REVISTA
BRASILEIRA
DE
ANESTESIOLOGIA
OfficialPublicationoftheBrazilianSocietyofAnesthesiologywww.sba.com.br
SCIENTIFIC
ARTICLE
Determination
of
the
minimum
effective
volume
of
0.5%
bupivacaine
for
ultrasound-guided
axillary
brachial
plexus
block
Leonardo
Henrique
Cunha
Ferraro
∗,
Alexandre
Takeda,
Luiz
Fernando
dos
Reis
Falcão,
André
Hosoi
Rezende,
Eduardo
Jun
Sadatsune,
Maria
Angela
Tardelli
DisciplinadeAnestesiologia,DoreTerapiaIntensiva,EscolaPaulistadeMedicina,UniversidadeFederaldeSãoPaulo,SãoPaulo, SP,Brazil
Received19December2012;accepted20March2013
KEYWORDS
Regionalanesthesia; Brachialplexus; Minimumvolume; Ultrasound; Bupivacaine
Abstract
Backgroundandobjective: Theuseofultrasoundforneedlecorrectplacementandlocal anes-theticspreadmonitoringhelpedtoreducethevolumeoflocalanestheticrequiredforperipheral nerveblocks.Therearefewstudiesoftheminimumeffectivevolumeoflocalanestheticfor axillarybrachialplexusblock.Theaimofthisstudywastodeterminetheminimumeffective volume(VE90)of0.5%bupivacainewithepinephrine(1:200,000)forultrasoundguidedABPB. Method: MasseyandDixon’sup-and-downmethodwasusedtocalculatetheminimumeffective volume.Theinitialdosewas5mLpernerve(radial,median,ulnar,andmusculocutaneous).In caseofblockadefailure,thevolumewasincreasedto0.5mLpernerve.Asuccessfulblockade resulted indecreasedvolume of0.5mLper nervetothe nextpatient. Successfulblockade wasdefined asamotorblock≤2,accordingtothemodified Bromagescale;lackofthermal
sensitivity; and responseto pinprick.The achievement offive casesof failurefollowed by successcaseswasdefinedascriteriontocompletethestudy.
Results:19patientswereincludedinthestudy.Theminimumeffectivevolume(VE90)of0.5% bupivacainewith1:200,000epinephrinewas1.56mL(95%CI,0.99---3.5)pernerve.
Conclusion: Thisstudy isinagreementwithsomeotherstudies,whichshowthatitis possi-bletoachievesurgicalanesthesiawithlowvolumesoflocalanestheticforultrasound-guided peripheralnerveblocks.
© 2013SociedadeBrasileirade Anestesiologia.Publishedby ElsevierEditoraLtda.Allrights reserved.
∗Correspondingauthor.
E-mail:leohcferraro@yahoo.com.br(L.H.C.Ferraro).
Introduction
Brachialplexusblockisananesthetictechniqueoftenused
forupperlimbsurgicalprocedures.Axillarybrachialplexus
block(ABPB)isoneofthemostcommonlyusedtechniquesto
achieveupperlimbregionalanesthesiaanditisperformed
byblocking the terminal branchesof the brachialplexus,
which include the musculocutaneous, ulnar, median, and
radialnerves.Itwasbelievedthatthefailuresorincomplete
blockadedue tothis techniquewere theresult ofneedle
malpositionorbrachialplexusseptaintheaxillaryregion.1---3
Toincreasethesuccessrate,volumeupto80mLhavebeen
reported.4However,theuseoflargevolumesoflocal
anes-theticincreasesthelikelihoodofsystemictoxicity.5,6Thus,a
possibletechniquetopreventthiscomplicationandincrease
patient safety would be to reduce the mass of the local
anestheticusedduringtheprocedure.
Currently,technologiessuchasperipheralnerve
stimu-latorandultrasoundensuretheneedlecorrectpositioning
in relation to the complex and reduce the need for high
volumesof local anesthetic.7---13 Some studies have shown
thattheuseofultrasoundreducedthevolumeoflocal anes-theticforinterscalenicbrachialplexusblock,femoralnerve
block,andilioinguinal/iliohypogastricnerve blockwithout
compromisingthe quality.However,therearefew studies
of the minimum effective volume of local anesthetic for
ABPB.Therefore,thisstudywasperformedinorderto
calcu-latetheminimumeffectivevolumeof5%bupivacainein90%
(VE90)ofcasesreceivingultrasound-guidedaxillarybrachial plexusblock.
Method
Study conducted at the surgical center of the Hand and
UpperLimb Unit, withthe coordinationof the anesthesia
servicefortheanesthesiology,intensivecareandpain
dis-cipline,UniversidadeFederaldeSãoPaulo/EscolaPaulista
de Medicina, from December 2011 to June 2012. The
studywasregisteredatClinicaltrials.govunderthenumber
NCT01421914.
AfterapprovalbytheEthicsCommitteeofthe
Universi-dadeFederaldeSãoPaulo,patients scheduledtoundergo
handsurgerywereinvitedtoparticipateinthestudy.
Inclu-sioncriteriawereageover18andunder65years,informed
consent(IC)signedby thepatient,indication for brachial
plexus block (anesthesia and analgesia) in candidates for
elective hand surgery lasting less than 2h, ASA physical
statusIorIIaccordingtotheAmericanSocietyof Anesthe-siologists,andbodymassindex(BMI)<35kg/m2.Exclusion
criteria were cognitive impairment or active psychiatric
condition,infectionattheblockadepuncturesite,bleeding
disorders,andhistoryofallergytobupivacaine.
Protocoldesign
Afterinclusion in the study, all patients had their
demo-graphicsrecorded,followedbyroutinesurgicalmonitoring
withECG,noninvasivebloodpressure,andpulseoximetry.
Intravenousaccesswasmadeintheupperlimbcontralateral
totheprocedureandmaintainedwithcrystalloidinfusion.
Axillarybrachialplexusblockwasperformedusing
ultra-sound(M-Turbo R System with HFL38×linear transducer
6---13MHz, SonoSite, Bothell, WA USA) and a peripheral
nerve stimulator (Stimuplex R DIG RC, B. Braum,
Mell-sung, Germany), with the patient in the supine position.
Theneedleusedwasa22G×50mm(AEQ2250,BMDGroup,
Venezia,Italy). Afterdisinfectionand skin antisepsiswith
chlorhexidine, the puncture site was infiltrated with 1%
lidocaine. After brachial plexus nerve visualization using
ultrasound, theidentification of structureswas confirmed
withaperipheralnervestimulator.Astartingdoseof5mLof
0.5%bupivacainewith1:200,000epinephrinewasinjected
aroundeachnerve.Theneedlewasrepositionedduringlocal
anestheticinjection,andepiduralinjectionwasensuredby
ultrasound image. The patient would have been removed
fromthestudyiftherewereavisualchangeinnerve
diam-eter or if there were a significant pain during injection.
Inthesecases,patientswerefollowed postoperativelyfor
possibleintraneuralinjection.
Theendoflocalanestheticinjectionwasconsideredtime
zerotoassesstheblockadeeffectiveness.Anobserverwho
wasnot present duringthe procedureand wasblindedto
thevolumeofanesthetic usedevaluatedthenerveblocks
studied.Thisassessmentwasdoneeveryfive5minuntil
sur-gical anesthesia wasachieved or up to30min after local
anestheticinjection.
Theblockadesuccess orfailureledtothereductionor
increase in the volume of local anesthetic for the next
patient, respectively. When the blockade wasconsidered
effective, the subsequentpatientreceived areduction of
0.5mL in the local anesthetic volume. In case of
block-ade failure, patients received supplemental block at the
elbowlevel, andthelocalanestheticvolumefor thenext
patient was increased by 0.5mL. After blockade
evalua-tion,thepatientswerereleasedtothesurgicalprocedure.
During the surgical procedure, patients received propofol
15---25mcg/kg/min for sedation. Moreover, if the patient
reportedpainduringtheprocedure,theblockadewas
con-sideredasafailureandgeneralanesthesiawasperformed.
After surgery, the patient was admitted to the
post-anesthesiacareunit(PACU)andremainedmonitored(ECG,
noninvasive blood pressure, and pulse oximetry) until
meeting therequired conditions for outpatientdischarge.
Postoperative analgesia was assessedin thePACU using a
visualanalogscale3haftertheblockade.
AssessmentofABPBsuccess
A successful blockade was considered when there were
motorfunction≤2accordingtothemodifiedBromagescale,
lack ofthermal sensitivityandresponsetopinprickin the
regionsofthemedian,ulnar,musculocutaneous,andradial
nerves. Furthermore,theprocedure shouldbe done
with-outadditionalanalgesiatoconfirmtheanestheticprocedure success.
Assessmentofmotorfunction
Formotorfunctionevaluation,themodifiedBromagescale
wasused(Table1).
Thefollowingtestswereusedtoassessmotorfunction:
fingerflexion(mediannerve),wristextension(radialnerve),
thumbadduction(ulnarnerve),andelbowflexion
(muscu-locutaneous nerve). Values ≤2 according to the modified
Table1 ModifiedBromagescale.
Grade Definition
4 Fullmusclestrengthinrelevant
musclegroups
3 Reducedstrength,butabletomove
againstresistance
2 Abilitytomoveagainstgravity,but
notagainstresistance
1 Discretemovements(trembling)of
musclegroups
0 Lackofmovement
Assessmentofthermalsensitivity
Theevaluation ofupperlimbthermal sensationwasmade withgauze and alcohol totest the sensitivity of the der-matomesinnervatedby theulnar (hypothenareminence), median(thenareminence),radial(dorsumofthehand),and musculocutaneous(baseofthefirstmetacarpal)nerves.The coldsensationwasregardedas1andlackofcoldsensation as0.Asuccessfulblockadewasconsideredwhentherewas noperceptionofcoldinthedermatomesstudied.
Assessmentofpainsensitivity
Theevaluationofupperlimbpainsensationwasperformed withthepinpricktestusinga23Gneedletotestsensitivity atthedermatomesareasoftheulnar,median, musculocu-taneous,andradialnerves.
Positive response to pinprick was considered as1 and lackofresponsetopinprickas0.Asuccessfulblockadewas regardedasthelackpinpricksensationinthedermatomes evaluated.
Criteriatocompletethestudy
The criterion to complete the study was defined as the achievement of five cases of failure followed by success cases.
Statisticalanalysis
Theminimumeffectivevolumeof0.5%bupivacainewas esti-matedusingtheup-and-downsequencesproposedbyDixon andMassey,focusingonanalysisoftheminimumeffective volumewith50%probabilityofaneffectivenerveblock.14,15
Subsequently,thesequenceswerealsoevaluatedusing
pro-bit regression to determine the effective volumes in 90%
of cases. Nonparametric data were expressed as median
andquartiles(P25---P75).Categoricaldatawereexpressedas
absoluteandrelativefrequencies.Calculationsweremade
in Microsoft Excell spreadsheet for WindowsTM (Microsoft
Corp.,Redmond,WA,USA)andGraphPadPRISMTMfor
Win-dows(GraphPadSoftwareInc,SanDiego,CA,USA).
Table2 Demographiccharacteristicsofpatients.
Age(years) 36.5(27.5---46.5)
Gender(M:F) 14:5(M:F)
ASA
I 12
II 7
Table3 Distributionofsurgicalprocedures.
Procedures n(%)
Metacarpalfracture 5(26)
Synthesismaterialremoval 1(5)
Extensorinjury 3(16)
Scaphoidfracturerepair 1(5)
Synovectomy 3(16)
Dupuytren 2(11)
Flexorinjury 1(5)
Pseudoarthrosisofthephalanx 2(11)
Excisionofbonetumor 1(5)
Duration,min(P25---75) 65(50---77.5)
Results
Thestudyprotocolincluded19patients.Inallpatientsitwas possibletovisualizethe anatomicalstructuresrelevant to theblockade.Thestudyendedwhentherewasasequence offivecyclesoffailure/success.The demographic charac-teristicsofpatientsandsurgicalproceduresperformedare showninTables2and3,respectively.
The sequence of positive and negative responses to
theblocksin consecutivepatients is shownin Fig.1. The
VE90 of 0.5% bupivacaine with1:200,000 epinephrine for
ultrasound-guidedaxillarybrachialplexusblockwas1.56mL (95%confidenceinterval[CI]:0.99---3.5).
The median latency of effective blockades was20min
(10---30).Whenonlytheblockadeswithvolumesof1mLwere
considered, the median latency was 25min (20---30). For
6
5
4
3
2
1
0
1 2 3 4 5 6 7 8 9 10
Sequence of patients
0.5% b
upiv
acaine with 1:200,000 epinephr
ine (mL)
11 12 13 14 15 16 17 18 19
surgicalproceduresinwhichblockadesweremadewith1mL pernerve,themediandurationwas60min(35---75).Duration
ofsensoryandmotorblockwasnotassessedinthisstudy.
Thesurgicalprocedurewasuneventfulinallpatientsin
whomthe blockade wasconsidered successful,and there
wasnoneedforadditionalanesthetic.
Regardingpostoperative analgesia,nopatientreported
pain up to 3h after the blockade. There were no
complicationssuchasvascularpunctureorlocalanesthetic
intoxicationduringthestudy.Allpatientsweredischarged
onthesamedayoftheprocedureandtherewasnocaseof
hospitalreadmission.
Discussion
Inmodernpracticeofregionalanesthesia,reductionsinthe
volumeanddoseoflocalanesthetichavebecomeimportant
strategiestopreventsystemictoxicitybylocalanesthetics.
Therefore, the use of ultrasound toguide the precise
location of local anesthetic injection in peripheral nerve
blockshasbecomeincreasinglyfrequent.Theadvancement
inultrasoundequipmentandmethodsenabledthe
identifi-cationofvascularandneuralstructureswithhighaccuracy,
benefits compared to classical techniques, lower failure
rate,andreductionoflocalanestheticdosage.16
Theaxillaryapproachtobrachialplexusblockwaschosen
forthisstudybecauseitisoneofthemostusedtechniques inclinicalpractice.Consideringtheterritoryofanesthesia providedbythisblockade,onlypatientsundergoingsurgical
proceduresinthehandswereselected.
Dueto lack ofknowledge about the blockadeduration
withlowvolumesofbupivacaine,it wasdecidedtoselect
procedureslastinglessthan2h.
Thisstudydemonstratedthatwiththeuseofultrasound
itispossibletoperformthebrachialplexusblockachieved
byaxillary approach withaminimum effective volumeof
0.5%bupivacainewith1:200,000epinephrine(1.56mL)for
eachnerveinhandsurgery.
O’DonnelandIohomreportedeffectiveblockadeofthe
brachialplexusviaaxillaryroutewith1mLof2%lidocaine
with 1:200,000 epinephrine per nerve. However, one of
the study’slimitations, reportedby the authors, wasthe
choice of superficial procedures such as synovectomy or
tenorraphies.17Marhoferetal.describedtheABPBwith
sim-ilarvolumesof1%mepivacaine.18 However,thiswasjusta
volunteerstudy inwhich surgical anesthesiawasassessed
only by pinprick test. In our study, even with low doses
of localanesthetic, it waspossible to performsuperficial
procedures, such as thumb extensor injury, and surgery
withbonystructuresmanagement,suchasthirdandfourth
metacarpalfractures,showingthat,despitethedecreased
dose,itwasalsopossibletoperformproceduresinvolving
deepstructuresofthehand.
The choice of bupivacaine was made due to its
phar-macokinetic characteristics, which provide longer lasting
blockadecomparedtolidocaine.Ontheotherhand,
block-adeswithhigherlatencywereachievedwhencomparedwith
theresultsfromthestudybyO’DonnellandIohom.17
According to Hadzic, the use of low volumes of local
anestheticmayresultinintraneuralinjectionbecauseitis difficultto visualizean increasein nervediameter inthis
situation.19 Inordertoavoidthiscomplication,the
visual-ization of nerveand adjacent structures,as well aslocal
anestheticspreadbyultrasound,isanimportantfactor.
Ourstudyreaffirmsthattheminimumeffectivevolume
for ABPB is smaller than that described previously. One
possibleexplanationforthisfactisthatwiththeaidof
ultra-sound,itispossibletoperformadynamicblockade,which
involves the entire nerveperipherywithlocal anesthetic.
The ultrasoundallowstheanesthesiologistvisualization of
thenerveduringtheblockade,whichallowsredirectionof
theneedleandlocalanestheticinjectionintheentirenerve
periphery,allowingeffectiveblockadeswithlowvolumesof
localanesthetic.
Somestudies haveshown thatlow dosesof local
anes-theticdecreasedtheblockadeduration,definedasthetime
betweentheonsetofblockadeinstallationandthereturnof
motorandsensoryfunctions.20Alimitationofourstudywas
thatwedidnotassesstheblockadedurationwith0.5%
bupi-vacaine,we justfound thatthe blockades withlow doses
of local anesthetic were sufficient toperform the
proce-dureswithlessthan2hdurationandthatallblockadeshad
alatencylessthanorequalto30min.
The use of low doses of local anesthetic provides a
safer blockade,with lessrisk of complications, especially
relatedtothesystemictoxicityoflocalanesthetics.Despite
thedevelopmentofeffectiveapproachesfortreatingthese
complications,suchastheuseoflipidemulsions,21,22 the
useoflocalanesthetics atlowdosespromotes ablockade
withananestheticmasswithawiderangeofsafetyforthe
toxicdose.
Theuseoflowdosesoflocalanestheticprovidesasafer
blockade,withless riskof complications,especiallythose
relatedtothesystemictoxicityoflocalanesthetics.Despite
thedevelopmentofeffectiveapproachesfortreatingthese
complications,suchastheuseoflipidemulsions,21,22 the
useoflocalanesthetics atlowdosespromotes ablockade
withananestheticmasswithawiderangeofsafetyforthe
toxicdose.
Insummary,thisstudyshowsthattheVE90
ultrasound-guidedABPBis1.56mLof0.5%bupivacainewith1:200,000
epinephrinepernerve.Thiscorroboratessomestudies
show-ing that it is possible to obtain peripheral nerve blocks
withlowvolumesoflocalanesthetic.Additionalstudiesof
dose---responseshouldbeconductedtoassesstheinfluence
ofbupivacaineconcentrationforthistechnique.
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
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