Effects of vasoactive drugs on crystalloid fluid kinetics in septic sheep

13 Pages·2017·2.21 MB·English

RESEARCHARTICLE
Effects of vasoactive drugs on crystalloid fluid
kinetics in septic sheep
YuhongLi1,2☯,ZhengXiaozhu3☯,RuGuomei2,DingQiannan2,RobertG.Hahn4*
1 DepartmentofAnesthesiology,ShaoxingPeople’sHospital,Shaoxing,ZhejiangProvince,PRofChina,
2 ResearchCenter,ShaoxingPeople’sHospital,Shaoxing,ZhejiangProvince,PRofChina,3 The
DepartmentofAnesthesiology,ZhejiangHospital,Hangzhou,ZhejiangProvince,PRofChina,4 Research
Unit,So¨derta¨ljeHospital,So¨derta¨lje,Sweden
☯Theseauthorscontributedequallytothiswork.
*[email protected]
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a1111111111 Abstract
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Purpose
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Crystalloidfluidandvasoactivedrugsareusedintheearlytreatmentofsepsis.Thepurpose
ofthepresentstudywastoexaminehowthesedrugsalterplasmavolumeexpansion,
peripheraledema,andurinaryexcretion.
OPENACCESS
Methods
Citation:LiY,XiaozhuZ,GuomeiR,QiannanD,
HahnRG(2017)Effectsofvasoactivedrugson Twenty-fiveanesthetizedsheepweremadesepticbycecalpunctureandashortinfusionof
crystalloidfluidkineticsinsepticsheep.PLoSONE lipopolysaccharide.After50min,aslowinfusionofisotonicsalinewasinitiated:thesaline
12(2):e0172361.doi:10.1371/journal.
eithercontainednodrug,norepinephrine(1μg/kg/min),phenylephrine(3μg/kg/min),dopa-
pone.0172361
mine(50μg/kg/min),oresmolol(50μg/kg/min).Tenminlater,20mL/kgRinger´slactate
Editor:Zheng-LiangMa,NanjingUniversity
solutionwasgivenover30min.Centralhemodynamics,acid-basebalance,andtheurinary
MedicalSchoolAffiliatedNanjingDrumTower
Hospital,CHINA excretionweremonitored.Frequentmeasurementsofthebloodhemoglobinconcentration
wereusedasinputinakineticanalysis,usingamixedeffectsmodelingsoftware.
Received:August30,2016
Accepted:February4,2017
Results
Published:February23,2017
ThefluidkineticanalysisshowedslowdistributionandeliminationofRinger´slactate,
Copyright:©2017Lietal.Thisisanopenaccess althoughphenylephrineanddopamineacceleratedthedistribution.Oncedistributed,the
articledistributedunderthetermsoftheCreative
fluidremainedintheperipheraltissuesanddidnotequilibrateadequatelywiththeplasma.
CommonsAttributionLicense,whichpermits
Overall,stimulationofadrenergicalpha -receptorsaccelerated,whilebeta -receptors
unrestricteduse,distribution,andreproductionin 1 1
anymedium,providedtheoriginalauthorand retarded,thedistributionandeliminationoffluid.ApharmacodynamicE modelshowed
max
sourcearecredited. thatRinger´slactateincreasedstrokevolumeby13ml/beat.Alpha -receptors,butnot
1
DataAvailabilityStatement:Theoriginaldatais beta -receptors,furtherincreasedstrokevolume,whilebothraisedthemeanarterialpres-
1
providedintheSupportingInformationasS1 sure.Modulationofthebeta -receptorslimitedtheacidosis.
1
Dataset.
Funding:TheprojectwassupportedbyMedical Conclusions
HealthScienceandTechnologyProjectofZhejiang
province(№2014KYB277)andZhejiangProvincial Stimulationofadrenergicalpha1-receptorswithvasoactivedrugsaccelerated,whilebeta1-
ScienceFoundation(№LY15H030013). receptorsretarded,thedistributionandeliminationoffluid.Thetendencyforperipheral
Competinginterests:Theauthorshavedeclared accumulationoffluidwaspronounced,inparticularwhenphenylephrinewasgiven.
thatnocompetinginterestsexist.
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Fluidkineticsinsepsis
Introduction
Crystalloidfluidloadingandtheadministrationofvasoactivedrugsareessentialstepsinthe
earlytreatmentofsepticpatientswithsuspectedhypovolemiaandtissuehypoperfusion[1,2].
Thetreatmentforanadultconsistsofaninfusionofatleast30ml/kgofcrystalloidfluidsuch
asRinger´slactate.Ifthehypovolemiaandhypotensionisnotresolvedbyvolumeloading,the
treatmentshouldbeaugmentedbyadministrationofnorepinephrine,phenylephrine,ordopa-
mine[3,4].
Inhealthysheep,vasoactivedrugsmarkedlychangethedistributionandeliminationof
crystalloidfluid,therebyalteringtheplasmavolumeexpansion,urinaryexcretion,andtherisk
ofperipheraledema[5].However,theinteractionsbetweenfluidandvasoactivedrugshave
notbeenstudiedwithrespecttosepsis.Thistypeofstudyisofpotentialimportanceinthe
searchforoptimalcombinationsofcrystalloidsandvasoactiveagents.
Thepurposeofthepresentstudywastousevolumekineticstodescribethedistribution
andeliminationofcrystalloidfluidinanexperimentalsepsismodel,basedonserialmeasure-
mentsofthehemodilutionduringandafteraninfusion[6–8],andhowthisisinfluencedby
variousvasoactivedrugs(norepinephrine,phenylephrine,dopamine,andesmolol).Volume
kineticsispharmacokineticsforinfusionfluidsandhasbeenappliedinapproximately50stud-
iesofvariousfluidtherapies[6].Notuntilrecentlyhasthepopulationkinetic(mixedmodels)
approachbeendevelopedthatisnecessaryfortheanalysisoftherelationshipbetweenfluid
distributionandadrenergicstimulation[8].
Materialsandmethods
Animals
Twenty-fivehealthymalesheepweighing14–26kg(mean,20kg)werestudied.Theprotocol
andtheexperimentalprocedureswereapprovedbytheAnimalCareandUseCommitteeof
theShaoxingPeople’sHospital(PRofChina,approvalnumberZJU20140252),andthestudy
wasconductedinadherencewiththeGuideforCareandUseofLaboratoryAnimals.
Anesthesiaandsurgicalpreparation
Afteranovernightfast,anesthesiawasinducedwithpropofol(5mg/kg).Theanimalswere
intubatedviatracheotomyandventilatedatatidalvolumeof10ml/kgandrespiratoryrateof
15breathsperminute.Theanesthesiawasmaintainedwith1.5–2.5%sevofluraneandinter-
mittentdosesofsufentanil(0.6μg/kg)andcisatricurium(0.2mg/kg),asneeded.
Inasterileoperatingenvironment,a3-lumenvascularcatheterwasplacedintheright
internaljugularfordrugadministrationandfluidinfusion,aswellasforregistrationofthe
centralvenouspressure(CVP).Onefemoralarterywascannulatedformeasurementofblood
pressureandforsamplingofblood.Amiddlelaparotomywasperformedandacystostomy
catheterwasplacedinthebladderforcollectionofurine.
Sepsismodelandvasoactivedrugs
Sepsiswascreatedbycecalligationandpuncture,combinedwitha10-minintravenous(i.v.)
infusionof0.5mg/kgoflipopolysaccharide(LPS).FiftyminutesaftertheinfusionofLPS,a
continuousinfusionwasinitiatedconsistingof10ml/kg0.9%sodiumchloridecontainingno
vasoactivedrug(control),dopamine(50μg/kg/min),noradrenaline(1μg/kg/min),phenyleph-
rine(3μg/kg/min),oresmolol(50μg/kg/min).Theratesofadministrationofphenylephrine
anddopaminewerechosentoagreewithapreviousstudyoffluidkineticsinsheep[5].The
doseofnorepinephrinecorrespondstothemeandoseusedinclinicaltrialsofsepticshock.
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Fig1.Schematicdrawingofthetime-lineinthestudy.
doi:10.1371/journal.pone.0172361.g001
Esmololisabeta -receptorblockerandisnotusedtosupporthemodynamicsinseptic
1
patients.Thisdrugwasincludedtoincreasethewidthofourmanipulationofthebeta -recep-
1
torsandforitsabilitytoincreaseurinaryexcretion,andthedosecorrespondstotheoneused
inastudyofvolumekineticsduringlaparoscopicsurgery[7].
Tenminutesafterinitiationoftheinfusionofavasoactivedrug,plasmavolumeexpansion
wasinducedbyinfusing20ml/kgofRinger’slactate(Pharmacia-Baxter,Shanghai,China)
overa30minperiod.Thevasoactivedrugsweremaintainedfor150min,andthentheexperi-
mentwasendedandtheanimalsweresacrificed.
ThephasesofthestudyprotocolareillustratedinFig1.
Measurements
ThearterialcannulawasconnectedtoaFloTracTMsensorandthesensordataweresenttoa
Vigileomonitor(Softwareversion3.6;EdwardsLifesciences,Irvine,CA)formeasurementsof
cardiacoutput(CO)andstrokevolume(SV).Thesedatawerecalibratedagainstthecardiac
indexyieldedbythermodilutioninanesthetizedsheep[9].
Monitoringalsoincludedmeanarterialpressure(MAP),centralvenouspressure(CVP),
electrocardiography,andheartrate.Allresultsweredisplayedonthemultifunctionmonitor
(Datex-Ohmeda,Hoevelaken,TheNetherlands)andsaveddigitally.Arterialbloodsamples(2
mleach)werecollectedevery5minfor60minafterthestartingtheinfusionofLPSandagain
duringthefirst60minafterinfusionofRinger’ssolution,andthenevery10minduringthe
following90min.
Thetotalbloodhemoglobin(Hb)concentrationwasmeasuredonaGEMPremier3000
instrument(InstrumentationLaboratory,Lexington,IL).Duplicatesamplescollectedatbase-
lineensuredacoefficientof1.5%.Serumlactateandbaseexcess(BE)werealsomeasuredat
thesametime.Urineoutputsweremeasured60minafterthececalpunctureandattheendof
thestudy.
Allanimalsweresacrificedbyaninjectionofpotassiumchlorideuponcompletionofthe
experiment.
Kineticanalysis
Hemodilutionistheinverseofthebloodwaterconcentration[10]andwasusedastheinput
functioninthekineticanalysisbecauseRinger´slactateis99%water.Theplasmadilutionwas
thenfittedtotwo-volumekineticmodelwithmicro-constants,andtheinfluenceofcovariates
(adrenergicreceptorstimulationorblockade)wastested[7].
FluidwasinfusedatrateR toexpandthevolumeofthecentralbodyfluidspace(i.e.the
o
plasmavolume)fromV tov .Therateofeliminationwasgivenastheproductofthevolume
c c
expansionofV andaneliminationrateconstant,k .Thedistributiontotheperipheralbody
c 10
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Fig2.Thefluidkineticmodelusedtoanalyzethedilutionofarterialplasma.Abbreviations:V and
c
V =centralandperipheralfluidspaceexpandedbyinfusedfluidtov andv.k andk =rateconstants
t c t 12 21
governingthefluidtransferfromv andv andviceversa.k =eliminationrateconstant.
c t 10
doi:10.1371/journal.pone.0172361.g002
fluidspaceV (i.e.theinterstitialfluidspace)wasgovernedbyarateconstantk anditsreturn
t 12
fromv tov byanotherrateconstant,k (Fig2).
t c 21
Thedifferentialequationsare:
dv=dt ¼R (cid:0) k ðv (cid:0) VÞ(cid:0) k ðv (cid:0) VÞ(cid:0) k ðv (cid:0) VÞþk ðv (cid:0) VÞ
c o 10 c c b c c 12 c c 21 t t
dv=dt ¼k ðv (cid:0) VÞ(cid:0) k ðv (cid:0) VÞ
t 12 c c 21 t t
TheHb-derivedfractionalplasmadilutionwasusedtoindicatethevolumeexpansionofV
c
resultingfromtheinfusion.Thisprovidesalinearrelationshipbetweentheaddedfluidvolume
andthechangeinHbinanexpandablefluidspace[6].Hence:
ðv (cid:0) VÞ=V ¼ððHb=hbÞ(cid:0) 1Þ=ð1(cid:0) hematocritÞ
c c c
Thesymbolsincapitallettersdenotebaselinevalues.The"false"plasmadilutioncausedby
thebloodsamplingwascorrectedbyamathematicalprocedureexplainedelsewhere[6].On
assumingthatHbisevenlydistributedinthecirculation,theHb-derivedfractionalplasma
dilutionalsoindicatestheexpansionoftheplasmavolume.
Theprimaryparametersinthemodel(V ,k ,k ,andk )andtheircovariateswereesti-
c 12 21 10
matedusingthePhoenixsoftwarefornonlinearmixedeffects(NLME),version1.3(Pharsight,
St.Louis,MO).
Theanalysiswasperformedinfourparts.First,thefourkineticparameterswereestimated
separatelyforeachofthestudygroupsseparately.Thedistributionoftheinfusedfluidbetween
bodycompartmentswasthensimulatedbasedonthebestestimatesoftheseparameters,using
MatlabR2012b(MathWorksInc.,Natick,MA).
Second,allexperimentswerepooled,andbasemodelwasdevelopedwhichincludedthe
fourkineticparametersinthemodel.
Third,covariatesintheformofvariousdegreesofreceptorstimulationwerethenaddedin
sequencetothebasemodel,whicheventuallyformedthefinalmodel[8–11].Receptoreffects
wereincludedthefinalmodeliftheywerestatisticallysignificant(95confidenceinterval,CI,
didnotinclude1.0)andtheircoefficientofvariationwas<30%.
Thedegreeofadrenergicreceptoreffectassumedtobeproducedbythevariousdrugsis
showninTable1.Thestrengthofallstatisticallysignificantreceptoreffects(beingeither
blockade-1,noeffect0,slightstimulation1,strongerstimulation2,orstrongeststimulation
3)wereappliedsimultaneouslyinthefinalanalysisofthefullmodel.Tostabilizethese
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Table1. Thelevelofstimulationofreceptorsusedinthevolumekineticanalysis. Zeromeansnoeffect,+3strongeffect,and-1meansinhibition.
Drugtreatment Alpha -adrenergicreceptors Beta -adrenergicreceptors Dopaminergicreceptors
1 1
None(control) 0 0 0
Norepinephrine 3 2 0
Phenylephrine 3 0 0
Dopamine 1 1 1
Esmolol 0 –1 0
BasedonReference[15].
doi:10.1371/journal.pone.0172361.t001
calculations,themeasuredurinaryexcretionineachexperimentwassetequaltok (theelimi-
10
nation)inthatexperiment.
Fourth,theeffectofplasmadilutiononkeyhemodynamicparameterswasfittedtoaphar-
macodynamiclineareffectmodel(E model)havingthefollowingappearance:
max
E ððv-VÞ=VÞ
E¼E þ max c c c
o EC ððv-VÞ=VÞ
50 c c c
whereEiseffect,E istheeffectatbaseline,E isthemaximumeffect,andEC isthefrac-
o max 50
tionalplasmadilutionrequiredtocause50%ofthefulleffect.
Statistics
Demographicandhemodynamicdatawerereportedasthemean(standarddeviation,SD)and
thekineticdataasthemean(95%confidenceinterval,CI).Changesinparameterswerecom-
paredbythepairedttestortheWilcoxonmatched-pairtest.Theeffectofadrenergicreceptor
stimulationonthehemodynamicswasevaluatedbyone-andtwo-wayANOVA.Correlations
werestudiedbylinearregressionanalysis,wherer=correlationcoefficient.P<0.05wascon-
sideredstatisticallysignificant.
Results
Ourevaluationdescribestheoveralleffectsofsepsisandfluidofthehemodynamics,analyses
thefluidkineticsforeachofthefivesubgroupsseparatelyaswellasthefluidkineticsforall25
animalstogether,inwhichthelatterusedthelevelsofadrenergicstimulationascovariates.
Finally,selectedanalysesoftheindependenteffectsoffluidtreatmentandadrenergicstimula-
tiononhemodynamicsandacid-basebalanceweremade.
Hemodynamics
Duringthe50minofearlysepsisalone,MAPgraduallydecreasedfrom97(17)to64(20)
mmHg,whileCOrosefrom4.0(1.8)to5.7(2.6)L/min(pairedttest,bothP<0.001).SV
increasedonlyslightly.Theplasmawasconcentratedby9.5%(median;95%CI4.4–12.7)
(Fig3).
Comparedwithearlysepsisalone,earlysepsisplusadrenergicdrugandfluidtreatmentwas
associatedwithahighermeanCO,SV,andserumlactate(P<0.001),whereastheMAP,CVP,
andbaseexcessdecreased(P<0.001,Table2).
Kineticsinthefivegroups
Aseparatepopulationkineticanalysiswasfirstmadeseparatelyforthecontrolsandforeach
ofthe4groupsof5sheepthatreceivedaspecificvasoactivedrug.Thedistributionrate
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Fig3.Hemodynamics.Earlysepsis(-60to-10min)comparedwithtreatmentusingvasoactivedrugsand
fluid(0to150min).Dataaremean(SD)basedonpatientmeanvaluesduringtheindicatedperiodoftime.
Duetothesmallnumberineachgroup(n=5),statisticalcomparionsweremadebyusingtheWilcoxon
matched-pairtest.*indicatesstatisticalsignificance.Abbreviations:CO=cardiacoutput,SV=stroke
volume,MAP=meanarterialpressure;CVP=centralvenouspressure,BE=baseexcess;
Nor=norepinephrine,Phe=phenylephrine,Dop=dopamine,Esm=esmolol.
doi:10.1371/journal.pone.0172361.g003
constant(k )washighforinthephenylephrineanddopamine,butlowintheothergroups.
12
Thekineticconstantgoverningtherateofforre-distribution(k )wasnegativeinmostgroups
21
(Table3).whichresultedinmarkedperipheralaccumulationofinfusedfluid(Fig4).
Covariateanalysis
Apopulationkineticanalysiswasthenperformedbasedonallinfusionexperiments.The
covarianceanalysiswasmostsuccessfulwithalinearmodel,wherethestrengthofeach
Table2. Hemodynamicsandbiochemicalevidenceofacidosis. Earlysepsis(-60to-10min)iscomparedtothetimeperiodwhenfluidandvasoactive
drugweregiven(0to150min).ThesedataareplottedinFig3.Eachgroupcontained5animals.
Control Nor Phe Dop Esm
CO(L/min)
Earlysepsis 5.2(2.4) 4.61.1) 5.0(1.7) 4.8(0.9) 5.9(1.5)
Drug+fluid 6.3(1.5) 6.9(1.0) 6.6(1.2) 7.0(2.6) 5.0(1.2)
SV(mL/beat)
Earlysepsis 58(16) 46(6) 44(15) 31(13) 55(12
Drug+fluid 66(17) 68(12) 74(22) 77(18) 60(11)
Serumlactate(mmol/L)
Earlysepsis 1.7(0.7 1.6(0.6) 1.0(0.3) 1.2(0.3) 1.5(0.6
Drug+fluid 3.1(1.1) 2.8(0.4) 2.0(0.8) 2.9(1.7) 2.9(1.6)
MAP(mmHg) )
Earlysepsis 100(10) 87(6) 92(6) 96(6) 78(4)
Drug+fluid 72(16) 75(12 78(12) 77(11) 49(7)
CVP(mmHg)
Earlysepsis 5.8(3.7) 3.9(1.4) 5.6(4.4) 3.6(3.2) 5.8(3.8)
Drug+fluid 2.5(1.6) 3.1(0.6) 4.1(1.0) 5.8(3.8) 3.2(1.2)
BE(mmol/L)
Earlysepsis 0.5(2.9) 0.8(3.4) 1.8(0.8) 2.1(2.2) 1.8(1.7)
Drug+fluid –3.3(3.1) –0.6(3.1) –2.8(0.5) –1.7(3.3) –0.7(1.6)
Abbreviations:CO=cardiacoutput,SV=strokevolume,MAP=meanarterialpressure;CVP=centralvenouspressure,BE=baseexcess;
Nor=norepinephrine,Phe=phenylephrine,Dop=dopamine,Esm=esmolol.
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Table3. Thepatternsofreceptorstimulationusedinthevolumekineticanalysis.
Control Norepinephrine Phenylephrine Dopamine Esmolol
V (L) 1.32(0.97–1.68) 2.65(1.96–3.35) 1.34(1.25–1.44) 1.60(1.18–2.03) 1.80(1.36–2.24)
c
k (10−3min-1) 5.2(0.3–10.0) 7.2(3.3–11.1) 22.3(17.0–27.7) 28.5(22.3–34.6) 6.3(2.4–10.1)
12
k (10−3min-1) -3.9(-9.5to1.8) -1.2(-1.9to-0.6) -4.1(-5.0to-3.1) 3.0(1.9–4.1) -6.8(-11.7to-2.0)
21
k (10−3min-1) 2.0(0.5–3.5) <0.01 <0.01 <0.01 1.4(0.5–2.4)
10
Thebestestimateofeachparameterisshowntogetherwithits95%confidenceinterval.Theadditivewithin-subjectresidualerrorstructureandthe
extendedleastsquares(ELS)analysismodelwithoutconsiderationofthemeasuredurinaryexcretionyieldedthemostpreciseestimatesofthefour
parameters.
doi:10.1371/journal.pone.0172361.t003
receptoreffect,accordingtoTable1,wasappliedasacontinuousvariable.Therewerefive
covariateeffects:k andk wereincreasedbystimulationofthealpha -receptorsbut
12 10 1
decreasedbythebeta -receptors.Inaddition,thebeta -receptorsincreasedV .Nosignificant
1 1 c
covariateeffectwasfoundforthedopaminereceptors.
ThecompletesetofparameterestimatesaregiveninTable4.Thebestestimatesinthe
modelwerethenmodifiedwithregardtoV ,k ,andk ,asfollows:
c 12 10
V ¼1:70ð1þ0:12beta Þ
c 1
k ¼6:4x10(cid:0) 3ð1þ1:45alpha Þð1(cid:0) 0:33beta Þ
12 1 1
k ¼0:5x10(cid:0) 3ð1þ1:93alpha Þð1(cid:0) 0:32beta Þ
10 1 1
wherethedigitsappliedforassumedstrength,accordingtoTable1,areusedtoreplacealpha
1
andbeta intheequations.
1
ThemeasuredplasmadilutionwhenalldatawerepooledisshowninFig5A.Theagree-
mentbetweenthemeasuredandpredictedplasmadilutionaccordingtothebasemodelis
giveninFig5Bandthesamecomparison,butwithconsiderationtakenofthecovariates,is
madeinFig5C.
Fig6illustrateshowchangesinthedegreeofadrenergicstimulationwouldalterthedistri-
butionofcrystalloidfluidaccordingtotheanalysismade.V wouldbecomelessexpanded,
c
whileV wouldbemoreexpanded,thestrongerthestimulationofthealpha -adrenergicrecep-
t 1
tors(Fig6A).Theeffectwouldbetheoppositeforstimulationofthebeta -adrenergicrecep-
1
tors(Fig6B).
Fig4.Fluiddistribution.Volumeexpansionofthecentralfluidspace(V,theplasma),theperipheralfluidspace(V)
c t
andtheexcretedurine(theelimination)duringinfusionexperimentswith20mL/kgofRinger´slactateover30minin
septicsheepwhowerealsogivenavasoactivesubstance.Computersimulationusingtheparameterestimatesshown
inTable3.
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Table4. Pharmacokineticandpharmacodynamicparametersinthefinalmodel.
Covariate Bestestimate(95%CI)
Kineticparameter
tvV (L) 1.70(1.47–1.93)
c
tvk (10−3min-1) 6.4(3.8–9.0)
12
tvk (10−3min-1) -4.1(-6.0to-2.1)
21
tvk (10−3min-1) 0.50(0.24–0.76)
10
Covariateeffect
tvk Alpha stimulation 0.45(0.24–0.65)
12 1
tvk Alpha stimulation 1.93(1.07–2.80)
10 1
tvV Beta stimulation 0.12(0.05–0.19)
c 1
tvk Beta stimulation -0.32(-0.49to–0.14)
12 1
tvk Beta stimulation -0.33(-0.51to–0.14)
10 1
E ,ΔSV
max
tvE 13(6–20)
0
tvE 9(4–14)
50
tvE 49(-6to106)
max
tv=typicalvalue,CI=confidenceinterval,
ΔSV=thechangeinstrokevolumesincetheonsetoffluidinfusion.
doi:10.1371/journal.pone.0172361.t004
Urinaryexcretion
Theurinaryexcretion(theelimination)wassmallinallgroups(Figs4and6).Duringearly
sepsisalone,themedianurineflowwas0.20ml/min(95%CI,0.16–0.40).Duringthetreat-
mentswithavasoactivedrugandfluid,thevalueswerequitesimilar,at0.16ml/min(0.13–
0.31).
Measuresofeffect
TheE modelanalysisshowedthatthefluidtreatmentassuchraisedSVby13ml/beat,but
max
furtherincreasesinresponsetoincreasingplasmadilutionwereslight(Table3,bottom).Simi-
larfindingswereobservedforMAP(datanotshown).
Fig5.Thecurve-fittingprocedure.A:Themeasuredplasmadilutionovertimeinallsheep,regardlessofvasoactivedrug.B:The
plasmadilutionpredictedfromthebasemodel(fourparametersonly)withoutconsiderationofcovariates(drugeffects),andC:The
plasmadilutionpredictedfromthefinalmodelwithcovariateeffects.
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Fig6.Simulationofadrenergiceffectsonfluiddistribution.Distributionof20ml/kgRinger´slactate
infusedover30mininsheepweighing20kg,dependingonthedegreeofalpha -adrenergic(A)andbeta -
1 1
adrenergic(B)stimulation,gradedbetween0and+3,accordingtoTable1.Thekineticparametersshownin
Table3wereusedforthesimulation.
doi:10.1371/journal.pone.0172361.g006
Two-wayANOVAwasusedtoexaminewhethertheadrenergicstimulationaffectedthe
hemodynamicparametersinadditiontofluidalone.Alpha -receptorsraisedSVby(cid:25)15ml/
1
beat(P<0.001)whereasthebeta -receptorsdidnotsignificantlyaffectSV.Stimulationof
1
thesereceptorsraisedMAPby(cid:25)15mmHg(P<0.0001andP<0.02,respectively)withoutan
additiveeffect;thiswas2–3morethanwithfluidalone.Agreaterhemodynamiceffectfor
strongerreceptorstimulationpotency,asgradedaccordingtoTable1,couldnotbediscerned.
Modulationofthebeta -receptors,butnotofthealpha -adrenergic,preventedareduction
1 1
ofBE[–0.7(2.7)mmol/Lversus–2.9(2.4)fortheothers,P<0.0001]andofpH[7.38(0.08)
versus7.33(0.08);P<0.001)].Incontrast,dopaminereceptorsofferedmarginalprevention
[–1.2(3.0)versus–1.7(2.8)mmol/L,P=0.08).
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Discussion
Theanimalmodelusedherecreatedamoderatelyseveresepsiswithhyperkineticcirculation
andwasusedtoinvestigatetheeffectofvasoactivedrugsonthekineticsofRinger´slactate.
Theinfusedfluidexpandedacentralfluidspace(theplasma)ofbetween1.3and2.7L,which
islargewhenconsideringthesmallsizeoftheseanimals(20kg).Thedistributionoffluidfrom
thecentraltotheperipheralfluidspaceinsepticsheepwithoutvasoactivedrugwasquiteslow,
whencomparedtopreviousworkinconscioushealthysheep[9].Amorenormalrateofdistri-
bution(k 30–5010−3min-1)wasachievedwithphenylephrineanddopamine.
12
Aslowdistributioncouldberegardedasabenefit,asitincreasestheplasmavolumeexpan-
sionresultingfromtheinfusion.Cardiacpreloadisthenbettermaintainedduetothelarger
fractionoftheinfusedfluidthatremainsinthecirculatingblood.Moreover,oxygenationof
peripheraltissueswillbebetterpreservedbecausethediffusiondistancebecomessmaller
whentheedemainperipheraltissues(V)islesspronounced[12].However,theoverallimpact
t
ofthefluidinfusionsonedemamustbeinterpretedwithaknowledgeofbothk andk ,
12 21
wherenormalfluidexchangeimpliesthattheformerrateconstantshouldbeabouttwiceas
highasthelatter[7,8].However,inthisstudythefluidexchangebetweenV andV was
c t
clearlynotnormal.Therateconstantk evenattainednegativevalues,whichhaspreviously
21
onlybeendescribedforthe"transurethralresectionsyndrome"[13].
Thenegativevaluedenotesthatfluidaccumulatedinperipheraltissueswithoutequilibrat-
ingadequatelywiththeplasma,indicativeofashock-likesituation.Thecombinationofanor-
malk ,negativek ,andlowk stronglypromotesthedevelopmentofperipheraledemaand,
12 12 10
inoursimulations,evenlatehypovolemia(Fig4).Edemawasaproblemencounteredwithall
thevasoactivedrugs,butparticularlywithphenylephrine.However,mostoftheslowelimina-
tion(lowk )canbeunderstoodonthebasisoftheuseofgeneralanesthesia[14],andthe
10
hypovolemiacausedbycapillaryleakageduringtheearlyphaseofthesepsis,whichamounted
to10%oftheplasmavolume.
Betterinsightintothefluidkineticswassoughtbyperformingthefullpopulationkinetic
analysiswheretherelativeeffectsofthedrugsonadrenergicreceptorswereusedascovariates
(Table1).Populationkineticanalysishasgraduallybecomeascientificandindustrialstandard
procedureindrugdevelopment[11],anditcanbeappliedtofluidvolumekineticsaswell[8].
Usingthisapproach,thedistributionandeliminationofRinger´slactateinallexperiments
couldbeanalyzedwithhigherprecisionthanwaspossiblewithaseparateanalysisforeach
drug,andeveninasinglerun.Ananalysisoftheindividualcontributionofdifferentadrener-
gicreceptorsonfluidkineticscouldalsobemade.
Theresultsshowthatalpha -adrenergicreceptorsaccelerated,whilebeta -adrenergic
1 1
receptorstimulationretarded,thedistributionofcrystalloidfluid.Themagnitudeofthese
influencescouldbequantified(Table3)andillustratedgraphically(Fig6).Thepronounced
edemafoundwithphenylephrinecanthenbeunderstoodfromthestrongalpha -receptor
1
effect,butlackofbeta -stimulation,associatedwiththeuseofthisdrug.Moreover,theacidosis
1
waslesspronouncedwhenthebeta -receptorswerestimulated,whichconfirmsthatmaintain-
1
ingplasmavolumeexpansion(V)attheexpenseofextravascularfluidaccumulation(V)is
c t
beneficialtooxygenationofthetissues[12].
Thepresentfindingsalsoindicatethatalpha -receptorstimulationincreasedwhilebeta -
1 1
adrenergicreceptorstimulationdecreasedtheurinaryexcretion.Hence,theseeffectswere
oppositetothoseexertedbytheadrenergicreceptorsontherateoffluiddistribution.Theyare
supportedbyapreviousstudyinconscioussheep[5],andalsobyastudyinanesthetized
womenundergoinglaparoscopicgynecologicalsurgery[7].Inthepresentstudytheincrease
inurinaryexcretioncausedbymodulationoftheadrenergicreceptors,wasstatistically
PLOSONE|DOI:10.1371/journal.pone.0172361 February23,2017 10/13