Anatomical differences in developing paediatric airway

Question 1

Supraglottic: head and facial configuration, how does this affect choice of facemask and position of intubation

Answer 1

Babies have
* Relatively large heads
* Prominent occiput
* Short neck
* Relatively less prominent frontonasal process

Choice of facemask
* Less prominent frontonasal process of newborns predisposes to leaks
* Should extend from bridge of nose to chin, avoiding the eyes,
* Circular mask provides better seal than one with exaggerated nasal contour

Head should be kept in a neutral position to maintain airway and for intubation. Usually unneccesary to raise the head

Question 2

Supraglottic: nose and pharynx: clinical implications for induction of anaesthesia

Answer 2

• Relatively large tongue can obstruct mouth breathing: tend to ‘nose’ breathe (i.e. can breathe even when feeding). Most obvious under 6 months - as child grows, relative size of tongue to oral cavity decreases, and coordination improves.
• 60% full-term newborn (more if preterm) cannot switch from nose to mouth breathing
• Pharyngeal structures are distensible, airway diameter increases in response to pressure

-> babies may develop pharyngeal obstruction in the early stages of induction of anaesthesia -> overcome by applying CPAP 5-10cmH20 using a well fitting mask

Question 3

Larynx (position)

Answer 3

• Infant larynx is approx 1 vertebral space higher than adult (C2-3 vs C3-4).
• Preterm larynx is approx 1 vertebral space higher than term infant
• Increased proximity to tongue -> more acute angulation between plane of tongue and plane of glottic opening -> appears more anterior.
• However is NOT more anterior - in fact, more rostrally placed in neck
• In mandibular hypoplasia, e.g. Pierre Robin syndrome, this is exaggerated

Question 4

Answer 4

Laryngeal inlet

Question 5

Larynx: epiglottis, vocal cords, shape-> implications for intubation

Answer 5

• Epiglottis is narrow and angled away from trachea -> more difficult to lift with laryngoscope blade -> straight blade lifts the tongue from field of view and exposes laryngeal inlet more effectively
• Vocal cords have a lower attachment anteriorly than posteriorly (vs adult where are at right angles to the trachea) -> tip of a tracheal tube may be held up at anterior commisure during attempted intubation, especially where the nasal route is used
• In the infant, larynx is cone shaped with narrowest point at cricoid. Cricoid is only complete ring of cartillage in the airway -> vulnerable to pressure from tightly fitting tube. In adult, more conical shaped.
• Too large tubes may cause pressure damage, too small will have too high resistance for spontaneous ventilation, and be too small for positive pressure ventilation.

Question 6

Impact of oedema on the airway

Answer 6

1 mm of oedema ->
* Infant [normal diameter 4mm]: 75% reduction in cross-sectional area, 16x increase in resistance
* Adult [normal diameter 8mm]: 44% reduction in cross-sectiona, area, 3x increase in resistance

Question 7

Trachea (length in infant, implications for endotracheal tube position)

Answer 7

• Trachea is relatively short (2-3cm in infant)
• Neck flexion causes movement of tracheal tube towards carina, extension causes movement of tracheal tube away from carina
• Movement can be 1-2cm depending on age of child, risk of
• Accidental extubation
• Bronchial intubation (R main bronchus is wider than left, arises at less acute angle to the midline, right upper lobe bronchus is easily obstructed by bronchial intubation)

Question 8

Why are young children more vulnerable to small airway collapse?

Answer 8

• Lower airways are narrow and easily compressed
• In young adult outward chest wall expansion forces equal lung recoil forces. In infant, chest wall is extremely compliant -> reduced outward recoil force. Therefore at end expiration transpulmonary pressure is inadequate to maintain the patency of the airways in the dependent areas of the lung -> small airway closure
• The chest wall has more horizontal ribs, increased risk of respiratory muscle fatigue and closing volume encroaches on functional residual (FRC), so increasing the need to use intermittent positive pressure ventilation (IPPV) in infants

Question 9

In young infants, what may cause:
1. Nasal obstruction
2. Pharyngeal obstruction

Answer 9

Nasal obstruction
* Nasal congestion (esp. caucasian infants)
* Choanal atresia (unilateral or bilateral congenital obstruction of the nasal passages) may cause acute airway obstruction at birth, especially if bilateral.
* NG tube insertion

Pharyngeal obstruction
* Induction of anaesthesia
* Pierre Robin syndrome (underdeveloped mandible, large tongue and cleft palate)

Question 10

Features of a face mask suitable for neonate

Answer 10

• Low dead space: total apparatus dead space should not exceed 1.5 ml/kg (or 1 ml/kg for infants weighing less than 2.5 kg).
• Soft cushion
• Circular (NOT exaggerated nasal contour)
• Cover nose and mouth
• Able to provide seal of 5-10cmH20

Question 11

How does Down’s syndrome affect the risk of airway obstruction

Answer 11

• Small mouths
• Hypoplastic mandibles
• Large tongues

Question 12

Choice of tracheal tube in infants

Answer 12

• Usually uncuffed (to reduce risk of subglottic damage)
• Should provide a small leak when 20cmH20 applied - otherwise may be too large

Question 13

What is the main reason airway closure occurs in newborn infants?

Answer 13

Increased chest wall compliance.
Chest wall compliance is 3-6 times that of the lung in infants so that outward recoil forces are reduced and inadequate to oppose inward lung recoil.