Paediatric Airway Anatomy
Differences to adult airways
-
Overall smaller airway
-
Small mandible
-
Large head / larger occiput --> Neck being flexed when child lying supine
-
Large tongue
-
High Larynx
-
Funnel shaped larynx with anterior angulation
-
Floppy and long epiglottis
-
Narrowest portion is the glottis / vocal cord level and not the cricoid cartilage
-
Small diameter of airways results in higher resistance to air flow and increased chance of airway obstruction
-
Trachea is short and in line with right bronchus
Dimensions of Vocal cords and Cricoid
Interesting Facts
-
The neonatal trachea is 5 cm long, therefore increasing the risk of inadvertent endobronchial intubation or unplanned extubation. It grows to 8 cm by 12-18 months of age
-
The cross section of the upper airway is not circular at any age. An uncuffed tube, even when a leak is audible, may therefore cause lateral pressure at the glottis or the cricoid ring
-
Although the cross section area of the cricoid is greater than that at the glottis, because the vocal cords are distensible but the cricoid ring is not, the cricoid remains the site at which circumferential oedema is likely to have the most impact on airway
-
With the smaller cross section area of the paediatric airway, comparatively minor degrees of inflammation, oedema and secretions may result in significant airway obstruction
-
Because of the relative prominence of the arytaenoid cartilages in the infant larynx, pressure injury in this area remains a risk with long term intubation regardless of endotracheal tube type
-
Due to differing airway diameters, 1 mm circumferential reduction in airway size from mucosal oedema at the cricoid in an infant would decrease the cross section area by 75% and in- crease resistance 16- to 32-fold; in an adult the cross section area decrease would be 44% and the increase in resistance would only be threefold to fivefold
Choice of ETT
Current evidence suggests use of high-volume, low-pressure cuffed endotracheal tubes for neonates 3kg and beyond
- ​Advantages include low-flow anaesthesia, reduced atmospheric pollution, decreased ETT exchanges to achieve correct ‘fit’, higher airway pressures achievable in non-compliant lungs, improved end-tidal carbon dioxide monitoring, and possible aspiration prevention during long-term ventilation
​
- The main disadvantages are the need to reduce the diameter of the ETT by 0.5 - 1 mm (thereby increasing both airway resistance and work during spontaneous respiration) and removal of the murphy eye
Uncuffed ETT
Children 2 years and older:​
​​​
- ETT Size = (Age/4) + 4.0mm
​​
- ETT Length = (Age/2) + 12cm (oral) or + 14cm (nasal)
Microcuff ETT
Cross-Section on an ETT
- An ETT has two diameters. The internal (ID) and outer diameter (OD)
- The size of the ETT refers to its internal diameter (ID)
​
As the internal diameter changes, the cross-sectional area changes according to the square power while the resistance changes to the 4th power.
