Rev. Bras. Anestesiol. vol.67 número4

REVISTA

BRASILEIRA

DE

ANESTESIOLOGIA

www.sba.com.br

SCIENTIFIC

ARTICLE

Use

of

ultrasound

for

gastric

volume

evaluation

after

ingestion

of

different

volumes

of

isotonic

solution

夽

Flora

Margarida

Barra

Bisinotto

,

Aline

de

Araújo

Naves

,

Hellen

Moreira

de

Lima

,

Ana

Cristina

Abdu

Peixoto

,

Gisele

Caetano

Maia

,

Paulo

Pacheco

Resende

Junior

_,

_Laura

_Bisinotto

_Martins

_,

_Luciano

_A.

_Matias

_da

_Silveira

a_{SociedadeBrasileiradeAnestesiologia,RiodeJaneiro,RJ,Brazil}

b_{UniversidadeFederaldoTriânguloMineiro(UFTM),HospitaldeClínicas,Uberaba,MG,Brazil} c_{UniversidadeEstadualPaulista‘‘JúliodeMesquitaFilho’’(UNESP),Botucatu,SP,Brazil}

d_{UniversidadeFederaldoTriânguloMineiro(UFTM),DisciplinadeAnestesiologia,Uberaba,MG,Brazil} e_{UniversidadeFederaldoTriânguloMineiro(UFTM),Servic¸odeRadiologiaeDiagnóstico,Uberaba,MG,Brazil} f_{UniversidadeFederaldoTriânguloMineiro(UFTM),Servic¸odeRadiologiaeDiagnóstico,Uberaba,MG,Brazil} g_{Fundac¸ãodeAmparoàPesquisadoEstadodeMinasGerais(FAPEMIG),BeloHorizonte,MG,Brazil}

h_{UniversidadeFederaldoTriânguloMineiro(UFTM),ProgramadePós-Graduac¸ãoemCiênciasdaSaúde,Uberaba,MG,Brazil} i_{UniversidadedeRibeirãoPreto(UNAERP),CursodeGraduac¸ãoemMedicina,RibeirãoPreto,SP,Brazil}

Received29January2016;accepted26July2016 Availableonline9April2017

KEYWORDS

Bronchoaspiration;

Gastricultrasound;

Preoperativefasting

Abstract

Backgroundandobjectives: Thecurrentpreoperativefastingguidelines allowfluidintakeup to2hbeforesurgery.Theaimofthisstudywastoevaluatethegastricvolumeofvolunteers afteranovernightfastandcompareitwiththegastricvolume2hafteringestionof200and 500mLofisotonicsolution,bymeansofultrasoundassessment.

Method: Eightyvolunteersunderwentgastricultrasound atthreetimes:after8hoffasting; 2hafteringestionof200mLisotonicsaline,followedbythefirstscan;andonanotherday,2h afteringestionof500mLofthesamesolutionafteranovernightfast.Theevaluationwas quan-titative(antrumareaandgastricvolume,andtheratioofparticipants’gastricvolume/weight) andqualitative(absenceorpresenceofgastriccontentsonrightlateraldecubitusandsupine positions.Ap-value<0.05wasconsideredsignificant).

Results:Therewas nodifferenceinquantitativevariables atmeasurementtimes(p>0.05). Fivevolunteers(6.25%)hadavolume/weightover1.5mLkg−1_{atfastingand2hafteringestion} of200mLand6(7.5%)after500mL.Qualitatively,thepresenceofgastricfluidoccurredinmore volunteersafterfluidingestion,especially500mL(18.7%),althoughnotstatisticallysignificant.

夽 _{StudyperformedattheHospitaldeClínicasdaUniversidadeFederaldoTriânguloMineiro(UFTM),Uberaba,MG,Brazil.} ∗_{Correspondingauthor.}

E-mail:[email protected](F.M.Bisinotto).

http://dx.doi.org/10.1016/j.bjane.2017.03.001

Conclusion: Ultrasoundassessmentofgastricvolume showednosignificant difference,both qualitativeandquantitative,2hafteringestionof200mLor500mLofisotonicsolution com-paredtofasting,althoughgastricfluidcontenthasbeenidentifiedinmorevolunteers,especially afteringestionof500mLisotonicsolution.

©2016SociedadeBrasileiradeAnestesiologia.Publishedby ElsevierEditoraLtda.Thisisan openaccessarticleundertheCCBY-NC-NDlicense

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

PALAVRAS-CHAVE

Broncoaspirac¸ão;

Ultrassonografia gástrica;

Jejumpré-operatório

Usodaultrassonografiaparaavaliac¸ãodovolumegástricoapósingestãodediferentes volumesdesoluc¸ãoisotônica

Resumo

Justificativaeobjetivos: Asdiretrizesrecentesdejejumpré-operatóriopermitemaingestão delíquidosaté2horasantesdacirurgia.Oobjetivodopresenteestudofoi,pormeiode ultra-ssonografiagástrica,avaliarovolumegástricodevoluntáriosapósjejumnoturnoecomparar comovolumegástricoduashorasapósaingestãode200e500mldesoluc¸ãoisotônica. Método: Foramsubmetidosàultrassonografiagástrica80voluntáriosemtrêsmomentos:após jejumde8horas;2horasapósaingestãode200mldesoluc¸ãoisotônica,seguidadoprimeiro exame; e,em outro dia,2horasapós aingestãode 500ml damesma soluc¸ão,após jejum noturno. A avaliac¸ão foi quantitativa (área do antro e volume gástricos e relac¸ão volume gástrico/pesodosparticipantes)equalitativa,pelaausênciaoupresenc¸adeconteúdogástrico nasposic¸õesdedecúbitolateraldireitoesupina.Foiconsideradosignificantep<0,05. Resultados: Não houve diferenc¸a nas variáveis quantitativas nos três momentos estudados (p>0,05).Cincovoluntários(6,25%)apresentaramumvolume/pesosuperiora1,5ml.kg−1_em jejume2horasapósaingestãode200mleseis(7,5%)após500ml.Qualitativamente,apresenc¸a delíquidogástricoocorreuemmaisvoluntáriosapósaingestãodelíquidos,principalmentede 500ml(18,7%),emborasemsignificânciaestatística.

Conclusão:Ovolumegástricopelaultrassonografianãoapresentadiferenc¸asignificativatanto qualitativa quanto quantitativa, 2horasapósa ingestãode200ml ou de500ml de soluc¸ão isotônicaemcomparac¸ãocomojejum,emboraconteúdolíquidogástricotenhasidoidentificado emmaisvoluntários,principalmenteapósaingestãode500mldesoluc¸ãoisotônica.

©2016SociedadeBrasileiradeAnestesiologia.PublicadoporElsevierEditoraLtda.Este ´eum artigo OpenAccess sobumalicenc¸aCCBY-NC-ND

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

Aspirationof gastriccontents isa majorcauseof morbid-ity andmortality during generalanesthesia, aswell asin the intensive care unit.1---3 _{The risk of mortality is up to}

5% and it is involved in over 9% of all deaths related to anesthesia.4,5_{Thepresenceofgastriccontentsatthetime}

of anesthesiainduction is an important risk factor for its occurrence,whichmakesthedietaryrestrictionrulebefore anesthesia essential for patient safety. Although there is a controversy about the gastric residualvolume,which is consideredcriticalbecausethisvolumeitselfincreasesthe riskofaspiration,studieshaveshownthathealthypatients underfastingoftenhaveresidualvolumeabove1.5mLkg−1 withoutsignificantlyincreasedriskforaspiration.6---8

Duringthe1980s,apatientundergoingextendedperiods offastingbeforeelectiveprocedureswasaroutinepractice, which still remains in various institutions. The preoper-ative fasting recommendations have become increasingly moreliberal, sothat thecurrent guidelinesfor preopera-tive fasting9,10 _{encourage the ingestion of clear liquids in}

volumesfrom100mLtounlimitedquantitiesforadultsupto 2hbeforesurgery.Thisapproachaimstoreducepatient dis-comfortandhemodynamiccomplicationsduringinductionof anesthesia,whichareoftenrelatedtodehydrationresulting fromprolongedfasting.11,12 _{The non-adherenceto}

recom-mendationsmayreflectamedicalpreferenceorflawsinthe guidelinesthemselves,suchasnotdeterminingtheallowed amountofliquid.Theclinicalaccesstotheriskofaspiration islimitedduetothelackofvalidatednon-invasiveteststo assessgastriccontents.Theincreaseduseofportable ultra-sound in surgical centers aroused interest in its use as a diagnostic methodfor gastric content evaluation. Studies haveshown thefeasibilityofusingultrasoundtoevaluate thegastriccontentbymeasuringtheantralcross-sectional area(ACSA).13---17 _Perlasetal.15 _{reported an almostlinear}

relationship between ACSA and gastric volume in healthy volunteers.

Method

After obtaining approval from the Ethics Research Com-mittee of the Universidade Federal do Triângulo Mineiro ---register 1.144.018 of June 19, 2015 --- andan informed consent, this prospective cross-sectional study was con-ductedwith80healthyvolunteers. Inclusioncriteriawere age between 18 and 60 years,American Society of Anes-thesiologists(ASA)physicalstatusIandII,bodymassindex (BMI)under30kgm−2 _{andability tounderstand the study} protocolandtheinformedconsent.Anyconditionthatmight interferewiththegastricemptyingtime,suchaspregnancy, diabetes,orpresenceofgastrointestinaldisease,was con-sideredanexclusioncriterion.

The volunteers underwent abdominal ultrasound for quantitative and qualitative analysis of gastric contents measured in three times. The first measurement time (named fasting)wasafter an overnight periodof at least 8h.Thesecondtime(named200mL+fasting)was2hafter ingesting 200mL of isotonic solution,which wasingested immediatelyafter the ultrasoundexamination at thefirst time.Thethirdmeasurementtime(named500mL+fasting) was performed on another day. After a minimum period of8h ofovernightfast,thevolunteersingested500mLof isotonicsolutionandafter2hunderwentultrasound exam-ination.Allisotonicsolutionswerethesameandcontained carbohydrates (8.4g), sodium (57mg), chloride (49mg), potassium(46mg),flavoringandpreservativesagents, calo-rie contentof 36kcal per 200mL, andwere refrigerated. Therewasno restrictiononambulationafter ingestion of solutions.

Theultrasoundassessmentofgastriccontentwasmade byaprofessionaloftheDepartmentofRadiologyofthe insti-tution.Testswereperformedusingthetechniquepreviously described,13---18 _{witha convexprobe(2---5MHz).Volunteers}

wereinitiallyexaminedinthesupineposition,followedby theright lateral decubitus (RLD)position. The transducer wasplacedinthesagittalplaneintheepigastricregionand then the antrum and gastric body were scannedby mov-ing the transducer from right to left, in order to obtain an overall qualitative impression of the cavity and gas-triccontents. A better viewof the antrum is obtained in parasagittalplanejusttotherightofthemidline.Theliver leftlobewastakenasreference,previously,andthe pan-creas, posteriorly. Inferior vena cava is located posterior tothe pancreas.The antrum has awall characterized by multiplelayersanditsvisibilitywasevaluatedina binary manner(visible or not)inboth positions,supineandRLD. Thesamesonographerperformedthequalitativeand quan-titativeassessmentsofthegastricantrum.Theantrumwas consideredemptywhenshowingtheanteriorandposterior walls juxtaposed and regarded as containing liquid when showingacavityviewwithhypoechoiccontentinsideand its distended walls. The antrum was judged as having a solidcontentwhenappearingdistendedwithcontentwith characteristics similarto‘‘frostedglass’’or an echogenic imagesimilartoliverparenchyma.Basedonlyonthis quali-tativeanalysisoftheantrum,thepatientswereclassifiedas Gradezero:emptyantruminbothsupineandRLDpositions, suggestinganemptystomach; Grade1:presenceofliquid apparentonlyinRLD,suggestingsmallamountoffluidinthe stomach;Grade2:presenceofliquidcontentsinbothsupine

andRLDpositions,suggestingthepresenceofincreased gas-tricvolume.

For quantitative analysis, we measured the antral cross-sectional area(ACSA) usingthe technique described originallybyBolondi18_{and,subsequently,byPerlasetal.}13---15

using theouter wallof the stomach. ACSA wasmeasured in RLD usingtwo perpendiculardiameters of theantrum, fromserosatoserosa,longitudinalorcraniocaudal(CC),and theanteroposterior(AP)usingtheellipseformuladeveloped byBolondietal.,18 _{inwhichACSA=((CC×AP)×)/4,with} -value=3.14.

After ACSA calculation, the stomach total volume (‘‘expectedvolume’’)wasestimatedforeachsubjectusing a mathematical model previouslytested and validated by otherauthors,15_inwhich:

Stomachvolume(mL)=27+14.6ACSA(cm2)

−1.28age(years)

Withtheexpectedvolumecalculation,wasobtainedthe relationshipbetweenthevolumeandweight(vol/wt)of vol-unteerswereobtained.

FriedmanANOVAwasusedforstatisticalanalysis. Sam-ple size(n=80) wascalculated toobtain 95% confidence, 80%powertest,androotmeansquareerror(RMSE)=0.25. Quantitative variables, antral gastric area (cm2_{), gastric} volume(mL),andtherelationshipbetweengastricvolume and weight (vol/wt) of subjects (mLkg−1_{) were initially} subjected toadescriptiveanalysisusingmeasuresof cen-tralityanddispersion.Thesevariablescomparisonbetween timepoints(fasting,200mL+fasting,500mL+fasting)was performed usingFriedman’snonparametricANOVA,dueto the non-normality in data assessed by the Shapiro---Wilk test.Regardingthegroupsqualitativeevaluationofgastric contents,anassociationanalysisusingthe2testwas per-formed,followedbyaresidueanalysiswhenthe2testwas significant.Thesignificancelevelfortheinferential proce-dureswas5%.

Results

The study included 84 volunteers and 80 completed all tests(240 tests),withoutanyadverse eventor delay that would undermine the results.Participants’ characteristics areshowninTable1.Theresultsofgastriccontent qualita-tiveassessmentareshowninTable2.Noneofthevolunteers hadsolidcontentduringtheexamination.Regarding qualita-tiveassessmentofgastriccontentsaccordingtothegroups,

Table1 Demographicdataofstudyparticipants.

Mean±standarddeviation

Age(years) 33.98±10.73

Weight(kg) 69.82±12.55

Height(m) 1.67±0.09

BMI(kgm−2_{) 24.86±3.85}

Sex

Male 24

Female 56

Table2 Distributionofstudyparticipantsregarding quali-tativeassessmentofgastriccontentsandgroups.

Grade0 Grade1 Grade2

Fasting 65(81.25%) 11(13.75%) 4(5%) 200mL+2h 55(68.75%) 14(17.5%) 11(13.75%) 500mL+2h 57(71.25%) 8(10%) 15(18.75%)

p=0.07,2stat=8.8.

therewasahighernumberofsubjectswithGradezeroin

fasting group (81.25%), Grade 1 in 200mL+fasting group

(17.5%),andGrade2in500mL+fastinggroup(18.75%),

sug-gestingthat a largervolumeingestedresults in increased

gastriccontentsafter2hoffasting.However,this

associa-tionwasnotstatisticallysignificant(p=0.07).

There was no difference at any time point regarding

theresultsofquantitativeassessment,antralarea,gastric

volume, and volume/weight ratio at the three

measure-ment times (p>0.05) (Figs. 1---3). Fivevolunteers (6.25%)

hada volume/weightratio over1.5mLkg−1_{,both at} fast-ingand200mL+fastingperiods,andsixpatients(7.5%)at 500mL+fasting(Fig.3).Noneofthemwasthesamesubject inthedifferentsituations.

Discussion

Theaimofthisstudywastoevaluatethegastriccontentin healthyvolunteersusingreal-timeultrasound.The qualita-tiveevaluationresultsshowedanincreaseinthepercentage ofsubjectswithliquidcontent2haftertheintakeoffluids, particularlywith500mLvolumein15subjects(18.75%)seen inthesupineandRLDpositions,whichsupportsanexpected gastric volume of 180±83mL.19 _{In the gastric volume}

Friedman ANOVA (p = 0.69)

Times

Gastric antral area (cm

2)

Night fasting

200 mL + 2h fasting 500 mL + 2h fasting

18

16

14

12

10

8

6

4

2

0

Median 25%-75% Min-Max

Figure 1 Box-plot showing the median and interquartile

rangeforthegastricantralareainthethreemeasurementtimes (p>0.05).

240

Fasting

200 mL + 2h fasting 500 mL + 2h fasting Friedman ANOVA (p = 0.58)

Times

Gastric volume (mL)

220

200 180 160

140 120

100 80

60 40

20 0

–20

Median 25%-75% Min-Max

Figure 2 Box-plot showing the median and interquartile

range for gastric volume in the three measurement times (p>0.05).

(antralarea,expectedgastricvolume,andvolume/weight ratio)quantitativeevaluation,theresultsobtainedafterthe overnightfastingperioddidnotdifferfromthoseafter2h ofingesting200mLor 500mLvolumes.Additionally,these resultsalsoconfirmedtheexistence ofvariablequantities ofgastric volume afterthe fastingperiod,which in some subjectswasover1.5mLkg−1_.

Gastricsonography is anovel point-of-careapplication ofdiagnosticultrasound,whichallowsanesthesiologiststo

3.5

5 (6.25%)

Fasting

200 mL + 2h fasting 500 mL + 2h fasting

5 (6.25%) _{6 (7.5%)}

Friedman ANOVA (p = 0.58)

Times

Gastric volume/weight (mL.kg

–1) 3.0

2.5

2.0

1.5

1.0

0.5

0.0

–0.5

Median 25%-75% Min-Max

Figure 3 Box-plot showing the median and interquartile

evaluatepatients’gastriccontentandvolumeandthusthe risk of aspiration at bedside, in addition tohelp decision makingforanestheticandairwaymanagement.Ithasbeen validated15_{andalsoconsideredhighlyreproducible.}20

Aspiration of gastric contents is one of the most feared anesthetic complications and is still considered a major cause of morbidity and mortality related to gen-eral anesthesia.20 _{Described almost 70 years ago in one}

of the most widely cited articles of the medical litera-ture,Mendelson,21,22_{whodescribedaspirationinobstetrics,}

helpedintheformationofanestheticmanagementthrough generations.And‘‘nothing by mouth’’(NPO), empirically, forlongerthan8---12hhasbecomeastandardpracticeinthe nameofsecurity.Thereasonwhysuchlongperiodsofliquid fastingwereintroducedintoclinicalpracticeisuncertain. However,atatimeinwhichpulmonaryaspirationwasoneof themaincausesofanestheticmortality,theextrapolation ofresults of studies withrhesus monkeys towomen arbi-trarilydefinedasatriskforaspirationthosewhopresented agastricvolumeabove25mL(0.4mLkg−1_{)andpH<2.5;the} conceptof criticalvolumeandpH wasintroduced.23 _That

claim later found support in another experiment carried outonrhesusmonkeysinwhichacidsolution(0.4mLkg−1₎ withpH=1.26wasinstilledintotheanimalbronchivia tra-cheotomy,resultingincardiacarrest.19_{Furtherstudies,}24,25

alsowithmonkeys,have shown thathigher volumeswere needed to result in severe pneumonitis and death and, again,extrapolation tohumansincreased thecritical vol-umefrom25mLto50mL(0.8mLkg−1_{),whichsignificantly} reduced the number of patients considered ‘‘at risk’’. Althoughthisvolumeisprobablyconsideredinsufficientby itselftolead topulmonary aspiration,thecombination of thiscriticalvolumewithotherfactors,suchashiatalhernia orinadequateanesthesia,maybeenoughtocause aspira-tionwithlunginjury.26 _{Untilthenpatientsweresubjected}

toprolonged fastingperiods. Andfor about 20 years,the approaches related to preoperative fasting began to be reviewed.7

Thus,currentguidelines9,10_{recommendclearliquidsup}

to2hbeforesurgery,whichisacompromisebetween com-fort, cooperation and hydration, on the one hand, and securityontheother.Andourresultsofquantitative ana-lyzessupportedexactlytheseguidelines,showingthat 2h after clear fluid intake there was no significant changes in gastric contents comparedtofasting over 8h. Another frequentquestionofallprofessionalsworkingwithsurgery and fast recommendation concerns the volume that can beingested. Our study found that ingestion of 200mL or 500mL showed no difference in gastric residual volume aftera periodof 2h fasting,compared toovernight fast-ing.Althoughfluidintakeisqualitativelyassociatedwiththe presenceofgastricfluidcontent,thevolumewasincreased aftertheingestionof500mL.

The stomach has many complexfunctions. It serves as a reservoir for everything we eat, efficiently macerates food, starts the early stages of digestion and then care-fullyandslowly,almostmethodically,releasesitscontents into the small intestine. Solids follow a zero-order emp-tying kinetics. That is, at a constant speed according to thenumberof calories(about 200kcalh−1_).27---29 _Clear

liq-uidsfollowadramaticallydifferentpath,emptyingquickly fromthestomach,followingafirstorderkinetics27 _(i.e.,a

decline described by an exponential curve). Some liquids such as waterand 0.9% saline have a very shorthalf-life ofabout 10min, andeffectivelyonlyhave aflushthrough thestomach.27,30_{However,high-calorieliquidshaveaslower}

emptyingrate,suchassolidfoods.Inthisstudyweusedan isotonicenergyvalueof36kcalper200mL.Thus,the num-berofcaloriesingestedwas36kcalbysubjectswhoreceived 200mLand90kcalbythosewhoreceived500mL.Allwereat thesametemperatureandtherewasnorestafteringestion, factorsthatcouldaltergastricemptying.Becausethesame volunteersweretestedinthethreetimepoints,individual factorsdidnotinfluencetheresultsobtained.Thus,the vol-umeandtheenergyvalueoftheingestedsolutionwerethe factorsthatinfluencedtheresults. Althoughtherewasno significantquantitativedifferenceintheresultsobtainedby statisticalcomparisonofthemeasurementtimes,therewas an increase in the number of volunteers withgastric vol-umeGrade2inthequalitativeevaluationafter200mLand, especially, after500mL comparedwith8hfasting.In this qualitativeevaluation,thepresenceofsomeamountof liq-uidinsidethestomachshouldbeconsideredeveninpatients whofastedformorethan8h.Inthisstudy,fivevolunteers (6.25%)(Fig.3)hadvolumesgreaterthan1.5mLkg−1_inthe first evaluation and four of them (5%) were classified as Grade2.Thesevolumesareconsidered commoninfasting patients,andconsideredsafe.15_{Oralandgastricsecretions}

areconstantlyaddedtothestomach,whichalwayscontains some amountof liquid.Salivaproduction occursata rate of 0.4---1.0mLkgh−1_{,withendogenous gastricsecretion in} a similarproduction rate.31 _{This explains the presence of}

varyingamountsofliquidshownbyultrasonographyin fast-ing volunteers,which were alsoseen after 2h of isotonic solutioningestion,irrespectiveofthevolume.

Although there are numerous studies on the safety of drinking clear liquids up to 2h before surgery and establishment of preoperative fasting guidelines, many anesthesiologistsandsurgeonsarestillunsureofthe prac-tice.Therefore,noninvasiveassessmentsatthebedsidethat coulddeterminethevolumeofgastriccontentsinthe peri-operativeperiodwouldbeofinteresttoassistinassessing theriskofpulmonaryaspiration.Untilrecentlytherewasa lackofanon-invasivediagnosticmethodthatcouldpromptly assessgastriccontentandbeappliedperioperative. Ultra-soundisthefirstnon-invasivetechniquethatprovidesboth quantitativeandqualitativevalidatedinformationofgastric contents at bedside.12---15 _{Several studies suggest that the}

gastricantrumisthestomachregionthatismoreamenable to ultrasound examination.13,17,32 _{It can be identified in}

98---100%ofcases.14,16,33_{Severalmathematicalmodelswere}

developed for gastricvolumecalculation usingthe gastric antrum imageandcalculatingitscross-sectionalarea.14---16

Thismethodcanpredictvolumesof0---500mLandappliesto adultpatientswithbodymassindexunder40kgcm−2_.The marginoferrorinmeasurementsisonly±6mL.15_Thereare

othermethodstoassessgastricemptying,butarenot appli-cabletotheperioperativeperiod.34,35_{Gammascintigraphyis}

anoninvasivemethodconsideredagoldstandard.35,36_Ithas

eval-uation.Perlasetal.,13_{inastudythatevaluatedthegastric}

volumeinfastingpatients,found3.5%ofsubjectsexamined withthestomachclassifiedasGrade2,whileinthepresent studywefound5%.Theportabilityandconvenienceofthese devices,combinedwiththelowcost,allowitsuseatbedside andvarioustypesofdiagnosticapproaches,suchasgastric evaluation.Afteryearsofuncertainty,studieshaveshown sufficientevidenceofitsaccuracyandreproducibility.

Although ithassome limitations,aswithallultrasound techniques, which isdependent onthe equipmentquality andalsotheoperator,theantrumis notidentifiablein all patients and several steps need tobe performed system-atically toobtain reliable results, besides not having the abilitytoevaluatethepH.Thepresentstudywasconducted withhealthyvolunteersand,thus, theresults maynotbe extrapolatedtopatientswithchronicdiseasesortaken med-icationsthat alter the digestivesystem motility. Forsuch patients,thefastingrecommendationsshouldbetailored.

We conclude that in fasting healthy volunteers after receiving200mLor500mLofisotonicsolutionand remain-ing2h fasting,thegastric antral area,stomach expected volume,andgastricvolume/weightshownosignificant dif-ferencescomparedtothesamedataafteraminimumfasting periodof8hinthesonographicevaluation.However, qual-itatively,thereisanincreaseinthepercentageofsubjects withdetectableliquidcontentsinbothsupineandright lat-eraldecubituspositions2hafteringestingboth200mLand especially500mLcomparedtofasting.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

Acknowledgements

Gilberto Araújo Pereira, Professor of Biostatistics of the NursingCourseofUFTM.

References

1.Ng A, Smith G. Gastroesophageal reflux and aspiration of gastric contents in anesthetic practice. Anesth Analg. 2001;93:494---513.

2.Neelakanta G, Chikyarappa A. A review of patients with pulmonary aspiration of gastric contents during anesthesia reportedtotheDepartmentalQuality Assurance Committee. JClinAnesth.2006;18:102---7.

3.MetznerJ,PosnerKL,LamMS,etal.Closedclaims’analysis. BestPractResClinAnaesthesiol.2011;25:263---76.

4.ShimeN,OnoA,ChiharaE,etal.Currentstatusofpulmonary aspirationassociatedwithgeneralanesthesia:anationwide sur-veyinJapan.Masui.2005;54:1177---85.

5.Schwartz DE, Matthay MA, Cohen NH. Death and other complicationsofemergencyairwaymanagementincriticallyill adults.Aprospectiveinvestigationof297trachealintubations. Anesthesiology.1995;82:367---76.

6.AgarwalA,ChariP,SinghH.Fluiddeprivationbeforeoperation: theeffectofasmalldrink.Anesthesia.1989;44:632---4.

7.PhillipsS,HutchinsonS,DavidsonT.Preoperativedrinkingdoes notaffectgastriccontents.BrJAnesth.1993;70:6---9.

8.HarterR,KaellyW,KramerM,etal.Acomparisonofthe vol-umeandpHofthegastriccontentsofobeseandleansurgical patients.AnesthAnalg.1998;86:147---52.

9.SmithI,KrankeP,MuratI,etal.Perioperativefastinginadults andchildren:guidelinesfromtheEuropeanSocietyof Anaes-thesiology.EurJAnaesthesiol.2011;28:556---69.

10.Practiceguidelinesfor preoperativefasting,theuseof phar-macologicagentstoreducetheriskofpulmonary aspiration: applicationtohealthypatientsundergoingelectiveprocedures. AnupdatedreportbytheAmericanSocietyofAnesthesiologists CommitteeonStandards,PracticeParameter.Anesthesiology. 2011;114:495---511.

11.ReadMS,VaughanRS.Allowingpre-operativepatientstodrink: effectsonpatients’safetyandcomfortofunlimitedoralwater until 2hours before anaesthesia. Acta Anaesthesiol Scand. 1991;35:591---5.

12.SrinivasaS,TaylorMH,SinghPP,etal.Randomizedclinicaltrial ofgoal-directedfluidtherapywithinanenhancedrecovery pro-tocolforelectivecolectomy.BrJSurg.2013;100:66---74.

13.PerlasA,DavisL,KhanM,etal.Gastricsonographyinthefasted surgicalpatient:aprospectivedescriptivestudy.AnesthAnalg. 2011;113:93---7.

14.PerlasA,ChanVW,LupuCM,etal.Ultrasoundassessmentof gastriccontentandvolume.Anesthesiology.2009;111:82---9.

15.PerlasAM,NicholasM,LuiL,etal.Validationofamathematical modelofultrasound-determinedgastricvolumebygastroscopic examination.AnesthAnalg.2013;116:357---63.

16.BouvetL,MazoitJX,ChassardD,etal.Clinicalassessmentof theultrasonographicmeasurementofantralareafor estimat-ingpreoperativegastriccontentand volume.Anesthesiology. 2011;114:1086---92.

17.FujigakiT,FukusakiM,NakamuraH,etal.Quantitative eval-uation of gastric contents using ultrasound. J Clin Anesth. 1993;5:451---5.

18.BolondiL,BortolottiM,SantiV,etal.Measurementofgastric emptyingtimebyreal-timeultrasonography.Gastroenterology. 1985;80:752---9.

19.RobertsRB,ShirleyMA.Antacidtherapyinobstetrics. Anesthe-siology.1980;53:83.

20.KruisselbrinkR,ArzolaC,EndersbyR,etal.Intra-and inter-rater reliability ofultrasound assessment ofgastric volume. Anesthesiology.2014;121:46---51.

21.LienhartA, AuroyY,PequignotF,etal.Surveyof anesthesia-relatedmortalityinFrance.Anesthesiology.2006;105:1087---97.

22.Mendelson CL. The aspiration of stomach contents into the lungs during obstetric anesthesia. Am J Obstet Gynecol. 1946;52:191---205.

23.Roberts RB, Shirley MA. Reducingthe riskof acid aspiration duringcesareansection.AnesthAnalg.1974;53:859---68.

24.RaidooDM,RockeDA,Brock-UtneJG,etal.Criticalvolumefor pulmonaryacidaspiration:reappraisalinaprimatemodel.Br JAnaesth.1990;65:248---50.

25.EngelhardtT,WebsterNR.Pulmonaryaspirationofgastric con-tentsinanaesthesia.BrJAnaesth.1999;83:453---60.

26.KlugerMT,ShortTG.Aspirationduringanaesthesia:areviewof 133casesfromtheAustralianAnaestheticIncidentMonitoring Study(AIMS).Anaesthesia.1999;54:19---26.

27.HuntJN.Mechanismsanddisordersofgastricemptying.AnnRev Med.1983;34:219---29.

28.HellströmPM,GrybäckP,JacobssonH.Thephysiologyofgastric emptying.BestPractResClinAnaesthesiol.2006;20:397---401.

29.Splinter WM,Schreiner MS.Preoperative fasting in children. AnesthAnalg.1999;89:80---9.

30.ErskineL,HuntJN.Thegastricemptyingofsmallvolumesgiven inquicksuccession.JPhysiol.1981;313:335---41.

32.CubillosJ,TseC,ChanVW,et al.Bedsideultrasound assess-mentofgastriccontent:anobservationalstudy.CanJAnaesth. 2012;59:416---23.

33.BouvetL,MiquelA,ChassardD,etal.Couldasingle standard-izedultrasoundmeasurementofantralareabeofinterestfor assessinggastriccontents?Apreliminaryreport.EurJ Anesthe-siol.2009;26:1015---9.

34.NaslundE,BogeforsJ,GrybackH.Gastricemptying:comparison ofscintigraphic,polyethyleneglycoldilutionandparacetamol

tracer techniques. Scand J Gastroenterol. 2000;35: 375---9.

35.HillyardS, Cowman S, Ramasundaram R, et al.Does adding milkto teadelaygastric emptying?Br J Anaesth.2014;112: 66---71.