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Miller: Miller's Anesthesia, 7th ed.

Copyright 2009 Churchill Livingstone, An Imprint of Elsevier

50 Airway Management in the Adult

John Henderson

Key Points

1. Three basic decisions needed before induction of anesthesia in every patient are whether to use

awake intubation, use a percutaneous technique, or maintain spontaneous ventilation.

2. Conditions requiring particular caution include lesions at the base of the tongue, recent onset of

hoarseness, upper airway obstruction, and obstructive sleep apnea.

3. The combination of mouth opening, jaw protrusion, and head extension is the core of airway

assessment. The examination described by El-Ganzouri (mouth opening, prognathic ability, head

extension, thyromental distance, and the Mallampati test) has been used with minor modification by

others. It can be performed rapidly and is the most quantifiable (recording of actual values is

recommended) of the tests included in the guidelines of the American Society of Anesthesiologists

(ASA).

4. Radiology studies have shown that head extension is the most important single maneuver in

maintaining space between the pharyngeal soft tissues. Head extension stretches the anterior neck

structures and moves the hyoid bone and attached structures anteriorly.

5. Four principles are central to prevention of complications during tracheal intubation:

Maintenance of oxygenation must take priority over all other issues. Preoxygenation should

be performed before induction of anesthesia. Mask ventilation should be used between

attempts at tracheal intubation.

Trauma must be prevented. The first attempt at tracheal intubation should be performed

under optimal conditions, including patient position, preoxygenation, and equipment

preparation. The number of attempts with blind techniques should ideally be zero and

certainly not more than four.

Anesthesiologists should have a sequence of backup plans in place before starting the

primary technique. They should have the skills and the equipment needed to execute these

plans. When unanticipated difficulty occurs in non-lifesaving surgery, the safest plan is to

terminate attempts at tracheal intubation, awaken the patient, and postpone surgery.

Anesthesiologist should seek the best help available (call for help) as soon as difficulty

with tracheal intubation is experienced.

6. Immediate confirmation of correct tracheal tube placement is an essential and integral part of

tracheal intubation. Several tests should be used because no single test is completely reliable. The

most important safeguard is clinical suspicion. Visual confirmation of passage of the tracheal tube

between the vocal cords is reliable, but not always possible, and experienced anesthesiologists are

occasionally misled.

7. All anesthesiologists should be skilled in at least one alternative technique of tracheal intubation

under vision. Strategies that include algorithms for the management of unanticipated difficult

intubation have been devised by several organizations, including the ASA and the Difficult Airway

Society, a U.K. organization. The ASA algorithm is the standard guide.

8. If noninvasive techniques do not restore oxygenation, cricothyrotomy is the percutaneous airway of choice because tracheotomy may take too long. It is not possible to define the SpO2 at which

cricothyrotomy should be performedit depends on the degree of hypoxemia and how rapidly it is

deteriorating.

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Anesthesia was developed to enable the performance of therapeutic and diagnostic procedures that could

not be performed in conscious or sedated patients. The reduction in consciousness produced by general

anesthesia (or trauma or disease) is necessarily associated with depression of other physiologic systems.

The depressant effects on airway, respiratory, and cardiovascular function can cause immediate threats to

the patient. Airway management differs from management of other depressed function in that it requires a

range of manual skills, as well as knowledge and judgment.

Some components of anesthesia respiratory care have become safer in the last 3 decades. American Society

of Anesthesiologists (ASA) Closed Claims analyses show that nonspecific adverse respiratory system events

decreased from about 37% of respiratory claims in the 1970s to 14% of claims in the 1990s. However, the

proportions of claims attributable to difficult tracheal intubation has more than doubled. [1] The probable

explanation is that monitoring has reduced the number of adverse outcomes from nonspecific events but

prevention of adverse tracheal intubation outcomes is more difficult. Evidence of the limitations of traditional

techniques has accrued and effective new techniques have been developed. However, many

anesthesiologists continue to rely on multiple attempts with ineffective techniques.

Anatomy

The nose warms, filters, and humidifies incoming air and is the organ of smell. It consists of the external nose

and the internal nasal cavity. The nasal cavities are divided by the nasal septum, which is frequently deviated

with the consequence that the nasal cavities are narrowed or obstructed. The roof of the nasal cavity is the

cribriform plate, a thin bone that is easily fractured, thereby resulting in communication between the nasal

and intracranial cavities. The bony lateral wall of the nasal cavity is the origin of the three bony turbinates that

project into the nasal cavity. They are easily damaged by force during the passage of nasotracheal tubes.

Openings in the lateral wall communicate with the paranasal sinuses. Prolonged nasotracheal intubation

impairs drainage through these openings, causing sinusitis. The lining of the nasal cavity is very vascular,

and application of nasal vasoconstrictors to shrink the mucosa and dilate the airway reduces the risk of

hemorrhage during the insertion of airway devices or tracheal tubes.

The roof of the mouth is bounded by the alveolar arch and teeth and consists of the hard palate anteriorly and

the soft palate posteriorly. The tongue makes up most of the floor of the mouth, which is bounded by the

mandible and teeth. Nonencapsulated lymphoid tissue on the posterior surface of the tongue (lingual tonsil) is

part of the ring of Waldeyer. This tissue is important in that hypertrophy can cause serious difficulty in airway

management. [2] [3] The ability to achieve good mouth opening is important for many airway procedures. Initial

mouth opening is achieved by rotation within the temporomandibular joint (TMJ) and subsequent opening by

sliding (also known as protrusion, translocation, or subluxation) of the condyles of the mandible within the

TMJ. The jaw-thrust maneuver uses the sliding component of the TMJ to move the mandible and attached

structures anteriorly. The scissors maneuver ( Fig. 50-1 ) achieves maximum mouth opening by the

application of internal pressure on the teeth to achieve both TMJ movements. It can facilitate the insertion of

oropharyngeal airways, supraglottic airway devices (SADs), and laryngoscopes. All movements of the TMJ

should be firm but gentle to minimize the risk of joint damage.



The pharynx is a fibromuscular tube that extends from the base of the skull to the lower border of the cricoid

cartilage. It joins the nasal and oral cavities above with the larynx and esophagus below. Both the pharynx

and esophagus can be perforated by blind attempts at tracheal intubation. The nasopharynx is the part of the

pharynx that lies posterior to the nose. Nasotracheal tubes can impinge on the posterior wall of the

nasopharynx, and application of increasing force when resistance is met can cause submucosal passage of

the tube.

The larynx is situated at the upper end of the respiratory tract, where it extends from the epiglottis to the

lower end of the cricoid cartilage. It evolved as a valve to protect the lower respiratory tract from alimentary

contents and later developed into an organ of speech. The larynx bulges posteriorly into the laryngopharynx,

with the piriform fossa lying on each side. The larynx consists of a framework of articulating cartilage

connected by fascia, muscles, and ligaments. It is suspended from the hyoid bone by the thyrohyoid

membrane. The principal cartilages are the thyroid, cricoid, and posterior (arytenoid, corniculate, and

cuneiform) cartilage and the epiglottis. The cricoid cartilage is a complete ring that articulates with the thyroid

Figure 50-1 Scissors maneuver. The rotation and sliding components of the temporomandibular joint are used to achieve

maximal mouth opening.



and arytenoid cartilage. The arytenoid cartilage sits on the posterolateral border of the cricoid, from where it

can be dislocated [4] during airway management. The laryngeal inlet is bounded by the epiglottis, aryepiglottic

folds, posterior cartilage, and interarytenoid notch. The vocal cords run between the vocal processes of the

arytenoid cartilage and the posterior surface of the thyroid cartilage. The lower end of the leaf-shaped

epiglottis is attached to the middle of the posterior surface of the thyroid cartilage. The anterior surface is

connected to the hyoid bone by the hyoepiglottic ligament and to the tongue by the median glossoepiglottic

fold. The valleculae (often called vallecula) are depressions between the median and lateral glossoepiglottic

folds that connect the lateral edges of the epiglottis to the base of the tongue. The Macintosh technique of

laryngoscopy involves insertion of the tip of the laryngoscope into the vallecula, where it tensions the

hyoepiglottic ligament to achieve indirect elevation of the epiglottis.

During swallowing the larynx is protected by several mechanisms. The larynx is tucked up behind the tongue,

and the epiglottis diverts food away from the laryngeal inlet. The laryngeal muscles can be grouped according

to their actions on the vocal cords: abductors, adductors, and regulators of tension. Motor innervation to

these muscles and the sensory innervation of the larynx are supplied by two branches of the vagus nerve: the

superior and recurrent laryngeal nerves. The superior laryngeal nerve can be anesthetized at the point where

it passes through the thyrohyoid membrane. The recurrent laryngeal nerve can be damaged during surgery

on the thyroid gland or by pressure from a cuff that lies just below the vocal cords. [5]

The cricothyroid membrane joins the thyroid with the adjacent cricoid cartilage. It is close to the skin,

relatively avascular, and the widest gap between the cartilage of the larynx and trachea, so it provides the

best access for percutaneous airway rescue techniques. It is normally easy to palpate, but identification may

not be possible in obese patients. In patients with fixed neck flexion, the cricothyroid membrane may lie

behind the sternum.

The trachea extends from the lower edge of the cricoid cartilage to the carina. It consists of U-shaped

cartilage joined by fibroelastic tissue and is closed posteriorly by the longitudinal trachealis muscle. The

tracheal rings and trachealis muscle are responsible for the characteristic endoscopic appearance of the

trachea.

Airway Assessment

Three basic decisions ( Fig. 50-2 ) needed before induction of anesthesia in every patient [6] are whether



These three strategies are safer than the use of an intravenous anesthetic with neuromuscular blocking drugs

(NMBDs) in patients with potential airway difficulty, but they require more time and effort, and the

anesthesiologist needs evidence on which to base these decisions. The purpose of airway assessment is to

identify possible difficulty with direct laryngoscopy (and hence tracheal intubation), mask ventilation, or

creation of a surgical (percutaneous) airway. This traditional approach may change with the introduction of

Figure 50-2 American Society of Anesthesiologists Difficult Airway Algorithm. (From American Society of Anesthesiologists

Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway. An updated report

by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 98:1269-1277,

2003.)

To use awake endotracheal intubation

To use a percutaneous technique

To maintain spontaneous ventilation



sugammadex, an antagonist to replace neostigmine, into routine clinical practice (see Chapter 29 ).

Rocuronium could be used to facilitate endotracheal intubation. If spontaneous ventilation is urgently needed,

sugammadex can reverse profound neuromuscular blockade (i.e., no response to peripheral nerve

stimulation) within 1.5 to 3.0 minutes.

Potential difficulty may be obvious in patients with anatomic or pathologic abnormalities, and further tests are

not needed. Conditions requiring particular caution include lesions at the base of the tongue, recent onset of

hoarseness, upper airway obstruction, and obstructive sleep apnea. However, the challenge is to detect

potential difficulty in apparently normal patients. Airway assessment includes taking a history and performing

a physical examination. Imaging is valuable in assessing a pathologic airway but is not practicable for routine

assessment.

The history includes review of available previous anesthesia records, direct questioning of the patient, and in

those with reduced consciousness, a search for communication about previous airway difficulty. A history of

previous airway difficulty has a higher positive predictive value and lower negative predictive value than any

tests. [7] However, a history of previous easy laryngoscopy does not guarantee straightforward intubation

inasmuch as increased age or pathology may result in increased difficulty.

Airway tests to detect difficulty with direct laryngoscopy are based on anatomic features, and values have

been selected as probable indicators of difficulty. The combination of mouth opening, jaw protrusion, and

head extension is the core of airway assessment. [8] There is little interobserver variation in the assessment

of mouth opening and jaw protrusion. [9] Mouth opening is measured as the interincisor distance, and a value

of 4 cm (2 fingerbreadths) has been proposed as an indicator of probable difficult intubation. [10] The

prognathic ability of the mandible depends on the size and shape of the mandible in relation to the maxilla

and on TMJ function. Prognathic inability of the mandible (the mandibular incisors cannot be brought in line

with the maxillary incisors) is associated with difficult intubation. Limited head (more accurately described as

occipito-atlanto-axial) extension [10] impairs direct laryngoscopy. It can be measured as the angle between

the occlusal surface of the maxillary teeth and the horizontal, with angles of less than 20 degrees suggesting

difficult laryngoscopy. However, it is difficult to prevent extension of the midcervical vertebrae, so true head

extension is frequently overestimated. The Mallampati test (visibility of pharyngeal structures) is of limited

value on its own [11] but can be combined with an assessment of dentition. [12] The thyromental distance is of

limited value as a predictor of difficult laryngoscopy, [13] but examination ensures that the laryngeal cartilage

is palpated and submandibular compliance assessed. Evaluation of dentition is important in that caries or

periodontitis increases the risk for dental damage. Some dental patterns, such as protruding or single or

missing maxillary incisors, [14] increase the difficulty of direct laryngoscopy. The examination described by El-

Ganzouri and colleagues [7] (assessment of mouth opening, prognathic ability, head extension, thyromental

distance, and Mallampati test) has been used with minor modification by others. [3] It can be performed

rapidly and contains the most quantifiable (recording of actual values is recommended) of the tests included

in the ASA guidelines. [6]

Ventilation via mask requires the ability to achieve a seal between the mask and face and to overcome upper

airway obstruction. Limited mandibular protrusion, abnormal neck anatomy, sleep apnea, snoring, and

obesity are independent predictors of moderate or severe difficulty with mask ventilation. Snoring and a

thyromental distance of less than 6 cm are independent predictors of severe difficulty. [15] No test can

accurately predict complete failure of mask ventilation because its prevalence is as low as 0.07%. [7] Some

pathologic causes of difficult mask ventilation cannot be predicted. [2]

Creation of a surgical airway (necessary for the management of a cannot intubate, cannot ventilate

situation) depends on percutaneous access to the cricothyroid membrane. In some patients the cricothyroid

membrane cannot be identified or lies behind the sternum, and creation of a percutaneous airway will not be

possible. In such patients who have indications that laryngoscopy or mask ventilation will be difficult, the

safest strategy is to secure the airway while the patient is conscious.

Integration of the evidence of difficulty with direct laryngoscopy, mask ventilation, and creation of a surgical

airway has many limitations. The causes of difficult laryngoscopy are multifactorial, and single tests have

limited value [11] as predictors. Prediction is improved by combining the results of different tests. [8] Scores [7]

[8] are formulas that combine the results of tests. These scores have been developed to improve prediction of

difficulty but many omit at least one test of some value, and the indicators are not usually weighted for



importance. It is more meaningful to describe the result of individual tests. Airway assessment cannot detect

some serious problems, including asymptomatic lesions [2] [3] in the vicinity of the larynx, skeletal factors, and

some varieties of TMJ dysfunction.

The problem with airway assessment is that the risk of difficulty is overestimated and not all cases of difficult

airway management can be predicted. However, serious airway morbidity, though infrequent, is a much

worse outcome than performing an awake intubation that might not have been necessary. Airway evaluation

gives some indication of potential difficulty and should always be performed. [6] The anesthesiologist must

then make a judgment of whether direct laryngoscopy, mask ventilation, and percutaneous rescue are likely

to be successful. The limitations of airway assessment mean that preparation of an airway strategy for the

management of unanticipated difficulty is the ultimate key to safe practice. Strategies are discussed later in

the section Challenging Airway Management Scenarios.

Physiology and Pathophysiology of the Upper Airway

Upper Airway Obstruction

In an awake patient, airway patency is maintained by muscle tone in the head and neck, particularly the

pharynx and tongue. As consciousness is lost and muscle tone is reduced, tissues fall backward under the

influence of gravity in a supine patient and can obstruct the upper airway. The order of importance of these

obstructing tissues is the soft palate (velopharynx), epiglottis, and tongue. Head extension (as a

consequence of tensioning the strap muscles) and jaw thrust move the hyoid bone and attached structures

anteriorly and relieve airway obstruction to a variable extent. Jaw thrust is also effective in reducing

obstruction at the velopharynx in slim but not in obese patients. The lateral position can be used alternatively

or in addition to the aforementioned techniques to allow the obstructing tissues to move downward so that

obstruction is reduced. [16]

There is now evidence of an additional dynamic component of upper airway obstruction when consciousness

is reduced. In the conscious state the tone of the pharyngeal muscles is increased by neural discharge just

before phrenic nerve discharge. Loss of pharyngeal tone and collapse of the narrow velopharynx play an

important role in upper airway obstruction during spontaneous ventilation in an anesthetized patient. [17] The

airway in the nose and nasopharynx is held open by bone and cartilage and in the larynx and trachea by

cartilage. Dynamic collapse of the intervening pharynx can occur when muscle tone is reduced. The structure

of a collapsible segment between two rigid tubes corresponds to the basic elements of a Starling resistor in

that flow can depend on the intraluminal pressure gradient or on transmural pressure in the collapsible area.[17] Flow through the collapsible segment depends on how the intraluminal pressure upstream and

downstream relate to the tissue pressure around the pharynx. Factors that narrow the pharynx, increase

pressure around it, reduce pressure within it, or make its walls more compliant will increase upper airway

obstruction. The therapeutic consequence of dynamic collapse is that nasal continuous positive airway

pressure (CPAP) reduces dynamic upper airway obstruction. Nasopharyngeal airways might reduce this

dynamic airway obstruction.

Laryngospasm

Laryngospasm (reflex closure of the true vocal cords alone or with the false cords because of stimulation of

the intrinsic laryngeal muscles) can result from the combination of reflex hyperactivity at an intermediate

depth of anesthesia and noxious distant surgical or local stimuli. Laryngospasm is usually maintained well

beyond the duration of the stimulus. It is responsible for a significant proportion of postoperative critical

events. Morbidity and mortality may result from the immediate (hypoxemia and hypercapnia) and delayed

(negative-pressure pulmonary edema) consequences of laryngospasm, and thus every effort should be

made to rapidly relieve the airway obstruction caused by laryngospasm. [18] Management is discussed later.

Negative-pressure pulmonary edema [18] is a consequence of forceful inspiratory effort in the presence of a

closed glottis or other cause of upper airway obstruction. The subatmospheric alveolar pressure generated

promotes transudation of fluid from pulmonary capillaries into the interstitial space and alveoli. Small vessel

damage may be responsible for frank hemorrhage into alveoli. Management consists of relief of the

obstruction, oxygen therapy, and standard management of pulmonary edema. Most cases resolve rapidly,

but reintubation and positive-pressure ventilation are sometimes required.



Oxygenation and Preoxygenation

Hypoxemia can occur in the time between induction of anesthesia and attainment of airway security and is

particularly likely if airway management proves difficult. It makes sense to maximize oxygen stores before

induction to prolong the period before the onset of hypoxemia in the event of serious difficulty with airway

management. The principal oxygen stores are in the lungs. These stores can be increased by using a

maneuver called preoxygenation (also know as denitrogenation), which is achieved by having the patient

breath 100% oxygen from a close-fitting facemask before induction of anesthesia. Several techniques of

preoxygenation have been described, and the most effective technique should be used. Deep breathing with

a high fresh gas flow for 1.5 minutes and tidal breathing for 3 minutes are equally effective. It is particularly

important to avoid leaks in the circuit, which are indicated by a flaccid reservoir bag and absence of a normal

capnograph waveform. Wherever possible, the end-tidal oxygen concentration should be used as a guide to

the adequacy of preoxygenation, with a value of 90% being well accepted. Preoxygenation in the semi-sitting

position prolongs the time to development of hypoxemia by increasing functional residual capacity in relation

to the supine position, particularly in an obese patient. [19] Use of positive end-expiratory pressure (PEEP)

during induction may further improve oxygenation. [20]

Pharmacology of Airway Management

The choice of pharmacologic technique is part of the essential planning of airway management and will be

influenced by both airway and surgical requirements, particularly for surgical access and neuromuscular

blockade. Satisfactory conditions for tracheal intubation are particularly demanding and may be facilitated by

several pharmacologic techniques, each of which has advantages and disadvantages. Direct laryngoscopy is

facilitated by a reduction in tone of the head and neck muscles. A high success rate and low risk for laryngeal

trauma are facilitated when the vocal cords are open and nonreactive, at the cost of reduced protection

against pulmonary aspiration.

Inhaled Induction of Anesthesia

Induction plus maintenance of anesthesia by the inhalation of gaseous and volatile anesthetics was the

original pharmacologic technique for anesthesia. It remains an important technique in situations such as lack

of venous access and anticipated airway difficulty in a patient who refuses awake techniques. A major

advantage of inhaled induction of anesthesia is that spontaneous ventilation is maintained while changes in

the depth of anesthesia and associated respiratory and cardiovascular effects occur gradually. Good

facemask technical skills are essential to prevent airway obstruction and leaks around the mask.

Deep anesthesia is necessary for direct laryngoscopy and tracheal intubation with inhaled anesthetics alone.

It can be complicated by hypotension, hypoventilation, and airway obstruction. A depth of anesthesia that

allows controlled ventilation has been recommended when sevoflurane is used. Prior administration of topical

anesthesia (e.g., 4% lidocaine, 3 to 5 mL) can facilitate tracheal intubation under lighter inhaled anesthesia.

Sevoflurane has advantages over other volatile anesthetics for inhaled induction of anesthesia. It has a low

blood-gas partition coefficient and causes minimal airway irritation, which facilitates rapid smooth attainment

of a depth of anesthesia sufficient for airway procedures. A rapid technique (single breath) in which the

patient breathes 8% sevoflurane from a prefilled anesthesia circuit has been advocated rarely but causes

apnea more frequently than the traditional technique does. Furthermore, seizure activity with sevoflurane is

more likely with rapid induction of anesthesia. [21]

Inhaled induction of anesthesia is very useful in a wide variety of difficult airway conditions. Its use has been

advocated in patients with stridor but can result in sudden airway obstruction, which prevents rapid reduction

of the depth of anesthesia. Relief of obstruction may be difficult or impossible, even when CPAP is used with

mask ventilation, so emergency cricothyrotomy may be required. Propofol infusion, with topical anesthesia

before endotracheal intubation, has been used successfully for the management of patients with a difficult

airway. [22] Caution is required because apnea can occur when propofol is infused in patients with normal

airways.

Intravenous Anesthesia with Neuromuscular Blocking Drugs



The combination of an intravenous anesthetic with an NMDB is the pharmacologic technique most frequently

used for tracheal intubation in routine practice (see Chapter 29 ). It provides good conditions rapidly in most

patients inasmuch as neuromuscular blockade facilitates laryngoscopy, opens the vocal cords, and prevents

coughing. The high quality of intubating conditions produced by NMBDs reduces the risk for postintubation

laryngeal damage. [23] However, the apnea caused by this pharmacologic approach has disadvantages. If

tracheal intubation of an apneic patient proves impossible, oxygenation requires effective ventilation with a

facemask or SAD, neither of which is completely reliable. Pharmacologic techniques that produce apnea

should not be used when difficulty with tracheal intubation or mask ventilation is predicted. As indicated

previously, the use of sugammadex may alter the approaches to difficult intubation.

In routine practice, nondepolarizing NMBDs are often preferable to succinylcholine to prevent its side effects

(as described in Chapter 29 ). Succinylcholine is chosen when rapid onset and offset are important. Use of

rocuronium as an alternative to succinylcholine has been suggested to avoid the side effects unique to

succinylcholine. Although the duration of paralysis produced by rocuronium is very much longer, the use of

sugammadex as a reversal agent makes recovery from an NMBD as quick as that from succinylcholine and

more predictable. It is now clear that a combination of rocuronium and sugammadex can restore

spontaneous ventilation more rapidly than waiting for succinylcholine to wear off. Possibly the need for

succinylcholine may disappear completely.

Intravenous Anesthesia with Narcotics

The use of short-acting narcotics instead of NMBDs to facilitate tracheal intubation has been advocated as a

means of avoiding the side effects of succinylcholine. This technique is effective in many patients who have

no risk factors for difficult intubation. However, it has serious disadvantages. [24] Conditions for direct

laryngoscopy and tracheal intubation are worse than when NMBDs are used, so there is a higher frequency

of failed intubation and airway trauma. Arterial hypotension is more likely when large doses of intravenous

anesthetics and narcotics are given. [24] A higher incidence of laryngeal trauma when intubation is performed

without NMBDs has been reported. [23] Use of a large dose of narcotics when ventilation with a facemask or

SAD is intended has other significant disadvantages. It may produce apnea and delay the return of

spontaneous ventilation. More importantly, it can make ventilation of the lungs with a mask or SAD difficult or

impossible as a consequence of vocal cord closure, a problem sometimes attributed to chest wall

rigidity. [25] The combination of intravenous anesthesia with topical anesthesia of the larynx produces good

conditions [26] and may be a better alternative to the use of NMBDs.

Local Anesthetic and Awake Techniques of Airway Management

Tracheal intubation of a conscious patient can allow uninterrupted respiration and airway protection while

avoiding the risk to airway maintenance and protection inherent with general anesthesia. It is indicated when

there is a possibility of difficulty with airway management. Tracheal intubation of a conscious patient is often

called awake intubation. Good topical airway anesthesia, rapport, and gentleness are the keys to success.

Sedation is often used but cannot compensate for inadequate topical anesthesia and is dangerous in patients

with a critical airway. [27]

Topical anesthesia of the airway can be used to facilitate the performance of many airway procedures ( Box

50-1 ) in a conscious patient in whom reduced consciousness is likely to cause difficulty in airway

management. Direct laryngoscopy has long been used for awake intubation but is often difficult and can be

distressing for all involved. Use of a flexible fiberoptic laryngoscope (FFL) for tracheal intubation under topical

anesthesia was a milestone in safe airway management because intubation of a conscious patient could now

be achieved with minimal discomfort. This technique has become the standard for management of an

anticipated difficult airway. Options are preserved if awake flexible fiberoptic intubation is not successful:

surgery can be postponed and the patient awakened, an unhurried surgical airway can be performed, or

tracheal intubation can be attempted in a breathing patient (awake or inhaled induction) with other visual

techniques.

Box 50-1



Topical anesthesia reduces the caliber of a normal airway. Use of topical anesthesia in a patient with a

compromised airway can lead to loss of the airway and should be performed only by experts who have a

team prepared for immediate creation of a surgical airway.

Lidocaine has a better safety profile than other agents used for airway anesthesia. However, excessive doses

can cause fatal toxicity. Administration should be titrated and the mental state of the patient monitored. Blood

concentrations are influenced by the technique chosen, and aerosol delivery to the lower respiratory tract

should be minimized.

Several techniques of airway anesthesia are shown in Box 50-2 . Each has advantages and disadvantages.

Nebulizers have been used to deliver topical anesthesia to the airway. The optimum particle size is larger

than that required for the treatment of asthma. Simple aerosol techniques, such as injection into oxygen

flowing in a narrow tube, appear to work satisfactorily. Most of the inhaled solution is exhaled, and up to 20

minutes may be required to achieve satisfactory topical anesthesia. Inhalation of an aerosol of local

anesthetic is usually well tolerated and can anesthetize the entire respiratory tract. The quality of topical

anesthesia achieved with nebulizers is not as good as that achieved with other techniques, but it is a useful

option when other techniques cannot be used or coughing is particularly undesirable.

Box 50-2

Local anesthetic sprays and gels achieve rapid topical anesthesia of the nose, mouth, and pharynx.

Pressurized aerosol sprays contain preservatives that may cause a sore throat postoperatively, and they are

less effective than gels. Lidocaine 4% administered by a spray attachment for syringes is popular. The first

spray is pungent and patients should be warned. Lidocaine gel (2%) is very effective and well tolerated, but

subsequent optical images through the gel may be slightly impaired. Most of the lidocaine applied with sprays

or gels is swallowed and the absorbed drug metabolized in first-pass hepatic metabolism.

Topical anesthesia of the larynx and trachea may be achieved by transtracheal injection or a spray as you

Airway Techniques That Can Be Performed Under Topical Anesthesia in an Awake Patient

Supraglotti airway device insertion

Direct laryngoscopy and intubation

Blind nasal intubation

Retrograde intubation

Flexible fiberoptic laryngoscopy and intubation

Rigid indirect optical devices and intubation

Tracheotomy/Cricothyrotomy

Techniques of Airway Anesthesia

Nebulizersentire airway

Topical sprays and gelsupper airway

Transtracheal injectionlarynx and trachea

Spray as you golarynx and trachea

Nerve blocksdistribution of the nerve supply

Combinations of the above



go (SAYGO) technique. SAYGO is an intermittent application technique that causes coughing and requires

time for recovery after each application. Use of an epidural catheter within the working channel of the

fiberscope is an effective means of administering SAYGO. Transtracheal injection through the cricothyroid

membrane is more invasive but quickly produces good topical anesthesia. Coughing spreads the local

anesthetic. A bolus of narcotic is frequently given before transtracheal injection to prevent excessive

coughing. Narcotics themselves can cause coughing, which can be suppressed by the inhalation of

salbutamol or beclomethasone or by intravenous lidocaine. [28] The quality of transtracheal anesthesia is

preferred by patients and endoscopists over that produced by nebulizers or SAYGO.

Nerve blocks produce more profound and longer-lasting anesthesia than topical anesthesia does. A superior

laryngeal nerve block created by injection through the thyrohyoid membrane is the least invasive of the

airway nerve blocks and provides good anesthesia of the area between the vocal cords and the epiglottis. [29]

Facemask Airway

Facemask techniques are a core skill that often requires considerable expertise. Use of a facemask with

spontaneous ventilation throughout induction and maintenance of anesthesia with inhaled agents is the

simplest and least invasive anesthesia technique. It is very suitable for short operations in all patients except

those with an increased risk of vomiting or regurgitation. Facemasks are also used for controlled ventilation

before and after the use of tracheal tubes.

Facemasks are designed to form a seal around the mouth and nose and to connect to a resuscitator or

anesthesia circuit. The two key elements of the technique are maintenance of a good seal between the mask

and the patient's face and an unobstructed airway. Clinical signs of air leak and airway obstruction must be

sought constantly. The quality of the seal during spontaneous ventilation is monitored by observing the

fullness and movement of the reservoir bag. Leaks occur most frequently around the nose and cheeks, the

latter particularly in edentulous patients with concave cheeks. It is possible to compensate for a leak by using

a high fresh gas flow, but use of the oxygen flush facility on the anesthesia machine will dilute the

concentration of any inhaled agents being administered.

The pathophysiology of upper airway obstruction has been considered. The clinical features of airway

obstruction depend on the site and degree of obstruction and whether spontaneous breathing or positive-

pressure ventilation is being used. Laryngospasm may be a component of airway obstruction and is

considered separately. The most important signs of airway obstruction are clinical. Noisy respiration

(snoring with supraglottic obstruction and inspiratory stridor with glottic obstruction) is a classic sign of

airway obstruction during spontaneous ventilation. However, noise depends on airflow, which is determined

by the degree of obstruction and the respiratory drive. Powerful inspiration in the presence of airway

obstruction produces the combination of inward movement of the upper chest region and outward movement

of the lower chest and upper abdominal regions, thereby creating the classic seesaw movement sign.

Powerful descent of the diaphragm in the presence of severe obstruction results in tracheal tug. Movement of

the reservoir bag is a guide to tidal volume, which can be supplemented by electronic measurement.

Reliance on the capnograph alone is dangerous. Serious hypercapnia caused by airway obstruction can exist despite a satisfactory SpO2.

Radiology studies have shown that head extension is the most important single maneuver for maintaining

space between the pharyngeal soft tissues. Head extension stretches the anterior neck structures and moves

the hyoid bone and attached structures anteriorly. In patients with an unstable cervical spine, head extension

should be used only if all other airway maneuvers fail to overcome the airway obstruction. Jaw thrust,

achieved by exerting anterior pressure behind the angles of the mandible, uses the sliding component of the

TMJ to move the mandible, hyoid bone, and attached structures anteriorly. Considerable strength is

sometimes required to overcome airway obstruction with head extension and jaw thrust. Use of the lateral

position can dramatically reduce airway obstruction. [16]

If head extension and jaw thrust fail to maintain an unobstructed airway, options include insertion of an

oropharyngeal airway, nasopharyngeal airway, or SAD and tracheal intubation. An oropharyngeal airway

( Fig. 50-3 ) is normally the first choice, provided that sufficient mouth opening is possible. The airway should

be inserted only when the pharyngeal and laryngeal reflexes are depressed to minimize the risk of provoking

coughing and laryngospasm. The risk of damage to the teeth during the insertion of oropharyngeal airways is



increased in the presence of caries and gingivitis.

If airway obstruction is not improved with the oropharyngeal airway, the next step has traditionally been

insertion of a nasopharyngeal airway ( Fig. 50-4 ), which often dramatically improves the airway.

Nasopharyngeal airways may be preferable to oropharyngeal airways in the presence of limited mouth

opening and dental caries or gingivitis. Once in place, a nasopharyngeal airway is less stimulating than an

oral airway and better tolerated by lightly anesthetized patients. Insertion of a nasopharyngeal airway can

cause epistaxis as a consequence of damage to the nasal mucosa, polyps, turbinates, or other tissues. This

risk is minimized by gentle insertion of a well-lubricated small airway and termination if resistance is met.

Unless other measures fail to maintain an adequate airway, nasopharyngeal airways should not be used in

patients with basal skull fracture because of the risk of intracranial insertion. Ventilation through an SAD may

be successful when facemask ventilation fails. A laryngeal mask airway (LMA) is now frequently inserted

Figure 50-3 Oropharyngeal airway in place. The airway follows the curvature of the tongue. It pulls the tongue and the epiglottis

away from the posterior pharyngeal wall and provides a channel for the passage of air. (Adapted from Dorsch JA, Dorsch SE:

Understanding Anesthesia Equipment, 4th ed. Baltimore, Williams & Wilkins, 1999.)



before trial of a nasopharyngeal airway if mouth opening is adequate and the depth of anesthesia is

sufficient. Successful tracheal intubation will improve the airway when facemask ventilation is inadequate but

may be hazardous because difficulty with facemask ventilation is associated with difficult tracheal intubation.

When airway obstruction makes facemask positive-pressure ventilation difficult, any of the aforementioned

maneuvers may be used. Use of increased airway pressure has a good theoretical basis as a means of

overcoming dynamic airway obstruction. Two-person techniques are of proven value. The more experienced

person maintains head extension, bimanual jaw thrust, and mask seal while an assistant squeezes the

reservoir bag under supervision. Excessive airway pressure should be avoided because it may insufflate gas

into the stomach, thereby increasing the risk for regurgitation. Mask ventilation may be difficult or impossible,[2] particularly when cricoid pressure is applied.

Figure 50-4 The nasopharyngeal airway in place. The airway passes through the nose and ends at a point just above the

epiglottis. (Adapted from Dorsch JA, Dorsch SE: Understanding Anesthesia Equipment, 4th ed. Baltimore, Williams & Wilkins,

1999.)



Laryngospasm during Anesthesia

The pathophysiology of laryngospasm has been discussed. Laryngospasm during surgery can occur during

use of a facemask or SAD. The clinical picture depends on the degree of obstruction and the respiratory

drive. High-pitched inspiratory stridor is a classic sign, but complete airway obstruction is silent. Obstruction

must be relieved rapidly to prevent hypoxemic damage and the development of negative-pressure pulmonary

edema. [18] Mild laryngospasm should be managed initially with positive-pressure ventilation by facemask

along with head extension and jaw thrust. The Larson maneuver of inward pressure in the laryngospasm

notch (between the mandible and mastoid process) has no disadvantages and should be attempted. [30]

When laryngospasm is severe with complete glottic closure, attempted facemask positive-pressure ventilation

is ineffective because it distends the piriform fossae and presses the aryepiglottic folds more firmly against

each other. The depth of anesthesia may be increased rapidly with intravenous anesthetics (preferably

propofol). Stimulating surgery should be interrupted. If the obstruction or hypoxemia does not improve, a

small dose (e.g., 0.1 mg/kg) of succinylcholine can relax the vocal cords for about 2 minutes and give time to

increase the depth of anesthesia. This dose usually causes brief apnea, and laryngospasm may recur when

neuromuscular transmission recovers. If the obstruction or hypoxemia is severe, an intubating dose of

succinylcholine followed by tracheal intubation is indicated. If tracheal intubation fails, a percutaneous airway

will be necessary.

Supraglottic Airway Devices

SADs have been used widely since the 1990s. They provide an airway intermediate between the facemask

and tracheal tube in terms of anatomic position, invasiveness, and security. All are designed to form a seal in

the pharynx between the respiratory and digestive tracts to protect the airway and facilitate gas exchange. All

have a proximal tube that is connected to an anesthesia circuit or other device. All SADs are inserted blindly,

and tests are then used to determine whether their function is satisfactory. Many classifications have been

proposed; a simple differentiation is between esophageal obturator and periglottic devices.

Esophageal Obturator Devices

A tube with a closed distal end that is designed for passage into the esophagus is common to all esophageal

obturator devices. A distal seal in the esophagus is provided by an inflatable cuff, and a proximal seal is

achieved with a facemask or oropharyngeal cuff. Holes in the tube between the proximal seal and the distal

cuff deliver gases to the laryngopharynx. The Combitube has been widely used in prehospital care. The

proximal seal is provided by an oropharyngeal cuff. It has a second open-ended tube that can function as a

tracheal tube if it is inadvertently inserted into the trachea. It gives protection against regurgitation similar to

that provided by modern periglottic devices. The incidence of esophageal damage should be reduced when

the SA (small adult) size is used. Its performance is inferior to that of the ProSeal LMA (PLMA) and the

Laryngeal Tube Sonda (LT), [31] but it has been successful when other devices have failed. The LT is a

single-lumen esophageal obturator device in which both cuffs are inflated from a single inflation line. Multiple-

and single-use versions are available, and the size and number of holes between the two cuffs have been

increased. Placement is rapid and the incidence of laryngospasm and coughing is low. The LT achieves a

high leak pressure, thus facilitating higher airway pressure than with the LMA classic (LMAc) during positive-

pressure ventilation. The LT has been used successfully in the cannot intubate, cannot ventilate situation

and LMA failure. A gastric drainage tube was added in the Sonda models and perform well. [31] Other

esophageal obturator devices are also available.

Periglottic Devices

Periglottic devices form a seal around the larynx, usually with an inflatable cuff. Most clinical experience has

been with the LMA family of devices, and only these will be described in detail here. This does not imply that

other devices are not of value.

The original LMA (now also known as the LMAc) was introduced into clinical practice in 1988 and has been

used in more than 200 million patients. All LMAs have three main components: mask, airway tube, and

inflation line. The mask has a bowl surrounded by an inflatable cuff, which is designed to form an airtight and

fluid-tight seal round the larynx. The airway tube has a standard 15-mm connector.



Technique

Large LMAs may increase the risk for sore throat postoperatively but achieve a better seal. [32] An LMA is

inserted blindly and thus gentleness is important. [33] Several insertion techniques will achieve an acceptable

position and function in most patients. The technique developed over many years by Archie Brain (the

inventor) ( Fig. 50-5 ) is reliable but not always successful, and alternative techniques are sometimes needed.

The sniff position is recommended for insertion of an LMA.

Propofol or sevoflurane give good conditions for insertion of an LMA. The combination provides particularly

good conditions with a low incidence of apnea and movement during insertion. [34] Short-acting narcotics

improve the ease of insertion and airway patency. [35] Alfentanil (10 g/kg) suppresses swallowing, coughing,

gagging, and laryngospasm without unduly long apnea. Intravenous lidocaine facilitates LMA insertion and

reduces the incidence of coughing and airway obstruction. Insertion should be performed only after an

adequate depth of anesthesia has been achieved, best demonstrated by the ability to perform a jaw thrust.

The recommended technique involves passing the device along the palate and then the posterior pharyngeal

wall until resistance increases, at which point the tip should be lie within the upper esophageal sphincter. This

route should reduce the risk of posterior displacement of the epiglottis. Malposition of the LMA is less likely if

Figure 50-5 Insertion of a laryngeal mask airway (LMA). A, The tip of the cuff is pressed upward against the hard palate by the

index finger while the middle finger opens the mouth. B, The LMA is pressed backward in a smooth movement. Notice that the

nondominant hand is used to extend the head. C, The LMA is advanced until definite resistance is felt. D, Before the index finger

is removed, the nondominant hand presses down on the LMA to prevent dislodgment during removal of the index finger. The cuff

is subsequently inflated, and outward movement of the tube is often observed during this inflation. (Courtesy of LMA North

America, Inc., San Diego, CA.)



jaw thrust or direct laryngoscopy is used to assist insertion. The laryngoscope-assisted technique has been

successful when the standard technique has failed.

When resistance to insertion is detected, the tube is left free while air is inflated into the cuff. Inflation to the

maximum recommended volume produces high cuff pressure and suboptimal function. Inflation to a cuff pressure not higher than 60 cm H2O is recommended. The tube is connected to the anesthesia circuit and

gentle manual ventilation begun. Initial checks of LMA function are now performed. Lung expansion is

observed. Slow refill of the reservoir bag is a feature of airway obstruction. Auscultation over the neck may

detect sounds of respiratory obstruction. When airway obstruction is detected, examination with an FFL is

recommended because management of LMA impaction in the glottis is different from that of vocal cord

closure.

LMA function is now assessed in more detail ( Box 50-3 ). Two tests that correlate well with optimum position are the ability to generate an airway pressure of 20 cm H2O and the ability to ventilate manually.

[36] Gas

exchange and the possibility of obstruction are assessed by capnography, expired tidal volume, and the flow-

volume loop. Airway leak pressure may be used to quantify the efficacy of the seal between the mask and

the larynx and indicates both the feasibility of positive-pressure ventilation and the degree of airway

protection. The test is performed by determining the airway pressure at which gas escapes.

Box 50-3

An effective seal depends on the size and position of the LMA, inflation of the cuff, low airway resistance, and

high pulmonary compliance. Poor initial function may be caused by laryngospasm or bronchospasm.

Withdrawal followed by readvancement (the up-down maneuver) may improve position and function of the

LMA. The number of maneuvers should be limited because airway obstruction is occasionally caused by

undiagnosed laryngeal lesions or laryngeal closure. If the airway remains unsatisfactory, the anesthesiologist

may reinsert the same or a different size of LMA and accept some leakage, or use a facemask or tracheal

intubation.

The laryngeal mask is secured. A bite block should be inserted and remain in place until the LMA has been

removed to reduce the possibility that biting will obstruct the airway or damage the tube.

Airway Obstruction

The final position of the LMA in relation to the vocal cords, epiglottis, and upper part of the esophagus varies

greatly and has been investigated with the FFL. The average views obtained in 26 studies included an

unobstructed view of the vocal cords in 40% and no view of the vocal cords in 6%. [37] Malposition occurs in

50% to 80% of patients, is usually associated with an undefined clinically acceptable airway, [37] but can

adversely affect the quality of the airway.

There have been few scientific investigations of airway resistance as a measure of obstruction during the

clinical use of SADs. An important study showed that although median airway resistance was similar in the

LMA (plus larynx) and tracheal tube groups, airway resistance was greatly increased in 3 of 12 patients in the

Assessment of Function of the Laryngeal Mask Airway

Observation of airway pressure and chest movement with a manual ventilation

Reservoir bag refill during expiration

Capnograph

Auscultation over the neck

Cuff leak pressure

Expired tidal volume and flow-volume loop

Examination with a flexible fiberoptic laryngoscope



LMA group, indicative of significant airway obstruction. [38] Conversion to tracheal intubation has been

required in 11.4% of patients in whom the LMA was used for tonsillectomy. [39] Head extension and jaw thrust

have been required in 5% of patients. Failure to achieve a satisfactory airway occurred in 4.7% of LMA

patients in one large study. [10] Variation in the incidence of acceptable or obstructed airways may be partly

a consequence of differences in clinical criteria. Airway obstruction unresponsive to simple measures should

be no more acceptable than with a facemask and should be relieved. Reversion to a facemask is often

effective. Emergency intraoperative tracheal intubation is sometimes necessary and is likely to be more

hazardous than elective intubation ( Box 50-4 ).

Box 50-4

Pulmonary Aspiration

The seal achieved by LMAs provides less protection against pulmonary aspiration than a properly inserted

cuffed tracheal tube does. LMA malposition in which the upper end of the esophagus lies within the bowl of

the LMA increases the risk that regurgitation or vomiting will result in pulmonary aspiration and has been

reported in a third (or more) of patients. Massive pulmonary aspiration during LMA anesthesia is infrequent

but can lead to death or serious morbidity. [40] The LMA should not be used in patients with an increased risk

for regurgitation or vomiting.

Positive-pressure ventilation, with or without NMBDs, is frequently used with the LMA. Despite reports of safe

use in large series, there is concern about the safety of this practice. [41] Positive-pressure ventilation

increases the risk for gastric insufflation, which in turn increases the risk for regurgitation.

Removal of the Laryngeal Mask Airway

Laryngeal function is depressed after LMA use. [42] Monitoring and oxygen administration should be

continued during emergence from anesthesia. Removal of the LMA should always be carried out at locations

where personnel and equipment are available to perform tracheal intubation. Most keep the LMA in place

until consciousness recovers, airway reflexes return, and patients can open their mouth on command.

Removal with the cuff inflated is associated with a higher incidence of hoarseness but not overall airway

complications, and many recommend this technique.

Comparison of the Laryngeal Mask Airway with the Facemask and Tracheal Tube

Basic skill is mastered more readily with an LMA than with a facemask. A reasonable success rate is

achieved more rapidly with an LMA than with the Macintosh technique of tracheal intubation. A greater

degree of skill is required for tracheal intubation. An LMA is inserted blindly, whereas a tracheal tube is

normally inserted under vision. Difficulty in LMA insertion occurs in at least 4.5% of patients, a incidence

comparable to that of difficulty with the Macintosh technique. LMA insertion causes less hemodynamic

stimulation than laryngoscopy and tracheal intubation do. The LMA has advantages over tracheal intubation

at the time of extubation. The incidence of minor laryngopharyngeal morbidity is similar with both devices.

However, coughing is less frequent at LMA than at tracheal tube removal, and adverse hemodynamic effects

Hazards of Intraoperative Tracheal Intubation

SurgeryAdverse Effects

Tracheal Intubation Problems

Interruption

Sterility, integrity, and outcome threatened

Patient position suboptimal

Hypoxemia and risk of increased hypoxemia

Risk of tissue trauma



occur less frequently. The glottic aperture is narrowed after tracheal intubation but not with use of an LMA. [42]

Complications and Contraindications

There are few published reports of serious complications as a consequence of LMA use, but there have been

unreported deaths and cases of brain damage. [43] Less serious complications include nerve damage.

Role of the Laryngeal Mask Airway

The LMA is extremely useful when used conservatively and has proved valuable as a rescue device. The

LMA is a key device at several places in the ASA algorithm for difficult airways. [6] There are many reports of

successful use of an LMA as a rescue airway when tracheal intubation had failed, including the cannot

intubate, cannot ventilate situation, and lives have been saved. However, the LMA does not always provide

a satisfactory airway in the failed tracheal intubation situation. [2] Cricoid pressure can interfere with the

insertion and function of SADs and should be reduced to a level that allows successful insertion and

adequate function. An LMA may be used to allow completion of surgery if the latter cannot be postponed,

although there is a risk of airway obstruction and pulmonary aspiration. The most prudent course is to

postpone surgery and awaken the patient or to convert to tracheal intubation with a visual technique such as

the Aintree intubating catheter (AIT).

Elective use of an LMA in a patient with a known or anticipated difficult airway has serious disadvantages.

The difficult airway remains and the development of airway obstruction could produce a critical situation that

requires immediate percutaneous airway rescue. Asai states, It is inadvisable to rely on the LMA when

tracheal intubation is predicted to be difficult. [43a] Although the LMA has been inserted under topical

anesthesia, gagging, coughing and a high incidence of sore throat have been reported. [44] The LMA has

failed to provide a satisfactory airway in patients with micrognathia, previous oral or cervical radiotherapy,

and laryngeal abnormalities and disease. Insertion of an LMA is frequently difficult in patients in whom

tracheal intubation is difficult. Use of an LMA when the patient's position is other than sniff will delay

conversion to tracheal intubation when necessary. The development of airway obstruction with such positions

places the patient at risk, requires rapid repositioning of the patient by staff, and jeopardizes the surgical

outcome. The risks associated with intraoperative tracheal intubation (see Box 50-4 ) will be increased.

The LMA has been used safely for major surgery, but the user must be very experienced with both the LMA

and tracheal intubation, and that is the paradox. If future generations of anesthesiologists were to have less

skill in tracheal intubation, use of an LMA instead of tracheal intubation for major surgery would become more

risky. Skill in tracheal intubation is essential, and it is generally the safer option. Insertion of an LMA is

regarded as less stressful for the anesthesiologist than the use of direct laryngoscopy for tracheal intubation.

However, a tracheal tube is a more reliable airway that provides better protection against pulmonary

aspiration. Most comparisons with tracheal intubation have used the Macintosh laryngoscope, the limitations

of which are now better understood. [45] It is probable that problems and complications with tracheal

intubation will become less frequent as alternative intubation techniques are used more regularly. [46] [47]

Expediency and some minor advantages of SADs must be offset against lower airway security and reliability.

Patient safety must always be the prime concern.

Newer Supraglottic Airway Devices

Flexible, intubating, and ProSeal LMAs have been introduced. Several changes have been made to improve

the performance of newer models. The LMA Flexible has a wire-reinforced, flexible airway tube designed to

resist kinking during oral or other head and neck surgery. Some SADs introduced by other manufacturers

perform well. The i-gel and LMA Supreme seem very promising, but there are still limited data and other new

devices will certainly appear.

ProSeal Laryngeal Mask Airway

The PLMA was designed to facilitate positive-pressure ventilation with higher airway pressure than possible

with the LMAc. A second posterior cuff and deeper bowl were designed to improve the seal around the

larynx. The PLMA has a drainage tube to provide access to the esophagus. Other features of the PLMA

include a reinforced airway tube that is narrower than that of the LMAc and an integrated bite block. The tip of



the PLMA lacks the semirigid back plate of the LMAc.

Insertion Technique

A greater depth of inhaled and intravenous anesthesia is required for insertion of a PLMA than an LMAc. The

technique of PLMA insertion is more demanding than that for an LMAc, but a high success rate can be

achieved. [48] This effort is rewarded by a superior quality of airway. Airway seal pressure is increased by

50% in relation to the LMAc, thus facilitating positive-pressure ventilation and probably providing better

airway protection. The device may be introduced digitally or with a special introducer. An alternative

laryngoscope introducer technique has been developed to prevent folding of the mask tip during insertion. A

lubricated introducer is passed through the PLMA drainage tube so that it protrudes beyond the tip. A

Macintosh laryngoscope is used to facilitate insertion of the introducer into the esophagus. The laryngoscope

is then removed and the PLMA inserted by using the introducer as a guide. This technique may be the most

reliable but is most invasive method of PLMA insertion. After insertion, the PLMA cuff is inflated to a pressure not greater than 60 cm H2O.

An incorrectly placed PLMA will result in unreliable or obstructed ventilation. The diagnosis of correct and

incorrect PLMA position is considered in detail because it may be relevant to a new generation of SADs that

incorporate a drainage tube. Correct placement of the PLMA should produce a leak-free seal around the

glottis with the mask tip and drainage tube lying inside the upper esophageal sphincter. There are three

important malpositions of the PLMA: (1) The PLMA may not be inserted sufficiently far, with the consequence

that the tip of the drainage tube lies in the pharynx. Positive-pressure ventilation is ineffective because

delivered gas passes out the drainage tube. (2) The tip of the PLMA may lie within the glottis, thereby

obstructing ventilation and impairing function of the drainage tube. (3) The tip may be folded over and

obstruct ventilation and the drainage tube. Malposition should be corrected by repositioning the PLMA, using

a different insertion technique, or replacing it with an alternative airway device.

Initial checks of function are identical to those used with the LMAc. In particular, chest expansion should be

good with reasonable airway pressure, and there should be no signs of obstruction of expiration, particularly

slow refill of the reservoir bag. The capnograph should be square and the flow-volume loop closed without expiratory scalloping or other signs of obstruction. Airway leak pressure should be greater than 20 cm H2O.

Additional checks unique to devices with a drainage tube may then be performed. A thin layer of water-

soluble gel or nontoxic soapy film is used to cover the proximal end of the drainage tube. The effect of

changes in pressure in the lungs (sternal compression or positive-pressure ventilation) or esophagus

(pressure on the suprasternal notch) are noted. Normal results are as follows:

Protection against Pulmonary Aspiration

The PLMA provides greater protection against pulmonary aspiration than the LMAc does. In clinical practice,

the PLMA has prevented aspiration in the presence of massive regurgitation. However, pulmonary aspiration

has occurred when malposition of the PLMA was not corrected and function checks had been satisfactory.

The PLMA provides good but incomplete protection against pulmonary aspiration.

Airway Obstruction

Significant airway obstruction has been reported with the PLMA. Intraoperative tracheal intubation was

required in 13% of obese patients undergoing laparoscopic cholecystectomy. [49] Obstruction may be caused

by malposition or obstruction of the bowl by folds of the inflated cuff, by narrowing of the glottis via direct

pressure, or by laryngospasm during use of a properly positioned PLMA.

Use of the PLMA during major surgery such as laparoscopic cholecystectomy has been advocated [49] but is

controversial. [41] Use of the PLMA for such surgery should be considered only in patients who have no extra

The drainage tube gel does not move with positive-pressure ventilation or brief firm pressure applied

to the sternum.

The drainage tube gel does not move when airway pressure is raised to 20 cm H2O.

The drainage tube gel moves slightly when brief bobbing pressure is applied to the suprasternal

notch (the mechanism is pressure on the esophagus).



risk factors (including obesity, symptomatic gastroesophageal reflux disease, reduced compliance, increased

airway resistance) for SAD use. The anesthesiologist must be ready to convert to tracheal intubation at any

time. [49] Tracheal intubation provides a more secure airway and should be the norm for major surgery.

Single-Use Supraglottic Airway Devices

The original LMAs were designed for use up to 40 times. Protein contamination occurs after the first use and

increases with each subsequent use despite proper cleaning and autoclaving. Single-use SADs have been

developed to prevent cross-infection. Ease and quality-of-use results from different studies have been

conflicting.

Tracheal Tubes

Tracheal tubes are designed to provide a secure channel through the upper airway. The distal end lies in the

mid to lower part of the trachea, whereas the proximal end lies outside the mouth or nose, where it is

connected to an anesthesia circuit or other device. Tracheal tubes used in adult patients have a cuff near the

distal end that is inflated to provide a seal against the tracheal wall to protect the lungs from pulmonary

aspiration and to ensure that the tidal volume delivered ventilates the lungs rather than escapes into the

upper airway. Cuffs are normally inflated with air and have an inflation tube with a pilot balloon that indicates

cuff inflation.

The size of the tracheal tube is normally described as the internal diameter (ID) in millimeters, but the

relationship of the ID to the external diameter varies between different designs and manufacturers. Use of the

largest possible tracheal tube was once considered good practice. Very small tracheal tubes may allow

insufficient time for completion of exhalation and produce air trapping (auto-PEEP) with the risk of

barotrauma and circulatory compromise. Others have found no evidence of obstruction to expiration with tube

sizes as small as 6-mm ID, and the increased workload created is usually of little clinical significance during

anesthesia. Use of small tracheal tubes reduces the incidence of sore throat and hoarseness. Small tracheal

tubes are easier to insert than larger tubes and may cause less tissue pressure at the larynx. It is easier to

pass small tracheal tubes over introducers or FFLs. [50] Restriction of gas flow through a tracheal tube is

markedly increased by the presence of an FFL or suction catheter within the lumen of the tracheal tube.

Tracheal tube sizes of 8 mm (ID) for males and 7.5 mm (ID) for females are often used.

Specialized tracheal tubes produced for anesthesia include preformed, adjustable shape, and reinforced.

Specialized tubes are also used for ear, nose, and throat (ENT) surgery (laser and microlaryngeal surgery)

and for thoracic anesthesia and critical care. Tracheal tubes can become kinked and hence obstructed when

they are angulated. Armored (reinforced) tubes have an embedded coil (usually stainless steel) that

minimizes kinking of the tube when it is subjected to angulation. Armored tracheal tubes are the tubes of

choice in many head and neck procedures and patient positions other than supine. However, an armored

tube that has been compressed remains pinched, so it is particularly important to prevent biting on such a

tube.

The material and bevel shape of the tip of the tracheal tube can affect the ease and probably the trauma of

tube passage. The tip of the earliest Magill tracheal tubes had a soft, simple bevel. The Murphy eye, a hole in

the wall of a firm tip opposite the bevel, was designed to provide a patent airway if the tracheal tube became

occluded at the bevel. Air leakage through the Murphy eye may facilitate early diagnosis of tracheal tube

displacement before complete accidental extubation has occurred.

Cuff inflation achieves a seal between the tracheal tube and the wall of the trachea. There should be no air

leak at airway pressures required for positive-pressure ventilation, and the lungs should be protected from

aspiration. The cuffs of early tracheal tubes produced a high pressure that could cause mucosal ischemia.

High-volume, low-pressure cuffs were developed to conform to the D-shaped cross section of the trachea

and provide a seal at a lower cuff pressure, thereby reducing the risk of tracheal damage.

Inflation of the cuff with a volume that just prevents an air leak (just-seal volume) is often recommended.

However, this cuff pressure varies greatly. Prevention of excessive cuff pressure may reduce the incidence of

tracheal damage, vocal cord dysfunction from recurrent laryngeal nerve palsy, and sore throat after surgery.

Because palpation is not a good guide to cuff pressure, use of a monitor to maintain cuff pressure in the



range of 25 to 30 cm H2O is recommended. [51]

Cuff pressure can change after initial inflation. Inhaled N2O diffuses into tracheal tube cuffs that have been

inflated with air and increases the volume and pressure within the cuff enough to cause tracheal lesions and

an increased incidence of sore throat. A leak in the cuff or valve or a reduction in trachealis muscle tone can

lower cuff pressure and increase the risk for pulmonary aspiration. Early detection of both low and high

pressure is important.

A properly inflated cuff protects against massive pulmonary aspiration, but silent aspiration (micro-aspiration)

of pharyngeal contents occurs along channels between folds in the cuff and is a major contributor to

ventilator-associated pneumonia in intensive care. New materials and cuff designs attempt to eliminate cuff

channels and may help prevent micro-aspiration.

Tracheal Intubation

Tracheal intubation (insertion of the tracheal tube) is an essential skill in anesthetic practice. Indications for

tracheal intubation are shown in Box 50-5 . There are no absolute contraindications to tracheal intubation.

Box 50-5

Principles of Clinical Practice of Tracheal Intubation

The incidence of complications should be minimized by using best practice. [6] Adequate personnel, drugs,

and equipment must be available. Four principles are central to prevention of complications [52] :

Indications for tracheal intubation

Surgical and Anesthetic Indications

Critical Illness

Surgical requirement for neuromuscular blocking drugs, e.g., abdominal surgery

Airway access shared with the surgeon, including ear, nose, and throat surgery

Patient position in which access to the airway is restricted or precludes rapid tracheal intubation,

e.g., lateral, prone

Predicted difficult airway

Risk of aspiration of gastric contents or blood, e.g., upper gastrointestinal obstruction or sepsis,

facial trauma, bleeding into the respiratory tract from any cause

Surgery that impairs gas exchange

Prolonged surgery

Other airway techniques ineffective

Inability to protect the airway, e.g., coma from any cause

Impaired respiratory function (hypoxemia or hypercapnia) unresponsive to noninvasive

management

Prevention of hypercapnia, e.g., raised intracranial pressure

1. Maintenance of oxygenation must take priority over all other issues. Preoxygenation should be

performed before induction of anesthesia. [6] Mask ventilation should be used between attempts at

tracheal intubation.

2. Trauma must be prevented. The first attempt at tracheal intubation should be performed under

optimal conditions (including patient position, preoxygenation, and equipment preparation). [53] The

number of attempts with blind techniques should ideally be zero and certainly not more than four.



Intravenous access is secured (occasionally achieved only during inhaled induction of anesthesia) and

standard monitoring is established. The patient should be in the optimal position. Time spent adjusting the

position after induction of anesthesia may delay successful tracheal intubation, prolong the time at risk for

pulmonary aspiration, and increase the risk for hypoxemia or airway trauma.

Nasotracheal Intubation

Nasotracheal intubation (NTI) is necessary when the oral route is not possible (e.g., limited mouth opening)

or would impede surgical access. NTI was formerly considered the technique of choice for resuscitation, but

orotracheal intubation using the rapid-sequence technique is now usually the first choice. NTI has been used

in critical care as an alternative to tracheotomy because it is better tolerated than oral intubation. However the

tube used must be longer and narrower than oral tracheal or tracheotomy tubes so that airway resistance is

greater and therapeutic aspiration of pulmonary secretions is more difficult. Problems associated with

prolonged duration of NTI include nasal damage, local abscesses, otitis media, and sinusitis. The nasal route

is contraindicated in patients with a history (old or new) of basal skull fracture or surgery. Nevertheless, if

there is no alternative, this infrequent complication may be less likely when a catheter is used as a guide.

The technique of NTI is influenced by the need to minimize the incidence of complications peculiar to this

route, including cuff tears, damage to the nasal cavity (epistaxis, fractured turbinates, avulsed nasal polyps,

septal abscess) and nasopharynx (avulsed adenoids). It is beneficial to use vasoconstrictors to shrink the

mucosa of both nasal cavities before passage of the tube. Another complication is a consequence of the right

angle through which the tube must turn when it passes from the nasal cavity into the oropharynx. The tube

may impact on and tear the mucosa of the posterior nasopharynx and pass submucosally. This complication

is less likely if a soft catheter is first passed into the oropharynx and then used as a guide. Tube factors that

reduce the risk of trauma include diameter not larger than 7.5-mm ID for men and 7.0-mm ID for women,

warming before insertion, and use of a soft tip. The tube is passed directly backward along the floor of the

nose. Resistance to nasal passage may be overcome by gentle rotation or use of a narrower tube or the

other nasal cavity. It is important to be gentle and stop if abnormal resistance is met. The risk of damage may

be reduced by passage through the nasal cavity under vision with an FFL.

Blind nasal intubation was first used in patients breathing spontaneously under deep inhaled anesthesia but

can also be performed in awake patients under topical anesthesia. Tube advancement is guided by changes

in breath sounds at the proximal end of the tube (amplification by a whistle can be very helpful) and by

external palpation of the larynx. Cessation of breath sounds indicates that the tip of the tube has entered the

esophagus, piriform fossa, or vallecula. The tube is withdrawn until breath sounds are heard, the head and

neck position is adjusted, and the tracheal tube is then readvanced. Temporary inflation of the cuff when in

the oropharynx may improve success rates. [54] If the tube is held up at the larynx, head flexion can help the

tracheal tube enter the trachea by improving alignment with the trachea. Blind nasal intubation during

spontaneous ventilation may still be useful when an FFL is not available. Attempted blind NTI in an apneic

patient risks trauma and failure.

NTI is often performed after the administration of intravenous anesthetics and NMBDs. A direct laryngoscope

is used to facilitate NTI under vision and is inserted once the tip of the tube has reached the oropharynx.

Magill forceps are frequently used to grasp the tracheal tube (avoiding the cuff) and guide it into the trachea.

An assistant then advances the tube. Rigid indirect laryngoscopes (RILs) can facilitate NTI under vision in

patients in whom this is not possible with direct laryngoscopes.

Direct Laryngoscopy: Theoretical Basis

Direct laryngoscopy is used to facilitate tracheal intubation under vision. Successful direct laryngoscopy

3. The anesthesiologist should have backup plans before starting the primary technique [6] and the

skills and equipment needed to execute these plans. When unanticipated difficulty occurs in non-

lifesaving surgery, the safest plan is to terminate attempts at tracheal intubation, awaken the patient,

and postpone surgery.

4. The anesthesiologist should seek the best help available (call for help) as soon as difficulty with

tracheal intubation is experienced.



depends on achieving a line of sight from the maxillary teeth to the larynx. The tongue and epiglottis are the

anatomic structures that intrude into the line of sight. Management of the tongue and epiglottis is therefore

central to successful direct laryngoscopy. Before the laryngoscope is inserted, the patient is normally placed

in the sniff position (see later). The direct laryngoscope is then used to displace the tongue and epiglottis

out of the line of sight. The tongue is displaced horizontally (normally to the left) from the line of sight, the

hyoid bone and attached tissues are moved anteriorly, and the epiglottis is elevated directly or indirectly to

reveal the larynx. The force applied to the laryngoscope handle should lift the hyoid bone and attached

tissues parallel to the line of sight. Adequate lifting force, which may cause considerable tissue distortion, [7]

[55] [56] is a key factor in successful direct laryngoscopy. [7] [56] It is important to achieve the best possible view

of the larynx without causing tissue trauma. It is not always possible to achieve line of sight with direct

laryngoscopy.

The theoretical basis of the head and neck position used for direct laryngoscopy was attributed to the need to

align the axes of the oral cavity, pharynx, and larynx on the basis of a radiology study. Magnetic resonance

imaging in awake patients has been used to challenge this hypothesis, but the conclusions have been

controversial. Understanding of management of the tongue and the epiglottis is more likely than the axis

alignment hypothesis to improve direct laryngoscopy technique.

miller+airway+management

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