Airway Evaluation and ManagementKey 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 life-threatening 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 musculartube forming the common upper pathway of alimentaryand respiratory tracts. It extends from the base of the skullto the level of C6. The pharynx lies posterior to, and communicates with,the nose, mouth and larynx. This relationshipdivides the pharynx into three sections: naso-, oro andLaryngo pharynx. The posterior surface of the pharynxlies 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 theepiglottis 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 cricoidcartilage (C6) to terminate at its bifurcation into the twomain bronchi at the sternal angle (T4). The length of theadult trachea varies between 10 and 15 cm. The walls ofthe trachea are formed of fibrous tissue reinforced by 15–20 incomplete cartilaginous rings. Internally the tracheais lined by respiratory epithelium. The trachea may bedivided into two portions, that in the neck and that in thethorax.

Bronchial tree

Extrapulmonary bronchiAt the carina, the two main bronchi arise. The rightmain bronchus is shorter, wider and more upright thanthe left. The right pulmonary artery and azygos vein areintimately related to the right main bronchus. The leftmain bronchus passes under the aortic arch anterior tothe oesophagus, thoracic duct and descending aorta. Thestructure of the extrapulmonary bronchi is very similar tothat of the trachea.Intrapulmonary bronchiBranching of the intrapulmonary bronchi gives rise tofunctional 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. Cervical spine mobility

2. Temporomandibular mobility

3. Prominent central incisors

4. Diseased or artificial teeth

5. Ability to visualize uvula

6. 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• 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

• 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-------------

Non reassuring finding Relatively long Prominent “overbite” (maxillary incisors

anterior to mandibular incisors) Patient’s mandibular incisors anterior

to (in front of) maxillary incisor

<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 airway2. Prevent inhalation (aspiration of gastric

content) 3. Need for frequent suctioning4. Facilitate Positive pressure ventilation 5. Operative position other than supine6. Operative site near or involved the upper

airway7. Airway maintenance by mask difficult8. Disease involving the upper airway

Complications of tracheal intubation

• During direct laryngoscopy and intubation of the trachea:

1. Dental and oral soft tissue trauma

2. Hypertension and tachycardia

3. Cardiac dysrhythmias

4. Myocardial ischemia

5. Inhalation (aspiration) of gastric contents

•While the tracheal tube is in place

1. Tracheal tube obstruction2. Endobrochial intubation3. Esophageal intubation4. Tracheal tube cough leak5. Barotrauma6. Nasogastric distention7. Accidental disconnection from breathing

system8. Tracheal mucosa ischemia9. Accidental extubation

•Immediate and delayed complications after extubation of the trachea

1. Laryngospasm2. Inhalation of gastric content3. Pharyngitis (sore throat)4. Laryngitis5. Laryngeal or subglottic edema6. Laryngeal ulceration with or without granuloma

formation7. Tracheitis8. Tracheal stenosis9. Vocal cord paralysis10. Arytenoid cartilage dislocation

Nasotracheal intubation

an endotracheal tube is passed through the nose and vocal apparatus into the trachea.

Indications:1. Intra-oral surgery2. 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. More stable tube fixation

2. Less chance for tube kinking

3. Greater comfort in awake patient

4. Fewer oropharyngeal section

Complications unique to Nasotracheal intubation

1. Epistaxis2. Dislodgement of pharyngeal tonsils

(adenoid)3. Eustachian tube obstruction 4. Maxillary sinusitis5. Bacteremia6. Gastric distension

Flexible Fiberoptic Brochoscope

• Indications:

1. Difficult laryngoscopy/mask ventilation

2. Unstable cervical spines

3. Poor cervical range of motion

4. TMJ dysfunction

5. 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 50-60%

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