Transcript Airway assessment preoperatively

Airway assessment
Dr James Hayward
SHO Anaesthetics Worthing
Introduction
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Respiratory events are the most common anaesthetic related injuries,
following dental damage. Three main causes:
– Inadequate ventilation
– Oesophageal intubation
– Difficult tracheal intubation
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Difficult tracheal intubation accounts for 17% of the respiratory related
injuries and results in significant morbidity and mortality.
Estimated that up to 28% of all anaesthetic related deaths are secondary to
the inability to mask ventilate or intubate.
Prediction of the difficult airway allows time for proper selection of
equipment, technique and personnel experienced in difficult airways
Airway
Nasal and oral cavities
 Pharynx
 Larynx
 Trachea and large bronchi
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Difficult airway
ASA definition of difficult airway:
“The clinical situation in which a
conventionally trained anaesthetist
experiences difficulty with mask
ventilation, difficulty with tracheal
intubation or both.”
Difficult ventilation
The inability of a trained anesthetist to
maintain the oxygen saturation > 90% using
a face mask for ventilation and 100%
inspired oxygen, provided that the preventilation oxygen saturation level was
within the normal range.
Difficult intubation
More than 3 attempts
 Longer than 10 minutes
 Failure of optimal best attempt
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Predictors of difficulty to face
mask ventilate (OBESE)
1. The
Obese (body mass index > 26
kg/m2)
2. The Bearded
3. The Elderly (older than 55 y)
4. The Snorers
5. The Edentulous
Prevalence
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Difficult face mask
– 0.1% - 5%
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Difficult LMA
– 0.2% - 1%
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Difficult intubation
– 1-2% of normal surgical population
– 50% of rheumatic cervical disease
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Causes of difficult
Stiffness airway
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Arthritis of neck/jaw/larynx.
Fixation devices
Scleroderma
Diabetes
Deformity
– Cervical and craniofacial
– Burns/trauma/infection
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Swelling
– Infection/tumour/trauma/burns
– Anaphylaxis/haematoma/acromegaly
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Reflexes
– Cough/breathholding
– Laryngospasm/salivation/regurgitation
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Foreign body
Other – Pregnant/full stomach/VIP
Airway assessment
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History
– Patient/notes/chart/medic-alert/spam letter
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Difficulty
Surgery/burns
Concurrent disease
Reflux/recent meals
General examination
– Do they just look difficult?
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Dentition (prominent upper incisors, receding chin)
Distortion (edema, blood, vomits, tumor, infection)
Disproportion (short chin-to-larynx distance, bull neck, large tongue, small mouth)
Dysmobility (TMJ and cervical spine)
– Massively obese or pregnant
– Beards +/- tubes
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Specific tests
Investigations.
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Nasoendoscopy
X-ray
CT/MRI
Flow volume loop
Mallampati Score
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Sensitivity: 44% - 81%
Specificity: 60% - 80%
Roughly corresponds to Cormack and Lehane’s
laryngoscopy views
Class I (easy)—visualization of the soft palate,
fauces, uvula, and both anterior and posterior
pillars
Class II—visualization of the soft palate, fauces,
and uvula
Class III—visualization of the soft palate and the
base of the uvula
Class IV (difficult)—the soft palate is not visible at all
Thyromental distance
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Measure from upper edge of
thyroid cartilage to chin with
the head fully extended.
– Normal is approx 7cm
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Relatively unreliable test unless combined with
other tests.
– Grade 3 or 4 Mallampati who also had a thyromental
distance of less than 7cm were likely to present
difficulty with intubation.
» Sensitivity: 90.9%
Specificity: 81.5%
Atlanto-occipital movement
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The patient is asked to hold head erect, facing directly to the front, then
he is asked to extend the head maximally and the examiner estimates the
angle traversed by the occlusal surface of upper teeth.
– Visual assessment or using a goniometer.
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Grade I >35 degrees
Grade II 22-34 degrees
Grade III 12–21 degrees
Grade IV <12 degrees
Assesses feasibility to make the optimal intubation position with
alignment of oral, pharyngeal and laryngeal axes into a straight line.
Limited A-O joint extension
– Spondylosis, rheumatoid arthritis, halo-jacket fixation, and in patients with
symptoms indicating nerve compression with cervical extension.
Further assessments
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Sterno-mental distance
– Measured from the sternum to the tip of the mandible
with the head extended.
» A sternomental distance of 12.5cm predicts a difficult
intubation.
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Mandibular protrusion
– If the patient is able to protrude the lower teeth beyond
the upper incisors intubation is usually straightforward
– If the patient cannot get the upper and lower incisors
into alignment intubation is likely to be difficult.
Wilson’s risk score
Score
Weight
0=<90kg
1=>90kg
2=>110kg
Head and
neck
movement
0=Above 90degrees
1=About 90degrees
2=Below 90degrees
Jaw
movement
0=IG>5cm or SLux >0
1=IG<5cm and SLux = 0
2=IG<5cm and SLux<0
Receding
mandible
0=Normal
1=Moderate
2=Severe
Buck teeth
0=Normal
1=Moderate
2=Severe
• Head movement assessed with
pencil taped to a patient’s forehead.
•IG = Interincisor gap measured
with mouth fully open.
•SLux = Maximal forward
protrusion of the lower incisors
beyond the upper incisors.
Results
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633 Patients
Risk factor
Weight
Head and
neck
movement
Jaw
movement
Receding
mandible
Buck teeth
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Score
0
1
2
0
1
2
0
1
2
0
1
2
0
1
2
Normal (%) Difficult (%)
95
90
27
6
1
4
91
54
6
22
3
24
92
38
7
34
0.4
28
97
58
3
32
0.2
10
96
64
3
24
0.4
12
P
0.05
0.001
0.001
0.001
0.001
True positive (%)
False positive (%)
Risk Criteria Initial Prospective Initial Prospective
>6
8
0
0
>5
17
0
0.3
>4
36
42
0
0.8
>3
52
50
1
4.6
>2
72
75
6
12.1
>1
86
92
24
26.2
Effect of varying the criterion for identifying "difficult patients".
LEMON trial
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156 A+E patients
– 114 Grade I
– 42 Grade II and above
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Look
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Facial trauma
Large incisors
Beard
Large tongue
Evaluate 3-3-2
» Interincisor distance (3 fingers)
» Hyoidmental distance (3 fingers)
» Thyroid to floor of mouth (2fingers)
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Mallampati
Obstruction
Neck movement – chin to chest
Results
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No significant difference
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Sex
Age
Facial trauma (11.3% vs 12.2%)
Large tongue (1.0% vs 4%)
Hyoid to chin (35% vs 45%)
Mallampati score (p=0.41)
Airway obstruction (6.5% vs 14.3%)
Neck mobility (16.2% vs 28.6%)
Results (2)
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Significant difference
– Large incisors (6.5% vs 28.6%, p<0.001)
– Reduced inter-incisor difference (38.2% vs 69%,
p<0.05)
– Reduced thyroid to floor of mouth difference (13.4% vs
41.2%, p<0.05)
– Total correlated with difficulty (r=0.38, p<0.001)
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Comments
– Easy to remember and simple.
– Look criteria
– Definition of “difficult intubation”
Intubation
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Equipment
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The safety of laryngoscopy can be increased by preoxygenating the patient prior to
induction and attempts at intubation.
Intubation is attempted by optimal direct laryngoscopy;
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TRAINED ASSISTANT
Laryngoscopes with a selection of blades
Variety of endotracheal tubes
Introducers for endotracheal tubes (stylets or flexible bougies)
Oral and nasal airways
A cricothyroid puncture kit
Reliable suction equipment
Laryngeal mask airways, sizes 3 AND 4
optimal head and neck positioning
optimal muscle relaxation
optimal laryngoscope blade
optimal external laryngeal manipulation
optimal use of the bougie
After intubation correct placement of the tube should be confirmed by:
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Observing the tube pass through the cords
Successful inflation of the chest on manual ventilation
Auscultation over both lung fields in the axillae
Capnograph
If in doubt – take it out
References
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Practice guidelines for management of the difficult airway: an updated
report by the American Society of Anesthesiologists Task Force on
Management of the Difficult Airway. Anesthesiology 2003; 98 (5):1269-77
Frerk CM. Predicting difficult intubation. Anaesthesia 1991; 46 (12):10058
Verghese C, Brimacombe JR. Survey of laryngeal mask airway usage in
11,910 patients: safety and efficacy for conventional and nonconventional
usage. Anesth Analg 1996; 82: 129–33
Gupta S, Sharma R, Jain D. Airway assessment – Predictors of a Difficult
Airway. Indian Journal Of Anaesthetics 2005; 49(4) : 257 -262
Wilson M, Spiegelhalter D, Robertson A, Predicting difficult intubation.
Br. J. Anaesth. (1988), 61, 211-216
The Difficult Airway Society Website: WWW.DAS.UK.COM
Reed M, Dunn M, McKeown D. Can an an airway assessment score
predict difficulty at intubation in the emergency department. Emerg Med J
2005;22:99–102.