RevBrasAnestesiol.2016;66(5):499---504
REVISTA
BRASILEIRA
DE
ANESTESIOLOGIA
PublicaçãoOficialdaSociedadeBrasileiradeAnestesiologiawww.sba.com.br
SPECIAL
ARTICLE
Minimum
anesthetic
volume
in
regional
anesthesia
by
using
ultrasound-guidance
Alessandro
Di
Filippo
∗,
Silvia
Falsini,
Chiara
Adembri
DipartimentodiScienzedellaSalute,SezionediAnestesiologia,TerapiaIntensivaeTerapiadelDolore, UniversitàdegliStudidiFirenze,Florence,Italy
Received19December2013;accepted6May2014 Availableonline2June2014
KEYWORDS
Anesthetics,local, conduction-blocking; Anesthetics,local, adverseeffects; Anesthetics,local, dose;
Ultrasoundguidance
Abstract Theultrasoundguidanceinregionalanesthesiaensuresthevisualizationofneedle
placementandthespreadofLocalAnesthetics.
OverthepastfewyearstherewasasubstantialinterestindeterminingtheMinimum Effec-tiveAnestheticVolumenecessarytoaccomplishsurgicalanesthesia.Thepreciseandreal-time visualizationofLocalAnestheticsspreadunderultrasoundguidanceblockmayrepresentthe bestrequisiteforreducingLocalAnestheticsdoseandLocalAnesthetics-relatedeffects.
Wewillreportaseriesofstudiesthathavedemonstratedtheefficacyofultrasound guid-anceblockstoreduceLocalAnestheticsandobtainsurgicalanesthesiaascomparedtoblock performedunderblindorelectricalnervestimulationtechnique.
Unfortunately,theresultsofstudiesarewidelydivergentandnotseemtoindicateadose consideredeffective,foreachblock,inadefinitiveway;butitistruethat,throughtheuse ofultrasoundguidance,itispossibletoreducethedoseofanestheticintheperformanceof anestheticblocks.
©2014SociedadeBrasileiradeAnestesiologia.Publishedby ElsevierEditoraLtda.Thisisan openaccessarticleundertheCCBY-NC-NDlicense( http://creativecommons.org/licenses/by-nc-nd/4.0/).
PALAVRAS-CHAVE
Anestésicoslocais, bloqueioda conduc¸ão;
Anestésicoslocais, efeitosadversos; Anestésicoslocais, dose;
Guiadoporultrassom
Volumemínimodeanestésicoemanestesiaregionalguiadaporultrassom
Resumo Ousodeultrassomemanestesiaregionalpermitevisualizaracolocac¸ãodaagulhae
apropagac¸ãodosanestésicoslocais.
Nos últimos anoshouve um grande interesseem determinaro volume mínimo eficaz de anestésiconecessárioparafazeraanestesiacirúrgica.Avisualizac¸ãoprecisaeemtemporeal da difusãodosanestésicos locaiscomo usode ultrassompodeser omelhorrequisito para reduziradoseeosefeitosrelacionadosaosanestésicoslocais.
∗Correspondingauthor.
E-mail:adifilippo@unifi.it(A.DiFilippo).
http://dx.doi.org/10.1016/j.bjane.2014.05.002
500 A.DiFilippoetal.
Revisamosumasériede estudosquerelataram aeficáciadebloqueios guiadospor ultra-ssomparareduzirousodeanestésicoslocaiseobteranestesiacirúrgica,emcomparac¸ãocom bloqueiosfeitoscomatécnicaàscegasedeestimulac¸ãoelétricadenervos.
Infelizmente,osresultadosdosestudossãomuitodivergentesenão parecemindicaruma doseconsiderada eficazpara cadabloqueio demododefinitivo, mas éverdadeque,como auxíliodoultrassom,épossívelreduziradosedosanestésicosembloqueios.
©2014SociedadeBrasileiradeAnestesiologia.PublicadoporElsevierEditoraLtda.Este ´eum artigoOpen Accesssobumalicenc¸aCCBY-NC-ND( http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
When traditional block techniques are used, the total amountofLocalAnesthetics(LA)injectedisoftentooclose tothethresholddoseofadverse/toxicreactionsespecially incaseofaccidentalvenouspuncture.
A new frontier for regional anesthesia is offered by the possibility to perform nerve blocks under ultrasound guidance(USG),whichallowsidentificationofnerve struc-tures. The LA dose needed in such cases is lower than theonenormallyusedinablind or inan ElectricalNerve Stimulation(ENS)technique.1,2
Somerecentstudieshavebeendesignedtocalculatethe MinimumEffectiveAnestheticVolume(MEAV)ofLAneeded toobtain a successful block.Others compared theMEAVs obtainedbyanENSandbyaUSGtechnique.3---6
Infact,underthedirectvisualizationofthenerve struc-tures and the real-time control of the spread of LA, the reductionoftheoverallvolumeofanestheticsandthe con-sequentoverdoserisk,ispossible.
In this review the actual knowledge about MEAV is describedanddiscussed.
Methods
AlltherandomizedprospectiveclinicaltrialsinwhichUSG were usedto achieve peripheral blockswith keywords in pubmedsearch‘‘Minimal+Effective+Anesthetic+Volume’’ and,‘‘Minimum+Effective+Anesthetic+Volume’’were col-lected.ThenthepublicationsweredividedbyLAdoses,by mainstudymethodandbysiteofblockandweredescribed (Table1).
Results
Upperlimb
ForUSGAxillaryBrachialPlexusBlock(ABPB),O’Donnelland Iohomreportedsuccessfulblockswithaslittleas1mLof2% lidocainewith1:200,000epinephrine(2%LidoEpi)pernerve in a group of 11 consecutive patients submitted to hand surgery. The LA wasadministrated by a perineural injec-tion,circumferentiallyaroundeachnerve.Theblockonset wasof10minwithameandurationof190min.7Thesame authorsthenuseda‘‘step-up/step-down’’modelwith non-probabilitysequentialdosing8basedontheoutcomeofthe previous pilot study.The starting dose of 2% lido-epi was
4mL per nerve. Block failure resulted in a dose increase of0.5mL;blocksuccessina reductionof 0.5mLuntilthe achievementofapredeterminedsignificantnumberof con-tinuoussuccesses.ThismodelforLAdosagewasthenused inmanyotherstudiestodeterminetheMEAV.4mLofLAwas sufficienttoobtainasuccessfulblock.9
Similarly,inanotherstudyaimedatevaluatingtheMEAV for a USG-ABPB10 in 19 patients undergoinghand or fore-arm surgery, the volumeof lidocaine1.5% with1:200,000 epinephrine(1.5%lido-epi)neededtosurroundeachnerve and toprovide effective analgesiawasof 3.42mL for the radial, 2.75mL for the median, 2.58mL for the ulnar, and 2.3mL for the musculocutaneous nerve. Although in everydaypracticeisitnoteasytoachievesuchprecise vol-umes--- thatwereobtainedbyloading1.5%lido-epiintoa syringedriverandadministratingthroughabolusfunctionat 600mL/h10 ---thepossibilitytoobtainasurgicalblockwith lowvolumeswasconfirmed.
Gonzálezetal.11 have, recently, studied the minimum effective volume of lidocaine for double injection USG-ABPB. Fifty patients were included in the study. Using isotonicregression andbootstrap confidenceinterval(CI), theMEV90wasestimatedtobe5.5mL(95%CI,3.0---6.7mL) and 23.5mL (95% CI, 23.1---23.9mL) for the musculocuta-neousandperivascularinjection,respectively.
The question of whether USG can reduce the required volume of LA when compared with ENS for Interscalene Brachial PlexusBlock (ISBPB) wasaddressed in a random-ized,double-blind,up/downsequentialallocationstudyin 21patientsundergoingshouldersurgery.3TheMEAVof0.5% ropivacainewas0.9mLintheUSGgroupand5.4mLinthe ENSgroup(p=0.034)thusdemonstratingthatultrasoundnot onlyreducestheLAvolume,butalsothenumberofattempts andpostoperativepainwhencomparedwithENSforISBPB. In2011,Gautier etal. investigatedthe MEAVfor ISBPB in 20 patients scheduled for shoulder surgery. Using the previously cited step-up/step-down method, the authors determined that 5mL of 0.75% ropivacaine, or approxi-mately 1.7mLforeachofthethreetrunksofthebrachial plexus (superior, middle, and inferior) were sufficient to accomplishsurgicalanesthesia.12
Furthermore,theMEAVcouldcontributetoreduceISBPB complications.
In 2008 Riazi et al.13 had examined the incidence
of phrenic nerve palsy with a low-volume ISBPB
US guidance allows to reduce anesthetic dosage 501
Table1 StudiesonMinimumEffectiveAnesthesticVolumeevaluatedforthereview:methods,numberofpatients,typeofblockandsurgery,typeoflocalanesthetic,dosage
andobservedcomplicationsaredescribedandcompared.
Methods Comparison Numberof patients
Interventions Surgery Localanesthetic LAdoses(mL)or mL/sectionalarea (mL/mm2)
Complications
O’Donnel 2009
DixonandMassey step-up/stepdown 11 Axillary brachialplexus block Handor forearm surgery Lidocaine 2%+epinephrine 1:200.000
4mL None
Harper2010 Pilotstudy 19 Axillary brachialplexus block Handor forearm surgery Lidocaine 1.5%+ epine-phrine 1:200,000
2---4mLto surroundeach nerve González 2013 Prospective, randomizedstudy
DixonandMassey step-up/stepdown 50 Double-injection axillaryblock Handor forearm surgery lidocaine1.5% withepinephrine 5g/mL
MEAV90:5.5mL
and23.5mL
None
Gautier 2011
Prospective, randomizedstudy
DixonandMassey step-up/stepdown 20 Interscalene brachialplexus block Arthroscopic shoulder surgery
Ropivacaine0.75% 5mL;1.7mLfor eachofthethree trunks
McNaught 2011
Randomized double-blindstudy
USGvsENS guidance/Dixon andMassey step-up/stepdown 40 Interscalene brachialplexus block Post-operative analgesiain shoulder surgery
Ropivacaine0.5% MEAV50:0.9mL
(US)vs5.4mL(NS)
Nodifferences
Renes2010 Prospective,observer andpatientblinded trial
DixonandMassey step-up/stepdown 20 Interscalene brachialplexus block Openshoulder surgery
Ropivacaine0.75% MEAV95:3.6mL Hemidiaphragmatic
paresis:None2h aftersurgery;55% follow-up24h Duggan2009 DixonandMassey
step-up/stepdown 21 Supraclavicular block Upperlimb surgery Lidocaine 2%+bupivacaine 0.5%with Epinephrine
MEAV50:23mL
MEAV95:42mL
Tran2011 Prospective,single blindedstudy
DixonandMassey step-up/stepdown 55 Infraclavicular block Upperlimb surgery Lidocaine 1.5%+ epine-phrine 5mcg/mL
MEAV90:35mL Vascularepuncture, n(%):1(1.8)
Ponrouch 2010
Prospective, randomizeddouble blindedstudy
USGvsENS guidance/Dixon andMassey step-up/stepdown
42 Medianand ulnarnerve block
Carpaltunnel surgery
Mepivacaine1.5% Median/ulnar nerve:MEAV50
2mL
None
Casati2007 Prospective, randomizeddouble blindedstudy
USvsENSguidance 60 Femoralnerve block
Knee arthroscopic
Ropivacaine0.5% MEAV50:15mL
(USG)vs26mL (ENS)ED95:
22mL(USG)vs 41mL(ENS)
502
A.
Di
Filippo
et
al.
Table1(Continued)
Methods Comparison Numberof patients
Interventions Surgery Localanesthetic LAdoses(mL)or mL/sectionalarea (mL/mm2)
Complications
Marhofer 1998
USvsENSguidance 60 3in1block Hipsurgery Bupivacaine0.5% 20mL Latzke2010 DixonandMassey
step-up/stepdown
20 Sciaticnerve block
Volunteers Mepivacaine1.5% MEAV50:0.04mL;
MEAV95:0.08mL;
MEAV:0.1mL
None
Danelli2009 Prospective,
randomized,up-down sequentialallocation, singleblindedstudy
USvsENSguidance 60 Sciaticnerve block
Knee arthroscopic
Mepivacaine1.5% MEAV50:
12mL(USG)vs 19mL(ENS)MEAV: 14mL(USG)vs 29mL(ENS)
None
Eichenberger 2009
Prospective, randomizeddouble blindedstudy
DixonandMassey step-up/stepdown
17 Ulnarnerve block
Healty volunteers
Mepivacaine1% mL/crosssectional area:MEAV50:
0.08mL/mm2
MEAV95:
USguidanceallowstoreduceanestheticdosage 503
complications with no change in postoperative analge-sia compared withthe standard-volume technique. Renes etal.14alsoconfirmedthesefindingsforhemidiaphragmatic paresis.
In a study conducted with an up-and-down design to determinetheMEAV of0.75%ropivacainerequiredto pro-duceeffectiveshoulder anesthesiaforUSG-ISPBatthe C7 rootlevelin20patientsscheduledforelectiveopen shoul-dersurgeryundercombinedgeneralanesthesia,pulmonary function wasalso investigated.MEAV50 and MEAV95 of the
patientswere2.9and3.6mL,respectively.Pulmonary func-tionwasunchangeduntil2haftersurgerycompletion,but reduced22hafterthestartofacontinuousinfusionof ropi-vacaine0.2%.15
TheMEAVrequiredforUSGSupra-ClavicularBlock(SCB) forsurgicalanesthesiausinga50:50mixtureof2%lidocaine and 0.5% bupivacaine withepinephrine wasstudied in 21 adultsundergoingelectiveupperlimbsurgery16:theMEAV
95
was42mLandtheauthorsdeducedthattherequired vol-ume of LAfor USG-SCB does notseem to differfrom the conventionallyrecommendedvolumeusingnon-USGnerve localizationtechniques.
SubsequentlyTranetal.17showedthattheMEAV
90of1.5%
lidocaine with 5g/mL epinephrine for double-injection
USG-SCBwas32mL.
Thesameauthorsadoptedthe‘‘doublebubble’’signin performingInfraClavicularBlockICB.18Thistechnique con-sists in exploring the axillary artery in short axis at the infraclavicularfossa;withanin-planeapproachtheneedle isplacedattheposteriorpoleoftheaxillaryarteryataround 6o’clock.Then,atestvolumeisinjectedtoensurethe cor-rectplacementofthetipoftheneedle,whichshouldcreate a ‘‘double bubble’’ sign. With this method, Tran et al.18 found a MEAV90 of 35mL for 1.5% lidocaine with 5g/mL
epinephrine.
A 2009 study basedonthe ultrasound measured
cross-sectional area calculated a mean volume of 0.7mL
(0.11mL/mmofcross-sectionalarea)of1%mepivacaineto blocktheulnarnerveattheproximalforearm.19
Ponrouch et al.4 designed a randomized, double-blind controlled comparisonbetween ENS and USG to estimate the MEAV of 1.5% mepivacaine in median nerve blocks. Twenty-one patients scheduled for carpal tunnel release wereenrolledwithastep-up/step-downstudymodel.The authors found that USG provided a 50% reduction in the MEAVincomparisonwithENSandthatdecreasingtheLA vol-umecandecreasesensoryblockdurationbutnottheonset time.
Lowerlimb
Fewerstudies weremade toestimatetheMEAV for lower limbblocks.
Casatietal.6testedthehypothesisthatUSGmayreduce MEAV of 0.5% ropivacaine required to block the femoral nervecomparedwithENS. Sixtypatients undergoingknee arthroscopywereenrolled.Thevolumeoftheinjected solu-tion was regulated for consecutive patients based on an up-and-downstaircasemethodaccordingtotheresponseof theprevious patient.USG guidanceprovideda42% reduc-tionintheMEAVof0.5%ropivacainerequiredtoblockthe
femoral nerve ascompared with the ENS; MEAV95 was of
22mLfortheUSGgroupandof41mLfortheENSgroup. Enrollingasampleof60patientsundergoinghipsurgery followingtraumaMarhoferetal.20 demonstratedthatUSG canalsoreducetheamountoflocalanestheticforthe3-in-1 blockwhencomparedwithconventionalENStechnique.
Latzkeetal.21 conductedthefirstrandomized, double-blinded volunteerstudy designed toevaluate the volume ofLAfor a sciaticnerve blockusing astep-up/step-down methodology. 20 volunteers were included. The effective doseof 1.5% mepivacainefor sciaticnerveblock was cal-culatedfor0.10mL/mm2cross-sectionalnervearea.
Danelli et al.5 tested the MEAV of 1.5% mepivacaine requiredtoblock the sciaticnerve withasubgluteal USG approachcomparedwithENS.Forthispurpose,60patients undergoingknee arthroscopy were randomly allocated to receive a sciatic nerve block with either USG (n=30) or ENS (n=30). Again the volume of 1.5% mepivacaine was variedfor consecutive patients based onan up-and-down method,accordingtotheresponseofthepreviouspatient. Ultrasoundprovideda37%reductionintheMEAV50 of1.5%
mepivacainerequiredtoblockthesciaticnervecompared withENS.TheMEAV95was14mLintheUSGgroupand29mL
intheENSgroup.
Discussion
NumerousstudiesemphasizedtheimportanceofUSGinthe managementofperipheralnerveblocks.22---26
However,itisnotyet clearwhethertheUSG fornerve locationis superior over other existing methods. In order toassesstheadvantagesofUSGperipheralnervelocation, Walkeretal.searchedthe relevantpublishedtrials, from year1945 till year 2008,comparing USGperipheral nerve blockwithatleastoneothermethodofnervelocation.18 trialswereincludedcontainingdatafrom1344patientswith mosttrialscomparingUSGwithENS.Meta-analysiswasnot performedduetothevarietyofblocks,techniques,and out-comes,andthereviewwasbasedontheauthors’assessment ofthetrials.Walkeretal.27concludedthatinexperienced hands,ultrasound providesat least asgood success rates asothermethodsofperipheralnervelocation;itmayalso improveonsettimeandquality, reduceperformance time andcomplicationrates particularly vascular punctureand hematomaformation.
Furthermore, the skills required to perform success-fulultrasound-guidedaxillary brachialplexusblockcanbe learntfasterandleadtoahigherfinalsuccessratecompared tonervestimulator-guidedaxillarybrachialplexusblock.28
On the other hand, theuse of ultrasoundenabled the direct visualization of LA spread around the nerve struc-tures; this revolutionary real-time procedural assessment allowedthestudyofthecorrelationbetweentheLAdosage and the efficacy of the peripheral nerve block.1,2 In this reviewweincluded thestudiesthatinvestigatedtheMEAV for surgical anesthesia.3---7,9---21 We divided the studies by blocktype,brieflydiscussedeachofthemandsummarized inTable1theresults.
504 A.DiFilippoetal.
way.In fact, often,there aresinglecenter case histories andthenumberof casesissmall;the methodsof investi-gationarealsodifferentandanesthetictechniquesarenot standardized.
Conclusion
Through the use of ultrasound guidance, it is possible to reducethedoseofanestheticintheperformanceof anes-theticblocks.Inouropinion,theLAdosereductionmaybe averyrelevant contributiontheUSGcanoffertoregional anesthesia.
However, more homogeneous studies should be
per-formedtoidentifytheMEAV foreach kindofnerveblock; techniquesanddrugadministrationshouldbestandardized inordertoreduceconfoundingfactorssothatreliable meta-analyseswouldbeperformed.
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
References
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