one riskfactor, and their overall infection rate was 3.6%. “High risk”patients had 2, 3, or 4 risk factors and had an overallinfection rate of 8.9%, 17.2%, and 27.0%, respectively. Thefour risk factors not only take into account the level ofcontamination of the surgical site, but also the intrinsicpatient susceptibility to infection and duration of exposureto potentially harmful microbes and the extensive handlingof tissues.

In 1991, the National Nosocomial Infection Surveillanceclassification system was proposed, based on the SENICProject [5]. Data for the NNIS system were derived from 44participating hospitals and conducted by the Centers forDisease Control (CDC). A total of 84,691 surgical proce-dures (including general, cardiac, vascular, urologic, ortho-pedic, transplant, and neurosurgical procedures) resulted in2,376 surgical site infections. Traditional wound class ofcontaminated or dirty/infected was maintained as one of thefactors used to predict risk for wound infection and wasvalued at one point. The American Society of Anesthesiol-ogists (ASA) physical status classification replaced thenumber of discharge diagnoses as the second factor. AnASA score of 3 or greater garners one point in the NNISsystem. Duration of the operation is the third factor, and isworth one point if the procedure lasts longer than 75% ofsimilar procedures. Abdominal operation was eliminated inthe NNIS index. A patient’s risk for surgical site infectioncan therefore be stratified as NNIS class 0, 1, 2, or 3, basedon which of the three risk factors the patient has (Table 2).

In the NNIS study, patients with no risk factors (class 0)had a surgical site infection rate of 1.5%, patients with onerisk factor (class 1) had a 2.9% infection rate, patients withtwo risk factors (class 2) had a 6.8% infection rate, andpatients with all three risk factors (class 3) had a 13.0%

infection rate. When stratified by the traditional woundclassification system (clean, clean-contaminated, contami-nated, dirty/infected), these same 84,691 patients hadwound infection rates of 2.1% in clean wounds, 3.3% inclean-contaminated wounds, 6.4% in contaminated wounds,and 7.1% in dirty/infected wounds. The traditional systemdoes not stratify the patients as broadly as the NNIS index(Table 3).

Of the 84,691 patients in the NNIS study, a subset of49,333 patients was identified as having clean wounds. Forthis group, the overall surgical site infection rate was 2.1%.However, in the NNIS system, these clean wounds can befurther substratified as class 0, 1, or 2. (Class 3 is notpossible in clean cases, as the third point is given for acontaminated or dirty/infected wound.) Patients with cleanwounds in class 0 had a 1.0% infection rate, class 1 had a2.3% infection rate, and class 2 had a 5.4% infection rate.

One common measure taken to reduce the risk of surgi-cal site infection is the administration of prophylactic anti-biotics. No specific guidelines exist for use of prophylacticantibiotics in the NNIS system. Currently, the CDC recom-mends prophylactic antibiotics for operations associatedwith a high risk of infection or in those that occurrence of aninfection is associated with severe consequences [6]. Theserecommendations are nonspecific and leave the determina-tion of who needs prophylactic antibiotics to the surgeon.Current guidelines for use of prophylactic antibiotics arebased on the traditional wound classification system, whichsuggests that all categories of wounds be given prophylacticantibiotics except clean wounds. Patients with clean woundsreceive prophylactic antibiotics only if there is placement of

Table 1Traditional classification of operative wounds [2,3]

Clean (class I) Nontraumatic, uninfected wounds; noinflammation; primarily closed; no breakin aseptic technique

Clean-contaminated(class II)

Alimentary, respiratory or genitourinary tractentered under controlled conditions; nocontamination; minor break in aseptictechnique

Contaminated(class III)

Fresh traumatic wounds; gross spillage fromgastrointestinal tract; acute, nonpurulentinflammation; major break in technique

Dirty/infected(class IV)

Traumatic wounds with retained devitalizedtissue, foreign bodies or fecalcontamination; perforated viscus; acute,purulent bacterial inflammation

Table 2National Nosocomial Infection Surveillance classification system [3]

Risk factor Points

Wound classClean or clean-contaminated 0Contaminated or dirty/infected 1

ASA class1 or 2 03, 4, or 5 1

Length of procedure�75th percentile of similar procedures 0�75th percentile of similar procedures 1

ASA � American Society of Anesthesiologists.

Table 3Surgical site infection rates by wound class versus National NosocomialInfection Surveillance (NNIS) class from the NNIS study [3]

Wound class All NNIS 0 NNIS 1 NNIS 2 NNIS 3

Clean 2.1% 1.0% 2.3% 5.4% N/AClean-contaminated 3.3% 2.1% 4.0% 9.5% N/AContaminated 6.4% N/A 3.4% 6.8% 13.2%Dirty/infected 7.1% N/A 3.1% 8.1% 12.8%All 2.8% 1.5% 2.9% 6.8% 13.0%

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an implantable device, a vascular prostheses, or other for-eign material. While a single dose of antibiotics may at firstseem harmless, antibiotics may pose the risk of an allergicreaction, superinfection, or contribute to development ofbacterial resistance. Unnecessary cost should also be a con-cern of the surgeon. We performed this study in an attemptto establish guidelines for the use of prophylactic antibioticsin clean general surgery cases in our own hospital.

Methods

Our hospital switched to the NNIS system 6 years ago inorder to better survey and predict wound infections. For thispaper, we performed a retrospective review of patients whounderwent clean general surgical procedures over the 1-yearperiod from July 1, 1998, to June 30, 1999. During the sametime frame, cardiac and peripheral vascular cases were an-alyzed separately because in our hospital all these casesreceive prophylactic antibiotics per antibiotic protocol.

Patients were stratified into NNIS class 0, 1, or 2. As inthe SENIC Project, we used operating time of greater than2 hours rather than an operating time of greater than the75th percentile of similar cases in our hospital as one of thethree risk factors. The surgeon’s average time for a partic-ular case is used to preoperatively determine the patient’sNNIS class to guide the decision on whether to administerprophylactic antibiotics.

Within each of our NNIS classes, prophylactic antibioticuse for the general surgery cases was determined by arandom retrospective chart review. All cardiac and vascularcases had prophylactic antibiotics. Patients with surgicalsite infections were identified and their charts were re-viewed to determine who received prophylactic antibiotics.Data were analyzed by Fisher’s exact test. InstitutionalReview Board approval was obtained for this study.

Results

We identified 1,223 total clean general surgery cases.Eight hundred forty-one (69%) were NNIS class 0; 345(28%) were NNIS class 1; and 37 (3%) were NNIS class 2.(NNIS class 3 is not possible for a clean case.) Sixteen (1%)of the 1,223 patients had a surgical site infection. Of these,5 of 841 were class 0 for an infection rate of 0.59%; 9 of 345were class 1 for an infection rate of 2.6%; and 2 of 37 wereNNIS class 2 for an infection rate of 5.4%. Four hundredtwenty-seven of 841 (50.8%) of the NNIS class 0 patientsreceived prophylactic antibiotics. The rate of wound infec-tion in these patients was 0.94% (4 of 427), compared with0.2% (1 of 414) of the class 0 patients who did not receiveantibiotics (P � 0.118). Two hundred forty-six of 345(71.4%) of the NNIS class 1 patients received prophylacticantibiotics. The rate of wound infection in these patientswas 2.44% (6 of 246), compared with 3.03% (3 of 99) of the

class 1 patients who did not receive antibiotics (P � 0.534).Thirty of 37 (82.0%) of the NNIS class 2 patients receivedprophylactic antibiotics. The rate of wound infection inthese patients was 6.67% (2 of 30), compared with 0% (0 of7) of the class 2 patients who did not receive antibiotics(P � 0.999). We did not find a statistically significantdifference in surgical site infection rate between the generalsurgery patients with clean wounds who received prophy-lactic antibiotics and those who did not, regardless of theirNNIS classification.

We then identified 891 clean cardiac or peripheral vas-cular surgeries, including vascular access procedures fordialysis. Ninety-two (10.2%) were NNIS class 0; 653(73.3%) were NNIS class 1, and 146 (16.4%) were NNISclass 2. Nineteen (2.1%) of the 891 patients had a surgicalsite infection. Of these, 1 was class 0 for an infection rate of1.1%; 7 were class 1 for an infection rate of 1.1%; and 11were class 2 for an infection rate of 7.5%. Based on ourinstitution’s established protocol, all of these patientsshould have received prophylactic antibiotics. Table 4 com-pares the data from our clean general surgery cases in whichprophylactic antibiotics were given, our clean general sur-gery cases in which antibiotics were not given, our cardiacand vascular cases, and the clean surgery cases from theNNIS data.

Comments

Our data indicate that regardless of the NNIS class inclean general surgery cases, administering prophylactic an-tibiotics does not statistically reduce the rate of surgical siteinfection. We do not recommend that prophylactic antibi-otics be given to general surgery patients in NNIS class 0 or1. We question the value of prophylactic antibiotics in cleanNNIS class 0 and 1 vascular surgery patients. However, ourvascular surgeons refuse to participate in any study thatwould withhold antibiotics, believing that the disastrousconsequences of a graft infection outweigh any potentialbenefit of withholding prophylactic antibiotics.

Table 4Comparison of overall infection rates

Group Total NNISclass 0

NNISclass 1

NNISclass 2

Clean general surgery caseswith prophylacticantibiotics

1.71% 0.94% 2.44% 6.67%

Clean general surgery caseswithout prophylacticantibiotics

0.77% 0.2% 3.03% 0%

Cardiac and vascularsurgery cases withantibiotics

2.13% 1.1% 1.1% 7.53%

NNIS study clean surgerycases [4]

2.1% 1.0% 2.3% 5.4%

NNIS � National Nosocomial Infection Surveillance study.

684 R. Knight et al. / The American Journal of Surgery 182 (2001) 682–686

We expect a higher rate of surgical site infection in theNNIS 2 category. The cardiac and vascular patients who allreceived prophylactic antibiotics dramatically demonstratedthis. We have far too few clean NNIS class 2 generalsurgery cases to make meaningful recommendations. Weacknowledge that our small number of patients and there-fore lack of statistical power many account for a type IIerror in this analysis, but we put forth that a multi-institu-tional, prospective, randomized study should be done totruly evaluate the efficacy of prophylactic antibiotics inclean general surgery cases in the NNIS 2 group. However,we do not believe it is appropriate to wait for this study tooccur or to extrapolate data from other individual hospitalsto provide guidelines for our own hospital. Rather, it is mostappropriate for us to look at our own data and attempt tomake a rational guideline for prophylactic antibiotic use inclean general surgery cases. We could never create a singleinstitutional study that could show a 1% difference betweengroups with statistical significance; this would require thou-sands of cases. However, based on the numbers presentedhere, common sense would indicate no dramatic harmwould come to our patients if our guidelines are followed.

References

[1] Howard JM, Barker WF, Culbertson WR, et al. Postoperative woundinfections: the influence of ultraviolet irradiation of the operating roomand of various other factors. Ann Surg 1964;160(suppl):1–192.

[2] Altemeier WA, Burke JF, Pruitt BA, Sandusky WR, editors. Manualon control of infection in surgical patients. 2nd ed. Philadelphia:Lippincott, 1984.

[3] Mangram AJ, Horan TC, Pearson ML, et al, for the Hospital InfectionControl Practices Advisory Committee. Guideline for the prevention ofsurgical site infection, 1999. Infect Control Hosp Epidemiol 1999;20:247–80.

[4] Haley RW, Culver DH, Morgan WM, et al. Identifying patients at highrisk of surgical wound infection. A simple multivariate index of patientsusceptibility and wound contamination. Am J Epidemiol 1985;121:206–15.

[5] Culver DH, Horan TC, Gaynes RP, et al. Surgical wound infectionrates by wound class, operative procedure, and patient risk index. Am JMed 1991;91(suppl 3B):152–7.

[6] Mangram AJ, Horan TC, Pearson ML, et al. Guideline for preventionof surgical wound infections, 1999. Center for Disease Control Hos-pital Infection Control Practices Advisory Committee. Am J InfectControl 1999;27:97–132.

Discussion

Dr. Jeffrey R. Saffle (Salt Lake City, UT): The issue ofpredicting wound infections and preventing them is impor-tant in reducing patient suffering, providing cost-effectivecare, and avoiding complications. In examining this issue,these authors studied all the general surgery in their hospitalundergoing clean surgical procedures, this designation be-ing derived from the old 1964 classification of wounds, withwhich we are all familiar. Patients were apparently assigned

randomly to receive prophylactic antibiotics, the type andduration of which were not specified, and were reclassifiedusing the new classification system devised by the NationalNosocomial Infection Surveillance System into class 0, 1, or2.

No significant differences were found in infection ratesbetween patients undergoing clean procedures when strati-fied by these classes, nor by whether antibiotics were given.Infection rates were commendably low and that fact itselfprobably justifies most of the authors’ work. We all need tolook objectively at our outcomes from time to time, but intrying to interpret these results, I have three questions forDr. Knight.

First, part of the NNIS system includes scoring the lengthof the surgical procedure. One point is given if the operationexceeds the 75th percentile for that procedure, or in yourstudy, 2 hours. Since you can’ t know that until after theoperation is over and it is then too late to use prophylacticantibiotics, how does the surgeon use this system in decid-ing about preoperative antibiotic administration?

Second, in your manuscript, you state that “ regardless ofthe NNIS class, in clean general surgical cases, administer-ing prophylactic antibiotics does not statistically reduce therate of surgical site infection.” To my simplistic reading, itsounds like you’ re saying that the familiar system of des-ignating cases as clean is good enough and that the NNISsystem adds nothing to this designation. That would becomforting to an old guy like me. Am I right?

My final question pertains to the political correctness ofyour study. You apparently randomized your patients toreceive antibiotics. Was this done with IRB approval? Withpatient informed consent? Were patients randomized to re-ceive antibiotics charged for them? Did no one refuse par-ticipation out of the 1,200 cases you reviewed?

Closing

Dr. Rebecca Knight: Regarding the first question, howcan you predict how long the operation is going to take you,we pretty much rely on the surgeon’s best guess or theirown estimation of how long they think the procedure isgoing to take. If they think they’ re going to encounter ahostile abdomen or for whatever reason that it might takelonger than their average. So, even though we try to makemore of a science of making a guideline of using prophy-lactic antibiotics, I guess we still have to rely on the art andthe surgeon’s best guess for how long the operation mighttake.

Your second question regarding whether the NNIS clas-sification really adds anything to what we refer to as thetraditional system of clean, clean-contaminated, et cetera, Ithink in our study we can say that might be true for ourclean class 0 and 1 cases, but we really can’ t say for sure forour class 2 classes. We also can’ t say that that is true for

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anything other than clean cases because we didn’ t look atour clean-contaminated, contaminated, or dirty cases.

I would say, though, that when you read the NNIS paperand look at their data, by applying the other risk factors,including duration of procedure and the patient’s health topredicting their risk for wound infection, that it is morebroadly stratified when you consider all of those risk factors.

Regarding our political correctness, yes, we did receiveIRB approval for our study. The IRB in our hospital is very

rigorous and they approve all our studies, whether they beprospective or retrospective. We did a retrospective reviewand so our patients were not randomized at the time. Basi-cally, the surgeons were the ones who determined whoreceived prophylactic antibiotics, most likely based on theCDC recommendation that in their estimation, if the patientwasn’ t high risk, they should receive antibiotics, or if aninfection would result in severe consequences. So, we didnot randomize our patients because this was retrospective.

686 R. Knight et al. / The American Journal of Surgery 182 (2001) 682–686