Unit 1: Airway Anatomy

Question 1

What are the two classifications of laryngeal muscles? What is the function of each?

Answer 1

Intrinsic Laryngeal Muscles: control the tension and position of the vocal cords

Extrinsic Laryngeal Muscles: support the larynx inside the neck and assist with swallowing
*all extrinsic muscles (except the digastric) end in “-hyoid”

Question 2

What nerves innervate the intrinsic laryngeal muscles?

Answer 2

Recurrent Laryngeal Nerve – innervates all intrinsic laryngeal muscles except for the cricothyroid muscle

External Branch of Superior Laryngeal Nerve – innervates cricothyroid muscle

Question 3

What is the function of the cricothyroid muscle?

Answer 3

Elongates (tenses) the vocal cords

CricoThyroid : Cords Tense

*innervated by external branch of superior laryngeal nerve

Question 4

What is the function of the vocalis muscle?

Answer 4

Shortens (relaxes) the vocal cords

*innervated by recurrent laryngeal nerve

Question 5

What is the function of the thyroarytenoid muscle?

Answer 5

Shortens (relaxes) the vocal cords
ADDucts vocal cords – closes glottis

ThyroaRytenoid : They Relax

*innervated by recurrent laryngeal nerve

Question 6

What is the function of the lateral cricoarytenoid muscle?

Answer 6

ADDucts vocal cords – closes glottis

Lateral CricoArytenoid : Let’s Close Airway

*innervated by recurrent laryngeal nerve

Question 7

What is the function of the posterior cricoarytenoid muscle?

Answer 7

ABducts vocal cords – opens glottis

Posterior CricoArytenoid : Pull Cords Apart

*innervated by recurrent laryngeal nerve

Question 8

What is the function of the aryepiglottic muscle?

Answer 8

Closes laryngeal vestibule

*innervated by recurrent laryngeal nerve

Question 9

What is the function of the interarytenoid muscle (transverse and oblique)?

Answer 9

Closes posterior commissure of glottis

Question 10

What is the laryngeal muscular innervation mnemonic SCAR?

Answer 10

• *S**uperior Laryngeal Nerve = Cricoarytenoid Muscles
• *A**ll Other Muscles = Recurrent Laryngeal Nerve

Question 11

Where does the trigeminal nerve (CN V) provide sensory innervation? What are the three branches?

Answer 11

Trigeminal Nerve (CN V): sensory innervation to face and head

• V1 (Ophthalmic): nares and anterior ⅓ of nasal septum
• V2 (Maxillary): turbinates and nasal septum
• V3 (Mandibular): anterior ⅔ of tongue (somatic); innervates muscles of mastication

Question 12

Where does the glossopharyngeal (CN IX) provide sensation?

Answer 12

From the oropharynx down to the anterior side of the epiglottis

*afferent limb of gag reflex

Question 13

What nerves does the vagus (CN X) give rise to?

Answer 13

Superior Laryngeal Nerve (this divides into the internal and external branches)

Recurrent Laryngeal Nerve

Question 14

What is the sensory and motor function of the internal and external branches of the superior laryngeal nerve?

Answer 14

• SLN Internal Branch
  
  • Sensory function = Posterior side of epiglottis (level of the vocal cords)
  • Motor function = None
• SLN External Branch
  
  • Sensory function = none
  • Motor function = Cricothyroid Muscle

Question 15

What is the function of the recurrent laryngeal nerve?

Answer 15

Provides sensation below the level of the vocal cords (trachea)

Innervates all intrinsic laryngeal muscles except for the cricothyroid muscle

Question 16

What occurs if the recurrent laryngeal nerve is paralyzed?

Answer 16

It innervates the posterior cricoarytenoid muscle (which pulls the cords apart) and when paralyzed the cord tensing action of the cricothyroid muscle acts unopposed

Question 17

What is the patient clinical presentation for injury to the recurrent laryngeal nerve?

Answer 17

Unilateral RLN Injury → No respiratory distress; Hoarseness

Bilateral RLN Injury (Acute) → Respiratory distress (stridor) due to unopposed action of cricothyroid muscles

Bilateral RLN Injury (Chronic) → No respiratory distress (typically well tolerated)

Question 18

What are the risk factors for a recurrent laryngeal nerve injury on either side?

Answer 18

• Overinflation of ETT/LMA cuff
• Tumor
• Excessive Neck Stretching
• Neck Surgery (i.e. Thyroidectomy) **Most Common**

Question 19

What increase the risk for a left sided recurrent laryngeal nerve injury?

Answer 19

• PDA ligation
• Left atrial enlargement (mitral stenosis)
• Aortic arch aneurysm
• Thoracic tumor

Question 20

What is the clinical presentation for a superior laryngeal nerve injury?

Answer 20

Bilateral injury can cause hoarseness

*Rarely injured, but if it is, it does NOT cause respiratory distress

Question 21

What must you anesthetize for an awake intubation? What local anesthetic is typically used?

Answer 21

Base of the tongue, oropharynx, hypopharynx, and larynx
*anesthetizing the mouth is not required

Benzocaine spray is common
Cocaine can be used (avoid in pt w/ PChE deficiency, on MAOI durgs, or if increase in SNS tone is a problem)

Question 22

What is a key risk of benzocaine spray? How do you treat it?

Answer 22

Risk = Methemoglobinemia

Treatment = Methylene Blue

Question 23

What airway nerve blocks can be used to anesthetize the airway for awake intubation?

Answer 23

Glossopharyngeal Block

Superior Laryngeal Nerve Block

Transtracheal Block (Recurrent Laryngeal Nerve)

**Must block all 3 nerves

Question 24

How do you perform a glossopharyngeal block?

Answer 24

• Insert needle at base of the palatoglossal arch (anterior tonsillar pillar) to a depth of ¼ - ½ cm
  
  • aspiration of air → needle is too deep
  • aspiration of blood → withdraw needle and redirect medially (carotid is close)
• Inject 1-2 mL of local and repeat on other side

*5% incidence of intracarotid injection → seizure risk

Question 25

How do you perform a superior laryngeal nerve block?

Answer 25

* Inject local at the inferior border of the greater cornu of the hyoid bone * 1mL outside the thyrohyoid membrane * 2mL 2-3cm deep to the thyrohyoid membrane * Repeat on other side \*aspiration of air → needle is too deep

Question 26

How do you perform a transtracheal block?

Answer 26

* Insert needle through the cricothyroid membrane (in a caudal direction to reduce risk of VC injury) * After aspiration, but before injection, tell pt to take a deep breath * Inject 3-5mL of local into tracheal lumen during inspiration * Pt will cough, spraying local upward toward the cords

Question 27

What spinal cord level does the adult larynx lie? What are the 3 primary functions?

Answer 27

Anterior to C3-C6 Primary Functions: airway protection, respiration, phonation

Question 28

What are the names of the bumps you see on the aryepiglottic folds during laryngoscopy?

Answer 28

Corniculates and Cuneiforms \*\*NOT the arytenoids

Question 29

What is the narrowest region of the adult and pediatric larynx?

Answer 29

Adult Larynx: Glottic Opening Pediatric Larynx: - Cricoid Ring ("fixed" region) - Vocal Cords ("dynamic" region)

Question 30

What are the components of the larynx?

Answer 30

* Hyoid Bone * Thyrohyoid Ligament (Membrane) * Cricothyroid Ligament (Membrane) * Unpaired Cartilages * Epiglottis * Thyroid * Cricoid (only complete cartilaginous ring in the airway) * Paired Cartilages * Corniculate * Cuneiform * Arytenoid

Question 31

What are the complication of laryngospasm?

Answer 31

* Airway Obstruction * Negative Pressure Pulmonary Edema * Pulmonary Aspiration of Gastric Contents * Cardiac Dysrhythmias * Cardiac Arrest * Death

Question 32

What are the signs of laryngospasm?

Answer 32

* Inspiratory stridor * Lower rib flailing * Increased diaphragmatic excursion * Absent or altered EtCO2 waveform * Suprasternal/Supraclavicular retraction during inspiration * “Rocking Horse” appearance of chest wall (paradoxical movement)

Question 33

What are the common causes of laryngospasm?

Answer 33

* Airway manipulation (practically during light anesthesia) * Airway secretions (saliva or blood) * Surgery in the airway * Active or recent respiratory tract infection (\<2 weeks) * Age \<1 year * GERD * Reactive airway disease * 2nd hand smoke exposure * Hyperventilation/Hypocapnia

Question 34

How do you decrease the risk of laryngospasm?

Answer 34

* Avoid airway manipulation during light anesthesia * CPAP 5-10 during inhalation induction/immediately after extubation * Remove pharyngeal secretions/blood before extubation * Tracheal extubation when deep or fully awake * Laryngeal lidocaine * IV lidocaine before extubation

Question 35

How do you treat a laryngospams?

Answer 35

1. FiO2 100% 2. Remove noxious stimulation 3. Deepen anesthesia 4. Larson's maneuver, Chin lift, CPAPA 15-20 5. Consider SUX -Adult/Child: 0.1-1 mg/kg IV or 4 mg/kg IM -Neonate/Infant: 2 mg/kg IV or 5 mg/kg IM \*give atropine 0.2 mg/kg in children \<5 yo

Question 36

What is a Valsalva's maneuver?

Answer 36

**Exhalation** against a closed glottis or obstruction ## Footnote Example: coughing, bucking, bearing down Risk: increased pressure in thorax, abdomen, and brain

Question 37

What is a Muller's maneuver? What's a risk of this?

Answer 37

**Inhalation** against a closed glottis or obstruction ## Footnote Example: patient bites down on ETT and take a deep breath Risk: subatmospheric pressure in the thorax → negative pressure pulmonary edema

Question 38

What are the primary functions of the upper airway?

Answer 38

Warming and humidifying inspired air Filtering particulate matter Preventing aspiration

Question 39

Relaxation of what muscles cause airway obstruction at: - level of the tongue - level of soft palate

Answer 39

Genioglossus Muscle Relaxation = obstruction at level of the tongue \*\*Most common Tensor Palatine Muscle Relaxation = obstruction at level of the soft palate

Question 40

What conditions impact airway patency?

Answer 40

Conditions that decrease Pharynx Diameter - reduced pharyngeal dilator muscle tone - negative pressure during inspiration Conditions that decrease size of Head/Neck - increased soft tissue inside the “box” → obesity, large tongue, tonsil/adenoid hypertrophy - decreased size of the “box” → small craniofacial structures, craniofacial deformity

Question 41

What are the 3 sets of dilator muscles that hold open the upper airway during the awake state?

Answer 41

Tensor Palatine (opens nasopharynx) Genioglossus (opens oropharynx) Hyoid Muscles (opens hypopharynx)

Question 42

Describe the anatomy of the trachea What nerve provides sensory innervation? Where does the blood supply come from?

Answer 42

* Begins at C6 and Ends at T4-5 at carina * 2.5cm wide and 10-13cm long * Semi-circular rings open posteriorly * Ciliated columnar epithelium * Sensory Innervation = Vagus nerve * Blood Supply = inferior thyroid artery, superior thyroid artery, bronchial artery, internal thoracic artery

Question 43

Describe the anatomy and characteristics of the carina

Answer 43

T4-5 Corresponds w/ Angle of Louis Ciliated Columnar Epithelium

Question 44

Describe the anatomy and characteristics of the mainstem bronchi

Answer 44

**Right:** - 2.5cm long - 25* take off - explains greater likelihood of right mainstem intubation **Left:** - 5 cm long - 45* take off - Cuboidal epithelium **children up to 3yo → both bronchi take off 55* from long axis of trachea

Question 45

Describe the anatomy and characteristics of the alveoli

Answer 45

* Humans have 300 million by age 9 * Squamous epithelium * **Pores of Kohn** allow air movement between alveoli

Question 46

What are the functions of the different types of Pneumocytes?

Answer 46

**Type I:** provide surface for gas exchange - flat squamous cells - cover ~80% of alveolar surface - form tight junctions **Type II:** produce surfactant - resistant to oxygen toxicity - capable of cell division - can produce type I cells **Type III:** are macrophages - fight lung infection - produce inflammatory response **Neutrophils are present in the alveoli in smokers and patients w/ acute lung injury

Question 47

What increases as the airway bifurcates? What decreases?

Answer 47

**Increases:** number of airways, cross-sectional area, and muscular layer **Decreases:** airflow velocity, amount of cartilage, goblet cells (produce mucus), and ciliated cells (clears mucus)