Neuraxial AnesthesiaSpinal Epidural and Caudal.docx

Neuraxial AnesthesiaSpinal Epidural and Caudal.docx

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NeuraxialAnesthesiaSpinalEpiduralandCaudal

NeuraxialAnesthesia—Spinal,Epidural,andCaudalAnesthesia

Neuraxialanesthesiacanbeusedalone,incombinationwithgeneralanesthesia,orforpost-oppaincontrol.Itisalsousefulinthemanagementofchronicpain.

∙Advantagesofthesetechniques—apotentialreductioninpost-operativemorbidity,（andmaybemortality）

oDecreasedincidenceofvenousthrombosisorpulmonaryembolism

oFewercardiaccomplicationsinhighriskpatientsbyalleviatingthestressresponse

oLessbleedingandfewertransfusionrequirements

oDecreasedincidenceofvasculargraftocclusion

oDecreasedincidenceofpneumoniaandrespiratorydepression

afterupperabdominalandthoracicsurgeryinpatientswithCOPD

oPossiblyearlierreturnofGIfunction

oInOB,neuraxialanesthesiaallowsthemothertostayawakeforlabor,vaginaldelivery,orcesareansection,andisassociatedwithlessmorbidityandmortalityincesareansectionsthangeneralanesthesia.

∙Proposedmechanismstoachievethesebenefits:

oAmeliorationofthehyper-coagulablestateassociatedwithsurgery

oSympathectomy-inducedincreasesintissuebloodflow

oImprovedoxygenationfromdecreasedsplinting

oEnhancedperistalsis

oSuppressionoftheneuro-endocrinestressresponsetosurgery

∙Anatomy

oSpinalcanalcontainsthespinalcordenclosedintheduramaterandbathedinCSF

oTheepiduralspace:

▪Isboundedanteriorlybytheposteriorlongitudinalligament,laterallybythevertebralpedicles,andposteriorlybytheligamentumflavum.

▪Communicateswiththeparavertebralspacebywayoftheintervertebralforamina.

oThespinalcordextendsfromtheforamenmagnumtoL1inadults,L3inchildren.

oAnterior（motor）andposterior（sensory）nerverootsfromthespinalcordjoinandexitthespinalcanalthroughtheintervertebralforamenatoformspinalnerves.Thelowernerverootsformthecaudaequina

oTheduralsacextendstoS1.

oBloodsupplytothespinalcord:

anteriortwo-thirdsbytheunpairedanteriorspinalarteryfromthevertebralartery.Posterioronethirdbypairedposteriorspinalarteriesfromtheinferiorcerebellararteries.Additionalflowcomesfromtheintercostalsandlumbararteries.

∙Mechanismsofactionforneuraxialanesthesia

oTheprinciplesiteofactionforneuraxialblockadeisthenerveroot.LocalanestheticisinjectedintotheCSF（spinalanesthesia）orintotheepiduralspace（epiduralandcaudalanesthesia）,whereitthenbathesthenerverootinthesubarachnoidspaceorintheepiduralspace,respectively.

oDirectinjectionoflocalanestheticintotheCSFforspinalanesthesiaallowsarelativelysmalldoseandvolumeoflocalanesthetictoachieveadensesensoryandmotorblock.Achievingthesameblockwithepiduralorcaudaladministrationoflocalanestheticrequiresmuchhighervolumesandquantitiesofdrug.

oOtherCNSeffects:

sedation,potentiationofsedativeandhypnoticdrugs,markedreductionofanestheticrequirements

∙AutonomicBlockade

oSympatheticpre-ganglionicnervefibers（smallmyelinatedBfibers）exitthespinalcordwiththespinalnervesfromT1toL2andcourseupordownthesympatheticchainbeforesynapsingwithapost-ganglioniccellinasympatheticganglia.

oParasympatheticpre-ganglionicfibersexitthebrainandspinalcordwithcranialandsacralnerves.Neuraxialanesthesiadoesnotblockthevagusorothercranialnerves.Sothephysiologiceffectsofneuraxialblockaderesultsfromdecreasedsympathetictoneand/orunopposedparasympathetictone.

oNeuraxialblocksproducesomaticblockade（interruptionoftransmissionofpainfulstimuli,andabolitionofskeletalmuscletone）,withdecreasedsympathetictoneand/orunopposedparasympathetictone.

Systemiceffectsofneuraxialblocks

∙Cardiovascular

oCardiovasculareffects,principallyhypotensionandbradycardia,arethemostcommonandimportantphysiologicchangesassociatedwithneuraxialanesthesia.

oBlockadeofsympatheticefferentsisthemechanismbywhichtheseCVeffectsareproduced.

oThehighertheblock,thegreaterthesympathectomy

oSympathectomyproduces

▪Venouspoolingincapacitancevessels

∙Consequentdecreasedvenousreturntotheheart

∙Decreasedcardiacoutput

▪Arteriolarvasodilation

∙Decreasedperipheralvascularresistance

∙Decreasedbloodpressure

▪Decreaseinheartratemayoccur

∙Duetoblockadeofcardio-acceleratorfibersatT1–T4,leavingunopposedvagaltonetotheheartwhich,combinedwithprofoundhypotension,canprogresstocardiacarrest.

∙Pre-existingheartblockmaybeariskfactorforprogressiontohighergradeblockunderneuraxialanesthesia.

oThedeleteriousCVeffectsshouldbeanticipatedandpreventativemeasurestaken:

▪IVvolumeloading

▪Leftuterinedisplacementinadvancedpregnancy

▪Head-downpositioning

▪Atropineforbradycardia

▪Vasopressorsforhypotension

oAdditionofepinephrinetoepiduralsolutionswillhelpcounteractthecardiovasculareffectsoftheanesthetic.

∙Pulmonary

oPulmonaryalterationswithneuraxialanesthesiaareusuallyminimal（unlesstheblockisveryhigh）becausethediaphragmisinnervatedbythephrenicnerve（C3-C5）withisrarelyblocked.

oPatientswithseverechroniclungdiseasewhorelyontheiraccessorymusclesofrespirationmayexperiencedifficultycoughingandclearingsecretions.Neuraxialanesthesiashouldbeusedwithcautioninsuchpatients.

∙Gastro-intestinal

oSympatheticblockadeallowsdominanceofvagaltoneandresultsinasmallcontractedgutwithactiveperistalsis.

∙Endocrine

oBlockssurgicalstressresponse

oCatecholaminerelease

Indicationsforneuraxialanesthesia

Itcanbeutilizedforanymostanysurgicalprocedurebelowtheneck,butitismostusefulforsurgerybelowtheumbilicus.

Contraindicationsforneuraxialanesthesia

∙Patientrefusal

∙Bleedingdiathesis

∙Severehypovolemia

∙ElevatedICP

∙Infectionatthesiteofinjection

∙SevereaorticstenosisorLVoutflowtractobstruction

Neuraxialblocksandconcomitantanti-coagulantsandanti-plateletdrugs.

Theconcernwiththesedrugsistheriskofspinalhematomawhentheblockisperformedorwhenanepiduralcatheterismanipulatedorremoved.

∙Oralanti-coagulants-Coumadin

oCoumadinmustbestopped5-7dayspriortosurgery,andanormalizedPTandINR（<1.2）mustbedocumentedbeforeneuraxialanesthesiacanbeinitiated.

oIfthepatientreceivedonedoseofcoumadinforDVTprophylaxislessthan24hourspriortotheblock,itisprobablysafetoproceed.Ifthepatientreceivedmorethanonedose,orifthedosewasgivenmorethan24hourspriortotheblock,anormalizedPTandINRmustbedocumented.

oBesidesstoppingCoumadin,oraladministrationofVitaminKoverseveraldayswillhelpnormalizetheINR.Ifthesurgerycannotbedelayed,IVadministrationofFFPshouldbeusedtoprovidecoagulationfactors.

∙Anti-plateletdrugs

oAspirinandNSAIDsdonotappeartoincreasetheriskofspinalhematoma.

oOthersplateletinhibitorsmustbestoppedlongenoughfortheireffectstowearoff:

▪Ticlopidine（Ticlid）—14days

▪Clopidogrel（Plavix）—7days

▪Abciximab（Rheopro）—48hours

▪Eptifibatide（Integrilin）—8hours

∙Unfractionatedheparin

oMinidosesubqheparinisnotacontraindicationtoneuraxialanesthesia.

oBlocksmaybeperformed1hrormorebeforeintraoperativeheparin

oEpiduralcathetersshouldberemoved1hr.priorto,or4hrs.aftersubsequentheparindoses

oAvoidneuraxialanesthesiainpatientsontheraputicdosesofheparinandpatientswithincreasedPTT

oIfepiduralcatheterisalreadyinplacewhenthepatientisheparinized,waittoremovethecatheteruntilheparinisstoppedandcoagsarechecked.

∙Lovenox

oAvoidneuraxialanesthesiainpatientsalreadytakinglovenox

oIfbloodyneedleorcatheterplacementoccurs,delaylovenox24hrs

oRemoveepiduralcatheters2hrs.priortoinitiationoflovenox.Ifalreadypresent,removecatheters10hrsafterlastdoseoflovenox,andwait2hrsbeforeanysubsequentdosing.

ComplicationsofNeuraxialAnesthesia

∙Highblock

oHeraldedbyinabilitytotalk,weakupperextremities

▪Intubatetocontrolventilationandprotectairway.

▪Atropineforbradycardia

▪Volumeexpansionandvasopressorsforhypotension.

∙Cardiacarrestduringspinalanesthesia

oManycaseswereprecededbybradycardia.

oOftenoccurredinyoung,healthypatients,i.e.patientswithhighvagaltone.

oProphylacticvolumeexpansionisrecommended,alongwithaggressivetreatmentofbradycardiawithatropine,andvasopressorsifnecessary.

∙Urinaryretention

oBlockadeofS2-S4footsdecreasesbladdertoneandinhibitsthevoidingreflex.

oTreatment:

Foleycatheterizationuntilbladderfunctionrecovers.

∙Failedblock–nothighenough,notlongenough

∙Intravascularinjectionduringepiduralorcaudalblocks

oHighserumconcentrationsoflocalanestheticsaffecttheCNS（seizures,unconsciousness）andtheCVsystem（hypotension,rhythmandconductionabnormalities）

oMinimizeincidencebycarefullyaspiratingbeforeeveryinjection,usingatestdose,injectinglocalanestheticinincrementaldoses,andobservingforsignsofintravascularinjection.

∙Subduralinjectionduringepiduralanesthesia

oProducesatotalspinal,exceptdelayed15-30minutes

oRequiresintubation,mechanicalventilation,andCVsupport.

∙Backache

oUsuallymildandself-limiting

oUseTylenol,Nsaids,andheatingpad

o25-30%ofpatientsreceivingonlygeneralanesthesiahavepost-operativebackache.Manyalsohavechronicbackpain.

∙Post-DuralPunctureHeadache.（PDPH）

oHeadacheusuallystarts12-72hrsafter