Download - Anatomy of larynx
ANATOMY OF LARYNX AND TRACHEOBRONCHIAL TREE
Guide: Dr. Bhanu Chaudhary MD Presented by, Professor & Head of Department Dr. Ranjith kumar Dept of Anaesthesiology PG Resident
G.R.Medical college Gwalior.
Respiratory System
Descriptive Anatomy - Larynx
Situation & Extent:
– Lies in anterior midline of neck
– Opp to C3 to C6 vertebra in men
– Level is higher in female & children
Infants b/w 6 and 12 months of age - the tip of the epiglottis lies little above the level of fibrocartilage b/w the odontoid process and body of the axis.
SIZE
According to Sappey the average measurements of the adult larynx are as follows:
In Males In Females.Length 44 mm. 36 mm.
Transverse diameter 43 mm. 41 mm.
Antero-posterior diameter 36 mm 26 mm.
Circumference 136 mm. 112 mm.
Until puberty there is little difference b/w male & female larynx.
After puberty - male larynx undergoes considerable increase; all the cartilages are enlarged and the thyroid cartilage becomes prominent in the middle line of the neck.
General principles of development
The development of the larynx - prenatal and postnatal stages.
At birth - larynx is located high in the neck b/w C1 and C4 vertebrae, allowing concurrent breathing or vocalization and deglutition.
At 2 years - larynx descends inferiorly;
At 6 years - reaches the adult position between C4 and C7 vertebrae.
This new position provides a greater range of phonation (because of the wider supraglottic pharynx) at the expense of losing this separation of function, i.e., deglutition and breathing.
Embryology
• Larynx - develops from endodermal lining and the adjacent mesenchyme of the foregut b/w the 4 & 6th branchial arches.
• At 20 days' gestation - the foregut is first identifiable with a ventral laryngotracheal groove. It continues to deepen until its lateral edges fuse.
• Trachea becomes separated from the esophagus by the tracheoesophageal septum with a persistent slit like opening into the pharynx
• Fusion occurs in the caudal-to-cranial direction, and incomplete fusion results in development of persistent communication between the larynx or trachea and the esophagus(tracheoesophageal fistula)
The main changes occurring in the larynx postnatally are a change in the axis, luminal shape, length, and
proportional growth of the laryngeal elements.
The larynx grows rapidly during the first 3 years of life.
The larynx elongates as the hyoid, thyroid, and cricoid cartilages separate from each other.
The cricoid cartilage continues to develop during the first decade of life, gradually changing from a funnel shape to a wider adult lumen; therefore, it is no longer the narrowest portion of the upper airway.
Larynx - Structure
Constituents of larynx
• 9 Cartilages– 3 paired– 3unpaired
• 8 Muscles(Intrinsic)
• Ligaments
Cartilages of Larynx
3 Unpaired cartilages• Thyroid• Cricoid• Epiglottis
3 Paired cartilages• Arytenoid• Corniculate• Cuneiform
Histology: Hyaline – Thyroid, Cricoid & base of Arytenoids are Hyaline.
May ossify after 25 yrs of age Other cartilages are Elastic & they do not ossify.
Thyroid Cartilage
• Shield shaped, open posteriorly, angulated anteriorly.
• Largest cartilage of larynx
• Angulation more acute in males(90) & in females it is 120.
• Its function is to shield larynx from injury and provide an
attachment to vocal cords
Cricoid Cartilage
• Signet ring shaped
• Stronger than thyroid cartilage.
• Narrow ant part - arch
• Broad post part - lamina
Important from structural & functional point of view
– Base for entire larynx
– Support to arytenoid
– Attachment to intrinsic muscles
– Only part of cartilagenous framework that forms continuous 360
degree ring
The narrowest portion of the airway in an infant.We use this fact when ventilating infants as infant ET tubes do not have cuffs to seal the trachea
Epiglottis
• Thin leaf shaped fibro-cartilage, situated in midline
• Upper free end broad & rounded, projects up behind base
of tongue
• Spoon-shaped cartilage prevents aspiration by covering
the opening of the larynx during swallowing.
• The tongue and the epiglottis are connected by folds �of mucous membranes which form a small space called
the vallecula.
Vallecula
Arytenoids
• Paired cartilages, pyramidal in shape
• Base articulated with cricoid• PCA & LCA muscles attach on
muscular process• Anterior angle elongated into
vocal process which receives insertion of vocal ligament
Paired cartilages
Laryngeal compartments
1. Glottis or superior vestibule
2. Supraglottis or
ventricle/sinus of larynx
3. subglottis
Supraglottis
• Consists of ventricles, false
cords, laryngeal surface of
epiglottis & aryepiglottic folds .
• Vestibular folds- narrow band of
fibrous tissue passing from
anterolateral surface of arytenoid
to angle of thyroid cartilage.
• Separated from true vocal cords
by larngeal sinus.
Glottis or superior vestibule• Consists of true cords, anterior commissure
and posterior commissure.
• Vocal cords – 2 pearly white folds of mucous
membrane stretching from angle of thyroid
cartilage to vocal process of arytenoid.
• Narrow triangular space between the true
cords is called rima glottis.
• Anterior 2/3 is membranous
• Posterior third consists of vocal processes of
arytenoids.
• Posterior 1/3 of cords and covering mucosa
are called posterior commissurePearly white – since there is no true submucosa with usual network of blood vessels
Sub-glottis
• Begins about 5mm below free
margins of Vocal cord.
• Extends from vocal folds to the
lower border of cricoid cartilage.
• Consists of a mobile upper and
fixed lower part.
• Narrowest part of laryngeal cavity
in children under 10 years of age.
Clinical significance – During intubation in small children an ET tube can pass between vocal cord may yet too large to pass beyond cricoid ring
Mucosa
• Mucosa of glottic and Supraglottic regions is stratified
squamous epithelium.
• Mucosa of ventricles and sub-glottic regions is pseudo-
stratified ciliated epithelium.
• Supra and sub glottic regions particularly ventricles are rich in
submucosal mucous or minor salivary glands while glottis is
not.
Muscles of Larynx
Intrinsic:
Cricothyroid
Posterior cricoarytenoid
Lateral cricoarytenoid
Transverse arytenoid
Oblique arytenoid
Aryepiglotticus
Thyroarytenoid
Thyroepiglotticus
Vocalis
Extrinsic:
(connect larynx to its neighbour)
Sternothyroid – Depresses
larynx.
Throhyoid – Elevates larynx.
Inferior constrictor
Action of muscles
open close
Glottis Posterior Cricoarytenoid Lateral cricoarytenoidTransverse arytenoid Cricothyroid Thyroarytenoid
Laryngeal inlet Thyroepiglotticus Oblique arytenoid Aryepiglotticus
Vocal folds Cricothyroid(Tense) Thyroarytenoid & Vocalis(Relax)
Cricothyroid Muscle
Adductors of the Vocal Folds
Abductor of Larynx
Laryngeal Ligaments
A series of intrinsic ligaments binds all 9 cartilages together to form the larynx.
Extrinsic ligaments attach the thyroid cartilage to the hyoid bone and the cricoid cartilage to the trachea.
The vestibular ligaments and the vocal ligaments extend between the thyroid cartilage and the arytenoids.
The vestibular and vocal ligaments are covered by folds of laryngeal epithelium that project into the glottis.
Ligaments of Larynx
Ligaments Cont…
The vestibular folds, which are relatively inelastic, help prevent foreign objects from entering the glottis and provide protection for the more delicate vocal folds.
The vocal folds are highly elastic, because the vocal ligament is a band of elastic tissue.
The vocal folds are involved with the production of sounds hence known as the true vocal cords.
Because the vestibular folds play no part in sound production - called the false vocal cords.
Blood Supply
These vessels accompany superior and recurrent laryngeal nerves
Sup.laryngeal vein drains into Sup.Thyroid Vein
Inf.laryngeal vein drains into Inf. Thyroid veins
Lymphatic drainage
Above vocal folds – Antero superior group of Deep cervical nodes.
Below Vocal folds – Postero inferior group of deep cervical nodes through prelaryngeal & pretracheal nodes.
Nerve Supply: Derived from the Vagus• Superior Laryngeal Nerve -It leaves
the vagus nerve high in the neck– Internal - provides sensation of
the glottis and supraglottis, which includes the pharynx, underside of the epiglottis and the larynx above the cords.
– External -It supplies motor function to the cricothyroid muscle which tenses the vocal cords and could cause laryngopasm.
• Recurrent Laryngeal Nerve - provides sensation to the subglottic area which includes the larynx below the vocal cords and upper esophagus. Motor function to most of intrinsic muscles of the larynx
• It branches from the vagus in the mediastinum and turns back up into the neck. On the right, it travels inferior to the subclavian and loops up, and on the left it travel inferior to the aorta and loops up.
Motor nerves :All the muscles of larynx are supplied by the recurrent laryngeal nerve except cricothyroid which is supplied by external laryngeal nerve�Sensory nerves :Internal laryngeal nerve-upto level of vocal fold
Reccurent laryngeal nerve-below vocal fold
Position of vocal cord in health &disease
Positon of cordLocation of cord
from midline
Situations in
health disease
Median Midline Phonation RLN paralysis
Paramedian 1.5 mm Strong whisperRLN paralysis
Intermediate(cadaveric)
3.5 mm. (This is neutral position of cricoarytenoid joint. Abduction and adduction takes place from this position.)
-Combined paralysis ( both RLN & SLN)
Gentle abduction 7 mm Quiet respiration Paralysis of adductors
Full abduction 9.5 mm Deep inspiration -
Vocal cord
The opening into trachea is maximum at the end of deep inspiration.In order to minimise the risk of trauma to voca cords Intubation and Extubation should be carried out during inspiration
Types Of Vocal cord Paralysis
Unilateral Abductor Paralysis
Bilateral Abductor Paralysis
Unilateral Adductor Paralysis
Bilateral Adductor Paralysis
RLN Paralysis• It carries fibres for both abductor and adductor muscles of larynx.• Injury – partial or complete• Abductor fibres - more vulnerable even for mild injury
Moderate trauma produces only abductor paralysis.
Severe injury or section of nerve produces both abductor and adductor paralysis.
Semon's law: This theory proposed by Rosenbach and Semon in 1881, depends on the concept that abductor fibres in the recurrent laryngeal nerves are more susceptible to pressure than the adductor fibers.
Wagner and Grossman theory (1897).: most popular and widely accepted theory, states that in complete paralysis of RLN the cord lies in the paramedian position because the intact cricothyroid muscle adducts the cord. (Because the superior laryngeal nerve is intact).
If the superior laryngeal nerve is also paralysed the cord will assume an intermediate position because of the loss of adductive force.
Unilateral Abductor Paralysis
Paralysis of recurrent laryngeal nerve.
Vocal cord lies in median or paramedian position, doesn’t move on
deep inspiration.
Initial hoarseness.
No regurgitation.
Vocal cord compensation occurs leading
to improvement of voice.
Bilateral Abductor Paralysis
Paralysis of both recurrent laryngeal nerves.
Thyroid surgery - cause
Both vocal cord lies in paramedian position
due to unopposed action of cricothyroid.
Severe dyspnoea and stridor.
Voice is good and there is no regurgitation
Vocal cord compensation may occurs leading to improvement
Immediate tracheostomy & various procedures for Lateralisation of
cord.
Unilateral Adductor Paralysis
1.Paralysis of both superior and recurrent laryngeal nerves
2. Vocal cord lies in Lateral (cadaveric) position
3. Weak husky voice
4. There is aspiration of food and fluid
5. Vocal cord compensation occurs leading to improvement of voice
Medialization of vocal cord or reverse cordopexy ---- Treatment
Bilateral Adductor Paralysis
1. Paralysis of combined both recurrent and superior laryngeal nerves
2. Psychiatric Illness or widespread neurological lesion or neoplastic lesion
in the base of skull, upper neck etc.
3. Both vocal cord lies in lateral (cadaveric) position
4. Severe regurgitation of food and fluid.
5. Voice is breathy
6. Vocal cord compensation may occurs leading to improvement
7. If compensation does not occur than total laryngectomy and
epiglottopexy ---- Treatment
TRACHEA
It is a cartilaginous & membranous tube,10 - 11cm long & 2.5cm(1 inch) in diameter.
Cartilages – deficit posteriorly. Extend from lower border of cricoid cartilage(C6) to carina(T5)
where it bifurcates into right & left main bronchus. Lined by ciliated columnar epithelium Trachea moves upward during swallowing, & downward
forward during inspiration.
Extension of head & neck can increase the length of the trachea by as much as 23 to 30 %.
TRACHEOBRONCHIAL TREE
Bronchiole
Respiratory Bronchioles
Alveolar Ducts
Pulmonary Atria
Alveolar sac & Pulmonary Alveoli
Terminal Bronchioles
Dichotomous division – starting with trachea & ending in alveolar sacs (23 generations)First 16 generation – only conductiveLast 7 generation – Respirative (involves in gas exchange)
Right main bronchus:• 5 cm long, wider,
shorter & more vertical then the Lt main bronchus.
• It makes 25-300 with carina
Left main bronchus:• 5.5cm long,2-
3mm narrower then the Right main bronchus.
• more horizontal & making an angle of 450 with trachea
Rt main bronchus – since it is more vertical there is much greater tendency for ET tubes or Suction catheters to enter this lumen.In small children <3yrs of age - angulation of 2 main bronchi at the carina is equal on both sides.
Bronchopulmonary segments
Aspiration pneumonitis• Aspiration pneumonitis (Mendelson’s syndrome) is a chemical injury
caused by the inhalation of sterile gastric contents.• A reduced level of consciousness can lead to an unprotected airway. If
the patient vomits they can aspirate the vomitus contents into their lungs. This can set up lung inflammation with infection.
• Also occur in spinal anaesthesia if the level of spinal block is too high, leading to paralysis or impairment of the vocal cords and respiratory impairment.
• Most authors agree that a pH < 2.5 and a volume of gastric aspirate greater than 0.3 ml per kilogram of body weight (20 to 25 ml in adults) are required for the development of aspiration pneumonitis.
• Aspiration of particulate food matter from the stomach may cause severe pulmonary damage, even if the pH of the aspirate is above 2.5.
Risk factor of aspiration
• Gastric oro-esophageal disease state.
• Incompetent lower esophageal sphincter .
• Emergency surgery.
• Drugs decreasing esophageal sphincter tone. (opioids , anticholinergics, benzodiazepines, thiopentone , volatile agents.)
• Obesity.,Diabetes, peptic ulcer disease, stress, pain & trauma.
Location
Patients who aspirate
In a lateral position, the inhaled materials tends to gravitate into the lateral portion of posterior segment of upper lobe.
In supine position, the material accumulates in the apical segment of lower lobe.
When patient is propped up in post operative period, secretions tend to gravitate to the lower lobes.
Prevention
• Use regional technique, awake intubation.
• Ensure empty stomach.(Fasting)
• Inhibit secretion of gastric acid .
• Rapid sequence induction. (sellick maneuver)
• Extubate when pt fully awake.
Fasting RecommendationsIngested Material Minimum Fasting Period
• Clear liquids 2 h• Breast milk 4 h• Infant formula 6 h• Nonhuman milk 6 h• Light meal 6 h
Examples of clear liquids include water, fruit juices without pulp, carbonated beverages, clear tea, and black coffee.
Brian A Sellick 1918-1996, London Anaesthetist
"Cricoid pressure must be exerted by an assistant.
Before induction, the cricoid is palpated and lightly held between the
thumb and second finger.
As anaesthesia begins, pressure is exerted on the cricoid cartilage
mainly by the index finger. Even a conscious patient can tolerate
moderate pressure without discomfort but as soon as consciousness is
lost, firm pressure can be applied without obstruction of the patient's
airway.
Pressure is maintained until intubation and inflation of the cuff of the
endotracheal tube is complete.”
Essential Elements of Cricoid Pressure
• Must apply force to the cricoid cartilage
• Must apply force in correct direction
• Must apply correct amount of force
• Must apply force for correct duration of time
How Much Force?
• A force of 30 N (3 kg) is recommended for an unconscious patient”
Clayton TJ, Vanner RG. A novel method of measuring cricoid force. Anaesthesia. 2002;57:326-9.
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