Download 6._Airway

Airway Evaluation and
Management
Key Learning Objectives
•Review the anatomy relevant to airway management
•Understand the components of an airway examination
•Learn the principles of mask ventilation and intubation
Introduction
Despite the site of surgery or the anesthetic technique
chosen, every patient receiving anesthetic care is
exposed to a varying degree of risk of airway
compromise. That is, all levels of sedation, general
anesthesia, and regional anesthesia carry with them at
least a small risk of airway obstruction and apnea.
Therefore, every anesthesia provider must examine each
patient in anticipation of a need to mechanically ventilate
and intubate, regardless of whether or not such
interventions were part of the primary anesthetic plan. A
thorough airway examination and history, combined with
expert airway management, guard against the lifethreatening risks of airway obstruction and apnea.
Airway Anatomy
The human airway is a dynamic structure
that extends from the nares to the alveoli.
Obstruction can occur at any point because
of anatomic collapse or a foreign body
which includes liquids such as mucous,
blood, and gastric contents
Pharynx
The pharynx is basically a wide muscular
tube forming the common upper pathway of alimentary
and respiratory tracts. It extends from the base of the skull
to the level of C6.
The pharynx lies posterior to, and communicates with,
the nose, mouth and larynx. This relationship
divides the pharynx into three sections: naso-, oro and
Laryngo pharynx. The posterior surface of the pharynx
lies on the prevertebral fascia and cervical vertebrae.
Larynx
The larynx is a functional sphincter at the
beginning of the respiratory tree to protect
the trachea from foreign bodies. It is lined
by ciliated columnar epithelium and
consists of a framework of cartilages
linked together by ligaments which are
moved by a series of muscles.
Cartilages of the larynx
The thyroid cartilage is said to be shaped like a
shield. It consists of two plates that join in the
midline inferiorly to form the thyroid notch (Adam’s
apple). Each plate has a superior and inferior horn
or cornua at the upper and lower limit of its
posterior border, respectively. The inferior horn
articulates with the cricoid cartilage.
The cricoid cartilage is shaped like a signet
ring, with the large laminal portion being
posterior.
Each lateral surface features a facet that
articulates with the inferior horn of the
thyroid cartilage. The upper border of the
lamina has an articular facet for the
arytenoid cartilage.
There is a pair of arytenoid cartilages, each
shaped like a triple-sided pyramid
possessing medial, posterior and
anterolateral surfaces.
Each arytenoid cartilage projects anteriorly
as the vocal process and in a similar
fashion laterally as the muscular process.
The posterior and lateral cricoarytenoid
muscles are inserted into the muscular
process.
The epiglottis is a leaf-shaped cartilage. It has a
lower tapered end which is joined to the thyroid
cartilage by the thyroepiglottic ligament.
The free upper end is broader and projects
superiorly behind the tongue.
The lowest part of the anterior surface of the
epiglottis is attached to the hyoid by the
hyoepiglottic ligament.
Two other minor cartilages are the corniculate and
the cuneiform.
Ligaments of the larynx
Extrinsic ligaments are the:
thyrohyoid membrane, cricotracheal,
cricothyroid, and hyoepiglottic ligaments.
The intrinsic ligaments of the larynx are of
minor importance, being the capsules of
the small synovial joints
Muscles of the larynx
• Extrinsic group:
Sternothyroid, thyrohyoid and inferior
constrictor is a constrictor of the pharynx
• Intrinsic group: These are paired, with the
exception of the (transverse arytenoid).
Cricothyroid, posterior cricoarytenoid,
lateral cricoarytenoid, aryepiglottic,
thyroarytenoid
Nerve supply
The mucous membrane of the larynx above
the vocal cords is supplied by the internal
laryngeal nerve, that below by the
recurrent laryngeal nerve.
All muscles of the larynx are supplied by the
recurrent laryngeal nerve except for the
cricothyroid, which is supplied by the
superior (also known as external)
laryngeal nerve.
Trachea
The trachea descends from the lower border of the cricoid
cartilage (C6) to terminate at its bifurcation into the two
main bronchi at the sternal angle (T4). The length of the
adult trachea varies between 10 and 15 cm. The walls of
the trachea are formed of fibrous tissue reinforced by 15–
20 incomplete cartilaginous rings. Internally the trachea
is lined by respiratory epithelium. The trachea may be
divided into two portions, that in the neck and that in the
thorax.
Bronchial tree
Extrapulmonary bronchi
At the carina, the two main bronchi arise. The right
main bronchus is shorter, wider and more upright than
the left. The right pulmonary artery and azygos vein are
intimately related to the right main bronchus. The left
main bronchus passes under the aortic arch anterior to
the oesophagus, thoracic duct and descending aorta. The
structure of the extrapulmonary bronchi is very similar to
that of the trachea.
Intrapulmonary bronchi
Branching of the intrapulmonary bronchi gives rise to
functional units – the bronchopleural segments.
Airway assessment
 History
• Adverse events related to prior airway
management
• Radiation/surgical history
• Burns /swelling/ tumor /masses
• Obstructive sleep apnea (snoring)
• Temporomandibular joint dysfunction
• Problems with phonation
• C-spine disease (disc dz, osteoarthritis,
rheumatoid arthritis, Down’s syndrome)
 Examination of the upper airway:
1.
2.
3.
4.
5.
6.
Cervical spine mobility
Temporomandibular mobility
Prominent central incisors
Diseased or artificial teeth
Ability to visualize uvula
Thyromental distance
Malampatti/ Samson–Young classification of the
oropharyngeal view
• Class I: uvula, faucial pillars, soft palate
visible;
• Class II: faucial pillars, soft palate visible;
• Class III: soft and hard palate visible;
• Class IV: hard palate visible only
Components of the preoperative airway physical examination
Component
•
•
Non reassuring finding
Length of upper incisors------------------------Relation of maxillary and mandibular-------incisors during normal jaw closure
Relation of maxillary and mandibular-------incisors during voluntary protrusion of the
jaw
 Relatively long
 Prominent “overbite” (maxillary incisors
anterior to mandibular incisors)
 Patient’s mandibular incisors anterior
to (in front of) maxillary incisor
•
•
Inter-incisor distance (mouth opening)------Visibility of uvula------------------------------------
•
•
Shape of palate------------------------------------Compliance of submandibular space—------
•
•
•
•
Thyromental distance-----------------------------Length of neck--------------------------------------Thickness of neck----------------------------------Range of motion of head and neck-------------
 <3 cm
 Not visible when tongue is protruded
with patient in sitting position (e.g.,
Malampatti class > II )
 Highly arched or narrow
 Stiff, indurated, occupied by mass, or
non-resilient
 <3 fingerbreadths or 6–7 cm
 Short
 Thick neck (size > 17 inches)
 Patient cannot touch tip of chin to
chest or cannot extend neck
•
Airway Devices
• Oral and nasal airways:
Typically inserted secondary to loss of upper
airway muscle tone in anesthetized patient
Airway obstruction caused by tongue falling
against posterior pharyngeal wall.
Length of nasal airway estimated by measuring
from the nares to meatus of ear, use caution
when used with patients on anticoagulants or
has basal skull fractures
Mask
Laryngeal mask airway (LMA)
Tracheal intubation
usually simply referred to as intubation, is
the placement of a flexible plastic or
rubber tube into the trachea to maintain an
open airway or to serve as a conduit
through which to administer certain drugs.
Endotracheal tubes
Modified for variety of specialized applications:
Flexible, wired-reinforced (armored), rubber,
Microlaryngeal, oral/nasal RAE, double lumen,
cuffed non cuffed.
All endotracheal tubes has a radio-opaque line.
Airflow resistance depends on tube diameter,
curvature and length.
Indications for orotracheal
intubation
1. Provide patent airway
2. Prevent inhalation (aspiration of gastric
content)
3. Need for frequent suctioning
4. Facilitate Positive pressure ventilation
5. Operative position other than supine
6. Operative site near or involved the upper
airway
7. Airway maintenance by mask difficult
8. Disease involving the upper airway
Complications of tracheal
intubation
•
1.
2.
3.
4.
5.
During direct laryngoscopy and
intubation of the trachea:
Dental and oral soft tissue trauma
Hypertension and tachycardia
Cardiac dysrhythmias
Myocardial ischemia
Inhalation (aspiration) of gastric contents
•While the tracheal tube is in place
1.
2.
3.
4.
5.
6.
7.
Tracheal tube obstruction
Endobrochial intubation
Esophageal intubation
Tracheal tube cough leak
Barotrauma
Nasogastric distention
Accidental disconnection from breathing
system
8. Tracheal mucosa ischemia
9. Accidental extubation
•Immediate and delayed complications after
extubation of the trachea
1.
2.
3.
4.
5.
6.
Laryngospasm
Inhalation of gastric content
Pharyngitis (sore throat)
Laryngitis
Laryngeal or subglottic edema
Laryngeal ulceration with or without granuloma
formation
7. Tracheitis
8. Tracheal stenosis
9. Vocal cord paralysis
10. Arytenoid cartilage dislocation
Nasotracheal intubation
an endotracheal tube is passed through the nose
and vocal apparatus into the trachea.
Indications:
1. Intra-oral surgery
2. Anatomical abnormalities or disease of the
upper airway make direct laryngoscopy difficult
or impossible
3. When long-term intubation of the trachea is
anticipated
Advantages of Nasotracheal
intubation
1.
2.
3.
4.
More stable tube fixation
Less chance for tube kinking
Greater comfort in awake patient
Fewer oropharyngeal section
Complications unique to
Nasotracheal intubation
1. Epistaxis
2. Dislodgement of pharyngeal tonsils
(adenoid)
3. Eustachian tube obstruction
4. Maxillary sinusitis
5. Bacteremia
6. Gastric distension
Flexible Fiberoptic Brochoscope
•
1.
2.
3.
4.
5.
Indications:
Difficult laryngoscopy/mask ventilation
Unstable cervical spines
Poor cervical range of motion
TMJ dysfunction
Congenital/acquired upper airway
anomalies
Awake Flexible Fiberoptic Intubation
• Equipment: airway, topical anesthesia,
vasoconstrictors, antisialagogues, suction,
fiberoptic scope with lubricated ETT
• Indications: Cervical spine pathology,
obesity, head and neck tumors, history of
difficult airway
• Premedication: Sedation (midazolam,
Fentanyl, Ketamine)
Light wand
Retrograde Tracheal Intubation
Airway Bougie
Cricothiroidotomy
Oxygen therapy
Oxygen therapy administered as increased
inhaled concentration of oxygen is
indicated for a PaO2 lower than 60 mmHg.
Supplemental inspired oxygen is often
routinely provided in the post operative
period regardless of the duration or type of
surgery.
In the presence of chronic obstructive
pulmonary disease associated with carbon
dioxide retention, graded doses of
supplemental oxygen administered via an
air entrainment (Venturi) mask increase
the patient’s PaO2 to acceptable level
Nasal Cannula
Supplemental oxygen can be administered
through a nasal cannula with minimal
patient discomfort.
A nasal cannula incorporates two prongs
that extend about 1 cm into the patient’s
nares and is held in place by an adjustable
elastic head strap
Inspired oxygen concentrations achieved
with nasal cannula depends on:
1. The flow rate of oxygen through the flow
meter (L/min)
2. Patient’s tidal volume
3. breathing frequency
4. Volume of nasopharynx
Oxygen flow rate 6L/min gives inhaled oxygen
concentrations about 44%
Excessive flow rates of oxygen may result in air
swallowing and gastric distension without
increasing inhaled oxygen concentration
Mouth breathing does not decrease the
effectiveness of oxygen therapy delivered by
nasal cannula because inspiratory airflow
through the posterior pharynx entrains oxygen
from the nose
Face Mask
Face masks used for oxygen therapy are
categorised as:
• Simple
• Partial rebreathing
• Nonrebreathing
• Air-entrainment
Simple Face mask
• It does not include a valve or oxygen
reservoir bag
• can provide inhaled concentration of
oxygen between 35% and 50% with O2
flow rate of 5-8 L/min
• Provides little advantage over nasal
cannula in term of delivering constant
inhaled concentrations of oxygen
Partial Rebreathing
Its valveless system that includes an O2
resrvoir bag
With O2 flow10L/min the inhaled
concentration of oxygen are between 5060%
Non rebreathing
It includes a unidirectional valve plus an
oxygen reservoir bag
Inhaled concentration of O2 can reach 100%
if the mask was fixed tight on the patient
face to completely eliminate entrainment
of room air
The flow rate of oxygen into this system
should be sufficient to maintain an inflated
reservoir bag
Air-Entrainment (Ventimask)
Venturi Face mask
It employs the Bernolli principle to entrain large
volumes of room air to mix with oxygen flowing
through an injector the resultant mixture of
gases produces stable inhaled concentrations of
oxygen(24-50%) depending on the bore of the
O2 injector
The high flow of gas into the face mask result in
constant inhaled concentrations of O2 despite of
changes in the patient ventilation