临床麻醉学 英文版2.docx
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临床麻醉学英文版2
CHAPTER3
ManagingtheAirway
Basictechniques,37Thelaryngealmaskairway,42Emergencyairway
Simpleadjuncts,39Trachealintubation,43techniques,50
Maintenanceofapatentairwayisanessentialprerequisiteforthesafeandsuccessfulconductofanesthesia.Inaddition,duringresuscitationpatientsoftenhaveanobstructedairwayeitherasthecauseorresultoftheirlossofconsciousness.Theskillofairwaymaintenanceshouldbeacquiredbyalldoctors,andnotsimplyregardedastheresponsibilityoftheanesthetist.Thedescriptionsofairwaymanagementtechniques,whichfollow,areintendedtosupplementpracticeeitheronamanikinorpreferablyonandanesthetizedpatientunderthedirectionofaskilledanesthetist.
Basictechniques
Anesthesiafrequentlyresultsinlossoftheairwayanditismosteasilyrestoredbyacombinationoftheheadtiltalongwithajawthrust(seeChapter2).Thelatterisprovidedbytheanesthetist’sfourthandfifthfingers(ofoneorbothhands)liftingtheangleofthemandible.Theoveralleffectdesiredisthatthepatient’smandibleis‘lifted’intothemaskratherthanthemaskbeingpushedintotheface(Fig.3.1).
FACEMASKS
●ThemostcommonlyusedtypeinadultsistheBOCanatomicalfacemask(Fig.3.2)whichisdesignedtofitthecontoursofthefacewiththeminimumofpressure.
●Leakageofanestheticgasesisminimizedbyanair-filledcuffaroundtheedge.
●Masksatemadeinavarietyofsizesandthesmallestone,whichprovidesagoodseal,shouldbeused(tominimizetheincreaseindeadspace,whichoccurs).
●TheAmbumask(Fig.3.2)hasatransparentbody—allowingidentificationofvomit–makingitpoplarforresuscitation.
●Allmasksmustbedisinfectedbetweeneachpatient.
Simpleadjuncts
Themostcommonlyandusedaretheoropharyngeal(Guedel)andnasopharyngealairways,insertedaftertheinductionofanesthesiatohelpmaintaintheairwayinconjunctionwiththetechniquesdescribedabove.
OROPHARYNGEALAIRWAY
●Thesearecurvedplastictubes,flattenedincross-sectionandflangedattheoralend,whichlieoverthetongue,preventingitfromfallingbackintothepharynx.
●Theyareavailableinavarietyofsizesfromneonatestolargeadults.Thecommonestsizesare2-4,forsmalltolargeadults,respectively.
●Aguidetothecorrectsizeisdeterminedbycomparingtheairwaylengthtotheverticaldistancefromthecornerofthepatient’smouthtotheangleofthemandible.
●Itisinitiallyinserted‘upsidedown’asfarasthebackofthehardpalate(Fig.3.3a),rotated180(Fig.3.3b)andfullyinsertedutiltheflangeliesinfrontoftheteethorgumsinanedentulouspatient(Fig.3.3c).
NASOPHARYNGEALAIRWAY
●Theseareround,malleableplastictubes,beveledatthepharyngealendandflangedatthenasalend.
●Theyaresizedontheirinternaldiameterinmillimeters,withlengthincreasingwithdiameter.Thecommonsizesinadultsare6-8mm,forsmalltolargeadults,respectively.
●Aguidetothecorrectsizeismadebycomparingthediametertotheexternalnaris.
●Priortoinsertion,thepatencyofthenostril(usuallytheright)shouldbecheckedandtheairwaylubricated.
●Theairwayisinsertedalongthefloorofthenose,withthebevelfacingmediallytoavoidcatchingtheturbinates(Fig.3.4).
●Asafetypinmaybeinsertedthroughtheflangetopreventinhalationoftheairway.
●Ifobstructionisencountered,forceshouldnotbeusedasseverebleedingmaybeprovoked.Instead,theothernostrilcanbetried.
PROBLEMSWITHAIRWAYS
Thepresenceofsnoring,indrawingofthesupraclavicular,suprasternalandintercastalspaces,useoftheaccessorymusclesorparadoxicalrespiratorymovement(see-sawrespiration)suggestthattheabovemethodsatefailingtomaintainapatentairway.Commonproblemsarisingusingthesetechniquesalongwithafacemaskduringanesthesiaare:
1inabilitytomaintainagoodsealbetweenthepatient’sfaceandthemask,particularlyinthosewithoutteeth;
2fatigue,whenholdingthemaskforprolongedperiods;
3theriskofaspiration,duetothelossofupperairwayreflexes;
4theanesthetistisnotfreetodealwithanyotherproblems,whichmayarise.
Thelaryngealmaskairway(LMA)ortrachealintubationmaybeusedtoovercometheseproblems.
Thelaryngealmaskairway
Thisdevicewasdesignedforuseinspontaneouslybreathingpatients.Itconsistsofa‘mask’,whichsitsoverthelaryngealopening,attachedtowhichisatube,whichprotrudesfromthemouthandconnectsdirectlytotheanestheticbreathingsystem.Ontheperimeterofthemaskisaninflatablecuff,whichcreatesasealandhelpstostabilizeit.TheLMAisproducedinavarietyofsizessuitableforallpatients,fromneonatestoadults,withsizes3and4beingthemostcommonlyusedinfemaleandmaleadults,respectively.PositivepressureventilationcanbeperformedviatheLMAprovidedthathighinflationpressureisavoided,otherwiseleakageoccurspastthecuff,reducingventilationandcausinggastricinflation.Aversionwithareinforcedtubeisalsoavailable.TheLMAisreusable,providedthatitissterilizedbetweeneachpatient.
Theuseofthelaryngealmaskovercomessomeoftheproblemsoftheprevioustechniques:
●itisnotaffectedbytheshapeofthepatient’sfaceortheabsenceofteeth;
●theanesthetistisnotrequiredtoholditinposition,avoidingfatigueandallowinganyotherproblemstobedealtwith;
●itreducestheriskofaspirationofregurgitatedgastriccontents,butdoesnoteliminateit.
Itsuseisrelativelycontraindicatedwherethereisanincreasedriskofregurgitation,forexampleinemergencycases,pregnancyandpatientswithahiatushernia.
Recently,thelaryngealmaskhasbeenshowntobeusefulintwootherareas:
1Indifficulttrachealintubationwhereitwilloftenallowmaintenanceoftheairway.Alternatively,asmalldiametertrachealtubeorintroducecanbepassedintothelarynxviatheLMA.
2Duringcardiopulmonaryresuscitation,ithasbeenshownthatnon-anesthetistsareabletoinsertanLMAmorerapidlyandsuccessfullythanatrachealtubeandachievemoreeffectiveventilationthanusingaself-inflatingbagandfacemask.ItislikelythatinthefuturetheLMAwillfindaroleinairwaymanagementduringresuscitation.
TECHNIQUEFORINSERTION
Thepatient’sreflexesmustbesuppressedtoalevelsimilartotherequiredfortheinsertionofanoropharyngealairwaytopreventcoughingorlaryngospasm.
●Thecuffisdeflatedandthemasklightlylubricated(Fig.3.5a).
●Aheadtiltisperformed,thepatient’smouthopenedfullyandthetipofthemaskinsertedalongthelardpalatewiththeopensidefacingbutnottouchingthetongue(Fig.3.5b).
●Themaskisthenfurtherinserted,usingtheindexfingertoprovidesupportforthetube(Fig.3.5c).Eventually,resistancewillbefeltatthepointwherethetipofthemaskliesattheupperoesophagealsphincter(Fig.3.5d).
●Thecuffisnowfullyinflatedusinganair-filledsyringeattachedtothevalveattheendofthepilottube(Fig.3.5e).
●Thelaryngealmaskissecuredeitherbyalengthofbandageoradhesivestrappingattachedtotheprotrudingtube.
Trachealintubation
Thisisthebestmethodofprovidingandsecuringaclearairwayin-patientsduringanesthesiaandresuscitation,butsuccessrequiresabolitionofthelaryngealreflexes.Duringanesthesia,thisisusuallyachievedbytheadministrationofamusclerelaxant(seeChapter4).Deepinhalationalanesthesiaorlocalanesthesiaofthelarynxcanalsobeused,buttheseareusuallyreservedforuseinthosepatientswheredifficultywithintubationisanticipated,forexampleinthepresenceofairwaytumorsorimmobilityofthecervicalspine.
COMMONINDICATIONSFORTRACHEALINTUBATION
●Wheremusclerelaxantsateusedtofacilitatesurgery(e.g.abdominalandthoracicsurgery)therebynecessitatingtheuseofmechanicalventilation.
●In-patientswithafullstomach,toprotectagainstaspirationofregurgitatedgastriccontents.
●Wherethepositionofthepatientwouldotherwisemakemaintenanceoftheairwaydifficult,forexamplethelateralorproneposition.
●Wherethereiscompetitionbetweensurgeonandanesthetistfortheairway(e.g.operationsontheheadandneck).
●Inthosepatientsinwhomtheairwaycannotbesatisfactorilymaintainedbyanyothertechnique.
●Duringcardiopulmonaryresuscitationwhenintubationallows:
(a)ventilationwith100%oxygenwithoutleaks;
(b)suctionclearanceofinhaleddebris;
(c)aroutefortheadministrationofdrugs.
EQUIPMENTFORTRACHEALINTUBATION
Avarietyofequipmentexistsandthatchosenwillbedeterminedbythecircumstancesandbythepreferencesoftheindividualanesthetist.Thefollowingisalistofthebasicneedsforadultoralintubation.
●Laryngoscopewithacurved(Macintosh)bladeandfunctioninglight.
●Trachealtubesinavarietyofsizesandinwhichthecuffswork..Theinternaldiameterisexpressedinmillimetersandthelengthincentimeters.Theymaybelightlylubricated.
(a)Formales:
8.0–9.0mminternaldiameter,22–24cmlengths.
(b)Forfemales:
7.5–8.5mminternaldiameter,20–22cmlengths.
●syringetoinflatethecuffoncethetubeisinplace.
●Cathetermountsor‘elbow’toconnectthetubetotheanestheticsystemorventilatortubing.
●Suction,switchedonandimmediatelytohandincasethepatientvomitsorregurgitates.
●Extras:
asemi-rigidintroducertohelpmouldthetubetoaparticularshape;Magill’sforceps,designedtoreachintothepharynxtoremovedebrisordirectthetipofatube;bandageortapetosecurethetube.
Trachealtubes
●Theseweretraditionallymanufacturedfromredrubberandwe