functional airway anatomy relevant to anaesthesia

1. AIRWAY
ANATOMY
Dr.P.Sivaraj MD DA
Assistant Professor
Department of Anaesthesiology
Government Villupuram Medical College

2. CONTENT
 Anatomy of the airway
 Innervation of the airway
 Anaesthetic implications

3. LATERAL CROSS-SECTIONAL VIEW OF
THE HEAD AND NECK

4. ANATOMY OF THE UPPER AIRWAY

7. EXTERNAL NOSE-ANAESTHETIC
CONSIDERATIONS
1. Alae nasi are lateral margins of nostrils. They flare during airway obstruction.
2. Skin over the ala nasi tends to peel off with tight fixing of tape.
3. There may be infolding of ala nasi while introducing any tube.
4. Tip of the nose is used as a reference point to measure the length of
nasopharyngeal airways (tip of the nose to external auditory meatus or tragus).
5. Apex of the properly fixed facemask should lie at the junction of nasal bridge with
the forehead.

8. THE LATERAL WALL OF THE RIGHT
NASAL CAVITY; THE CONCHAE HAVE
BEEN PARTIALLY
REMOVED

9. INTERNAL NOSE/LATERAL WALL-
ANAESTHETIC IMPLICATIONS
 Superior, Middle, and Inferior nasal turbinates or conchae and the space under
each is called as the meatus.
 The mucus membrane is the thickest, and most vascular, over the nasal conchae.
 The vascular mucous membrane overlying the turbinates can be damaged easily
during airway procedures through the nose, leading to profuse hemorrhage.

10. INTERNAL NOSE/LATERAL WALL-
ANAESTHETIC CONSIDERATIONS
 The middle meatus lies under the middle turbinate and is the most important
functional area.
 All the sinuses open into this meatus with the exception of the sphenoidal and the
posterior ethmoidal cells. This is a key area because pathology in this region can
interfere with ventilation and mucociliary clearance of the sinuses.
 Prolonged obstruction of these ostia during prolonged nasotracheal intubation can
lead on to chronic sinusitis

11. INTERNAL NOSE/MEDIAL WALL-
ANAESTHETIC CONSIDERATIONS
 Medial Wall or septum is often deviated to one side & have spurs of bone growing
into the cavity.
 This is important in the context of airway management because airflow through
one nostril will be worse than through the other, besides the chance of tubes
getting stuck.
 The veins form a close cavernous plexus beneath the mucous membrane. This
plexus (Kiesselbach's plexus) is especially well marked over (Little's area) and
over the middle and inferior conchae.
 Epistaxis most often originates from Little's area.

13. INTERNAL NOSE- ANAESTHETIC
CONSIDERATIONS
 Tubes passing through nose can injure on either side (medial or lateral). So, the
side of bevel is less important than the importance of using smaller, softer, well
lubricated tubes.
 The nasal mucosa is exquisitely sensitive to topically applied vasoconstricting
medications. Shrinking the nasal mucosa with a vasoconstricting agent can
increase the caliber of the nasal airway by as much as 50% to 75% and may reduce
epistaxis incited by nasotracheal intubation.
 Before nasal intubation it may be advisable to dilate the nasal cavity by inserting
the gloved and lubricated little finger to ensure patency and to maximally dilate
before the insertion of the nasal tube.

14. FLOOR OF THE NOSE
 Floor of the nose is horizontal antero-posteriorly (i.e., perpendicular to the plane of
face), tilted slightly downward front to back, approximately 10 to 15 degrees.
 Thus, when a nasal conduit is inserted through the nose, it should not be directed
upward or even straight back.
 Instead, it should be directed slightly inferiorly, perpendicular to the plane of face
to follow this major channel to be least traumatic.

15. ROOF OF THE NASAL CAVITY
 Roof of the nasal cavity is made by the base of skull & cribriform plate.
 The cribriform plate is located cephalad of the nares, another reason that tube
insertion should be directed caudad. Otherwise they can travel into the brain if
there is fracture base of skull.
 The non-olfactory sensory nerve supply to the nasal mucosa is derived from the
first two divisions of the trigeminal nerve, the anterior ethmoidal and maxillary
nerves.
 Airborne chemical irritants cause firing of the trigeminal nerves, which
presumably are responsible for reflexes such as sneezing and apnea.

16. NASAL ANAESTETIC
CONSIDERATIONS
 The nasal airway is formed and supported by the bones of the skull, and needs no
internal artificial support to keep it open – but it becomes easily obstructed by
congestion or oedema of the mucosa. In children, adenoidal lymphatic tissue in the
nasopharynx can cause chronic obstruction.
 An upset or crying child will often have a congested, blocked nose – this may first
be apparent after the induction of anaesthesia, when after applying the facemask
you find that the airway is completely obstructed. The remedy is to place an
oropharyngeal airway – if the patient is lightly anaesthetised use a short one to
avoid gagging – your only aim is to part the lips and allow oxygen to pass into the
oropharynx.
 In elderly patients with no teeth, a similar situation can occur when your “chin
lift” manoeuvre causes the chin and lips to overlap the nostrils

18. THE ORAL
CAVITY The mouth, or oral cavity, is bounded externally by the
lips and is contiguous with the oropharynx posteriorly.
 The tongue is attached to the symphysis of the mandible
anteriorly and the stylohyoid process and hyoid bone
posteriorly.
 The mouth/oral cavity consists of the upper and lower
dentition, the tongue and floor of the mouth, the hard
palate and the openings of the major salivary glands.
 The anterior border of the tonsil is known as the
anterior pillar of the fauces and marks the start of the
oropharynx itself.

19. IMPORTANT ANAESTHETIC
CONSIDERATIONS
 1. Teeth may be loose or buck leading to difficulty while introducing laryngoscope
blade.
 2. Cheeks are made of muscle and buccal fat. In old age, depletion of buccal fat
leads to sinking of cheeks and hence difficult mask ventilation.
 3. The potential spaces in the hollow of the mandible are collectively called the
submandibular space
 During conventional laryngoscopy, the tongue is ordinarily displaced to the left and into
the submandibular space, permitting one to expose the larynx for intubation under
direct vision. If the submandibular space is small relative to the size of the tongue (e.g.,
hypoplastic mandible, lingual edema in angioedema, carcinoma of mandible), the ability
to visualize the larynx may be compromised.
 4. Subtle geometric distortions of the oral cavity that limit one's working and
viewing space, such as a high arched palate with a narrow oral cavity or buck
teeth with an elongated oral cavity, may render orotracheal intubation difficult.

20. THE MANDIBLE -IMPORTANT
ANAESTHETIC CONSIDERATIONS
 The mandible figures prominently in alleviating functional airway obstruction. It
is crucial for multiple reasons:
a. Angle of mandible is used a reference point to measure length of oropharyngeal airways.
It is also held forward to keep the tongue and epiglottis away from posterior oro-
pharyngeal wall.
b. As the inferior aspect of the tongue is attached to the mandible, anterior translocation
of the jaw elevates the tongue away from the posterior pharyngeal wall, helping to attain a
clear airway in the obtunded patient (Jawthrust maneuver).
c. During laryngoscopy, the laryngoscope blade moves the mandible forward, helping to
displace the tongue anteriorly and away from obstructing the line of view of the laryngeal
inlet.
d. Mentum of mandible is used as a reference point to assess airway (hyomental, thyro-
mental distances). It is also a reference to place face mask properly (base of mask should
lie over mental groove)

21. THE PHARYNX
 The pharynx is a fibromuscular tube extending from the base of the skull to the
lower border of the cricoid cartilage where, at the level of the sixth cervical
vertebra, it is continuous with the esophagus.
 Posteriorly, it rests against the fascia covering the prevertebral muscles and the
cervical spine.
 Anteriorly, it opens into the nasal cavity (the nasopharynx), the mouth (the
oropharynx), and the larynx (the laryngo- or hypopharynx).

22. THE PHARYNX

23. NASOPHARYNX
 Extends from posterior end of turbinates to posterior pharyngeal wall behind the
free margin of soft palate.
 Roomier than nasal cavity, its side walls have eustachian tube opening on either
side.
 The nasopharyngeal tonsils, also called adenoids, are located posteriorly in the
nasopharynx just above the soft palate, where the eustachian tube enters the
nasopharynx.
 Hypertrophied adenoids may cause obstruction or hemorrhage while passing any
device through nose
 Head extension aligns the nasopharynx with oropharynx better and smoothens
the passage of tubes/devices

25. OROPHARYNX
 The oropharynx extends from anterior tonsillar pillars anteriorly to posterior
pharyngeal wall posteriorly. It includes the base of the tongue and epiglottis
below, the soft palate above.
 In the lateral walls of the oropharynx are situated the fauces. One being anterior,
known as the palatoglossal arch and the second is posterior, the palatopharyngeal
arch.
 The anterior pillar contains the palatoglossus muscle, and the posterior pillar
contains the palatopharyngeus muscle.
 Between these two arches is the palatine tonsil.
 The posterior wall sits on the cervical spine and moves forward on cervical
extension & backward on flexion.
 Vallecula is the entire space between epiglottis and the base of the tongue.

27. OROPHARYNX- ANAESTHETIC
CONSIDERATIONS Oropharynx is the MOST important area in terms of airway obstruction and
maintenance as it is made up of collapsible soft tissue all around.
 The wall of the oropharynx consists of two layers of muscles, an external circular
layer and an internal longitudinal layer. Oropharyngeal musculature has a
normal tone, like any other skeletal musculature. This tone serves to keep the
upper airway open during quiet respiration.
 Tongue falls into oropharynx when relaxed. Pulling out of the tongue relieves
obstruction.
 Head extension opens the oropharyngeal space.
 All devices used to maintain airway patency either lodge in oropharynx or pass
beyond it keeping it open.
 Lingual tonsils and epiglottis are invaluable guides during endoscopy to direct the
scopist to the laryngeal inlet.
 Laryngoscope blade tip lies in vallecula during classical Macintosh laryngoscopy
 Neck extension takes the nasally introduced device tip in oropharynx anteriorly
while flexion takes it posteriorly.

28. OROPHARYNX- ANAESTHETIC
CONSIDERATIONS
 The glossopharyngeal nerve supplies sensation to the posterior one-third of the
tongue, the valleculae, the superior surface of the epiglottis, and most of the
posterior pharynx.
 This nerve is accessible to blockade (topically or by injection) because it runs just
deep to the inferior portion of the palatopharyngeus muscle (the posterior tonsillar
pillar).
 The large adenoids can cause airway obstruction.
 The pharyngeal bursa can impede the ET, if force applied- false passage- sepsis,
bleeding and post op collection of secretions.
 Peritonsilar abscess – ET may impinge and rupture the abscess- aspiration and
pneumonitis

29. IMPORTANT DISTANCES FOR
PROPER ENDOTRACHEAL TUBE
PLACEMENT.

30. LARYNGOPHARYNX
 Extends from epiglottis above to the beginning of esophagus below, at C6 behind
cricoid.
 Also called hypopharynx

31. IMPORTANT ANAESTHETIC
CONSIDERATIONS
 Masked supra-glottic airway devices (SADs) enter the hypopharynx with tip at
upper esophageal sphincter.
 Tubes/devices passed down from mouth or nose into larynx can get stuck in the
piriform fossae and have to be pulled cephalad to laryngeal inlet before
proceeding.
 Pressing on cricoid obliterates hypopharynx and can prevent proper placement of
SADs.

32. THE LARYNGEAL INLET

33. VENTRICLE OF THE LARYNX

34. CARTILAGES OF THE LARYNX
 There are nine cartilages of the larynx,
 Three paired and three unpaired.
 Corniculate, Cuneiform and Arytenoid are paired.
 Thyroid, epiglottis and cricoid are unpaired.

36. BLOOD SUPPLY OF THE LARYNX
 Derived from the external carotid and subclavian arteries.
 The external carotid- superior thyroid artery- superior laryngeal artery.
 This artery courses with the superior laryngeal nerve through the thyrohyoid
membrane to supply the supraglottic region.
 The thyrocervical trunk- inferior thyroid artery- terminates as the inferior
laryngeal artery.
 This vessel travels in the trachea-esophageal groove with the recurrent laryngeal
nerve and supplies the infraglottic larynx

37. SENSORY SUPPLY OF THE
LARYNX
 The main nerves of the larynx are the recurrent laryngeal nerves and the internal
and external branches of the superior laryngeal nerves, both derivatives of the
vagus nerve.
 The recurrent laryngeal nerve provides all other motor supply to the laryngeal
musculature.
 Topical anesthesia of the larynx may affect the fibers of the external branch of the
superior laryngeal nerve and paralyze the cricothyroid muscle, signified by a
“gruff” voice.
 Similarly, a superior laryngeal nerve block may affect the cricothyroid muscle in
the same manner as surgical trauma does. These factors must be taken into
consideration when evaluating post-thyroidectomy vocal cord dysfunction after
surery.

40. INNERVATION OF THE LARYNX

43. Paralysed
laryngeal
nerve
Extent Position of
vocal cord
voice Respiration swallowing
Unilateral
recurrent
Laryngeal
nerve
Incomplete Median Normal
or
hoarse
Normal Normal
Complete Paramedia
n
Normal
Bilateral
recurrent
laryngeal
nerve
Median /
paramedia
n
Normal Dyspnoea Normal
Superior
with
recurrent
laryngeal
nerve
Unilateral
/ bilateral
Cadaveric/
slack/ wary
Feeble /
rough
Normal Aspiration

46. ANATOMIC
DIFFERENCES IN
THE PEDIATRIC
COMPARED WITH
THE ADULT
AIRWAY
▪ higher, more anterior position for
the glottic opening;
▪ relatively larger tongue in the
infant, which lies between the
mouth and glottic opening;
▪ relatively larger and more floppy
epiglottis in the child;
▪ the cricoid ring is the narrowest
portion of the pediatric airway (in
the adult, the narrowest portion is
the vocal cords);
▪different position and size of the
cricothyroid membrane (CTM) in
the infant;
▪ sharper, more difficult angle for
nasotracheal intubation;
▪ larger relative size of the occiput in
the infant.

47. COMPARISON OF ADULT AND
CHILDREN LARYNX

48. LARYNX-IMPORTANT ANAESTHETIC
CONSIDERATIONS
1.The larynx may be located somewhat higher in females and children. Until
puberty, no differences in laryngeal size exist between males and females. The
female larynx is smaller and more cephalad.
2. Tubes and devices that get engaged into the laryngeal inlet are still away from
the glottic aperture (rima glottidis). These devices may cause damage to these
obstructing structures if forced down without redirection.
3. Cricoid cartilage forms complete ring just below the true vocal cords, and is the
narrowest portion of upper airway in children.
4. False vocal cords (vestibular folds) are often mistaken for true VC and may
confound diagnosis of recurrent laryngeal nerve injury. While observing for cord
function true vocal cords should be identified carefully.

49. THE EPIGLOTTIS AND GLOTTIS OF AN
INFANT; NOTE THE APPOSITION OF THE
VOCAL CORDS FROM LARYNGOSPASM

50. THE TRACHEA
 The trachea extends from the inferior border of the cricoid cartilage at C6 up to
the tracheal carina, which is at T4 level (lower border), where it splits into the left
and right mainstem bronchi.
 The trachea is about 10-12cm long in the average adult and is composed of C-
shaped cartilages joined vertically by fibroelastic tissue and completed posteriorly
by the vertical trachealis muscle.
 Diameter of trachea is from 2 to 2.5 cm, being greater in the male than in the
female.
 In children the trachea is smaller, more deeply placed, and more movable than in
the adult.

51. THE TRACHEA- ANAESTHETIC
CONSIDERATIONS
1. Endotracheal tube tip is usually positioned at mid tracheal level.
2. One-third of the trachea lies external to the thorax: the first 3-4 tracheal rings lie
between the cricoid and the sternal notch.
a. These rings are the common location for elective tracheostomies.
b. Urgent percutaneous access to the trachea is more commonly achieved through the
relatively avascular and easily palpable cricothyroid membrane.
c. First ring reference for crico-tracheal membrane that provides passage for needle/guide
for retrograde intubation

52. THREE MAJOR NEURAL PATHWAYS
SUPPLYING SENSATION TO AIRWAY
STRUCTURES

53. THE AIRWAY REFLEXES IMPORTANT
FOR AWAKE INTUBATION
The aforementioned nerves participate in several brainstem-mediated reflex arcs.
1.Gag reflex - triggered by mechanical and chemical stimulation of areas innervated
by the glossopharyngeal nerve, and the efferent motor arc is provided by the vagus
nerve and its branches to the pharynx and larynx.
2.Glottic closure reflex - elicited by selective stimulation of the superior laryngeal
nerve, and efferent arc is the recurrent laryngeal nerve.- exaggeration of this reflex
is called laryngospasm.
3.Cough - the cough receptors located in the larynx and trachea receive afferent and
efferent fibers from the vagus nerve.

54. What is kratschmer reflex ?

55. FRONT OF NECK-SURFACE
ANATOMY IMPORTANT
ANAESTHETIC CONSIDERATIONS
 Hyoid bone
 a. Middle part overlies epiglottis, vallecula and 4th cervical vertebra
 b. Lateral most part (greater cornua) is close to the internal laryngeal branch of
the superior laryngeal nerve and serves as a reference point for superior laryngeal
nerve block.
 c. Reference point to assess airway.
 d. Foreign bodies stuck commonly stuck in vallecula.

56. FRONT OF NECK-SURFACE
ANATOMY IMPORTANT
ANAESTHETIC CONSIDERATIONS Thyroid cartilage
 attached by the thyrohyoid membrane to the hyoid bone above, and articulates
inferiorly with the cricoid cartilage.
 Thyroid notch -the highest point of larynx; it overlies the glottic opening
a. It act as a reference point to assess airway
b. It moves down sharply and appreciably during airway obstruction (Tracheal tug)
c. Vocal cords attached at midline
d. Inferior border is the reference point for cricothyrotomy
e. Reference area for BURP maneuver
f. Piriform fossae lie on either side below the level of thyroid notch. Foreign bodies (e.g.,
fish bones) occasionally become lodged there.

57. FRONT OF NECK-SURFACE
ANATOMY IMPORTANT
ANAESTHETIC CONSIDERATIONS
 The Cricoid cartilage Overlies sub-glottic area and 6th cervical vertebra
a. Reference for the Sellick maneuver
b. Reference for cricothyroidotomy
c. Larynx ends at its lower border
d. Laryngopharynx becomes esophagus at this level
e. Acts as a reference point for upper esophageal sphincter where tip of many supraglottic
devices rests.
f. It is the narrowest point of the airway in the pediatric patient (the glottic opening is
narrowest in the adult patient).

58. FRONT OF NECK-SURFACE
ANATOMY IMPORTANT
ANAESTHETIC CONSIDERATIONS
 The Cricothyroid membrane is an area of critical importance in performing an
emergency surgical airway.
a. Cricothyrotomy
b. Retrograde intubation
c. Overlies sub-glottic area
d. Transtracheal recurrent laryngeal nerve block is given through cricothyroid membrane.

59. FRONT OF NECK-SURFACE
ANATOMY IMPORTANT
ANAESTHETIC CONSIDERATIONS
 Suprasternal Notch
a. Overlies mid-trachea
b. Reference point for airway assessment
c. Cuff of correctly place ETT ballotable here
d. Tapped to elicit correct positioning of supra-glottic devices with drain tube
e. Glow of lighted stylet reaches here when it is withdrawn
f. Indrawn during airway obstruction
 Supraclavicular region
a. Overlies lung apices
b. Indrawn during airway obstruction
c. Neck muscles actively contract during airway obstruction
 Sternal angle (Angle of Louis)
a. Overlies carina

60. THANK YOU