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Tracheostomies
2
The Upper Airway
The upper airway is composed of the nose, mouth, pharynx, and larynx. Besides
providing a natural conduit for gas exchange, the structures of the upper airway
have additional functions in humidification of gases, protection of the lower
airway, deglutition, and phonation.
The Nose
The external nose consists of a bony vault and a cartilaginous vault. The bony
vault comprises the nasal bones, the frontal processes of the maxillae, and the
nasal portion of the frontal bone. The cartilaginous vault is formed by the upper
lateral cartilages, which meet the cartilaginous portion of the septum in the
midline. The cavities of each nostril are continuous with the nasopharynx posteriorly. The nasal airway is between the laterally placed inferior turbinate, the
septum, and the floor of the nose. The nasal cavities are bounded posteriorly by
the nasopharynx. The adenoids are located posteriorly in the nasopharynx just
above the nasal surface of the soft palate. The soft palate rests on the base of the
tongue during quiet nasal respiration, sealing the oral cavity.
Functional Anatomic Relevance
The nose provides moisture to approximately 10,000 liters of ambient ■
air that pass through the nasal airway every day (Grande, Ramanathan, & Turndorf, 1988). The moisture is constituted from transudated
fluid through the mucosal epithelium as well as secretions from glands
and goblet cells. These secretions have bactericidal properties.
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The floor of the nose is tilted slightly downward at approximately 10 to
15 degrees. Thus, when a nasal tube or fiberscope is inserted through
the nose, it should be directed slightly inferiorly to follow this major
channel.
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The nasal mucosa is exquisitely sensitive to topically applied vasoconstricting medications such as phenylephrine, epinephrine, or cocaine.
Cocaine has the added advantage of providing profound topical anesthesia and is the only local anesthetic agent that produces vasoconstriction;
the others cause vasodilatation.
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The contiguity of the paranasal sinuses with the nasal cavity leads to
infections of the paranasal sinuses with prolonged nasotracheal intubation. Surveillance for infected paranasal sinuses is important with longterm placement of airways or nasogastric tubes in the nasal passages.
The Mouth
The mouth, or oral cavity, is divided into two parts: the vestibule and the oral
cavity proper. The vestibule is the space between the lips and the cheeks externally and the gums and teeth internally. The oral cavity proper is bounded anterolaterally by the alveolar arch, teeth, and gums; superiorly by the hard and soft
palates; and inferiorly by the tongue. Posteriorly, the oral cavity communicates
with the palatal arches and pharynx.
Chapter 1 Functional Anatomy of the Airway
The Tongue
The tongue is a noncompressible muscular structure. The tongue is attached
to the symphysis of the mandible anteriorly and anterolaterally and the stylohyoid process and hyoid bone posterolaterally and posteriorly, respectively.
The posterior limit of the tongue corresponds to the position of the hyoid bone.
The sensory and motor innervations of the tongue include different sources.
Sensory fibers for the anterior two-thirds are provided by the lingual nerve.
Taste fibers are furnished by the chorda tympani branch of the nervus intermedius. Sensory fibers for the posterior third come from the glossopharyngeal
nerve (IX). Some sensory innervation is provided by the superior laryngeal
nerve. The major motor supply is from the hypoglossal nerve (XII).
Functional Anatomic Relevance
During laryngoscopy, the tongue is ordinarily displaced to the left and ■
into the mandibular space; thus, the larynx is exposed for intubation
under direct vision. Also, encroachment of the mandibular space by a
large tongue, a small mandible, infection (e.g., Ludwig’s angina), or masses
limits displacement of the tongue into this space and, thus, makes orotracheal intubation difficult or impossible.
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A forward jaw-thrust maneuver pulls the mandible and tongue forward to open the upper airway and alleviate upper airway obstruction.
Normally, the mandibular condyles articulate within the temporomandibular joint for the first 30 degrees of mouth opening. Beyond
30 degrees, the condyles translate out of the temporomandibular joint
anteriorly into the zygomatic arches. The jaw-thrust maneuver can
prove life saving for many patients with upper airway obstruction, and
it facilitates ventilation with a face mask as well as the insertion of
orogastric tubes.
3
The Pharynx
The pharynx is a U-shaped musculo-membranous tube that extends from the
base of the skull to the inferior border of the cricoid cartilage anteriorly and
the lower border of the sixth cervical vertebra (C6) posteriorly. It is approximately 15 cm long and, in the adult, has its widest point at the level of the
hyoid bone and its narrowest at the lower end, where it joins the esophagus.
Anteriorly, it opens into the nasopharynx, oropharynx, and laryngopharynx
(see Figure 1.1). The pharynx is the common pathway for food and respiratory
gases.
Functional Anatomic Relevance
Oropharyngeal muscle tone keeps the upper airway open during quiet ■
breathing. Respiratory distress is associated with pharyngeal muscular
activity attempting to open the airway further. Sedative hypnotic and
opiate agents may attenuate some of this tone and precipitate partial or
total airway obstruction.
Tracheostomies
4
1.1
Anatomy of pharynx and larynx.
The pharynx defends against pathogens through the presence of lym- ■
phoid tissue at its base. Inhaled micro-particles are removed by impaction as they pass in the posterior pharynx. An inhaled airstream changes
direction sharply by 90 degrees at the nasopharynx, thus causing some
loss of momentum of the suspended particles. The particles are then
trapped by a circular array of lymphoid tissue located at the entrance of
the respiratory and gastrointestinal tracts. The ring includes the tonsils,
which, if infected or enlarged, often impede the passage of endotracheal
tubes. Abscess formation, hemorrhage, or tumor growth may cause airway obstruction.
■
Patency of the pharynx is a critical component for proper gas exchange.
Upper airway obstruction in patients who are sedated or anesthetized
(with or without an endotracheal tube) or who have altered levels of
consciousness is caused by a tongue with loss of muscle tone falling
back against the posterior pharyngeal wall. Shorten, Opie, Graziotti,
Morris, and Khangure (1994) used magnetic resonance imaging (MRI)
to demonstrate a different mechanism for upper airway obstruction in
patients sedated with midazolam. A decrease in the anterior-posterior
dimension at the level of the soft palate and epiglottis occurred while
Chapter 1 Functional Anatomy of the Airway
sparing the tongue. Thus, the soft palate and epiglottis may have a more
important role than muscle tone in the development of upper airway
obstruction.
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Obstructive sleep apnea (OSA) results from a reduction in the size of the
pharynx, among other causes. Normally, the longer axis of the pharyngeal airway is transverse; however, in OSA patients the anterior-posterior
axis is predominant. It is believed this orientation is less efficient for airway muscle function. Imaging studies using MRI, computed tomography
(CT), nasopharyngoscopy, fluoroscopy, and acoustic reflections divulged
differences in anatomical structure between awake and asleep males
(Ayappa & Rapoport, 2003). In awake males with OSA, CT demonstrated
a reduced airway caliber at all levels of the pharynx when compared
with normal patients, with the narrowest point posterior to the soft palate (Haponik et al., 1983). The application of continuous positive airway
pressure (CPAP) increases the cross-sectional area, and thus volume, of
the oropharynx, especially in the lateral axis (Schwab, Gefner, Pack, &
Hoffman, 1993).
The Larynx
The larynx is the organ of phonation and is located in the anterior portion
of the neck. It extends from its oblique entrance formed by the aryepiglottic folds, the tip of the epiglottis, and the posterior commissure between the
arytenoids cartilages (interarytenoid folds) through the vocal cords to the cricoid ring (see Figure 1.2). It is a boxlike structure, 4 to 5 ml in volume, and is
5
1.2
Anatomy of larynx: (A) anterior view; (B) sagittal view.
Tracheostomies
6
made up of cartilages, ligaments, muscles, and mucous membrane. In adults,
it is situated in the anterior portion of the neck at the level of C3 through
C6. The larynx is shorter in women and children and is situated at a slightly
higher level. The larynx consists of three single cartilages—the epiglottis, the
thyroid, and the cricoid—and three paired cartilages—the arytenoids, the corniculates, and the cuneiforms. The laryngeal cavity is a space between the true
vocal cords and the arytenoid cartilages and is known as the rima glottidis. It
divides the larynx into two parts: the upper compartment extends from the laryngeal outlet to the vocal cords and contains the vestibular folds and the sinus
of the larynx; the lower compartment extends from the vocal cords to the upper
portion of the trachea. The piriform sinus is the space between the epiglottis
and the aryepiglottic folds medially and the hyoid bone, thyrohyoid ligament,
and thyroid cartilage laterally (known as the piriform fossa).
The larynx is innervated by two branches of the vagus: the superior laryngeal and the recurrent laryngeal nerves. The superior laryngeal nerve reaches
the internal side of the larynx. It divides into an external (motor) branch that
descends to supply the cricothyroid membrane and upper and lower branches
that supply the mucous membrane of the base of the tongue, pharynx, epiglottis, and larynx. The superior laryngeal branch of the vagus nerve supplies
sensation to the undersurface of the epiglottis, all of the larynx to the level of
the false vocal cords, and the pyriform recesses posterolaterally to either side
of the larynx.
The recurrent laryngeal nerve (RLN) arises from the vagus nerve and loops
around the subclavian artery on the right and the aortic arch on the left. After
ascending between the trachea and esophagus, it passes behind the thyroid
gland and innervates all the intrinsic muscles of the larynx except the cricothyroid. In addition, it supplies sensory branches to the mucous membranes of the
larynx below the vocal cords.
Functional Anatomic Relevance
The larynx is the most heavily innervated sensory structure in the body, ■
followed closely by the carina. Stimulation of the unanesthetized larynx
during intubation causes tremendous reflex sympathetic activation, with
significant elevation in heart rate, blood pressure, and intracranial pressure (particularly in patients with loss of autoregulation). This elevation
of heart rate and blood pressure may precipitate marked increase in
myocardial oxygen demand and significant afterload that could potentially lead to large vessel dissection or rupture (e.g., injured or dissected
carotic artery, thoracic aorta, or abdominal aorta).
■
The pyramidal arytenoid cartilages sit on the posterior aspect of the
larynx. The intrinsic laryngeal muscles cause them to swivel, opening
and closing the vocal cords. An endotracheal tube that is too large may,
over time, compress these structures, causing mucosal and cartilaginous
ischemia and resulting in permanent laryngeal damage. A traumatic intubation may dislocate these cartilages posteriorly (most commonly from
a MAC, or curved, blade) or anteriorly (most commonly from a Miller, or
straight, blade). Early diagnosis and intervention may avoid permanent
hoarseness.
Chapter 1 Functional Anatomy of the Airway
The larynx bulges posteriorly into the hypopharynx, leaving deep re- ■
cesses on either side called pyriform recesses or sinuses. Foreign bodies
(e.g., plastic, glass, or fish bones) occasionally become lodged there.
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During active swallowing, the larynx is elevated and moves anteriorly, the
epiglottis folds down over the glottis to prevent aspiration, and the bolus
of food passes midline into the esophagus. When not actively swallowing (e.g., the unconscious patient), the larynx rests against the posterior
hypopharynx such that a nasogastric tube must traverse the pyriform
recess to gain access to the esophagus and stomach.
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The cricothyroid membrane extends between the upper anterior surface
of the cricoid cartilage to the inferior anterior border of the thyroid cartilage. Its height tends to be about that of the tip of the index finger in
both male and female adults. Locating the cricoid cartilage and the cricothyroid membrane quickly in an airway emergency is crucial. It is usually easily done in men because of their obvious laryngeal prominence
(Adam’s apple).
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Clinical examination of the vocal cords (VC) with laryngoscopy and fiberoptic bronchoscopy determines their position, mobility, and structure
as well as their pathology and dysfunction during inspiration, expiration, and phonation. Under normal conditions, the vocal cords meet in
the middle in the production of phonation. On inspiration, they part from
each other and then return to midline during expiration, leaving a small
opening between them (see Figure 1.3). A reflexive, forceful contraction
of all laryngeal muscles, as commonly occurs when a foreign body lodges
in the larynx, is referred to as a laryngospasm. When laryngospasm occurs, both true and false VC lie tightly in the midline.
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VC palsies result from interrupted innervations of the larynx. The RLN
may be traumatized during surgery (commonly thyroid or parathyroid
7
1.3
Vocal cord position during phonation and inspiration.
Tracheostomies
8
■
1.4
procedures), damaged from a tumor growth or trauma in the neck, or
stretched due to pressure from an endotracheal tube (ETT) (Ellis & Feldman, 1993). The left RLN is more likely to be paralyzed than the right
because of its close proximity to many intrathoracic structures, making it
liable to injury from neoplasms, organ enlargement (aortic aneurysm or
left atrial dilation), ice-cold solutions, or erroneous surgical ligation.
The RLN carries both abductor and adductor fibers to the vocal cords.
The abductor fibers are more vulnerable, and moderate trauma causes
a pure abductor paralysis, whereas severe trauma causes both abductor and adductor fiber injury. In pure unilateral abductor palsy, both
VC meet in midline during phonation because adduction can still occur
on the affected side. However, only one cord abducts during inspiration: the unaffected one. By contrast, in complete unilateral RLN palsy
both abductors and adductors are affected, and the affected VC lies in a
paralyzed position midway between complete abduction and complete
adduction. During phonation, the unaffected VC crosses the midline to
meet the paralyzed cord (see Figure 1.4). On inspiration, the unaffected
Vocal cord position
during phonation
and inspiration
in the presence
of nerve palsies.
Top: left abductor
palsy; middle: left
abductor-adductor
palsy; bottom:
bilateral recurrent
laryngeal palsy.
Chapter 1 Functional Anatomy of the Airway
cord moves to full abduction. Bilateral RLN palsy produces a different
result. In incomplete bilateral abductor damage to the RLN, the adductor
fibers draw the VC toward each other, and the glottis opening is reduced
to a thin slit, which leads to significant respiratory distress. By contrast,
in complete bilateral palsy of the RLN each VC lies midway between adduction and abduction, producing a moderate glottis opening. Therefore,
bilateral incomplete RLN palsy is more life threatening than complete
bilateral palsy (Redden, 2000).
The Epiglottis
The epiglottis is shaped like a leaf, with its lower end attached to the thyroid
cartilage by the thyroepiglottic ligament and its upper, rounded part free and
posterior to the tongue. The epiglottis is attached to the hyoid bone anteriorly
by the hyoepiglottic ligament. Small depressions on either side of this ligament
are referred to as the valleculae.
Functional Anatomic Relevance
During swallowing, as the laryngeal muscles contract, the downward ■
movement of the epiglottis and the closure and upward movement of the
glottis prevent food from entering the larynx.
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When the epiglottis becomes acutely inflated and swollen (acute epiglottitis), a life-threatening airway obstruction may occur.
9
Physiology of Swallowing
Normal swallowing consists of three phases: oral preparatory and trans- ■
port, pharyngeal, and esophageal. The oral preparatory phase consists
of opening and closing the mouth, moistening food, masticating, preparing an appropriate size bolus with the movement of the tongue and
cheek muscles. The oral transport (or “buccal”) phase lasts 1 second
and begins with the compression of the food bolus against the hard palate. Next, the tongue retracts in a posterior direction to force the bolus
to the oropharynx. Then, the posterior tongue is lifted by the styloglossus and palatoglossus muscles, which also elevate the uvula and seal the
nasopharynx to prevent nasal aspiration. This phase is voluntary and involves important cranial nerves: V (trigeminal), VII (facial), and XII (hypoglossal). In the pharyngeal phase (1 second), the bolus is advanced
from the pharynx to the esophagus through the sequential contraction
of the constrictor muscles. The soft palate is elevated to the posterior
nasopharyngeal wall through the action of the levator veli palatini. The
palatopharyngeal folds on each side of the pharynx are brought close
together through the superior constrictor muscles so that only a small
bolus can pass. Then the larynx and hyoid are elevated and pulled forward to the epiglottis to relax the cricopharyngeus muscle. This passively
shuts off its entrance and pulls the vocal cords close together, narrowing
the passageway between them. This phase is passively controlled reflexively and involves cranial nerves V, X (vagus), XI (accessory), and XII
Tracheostomies
10
Neural Regulation of Swallowing
(hypoglossal). The respiratory center of the medulla is directly inhibited
by the swallowing center for the very brief time it takes to swallow. This
means it is briefly impossible to breathe during this phase of swallowing,
and the moment where breathing is prevented is known as deglutition
apnea. The bolus moves through the pharynx at a speed of 25 feet per
second (8 m/s). During the esophageal phase (8–20 seconds), the upper
esophageal sphincter relaxes to let food past, after which various striated
constrictor muscles of the pharynx as well as the peristalsis and relaxation of the lower esophageal sphincter sequentially push the bolus of
food through the esophagus into the stomach.
Swallowing is initiated by sensory impulses transmitted as a result of ■
stimulation of receptors on the fauces, tonsils, soft palate, base of the
tongue, and posterior pharyngeal wall.
Sensory impulses reach the brainstem primarily through the 7th, 9th,
■
and 10th cranial nerves, while the efferent (motor) function is mediated through the 9th, 10th, and 12th cranial nerves. The cricopharyngeal
sphincter opening is reflexive; relaxation occurs when the bolus reaches
the posterior pharyngeal wall prior to reaching this sphincter.
Cranial Nerves
CN V—Trigeminal nerve contains both sensory and motor fibers that in- ■
nervate the face and is important in chewing.
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CN VII—Facial nerve contains both sensory and motor fibers and is important for the sensation of oropharynx and taste to anterior two-thirds
of the tongue.
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CN IX—Glossopharyngeal nerve contains both sensory and motor fibers
and is important for taste to the posterior tongue and the sensory and
motor functions of the pharynx.
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CN X—Vagus nerve contains both sensory and motor fibers, provides
taste to oropharynx and sensation and motor function to the larynx and
laryngopharynx, and is important for airway protection.
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CN XII—Hypoglossal nerve contains motor fibers that primarily innervate the tongue.
Thyroid Cartilage
The thyroid cartilage is a shield-like structure composed of two plates that meet
to form a notch. The thyroid notch is more prominent in men than in women.
The prominence of the Adam’s apple in males is due to the more acute angle
at which the thyroid laminae meet, with a greater anteroposterior diameter. At
the posterior aspect of each lamina there are horns on the superior and inferior
aspects. The inferior horn has a circular facet that allows it to articulate with the
cricoid cartilage.
Chapter 1 Functional Anatomy of the Airway
Cricoid Cartilage
The cricoid cartilage is shaped like a signet ring. It has articular facets that attach to the thyroid cartilage and the arytenoids. It is separated from the thyroid
cartilage by the cricothyroid ligament, or membrane.
It is important to identify the cricoid cartilage because the cricothyroid
■
membrane is contiguous with it inferiorly. In acute airway obstruction,
the cricothyroid membrane may be penetrated with a needle, knife, or
tube and connected to an oxygen source via a standard 15-mm connector.
Cricothyrotomy is the first procedure performed to relieve asphyxiation
in situations where intubation and mask ventilation are impossible. The
hyoid bone, which is not part of the larynx proper, is attached to the thyroid cartilage by the thyrohyoid ligament. The inferior horn of the thyroid cartilage, joined by the cricothyroid ligaments, articulates with the
cricoid cartilage bilaterally. Cricothyrotomy is performed by penetrating
this ligament.
Paired Cartilage
The arytenoids are triangular structures located on the posterosuperior aspect
of the cricoid cartilage.
11
The Lower Airway
The lower airway is composed of the trachea, two mainstem bronchi, and terminal and respiratory bronchioles. The scope of this section will be limited to the
trachea and bronchi in relation to the patient with a tracheostomy.
Trachea
The trachea is a tubular structure, about 15 cm long in adults, extending from
the cricoid cartilage to the bronchial bifurcation. It has an outer diameter of
2.5 cm. It consists of 16 to 20 C-shaped cartilages joined by fibroelastic tissue
and closed posteriorly by the trachealis muscle. At the level of the fifth thoracic vertebra, the trachea bifurcates into right and left mainstem bronchi. The
right (more than the left) mainstem bronchus appears to be a vertical continuation of the trachea; furthermore, the right upper lobe bronchus has its origin
about 2 cm from the carina, compared to the left, which arises about 5 cm from
the carina. For these reasons, aspiration of food, liquid, or foreign bodies is far
more likely to occur on the right side, and right mainstem intubations are more
common than left.
The trachea begins at the inferior border of the cricoid ring. The sensory
supply to the tracheal mucosa is derived from the recurrent laryngeal branch of
the vagus nerve. The trachea is between 9 and 15 mm in diameter in the adult
and is 12 to 15 cm long. It may be somewhat larger in the elderly. The adult
male trachea will generally easily accept an 8.5-mm inner diameter (ID) ETT;
a 7.5-mm ID ETT may be preferable in women. If the patient being intubated