Airway
Management
Introduction
Expertise in airway management is important
in every medical specialty. Maintaining a patent airway is a vital aspect of
providing adequate oxygenation and ventilation. Failure to do so for even a
brief period can be disastrous. In fact, excluding dental damage, the single
largest category of anesthetic-related injury is respiratory events. The three
main causes of respiratory-related injury are inadequate ventilation, esophageal
intubation, and difficult tracheal intubation. Other adverse respiratory events
are much less common causes of injury.
Adverse
Respiratory Events
Complications
Difficult tracheal intubation accounts for 17% of the
respiratory-related injury and results in significant cost morbidity and
mortality. In fact, up to 28% of all deaths associated with anesthesia are due
to the inability to mask ventilate or intubate.
Other complications of difficult tracheal intubation
include the following:
1.
Laceration of soft
tissues.
2.
Laryngospasm.
3.
Vocal cord
paralysis.
4.
Dislocation of the
arytenoid cartilages or mandible.
5.
Perforation of the
trachea or the esophagus.
6.
Endobronchial or
esophageal intubation.
7.
Dental
damage.
8.
Hemorrhage.
9.
Aspiration of gastric
contents or foreign bodies.
10.
Increased intracranial
or intraocular pressure.
11.
Hypoxemia,
hypercarbia.
12.
Fracture or dislocation
of the cervical spine.
13.
Spinal cord
damage.
14.
Trauma to the eyes.
Summary
Adverse reflexes are responsible for the
ultimate demise of the patient. These reflexes include laryngovagal
(bronchospasm, apnea, arrhythmias, hypotension), laryngosympathetic
(tachycardia, tachyarrhythmias, or hypertension), and laryngospinal (bucking,
coughing, or vomiting).
In addition to the cost of treating airway
complications, litigation is expensive. The average settlement payment for
adverse respiratory events equaled $200,000, with a range from $1,000 to
$6,000,000. Settlement claims for injury due to difficult tracheal intubation
averaged $76,000.
The frequency of inability to ventilate and
intubate has been estimated at 0.01 to 2.0 per 10,000 anesthetics. The higher
incidence occurs primarily in obstetrical patients and the obese
patients.
In summary, airway problems result in
significant morbidity, mortality, and cost. By identifying which patient will
have a difficult airway, having a well-thought-out management plan and disaster
back-up plan, and by developing and improving our technical skills, we may
improve the quality of care administered.
Pathological
Conditions
Variations in "normal" anatomy and
characteristic airway anatomy resulting from pathological conditions can result
in problems despite proper positioning and equipment. A small mouth opening,
protruding upper teeth, a large tongue, immobility of the head, neck, and jaw
all may result in airway difficulty as may the following
conditions.
Conditions that predispose to a difficult
airway include:
|
epiglottitis, abscesses,
croup, bronchitis, pneumonia. | |
|
maxillofacial trauma,
cervical spine injury, laryngeal injury. | |
|
morbid obesity, diabetes
mellitus, acromegaly. | |
|
| |
|
ankylosing spondylitis,
rheumatoid arthritis. | |
|
upper and lower airway
tumors. | |
|
choanal atresia,
tracheomalacia, cleft palate, Pierre Robin syndrome, Treacher Collins
syndrome, Hallermann-Streiff syndrome. | |
|
pregnancy. |
Avoiding Airway
Problems
An airway may be difficult to manage either with mask
ventilation, endotracheal intubation or both. When you are unable to mask
ventilate with or without upper airway devices or with an external jaw thrust,
or when he or she is unable to intubate the trachea utilizing direct
laryngoscopy an airway is said to be difficult. The airway that is difficult to
mask ventilate may not necessarily be difficult to intubate and vice versa. The
two are not synonymous. Additionally, the degree of airway difficulty is
somewhat operator- and equipment-dependent, and ranges along a continuum from
easy to impossible.
Intubation difficulty may result from or be due
to:
- Incorrect position of the
patient.
- Inadequate or improper equipment.
- Unusual or abnormal anatomy.
- Pathologic causes.
Sniffing
Position
The patient should be supine in the sniffing position
with the neck slightly to moderately flexed on to the chest, and extended at the
atlantooccipital joint. This brings the oral, pharyngeal, and laryngeal axes
into alignment. Elevation of the head about 10 cm with pads under the occiput
and with the shoulders remaining on the table aligns the laryngeal and
pharyngeal axes. In this position, less of the tongue obstructs the laryngeal
view and the shortest distance and straightest line is created from the incisor
teeth to the laryngeal aperture. Firm forward traction on the laryngoscope and
firm backward pressure on the hyoid bone allow an optimum
view.
Sniffing
Position
Laryngoscopic View
Grades
Laryngoscopic view may be clasified into four
grades:
Grade I = visualization of the entire laryngeal
aperture.
Grade II = visualization of just the posterior
portion of the laryngeal aperture.
Grade III = visualization of only the
epiglottis.
Grade IV = visualization of just the soft palate
only, not even the epiglottis is visible.
Grade II or III laryngoscopic views are relatively
common and occur in 1 to 18% of surgical patients. The Grade III view occurs in
about 1-4% of patients. A severe grade III or grade IV view with failed
endotracheal intubation occurs 0.05 of 0.35% of patients.
Laryngoscopic
View Grades
Mask
Ventilation
A good mask fit is essential for assisted or
controlled mask ventilation. With a poor mask fit, you must maintain steady
pressure holding the mask to the face which leads to fatigue of the hand and
arms. In addition, the reservoir bag will not be an adequate reservoir, making
it difficult to achieve adequate positive pressure for assisted or controlled
ventilation. The best size mask is the smallest mask that will accomplish the
job. This will cause the least increase in dead space and be easier to hold.
Caution should be used in patients with thick beards. The oropharyngeal airway
or nasopharyngeal airway may relieve upper airway obstruction by lifting the
epiglottis and posterior tongue off the posterior pharyngeal wall. An
oropharyngeal airway that is too small may actually push the tongue back causing
airway obstruction.
Nasal
and Oral Airways
Description: Numerous devices that assist in
maintaining patency of the upper airway. May allow ventilation by mask of a
patient that you are initially unable to ventilate. Some of the devices allow
passage of small fiberoptic laryngoscopes, flexible stylets, or wire guides.
Some of the devices facilitate passage of fiberoptic bronchoscopes into the
larynx.
Advantages: Generally allow rapid, easy
placement in most patients.
Disadvantages: Depend on mask ventilation.
May not be successful.
Examples of Use: Adjunct to mask ventilation
or other technique of airway management.
Nasal
and Oral Airways
Esophageal
Airways
Esophageal Obturator, Combitube
Description: Allow positive pressure ventilation by
blocking the esophagus with a large balloon cuff. Air is forced through the
larynx from the pharynx. The Combitube has two cuffs to improve
ventilation.
Advantages: Easy to place. Do not require
laryngoscopy.
Disadvantages: Improper placement can obstruct the
airway or heighten the risk of aspiration. Will not work in patients with
obstruction of the airway at or below the vocal cords.
Examples of use: Emergency airway management when
endotracheal intubation is not possible because of lack of skilled personnel or
possibly because of inability to visualize the airway.
Combitube
Intubation
The laryngoscope is the tool used for direct
laryngoscopy. The laryngoscope base should be held in the left hand and the
blade inserted into the right side of the patient's mouth. Special care must be
taken to avoid pinching the lips between the blade and the teeth. Next, the
blade is lifted upward and forward along the axis of the handle, lifting the
tongue and the epiglottis forward, exposing the vocal cords. During this lifting
process, one should be careful not to use the teeth as a fulcrum to lift the
epiglottis which can damage the teeth or may push the larynx upwards and out of
site. When a curved blade is used, the tip should be advanced to the vallecula,
where the base of the tongue and the base of the epiglottis meet. With a
straight blade, the tip of the blade is placed posterior to the
epiglottis.
In patients with short necks, pregnant patients,
patients with large breasts or with an increased A-P chest diameter, the
standard length laryngoscope handle may abut against the chest. A shorter handle
may facilitate placing the laryngoscope blade into the mouth. A "difficult"
laryngoscopic view may improve by using a different blade. For instance, a
straight blade may help improve the view in the patient with anterior vocal
cords or with a small mouth opening. The curved blade may be advantageous if
more room is needed for instrumentation (i.e., use of Magill forceps).
Ultimately, the best blade is probably the one with which you are most familiar
and most proficient.
Gentle external pressure on the thyroid cartilage may
push the glottis posteriorly and help bring anterior cords into view. The
endotracheal tube is inserted into the right side of the mouth, the tip passing
between the vocal cords, and depth adjusted appropriately.
Airway
Examination
Note factors that may make mask ventilation
difficult, such as the presence of a beard or
edentulousness.
Carefully assess mouth opening. An opening of at
least two large finger breadths between the upper and lower incisors in the
adult is desirable. The presence of loose teeth or protruding upper teeth, a
high-arched palate or a long narrow mouth, and temporomandibular joint problems
may predispose to difficulty with direct laryngoscopy.
The neck should be examined for masses, mobility, and
deviation of the trachea. The presence of a hoarse voice, stridor or previous
tracheostomy should alert the clinician to possible stenosis at some
level.
One should identify the location of the cricothyroid
membrane for possible use in unexpected airway loss. Determine if the patient is
able to assume the sniffing position in the awake state.
There are three specific tests which when used together have almost 100% reliability in predicting airway difficulty. These are the Mallampati test, the thyromental distance, and extension at the atlantooccipi
Mallampati
Classification
The Mallampati classification relates tongue size to
pharyngeal size. This test is performed with the patient in the sitting
position, the head held in a neutral position, the mouth wide open, and the
tongue protruding to the maximum. The subsequent classification is assigned
based upon the pharyngeal structures that are visible.
Class I = visualization of the soft palate, fauces,
uvula, anterior and posterior pillars.
Class II = visualization of the soft
palate, fauces and uvula.
Class III = visualization of the soft palate and
the base of the uvula.
Class IV = soft palate is not visible at
all.
The classification assigned by the clinician may vary
if the patient is in the supine position (instead of sitting). If the patients
phonates, this falsely improves the view. If the patient arches his or her
tongue, the uvula is falsely obscured. A class I view suggests ease of
intubation and correlates with a laryngoscopic view grade I 99 to 100% of the
time. Class IV view suggests a poor laryngoscopic view, grade III or IV 100% of
the time. Beware of the intermediate classes which may result in all degrees of
difficulty in laryngoscopic visualization.
Mallampati
Classification
Larynx
and Trachea
The rigid laryngeal structures are the hyoid
bone, thyroid cartilage, cricoid cartilage and arytenoid cartilage. Inferior to
the cricoid cartilage are tracheal cartilages. The cricoid cartilage is a
complete ring and is used to prevent passive reflux of stomach contents during
cricoesophageal occlusion pressure.
Many airway techniques involve
identification and puncture of the cricothyroid membrane. Palpate the thyroid
cartilage and move down to the space between the thyroid and cricoid cartilages
to identify the membrane. The thyroid cartilage is usually prominent in males.
In females the thyroid cartilage is less prominent. An alternative method is to
palpate the tracheal cartilages and move in a superior direction until the
cricoid and thyroid cartilages are appreciated.
Larynx and Trachea
Laryngeal
Cartilages
The Cricothyroid artery is a small branch of
the superior thyroid artery. It travels along the inferior border of the thyroid
cartilage and becomes smaller as it reaches the midline. Cricothyroid puncture
in the midline, inferior part of the membrane above the cricoid cartilage is
least likely to produce bleeding.
The thyroid gland is supplied by the large
superior and inferior thyroid arteries. The gland is highly vascular. A
pyramidal lobe may extend to the hyoid bone. Puncture below the cricoid
cartilage has increased risk of bleeding. Palpate the puncture site carefully
and avoid any masses.
Laryngeal
Cartilages
Laryngoscopic
View
View during laryngoscopy is variable. Under
ideal circumstances the epiglottis, arytenoid cartilages and nearly the entire
vocal cords will be visible.
Laryngoscopic
View
Airway
Illustration
Airway
Illustration
Local
Anesthesia of the Airway
Local anesthesia of the airway can minimize
discomfort during awake intubation. Awake intubation is desirable in many cases
of anticipated difficult intubation. Airway muscle tone and patency are
preserved and spontaneous ventilation continues. Risk of aspiration is
minimized. If the intubation attempt fails, the patient can still breathe.
Adequate patient preparation is critical to
the success of awake intubation. Inadequate preparation will lead to an
uncomfortable patient and great difficulty with the intubation. The best results
require time. You should set aside at least a half an hour to produce the
desired effect.
Use caution with sedation during awake
intubation. Sedation can help the patient tolerate the local anesthetic and
intubation technique, but sedation may diminish spontaneous respiration, airway
muscle tone and patency and protection from aspiration. Discussion of the local
anesthesia and intubation techniques with the patient is important to reduce
patient anxiety and help secure cooperation.
Topical
Anesthesia
Sensation from the nasal mucosa and
nasopharynx are supplied by branches of the trigeminal nerve. Sensation from the
oral mucosa and oropharynx are supplied by branches of the glossopharyngeal
nerve.
Topical anesthesia of the mouth and
oropharynx may be accomplished with topical sprays such as cetacaine spray and
10 % lidocaine spray. Local anesthetics are absorbed through the mucosa. These
sprays take several minutes to provide anesthesia and may be applied repeatedly
for best effect.
Secretions can dilute and wash away local
anesthetic for topical anesthesia. Antisialagogues can improve the effectiveness
of topical agents. Glycopyrrolate is a good antisialagogue that causes minimal
tachycardia.
Direct spray of topical local anesthetics to
the nose can be uncomfortable. Topical anesthesia of the nose and nasopharynx
may be accomplished by directing the patient to inhale nebulized local
anesthetic. 4 ml of 4% lidocaine may be used.
Topical
Agents
Airway
Cart
Airway emergencies require quick action to
avoid patient injury. A difficult airway cart stocked with critical supplies and
kept in a known, convenient location can save valuable time during an emergency.
A difficult airway cart can provide an obvious location for infrequently used
items and can support a variety of techniques.
Difficult
Airway Cart
Confirmation of
Tracheal Intubation
It is critical to confirm correct placement of the
endotracheal tube after an intubation attempt. The most reliable method for
determination of tube placement is direct vision of the endotracheal tube
through the vocal cords. When direct vision is not possible, tube position may
be confirmed by passing a fiberoptic bronchoscope down the endotracheal tube.
The carina is an easily recognized landmark.
The presence of exhaled CO2 suggests that the
endotracheal tube is somewhere in the airway. The mouth, nose, pharynx and
larynx are part of the airway. CO2 in the stomach from carbonated beverages or
airway gasses put there during mask ventilation is less prominent than
respiratory CO2 and tends to diminish with each breath.
A-P and lateral fluoroscopy can indicate endotracheal
tube position.
Other methods are less reliable. Breath sounds can be
difficult to diagnose especially with aspiration, pneumonia or chronic
obstructive pulmonary disease. Breath sounds can indicate endobronchial
placement of the endotracheal tube. Palpation of the anterior neck during
passage of the endotracheal tube, condensation inside the tube, and light
visible through the skin of the anterior neck are less reliable
signs.
You should combine several observations to make the
diagnosis of endotracheal tube position, including a C02
detector.