Airway anatomy refresher

Question 1

Function and innervation of nasal passages?

Answer 1

Includes:

• Septum
• Turbinates
• Adenoids

Function:

• Accounts for 2/3 of total upper airway resistance
• Humidify
• Filter
• Warm

Innervation:

• Branches of the trigeminal nerve (CN V)

Question 2

innervation of oral cavity?

Answer 2

Includes:

• Teeth
• Tongue
• Predominate cause of airway resistance in oral cavity
• Hard palate
• Soft palate

Innervation:

• Trigeminal Nerve (CN V)
  
  • Hard and Soft palate
  • Anterior 2/3 tongue
• Glossopharyngeal (CN IX)
  
  • Posterior 1/3 tongue
  • Soft palate
  • Oropharynx

Question 3

What are the divisions of the pharynx?

Innervation of the pharynx/

Answer 3

Connects the nasal and oral cavities to larynx and esophagus

Divided into:

• Nasopharynx
  
  • Border is the soft palate
• Oropharynx
  
  • Border is the epiglottis
  • Tonsils, Uvula
• Hypopharynx/
• Laryngopharynx

Innervation:

• Glossopharyngeal (CN IX)
• Vagus (CN X)

Question 4

Where is larynx located?

Answer 4

• C4-C6 in adult
• Functions
  
  • airway protection
  • respiration
  • phonation

Question 5

Describe the laryngeal cartilages.

Answer 5

9 Cartilages

3 Paired

• Arytenoid
  
  • Posterior attachment for Vocal Cords
  • Falsely identified in an anterior airway
• Corniculate
  
  • Posterior portion of the aryepiglottic fold
• Cuneiform
  
  • In the aryepiglottic fold, not always present
  • Lateral to corniculates

3 Unpaired

• Thyroid
  
  • Large and most prominent
  • Anterior attachment for vocal cords
• Cricoid
  
  • Only complete cartilaginous, signet-shaped, ring
  • Narrowest portion of the pediatric airway
• Epiglottis
  
  • Covers opening to the larynx during swallowing

Question 6

Describe the vocal cords and glottic opening

Answer 6

Vocal Cords

• Appear pearly white
• Formed by the thyroarytenoid ligaments
• Attached anteriorly to the thyroid cartilage and posteriorly to the arytenoid cartilages

Glottic Opening

• Triangular fissure between the cords
• Narrowest portion of the adult airway

Question 7

What are the laryngeal muscles and their function in glottic opening?

Answer 7

• Lateral Cricoarytenoid
  
  • Adducts the vocal cords
• Arytenoid Muscles
  
  • Oblique arytenoids and transverse arytenoids
  • Adduct the vocal cords
• Posterior Cricoarytenoid
  
  • The only vocal cord abductors
• Cricothyroid
  
  • Tenses/Elongates vocal cords
• Thyroarytenoid
  
  • Relaxes/shortens vocal cords
• Vocalis
  
  • Relaxes/shortens vocal cords

Question 8

Describe the innervation to the laryngeal muscles.

Answer 8

• Cricothyroid muscle innervated by the external branch of the superior laryngeal nerve a branch of the Vagus nerve (CN X)
• All others innervated by the recurrent laryngeal nerve a branch of the Vagus nerve (CN X)

Question 9

Describe the trachea.

Answer 9

• Fibromuscular tube
• 10-20 cm length & 22 mm diameter (Adult)
• 16-20 U shaped cartilages
• Posterior side lacks cartilage
• Bifurcates lower border T4- carina
• Carina
  
  • Trachea divides into Right & Left mainstem bronchi
  • Right bronchi is 2.5 cm long with angle of 250
  • Left bronchi is 5 cm with an angle 450

Question 10

What is the cormack and lehane score?

Answer 10

• Cormack and Lehane score is the laryngoscopic view of the glottis
• Mallampati class is correlated to what can be seen on direct laryngoscopy (Cormack and Lehane score)
• Cormack and Lehane Score
• Grade I: most of the glottis visible
• Grade II: Only the posterior portion of glottis visible
• Grade III: Only epiglottis visible
• Grade IV: No airway structures visualized

Question 11

Normal Thyromental distance?

Answer 11

• Distance from lower border of mandible to thyroid notch with neck fully extended
• Normal 6-6.5 cm or 4 Fingerbreadths
• Difficult intubation < 3 fingers, receding mandible; “anterior airway”

Question 12

What is adequate pre-oxygenation?

Answer 12

• Goal = Increase O2 concentration in functional residual capacity (FRC) by “washing out” nitrogen (79% in RA) in the FRC with oxygen
  
  • FRC= volume of air left in the lung at end of passive expiration
• 3-5 minutes of “tight” mask fit during normal tidal breathing with100% FiO2 at> 6L/min flow = 10 minutes of safe apnea time
• 4 vital capacity breaths within 30 seconds with 100% FiO2 at >6L/min= 5 minutes of safe apnea time
  
  • 8 breaths over 60 seconds will > effectiveness over 4br/ 30sec
• An end-tidal concentration of oxygen greater than 90% is considered to maximize apnea time.