The evolution of airway management

13 Pages·2017·0.57 MB·English

BritishJournalofAnaesthesia,119(S1):i154–i166(2017)
doi:10.1093/bja/aex385
RespirationandtheAirway
RESPIRATION AND THE AIRWAY
The evolution of airway management – new concepts
and conflicts with traditional practice
A. F. McNarry1,* and A. Patel2
1NHSLothian,Edinburgh,UKand2RoyalNationalThroatNoseandEarHospitalandUniversityCollege
LondonHospital,London,UK
*Correspondingauthor.E-mail:[email protected]
Abstract
Inthelast25yr,therehavebeenseveraladvancesinthesafemanagementoftheairway.Videolaryngoscopesandsupra-
glotticairways,nowinroutineusebynewtraineesinanaesthesia,havehadtheirgenesisintherecentpast.The4th
NationalAuditProjectoftheRoyalCollegeofAnaesthetistsandtheDifficultAirwaySocietypublishedin2011aseminal
reportthathasinfluencedairwaymanagementworldwide.Understandinghowthereport’srecommendationswerecon-
structedandhowclinicalguidelinescomplimentratherthancontradictthemisimportantinunderstandingthetenetsof
safeairwaymanagement.Overthelast25yrtherehasbeenanincreasingunderstandingoftheeffectsofhumanfactorsin
anaesthesiology:wemaynotperforminapredictableoroptimalmannerwhenfacedwithunusualandthreateningchal-
lenges.Theplaceofcricoidpressureinanaestheticpracticehasalsoevolved.Currentrecommendationsarethatitbe
applied,butitshouldbereleasedrapidlyshouldairwaydifficultybeencountered.Theneedtopreventhypoxaemiaby
preoxygenationhaslongbeenrecognized,buttheroleofhigh-flownasaloxygeninanaesthesiaisnowbeingrealizedand
developed.Cliniciansmustdecidehownoveltherapiesandlong-standingpracticesareadaptedtobestmeettheneedsof
ourpatientsandpreventharmduringairwaymanagement.
Keywords:airwaymanagement;laryngealmaskairway;oxygen,Inhalationtherapies;intubation,endotracheal
Airwaymanagementisthecornerstoneofanaestheticpractice, first description of a supraglottic airway,2 but it was and still
andvirtuallyeveryanaestheticinnovationinthepast25yrhas remainsarevolutioninsafeairwaymanagement.InVerghese
hadanimpactonsomeaspectofairwaycare.Pulseoximetry, and Brimacombe’s 1993 study3 the cLMA was being used in
sevoflurane, remifentanil, disposable equipment, rocuronium almost one third of cases with a success rate of 99.8%. They
and sugammadex have all altered clinical practice. The chal- noted that fewer than 5% of patients had a laryngeal mask in
lengewhenconsideringtheseinnovationsisknowinghowthey situforprocedureslastingmorethantwohours.Bythetimeof
willeffectclinicalpracticeinthenext25yr. the4thNationalAuditProject(NAP4),supraglotticairwaydevi-
ces(SADs)werebeingusedin56.2%ofgeneralanaesthetics.4In
2017,acaseseriesdescribedSADuseinpatientsforupto11h.5
Supraglotticairwaydevices
Similar SADs were developed by other companies, and an
Brain’sdescriptionoftheclassicLaryngealMaskAirway1(cLMA, entirelynewnomenclaturebasedonthesealofthemaskwith
theoropharynx(oropharyngealleakpressure)wascreated.267
manufactured by Bivona and initially distributed by Colgate
Underlining its place in safe airway management, the term
Medical)intheBritishJournalofAnaesthesiain1983wasnotthe
VCTheAuthor2017.PublishedbyOxfordUniversityPressonbehalfoftheBritishJournalofAnaesthesia.Allrightsreserved.
ForPermissions,pleaseemail:[email protected]
i154
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Evolutionofairwaymanagement | i155
Laryngeal Mask Airway became a MeSH keyword in 1993. Howthendoestheclinicianproceed?Forinstance,istheLMA
Brimacombereportedtherewere295articles,abstractsorchap- Protector36 a better device than the Intubating Laryngeal Tube
tersfeaturingthecLMAin1994alone.2 withDrainTube(iLTS-D;https://www.vbm-medical.com/products/
Supraglottic airway devices enable anaesthetists to be airway-management/intubating-laryngeal-tube-ilts-d/; accessed 7
hands-freeduringaprocedure,butthecLMA’ssuccesswasasa October2017)?DoestheBaskaMask3738withitsself-sealingcuff
resultofmorethanitslabour-savingproperties.Brainstatedit provideabetterairwaythananyother?WhichisthebestSADto
islikelytobe‘ofparticularvaluewheredifficultyisexperienced useforairwayrescueafterfailedtrachealintubation?Isonefamily
inmaintainingtheairway’.Theincreasedinterestinthepoten- ofdevicesaseffectiveinadultsandchildren?
tialofdaysurgery8andtheavailabilityofpropofolasanemul- Cliniciansmustprioritisethreeissues:1.Effectiveoxygena-
sionin1986werealsomajorcontributorstothesuccessofthe tionandventilation;2.Minimizingaspirationrisk;and3.Ability
device(theoriginaldescriptionrecommendeditsuseafterthio- to insert the device effectively without resorting to complex
pentalandalcuronium0.2mgkg(cid:2)1).By1988thebenefitpropofol methodsorrepeatedattempts.Cost,educationalopportunities
offered in terms of suppression of pharyngeal and laryngeal and the likelihood of airway trauma also inform any choice.
reactivityoverthiopentalwasreported,8anditsuseadvocated.9 Regular rehearsal and clinical experience with any device will
Brain’s contribution to anaesthetic practice has already been improveitsutility.Brimacombefoundthatasmanyas750LMA
celebrated as the cLMA reached its 30th birthday,10 11 and the insertions were required to overcome the long-term learning
impact of his innovation cannot be overstated. This article, curveofthecLMA.39
however,looksforwardtothenext25years.
Amidst the technological and clinical research that under-
pinnedthedevelopmentofSADssomesimplerinnovationshave
Videolaryngoscopy
also revolutionised anaesthetic practice. The Aintree Catheter
facilitatestrachealintubationthroughaSAD.12–16Itwasoriginally ManyregardJackPacey,thevascularsurgeonwhoinventedthe
describedasa‘disposableplastictube’,althoughitwascleverly Glidescope40–42in2001,asthefatherofvideolaryngoscopy(VL).
designedtobejustshorter(by3cm)thanthelengthofthecord However,opticaldevicesdesignedtofacilitatedifficulttracheal
onafibrescopeallowingcontinuedmanoeuvrabilityofthefibre- intubationexistedbeforethisdate.KatzandBerci43coinedthe
scopetip.17Aguidetoitsusecanbefoundathttp://www.das.uk. phraseOpticalStyletin1979.Regardlessoftheirhistory,video-
com/files/AIC_abbreviated_Guide_Final_for_DAS.pdf (accessed 7 laryngoscopes are effective. A retrospective analysis by the
October 2017). Supraglottic airway devices can also be used to MulticenterPerioperativeOutcomesGroup44reported92%suc-
facilitatetrachealintubationdirectly18–20andhaveanimportant cess using a videolaryngoscope as a rescue device after failed
roleinrescuingfailedintubation.2122Sincethemanufactureof intubation.ACochraneReview45comparingvideolaryngoscopy
theLMAProseal,variousdeviceshavealsoofferedenhancedsep- withdirectlaryngoscopystated‘statisticallysignificantlyfewer
arationoftherespiratoryandgastrointestinaltracts.Theyhave failedintubationswerereportedwhenavideolaryngoscopewas
even been used as the primary airway for Caesarean section.23 used’,and‘therewerefewerfailedintubationsinthosewithan
Althoughblindintubationtechniquesarepossiblethroughdevi- anticipated difficult airway when using a videolaryngoscope’.
ces such as the intubating laryngeal mask,24 reports of harm25 Reassuringasthesestatementsappear,theyweremadebased
and the wide availability of fibreoptic equipment in the UK,26 on 38 studies with 4127 participants and six studies with 830
havemadesuchtechniquesredundant. participants, making the average number of participants per
Examples of SAD use in ‘extreme circumstances’ such as study108and138,respectively.
a bridge to extubation in the ICU,27 managing the airway for Studies of videolaryngoscopy generate their own issues.
cardiac surgery,28 or for surgery in the prone position both Studiesusingtrachealintubationsuccessastheirprimaryout-
electively29 30 and with unexpected extubation31 are reported. come measure require many subjects (>1,000) in each arm to
Clinicians must decide when to choose a specific device, not effectivelydemonstratesuperiorityofonedeviceoveranother,
just based on how it works, but on how likely it is to fail.32 if the VLs studied are 98% - 99% effective. This need for large
Individual anaesthetists must combine their knowledge of a numbershasledtoseveralstudiesthatlookedatsurrogatesof
device’s performance alongside their ability touse that device intubationdifficulty,suchastimetointubation,4647orthesuc-
effectivelyineachsituation. cessratesofnovicesormedicalstudents.48Similarly,giventhe
Ramachandran’s study33 of 15,795 uses of the LMA Unique relatively low incidence of difficult intubation in the general
reported a failure rate of 1.1%, but if an anaesthetist does population,studieshavechosentousemanikins,4950simulated
around400casesperyrandworksfor30yrasaconsultant,it difficulty,51 52 or anticipated difficulty rather than actual
willtakeyearsforoneindividualtogenerateadequatedatato difficulty. This myriad of inclusion criteria has led to some
prove the safety profile of a single device. Cook suggested a potentiallyconflictingresults.Forinstance,ameta-analysisof
scoring system for choosing the best SAD34 based on seven thePentaxAWS53vsMacintoshlaryngoscopein2014suggested
factors from the presence of a sore throat to overall insertion thatdespiteasuperiorlaryngealview,thePentaxAirwayScope
success. With the perpetual advent of new devices, findings providedlittleclinicalbenefitoveraconventionallaryngoscope.
rapidlybecomeoutofdatebutitisthemethodologythatmust Cook’ssuggestion54thatdevicesshouldbestudiedsequentially
beretained. frommanikintohumansubjecthasmerit,althoughthisisper-
TheDifficultAirwaySociety’sADEPT(AirwayDeviceEvaluation hapsnotdirectlyapplicabletoVLs.Inameta-analysis,55only13%
Project Team) process35 set out a framework whereby airway of‘non-standard’laryngoscopeshadbeentestedonpatientswith
equipmentshouldbeevaluatedusingatleastlevel3b(singlecase anticipated or known difficult airways. Mihai and colleagues55
controlorhistoricalcontrol)evidence.Thislevelofevidencecould then suggested that multicentre collaborations are likely to be
then be used to inform purchasing decisions, based on properly needed, studying known difficult patients to fully understand
conducted trials rather than evaluations with small numbers. thesedevices.AtaxonomydescribingVLshasbeendeveloped56
Despiteinterestandongoingworkinthisarea,aUK-basedstudy by Healy and colleagues (Fig. 1). While some parts of this are
specificallyusingtheADEPTmethodologyhasyettobepublished. already redundant (the Ctrach, a laryngeal mask witha camera
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i156 | McNarryandPatel
Video laryngoscopes
Integrated channel Rigid blade
Video stylets
laryngoscopes laryngoscopes
Standard Angled
Airway Blade Rigid
blade blade
CTrach Pentax AWS Bonfils V-MAC GlideScope
Airtraq* C-MAC McGrath
Fig1Aclassificationofvideolaryngoscopicdevices.CTrachimagecourtesyofLMANorthAmerica.PentaxAWSimagecourtesyofAmbuUSA.Airtraqimagecour-
tesyofProdolMeditecS.A.BonfilsandC-MACAˆVC2012PhotoCourtesyofKARLSTORZEndoscopy-America,Inc.GlideScopeimagecourtesyofVerathon,USA.The
McGrathseries5imagecourtesyofAircraftMedical,UK.ThisfigureistakenfromHealyetalBMCAnesthesiol.2012;12:32.VC2012Healyetal.;licenseeBioMed
CentralLtd.ReproducedunderthetermsofitsCreativeCommonsAttributionLicense(2.0).
allowingvisualisationoftheglottisfromthebowlofthedeviceis TheDAS201521guidelinesadoptedZaouter’sstance68recom-
nolongermanufactured),itsbroaddivisionsintochannelled,rigid mending ‘all anaesthetists should be trained to use, and have
videostylet,standardbladeandangulatedbladeareuseful. immediate access to, a videolaryngoscope’, but did not specify
Giventhevarietyofdevicesavailable,itisnotsurprisingthat whichlaryngoscope,astheevidencedidnotexisttorecommend
theyhavedifferentfeatures,differentmodesoffailureanddif- oneoveranother.Proficiencywithanydevicerequirestraining
ferentrecommendationsforsuccessfuluse.5758Acommonearly andregularpractice.69Thisisunlikelytobeachievedifthereare
statementaboutVLswasthattheyofferedanexcellentviewof several devices across one hospital and neither trainees nor
theglottisbutdidnotnecessarilyfacilitatetrachealintubation.59 consultantsarelikelytobecomeproficientintheiruseinsuch
However,thismayrelatemoretoourunderstandingoftheproc- circumstances,particularlyinpotentiallydifficultairways.
essoftrachealintubationthanthepropertiesofthedeviceitself. After considering the evidence of efficacy, departments
Theideaof‘axesofalignment’wasintroducedbyBannisterand shouldchooseaVLbasedonavarietyoffactorsincludingcost
Macbethin1944,60ayearafterMacintoshdescribedhislaryngo- oftheinitialdeviceandanydisposables,cleaningprotocolsand
scope.61 Greenland suggested considering this as two curves portability. Developing expertise will require frequent rather
(oro-pharyngeal and pharyngo-glotto-tracheal) may be more thanexceptionaluse.Thiswillenableunderstandingnotjustof
useful62 with VLs serving to move the eye along the primary how it works but recognition of those situations and airways
curve.Thishasbeendisputedasthecompletetheoryoflaryngo- whereitmayproveineffective,asnoVLisperfect.70–72Practice
scopyandintubation,63butitoffersaneffectivewaytoconsider todevelop,retainandbeabletopassonskillsisessential.
videolaryngoscopy,andtheshapingofastyletorbougieshould Looking to the next 25yr, the anaesthetic community needs
tubeinsertionprovedifficult.Thisisparticularlythecasewith ongoing quality research into videolaryngoscopes, considering
hyper-angulated blades where a 60(cid:3) curve is advocated.42 64 65 bladedesignandshape,andalsohowweviewtheroleofthelar-
However useful, these adjuncts have been known to cause yngoscope,whichisnotactuallytoviewthelarynx,buttofacili-
traumathemselves.6667Withmanydevicesnowavailable,shap- tatetrachealintubation.Largemulticentrestudieswillberequired
ingthestylettotheshapeofthebladeinusemaybetheeasiest to establish how effective these devices are in difficult airways
option. Similarly, operators must not become fixated on the andwhetheranyoneissuperior toanother.Theultimate chal-
screenbutadopta‘patient-screen-patient’approachtoobserve lenge is to be able to determine those patients where videolar-
thepassageofthetrachealtubeasitinitiallyenterstheoralcav- yngoscopywillbeineffectivebeforetheinductionofanaesthesia.
ity.ThedesignofcertainVLsmaymeanthatthecameradoes
notprovideaviewfromthetipoftheblade.Thismeansthatthe
Humanfactorsandguidelines
best glottic view may not correspond with the best chance of
passing the tracheal tube easily, and in these situations with- AlexanderPopewrote‘toerrishuman’ inapoeminthe18th
drawingthebladeslightlymaybebeneficial. Century.Thenotionthathumanscananddomakemistakesis
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Evolutionofairwaymanagement | i157
longer standing than the practice of modern anaesthesia. donotclaimtobeandarenotperfect,andtheyarenotdesigned
However,inasafetycriticalareasuchasanaesthesiastrategies todictatepractice,comingwithadisclaimertothiseffect.They
to limit potentially catastrophic clinical errors should be distiltheevidencefrompublishedliterature,nationalandinter-
embraced.Inthe21stCentury,anaesthetistswilloftencitethe nationalexpertopinion,andtheentireDASmembershiptosup-
tragiccaseofElaineBromiley7374andtheoutstanding,unselfish portbestpracticeinairwaymanagement,includingademand
work done by herwidower Martin inraising awarenessof the towakethepatientupifappropriate.Theguidelinesshouldat
role of human factors in anaesthetic practice. The Clinical least serve to stimulate an anaesthetist into developing more
HumanFactorsGroupwhichhefoundedin2007(www.chfg.org; thanoneairwaymanagementplanfortheirpatient,whichthey
accessed7October2017)hasavisionthatextendsbeyondsafe thenmustcommunicatewiththeirteam.
anaesthesia,to‘ahealthcaresystemthatplacesanunderstand- The guidelines were specifically written to support UK and
ingofhumanfactorsattheheartofimprovingclinical,manage- Irelandbasedpracticeandshouldbereadinthatway,although
rial and organisational practice leading to significant they are used throughout the world. Other countries have
improvements in safety and efficiency’. The NAP4 report alreadypublishedtheirownguidelines.Figure2showsanair-
included a chapter on human factors and stated that human waytrolleydesignedtocomplywiththeunanticipateddifficult
factorscontributedtoairwayissues,relatingtoeithertheindi- intubation guidelines, also serving as a cognitive aid to the
vidualortheteam,in75(40%)ofcases.Afollowupstudywhere guidelines.Figure3showssomeofthemanydevicescurrently
12 contributing anaesthetists were interviewed, identified availableonthesetrolleys.
human factors as causative in all cases, with a median of 4.5
factorspercase.75TheRCoA’sroleinacknowledgingandunder-
standing the challenges of human factors predates NAP4. The NAP4
firstPresidentofthenewCollegeofAnaesthetists,AASpence,
Anyconsiderationofairwaymanagementinthepast25yrmust
wroteaneditorialin1997entitled‘Theexpandingroleofsimu-
includethedetailedfindingsoftheNAP4report.488Itisthelarg-
latorsinriskmanagement’.76Hehopedthatsimulatorswould
estauditofseriousairwaycomplicationsintheworldliterature.
help anaesthetists in their formative years learn tricks of the
Itwasaprospectivestudyofallthemajorairwayeventsoccur-
mind,andoperateinamoredisciplinedmanner.
ringinoperatingtheatres,ICUortheemergencydepartmentthat
Anaesthetists are unlikely to ever train as frequently as
resultedinseriousharmoccurringacrosstheUKina12month
Formula1pitcrews,butanaesthesiaisimproving.TheCockpit
period, beginning September 2008. For inclusion, complications
Resource Management programmes in the aviation industry
ofairwaymanagementhadtohaveledtodeath,braindamage,
becameAnaestheticCrisisResourceManagementcourses,first
theneedforanemergencysurgicalairway(frontofneckaccess),
establishedbyGabaintheUSA.77Anaesthetistsarerecognizing
unanticipated ICU admission or prolonged ICU stay. Each
that poor non-technical skills are contributory to adverse
includedcasewasthenreviewedbyanexpertpanel.Onehun-
events.78Unfortunately,despiteincreasedawareness,evidence
dredandeighty-fourcaseswerereported,including38deaths.
suggests that Can’t-Intubate, Can’t-Oxygenate situations have
Thereportgenerated167recommendations,divisibleintorec-
beenpoorlymanaged.79Theuseofagradedassertivenesscom-
ommendations for the institution, for the department, and for
munication tool such as PACE (Probe, Alert, Challenge,
the individual practitioner. The recommendations complement
Emergency), adapted from the aviation industry,80 may be of
theguidelineseventhoughtheywerecreatedasrecommenda-
benefit in averting an airway catastrophe. For effective use,
tions from ‘non-ideal practice’ rather than literature review.
everyoneinvolvedmustunderstandhowitworks,andhavethe
NAP4identifiedseveralrecurringthemesincludingpoorairway
knowledge to know when to deploy it.81 By 2016, Merry noted
assessment, poor planning in the face of potential difficulty, a
events leading to harm during anaesthesia often result from
failuretoplanforfailure,andtheinappropriateuseorlackofuse
omissionofkeyplanningsteps(suchasfailuretoanticipateand
ofvariouspiecesofairwayequipment.Theobeseandthosewith
planforadifficultairway)orotherformsofbasicoversight.82
headandneckpathologyfeaturedtoocommonly,andpoorjudg-
mentandalackofeducationandtrainingwerecontributory.
In recent years, anaesthetic departments have been inun-
Difficultairwaysocietyguidelines dated with guidelines and recommendations on airway man-
agement. Every anaesthetist must individually develop a plan
TheoriginalDifficultAirwaySociety(DAS)guidelineswerenot
thatwilleffectivelyoxygenatetheirpatient.Departmentsmust
thefirsttosuggestamethodofdealingwithafailedintubation.
ensurethattheequipmentandtrainingisprovidednotjustfor
Tunstall described a Failed Intubation Drill for obstetrics in
anaesthetistsbutfortheentireoperatingtheatreteamtofacili-
1976.83Manyofhisthemesstillresonateincurrentguidelines
tate effective airway management. The RCoA and DAS must
suchasthedecisiontoabandonrepeatattemptsatintubation
strivetowardsbetterairwaymanagementatlocalandnational
beingmadepromptly,askingthesurgeonandthetheatresister
levelswithauditandresearchintobestpractice.
tounscrubandhelp,andreleasingcricoidpressure.Thefirstset
of DAS Guidelines (for the management of the unanticipated
difficultairway)84werebegunin1999andsetouttoprovidea
Cricoidpressure
step-wiseseriesofplanstoremedythesituationwhenthepri-
maryintubationplanfailed.Althoughtheysetouttobesimple, Theapplicationofcricoidpressuretoreducegastricinsufflation
clearanddefinitive,whenthetimecametoupdatethem,one andregurgitationandtopreventpulmonaryaspirationinthose
ambition was to simplify them further and make them even at risk is an integral part of anaesthetic practice. It was origi-
moredidactic. nally described in 1961 by Sellick (The Middlesex Hospital,
To date DAS has produced guidelines on unanticipated London) as a ‘simple manoeuvre’ to cause ‘occlusion of the
difficulty with intubation (200484 and 201521), extubation,85 upper oesophagus by backwards pressure on the cricoid ring
paediatrics,86andobstetrics,87withguidelinesforthemanage- against the bodies of the cervical vertebrae’.89 In his original
mentofthedifficultairwayincriticalcareinpreparation.They paper,Sellickreportedinstillationofwateratpressuresofupto
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Fig2Anairwaytrolleydrawer-frontcombiningairwayequipmenttomanageanunanticipateddifficulttrachealintubationwithacognitiveaidtotheDAS2015
Guidelines.
100cm H O into the stomach of cadavers in a steep anaestheticcommunitywithminimalfurtherresearch,becom-
2
Trendelenburg position and found that cricoid pressure pre- inganintegralpartoftherapidsequenceinduction/intubation
vented water from regurgitating into the pharynx. In a para- techniqueforalmost50yr.90Overthelast25yrwehavegained
lysed, anaesthetised patient with a latex tube filled with abetterunderstandingofthefactorsthatinfluencetheefficacy
contrastplacedintheoesophagus,hefoundtheapplicationof of cricoid pressure as described by Sellick. These include the
cricoid pressure led to a loss of contrast at the level of the risk of pulmonary aspiration, whether a force applied to
appliedpressure.Hethenwentontostudycricoidpressurein the cricoid reduced these risks, the reliability of oesophageal
patientsconsideredathighriskforaspiration.Inaseriesof26 occlusion, optimal manual delivery of cricoid pressure, and a
patientsnoregurgitationoccurredin23beforeoraftertheappli- recognitionthatapplicationofcricoidpressureitselfcaninter-
cationofcricoidpressure.Inthreepatientshewitnessedregur- ferewithallaspectsofairwaymanagement.
gitation after cricoid pressure was released after tracheal
intubation.89
Anatomyofhypopharyngeal/oesophagealcompression
Anatomicallytheformationofabarrierappearedtoprovide
a good reason for using cricoid pressure in high-risk patients, Thepositionoftheoesophagusrelativetothecricoidringinthe
and the practice was quickly and widely adopted across the axialplanewasassumedbySellicktobeimmediatelyposterior
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Evolutionofairwaymanagement | i159
cervical vertebra to occlude the hypopharyngeal lumen,
(iv) paralaryngeal pressure may achieve the desired compres-
sion at the oesophageal level, and (v) inappropriate cricoid
pressure (paralaryngeal) may achieve effective oesophageal
compression.95
Doescricoidpressurereducetheriskofregurgitation
andaspiration?
InMendelson’s1946paperdescribingobstetricpatientsunder-
going face mask ventilation with ether and nitrous oxide, the
incidence of aspiration was 1:667, with a mortality rate of
1:22,000.96Subsequentstudiesduringgeneralanaesthesiasug-
gestanincidenceofpulmonaryaspirationthatrangedbetween
1:200097and1:300098increasingto1:900duringemergencysur-
gery.99 The mortality associated with this incidence of aspira-
tion was between 1:45,000 and 1:70,000.98–100 More recent
studiesshowanincidenceofaspirationof1in7000forelective
patientsandamortalityat1:1,000,000.101The4thNationalAudit
Project,88 described in total 42 cases of aspiration in 2,872,600
generalanaestheticsofwhichtherewere36casesofaspiration
Fig3Airwaydevicesdescribedinthepast25yr.Fromlefttoright(top of gastric contents. Twenty-nine of these 36 patients required
row):AmbuAuraGain,LMASupreme,ProsealLMAmountedonintroducer ICUadmissionandhalfrequiredaprolongedstay.88Therewere
tool, Airtraq, and McGrath MAC with X-blade. An Aintree (intubation) eight deaths as a result of aspiration of gastric contents
catheterisplacedbeneaththem.
accounting for the single most common cause of death in
anaesthesiaevents.88
NAP4 highlighted that protection from regurgitation and
aspirationofgastriccontentswasstillanimportantissueforall
tothecricoidring,providingananatomicalexplanationforthe anaesthetists,withthemajorityofaspirationeventsoccurring
occlusionhesawinhiscadavericexperimentsandinhisseries during maintenance (inappropriate supraglottic airway device
of 26 patients. However, a retrospective review of CT scans of use) or extubation compared with before or during induction.
healthypatientsshowedthisnottobetrue;in50%ofsubjects However, NAP4 still identified several cases where there was
theoesophagussitsposterolateraltothecricoidring,mainlyon omission of a rapid sequence induction with cricoid pressure
theleftside.91Oesophagealpositionwasalsoinvestigatedusing despitestrongindicationsforitsuse,followedbypatientharm
MRI imaging with and without cricoid pressure in 22 awake or death from aspiration. There were no cases where cricoid
patients.Itshowedsimilarfindingsofposterolateralpositioning pressure was reported to lead to major complications. NAP4
oftheoesophagus,mainlyontheleftsidewithanincreasein concluded rapidsequence induction with cricoid forcedidnot
the lateral displacement of the oesophagus from 53% to 91% provide100%protectionagainstregurgitationandaspirationof
with cricoid pressure.92 Ultrasound examination to assess the gastriccontents,butremainedthestandardforthosepatients
degree to which cricoid pressure compressed the oesophagus atrisk.88
showed no reduction in the anteroposterior diameter of the
oesophagus.However,anovelpressuresite(paralaryngeal)did
Iscricoidpressureperformedoptimallyandisit
achievethedesiredcompressionoftheoesophagus.93Ourtradi-
harmless?
tionalunderstandingoftheanatomicalpositionoftheoesopha-
gusmaybeincompleteand‘occlusionoftheupperoesophagus AlthoughSellickoriginallydescribed‘cricoidpressure’withfirm
bybackwardspressureonthecricoidringagainstthebodiesof pressurebeingappliedonceconsciousnesswaslost,ourcurrent
thecervicalvertebrae’90maybesuboptimalormistaken. understandingofaforcethatisappliedmaymeanthatcricoid
Further MRI studies on awake volunteers found the hypo- forceisamoreaccurateterm.Mostproblemswithcricoidforce
pharynxnottheoesophaguslaybehindthecricoidringandit occurwhentoomuchforceisapplied,102 butknowledgearound
wasthehypopharynxnottheoesophagusthatwascompressed howmuchforcetoapply,whentoapplyit,anditsapplicationis
bycricoidpressure.94Withcricoidpressure,themeananterio- inconsistent.103–106
posterior diameter of the hypopharynx was reduced by 35% Cricoid pressure is uncomfortable in the awake patient,103
(3.2mm)whichwasthoughttorepresentcompleteocclusionof particularly when the force is greater than 20N (2kg) causing
thelumen.94Thiscompressionwasmaintainedevenwhenthe retching,107andleadingtopulmonaryaspiration108oroesopha-
cricoid ring was lateral to the vertebral body whilst the distal gealrupture.109110Currentguidelinesrecommenda10N(1kg)
hypopharynx,theportionofthealimentarycanalatthecricoid forceinitiallytotheawakepatientincreasingto30N(3kg)after
level, was fixed with respect to the cricoid ring by a complex lossofconsciousness.2187101109Theapplicationofcricoidpres-
networkofmuscularandligamentousstructuresminimizingits suremayalsoinfluencetheloweroesophagealsphinctercaus-
mobility.94 ing relaxation and an increased potential for vomiting,
The significance of these findings is: (i) compression regurgitationandaspiration.110–113
andobliterationofthelumenmaybeatthelevelofthehypo- If active vomiting occurs when cricoid pressure is applied,
pharynxandnotattheleveloftheoesophagus,(ii)appropriate cricoid pressure should be removed immediately. The very
cricoid pressure compresses the post-cricoid hypopharynx, problemwesetouttopreventmayactuallybetriggeredbyour
(iii) it may not be necessary to fix the cricoid ring against a actions.95
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i160 | McNarryandPatel
Cricoidpressurecanaffect: Prolongationofapnoeatimeafterinductionof
anaesthesia
i. Facemask ventilation - increasing inspiratory pressures,
reducingtidalvolumes,andmayevencausecompleteair- Methods to prolong the apnoea time after the induction of
wayobstruction.114–119 anaesthesia and administration of neuromuscular blocking
ii. Directlaryngoscopy-causingdistortionoflaryngealstruc- agentsinclude;(i)pharyngealinsufflationofoxygen(3–10 litre
tures.120Failedintubationisalmosteighttimesasfrequent min(cid:2)1),147148(ii)nasaloxygendeliveredatflowratesof<15litre
inpatientshavingarapidsequenceinduction.88 min(cid:2)1(describedasnasaloxygenationduringeffortstosecurea
iii. Laryngeal mask airway placement - impeding successful tube or NO DESAT),144 149 150 and more recently (iii) high flow
placementandventilation.121122 humidifiednasaloxygenat30–70litremin(cid:2)1,146151–158forwhich
the acronym THRIVE has been used (transnasal humidified
Duringthelast25yrthepracticalapplicationofcricoidpres-
rapidinsufflationventilatoryexchange).
sure/force has been discussed123–128 and challenged.129–132 In
Unlike regular breathing where oxygen removal from and
the UK it remains a standard component of a rapid sequence
carbondioxide(CO )deliverytothealveoliarepredictableusing
induction and intubation. Cricoid pressure may reduce gastric 2
the respiratory quotient, during apnoeic oxygenation signifi-
distension during mask ventilation (the purpose for which it
cantly more CO (90%) is buffered in the bloodstream and tis-
wasoriginallydescribed),89increasingthetimetodesaturation 2
sues, meaning only approximately 20ml min(cid:2)1 is delivered to
in those at risk with poor respiratory reserve, sepsis, or high
thealveoliduringapnoea.144159160Thesubsequentreductionin
metabolicrequirementsandprovidinganearlyindicationofthe
lungvolume generates apressuregradientbetween theupper
ease of ventilation.21 The force used can be reduced to 20N
airwayandthealveoli,whichresultsinmassmovementofoxy-
(2kg)ifthepatientisinahead-upposition.125
gen down the trachea into the alveoli replenishing oxygen
Theroleofcricoidpressurehasevolvedfromaprocedurethat
storesandincreasingthesafeapnoeatime.Thesafetimeislim-
wasneverorrarelyreleasedwhendifficultieswereencountered
itedbyasignificantincreaseinthealveolarCO concentration
toapragmaticapproachrecognizingcricoidpressurecanaffect 2
leadingtoprogressiverespiratoryacidosis.
allaspectsofairwaymanagement.Itshouldbereleasedimmedi-
1. Pharyngeal insufflation . Pharyngeal insufflation of oxygen
atelywhenairwaydifficulty(laryngoscopy,facemaskventilation
involvestheadministrationofoxygenat3–10 litresmin(cid:2)1viaa
orlaryngealmaskairwayplacement)isencountered.218795Ifcri-
nasalcatheterplacedthroughthenoseintotheoropharynxor
coidpressureisremoved,thisshouldbedoneunderdirectvision
an oral tube placed through the mouth directly into the oro-
withsuctionavailableandtheassistantreadytoreapplycricoid
pharynx. Oxygen insufflated at 3 litre min(cid:2)1 through an 8Fr
pressureintheeventofregurgitationoraspiration.
catheter inserted through the nose and emerging in the
oropharynx of apnoeic patients undergoing elective surgery,
Preoxygenationandincreasingsafeapnoea sustained peripheral oxygen saturations >97% throughout a
10minstudyperiod,whilstthosewhodidnotreceivepharyng-
time
eal oxygenation desaturated.147 The authors concluded phar-
Fromthe1940’sonwardspreoxygenationhasbeenrecognised yngeal oxygenation provided 10min of ‘safe’ apnoea time in
as an important technique before the induction of general ASAIorIIpatientswithunobstructedairways.147
anaesthesiatodelaytheonsetofhypoxia,allowingmoretime 2.Nasaloxygenationduringintubation(<15litremin(cid:2)1).Thissim-
forlaryngoscopy,trachealintubationandairwayrescue.132–137 pletechnique,firstdescribedbyLevitanasNODESATin2010,149
Inthe1960spreoxygenationwasemphasisedwiththeintro- involvestheapplicationofsimplenasalcannulaeonthepatient
ductionofcricoidpressureandinthe1970sbecameessential under a face mask during preoxygenation. After induction of
aspartoftherapidsequenceinductionandintubationtechni- anaesthesiathenasalcannulaflowrateisincreasedtoamaxi-
que.90Asthedevelopmentofa‘can’tintubatecan’toxygenate’ mum of 15litre min(cid:2)1, whilst airway patency is maintained by
situation is unpredictable, national guidelines have recom- eitherajawthrustordirectlaryngoscopy.Atthisflowratenearly
mendedpreoxygenationasdesirableinallpatients.138TheDAS 100% FiO isachievedandtheapnoeatimeincreased.Thesim-
2
2015 guidelines for management of unanticipated difficult plicity of the technique, the universal availability of equipment
intubation in adults recommend ‘All patients should be pre- andminimalchangetoexistingpracticesuggestitshouldbeused
oxygenatedbeforetheinductionofgeneralanaesthesia’.2187 morewidelytoincreasetheapnoeatimeinthoseatrisk.144149
3. Humidified high flow nasal oxygen (30–70litre min(cid:2)1). The
term THRIVE was coined in 2015 by Patel and Nouraei to
Optimisingtheoxygenreservoirbeforeinductionof
describetheapplicationofhigh-flow(30–70litremin(cid:2)1)warmed
anaesthesia
humidified oxygen (Fig. 4) in adult patients with difficult air-
Overthelast25yrtheoptimumtechniqueforfacemaskpreoxy- ways.146Thehighflowratesassociatedwiththistechniqueare
genationhasbeeninvestigated.Thesestudiesdescribetechni- onlytoleratedbecausetheoxygenadministerediswarmedand
quesofadministeringoxygentooptimisetheoxygenreservoir humidified.Incontrast,colddryoxygenathighflowratesleads
beforetheinductionofanaesthesiaandinclude;(i)tidalvolume tomucosaldrying,pain,discomfort,sinusheadachesandbleed-
breathing, (ii) single tidal capacity breathing, (iii) one vital ingfromthenasalmucosalimitingcolddryoxygento10–15litre
capacity breath followed by tidal volume breathing, (iv) four min(cid:2)1intheawakepatient.‘THRIVE’significantlyextendsthe
deep (inspiratory capacity) breaths, (v) eight deep (inspiratory apnoeatimebutunliketraditionalapnoeicoxygenationtechni-
capacity) breaths, and (vi) extended deep breathing (12–16 ques it also improves the clearance of CO2, preventing the
inspiratory capacity breaths).139 Other techniques to increase increase seen in traditional apnoeic oxygenation techniques.
theoxygenreservoirbeforetheinductionofanaesthesiainclude: TheclearanceofCO2146hasbeenreplicatedinclinicaltrialsby
(i)continuouspositiveairwaypressure(CPAP),140–143(ii)nonin- Gustafsson158andTo.156ThemechanismofCO2clearancedur-
vasivebilevelpositiveairwaypressure143and(iii)headupposi- inghighoxygenflowrateshasrecentlybeeninvestigatedandis
tioning.21144–146 thoughttobemediatedbytheinteractionbetweensupraglottic
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Evolutionofairwaymanagement | i161
hypoxiaduringapnoea,prolongingthesafeapnoeatimeininfants
andchildren.153Theaccompanyingeditorialconcludedthatasa
newtechniqueTHRIVEhadnotbeenfullycharacterisedinchil-
dren,butheldgreatpromiseandmayrepresentatransformative
techniqueforthesafemanagementofdifficultairways.154
Overthelast25yrimprovementstopreoxygenationtechni-
ques in different clinical situations have identified head up
positioning, continuous positive airway pressure, positive
end-expiratory pressure, bilevel positive airway pressure and
apnoeicoxygenationtechniquestooptimisetheoxygenreser-
voir before induction of anaesthesia and prolong the apnoea
timeaftertheinductionofanaesthesia.
Conclusions
The NAP4 reported that anaesthetists are almost defined by
theirabilitytomanagetheairway.However,thisisnotasimple
taskansweredbyasimpleclinicaltrial,asitinvolvestheinter-
action between the patient and their (patho-)physiology, any
airway management equipmentusedanditsefficacy, andthe
skilloftheoperator.Asweseektomakeairwaymanagement
saferinthenext25yr,lookingatthesefactorsinisolationmay
proveoverlysimplistic.Anabilitytoeffectivelystratifypatients
betweenlowandhighriskandthenanabilitytodealwiththose
patientsidentifiedasdifficult,presumesthatanysuchstratifi-
cationordeviceorinnovationtomanagedifficultyisonehun-
dred percent effective, which it cannot be. Regardless of the
clinical and scientific discoveries of the present146 and the
future,161 162 anaesthetists must continue to make an airway
managementplanforeverypatientthatincludesasecondplan
should their primary plan fail. Together with their team they
mustbetrainedinitsexpertdelivery.
Authors’contributions
Manuscriptpreparation:allauthors
Fig4Ahumidifiedhighflownasaloxygencircuitbykindpermissionof Writingpaper:allauthors
FisherandPaykel. Revisingpaper:allauthors
Declarationofinterest
flowvorticesgeneratedbythehighnasalflowandcardiopneu- A.F.M. has been loaned a variety of equipment by Amby and
maticmovements. Aircraft(Medtronic)forevaluationpurposesinthepast5years.
PatelandNouraei146concludedthatwarmedhumidifiedhigh A.F.M.hasalsobeenloanedequipmentbyAccutronic,Aircraft
flowoxygenhasthepotentialtotransformthepracticeofanaes- Medical,AMBU,Cook,Fannin,Freelance,Medtronic,Storz,and
thesiabymaintainingoxygensaturationsaftercommencement Teleflex Medical for use in Airway Workshops. He has been
ofapnoeatolevelsthatchangethenatureofsecuringadefinitive loaned equipment for clinical use by Fisher and Paykel, who
airway in emergency and difficult intubations from a hurried havealsofundedtravelcostsforaTHRIVEdevelopmentdayin
stop-start,potentiallytraumaticundertaking,toasmoothevent 2015.In2017A.F.M.actedasanexpertadvisortotheMHRAand
undertakenwithinanextendedsafeapnoeicwindow. receivedconferencefundingfromMSD.A.F.M.istheRCoAand
Wheninvestigatedinarandomizedcontrolledtrialofrapid DASAirwayLeadsAdvisor.A.P.hasreceivedtravel,accommo-
sequence induction of anaesthesia during emergency surgery, dationandconsultancysupportfromF&PHealthcareandisthe
highflownasaloxygenat30–70litremin(cid:2)1wasshowntobea currentpresidentoftheDifficultAirwaySociety.
feasible and safe method for oxygenating patients. The high
flow group had a significantly longer apnoea time when com-
Funding
pared with face mask preoxygenation, whilst an equivalent
bloodgasprofilewasmaintainedbetweenthegroups.48155This Nonedeclared
isapowerfuldemonstrationofthebenefitsofhighflowoxygen-
ation, but the increased length of time to tracheal intubation
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