10/26/2014

1

Anatomy of the Airway

Nagelhout, 5th edition, Chapter 26

Morgan & Mikhail, 5th edition, Chapter 23

Mary Karlet, CRNA, PhD

Airway Anatomy

The airway consists of the nose, pharynx, larynx, trachea, and lower airways

I. Nose - heat, humidification, filtration

� Except with extreme cold, nose warms inspired air to body temperature

� Nearly 100% humidification

Airway Anatomy

II. Pharynx – wide muscular tube that is a part of both the respiratory tract and the alimentary tract

� Upper border is base of skull; lower border cricoid cartilage (C-6) where it continues with esophagus

1. Nasopharynx: nasal passage → soft palate

2. Oropharynx: soft palate → epiglottis

3. Laryngopharynx (hypopharynx): epiglottis →level of C-6 (beginning of esophagus)

10/26/2014

2

Nasopharynx: opens anteriorly to

nasal cavity

Oropharynx: opens anteriorly to

mouth

Laryngopharynx: opens anteriorly

to larynx

Palatine, Lingual, and Adenoid Tonsils

Palatine tonsils

Airway Anatomy

III. Larynx:� Extends C-3 to C-6

vertebrae

� Consists of:

� One bone (hyoid)

� 9 cartilages

� Muscles, Ligaments,

Membranes

� Hyoid bone chief support for larynx via thyrohyoid

membrane

� Thyroid and cricoid

cartilages major framework

� Protective structure

that prevents aspiration during

swallowing

� Site of vocalization

10/26/2014

3

Airway Anatomy – 9 Laryngeal

Cartilages

Unpaired Cartilages

Epiglottis: separates oropharynx from hypopharynx; covers entrance to larynx

Thyroid: vc attaches to anterior thyroid cartilage

Cricoid (C-6): ring of cartilage immediately below thyroid cartilage; marks the beginning of trachea; below the vocal cords; narrowest in age < 10

Larynx

� Vocal cords attached anteriorly to thyroid cartilage and posteriorly to arytenoids

� Includes glottis = space between vocal cords

In adults, glottis smallest airway circumference

In child < age 10, cricoid cartilage smallest

circumference

Airway Anatomy – 9 Laryngeal

Cartilages

Paired Cartilages

Arytenoid (2): attached to posterior ends of vc

Corniculate (2) embedded in aryepiglottic

Cuneiform (2) folds

10/26/2014

4

Membranes of the Larynx

� Thyrohyoid membrane –suspends the larynx from the hyoid bone

� Cricothyroid membrane –recommended site for emergency establishment of airway; also site of “transtracheal block”

Muscles of the Larynx

Intrinsic Muscles (9)

1. Post. Cricoarytenoid (2):

Abducts (opens) glottis

2. Lat. Cricoarytenoid (2)

Adducts (closes) glottis

3. Transverse or Inter-arytenoids

between arytenoids – helps close glottis

4. Cricothyroids (2)

Regulates tension, elongates and tightens cords

5. Thyroarytenoids (2)

Regulates tension, shortens and loosens the cords

Extrinsic Muscles (3)

1. SternohyoidDepresses larynx

2. ThyrohyoidElevates larynx

3. Inferior constrictorConstricts pharynx

10/26/2014

5

Innervation to the Upper Airway

1. Trigeminal n. Sensory innervation to the nasal mucosa, anterior ⅔’s of tongue, hard and soft palate

2. Glossopharyngeal n. Sensory innervation to the oropharynx, undersurface of soft palate, and posterior ⅓ of tongue, tongue side of epiglottis, tonsils,and vallecula

Innervation to the Upper Airway

3. Vagus n. – innervates distal airways, epiglottis and below

� Superior laryngeal n. - sensory to laryngeal side of epiglottis → vocal cords, arytenoid cartilages, mucus membranes immediately above larynx; motor to cricothyroid m.

� Recurrent (inferior) laryngeal n. -sensory to mucus membranes below vc; motor to all laryngeal muscles except cricothyroid m.

Sensory Innervation of the Upper

Airway

V2 = maxillary division of Trigeminal nerve (sphenopalatine nerve)V3 = mandibular division of Trigeminal nerve (lingual nerve)

10/26/2014

6

Effect of laryngeal nerve injury

Superior laryngeal n.

a) unilateral

b) bilateral

a) minimal effects

b) hoarseness; tiring of voice

Recurrent laryngeal n.

a) unilateral

b) bilateral – acute

c) bilateral - chronic

a) hoarseness

b) stridor or aphonia, respiratory distress

c) compensatory mechanisms often prevent resp. distress

Tracheobronchial

Tree

� Major function to conduct air → alveoli

� Lined by ciliated columnar epithelium

� 23 generations or divisions� ↑ cross-sectional area

� ↓ diameter

Trachea

� Extends from inferior larynx to carina; C6 → T5

� Distance from incisors to larynx = 13 cm; distance from larynx to carina = 13 cm ∴ distance from incisors to carina = 26 cm

� Diameter approximated by diameter of index finger

� Horseshoe-shaped cartilage and fibrous muscle tissue

� At T5 (carina) divides into two primary bronchi

10/26/2014

7

Trachea

� The trachea is not “fixed” – it moves with head and neck movement

� Neck flexion → trachea moves upward →ETT moves downward → endobronchial intubation possible

� Neck extension → trachea moves downward and ETT moves upward →extubation possible

� Trachea moves upward if patient turns head right or left

Tracheobronchial

Tree

� The bronchi (generation #1)� Right mainstem bronchus:

� Shorter (2.5 cm), wider, and more vertical (25° angle)

� Left mainstem bronchus:� Longer (5 cm) and more horizontal (45° angle)

� Cartilagenous rings down to bronchioles →maintain rigidity

� With decreased cartilage → ↑ sm.m.� Wall of bronchioles almost entirely sm.m. down to “respiratory zone”

� Terminal bronchioles last structures perfused by bronchial circulation and the end of conducting airways