Janet Pickles is Chairwoman, RA Medical Services Ltd, Steeton, West Yorkshire
Email: [email protected]
Inhalation sedation
and health
GUIDETO...
This guide is supported by an educational grant from
Learning outcomes
After reading this ‘Guide to Inhalation Sedation’, you should:
nRecognise specific biological issues and health concerns associated with exposure to nitrous oxide
nIdentify methods for detection and monitoring of nitrous oxide gas in ambient surgery air
n Understand exactly what is meant by a nitrous oxide scavenging system and its components
nBe able to identify best practice in order to minimise exposure to nitrous oxide
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minimisingexposuretonitrousoxideincludes:nUseanappropriate(i.e.dedicated)sedationflowmeterwithactivedentalscavengingi.e.45 L/minnThebreathingsystemshouldhaveavarietyofmasksizesavailable,whichcanbecleanedinanautoclave,oraredisposablenAssessthesurgeryventilationavailable—i.e.naturalormechanical.EnhanceifnecessarynMonitorexposureonaregularbasis—atleastonceayearnAlwaysemployamachinepre-usechecklistnInspectcylinderconnections,hoses,tubingsandreservoirbagforholesand/orleaksandreplaceatrecommendedintervals(Figure4)nEnsureregularequipmentmaintenancebytheoriginalequipmentmanufacuturer’sapprovedprovideratleastonceayearnCarefulpatientmanagement—e.g.discouragethepatientfromtalking.
SummaryAllmembersofthedentalteamhavea
responsibilitytoensurethattheworkingenvironmentissafe.Thereisnoexcuseforignoranceormismanagement.Awealthofinformationisnowavailable—bothinprintedformandontheinternet—andallstaffshouldensuretheyarewell-educatedonthesubject.Nitrousoxideexposureisunlikelytocausemajorhealthproblemsduringnormalworkingconditionswherecorrect,activedentalscavenging,isemployed.Ifindoubt,seekspecialistadvice.
BrodskyJB,CohenEN(1986)Adverseeffectsofnitrousoxide.MedToxicol1(5):362–374DepartmentofHealth(2006)HealthTechnicalMemorandum02-01:Medicalgaspipelinesystems.DH, LondonMalamedSF(2010)Sedation:AGuidetoPatientManagement.5thedn.StLouis,MosbyElsevierOstreicherJS(1994)VitaminB12supplementsasprotectionagainstnitrousoxideinhalation.NYStateDentJ60:47–49RowlandAS,BairdDD,WeinbergCR,ShoreDL,ShyCM,WilcoxAJ(1992)Reducedfertilityamongwomenemployedasdentalassistantsexposedtohighlevelsofnitrousoxide.NEnglJMed327(14):993–997
Figure 4. Potential leakage risks in a surgery setting
coursethekeyhereis‘notusingscavengingequipment’.Scavengingdefinitelyseemstobethekeyelementtoprotectingreproductivehealthinwomen.
Managing the risksAllrecentarticlespublishedfromthe1990sonwardsrefertoscavengedvsunscavengednitrousoxidelevels.Efficientscavengingsystemswerenotreallymuchinevidencebeforethemid1990swhenthePorterBrownDoubleMasksystemwasintroducedintotheUK(Figure1).Beforethat,mostdentaloperativeswereusingavarietyofnon-scavenging/passivescavengingsystemswithonlyafewactuallyusingwhatwenowadaysterm‘active’.
Atthattime,thevastmajorityofclinicianswereusinganon-scavengingsystemcomposedofgreysidetubesandasinglenasalmaskwithanexhalingvalve.SomehadtheMatrxPassiveSystem:clear22mmcorrugatedtubesattachedtoasinglemaskwithablankingcap,withthehosefrequentlybeinghungoutofthewindoworlefttolieonthesurgeryfloor.AverysmallamountemployedtheActiveNitrousScavenger—theonlybreathingsystematthattimewithanactivedraw.ThedefinitionofanactivedentaldrawbothintheUKandUSAhasbeendeterminedas45L/minute.
ThePorterBrownDoubleMaskwasaradicallydifferentsystem,butaproblemsoonarose.Itrequiredasteadyandsustainable
drawonthemaskandtubingstopreventleakagefromthenasalmaskuponpatientexhalation.IntheUSA,mostsystemswereconnectedtochairsidesuction,butthiswasnotalwayspossiblehere.Inlargerhealthcareestablishments,aconnectioncouldbeestablishedtothecentralanaestheticgasscavengingsystembyremovingtheairbrakeandfittingananaestheticgasscavengeradapter—butnoteverybodyhadaccesstothis.Thereforeintheearly2000s,theMiniscavwasdevelopedtomeetthegap(Figure2).
Sincethattime,apartfromadisposabledoublemask,therehasbeennofurtherenhancementinscavengerbreathingsystemsuntilnow.
InJuly2015attheInternationalAssociationofPaediatricDentistryinGlasgow,thenewSilhouettenasalmaskwaslaunched.Thisisaradicaldesign,beingmoreakintoanasalcannula.Itisaverylightweightandform-fittingmask—withanadhesivestripandasinglenasalprong—whichfitslikeagloveoverthenose.Availableinfoursizes,itallowsabetterfittobeachieved.Thelowprofiletubingconnectstothesedationflowmeterandthenisscavengedintheusualfashion.Themajordifferencebeingthatnoreservoirbagisrequiredwiththissystem.Thismayrequiresometraining,asmostdentalstaffaretaughttocloselyobservethereservoirbag.However,itisfeltthattheongoingefficiencyofthismaskmaywelloutweightheproblemscaused.
Other risk management methodsOtherriskmanagementmethodsthatcanbeimplementedare:nRegular,documentedequipment
maintenance,accordingtotheoriginalequipmentmanufacturer’srecommendationsandbymanufacturer-approvedengineers
nUseofanapproved‘pre-usechecklist’,asthiswillidentifyanyleaksintheequipmentorsystem.Itshouldincludeinspectionofthereservoirbagbygentlypullingdownonthebodyofthebagandlookingcloselyattheareaoftheferruleneck.Sparebagsshouldbekeptanddamagedorwornonesreplacedimmediately
nInthecaseofamobile4cylinderstandbeingused,sparebodoxsealsshouldalsobekept.Itisvitallyimportantthatasealisalwaysinplacedbetweenthestandandthecylinder.Wornsealsshouldbereplacedimmediatelyasthesecanallowgastoescape
nRegularongoingtrainingnMonitoringofnitrousoxide(Figure3)—there
arenospecificrecommendedperiodsforthis,althoughonceayearappearstobetheacceptednorm.However,ifhighorunexpectedlevelsareencountered,thenequipmentandtechniquesshouldbeconsideredandfollowingremedialaction,and/ortraining,themonitoringshouldberepeated.
Know your exposure levelsIntheUK,thepermittedexposurelevelfornitrousoxideis100partspermillion(ppm)overan8-hourtimeweightedaverage.Thisallowsfortimebothinthesurgeryandrestbreaks.
Withmodernscavengingthatiscorrectlyemployed,itispossibletolimitexposuretosinglefigures.Contrastthiswithpermittedexposurelevelsinothercountries:
nAustralia:25ppmnCanada:25ppmnUSA:25ppm(NIOSH)and50ppm(ACGIH)nSweden:100ppmnGermany:100ppm.
ItissometimesconsideredthattheUSAequivalentofourHealthandSafetyExecutive—TheNationalInstituteforOccupationalSafetyandHealth—aremuchmore‘ontheball’whenitcomestoenforcingthecontrolsonexposuretonitrousoxide.
WhileweareprettygoodhereintheUK,itcouldbeconsideredthatwefallbehindothercountrieswhoaremuchmoreproactivewiththeirapproachandenforcement.Thecurrentstandardsandrecommendationsinplace—amongwhichistheageingHealth Technical Memorandum 02-01: Medical gas pipeline systems(DepartmentofHealth,2006),donotalwaysmakeitabsolutelycompulsorytohavethebestandmostefficientscavenginginplace,orevenexplainfullywhatis required.
Nitrousoxidesedationisanextremelysafeandeffectivemethodofpainreliefacrossmanymedicalprocedures,beingthemostwidelyusedindentistryatthepresenttimeand,ifthecorrectequipmentandtrainingisused,thenoccupationalexposurelevelsshouldnormallybeextremelylow.
However,asasafetyfactor,itisalwaysadvisablethatfemaledentalstaff,whileundergoingfertilityorIVFtreatmentorinthefirsttrimesterofpregnancy,shouldavoidcontactwithnitrousoxideasaprecaution.Itisgenerallyacceptedthatthesecondandthirdtrimestersaresafeforoccupationalexposure,aslongasefficientscavengingmeasuresareinplace.
Protocol for minimising exposureAneasy-to-followsuggestedprotocolfor
Thereissomeevidencetosuggestthatchronicexposuretohighlevelsofnitrousoxidecanhaveaneffectonreproduction,anditisgenerallyagreedthatfemaledentalstaffshouldnotbeexposedtonitrousoxideinthefirsttrimester(3months)ofpregnancy.Thisismainlyduetothesignificantdemandforfolicacidduringorganogenesisinthefirstthreemonthsand,therefore,avoidanceofnitrousoxidesedationisrecommendedduringthisperiod.
ThereissomesuggestionthattakingavitaminB12supplementgivessomeprotectionandreducesfetotoxiceffects(Ostreicher,1994).However,asyet,therehasbeennodefinitivestudyanditremainsasuggestiononly.
Certainly,forapregnantfemaleemployedinasettingthatusesnitrousoxideitisimportanttoknowtheexposurelevels.Therefore,safeguardsshouldbeinplace,includingregularmaintenanceanddocumentedmonitoring.
Overview of health risksAgreatdealhasbeenwrittenovertheyearswithregardtohealthhazardsthatmaybeassociatedwithanychronicexposure(or
indeed,overexposure)tonitrousoxide.TheUSAhasledtheresearchintothissubjectwithanumberofarticlesfromthe1970sspecificallydealingwithanaestheticgashazardsinadentalsetting.
Onearticle(Rowlandetal,1992)containedastudythatsurveyedmorethan50000dentistsanddentalstaffwhowereexposedtotraceanaesthetics.Theseresultssuggestedthatlong-termexposuretothesegasescouldbeassociatedwithanincreaseingeneralhealthproblems,withanemphasisondiseaseofthereproductivesysteminparticular.However,thewholestudywasretrospectiveinnatureandonlyfuelledtheconcernregardingthesafetyofnitrousoxideinthedentalsetting.Thewholestudywascriticisedforlackofadequatedataonthetracegasesinvolved.
Specific biologic issuesNitrousoxideinterfereswithcobalamin(vitaminB12)andpreventsefficientmethioninesynthetase.ThisisvitalfornormalDNAproductionandcellularreproduction(BrodskyandCohen,1986).Althoughmostemphasisistowardsfemaledentalstaff,malefertilitycanalsobeaffected.
Itissometimesdifficulttoestablishthataclearconnectionbetweennitrousoxideandbiohazardouseffectsexists.StanleyMalamed’s(2010)bookSedation: A Guide to Patient Management states:‘Therelationbetweenanestheticgasexposureandspontaneousabortionremainsunresolved’.Thissectiondiscussestheresultsofaquestionnairesentto7000dentalassistantsbetweentheageof18–39inthe1980s.Itindicatedthat‘Anelevationinriskofspontaneousabortionwasseenamongwomenwhoworkedwithnitrousoxidefor3ormorehoursperweekinofficesnotusingscavengingequipment’.Of
This edition of the popular Guide To series is intended as a ‘follow on’ tothepreviouseditionGuide to inhalation safety,anddiscussestheeffectsofnitrousoxideonpregnancy
GUIDE TO... Inhalation sedation and health
Figure 1. Porter Brown breathing system
Figure 2. DMDM on a 4-cylinder stand
Figure 3. Diffusion tube for personal monitoring of nitrous oxide levels
