Minimum anesthetic volume in regional anesthesia by using ultrasound-guidance

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Please cite this article in press as: Di Filippo A, et al. Minimum anesthetic volume in regional anesthesia by using ultrasound-guidance.RevBrasAnestesiol.2014.http://dx.doi.org/10.1016/j.bjane.2014.05.002

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BJANE-233; No.ofPages6

RevBrasAnestesiol.2014;xxx(xx):xxx---xxx

REVISTA

BRASILEIRA

DE

ANESTESIOLOGIA

OfﬁcialPublicationoftheBrazilianSocietyofAnesthesiology

www.sba.com.br

SPECIAL

ARTICLE

Minimum

anesthetic

volume

in

regional

anesthesia

by

using

ultrasound-guidance

Alessandro

Di

Filippo

∗

,

Silvia

Falsini,

Chiara

Adembri

DepartmentofHealthSciences,SectionofAnesthesia,IntensiveCareandPainTherapy,UniversityofFlorence,Florence,Italy Received19December2013;accepted6May2014

KEYWORDS Anesthetics,local, conduction-blocking; Anesthetics,local, adverseeffects; Anesthetics,local, dose,ultrasound guidance

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.

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

∗_{Corresponding}_author.

E-mail:adiﬁlippo@uniﬁ.it(A.DiFilippo).

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 successfulblock. Others comparedthe MEAVs obtainedbyanENSandbyaUSGtechnique.3---6

Infact,underthedirectvisualizationofthenerve struc-turesand the real-time control of the spread of LA, the reductionoftheoverallvolumeofanestheticsandthe con-sequentoverdoserisk,ispossible.

http://dx.doi.org/10.1016/j.bjane.2014.05.002

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2 A.DiFilippoetal.

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.7_The_same

authorsthenuseda‘‘step-up/step-down’’modelwith non-probabilitysequentialdosing8_based_on_the_outcome_of_the

previous pilot study.The starting dose of 2% lido-epi was 4mL per nerve. Block failure resulted in a dose increase of0.5mL;blocksuccess inareductionof0.5mLuntilthe achievementofapredeterminedsigniﬁcantnumberof con-tinuoussuccesses.ThismodelforLAdosagewasthenused inmanyotherstudiestodeterminetheMEAV.4mLofLAwas sufﬁcienttoobtainasuccessfulblock.9

Similarly,inanotherstudyaimedatevaluatingtheMEAV for a USG-ABPB10 _in ₁₉ _patients _undergoing_hand _or

fore-arm surgery,the volumeof lidocaine1.5% with1:200,000 epinephrine(1.5%lido-epi)neededtosurroundeachnerve andtoprovide effective analgesiawas of3.42mLfor 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-epi intoa syringedriverandadministratingthroughabolusfunctionat 600mL/h10 _---_the_possibility_to_obtain_a_surgical_block_with

lowvolumeswasconﬁrmed.

González etal.11 _have, _recently, _studied _the_minimum

effective volume of lidocaine for double injection USG-ABPB. Fifty patients were included in the study. Using isotonicregressionand bootstrapconﬁdence interval(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 BrachialPlexus Block (ISBPB)wasaddressed in a random-ized,double-blind,up/downsequentialallocationstudyin 21patientsundergoingshouldersurgery.3_The_MEAV_of_0.5%

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 com-pared with a standard-volume technique both guided by ultrasound. They concluded that the use of low-volume USG-ISBPB is associated withfewer respiratory and other complications with no change in postoperative analge-sia compared withthe standard-volume technique. Renes etal.14_also_conﬁrmed_these_ﬁndings_for_{hemidiaphragmatic}

paresis.

In a study conducted with an up-and-down design to determine theMEAVof0.75%ropivacainerequiredto pro-duceeffective shoulderanesthesiaforUSG-ISPBat theC7 rootlevelin20patientsscheduledforelectiveopen shoul-dersurgeryundercombinedgeneralanesthesia,pulmonary function wasalso investigated.MEAV50 andMEAV95 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_:_the_MEAV

95 was42mLandtheauthorsdeducedthattherequired vol-ume of LAfor USG-SCB does notseem todifferfrom the conventionallyrecommendedvolumeusingnon-USGnerve localizationtechniques.

SubsequentlyTranetal.17_showed_that_the_MEAV

90of1.5% lidocaine with 5␮g/mL epinephrine for double-injection USG-SCBwas32mL.

Thesameauthorsadoptedthe‘‘doublebubble’’signin performingInfraClavicularBlockICB.18_This_technique

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% lidocainewith 5␮g/mL epinephrine.

A2009 study basedon theultrasound 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 comparison between 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.

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Please cite this article in press as: Di Filippo A, et al. Minimum anesthetic volume in regional anesthesia by using ultrasound-guidance. Re v Bras Anestesiol. 2014. http://dx.doi.org/10.1016/j.bjane.2014.05.002

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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 5_␮g/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) None

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Please cite this article in press as: Di Filippo A, et al. Minimum anesthetic volume in regional anesthesia by using ultrasound-guidance. Re v Bras Anestesiol. 2014. http://dx.doi.org/10.1016/j.bjane.2014.05.002

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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:

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Lowerlimb

Fewerstudies weremade toestimatetheMEAV for lower limbblocks.

Casatietal.6_tested_the_hypothesis_that_USG_may_reduce

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 as compared withthe ENS; MEAV95 wasof 22mLfortheUSGgroupandof41mLfortheENSgroup.

Enrollingasampleof60patientsundergoinghipsurgery followingtraumaMarhoferetal.20 _demonstrated_that_USG

canalsoreducetheamountoflocalanestheticforthe3-in-1 blockwhencomparedwithconventionalENStechnique.

Latzkeetal.21 _conducted_the_ﬁrst_randomized,

double-blinded volunteer study designed to evaluate the volume of LAfor asciatic nerveblock usinga step-up/step-down methodology. 20 volunteers were included. The effective dose of1.5% mepivacainefor sciaticnerve blockwas cal-culatedfor0.10mL/mm2_{cross-sectional}_nerve_area.

Danelli et al.5 _tested _the _MEAV _of _1.5% _mepivacaine

required toblock thesciatic nervewitha subglutealUSG approachcomparedwithENS.Forthispurpose,60patients undergoing knee 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 basedon an up-and-down method,accordingtotheresponseofthepreviouspatient. Ultrasoundprovideda37%reductionintheMEAV50 of1.5% mepivacainerequiredtoblockthesciaticnervecompared withENS.TheMEAV95was14mLintheUSGgroupand29mL intheENSgroup.

Discussion

NumerousstudiesemphasizedtheimportanceofUSGinthe managementofperipheralnerveblocks.22---26

However,itis notyetclear whethertheUSGfor nerve locationis superior over other existingmethods. In order toassesstheadvantagesofUSGperipheralnervelocation, Walkeretal. searchedtherelevant publishedtrials,from year 1945 tillyear 2008, comparingUSG peripheral nerve blockwithatleastoneothermethodofnervelocation.18 trialswereincludedcontainingdatafrom1344patientswith mosttrialscomparingUSGwithENS.Meta-analysiswasnot performedduetothevarietyofblocks,techniques,and out-comes,andthereviewwasbasedontheauthors’assessment ofthetrials.Walkeretal.27 _concluded_that_in_experienced

hands,ultrasound provides at least asgood success rates asothermethodsofperipheral nervelocation;itmayalso improveonsettimeandquality,reduce performancetime andcomplication rates particularlyvascular puncture and hematomaformation.

Furthermore, the skills required to perform success-fulultrasound-guidedaxillarybrachialplexusblockcanbe 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.

Unfortunately,theresultsofstudies,conducteduptothis moment,arewidelydivergent andnotseemtoindicatea dose considered effective, for each block, in a deﬁnitive way.In fact, often,there aresinglecenter case histories andthenumberof casesissmall;themethods of 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

Theauthorsdeclarethattheyhavenoconﬂictofinterestin writingthisarticle.

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