Andersons pediatric cardiology 1600

instrument.9Followingconcernsregardingthesafetyofmercuryforusersinthe
clinicalenvironment,fortechnicianswhohavetoservicetheinstrument,andfor
theenvironmentitself,theseinstrumentshavenowbeenphasedoutofclinical
practice.10,11
Anissuewithanymethodusingauscultationistheintroductionofthe
phenomenonofterminaldigitpreference,andbiasoftheobserverbecauseof
knowledgeofpreviousmeasurements.Anyinstrumentthateliminatesorreduces
thesetwoistobewelcomed.Thisinitiallyledtothedevelopmentofthe
random-zerosphygmomanometer,whichwasdevelopedandshowntominimize
oreliminateboththeseitems.12,13Unfortunately,thesedeviceswereshown
subsequentlysignificantlytounderestimatebloodpressure,andweretherefore
abandoned.14,15
Automatedoscillometricdeviceshavesimilarlybeendeveloped.These
improveontheshortcomingsoftheauscultatorymethodbyeliminatingboth
terminaldigitpreferenceandthebiasoftheobserver.Theyworkbythe
detectionofpressurepulsesinthecuff.Thesearegeneratedasaresultofthe
volumepulsesoftheartery.Whenbloodstartsflowingthroughthearteryatthe
pointofsystolicpressure,apressurepulseisgenerated.Aspressurewithinthe
deflatingcuffisreducedinastepwisemanner,aseriesofpressurepulses
generatethepulseoscillogram.Thepulseamplitudesofthisoscillogramprovide
anenvelopecurve,withthemaximalvalueonthiscurveequatingtothemean
arterialpressure.Systolicanddiastolicpressuresarecalculatedfrompreset
algorithmsintheinstrumentmicrochip,andareafunctionofthemean.The
algorithmsarespecifictotheinstrument,andarenotdeclaredbythe
manufacturers,althoughonewouldpresumethesealgorithmshavebeen
improvedovertheyearsbythemanufacturers.16,17Althoughtheseautomated
devicesareincreasinglybeingusedinprimarycareandpediatricdepartments,
therearesomeparticularconcernsthatneedtobehighlighted.TheDinamap
devicesarethemostcommonlystudiedautomatedoscillometricdevices
reportedinpediatricseries.Anearlierversionofthisdevice,model1846SX,
hadbeenshowntohavesuperiorcorrelationwithintra-arterialmeasurements.18

Otherstudies,however,reportedhighermeansystolicmeasurementsusing
models1846,8100,and845whencomparedwiththerandom-zero
sphygmomanometerandmercurysphygmomanometer.19,20Diastolic
measurementshadbeenreportedtohavebetteragreement.19Amorerecent
reportusingtheDinamap8100monitorhighlightedthediscrepancybetweenthe


twomethods,withmeasurementsusingthedevicehigherbyameanof10mm
Hgforsystolicand5mmHgfordiastolicbloodpressure.21Therefore,although
normativelimitshavebeenproposedusingtheDinamap8100instrumentfrom
theUnitedKingdom,cautionneedstobeproposedbeforeapplyingtheselimits
inclinicalpractice.22Anotherparticularpracticalobservationwithoscillometric
devicesisthephenomenonofmeasurementsbeinghigherbyabout3to5mm
Hgonfirstmeasurement,despitecontroloffactorsinvolvingthepatient,the
observer,andtheenvironment.20,23Thesecondreadinghasbeenreportedtobe
moreaccurate.
Automaticallyinflatedcuffshaverecentlybeenintroduced.Theseinstruments
measurebothsystolicanddiastolicpressures,recordingtheresultsatpreset
intervalsbydetectingoscillationsinthepressurefromthecuff.Theyare
especiallyusefulinthecareofthecriticallyillchild,savingnursingtimeand
reducingdisturbancetothepatient.Thecalibrationneedstobechecked
frequentlyiftheresultistoberegardedasaccurate,buttheyareusefulin
detectingchanges.Indeed,theywillalarmautomaticallyifpresetparametersare
exceeded.
Aneroidsphygmomanometershavealsogainedpopularityinclinicalpractice
becauseoftheirportabilityandtheirrelianceontechniquessimilartothe
standardmercurysphygmomanometer.Becauseofthis,however,theyhaveno
influenceonthebiasesexistingwiththemercurysphygmomanometer.The
deviceshaveproventheiraccuracywhenregular6-monthmaintenanceisin
placetoservicetheinstruments.24

Themajorityofdevicesinclinicaluse,nonetheless,havenotbeenevaluated
independentlyforaccuracyusingthetwomostwidelyacceptedprotocolsfor
validation.25,26TheseprotocolshavebeenproposedbytheBritishHypertension
SocietyandtheAssociationfortheAdvancementofMedicalInstrumentation.
Severalupdatesofvalidationhavebeenpublished,butthebestmethodof
findingup-to-dateinformationisonthenonprofitwebsite
.27

TechniqueofMeasurement
Thechildshouldberelaxedandquietwhenbloodpressureisrecorded.Should
thisnotbepossible,butreadingsaremade,thentheconditionsshouldbe
recorded.Asimpledescriptionoftheprocessofmeasurementofachildata
levelappropriateforagewillusuallyleadtoacooperativepatient,thusallowing


accuraterecordings.Measuringpressuresininfantswhoarecryingisnotuseful.
Thestandardpositionisthesittingpositionwhenchildrenareolderthan3years,
withthefullyexposedarmsupportedorrestingonatableatthelevelofthe
heart.23Anarmhigherthantheheartwillunderestimatethepressure,whilea
lowerpositionwillproduceoverestimations.28Inyoungerchildrenandinfants,
pressureshouldberoutinelymeasuredwhenthepatientisinthesupineposition.
Thesphygmomanometershouldbeplacedattheleveloftheeyeoftheobserver
toeliminateerrorfromparallax.Thecuffshouldbeinflatedabout30mmHg
abovethepointatwhichtheradialpulsedisappears.Insomepatients,therewill
beasilentgapbetweenthesystolicanddiastolicpressures.Simplyinflatingthe
cuffuntilthesounddisappearsinsuchindividualsmayproduceaserious
underestimationofsystolicpressure.Onceinflated,thecuffshouldbedeflatedat
arateof2to3mmHg/swhileauscultatingwiththestethoscope.Thesudden
distensionofthecollapsedarteryatthesystolicpressureisassociatedwitha
cleartappingsound,definedasphase1oftheKorotkoffsounds.Themurmurof

turbulentbloodflowingthroughthepartiallyoccludedarteryisphase2.Phase3
isahigh-pitchedsoundproducedwhentheartery,closedduringdiastole,opens
insystole.Whenthearterynolongerclosesduringdiastole,thetappingsounds
arelowpitchedandmuffledandquieter.Thisisphase4.Phase5iswhenthe
soundsdisappear.Thisisvariableandmaynotoccurinsomechildren.The
fourthphase,however,tendstooverestimatethediastolicpressure,whilethe
fifthphaseunderestimatesit.Althoughthefifthsoundiswidelyacceptedasthe
optimalmeasurementofdiastolicpressureamongadolescentsandadults,there
hasbeenconsiderabledebateintheliteratureconcerningitsvalueinchildren
youngerthan13years.Fortheseyoungerchildren,thefourthsoundhad
generallybeenpreferred,andwasrecommendedbytheTaskForceReportson
BloodPressureControlinChildren.29,30Aninternationalcommittee,
nonetheless,recommendedthefifthsound,31,32andtheupdateoftheTaskForce
Recommendationsalsoadvocatesusingthissound.Itispreferredbecauseofits
easieridentificationbyobserversandthecomparabilityitprovidesfor
measuringdiastolicpressuresacrossagegroups.Thetwosoundsarenotequalin
mostchildren,andmayvaryconsiderably,byupto10mmHg.33
Themeasurementofbloodpressureininfants,andinsomeolderchildren,is
sometimesdifficultbecausethesoundsareinaudible.Theoldflushtechniqueis
unreliable.IthasnowbeensupersededbytheuseofDopplerultrasound,using
anultrasonicbeamtodetectmotionofthearterialwallwhenthecuffisdeflated.
Thistechniqueisremarkablyreliableformeasurementofthesystolicpressure,