Anaesthesiology: Airway Assessment

Question 1

Airway assessment

Answer 1

Assess difficulty in:

1. Laryngoscopy (Endotracheal intubation)
2. Mask ventilation (patients may be difficult to intubate but able to ventilate)
3. Rescue techniques
   - supraglottic airway device (e.g. laryngeal mask)
   - infraglottic interventions (e.g. tracheostomy, cricothyrotomy)

Done by:

1. ***History
2. ***P/E
3. Investigations (in selected patients)

Question 2

1. History

Answer 2

Aim:

• To identify potential difficulty in maintenance + securing of airway
• Routinely performed for ALL patients undergoing ALL types of anaesthesia (e.g. sedation (∵ may have respiratory depression + loss of airway patency), regional anaesthetic)
• Failure to do so —> Poor outcomes

Assess:

1. Congenital
   - Down’s syndrome (large tongue, neck instability)
   - Craniofacial syndromes
2. Acquired
   - Obesity
   - Pregnancy
   - Ankylosing spondylitis
   - OSA
3. Iatrogenic
   - Cervical spine fusion (Anything that affects ***neck mobility)
   - RT for NPC (causing stiff neck)
4. Previous anaesthetic problems
   - Check anaesthetic record for difficult intubation history (single most predictive factor for difficult intubation)

Symptoms:
1. Often no symptoms

2. OSA symptoms (***STOP-Bang questionnaire, Epworth Sleepiness Scale)
   - snoring
   - daytime lethargy
   - witnessed apnea
3. Airway pathology symptoms
   - hoarseness
   - voice change
   - difficulty lying flat
   - SOB

Question 3

2. P/E

Answer 3

General inspection:

1. Obesity (thick short neck)
2. Beard
3. Obvious H&N pathology (e.g. massive goitre —> airway obstruction, impair infraglottic rescue techniques)
4. Medical equipment (e.g. halo traction, neck collar —> cannot move neck)

Dental condition:

1. Loose teeth (might fall into airway)
2. No teeth
3. Dentures
4. Single incisors
5. Overbite / Buck teeth (Protruding teeth)

Question 4

**Predictive tests for difficult **Laryngoscopy

Answer 4

Limited sensitivity + specificity when used alone (may have high ***false positive rate)
—> Use several together
1. Mallampati score (> Class 3)
2. Thyromental distance (< 6cm)
3. Interincisor distance (< 3cm)
4. Sternomental distance (< 12.5cm)
5. Cervical spine movement (< 90o)
6. Jaw protrusion

Question 5

1. Mallampati score

Answer 5

Ask the patient to sit upright
—> Open mouth as much as possible
—> Protrude tongue

Class 1:
- Faucial pillars, Soft palate, Uvula visible

Class 2:

• Faucial pillars, Soft palate visible
• ***Uvula obscured by tongue

Class 3:
- Only soft palate visible (***Faucial pillars / Uvula obscured)
—> associated with difficult airway

Class 4:
- ***Soft palate not visible
—> associated with difficult airway

Limitation:
- False positive

Question 6

2. Thyromental distance

Answer 6

Distance from **Thyroid notch (喉核) to **Mental prominence (下巴尖) with head fully extended
- Longer: more space to push soft tissue away —> easier intubation / direct laryngoscopy

Normal: 6.5 cm
Concern: <6 cm (i.e. short neck / immobile neck)

• Distance ***>6.5 cm (3 finger breadths) rarely associated with difficulty
• Distance 6-6.5 cm may be associated with difficulty laryngoscopy but ***intubation usually possible
• Distance <6 cm associated with ***difficult direct laryngoscopes

Question 7

3. Interincisor distance

Answer 7

Distance between incisors when mouth **fully open
—> for direct laryngoscopy
- affected by **TMJ, ***Upper C spine mobility
- <3 cm —> More difficult intubation
- <2.5 cm —> Supraglottic airway device (SAD) insertion more difficult

Question 8

4. Sternomental distance

Answer 8

• **Sternal notch to ***Tip of mandible / Mental prominence when neck fully extended
• <12.5 cm: Difficult direct laryngoscopy

Question 9

5. Cervical spine movement

Answer 9

• Full extension of Upper cevical spine
  or
• Extend neck by placing 1 finger on chin + 1 finger on occipital tuberosity
  —> Limited (<90o) / Chin finger level with or still lower than Occipital finger
  —> Difficult direct laryngoscopy

Question 10

**Predictive tests for difficult **Mask ventilation

Answer 10

1. Obese (BMI >26)
   - overlap with difficult laryngoscopy
2. Beard
   - only affect mask ventilation
   —> ∵ difficult to get good seal
3. Absence of teeth
   - only affect mask ventilation
   —> ∵ difficult to get good seal
4. Facial abnormalities
   - overlap with difficult laryngoscopy
5. Receding chin
   - overlap with difficult laryngoscopy
6. Mallampati 3-4
   - overlap with difficult laryngoscopy

Question 11

**Predictive tests for difficult **Supraglottic airway device

Answer 11

May be used as rescue plan:

1. Mouth opening (Interincisor distance) <2.5cm
2. Intraoral / Pharyngeal masses
3. Obesity
4. Poor dentition

Question 12

Combined tests

Answer 12

• Individual tests perform poorly
• Combination of Mallampati + Thyromental distance
  —> more predictive than either test alone
• ↑ specificity but ↓ sensitivity (↑ false negative)

Question 13

3. Investigations

Answer 13

• Sometimes useful to supplement history + P/E
• More information on existing airway pathology
• Not routinely required

1. Nasoendoscopy (when suspect upper airway obstruction)
2. CT / MRI
3. USG
4. Plain radiographs
   - CXR (for trachea narrowing)
   - Facial X-ray
   - C-spine X-ray (flexion + extension view for atlantoaxial instability, for soft tissue swelling + neck fractures)

Question 14

Upper Airway obstruction

Answer 14

Can happen at different levels:

1. Nasal (Base of skull —> Soft palate)
   - Nasopharynx / Epipharynx
2. Oral (Hard palate —> Hyoid bone)
   - Oropharynx
3. Laryngeal (Upper border of epiglottis —> Lower border of cricoid cartilage)
   - Laryngopharynx / Hypopharynx
   - Larynx
4. Trachea

• **Symptoms:
  1. SOB
  2. Change in voice
• **Signs:
  1. Noisy expiration / inspiration (snoring, stridor)
  2. Absence of chest expansion with inspiratory effort
  3. Silent chest
  4. Absence of perceivable air flow (hand over mouth to feel)
  5. Respiratory distress: tachypnea, use of accessory muscles (neck, intercostal insucking)

Question 15

Rapid airway assessment

Answer 15

Look:

1. Decreased chest movement
2. Use of accessory muscles

Feel:
1. Airflow at mouth / nose

Listen:

1. Any breath sounds
2. Noisy breathing (stridor)
3. Change in patient’s voice

Question 16

Establish airway patency

Answer 16

Triple maneuver:
1. Head tilt
2. Chin lift
3. Jaw thrust
—> To open the airway with obstruction

**Avoid head tilt / chin lift in patients with **Cervical spine instability

Question 17

Ventilation

Answer 17

Proper positioning:
1. Pillow under head to **elevate head
—> head on **7-9 cm pillow / firm surface
—> ***horizontal alignment of external auditory meatus + sternal notch

2. Bag mask ventilation
   - E + C clamp
   —> Thumb + Index finger: press down on mask for good seal
   —> Middle + Ring finger: lift mandible
   —> Little finger: jaw thrust
   - Two hand approach

Failure to oxygenate + ventilate —> Severe adverse outcome
- even more important than direct laryngoscopy / intubation

Question 18

Assessment of ventilation

Answer 18

Bag mask ventilation:

1. Chest expansion (instead of stomach only)
2. Exhaled tidal volumes (if connected to mechanical ventilator) (***6-7 mL/kg)
3. Presence of breath sounds
4. Listen + Feel for air leaks / Difficulty in generating positive pressure with bag
5. Capnography (detect EtCO2, if available)
6. Pulse oximetry reading (look for desaturation but it is a late sign)

Reasons for inadequate facemask ventilation:

1. Poor mask seal
2. Airway obstruction (partial / complete)
3. Special cases
   - Facial hair
   - Dentures, Edentulous, Sunken cheek / absence of teeth
   - Obese patients

Question 19

Ways to alleviate difficult mask ventilation

Answer 19

1. ***2 person, 2 hand technique
2. ***Use of oropharyngeal / nasopharyngeal airway (difficult mask ventilation occur in ~5% of patients —> further decrease to 0.5%)
3. Ask assistant to support soft tissues of cheek (e.g. push cheek up against mask)
4. Optimise head position + Triple maneuver
5. Ensure no leak / occlusion in equipment / circuit
6. Facial hair —> aqueous gel, occlusive dressing
7. Consider leaving dentures in place
8. Rescue technique: ***Supraglottic airway device (in case all maneuvers failed in bag mask ventilation)

Question 20

Complications of bag mask ventilation

Answer 20

1. ***Aspiration (esp. in paediatric / not holding airway well, ∵ air going into stomach —> over-insufflated —> gastric regurgitation)
2. Lip + Dental trauma (e.g. too small mask size)
3. Ocular pressure injury (e.g. too large mask size)
4. Facial injury (esp. in pre-existing facial fractures)

Question 21

***Oropharygeal / Nasopharyngeal airway

Answer 21

Both displace tongue away —> prevent tongue falling back onto posterior pharyngeal wall —> open up airway

Nasopharyngeal airway:

• Rapidly + easily inserted blindly
• Used in presence of ***gag reflex (e.g. awake, semi-conscious (e.g. under sedation))
• Used in ***oral trauma
• Used when teeth clenched
• Sizing: Nose to Tragus of ear
• Insertion: Lubrication + Tip point caudally

Absolute CI:

• ***Base of skull fracture (airway may enter brain)
• Nasal, midface fracture

Relative CI:

• Coagulopathy (∵ nasal mucosa is vascular)
• Large nasal polyp
• Recent nasal surgery
• Suspected epiglottitis

Oropharyngeal airway:

• Use in patients ***without gag reflex (e.g. GA patients, CPR patients)
• Rapidly + easily inserted
• Serves as a ***bite block
• Facilitate suction of pharynx / oral cavity
• No epistaxis
• Sizing: Angle of mouth to Angle of jaw (too long will induce laryngospasm, too short cannot open airway)
• Insertion: Point cranially —> touches hard palate —> rotate 180o

Question 22

Advanced airway management

Answer 22

1. Supraglottic approach
   - Supraglottic airway devices (i.e. Laryngeal mask airway)
   - Endotracheal intubation
2. Infraglottic approach
   - Crycothyrotomy (Needle, Surgical)
   - Tracheostomy

Question 23

Endotracheal intubation

Answer 23

Most common method to obtain ***definitive airway (i.e. tube in trachea + cuff below vocal cord —> able to control ventilation + airway protection from gastric aspiration)

Indications:

1. Controlled ventilation + oxygenation
2. ***Airway protection (e.g. low GCS)
3. ***High pressure ventilation (cannot be achieved by bag mask ventilation)
4. Prolonged post-op intubation / mechanical ventilation

**Techniques for ET intubation:
1. Preoxygenation
2. “Sniffing” position (頭伸向前聞野)
- most widely used position for ET intubation
- flexion of neck (Cervical spine) + extension of head (Atlanto-occipital joint)
—> head on 7-9 cm pillow / firm surface
—> horizontal alignment of **external auditory meatus + **sternal notch
—> align axis of **line of sight with ***laryngeal vestibule axis —> easier direct laryngoscopy

Preparation for intubation:

1. Correctly sized ET tube
   - generally size **8 for male adults, **7 for female
2. Laryngoscope (with adequate light source)
3. O2 source
4. Suctioning equipment (∵ sputum / blood may obstruct view)
5. Tapes to secure ETT, syringe to inflate cuff
6. Equipment for ventilation (e.g. Ambubag, Mechanical ventilator)
7. Skilled assistant (to hand out equipment quickly + help if problem arise)
8. Other airway equipment to assist intubation (e.g. Oropharyngeal / Nasopharyngeal airway)

Types of ET tube:

1. Material (PVC / Rubber / Silicon)
2. Shape
3. Reinforced tube (contain steel wire —> ↓ chance of kinking)

Features:

1. 15mm connector
2. Radio-opaque line
3. Line markings (Male: 22-24cm at level of lip, Female: 20-22 cm)
4. Line marking for level of vocal cords (line should just pass vocal cord)
5. Murphy’s eye (an extra hole just next to ET tube outlet to avoid obstruction of main hole)
6. Malleable stylet (create best curvature (***Hockey stick shape) to facilitate intubation)

Question 24

Preoxygenation

Answer 24

• ALL patients before induction of anaesthesia
• ↑ O2 reserves of body —> ↑ margin of safety (in case unable to intubate / ventilate —> buy more time before desaturation
• 100% O2 delivered via a tight fitting face mask in a spontaneously breathing patient (for ~3 mins / until ***EtO2 >=90%)
• Fill functional residual capacity with O2
• ↑ duration of apnea without desaturation —> ***6-7 mins

Question 25

Direct laryngoscopy

Answer 25

* **BURP (Backward, Upward, Rightward pressure) 1. Open mouth 2. Insert direct laryngoscope over patient’s right side of mouth 3. Displace tongue to left side 4. Advance blade until reaches vallecula (space between base of tongue and epiglottis) 5. Direct lift laryngoscope upwards 6. Look for glottic opening 7. Insert ET tube into trachea * **Grades of laryngeal view: - Grade 1: Full view of ***glottis (i.e. vocal cords) - Grade 2: Partial view of glottis / only ***arytenoids - Grade 3: Only ***epiglottis visible —> more difficult intubation - Grade 4: Neither glottis nor epiglottis visible —> more difficult intubation ``` Types of laryngoscope: 1. Macintosh blade - most commonly used - light source - beak - spatula - flange (push tongue away) —> adult: size 3/4 ``` 2. Miller blade 3. Video laryngoscope

Question 26

Confirmation of ETT position

Answer 26

1. ***Sustained detection of normal EtCO2 waveform on ***Capnograph (Gold standard, most accurate) - normal range 35-45 mmHg (5% volume) - very tiny CO2 waves may be seen in esophageal intubation (if patient drank carbonated drinks, but rarely sustained) - even cardiac arrest patient with have detectable CO2 trace - no trace —> not in trachea / complete airway/tube obstruction (rare) / disconnection 2. Direct visualisation - ETT between vocal cords / fibreoptic bronchoscopic through ETT to visualise tracheal rings + carina 3. Less reliable signs - Chest rise + fall with ventilation - Breath sounds in axillary chest wall (5 point auscultation in chest: epigastrium (should hear nothing) + 2x just under clavicle on either side of sternum + 2x axillary line 5th ICS) - Absence of breath sounds over stomach - Condensation in ETT If in doubt —> take it out —> continue bag mask ventilation

Question 27

Complications of ET intubation

Answer 27

Can occur during intubation / tube in place / after extubation: 1. Malpositioning - ***Esophageal intubation: potentially catastrophic - ***Bronchial intubation: too deep (need to auscultate both sides of chest) —> oxygen desaturation + higher airway pressure - Laryngeal cuff position: not deep enough —> laryngeal / vocal cord trauma / paralysis, tube dislodgement 2. Induce undesirable physiological response (ET intubation a stimulating maneuver —> stimulate sympathetic system) - ***Hypertension - ***Tachycardia - ***Laryngospasm (Vocal cord close off —> upper airway obstruction) - ***Bronchospasm - Intracranial hypertension - Intraocular hypertension - Negative pressure pulmonary edema (when patient bite on tube before extubation then start inspiring deeply (變相將肺抽真空) —> intense inspiratory effort against obstructed airway —> large negative intrathoracic pressure) 3. Airway trauma - Dental damage / dislodgement (1 in 4500) - Sore throat (50% of patients) - Laceration: lip, tongue, mucous - Dislocated mandible - Edema + stenosis (laryngeal / tracheal) (∵ cuff inflation —> too high pressure —> ischaemia of airway mucosa —> fibrosis + stenosis, more likely in paediatric —> microcuff tube / uncuffed tube) - Vocal cord paralysis —> hoarseness, aspiration (∵ direct damage to vocal cord / inadvertent damage to RLN) 4. Tracheal tube malfunction - Cuff perforation / cut (by teeth) / Valve damage - Obstruction: kinking, thick secretions - Airway fire: PVC tube ignition in oxygen enriched environment + laser procedures

Question 28

Supraglottic airway device

Answer 28

A group of airway devices designed to be inserted into ***oropharynx - NOT enter larynx - ***NOT provide airway protection (not protect from aspiration / regurgitation) - for airway ***rescue after failed intubation + mask ventilation - as a conduit for tracheal intubation - less physiological stimulation / haemodynamic response ``` Example: - Supreme laryngeal mask airway —> Airway tube (15mm connector) —> Drain tube (provide access to esophagus —> pass Ryle’s into stomach —> allow stomach decompression —> ↓ risk of gastric insufflation) —> Airway tube —> Cuff —> Drain tube orifice —> Pilot balloon —> Valve ``` Contraindications: 1. Oral maxillary surgery / ENT surgery - ∵ block view of surgery 2. Full stomach / Intestinal obstruction - ∵ chance of aspiration Insertion: - Size: Piriform fossa - Tip of mask: Upper esophageal sphincter - Base of mask: Base of tongue Complications: 1. Minor: Dry mouth, Sore throat 2. Serious complications rare - Trauma (e.g. larynx) - Dysphonia (∵ RLN damage) - Nerve injury —> Hypoglossal, Lingual nerve palsy (lose sensory + motor tongue function) - Pulmonary aspiration - Gastric insufflation - Laryngospasm

Question 29

Infraglottic approach (Front of neck access)

Answer 29

Indications: 1. Emergency: cannot intubate + cannot ventilate + no other options 2. Acute upper airway obstructions Techniques: 1. Needle cricothyrotomy - insert large bore cannula into cricothyroid membrane —> high pressure to oxygenate through needle 2. Surgical cricothyrotomy - bigger incision —> insert cuffed tube through cricothyroid membrane into upper airway - technique: stab (transverse stab), twist (so sharp edge point caudally), bougie, tube Nearby structures of cricothyroid membrane: 1. ***Cricothyroid artery + vein (upper part of cricothyroid membrane) 2. Thyroid gland 3. Esophagus (behind)

Question 30

Complications of Cricothyrotomy

Answer 30

Can have serious complications: 1. Prolonged execution time 2. Bleeding (cricothyroid artery —> bleeding into airway) 3. Aspiration, subcutaneous emphysema 4. False placement: esophagus, pneumothorax 5. Tube obstruction 6. Late: Dysphonia, Infection, Subglottic stenosis

Question 31

Equipment for airway management: Closed face mask

Answer 31

1. Body 2. Rim 3. Connector (standard 15mm) 3. Valve (inflate air into the rim to distend rim) Application: - Upper border align with pupil - Lower border between lower lip + chin - Side just lateral to nasolabial fold Uses of face mask: 1. Bag mask / ***Mechanical ventilation 2. Preoxygenation prior to GA induction 3. ***Non-invasive ventilation for respiratory failure 4. Inhalational induction of GA 5. Maintenance of GA

Question 32

Ambubag

Answer 32

Use: 1. High flow O2 (larger than minute ventilation, >=15 L/min) + High FiO2 (can deliver ~100% O2) 2. Controlled ***positive inspiratory pressure 3. Provide ***positive end expiratory pressure 4. Augmentation of spontaneous ventilation Features: 1. Self-inflating bag 2. Oxygen inlet + tubing (allow 100% O2 to be connected, otherwise just pump room air (FiO2 21%) to patient) 3. Reservoir bag (allow 100% O2 to be delivered, need to ensure it is distended but not over-inflated: excessive airway pressure) 4. Expiratory valve (ensure expired air do not go back to self-inflating bag) 5. Air-inlet valve (allow fresh O2 from reservoir to go into self-inflating bag) 6. Pressure release valve (allow O2 to go out if pressure is excessive) 7. Air-inlet one-way valve (prevent O2 going back to reservoir when pumping) 8. Pop off valve (allow O2 to go out if pressure is excessive, ↓ risk of barotrauma) 9. PEEP valve (allow PEEP delivery)

Question 33

Summary

Answer 33

- Airway assessment should be performed in ***ALL patients prior to anaesthesia / any airway intervention - Early recognition of airway obstruction is important + require actively monitoring for clinical signs - Priority is to maintain ***oxygenation + ***ventilation using simple airway maneuvers + bag mask ventilation (instead of intubation)