Airway Anatomy & Innervation Flashcards
Laryngeal Muscles
INTRINSIC
Move vocal cords & phonation
- Cricothyroid
- Vocalis
- Thyroarytenoid
- Lateral cricoarytenoid
- Posterior cricoarytenoid
- Aryepiglottic
- Interarytenoid
What muscle shortens or relaxes the vocal cords?
Vocalis
ThyroaRytenoid = They Relax
What muscle elongates or tenses the vocal cord?
CricoThyroid = Cords Tense (SLN external innervation)
What muscle ABducts or opens the vocal cords?
Widens the glottis
Posterior CricoArytenoid = Please Come Apart
What muscle ADducts or closes the vocal cords?
Narrows the glottis
- Lateral CricoArytenoid = Let’s Close the airway
- Thyroarytenoid
What nerve innervates the cricothyroid?
Superior laryngeal nerve SEM
External branch
What sphincter closes the laryngeal vestibule?
Aryepiglottic
What sphincter closes the glottis posterior commisure?
Interarytenoid
Laryngeal Muscles
EXTRINSIC
Support the larynx & assist w/ swallowing
- Thyrohyoid
- Omohyoid
- Sternohyoid
- Digastric*
- Mylohyoid
- Stylohyoid
What muscles elevate the larynx?
Extrinsic laryngeal muscles
- Digastric (anterior & posterior)
- Mylohyoid
- Stylohyoid
- Thyrohyoid
- Omohyoid
- Sternohyoid
What muscles depress the larynx?
Extrinsic laryngeal muscles
- Thyrohyoid
- Omohyoid
- Sternohyoid
Trigeminal Nerve
Cranial nerve V
Provides sensory information to the face & head
1. Opthalmic - anterior ethmoidal nerve
2. Maxillary - sphenopalatine nerve
3. Mandibular - lingual nerve
V1
Opthalmic SENSORY
Nares & anterior 1/3 nasal septum
V2
Maxillary SENSORY
Turbinates & nasal septum
V3
Mandibular
Anterior 2/3 tongue (somatic)
Motor = mastication
Glossopharyngeal Nerve
Cranial nerve IX
Provides sensation from the oropharynx down to the anterior epiglottis - soft palate, oropharynx, tonsils, posterior 1/3 tongue, vallecula, anterior epiglottis
Gag reflex = afferent limb
Motor = swallowing & phonation
Vagus Nerve
Cranial nerve X
SLN & RLN
Innervates the larynx
SIS - internal branch
SEM - external branch
Superior Laryngeal Nerve
Internal Branch
Sensory SIS
Innervates the posterior side of the epiglottis to the vocal cords level (true vocal cords are ligaments - not innervated)
Superior Laryngeal Nerve
External Branch
Motor SEM
Innervates the CricoThyroid muscle
Cords tense
SLN Injury
RARE
Does not cause respiratory distress
Acute bilateral injury = hoarseness
- Vocal quality affected
Recurrent Laryngeal Nerve
Branches off the Vagus nerve inside the thorax
Sensory innervation below the vocal cords to the trachea
Motor innervation to ALL intrinsic laryngeal muscles except the cricothyroid
Unilateral RLN Injury
No respiratory distress
Most common nerve injury following subtotal thyroidectomy
Bilateral RLN Injury
Acute presentation w/ stridor & respiratory distress (unopposed cricothyroid muscles tensing)
- Similar presentation to laryngospasm
- EMERGENCY
- Treatment = emergent intubation or surgical airway
Chronic - no respiratory distress & typically well-tolerated
RLN Injury
Risk Factors
Overinflation ETT cuff or LMA, excessive neck stretching, neck tumor, neck surgery thyroid or parathyroid
Most common = thyroidectomy
Left side (RLN loops under the aortic arch):
PDA ligation, L atrial enlargement (mitral stenosis), aortic arch aneurysm, & thoracic tumor
What areas need to be anesthetized to facilitate an awake intubation?
Tongue base
Oropharynx
Hypopharynx
Larynx
- Upper airway & vocal cords
Airway Blocks
- Glossopharyngeal IX
- Superior laryngeal
- Transtracheal or recurrent laryngeal
Glossopharyngeal Block
How to Perform
- Insert the needle at the anterior tonsillar pillar (base of the palatoglossal arch) & aspirate
- Confirm aspiration negative for air & blood
- Depth 0.25-0.5 cm inject 1-2 mL LA
- Repeat on the contralateral side
What indicates a successful glossopharyngeal block?
Soft palate, oropharynx, tonsil, posterior 1/3 tongue, & vallecula are anesthetized
Glossopharyngeal nerve →
afferent gag reflex
What risks are associated w/ the glossopharyngeal block?
5% siezure risk d/t intracarotid injection
Superior Laryngeal Block
How to Perform
- Inject LA at the inferior border of the greater cornu of the hyoid bone
- Outside thyrohyoid membrane 1 mL + 2-3 mm deep to the thyrohyoid membrane 2 mL
- Repeat on the contralateral side
What does air aspiration indicate when performing a superior laryngeal block?
Needle too deep
Transtracheal Block
How to Perform
Recurrent laryngeal nerve block
1. Insert the needle through the cricothyroid membrane in the caudal direction
2. Aspirate
3. Ask patient to take deep breath before injection (cough will spray the LA upwards through the cords)
4. Inject 3-5 mL LA into the tracheal lumen
Adult Larynx
Provides airway protection, respiration, & phonation
Anterior to C3-6
What components make-up the larynx?
Hyoid bone
Thyrohyoid & cricothyroid ligaments
Unpaired cartilages = epiglottis, thyroid, & cricoid
Paired cartilages = arytenoid, corniculate, & cuneiform
Narrowest region in the adult airway:
Glottic opening
Pediatric Larynx
< 5 years old = funnel shaped
Narrowest regions:
- FIXED cricoid ring
- Dynamic vocal cords
What is laryngospasm?
Sustained & involuntary laryngeal muscle contraction → inability to ventilate
Laryngospasm Reflex Pathway
Afferent = SLN internal branch
Efferent = SLN external branch SEM
- Cricothyroid elongates & tenses the vocal cords
Laryngospasm Causes
Airway manipulation during light anesthesia
Airway secretions
Surgery in the airway
Hyperventilation/hypocapnia
Surgical procedures in the airway
Active or recent respiratory tract infection < 2 weeks
Exposure to 2nd hand smoke
Reactive airway disease
GERD
Age < 1 year old
Laryngospasm Prevention
Avoid airway manipulation during light anesthesia
CPAP 5-10 cmH2O during inhalational induction & immediately after extubation
Remove pharyngeal secretions & blood before extubation
Tracheal extubation when deeply anesthetized or fully awake
Laryngeal lidocaine DOA ≈ 30 minutes
Lidocaine IV before extubation
Laryngospasm S/S
Inspiratory stidor
Suprasternal & supraclavicular retractions during inspiration
Paradoxical chest wall movement
Increased diaphragmatic excursion
Lower rib flailing
Absent or altered ETCO2 waveform
Laryngospasm Treatment
- 100% FiO2
- Remove noxious stimuli
- Deepen anesthesia
- Larson maneuver, chin lift, and/or CPAP
- Succinylcholine
Succinylcholine
Laryngospasm Dose
Adult & child
0.1-1 mg/kg IV
*Lower dose tends to preserve ventilation
IM 4 mg/kg
Children < 5 yo co-admin Atropine 0.02 mg/kg to prevent bradycardia
Succinylcholine
Neonate & Infant Laryngospasm Dose
2 mg/kg IV
IM 5 mg/kg
Laryngospasm Complications
Airway obstruction
NPPE
Pulmonary aspiration of gastric contents
Cardiac dysrhythmias
Cardiac arrest & death
Valsalva Maneuver
Exhalation against a closed glottis or obstruction
Ex: Coughing, bucking, or bearing down
↑pressure in the thorax, abdomen, & brain
Muller Maneuver
Inhalation against a closed glottis
Ex: Patient bites down on ETT & takes a deep breath
Sub-atmospheric pressure in the thorax → negative pressure pulmonary edema
Upper Airway
Mouth & nares to the cricoid cartilage
1° functions to warm & humidify inspired air, filter particulate matter, & prevent aspiration
Upper Airway Obstruction
Awake patient - upper airway held open by dilator muscles that counteract the tendency for the airway to collapse when patient breathes (negative pressure gradient)
Anesthetic agents reduce pharyngeal dilator muscle tone
1. Soft palate
2. Tongue
3. Epiglottis
Soft Palate Airway Obstruction
Tensor palatine muscle opens the nasopharynx
Relaxation → obstruction
Tongue Airway Obstruction
Genioglossus muscle opens the oropharynx
Relaxation → obstruction
MOST COMMON
Epiglottis Airway Obstruction
Hyoid muscles open the hypopharynx
Relaxation → obstruction
What other factors contribute to upper airway obstruction?
Obesity, tongue size, tonsil & adenoid hypertrophy, & craniofacial deformities
↑soft tissue (neck) inside the box (head)
Small craniofacial structure or craniofacial deformity ↓box size
Airway Resistance
Oral vs. Nasal
Nasal passage airway resistance 2x as compared to through the mouth
Nasal Turbinates
3 on each side project from the lateral wall
Highly vascular structures
- Superior
- Middle
- Inferior
↑airway resistance through nasal passage
How to prevent nasal trauma during airway instrumentation (nasal ETT or NPA)?
Insert nasal ETT or NPA at 90° angle
Direct b/w inferior turbinate & nasal cavity floor
Orient bevel towards the turbinates - ensures leading edge travels along the septum to decrease injury to highly vascular turbinates risk
What adaptors are utilized w/ intubated patients to perform upper airway functions?
Heat & moisture exchanger HME warms & humidifies inspired air
EFF cuff protects against aspiration
Lower Airway
Begins at the trachea & ends at the alveoli
Incisors → carina ≈ 23 cm
Bifurcations x23 generations ↑airways, total cross-sectional area
↓airflow velocity, cartilage, goblet cells, and ciliated cells
Goblet Cells
Produce mucus
Ciliated Cells
Clear mucus
Trachea
Begins at inferior cricoid cartilage border C6
Ends at the carina T4-5
2.5 cm wide
10-13 cm long
16-20 semi-circular cartilaginous rings open posteriorly
Ciliated columnar epithelium
Sensory innervation = Vagus
Carina
T4-5 (Angle of Louis)
Bifurcates into the L & R mainstem bronchi
Ciliated columnar epithelium
Mainstem Bronchi
L bronchus 5 cm 45°
R bronchus 2.5 cm 25°
– Mainstem more common
Cuboidal epithelium
Pediatric Bronchi
Children up to 3 yo bronchi take off at 55° angle
Alveoli
Squamous epithelium
Pneumocytes 1, 2, & 3
Neutrophils are present in smokers & patients w/ acute lung injury
300 million alveoli by 9 yo
Type 1 Pneumocytes
Provide gas exchange surface
Flat squamous cells
Cover 80% alveolar surface
Form tight junctions
Type 2 Pneumocytes
Produce surfactant & type 1 pneumocytes
Resistant to oxygen toxicity
Able to perform cellular division
Type 3 Pneumocytes
Macrophages
Fight lung infection
Produce an inflammatory response
What increases as the airway birfurcates?
Number airways
Total cross-sectional area
What decreases as the airway bifurcates?
↓airflow velocity
↓cartilage amount
↓goblet cells
↓ciliated cells
How many bifurcations are present?
23 generations
Trachea 0
Bronchi 1-3
Bronchioles 4
Respiratory bronchioles 17
Alveolar ducts 20
Alveolar sac 23
What allows air movement b/w alveoli?
Pores of Kohn
