Unit 1: Airway Anatomy Flashcards
What are the two classifications of laryngeal muscles? What is the function of each?
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”
What nerves innervate the intrinsic laryngeal muscles?
Recurrent Laryngeal Nerve – innervates all intrinsic laryngeal muscles except for the cricothyroid muscle
External Branch of Superior Laryngeal Nerve – innervates cricothyroid muscle
What is the function of the cricothyroid muscle?
Elongates (tenses) the vocal cords
CricoThyroid : Cords Tense
*innervated by external branch of superior laryngeal nerve
What is the function of the vocalis muscle?
Shortens (relaxes) the vocal cords
*innervated by recurrent laryngeal nerve
What is the function of the thyroarytenoid muscle?
Shortens (relaxes) the vocal cords
ADDucts vocal cords – closes glottis
ThyroaRytenoid : They Relax
*innervated by recurrent laryngeal nerve
What is the function of the lateral cricoarytenoid muscle?
ADDucts vocal cords – closes glottis
Lateral CricoArytenoid : Let’s Close Airway
*innervated by recurrent laryngeal nerve
What is the function of the posterior cricoarytenoid muscle?
ABducts vocal cords – opens glottis
Posterior CricoArytenoid : Pull Cords Apart
*innervated by recurrent laryngeal nerve
What is the function of the aryepiglottic muscle?
Closes laryngeal vestibule
*innervated by recurrent laryngeal nerve
What is the function of the interarytenoid muscle (transverse and oblique)?
Closes posterior commissure of glottis
What is the laryngeal muscular innervation mnemonic SCAR?
- *S**uperior Laryngeal Nerve = Cricoarytenoid Muscles
- *A**ll Other Muscles = Recurrent Laryngeal Nerve
Where does the trigeminal nerve (CN V) provide sensory innervation? What are the three branches?
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
Where does the glossopharyngeal (CN IX) provide sensation?
From the oropharynx down to the anterior side of the epiglottis
*afferent limb of gag reflex
What nerves does the vagus (CN X) give rise to?
Superior Laryngeal Nerve (this divides into the internal and external branches)
Recurrent Laryngeal Nerve
What is the sensory and motor function of the internal and external branches of the superior laryngeal nerve?
- 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
What is the function of the recurrent laryngeal nerve?
Provides sensation below the level of the vocal cords (trachea)
Innervates all intrinsic laryngeal muscles except for the cricothyroid muscle
What occurs if the recurrent laryngeal nerve is paralyzed?
It innervates the posterior cricoarytenoid muscle (which pulls the cords apart) and when paralyzed the cord tensing action of the cricothyroid muscle acts unopposed
What is the patient clinical presentation for injury to the recurrent laryngeal nerve?
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)
What are the risk factors for a recurrent laryngeal nerve injury on either side?
- Overinflation of ETT/LMA cuff
- Tumor
- Excessive Neck Stretching
- Neck Surgery (i.e. Thyroidectomy) **Most Common**
What increase the risk for a left sided recurrent laryngeal nerve injury?
- PDA ligation
- Left atrial enlargement (mitral stenosis)
- Aortic arch aneurysm
- Thoracic tumor
What is the clinical presentation for a superior laryngeal nerve injury?
Bilateral injury can cause hoarseness
*Rarely injured, but if it is, it does NOT cause respiratory distress
What must you anesthetize for an awake intubation? What local anesthetic is typically used?
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)
What is a key risk of benzocaine spray? How do you treat it?
Risk = Methemoglobinemia
Treatment = Methylene Blue
What airway nerve blocks can be used to anesthetize the airway for awake intubation?
Glossopharyngeal Block
Superior Laryngeal Nerve Block
Transtracheal Block (Recurrent Laryngeal Nerve)
**Must block all 3 nerves
How do you perform a glossopharyngeal block?
- 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
How do you perform a superior laryngeal nerve block?
- 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
How do you perform a transtracheal block?
- 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
What spinal cord level does the adult larynx lie? What are the 3 primary functions?
Anterior to C3-C6
Primary Functions: airway protection, respiration, phonation
What are the names of the bumps you see on the aryepiglottic folds during laryngoscopy?
Corniculates and Cuneiforms
**NOT the arytenoids
What is the narrowest region of the adult and pediatric larynx?
Adult Larynx: Glottic Opening
Pediatric Larynx:
- Cricoid Ring (“fixed” region)
- Vocal Cords (“dynamic” region)
What are the components of the larynx?
- 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
What are the complication of laryngospasm?
- Airway Obstruction
- Negative Pressure Pulmonary Edema
- Pulmonary Aspiration of Gastric Contents
- Cardiac Dysrhythmias
- Cardiac Arrest
- Death
What are the signs of laryngospasm?
- 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)
What are the common causes of laryngospasm?
- 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
How do you decrease the risk of laryngospasm?
- 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
How do you treat a laryngospams?
- FiO2 100%
- Remove noxious stimulation
- Deepen anesthesia
- Larson’s maneuver, Chin lift, CPAPA 15-20
- 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
What is a Valsalva’s maneuver?
Exhalation against a closed glottis or obstruction
Example: coughing, bucking, bearing down
Risk: increased pressure in thorax, abdomen, and brain
What is a Muller’s maneuver? What’s a risk of this?
Inhalation against a closed glottis or obstruction
Example: patient bites down on ETT and take a deep breath
Risk: subatmospheric pressure in the thorax → negative pressure pulmonary edema
What are the primary functions of the upper airway?
Warming and humidifying inspired air
Filtering particulate matter
Preventing aspiration
Relaxation of what muscles cause airway obstruction at:
- level of the tongue
- level of soft palate
Genioglossus Muscle Relaxation = obstruction at level of the tongue **Most common
Tensor Palatine Muscle Relaxation = obstruction at level of the soft palate
What conditions impact airway patency?
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
What are the 3 sets of dilator muscles that hold open the upper airway during the awake state?
Tensor Palatine (opens nasopharynx)
Genioglossus (opens oropharynx)
Hyoid Muscles (opens hypopharynx)
Describe the anatomy of the trachea
What nerve provides sensory innervation?
Where does the blood supply come from?
- 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
Describe the anatomy and characteristics of the carina
T4-5
Corresponds w/ Angle of Louis
Ciliated Columnar Epithelium
Describe the anatomy and characteristics of the mainstem bronchi
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
Describe the anatomy and characteristics of the alveoli
- Humans have 300 million by age 9
- Squamous epithelium
- Pores of Kohn allow air movement between alveoli
What are the functions of the different types of Pneumocytes?
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
What increases as the airway bifurcates? What decreases?
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)
