Session 10 Flashcards
What are the functions of the larynx?
- Airway protection
- Ventilation
- Key role in cough reflex (rapidly expels anything inadvertently entering airway)
- Role in production of sound
Outline the location of the larynx in the body
- Suspended from hyoid bone
- Lies below hyoid bone
- Begins at laryngeal inlet
- Ends at lower border of cricoid cartilage (C6)
- Continues as trachea
- Sits in front of pharynx
Which system is the larynx a part of?
- Upper respiratory system
- Transmits air in and out of lower respiratory tract
DO NOT CONFUSE WITH PHARYNX (part of GI system)
What facilitates communication between the larynx, oropharynx and laryngopharynx?
- Laryngeal inlet
What is a piriform fossa?
- Recesses
- Part of laryngopharynx
- Formed because pharynx hugs around the back of the larynx
Outline the framework of the larynx
- Consists of series of cartilages and connective tissue membranes
- Epiglottis (leaf-like cartilage)
- Arytenoid cartilages - pyramid-shaped, sit on top of cricoid cartilage, swivel to allow action of vocal cords
- Cricoid cartilage (only complete ring-shaped cartilage)
- Thyroid cartilage
Where are connective tissue membranes found in the pharynx?
- Quadrangular sheet between arytenoid cartilage and epiglottis
- Sheet of connective tissue between hyoid bone and thyroid cartilage
What is the relationship between the epiglottis and the thyroid cartilage?
- Epiglottis connected by its stalk to inner surface of thyroid cartilage
What joints are found in the larynx?
- Synovial joints
- Thyroid-cricoid
- Cricoid-arytenoid
- Allows opening and closing of parts of larynx
What suspends the larynx from the hyoid bone?
- Thyrohyoid membrane
- Whenever hyoid bone moves, larynx also moves
Which cartilages and membranes of the pharynx are palpable?
- Hyoid bone
- Laryngeal prominence
- Cricothyroid membrane
- Cricoid cartilage
- 1st tracheal ring
- Isthmus and lobes of thyroid gland
What is a cricothyroidotomy?
- Provides emergency access to airway beneath vocal cords
- Done when patient cannot be intubated or ventilated
- Temporary device inserted into airway via cricothyroid membrane
What makes up the laryngeal inlet?
- Aryepiglottic folds x2 (upper free edges of quadrangular membrane)
- Upper edge of epiglottis
- Form oval-shaped opening of larynx
What creates the aryepiglottic fold?
- Free upper border of quadrangular membrane
What creates the false vocal cord?
- Free lower border of quadrangular membrane = vestibular ligament
What creates the true vocal cord?
- Free upper border of cricothyroid membrane = vocal ligament
- Inserts into internal surface of thyroid
What lines the larynx?
- Mucous membrane
- Internal anatomy is shaped by folds formed by various ligaments/membranes
What are the 3 regions of the larynx?
- Supraglottis - epiglottis up to and including false cords
- Glottis - narrowest part and includes true vocal cords until about 1 cm below
- Infraglottis - below true vocal cords to inferior boundary of cricoid
What type of epithelium lines the larynx?
- Pseudostratified ciliated columnar epithelium
- Except true vocal cords, which are lined with stratified squamous epithelium (protects against abrasive forces of air)
What is flexible nasoendoscopy?
- Insert flexible endoscope via nasal cavity and pharynx to then visualise larynx
What should be seen on a laryngoscopic view?
- Need to see vocal cord to ensure tube does not go through pharynx and oesophagus
- Tip of laryngoscope is inserted in vallecula (space between back of tongue and epiglottis)
What are the 2 main actions of the intrinsic laryngeal muscles?
- Alter size and shape of laryngeal inlet:
- muscles within aryepiglottic folds can contract
- narrow laryngeal inlet
- flatten position of epiglottis
- protects larynx during swallowing - Alter tension in and position of true vocal cords
- muscles within larynx alter position of arytenoid cartilages
- vary position of vocal cords
- adduction of vocal cords protects larynx during swallowing
- enables phonation
What nerve supplies the intrinsic laryngeal muscles?
- Recurrent laryngeal nerve of vagus nerve
- Except for cricothyroid muscle
When do we need to alter the size and shape of laryngeal inlet?
- Direct food away from laryngeal inlet and into piriform fossae
- When swallowing
- Epiglottis is flattened
Where are the vocal cords located?
- Run from arytenoid cartilages to inner surface of thyroid cartilage at level of laryngeal prominence
How is the position of the arytenoid cartilages altered?
- Arytenoid cartilages move to alter position of vocal cords
- Widens and narrows rima glottidis
- Majority of muscles narrow rima glottidis by adducting vocal cords together
- Only one muscle abducts vocal cords to widen rima glottidis
What is the position of the vocal cords when breathing?
- Abducted
- Laryngeal inlet open
What is the position of the vocal cords when swallowing?
- Adducted
- Laryngeal inlet also narrowed by muscles in aryepiglottic folds
What is the position of the vocal cords during phonation?
- Closely adducted but with a slight gap between them
- Expired air forced through closely adducted vocal cords
- Vibration of vocal cords creates sound waves
What is the position of the vocal cords during a cough?
- Vocal cords adduct and create a tight seal so no air escapes
- Pressure builds until vocal cords snap open
- Air is expelled
How do the vocal cords change pitch?
- High-pitched sounds = vocal cords taut
- Low-pitched sounds = vocal cords less taut
- Contraction of both cricothyroid muscles increases tension in vocal cords
- Muscle located outside of larynx
What is the action of the cricothyroid muscle?
- Tilts thyroid cartilage forward on cricoid
- Increases tension in vocal cords
- Allows higher pitches to be reached
Which nerve innervates the cricothyroid muscles?
- External branch of superior laryngeal nerve (branch of CN X)
- Closely related to superior thyroid artery
- Risk of injury in thyroid surgery
- Causes hoarseness of voice when attempting higher pitched sounds
What happens to the epiglottis during swallowing?
- Tongue pushes epiglottis posteriorly
- Aryepiglottic muscles contract
- Laryngeal inlet narrows
- Epiglottis positioned horizontally
Where is food directed towards on swallowing?
- Directed over curved upper surface of epiglottis into piriform fossae of laryngopharynx
What happens to the hyoid bone during swallowing?
- Hyoid bone elevated and moved anteriorly
- By suprahyoid muscles
- Larynx moves and forward (away from pharynx, makes it more open for receiving food)
What happens to the vocal cords during swallowing?
- True vocal cords are adducted
- Closure of rima glottidis
What are the sensory and motor nerves that supply the larynx?
- Sensory only to supraglottis and glottis = internal branch of superior laryngeal nerve
- Motor only to cricothyroid muscle = external branch of superior laryngeal nerve
- Recurrent laryngeal nerve supplies motor to intrinsic muscles and sensory to infraglottis
Which artery does the superior laryngeal nerve run to?
- Superior thyroid artery
Outline the route of the right and left recurrent laryngeal nerves
- Innervates all intrinsic muscles of larynx
- Passes anteriorly to and then loops under right subclavian artery and arch of aorta on left
- Ascends in tracheo-oesophageal (behind lobes of thyroid gland)
Which nerve is at risk of damage during thyroid surgery?
- Right and left recurrent laryngeal nerves
- Close anatomical relationship with thyroid gland and inferior thyroid arteries
- Results in paralysis of muscles moving a true vocal cord
What can cause injury to the recurrent laryngeal nerve?
- Disease or surgery involving larynx, oesophagus or thyroid
- Aortic arch aneurysm (left RLN)
- Cancer involving apex of lung (right RLN)
What does a unilateral RLN lesion lead to?
- Unilateral true vocal cord palsy
- Hoarse voice
- Ineffective cough
- No significant impairment to airflow during breathing
What happens to a vocal cord affected by a RLN injury?
- Affected VC assumes a resting paramedian position
- Paramedian = between fully abducted and fully adducted
Why are bilateral RLN injuries so dangerous?
- Both vocal cords assume a resting paramedian position
- Bilateral RLN lesions are rare
- Narrow rima glottis significantly
- Significant airway obstruction
- Emergency surgical airway needed
What is laryngitis?
- Inflammation of larynx often involving true vocal cords
- Can have infectious cause or non-infectious
- E.g. due to repetitive strain on voice
How is laryngitis diagnosed?
- Diagnosed clinically from history
- Hoarse/weak voice and sore throat (oedema affects pliability vocal cords and increases their bulk)
- History of URTI
- Infectious and non-infectious aetiology
- Usually self-limiting: fully resolves in 2-3 weeks
Outline laryngeal nodules
- Benign growth on vocal cords
- Acute trauma or chronic irritation
- Hoarseness of voice (>3 weeks)
- Requires visualisation of cords +/- biopsy
What is laryngeal oedema?
- Due to allergic reaction or swallowed foreign body
- Acute presentation
What is epiglottitis?
- Rare (more common in children)
- Potentially airway threatening
- Inflammation secondary to infection (usually Haemophilus Influenza type B)
- Cellulitis of epiglottis and surrounding tissues
- Child will be sitting forward in sniffing position, drooling, with stridor
- Don’t upset the child, don’t place anything in the mouth
What is croup?
- Acute laryngotracheobronchitis
- Barking cough
- Inspiratory stridor
- Classically caused by parainfluenza
- Can be managed at home with steroids (reduce inflammation)
- If stridor present at rest, give adrenaline/budesonide nebulisers and admit
How do patients with a compromised upper airway present?
- Stridor
- Raised respiratory rate
- Distress
- Hypoxia
- May or may not have cyanosis
How is the airway maintained?
- Actions and general tone in muscles of upper pharynx/larynx/tongue
- Protective reflexes e.g. gag, cough, swallow
- Complex neural pathways and reflexes involved to keep airway patent and safe
What happens to the airway when a person is unconscious?
- Decreased muscle tone
- Suppression of reflexes
- Airway at risk
- Tissues can relax and fall back onto upper airway resulting in occlusion
When do we need to manage a person’s airways?
- Can be planned e.g. in preparation for surgery involving general anaesthetic
- Can be emergency as there is an acute/immediate threat to airway e.g. laryngeal oedema/unconscious patient
What simple manoeuvres can be done to manage the airways?
- Head tilt
- Chin lift
When are airway adjuncts used?
- If patient is breathing spontaneously
- Can be oropharyngeal airway (Guedel) though this is contraindicated if minimal depression of consciousness (illicits gag reflex)
- Or nasopharyngeal airway
What are the pros and cons of airway adjuncts?
- Allow for spontaneous ventilation
- But offer no protection of lower respiratory tract from vomit/secretions
What are the pros and cons of supraglottic airways?
- E.g. iGel
- Maintains airway and affords some protection
- Minimal technical skills required to insert
- Often first line in cardiac arrest
- Not for long-term ventilation e.g. if in ITU
How is a definitive airway inserted?
- Endotracheal tube (oral cavity, oropharynx, pharynx, trachea)
- Technical skill
- Requires use of laryngoscope to visualize vocal cords
- Secures and protects lower respiratory tracts from secretions/vomit
- Patient anaesthetised prior to insertion
