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REVISTA

BRASILEIRA

DE

ANESTESIOLOGIA

PublicaçãoOficialdaSociedadeBrasileiradeAnestesiologia

www.sba.com.br

SCIENTIFIC

ARTICLE

Upper

airway

morphology

in

Down

Syndrome

patients

under

dexmedetomidine

sedation

Rajeev

Subramanyam

a,∗

,

Robert

Fleck

b

,

John

McAuliffe

a

,

Rupa

Radhakrishnan

b

,

Dorothy

Jung

b

,

Mario

Patino

a

,

Mohamed

Mahmoud

a

aDepartmentofAnesthesia,CincinnatiChildren’sHospitalMedicalCenter,OH,USA bDepartmentofRadiology,CincinnatiChildren’sHospitalMedicalCenter,OH,USA

Received29October2014;accepted26November2014 Availableonline19November2015

KEYWORDS

Airway;

Dexmedetomidine; Imaging;

DownSyndrome; Obstructivesleep apnea;

Sedation

Abstract

Backgroundandobjectives: ChildrenwithDownSyndromearevulnerabletosignificantupper

airwayobstructionduetorelativemacroglossiaanddynamicairwaycollapse.Theobjectiveof

thisstudywastocomparetheupperairwaydimensionsofchildrenwithDownSyndromeand

obstructivesleepapneawithnormalairwayunderdexmedetomidinesedation.

Methods:IRBapprovalwasobtained.Inthisretrospectivestudy,clinicallyindicateddynamic

sagittal midline magnetic resonance images ofthe upper airway were obtained under low

(1mcg/kg/h)andhigh(3mcg/kg/h)dosedexmedetomidine.Airwayanteroposteriordiameters

andsectional areaswere measuredas minimumandmaximumdimensionsby two

indepen-dentobserversatsoftpalate(nasopharyngealairway)andatbaseofthetongue(retroglossal

airway).

Resultsandconclusions: Minimum anteroposteriordiameter and minimumsectional area at

nasopharynxandretroglossalairwayweresignificantlyreducedinDownSyndromecomparedto

normalairwayatbothlowandhighdosedexmedetomidine.However,therewerenosignificant

differencesbetweenlowandhighdosedexmedetomidineinbothDownSyndromeandnormal

airway.ThemeanapneahypopneaindexinDownSyndromewas16±11.Under

dexmedetomi-dinesedation,childrenwithDownSyndromeandobstructivesleepapneawhencomparedto

normalairwaychildrenshowsignificantreductionsinairwaydimensionsmostpronouncedat

thenarrowestpointsinthenasopharyngealandretroglossalairways.

© 2015 Sociedade Brasileira de Anestesiologia. Published by Elsevier Editora Ltda. This

is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

Correspondingauthor.

E-mail:Rajeev.Subramanyam@cchmc.org(R.Subramanyam).

http://dx.doi.org/10.1016/j.bjane.2014.11.019

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PALAVRAS-CHAVE

Viasaéreas; Dexmedetomidina; Imagem;

SíndromedeDown; Apneiaobstrutivado sono;

Sedac¸ão

MorfologiadasviasaéreassuperioresempacientescomsíndromedeDownsob sedac¸ãocomdexmedetomidina

Resumo

Justificativaeobjetivos: Ascrianc¸ascomsíndromedeDown(SD)sãovulneráveisàobstruc¸ão

significativadasviasaéreassuperioresdevidoàmacroglossiarelativaecolapsodinâmicodas

viasaéreas.Oobjetivodesteestudofoicompararasdimensõesdasviasaéreassuperioresde

crianc¸ascomSDeapnéiaobstrutivadosono(AOS)comviasaéreasnormais(VAN)sobsedac¸ão

comdexmedetomidina(DEX).

Métodos: Aprovac¸ãoIRBfoiobtida.Nesteestudoretrospectivo,imagensclinicamenteindicadas

de ressonânciamagnética dadinâmica dasviasaéreas superioresem plano sagitalnalinha

médiaforamobtidassobdosebaixa(1mcg/kg/h)edosealta(3mcg/kg/h)deDEX.Osdiâmetros

ânteroposterioresdasviasaéreaseasáreasseccionaisforammedidascomodimensõesmínimas

emáximaspordoisobservadoresindependentes,nopalatomole(regiãonasofaríngea)enabase

dalíngua(regiãoretroglossal).

Resultadoseconclusões: Odiâmetromínimoanteroposteriore aáreaseccional mínimadas

regiõesnasofaríngeaeretroglossalestavamsignificativamentereduzidosnaSDemcomparac¸ão

comVAN,tantocomadosebaixaquantocomadosealtadeDEX.Contudo,nãohouvediferenc¸as

significativasentreasdosesbaixaealtadeDEXem SDeVAN.Amédiadoíndice deapneia

e hipopneianaSDfoide 16±11. Sobsedac¸ãocomDEX, ascrianc¸as comSDeAOS quando

comparadascomascrianc¸ascomVANapresentaramreduc¸õessignificativasnasdimensõesdas

viasaéreas,maispronunciadasnospontosmaisestreitosdasregiõesnasofaríngeaeretroglossal.

© 2015 Sociedade Brasileira de Anestesiologia. Publicado por Elsevier Editora Ltda. Este

é um artigo Open Access sob a licença de CC BY-NC-ND (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

Introduction

Down Syndrome (DS) or trisomy 21 is the most common geneticdisorderinhumanswithanestimatedbirthrateof 6000infants/year(1in691livebirths)intheUnitedStates.1 Obstructivesleepapnea(OSA)iscommonandnotedin79% ofchildrenwithDS(95%confidenceinterval,54---94%).2Risk factorsforOSAinthesechildrenincludemidfacehypoplasia, macroglossia,adenoidandtonsillarhypertrophy, laryngotra-chealanomalies,obesity,andmuscularhypotonia.3Evenin theabsenceofOSA,childrenwithDShavereducedairway sizecausedby softtissuecrowdingwithinasmallerfacial skeletalanatomy.4

Children with OSA, with or without DS, are sensitive to respiratory depression by opioids, sedatives, and hyp-notics.Theyareespeciallyvulnerabletothedevelopmentof upperairwayobstructionduring sedationandanesthesia.5 Dexmedetomidine(DEX)isan␣-2receptoragonistcurrently

being used off-label for sedation in pediatric patients at manyinstitutions.Incontrasttoothersedativeagents,DEX has been shown tohave sedative properties that parallel naturalnon-rapideyemovementsleep,withoutsignificant respiratory depression.6,7 These advantages make DEX an attractiveagentforsedatingchildrenwithOSA.8 Wehave previouslyusedmagneticresonanceimaging(MRI)toassess theeffectofincreasingdosesofDEXonairwaydimensionsin childrenwithnormalupperairways(agerange3---10years) andshowedthatincreasingdosesofDEXinthesechildrenis notassociatedwithsignificantincreaseinthedegreeof air-wayobstruction.9 Werecentlyusedasimilarmethodology tocompare the dose---response effectsof DEX and propo-folonairwaymorphology inchildren withOSA (agerange

1---16years).Wefoundthatasthedosageincreased, aver-ageairwaydimensionsweretypicallyunchangedorslightly increased with DEX compared to unchanged or slightly decreasedwithpropofol.10

Ouraim inthe present study wastotest the hypothe-sisthatDSchildrenwithOSAhavesignificantupperairway collapsibilityevenatlowdosesofDEXcomparedtochildren withnormalairway(NA).Wethereforedesigneda retrospec-tivecohortstudycomparingtheupperairwaymorphologies ofchildrenaged3---10yearswithDSandOSAtothosewith NAunderincreasingdosesofDEXsedation.

Materials

and

methods

After institutional review board approval, the data were obtainedinchildrenaged3---10yearswithDSandchildren withNAwhounderwentMRIairwayanalysiswithDEX. Writ-teninformedconsenthadbeenobtainedforsedation.The needforaseparateinformedconsentfortheretrospective reviewwaswaivedbyourIRB.

DownSyndrome(DS)group

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induction room with sevoflurane and/or nitrous oxide in oxygen. Atropine 10mcg/kg IV was administered and sevoflurane and/or nitrous oxide were discontinued. DEX wasstartedandMRimagingperformedasdescribedbelow.

Normalairway(NA)group

Themethodologyusedforevaluationofchildrenwith nor-mal airways wasdescribe in a previously study.9 Inbrief, childrenaged3---10yearswhopresentedforanelectiveMRI examination undersedation were included. Children with historyofOSAorsnoring,AmericanSocietyof Anesthesiol-ogyclassification>2,allergytoDEX,presenceofairwayor craniofacialabnormality,obesity,or severedevelopmental delaywereexcluded.

Dexmedetomidineprotocol

BaselineairwayimageswereobtainedduringtheLowDEX infusion (1mcg/kg/h). If the subject moved, a bolus of 0.5mcg/kgover10minwasgivenandtheDEXinfusionrate wasincreasedto1.5mcg/kg/h.Ifthesubjectmoveda sec-ondtime,theresearchstudywasterminatedandadditional anesthesiawasprovidedwithpropofol infusion. Afterthe initialsetofairwayimageswereobtained,abolusdoseof DEX2mcg/kgwasgivenover10minfollowedbyanincrease intheinfusionrateto3mcg/kg/h(highdoseDEX). Univer-sityof Michigan SedationScale (UMSS) wasusedtoassess sedation.11UMSSisasimpletouse,validatedtooltoassess thedepthofsedationinchildren.11Standardmonitoringand spontaneousbreathingwith2L/minofoxygenvianasal can-nulawasused.Levelofsedationwasassessedafterinitial

low dose of DEX before and after imaging. Sedation was not assessed during imaging as this may have necessi-tatedchangingthepatient’sheadpositionandsubsequently biasing airway measurement comparisons. Patients were transferredtothepostanesthesiacareunitfollowing imag-inganddischargedhomeaftermeetingcriteria.

MRimagingprotocol

All patients underwentclinically indicated MRIunder DEX sedation.Onceadequatesedationwasachieved,the cervi-calspinewasmaintainedinaneutralpositionbyplacingthe patient’sheadandneckinavascularcoil.Noartificial air-way(e.g.,oral airwayor nasaltrumpet)orpositioningaid (e.g.,shoulder roll) wasusedduringimaging. Noattempt wasmadetoopenorclosethemouth.ChildrenwithDSwere transferred to the imager after the sevoflurane end-tidal concentrationwasreducedto<0.1%.MRIwasperformedon a1.5Teslaimager(GEHealthcare,Milwaukee,WI,USA)with an8-channelreceiveronlyneurovascularphasedarraycoil (MEDRAD,Inc.,Indianola,PA,USA).Theprimaryimagesfor analysiswererapidlyacquired ina midline,sagittalplane usingfastgradient echoimaging(1 imageevery800ms).9 The scan parameters were: Repetition time/Echo time: 6.98/3.6,Fieldofview:24cm,slicethickness:5mm,matrix 256×128,numberofexcitations:1,flipangle:80◦,receiver

bandwidth 244.1Hz/pixel,baseline resolution: 256,phase resolution: 128. By playing a cine loop of the images, a movieofairwaymotionwascreated(Figs.1and2with asso-ciated video). Upper airwayimageswere obtained during low(1mcg/kg/h)andhigh(3mcg/kg/h)doseDEXsedation. TheimageswerestoredonthePACS(PictureArchivingand

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Figure2 Stillimage(A)fromthecineclipshowstheretroglossalairwayincross-sectionwhileopen(arrowheads)andthestill image(B)showstheairwaycompletelycollapsedcentrallycompatiblewithhypopharyngealcollapse.

CommunicationSystem)and reviewedbytwoscorerswho wereblindedtotheDEXdoses.

Theairwaywasmeasuredatthelevelofthesoftpalate (nasopharyngeal airway)and thebase of the tongue (ret-roglossal airway) (Figs. 1 and 2). The sectional area and anterior-posteriordiameterweremeasuredinthe nasopha-ryngeal area (NPA) and the retroglossal area (RGA). The nasopharyngealarea(NPA)wasdefinedanteriorlybya verti-callinetangentialtotheposteriorinferiornasalturbinate, posteriorly by the posterior wall of nasopharynx, superi-orlybythesuperiorwallofnasopharynx,andinferiorlyby superiorandposteriorpartofhardandsoftpalate.The ret-roglossal airwayarea(RGA) wasdefinedanteriorly by the backoftongue,posteriorlybytheposteriorpharyngealwall, superiorlybyahorizontallinedrawnattheinferiormargin ofthesoftpalate,andinferiorlybyahorizontallinedrawn atthebase ofthetongue. Thesectionalareaand antero-posteriordiameterweremeasured intheNPAandRGAon imagesofminimumandmaximumexpansionoftheairway.

Poweranalysis

Analyses performed with R statistical software indicated thatasamplesizeof7patientswouldhavean80%powerto detecta100mm2differenceinthemeansectionalareasof NAandDSairwaysinchildrenunderlowdoseDEX.12A differ-enceof100mm2waschosenbecausechildrenwithDShave baselinenarrowairwaysandwasbasedona95%confidence levelinthemeandifferences.13LowdoseDEXwaschosenin ordertodeterminethemostconservativeestimateof sam-plesizenecessarytoadequatelypowerthestudy.Thiswas doneundertheassumptionthathighdoseDEXwouldcause

moresignificantairwaynarrowingthanlow doseDEXand, subsequently,themeandifferenceinairwaymeasurements wouldbelarger.Aposthocpower analysiswasperformed toverifythisassumption.

Statisticalanalysis

Statistical analysis was performed with R statistical software.12 Normalityof distributionof data waschecked by Shapiro---Wilks test. Descriptive statistics are provided asmean and standard deviation or numbers as appropri-ate.Age, weight, and polysomnography derived variables betweenchildrenwithNAandchildrenwithDSwere com-paredwithWelchtwo-samplet-test.Genderwascompared withtheFischerexacttest.Hemodynamicdatawere com-paredwiththeunpairedt-test.Theminimumandmaximum anteroposteriordiameterandsectionalareasintheNPAand RGAwerecomparedbetweenchildrenwithDSandchildren withNAusingtheunpairedt-test.Thedifferencebetween ‘lowdoseDEX’and‘highdoseDEX’betweenchildrenwithDS andchildrenwithNAwascomparedusingthepairedt-test. Ap-valueof<0.05wasconsideredstatisticallysignificant.

Results

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Table1 Demographicandpolysomnographyfindings. Down

Syndrome (n=7)

Normal airway (n=23)

p

Age(years) 5±1 6±2 0.27

Weight(kg) 26±11 22±5 0.42

Male/females 4/3 12/11 1

Sedationscore

Induction 3±1 2±1 0.003

Postanesthesia

careunit

3±0 3±0 0.36

Obstructivesleep apnea(n)

7 0

Polysomnographyfindings

Apneahypopnea

index (events/hour)

17±11

(5.2---37.6)

---Minimaloxygen

saturation(%)

81±5

(72---85)

---All data in mean±standard deviation or absolute numbers.

Rangesarementionedinparenthesis.---,notapplicable.

Airwayanteroposteriordiameterandsectionalarea mea-surementsaresummarizedinTable3.

The following three dimensions were reduced signifi-cantlyin childrenwithDSascomparedtoNAat both low andhighdoseDEX:minimumRGAsectionalarea,minimum anteroposteriorNPAdiameter,andminimumanteroposterior RGAdiameter.SedationwithDEXdidnotyieldastatistically significantdose-dependent(lowvs.high)differenceinthe airwaymeasurementsofchildrenwithDSandNA(Table4).

Discussion

OurstudyshowedthatchildrenwithDSandOSAexhibited significantreductionsinanatomicalairwaydimensionswhen comparedtochildrenwithNAunderDEXsedation.Thesafe sedationofchildrenespeciallythosewithahistoryofOSA requiresaclearunderstandingofthepharmacokineticand pharmacodynamiceffectsofthesedativeusedaswellasan appreciationoftheeffectofthechosensedativeonairway collapsibility.Allpractitionersprovidingsedationmusthave anindepthunderstandingoftheinteractionbetweendepth ofsedationandairwaydynamics,rememberingthatdepth of sedation is a continuum fromminimal, moderate, and deepsedationtogeneralanesthesia.

Table2 Hemodynamicdata.

Baseline p Firstscan p HighdoseDEX p

Down Syndrome

Normal children

Down Syndrome

Normal children

Down Syndrome

Normal children

HR(bpm) 101±12 93±14 0.15 97±19 78±15 0.03 84±9 82±19 0.88

SBP(mmHg) 110±10 107±14 0.50 125±14 111±15 0.13 137±14 112±14 0.08

DBP(mmHg) 64±9 56±19 0.16 69±9 59±12 0.15 84±2 66±12 <0.001

HR,heartrate;SBP,non-invasivesystolicbloodpressure;DBP,non-invasivediastolicbloodpressure.

Table3 ComparisonofairwaydimensionsbetweenchildrenwithDownSyndromeandchildrenwithnormalairwayunderboth

lowandhighdosedexmedetomidine.

Dimensions Lowdosedexmedetomidine Highdosedexmedetomidine

Down Normal 95%CI p-Value Down Normal 95%CI p-Value

Nasopharyngeal

AP(mm)

Minimum 1±1 5±2 2.6---4.9 <0.001 1±1 5±2 2.3---4.7 <0.001

Maximum 2±1 5±2 2.6---5.1 <0.001 2±1 5±2 2.0---4.7 <0.001

Sectionalarea(mm2)

Minimum 157±41 265±80 59.5---154.7 <0.001 171±69 262±75 7.2---175.0 0.04

Maximum 198±28 279±82 39.8---122.1 <0.001 199±78 281±71 −12.2to175.8 0.08

Retroglossal

AP(mm)

Minimum 2±2 10±4 5.7---9.9 <0.001 4±3 9±4 1.5---9.2 0.01

Maximum 7±4 10±4 −0.0to7.5 0.05 8±4 10±5 −2.2to6.7 0.27

Sectionalarea(mm2)

Minimum 108±63 245±79 74.3---199.7 <0.001 121±48 247±104 60.1---191.5 0.001

Maximum 227±129 266±89 −81.8to160.1 0.48 210±78 268±108 −37.8to153.9 0.2

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Table4 Comparisonofmeandifferencesinairwaydimensionsbetweenlowandhighdosedexmedetomidineinchildrenwith

normalairwayandchildrenwithDownSyndrome.

Dimensions Down(lowvs.highdoseDEX) Normal(lowvs.highdoseDEX)

Meandifference 95%CI p-Value Meandifference 95%CI p-Value

Nasopharyngeal

AP(mm)

Minimum −0.4 −2.0to1.3 0.56 0.1 −0.4to0.5 0.79

Maximum −0.2 −1.9to1.5 0.76 0.3 −0.1to0.7 0.31

Sectionalarea(mm2)

Minimum −1.5 −120.5to117.5 0.97 2.2 −8.7to13.2 0.67

Maximum 6.3 −114.9to127.6 0.89 −2.4 −13.7to8.9 0.67

Retroglossal

AP(mm)

Minimum −1.5 −5.4to2.3 0.33 0.7 −0.0to1.5 0.06

Maximum −2.0 −9.4to5.5 0.51 0.3 −0.5to1.2 0.41

Sectionalarea(mm2)

Minimum 3.1 −109.4to115.7 0.94 −1.9 −17.8to14.0 0.81

Maximum 4.9 −168.0to177.8 0.94 −1.9 −19.8to16.0 0.83

Themeandifferencesinthistableareobtainedasapairedanalysisfromthedatasetanddonotrepresentsimplythedifferenceoftwo

correspondingmeansfromTable3.

Sedatingor anesthetizingachildknowntohave OSAis achallengebecauseanestheticagentsbluntarousal mech-anisms,decreaserespiratorydrive, andreducepharyngeal muscle tone. More than half of all children with DShave OSA, andthese childrenare at higherrisk of adverse air-wayeventsduringproceduralsedation.Ourstudyexamined theanatomicalsagittalsectionalareasanddiameteratthe criticalpartof theairway. Weshow thatairwaysectional areasanddiametersweresignificantlyreducedinchildren withDS compared tothose children withNA at both low andhighdoseDEX.Thechangesinairwaydimensionswere notdose-dependentwithinthe patientgroups. The seem-ingindependence of airwaydimensions andDEXdose can beexplainedbytherelationshipbetweenconsciousnessand upperairwaycollapsibility.Profoundchangesin upper air-waymuscleactivityandcollapsibilityoccurproximatetothe lossof consciousnessandrelatively modestchanges occur withincreasingdepthofanesthesia/sedation.14

Furthermore,wequantitatetheeffectofDEXsedationon airwaymorphologyinchildrenwithDS.Itisourhope that practitioners can utilize this information tobetter assess the depthof sedation of their DSpatients and ultimately avoid theadverse effects of over sedation(e.g. hypoven-tilation,airway obstruction). As pediatric DSpatients can rapidly obstructtheir airways evenat low doses of seda-tion,providersshouldalsoconfirmthatairwaymanagement instrumentsarereadilyavailablebeforesedatingthese chil-dren.

PatientswithDSalsohaveahigherchanceofpersistent OSA followingtonsillectomydue torecurrentenlargement of lingual tonsils and adenoid tissue, reduced muscular tone,hypopharyngealcollapse,andglossoptosis.15,16MRIof the airway in adolescents for evaluation of OSA revealed thatchildrenwithDShavedisproportionatelylargetongues in comparisonto the craniofacialparameters of age- and gender-matched controls.3 The findings from the present

studyshowthatairwaysizewasstablebetweenthedosage levels of DEX studied. This suggests that the airway col-lapsibilityisprobablycausedbyreducedmusculartoneand hypopharyngealcollapse,glossoptosis,midfacehypoplasia, andrelativemacroglossia.3,15,16Pharyngealcollapseismore severeinchildrenwithDScomparedtocontrols, indepen-dentofage,gender,andbodymassindex.17Theaugmented upperairwaydilatoractivitypresentin theawake stateis reduced at sleep onset, and is further attenuated during rapideyemovementsleep,contributingtopharyngeal col-lapse in children withOSA.18,19 Additionalcontributors to airwayobstructionduringsedationwithintravenous pento-barbital inchildren with moderateOSA includelarge soft palate,and,largeadenoidsandtonsils.20

Theairwaysectionalareaandanteroposteriordiameter weremeasuredasminimumandmaximum,whichrepresent dimensions during inhalation and exhalation respectively. Thiswas donetointerpret relative changesin theairway duringtherespiratorycycle.Thepeakimageacquisitionrate of800mswasperformedandallowedforrandomsampling during the respiratory cycle. Segmentation of the airway sizeover thebreathingcycle andtheuseof thepeaksize andminimal sizeobviatedtheneedforsynchronization to therespiratorycycle.Theairwayislargestduringexpiration andsmallestduringinspirationunlesstongue/jawthrusting ispresentandtheairwayismoredynamicinOSA.21

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higher fatigability seen in inspiratory muscles in patients withOSA.23

Thereareafewlimitationswithourstudy.Althoughour sample size remains a limitation and may limit our sta-tistical significance particularly withhigh dose DEX group nasopharyngealareameasurements(post hocpower71%), ourpreliminaryfindingsarerelevantindefiningand apply-ing interventionsto improveairway outcomes in children undergoingsedation outside the operating room. Second, all of the patients withDS in our study had moderate to severeOSA. Thefindings maybedifferentinthe minority ofthosepatients withDSwithnoOSA. Whileit wouldbe idealtostudyDSpatientswithnoOSAasathirdgroup,the availabilityofanadequatenumberofDSpatientshavingMRI ofairwayfornon-OSAindicationsisamajorlimitingfactor. Last,themeansedationscoreinchildrenwithDSwas sig-nificantlyhigherduringinduction ascomparedtochildren withNAand mayhaveaffected measurementsduringlow doseDEX.AlthoughUMSScaptureschangesinthedepthof sedation,theinabilityofthescaletodiscriminatemoderate anddeeplevelsofsedationmaylimititsusefulnessinsuch situations.24

Conclusions

Insummary,childrenwithDSwithOSAexhibitedsignificant reductionsinanatomicalairwaydimensionswhencompared to children with NA under DEX sedation, supporting our hypothesis.The relativereductioninairwaydimensions is equalatbothlow doseandhighdoseDEX,whichsuggests thattheobserveddifferencesareuniquetoDSandnotdue todifferences insedation.These changesaremost signif-icant at the narrowest points in the nasopharyngeal and retroglossalairways.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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Imagem

Figure 1 Still image (A) from a sagittal cine clip shows the nasopharynx airway (short arrows) and the retroglossal airway (long arrows) as open and the still image (B) shows the retroglossal airway as collapsed.
Figure 2 Still image (A) from the cine clip shows the retroglossal airway in cross-section while open (arrowheads) and the still image (B) shows the airway completely collapsed centrally compatible with hypopharyngeal collapse.
Table 3 Comparison of airway dimensions between children with Down Syndrome and children with normal airway under both low and high dose dexmedetomidine.
Table 4 Comparison of mean differences in airway dimensions between low and high dose dexmedetomidine in children with normal airway and children with Down Syndrome.

Referências

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