BAILYLOVE TEXTBOOK OF SURGERY0 INDEX 8.docx
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BAILYLOVE TEXTBOOK OF SURGERY0 INDEX 8.docx
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BAILYLOVETEXTBOOKOFSURGERY0INDEX8
7. Woundinfection
DAVIDJ.LEAPER
Physiologyandmanifestation
Background.ItisclearthattheEgyptiansknewaboutinfection.Theycertainlywereabletopreventputrefactionwhichistestifiedintheirskillsofmummification.Theirmedicalpapyrusesalsodescribetheuseofsalvesandantisepticstopreventwoundinfections.Thishadalsobeenknown,althoughlesswelldocumented,bytheAssyriansandtheGreeks,particularlyinHippocraticteachings,whichhadrefinedtheuseofantimicrobialpractice.Theuseofwineandvinegartoirrigateopeninfectedwoundsbeforesuccessfulsecondaryclosurewaspractisedwidely.Commontoallthesecultures,andthelaterRomanpractitioners,wasadictumthatwheneverpusdevelopedinaninfectedwounditneededtobedrained.
Galenrecognisedthatlocalisationofinfection(suppuration)inwoundsinflictedinthegladiatorialarenaoftenheraldedrecovery,particularlyafterdrainageofthepus(pusbonumetIaudabile).Sadly,thisdictumwasmisinterpretedbymanyuntilwellintotheRenaissance;manypractitionersactuallypromotedsuppurationinwoundsbyapplicationofmanynoxioussubstances,includingfaeces,inthemisbeliefthathealingcouldnotoccurwithoutpusformation.Therewasoccasionallightinthislong,darktunnel:
TheodoricofCervia,AmbroisePareandGuydeChauliacallrealisedthatcleanwounds,closedprimarily,couldhealwithoutinfectionorsuppuration.
Theunderstandingofthecausesofinfectioncameinthenineteenthcentury~Microbeshadbeenseenunderthemicroscope,butKochlaiddownthefirstdefinitionofinfectivedisease(Koch’spostulates).Thesewerebasicallythataparticularmicrobecouldbeconsideredresponsibleforaninfectionwhenitwasfoundinadequatenumbersinasepticfocus,couldbeculturedinpureformfromspecimenstakenfromthefocusandcouldcausesimilarlesionswheninjectedintoanotherhost.
TheAustrianobstetrician,IgnacSemmelweis,showedthatmaternalmortalitycausedbypuerperalsepsiscouldbereducedfromover10percenttounder2percentbythesimpleactofhandwashingbetweenpostmortemexaminationsandthedeliverysuite.
LouisPasteurrecognisedthatmicroorganismsspoiltwineandJosephListerappliedthisknowledgetothereductionoforganismsincompoundfracturesallowingsurgerywithoutinfection.However,histoxicphenolsprayandprinciplesofantisepticsurgerysoongavewaytoasepticsurgeryattheturnofthecentury—atechniquestillemployedinmodernoperatingtheatres.
Theconceptofa‘magicbullet’whichcouldkillmicrobesbutnottheirhostledtoearlysulphonamidechemotherapy.
Theantibioticpenicillin,thediscoveryofwhichisascribedtoAlexanderFleming,wasisolatedbyFloreyandChain.ThefirstpatienttoreceivepenicillinwasPoliceConstableAlexander,whohadaseverestaphylococcalillness.Hemadeapartialrecoverybeforethepenicillinranoutbutlaterrelapsedanddied.Sincethentherehasbeenahugeincreaseinantibioticgroupswithimprovedantibacterialspectra.Fewstaphylococciarenowsensitivetopenicillinbutstreptococcalillnessesrespond,althoughtheyareseenincreasinglyrarelyinsurgicalpractice.Manybacteriadevelopresistancethroughtheacquisitionofbeta-lactamaseswhichcanbreakupthe3-lactamring,commonintheformulaofmanyantibiotics.Ingeneralsurgery,thesynergyofaerobicGram-negativebacilliwithanaerobicBacteroidesspp.presentsthemostchallenginginfection.Wide-spectrumantibioticscanbegivenempiricallytotreatsuchinfections,ormorespecific,narrow-rangeantibioticsgivenbasedoncultureandsensitivity.Therangeofsurgerynowpractisedowesmuchtorationalantibioticuse—faecalperitonitismaynotbeconsideredtobelethal,andwoundsmadeinthepresenceofsuchcontaminationcanhealprimarilywithoutinfectionin80—90percentofpatients.Patientsundergoingprostheticsurgeryorwhoareimmunosuppressedcanbesparedinfectionintheirwoundsbytheappropriateuseofprophylacticantibiotics.
Physiology
Bacteriaarenormallypreventedfromcausinginfectionintissuesbyintactepithelialsurfaces,butthesearebrokendownbysurgery.Inadditiontothismechanicalbarrier,thereareotherprotectivemechanisms,i.e.chemical(suchasthelowgastricpH),humoral(antibodies,complementandopsonins)andcellular(phagocyticcells,macrophages,polymorphonuclearcellsandkillerlymphocytes).
Hostresponseisweakenedbymalnutritionwhichmaypresentasobesityaswellasrecentrapidweightloss(Table7.1)Metabolicdiseases,diabetesmellitus,uraemiaandjaundicemayweakendefences,anddisseminatedcancermayalsobeincludedtogetherwithimmunosuppressioncausedbyradiotherapy,chemotherapy,steroidsandacquiredimmunodeficiencysyndrome(AIDS)(Fig7.1andFig7.2).
Whenenteralfeedingissuspendedintheperioperativeperiod,thegutrapidlybecomescolonisedandbacteria,particularlyGram-negativebacilli,translocatetomesentericnodes.Releaseofendotoxinmayfollow,whichfurtherincreasessusceptibilitytoinfection.Inthesecircumstances,nonpathogensbecomeimportant(opportunism).
Thepathogenicityandsizeofbacterialinoculumalsorelatestothechanceofdevelopinganestablishedwoundinfectionaftersurgery.Poorsurgicaltechniquethatleavesdevitalisedtissue,excessivedeadspaceorhaematomamayincreasethisrisk.Foreignmaterialsofanykind,includingsuturesanddrains,promoteinfection.Alogarithmreductioninthenumberoforganismsisneededtocauseawoundinfectioninthepresenceofasilksuture.Thesefactorsneedconsiderationinprostheticorthopaedicandvascularsurgery.
Inthefirst4hoursafterabreachinanepithelialsurfaceandunderlyingconnectivetissuesmadeduringsurgeryortrauma,thereisadelaybeforehostdefencescanbecomemobilisedthroughacuteinflammatory,humoralandcellularprocesses.Thisperiodiscalledthe‘decisiveperiod’anditisduringthesefirst4hoursafterincisionthatbacterialcolonisationandestablishedinfectioncanbegin.Itislogicalthatprophylacticantibioticswillbemosteffectiveduringthistime.
Localandsystemicmanifestation
Infectionofawoundcanbedefinedastheinvasionoforganismsthroughtissuesfollowingabreakdownoflocalandsystemichostdefences.Sepsisisthesystemicmanifestationofadocumentedinfection,thesignsandsymptomsofwhichmayalsobecausedbymultipletrauma,burnsorpancreatitis.Bacteraemiashouldnotbeconfusedwiththissystemicinflammatoryresponsesyndrome(SIRS)althoughthetwomaycoexist(seeTable7.2).Septicmanifestationsaremediatedbyreleaseofcytokines[suchasinterleukins(IL)andtumournecrosisfactor(TNF)]andothermodulesfrompolymorphonuclearandphagocyticcellsand,initsmostsevereform,presentsasmultiplesystemorganfailure(MSOF).InfectionmaycauseSIRSthroughthereleaseoflipopolysaccharideendotoxinfromthewallsofdyingGram-negativebacilli(mainlyEscherichiacoli)andothertoxins,whichinturncausesreleaseofcytokines(Fig.7.3).Areduceddefencetowoundinfectionfollows.
Pathogensresisthostdefencesbyreleaseoftoxins,particularlyinunfavourableanaerobicconditions,whichfavourstheirspreadinwoundinfections.Clostridiumperfringens,whichisresponsibleforgasgangrene,releasesmanyspreadingproteasessuchashyaluronidase,lecithinaseandhaemolysin.Manyresistantpathogenscanproducebeta-lactamaseswhichdestroythebetalactamringofantibiotics.Thisresistancecanbeacquiredandpassedonthroughplasmids.
Thehumanbodyharboursapproximately1014organisms.Theyarereleasedintotissuesbysurgery,contamination beingmostseverewhenahollowviscusisopened(e.g.colorectalsurgery).Anyinfectionwhichfollowsmaybetermedprimary,communityacquiredorendogenous.Exogenousinfectionsareusuallyhospitalacquired(nosocomial)andaresecondary,beingintroducedintothetissuesaftersurgerynotduringit,unlessintroducedviainadequatelyfilteredairintheoperatingtheatre.
Amajorwoundinfectionisdefinedasawoundwhichdischargespusandmayneedasecondaryproceduretobesureofadequatedrainage(Fig.7.4).Theremaybesystemicsignsoftachycardiapyrexiaandaraisedwhitecount(SIRS).Thepatientmaybedelayedinreturninghomebeyondtheplannedday.Minorwoundinfectionsmaydischargepusorinfectedserousfluidbutshouldnotbeassociatedwithexcessivediscomfort,systemicsignsordelayinreturnhome(Fig.7.5).Thedifferentiationofmajorandminorwoundinfectionisimportantinaudittrialsofantibioticprophylaxisandisofrelevanceto‘leaguetables’ofhospitalinfectionasmajorwoundinfectionsmustbeaccountedfor.
Typesofinfection
Woundabscess
AwoundabscesspresentsalltheCelsianclinicalfeaturesofacuteinflammation:
calor(heat),rubor(redness),dolor(pain)andtumour(swelling),to whichcanbeadded functioleasa(lossoffunction).ithurtstheinfectedpartisnotused).Pyogenicorganisms,predominantlyStaphylococcusaureus,causetissuenecrosisandsuppuration.Pusisalsocomposedofdeadanddyingwhitebloodcellswhichreleasedamagingcytokines,oxygen-freeradicalsandothermolecules.Anabscessissurroundedbyanacuteinflammatoryresponse,andapyogenicmembranecomposedoffibrinousexudateandoedema,andthecellsofacuteinflammation.Granulationtissue(macrophages,angiogenesisandfibrobbasts)formslateraroundthesuppurationandbeadstocollagendeposition.Ifexcessiveorpartlysterilisedbyantibiotics(antibioma),achronicabscessmayresult.Abscessesusuallytrackalongplanesofleastresistanceandpointtowardstheskin.Woundabsces
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