The ‘Difficult’ AirwayThe ‘Difficult’ Airway

Barbara Stanley FRCABarbara Stanley FRCA

ObjectivesObjectives Define “difficult”Define “difficult” Factors associatedFactors associated Airway tests – pro’s and con’sAirway tests – pro’s and con’s PlanPlan

Some DescriptionsSome Descriptions ‘‘difficult airway’difficult airway’ Mask ventilation vs Mask ventilation vs

laryngoscopy vs bothlaryngoscopy vs both ‘‘difficult difficult

laryngoscopy’ = laryngoscopy’ = Cormack and Lehane Cormack and Lehane grade 3 or 4grade 3 or 4

‘‘difficult intubation’ difficult intubation’ = more than 3 = more than 3 attempts or >10 minsattempts or >10 mins

Importance Importance PredictablePredictable Serious Serious

consequences for consequences for patientpatient

Planning and Planning and preparationpreparation

Alternatives Alternatives What to do if it all What to do if it all

goes horribly wronggoes horribly wrong

The Size of the ProblemThe Size of the Problem Incidence variably quoted at 1-8% Incidence variably quoted at 1-8% 11 Unanticipated quoted up to 18% Unanticipated quoted up to 18% 11 Failure to ventilate as well as intubate occurs Failure to ventilate as well as intubate occurs

in 15% difficult intubations in 15% difficult intubations 33 Abandoned/failed intubation 0.05-0.35% Abandoned/failed intubation 0.05-0.35% 1,31,3

‘‘can’t intubate, can’t ventilate’ 0.0001-0.02% can’t intubate, can’t ventilate’ 0.0001-0.02% 33

CEMD 2000-2002 half the anaesthetic CEMD 2000-2002 half the anaesthetic deaths caused by failed intubation (3 out of deaths caused by failed intubation (3 out of 6) 6) 11

Risk Factors can be Identified Risk Factors can be Identified History History

Of a difficult airway Of a difficult airway previouslypreviously

Congenital conditionsCongenital conditions Medical conditionsMedical conditions Surgical conditionsSurgical conditions

Examination Examination Prominant teethProminant teeth Inability to mouth Inability to mouth

openopen Inability to extend Inability to extend

neckneck Receeding mandible –Receeding mandible –

(beware the beard!!)(beware the beard!!) Body habitusBody habitus

TestsTests

MallampatiMallampati Thyromental Thyromental

distancedistance Incisor gapIncisor gap Protrusion of teethProtrusion of teeth

But....Not particularly But....Not particularly sensitive or specific sensitive or specific in isolationin isolation

Mallampati score with Samsoon and Mallampati score with Samsoon and Young modificationYoung modification

Problems with TestsProblems with Tests Mallampati Mallampati

sensitivity 42-81% sensitivity 42-81% specificity 66-84%specificity 66-84%

Thyromental Thyromental distance –sensitivity distance –sensitivity 62-91% -specificity 62-91% -specificity 25-82% (<6-7cm)25-82% (<6-7cm)

More testsMore tests Wilson – weight, neck movement, incisor gap, Wilson – weight, neck movement, incisor gap,

retroagnathia and incisor appositionretroagnathia and incisor apposition ArneArne Naguib = 4.9504 + (thyrosternal distance x Naguib = 4.9504 + (thyrosternal distance x

1.1003) + (Mallampati score – 2.6076) + 1.1003) + (Mallampati score – 2.6076) + (thyromental distance x 0.9684) + (neck (thyromental distance x 0.9684) + (neck circumference – 0.3966)circumference – 0.3966)

But all these different tests prove there is no But all these different tests prove there is no single test which is reliablesingle test which is reliable

Combined tests increase the chance of Combined tests increase the chance of correct predictioncorrect prediction

Copyright restrictions apply.

Naguib, M. et al. Anesth Analg 2006;102:818-824

Table 2. Simplified Score Model Described by Arne et al

Evidence for their Evidence for their effectiveness effectiveness 11

Naguib model most Naguib model most sensitive 81.4%sensitive 81.4%

Arne model quite Arne model quite sensitive 54.6%sensitive 54.6%

Wilson model poor Wilson model poor sensitivity- 40.2% sensitivity- 40.2% and poor at and poor at correctly predicting correctly predicting difficult airwaydifficult airway

NaguibNaguib Prediction (l) =Prediction (l) = 0.2262 –0.4261 x 0.2262 –0.4261 x

thyromental distance + thyromental distance + 2.5516 x Mallampati 2.5516 x Mallampati score – 1.1461 x score – 1.1461 x incisor gap + 0.0433 x incisor gap + 0.0433 x heightheight

Height and length in cmHeight and length in cmIf l <zero – intubation easyIf l <zero – intubation easyIf l > zero – intubation If l > zero – intubation

difficultdifficult

Action plan for the Predicted Action plan for the Predicted Difficult IntubationDifficult Intubation

Do they need a GA?Do they need a GA? Do they need to be intubated?Do they need to be intubated? Should they have a rapid sequence?Should they have a rapid sequence? What if I can’t ventilate them on an LMA?What if I can’t ventilate them on an LMA? The action plan will largely depend on why The action plan will largely depend on why

they are a predicted difficult intubation – eg they are a predicted difficult intubation – eg simple difficult laryngoscopy in a normal bmi simple difficult laryngoscopy in a normal bmi normal anatomy patient vs airway tumour with normal anatomy patient vs airway tumour with stridor and distorted anatomystridor and distorted anatomy

The Unpredicted ScenarioThe Unpredicted Scenario Commonest in patients who are Commonest in patients who are

‘apparently’ normal‘apparently’ normal Invariably seems to occur at night and Invariably seems to occur at night and

on your ownon your own Key pointsKey points

Don’t panic!Don’t panic!Optomise patient positionOptomise patient positionLong/McCoy blade and bougieLong/McCoy blade and bougie2nd look2nd look

The ‘difficult laryngoscopy’ scenarioThe ‘difficult laryngoscopy’ scenario

Stay calmStay calm Call for helpCall for help Why is the view poor?Why is the view poor?

PositionPosition EquipmentEquipment cricoidcricoid

Oxygenation is now the Oxygenation is now the prioritypriority

Hand ventilate (keep cricoid Hand ventilate (keep cricoid on) on 100% O2 +/- Guidelon) on 100% O2 +/- Guidel

If you can oxygenate them – If you can oxygenate them – panic over and Decide:panic over and Decide: Do they need Ga?Do they need Ga? Can they be Can they be

ventilated/breathe ventilated/breathe spontaneously on LMA?spontaneously on LMA?

The failed intubation drillThe failed intubation drill This is for when you have had a 2This is for when you have had a 2 ndnd look look

in optimal position with a McCoy blade, in optimal position with a McCoy blade, can’t see anything resembling can’t see anything resembling identifiable structures and you can’t identifiable structures and you can’t hand ventilate them with a mask and hand ventilate them with a mask and simple oro – or naso-pharyngeal airway.simple oro – or naso-pharyngeal airway.

The key is to proceed quickly, The key is to proceed quickly, methodically but calmly until you can methodically but calmly until you can oxygenateoxygenate

Summary Summary Assess carefullyAssess carefully Allow yourself time to planAllow yourself time to plan Don’t anaesthetise them Don’t anaesthetise them

alonealone Have a backup planHave a backup plan Don’t give the muscle Don’t give the muscle

relaxants before checking relaxants before checking hand ventilationhand ventilation

Think of alternatives to a GAThink of alternatives to a GA Stay calm Stay calm Know your emergency airway Know your emergency airway

kit before you need it!!kit before you need it!!

Questions?Questions?

References References 1.1. ‘ ‘Predictive Performance of Three Multivariate Predictive Performance of Three Multivariate

Difficult Tracheal Intubation Models: A Double-Difficult Tracheal Intubation Models: A Double-Blind, Case-Control Study’ M. Naguib et al; Blind, Case-Control Study’ M. Naguib et al; Anaesthesia and Analgesia 2006;102:818-824Anaesthesia and Analgesia 2006;102:818-824

2.2. Difficult Airway Society Guidelines-Failed Difficult Airway Society Guidelines-Failed Intubation 2004Intubation 2004

3.3. University New South Wales: Medical education University New South Wales: Medical education files – intubationfiles – intubation

4.4. ‘‘Prediction and management of difficult tracheal Prediction and management of difficult tracheal intubation’ World Anaesthesia 1998intubation’ World Anaesthesia 1998