The original ASA DAA was developed over a 2-year period by the ASA Task Force on Guidelines for Management of the Difficult Airway.¹ The task force included academicians, private practitioners, airway experts, adult and pediatric anesthesia generalists, and a statistical methodologist. The algorithm was introduced by ASA as a practice guideline in 1993. In 2003, the ASA task force presented a revised algorithm that essentially retained the same concept but recommended a wider range of airway management techniques than was previously included, based on more recent scientific evidence and the advent of new technology.

This chapter presents and explains the ASA DAA and then provides a critical appraisal of the ASA algorithm based on recent evidence from the literature. This is followed by the presentation of a new, comprehensive airway management algorithm that provides an innovative and highly structured approach resembling the guidelines for cardiopulmonary resuscitation.

Both algorithms are concerned with the maintenance of airway patency at all times. Special emphasis is placed on an operating room setting, although the algorithm can be extrapolated to the intensive care unit, the ward, and the entire perioperative environment and beyond. Both algorithms are primarily intended for use by anesthesiologists or by individuals who deliver anesthetic care and airway management under the direct supervision of an anesthesiologist. The guidelines apply to airway management during all types of anesthetic care and anesthetizing locations, and to patients of all ages.

Both airway algorithms focus primarily on further improving patient safety during the perioperative period. Adherence to the principles of an airway management algorithm and widespread adoption of such a structured plan should result in a reduction of respiratory catastrophes and a decrease in perioperative morbidity and mortality.

II the ASA Difficult Airway Algorithm

A side-by-side comparison of the original (1993) and the updated (2003) versions of the ASA DAA is presented in Figure 10-1. The differences between the two algorithms are listed in Box 10-1. Certain aspects of the algorithm require further explanation.

Figure 10-1 A, The American Society of Anesthesiologists’ difficult airway algorithm (ASA DAA), published in 1993.B, The revised (2003) ASA DAA.

(A from American Society of Anesthesiologists Task Force on Management of the Difficult Airway: Practice guidelines for management of the difficult airway: A report. Anesthesiology 78:597–602, 1993; B from Practice Guidelines for the Management of the Difficult Airway: An updated report by the American Society of Anesthesiologists Task Force on the Management of the Difficult Airway. Anesthesiology 98:1269–1277, 2003.)

Box 10-1 Differences between 1993 and 2003 ASA Management of the Difficult Airway Algorithms

1. Difficult ventilation is now listed first under item 1, “Assess the Likelihood and Clinical Impact of Basic Management Problems.” Also, in the same category, Difficult tracheostomy was added.

2. A new item 2 was inserted: “Actively pursue opportunities to deliver supplemental oxygen throughout the process of difficult airway management.”

3. When considering the relative merits and feasibility of basic management choices (item 3), awake intubation versus intubation attempts after induction of anesthesia should now be considered first, before noninvasive versus invasive techniques as the initial approach to intubation.

4. Use of the laryngeal mask airway (LMA) was incorporated into the algorithm in the awake induction limb and in both the nonemergency and emergency pathways for induction after general anesthesia (either as a ventilatory device or as a conduit for tracheal intubation).

5. The option for “One more intubation attempt” was removed.

6. Use of the rigid bronchoscope was added as an option for emergency noninvasive ventilation.

A Patient Evaluation and Risk Assessment

The ASA DAA begins with the most basic question of whether or not the presence of a DA is recognized (see Chapter 9). Recognizing the potential for difficulty leads to proper mental and physical preparation and an increased chance of a good outcome. In contrast, failure to recognize this potential results in unexpected difficulty in the absence of proper mental and, likely, physical preparation, with an increased chance for a catastrophic outcome.

Airway evaluation should take into account any characteristics of the patient that could lead to difficulty in the performance of (1) bag-mask or supraglottic airway ventilation, (2) laryngoscopy, (3) intubation, or (4) a surgical airway. Routine patient evaluation can be best structured as follows (see Chapter 9 for details):

1. Obtain an airway history to identify medical, surgical, and anesthetic factors that may indicate the presence of a DA.

2. Evaluate for systemic diseases (e.g., respiratory failure, coronary artery disease) that might place limits on awake intubation, such as increased fraction of inspired oxygen (FIO₂), or require special attention, such as prevention of sympathetic nervous system stimulation.

3. Examine previous anesthetic records, which can yield useful information about previous airway management.

4. Conduct a physical examination of the airway to detect physical characteristics that might indicate the presence of a DA (Table 10-1):

• Maximal mouth opening with tongue extension and pharyngeal anatomy (e.g., uvula, tonsillar pillars)

• Length of the submental space (mandible to hyoid) and the thyromental distance (mandible to thyroid notch)

• Side view to determine the ability to assume the “sniffing” position (flexion of the neck on the chest and extension of the head on the neck) and to identify maxillary overbite

• Nostril patency

• Length and thickness of the neck

TABLE 10-1 Components of the Preoperative Airway Physical Examination

Airway Examination Component	Nonreassuring Findings
Length of upper incisors	Relatively long
Relation of maxillary and mandibular incisors during normal jaw closure	Prominent “overbite” (maxillary incisors anterior to mandibular incisors)
Relation of maxillary and mandibular incisors during voluntary protrusion of the jaw	Patient’s mandibular incisors anterior to (in front of) mandibular incisors
Interincisor distance	<3 cm
Visibility of uvula	Not visible when tongue is protruded with patient in sitting position (e.g., Mallampati class III or IV)
Shape of palate	Highly arched or very narrow
Compliance of mandibular space	Stiff, indurated, occupied by mass, or nonresilient
Thyromental distance	<3 ordinary finger breadths
Length of neck	Short
Thickness of neck	Thick
Range of motion of head and neck	Patient cannot touch tip of chin to chest or cannot extend neck

Although each risk factor individually has a rather low positive predictive value for difficult intubation, when combined these factors can provide a gestalt for DA management.

The findings of the airway history and physical examination may be useful in guiding the selection of specific diagnostic tests and consultation to further characterize the likelihood or nature of the anticipated airway difficulty.²

An “awake look” using direct laryngoscopy (after adequate preparation) may be performed to assess intubation difficulty further. If an adequate view is obtained, endotracheal intubation may be performed, followed immediately by administration of an intravenous induction agent.

Presence of a pathologic factor or a combination of anatomic factors (large tongue size, small mandibular space, or restricted atlanto-occipital extension) indicates that the airway should be secured while the patient remains awake (awake techniques).

B Difficult Bag-Mask Ventilation

The risk for difficult mask ventilation (DMV) is the first issue addressed in the most recent version of the DAA. Evidence from the literature ³ suggests that the incidence of DMV is 5% in the general adult population, that the presence of DMV is associated with difficult intubation, and that DMV is not accurately predicted by anesthesiologists.

Five independent criteria predict DMV (age >55 years, body mass index >26 kg/m², lack of teeth, presence of mustache or beard, and history of snoring), and the presence of two such risk factors indicates a high likelihood of DMV.³ It is important to keep these risk factors in mind, because some of them can be reversed. For example, DMV may possibly be preventable by shaving a patient’s beard, leaving dentures in place during bag-mask ventilation (BMV), and performing a workup and treating for possible obstructive sleep apnea.

C Awake Tracheal Intubation

Awake intubation is generally more time-consuming for the anesthesiologist and a more unpleasant experience for the patient. However, if a difficult intubation is anticipated, awake endotracheal intubation is indicated for three reasons: (1) the natural airway is better maintained in most patients when they are awake (i.e., “no bridges are burned”); (2) the orientation of upper airway structures is easier to identify in the awake patient (i.e., muscle tone is maintained to keep the base of the tongue, vallecula, epiglottis, larynx, esophagus, and posterior pharyngeal wall separated from one another)^4,⁵; and (3) the larynx moves to a more anterior position with the induction of anesthesia and paralysis, which makes conventional intubation more difficult.⁶

Crucial to the success of endotracheal intubation while the patient is awake is proper preparation (see Chapter 11 for further details). Most intubation techniques work well in patients who are cooperative and whose larynx is nonreactive to physical stimuli. In general, the components of proper preparation for an awake intubation are the following:

• Psychological preparation (awake intubation proceeds more easily when the patient knows and agrees with what is going to happen)

• Appropriate monitoring (i.e., electrocardiography, noninvasive blood pressure monitoring, pulse oximetry, and capnography)

• Oxygen supplementation (e.g., nasal prongs, nasal cannula, suction channel of a fiberoptic bronchoscope [FOB], transtracheal catheter)⁷^–¹⁰

• Vasoconstriction of the nasal mucous membranes (if performing nasal intubation)

• Administration of a drying agent

• Judicious sedation (keeping the patient in meaningful contact with the environment)

• Adequate airway topicalization (consider performance of bilateral laryngeal nerve blocks, blocking the lingual branch of the glossopharyngeal nerve and the superior laryngeal nerve)

• Aspiration prevention (see Chapter 12)

• Availability of appropriate airway equipment

Box 10-2 lists the suggested ASA guidelines for contents of a portable airway management cart.¹¹

Box 10-2 Suggested Contents of the Portable Storage Unit for Difficult Airway Management

Important: The items listed here represent suggestions. The contents of the portable DA management cart should be customized to meet the specific needs, preferences, and skills of the practitioner and health care facility.

1. Rigid laryngoscope blades of alternative design and size from those routinely used; may include a rigid fiberoptic laryngoscope

2. Endotracheal tubes of assorted sizes

3. Endotracheal tube guides, such as semirigid stylets, ventilating tube changer, light wands, and forceps designed to manipulate the distal portion of the endotracheal tube

4. Laryngeal mask airways (LMAs) of assorted sizes; may include the Fastrach intubation LMA and the ProSeal LMA (LMA North America, San Diego, CA).

5. Fiberoptic intubation equipment

6. Retrograde intubation equipment

7. At least one device suitable for emergency nonsurgical airway ventilation, such as the esophageal-tracheal Combitube (Tyco Healthcare, Mansfield, MA), a hollow jet ventilation stylet, and a transtracheal jet ventilator

8. Equipment suitable for emergency surgical airway access (e.g., cricothyrotomy)

9. An exhaled carbon dioxide detector

10. A rigid ventilating bronchoscope

There are numerous methods to intubate the trachea or ventilate a patient (see Part Four of this text). Box 10-3 shows a list of the techniques contained within the ASA guidelines. The techniques chosen depend, in part, on the anticipated surgery, the condition of the patient, and the skills and preferences of the anesthesiologist. Based on recent evidence from the literature¹²^–¹⁴ considerations should also include the use of video laryngoscopy, despite the fact that this technique is not mentioned in the recent ASA algorithm, but likely will be included in future revisions of the guidelines.

Box 10-3 Techniques for Difficult Airway Management

Important: This box lists commonly cited techniques in alphabetic order. It is not a comprehensive list, and no preference for a given technique or sequence of use is implied. Combinations of techniques may be employed. The techniques chosen by the practitioner depend on the specific needs, preferences, skills, and clinical constraints in the particular case.

Occasionally, awake intubation may fail owing to a lack of patient cooperation, equipment or operator limitations, or any combination thereof. An alternative route is chosen according to the precise cause of the failure:

• Surgery may be canceled (e.g., the patient needs further counseling, airway edema or trauma has resulted, different equipment or personnel is necessary).

• General anesthesia may be induced (the fundamental problem must be considered to be a lack of cooperation, and mask ventilation must be considered nonproblematic).

• Regional anesthesia may be considered (careful clinical judgment is required to balance risks and benefits; see Chapter 45).

• A surgical airway may be created (if the surgery is essential and general anesthesia is considered to be inappropriate until intubation is accomplished); this may be the best choice to secure the airway in patients with laryngeal or tracheal fracture or disruption, upper airway abscess, or combined mandibular-maxillary fractures.

D Difficult Intubation in the Unconscious or Anesthetized Patient

Three typical scenarios require the anesthesiologist to manage a DA in an unconscious patient with a DA: (1) a comatose patient (e.g., secondary to trauma or intoxication); (2) a patient who absolutely refuses or cannot tolerate awake intubation (e.g., a child, a mentally retarded patient, an intoxicated and combative patient); and perhaps most commonly, (3) failure to recognize intubation difficulty on the preoperative evaluation. Of course, the preoperative airway evaluation is important even in the first and second situations, because the findings may dictate the choice of intubation technique. In all three of these situations, the patient may also have a full stomach.

All of the intubation techniques that are described for the awake patient ^1,¹⁵ can be used in the unconscious or anesthetized patient without modification. However, direct laryngoscopy and fiberoptic laryngoscopy are likely to be more difficult in the paralyzed, anesthetized patient compared with the awake patient, because the larynx may move to a more anterior position, relative to other structures, as a result of relaxation of oral and pharyngeal muscles.⁶ In addition and more importantly, orientation may be impaired because the upper airway structures can coalesce into a horizontal plane instead of separating out in a vertical plane.^4,⁵

In the anesthetized patient whose trachea has proved difficult to intubate even with a video laryngoscope it is necessary to try to maintain gas exchange between intubation attempts (by mask ventilation) and, whenever possible, during intubation attempts through the use of (1) supplemental oxygen ¹¹; (2) positive-pressure ventilation via an anesthesia mask that incorporates a self-sealing diaphragm for entry of the FOB airway intubator (instead of the standard oropharyngeal airway)^5,¹⁶; or (3) a laryngeal mask airway (LMA; LMA North America, Inc., San Diego, CA) as a conduit for the FOB (see Chapters 19 and 22).¹⁷

One must not continue with the same technique that did not work before. The amount of laryngeal edema and bleeding is likely to increase after every intubation attempt, particularly with the use of a laryngoscope or retraction blade. The most common scenario in the respiratory catastrophes in the ASA closed claims study was the development of progressive difficulty in ventilating by mask between persistent and prolonged failed intubation attempts. The final result was inability to ventilate by mask and provide gas exchange (see Chapter 55).¹⁸

For each additional attempt, consider modifications, such as improved sniffing position, external laryngeal manipulation, a new blade or new technique, or involvement of a much more experienced laryngoscopist. However, the number of intubation attempts should be limited and the following options should be considered: (1) awaken the patient and do the procedure another day; (2) continue anesthesia by mask or LMA ventilation; (3) perform a surgical airway (tracheostomy or cricothyrotomy) before the ability to ventilate the lungs by mask is lost (see Fig. 10-1).

If awakening the patient is not an option, for instance because surgery is emergent (e.g., cesarean section), and ventilation can be maintained via mask or LMA, surgery may be conducted as needed. Nevertheless, in some cases, the airway must be secured by a surgical airway (e.g., thoracotomy, intracranial-head-neck cases, cases in which the patient is in the prone position). If regurgitation or vomiting occurs at any time during attempts at endotracheal intubation in an anesthetized patient,

• Immediately apply Trendelenburg position.

• Turn the head, and perhaps the body, to the left.

• Suction the mouth and pharynx with a large-bore suction device.

• Try endotracheal intubation while the patient is in the lateral position (the tongue may be more out of the way, but this position is unfamiliar to most anesthesiologists).

• If the endotracheal tube (ETT) has been passed into the esophagus, it may be left there; this may allow decompression of the stomach, and it identifies the esophagus during subsequent intubation attempts (the disadvantage is that it interferes with satisfactory mask seal).

• After securing the airway, consider tracheal suctioning, mechanical ventilation, positive end-expiratory pressure, fiberoptically guided saline lavage, steroids, antibiotics (see Chapter 35).

E The “Cannot Intubate, Cannot Ventilate” Scenario

In rare cases, it is impossible either to ventilate the lungs of a patient by mask or to intubate the trachea. This “cannot intubate, cannot ventilate” (CICV) scenario is an immediately life-threatening situation, and an alternative ventilation procedure must be performed. Established rescue methods are the LMA, Combitube (Tyco Healthcare, Mansfield, MA), transtracheal jet ventilation (TTJV), rigid bronchoscope, and, ultimately, cricothyrotomy.

The development of the LMA was a major advance in the management of difficult intubation and difficult ventilation scenarios. The LMA is suggested as a ventilation device or a conduit for a flexible FOB,^19,²⁰ and the Fastrach intubating LMA (ILMA) may also be utilized.^10,^17,²¹ The LMA and the Combitube are supraglottic ventilatory devices and are not helpful if the airway obstruction is located at or below the glottic opening.²² Use of the rigid bronchoscope may be required to establish a patent airway because it allows ventilation even past an obstruction at these levels. If immediately available, TTJV is relatively easy to perform and can be life-saving.²³ However, it carries significant risks such as subcutaneous emphysema (if the upper airway is not patent or the catheter is not entirely tracheal) and barotrauma (too forced ventilation or proximal airway obstruction)²⁴ The techniques mentioned can provide time until definitive airway management by tracheal intubation (via direct, fiberoptic, or retrograde technique) or by formal tracheostomy can be performed.^25,²⁶ Future research will determine the role of the new rigid video laryngoscopes in the rescue of the “cannot intubate, cannot ventilate” scenario.

Ultimately, a cricothyrotomy may be necessary, but fewer than 50% of anesthesiologists feel competent to perform one.²⁷ Nevertheless, when one is faced with a failed airway, preparations for a surgical airway must begin immediately, and once the decision is made, it is essential to use an effective technique (see Chapters 30 and 31). Despite limited familiarity with the procedure, the risks of an invasive rescue technique must be weighed against the risks of hypoxic brain injury or death.²⁸

F Extubation of a Patient with a Difficult Airway

Extubation of the patient with a DA should be carefully assessed and performed. The anesthesiologist should develop a strategy for safe extubation of these patients, depending on the type of surgery, the condition of the patient, and the skills and preferences of the anesthesiologist. Additional considerations include the following:

• Awake extubation versus extubation before return of consciousness

• Clinical symptoms with the potential to impair ventilation (e.g., altered mental status, abnormal gas exchange, airway edema, inability to clear secretions, inadequate return of neuromuscular functions)

• Airway management plan if the patient is not able to maintain adequate ventilation

• Short-term use of a ventilating tube exchanger (TE) or jet stylet (can be used for ventilation and guided reintubation)

The ideal method of extubation of a patient with a DA is gradual, step by step, and reversible at any time. Extubation over a ventilating TE or jet stylet closely approximates this ideal.¹⁶ The equipment that should be immediately available for the extubation of a DA includes that necessary for intubation of the DA (see Chapter 50).²⁹

G Follow-up Care of a Patient with a Difficult Airway

The presence and nature of the airway difficulty should be documented in the medical record. The intent of this documentation is to guide and facilitate the delivery of future care. Aspects of documentation that may prove helpful include the following:

• Description of the airway difficulties, which should distinguish between difficulties with mask ventilation and those with tracheal intubation

• Description of the airway management techniques used, which should indicate the beneficial or detrimental role of each technique in management of the DA

• Information given the patient (or responsible person) concerning the airway difficulty that was encountered. The intent of this communication is to assist the patient (or responsible person) in guiding and facilitating the delivery of future care. The information conveyed may include, for instance, the presence of a DA, the apparent reasons for the difficulty, and implications for future care.

The provider should also strongly consider dispensing or advising a Medic-Alert bracelet for the patient (see Chapter 54). Finally, the anesthesiologist should evaluate and observe the patient for potential complications of DA management, such as airway edema, bleeding, tracheal or esophageal perforation, pneumothorax, and aspiration.

III Summary of the ASA Algorithm

Difficulty in managing the airway is the single most important cause of major anesthesia-related morbidity and mortality.

Successful management of a DA begins with recognition of the potential problem. All patients should be examined for their ability to open their mouth widely, the structures visible on mouth opening, the size of the mandibular space, and the ability to assume the sniffing position.

If there is a good possibility that intubation or ventilation by mask, or both, will be difficult, the airway should be secured while the patient is still awake rather than after induction of general anesthesia. For a successful awake intubation, it is essential that the patient and the provider be properly prepared.

When the patient is properly prepared, any one of a number of intubation techniques is likely to be successful. If the patient is already anesthetized or paralyzed and intubation is found to be difficult, many repeated forceful attempts at intubation should be avoided, because laryngeal edema and hemorrhage will progressively develop, and the ability to ventilate the lungs by mask may consequently be lost.

After several unsuccessful attempts at intubation, it may be best to awaken the patient; administer regional anesthesia, if appropriate (see Chapter 45); proceed with the case using mask or LMA ventilation; or perform a semielective tracheostomy. If the ability to ventilate by mask is lost and the patient’s lungs cannot be ventilated, LMA ventilation should be instituted immediately. If LMA ventilation does not provide adequate gas exchange, either TTJV or a surgical airway should be instituted immediately.

Tracheal extubation of a patient with a DA over a jet stylet permits a controlled, gradual, withdrawal from the airway that is reversible in that ventilation and reintubation are possible at any time.

Four concepts emerge from the preceding discussion— four very important, take-home messages on the ASA DAA. These are presented in Box 10-4.

Box 10-4 ASA Difficult Airway Algorithm Take-Home Messages

1. If suspicious of trouble → Secure the airway awake

2. If you get into trouble → Awaken the patient

3. Have plans B and C immediately available and in place = think ahead

4. Intubation choices → Do what you do best

IV Problems with the ASA Algorithm and Likely Future Directions

The strength of the ASA DAA is twofold. First, it is very thorough and complete with respect to the options available when an anesthesiologist encounters a DA. Second, it emphasizes the need for and importance of an organized approach to airway management.³⁰

On the other hand, the algorithm has several deficiencies that diminish its application in clinical practice.

• Although it is intended to apply to all patients of all ages, there are certain populations of patients in which further considerations are necessary. Examples include pediatric patients (see Chapter 36), obstetric patients (see Chapter 37), nonfasted patients, and patients with obstruction at or below the level of the vocal cords.³¹

• The algorithm’s clinical end point is successful intubation, but endotracheal intubation may not be necessary, and successful ventilation may suffice.

• The algorithm is fairly complex, allowing a wide choice of techniques at each stage, and its multiplicity of pathways may limit its clinical usefulness in guiding day-to-day practice.³² Unlike the algorithm used in advanced life support (ACLS) guidelines, for example, the ASA DAA is not binary in nature.³³

• Somewhat vague terminology is used in its definitions of difficult tracheal intubation and difficult laryngoscopy. Definitions of optimal-best attempts at conventional laryngoscopy, mask ventilation, and difficult laryngoscopy or intubation are important because they provide an end point at which the practitioner should stop using a particular approach (limiting risk) and move on to something that has a better chance of working (gaining benefit).

• The algorithm mentions ablation of spontaneous ventilation with muscle relaxants but does not discuss the great clinical management implications of muscle relaxants that have different durations of action.

• Although the algorithm advises confirmation of endotracheal intubation, the usefulness of capnography for this purpose is limited during cardiac arrest, which is not an uncommon consequence of the CICV scenario; the esophageal detector device is not similarly limited (see Chapter 32).

• The algorithm does not provide a definitive flow chart for extubation of the DA that incorporates the use of a device that can serve as a guide for expedited reintubation or ventilation, if necessary.

• The role of regional anesthesia in patients with a DA requires further clarification (see Chapter 45).

• The algorithm does not include the use of rigid video laryngoscopy which has dramatically changed the day-to-day clinical practice in recent years and has been shown to be able to rescue failed direct laryngoscopy, particularly in the DA.^12,¹³

Several of the issues mentioned need more in-depth discussion, including the definition of difficult endotracheal intubation, the optimal-best attempt at laryngoscopy, the optimal-best attempt at mask ventilation, and the best muscle relaxant to use.

A Terminology in the ASA Difficult Airway Algorithm

The original publications that introduced the ASA algorithm and provided basic terms that define a DA were relatively vague in their terminology ¹:

• Difficult mask ventilation: “It is not possible for the anesthesiologist to provide adequate face mask ventilation due to one or more of the following problems: inadequate mask seal, excessive gas leak or excessive resistance to the ingress or egress of gas.”

• Difficult laryngoscopy: “Not being able to visualize any portion of the vocal cords after multiple attempts at conventional laryngoscopy.”

• Difficult intubation: “When tracheal intubation requires multiple attempts in the presence or absence of tracheal pathology.”

• Failed intubation: “Placement of the tracheal tube fails after multiple intubation attempts” (0.05% of surgical patients and 0.13% to 0.35% in obstetric patients).

These definitions do not identify a specific Cormack-Lehane grade to characterize larynx visibility, and they do not state a specific number of attempts; therefore, on both counts, they can be interpreted differently by individual practitioners. Also, there is no mention of adjuvants such as positioning and use of appropriate equipment to aid laryngoscopy, ventilation, and intubation. Such information would allow the anesthesiologist to proceed in a new direction at certain junctures, knowing that continuing the same maneuvers would accomplish diminishing returns.

In the same vein, it is important to define “attempt” in an airway management algorithm——for example, as physical placement and removal of the laryngoscope blade. Moreover, an ideal airway management algorithm should define and use the “optimal-best attempt” as the unit, because optimizing the conditions for the various maneuvers has clearly been shown to have a profound effect on successful intubation.

B Definition of Optimal-Best Attempt at Conventional Laryngoscopy

Difficulty in performing endotracheal intubation is the end result of the difficulties that occurred during laryngoscopy, which depends on the operator’s level of expertise, the patient’s characteristics, and circumstances. The problem with multiple repeated attempts at conventional laryngoscopy is the creation of laryngeal edema and bleeding, which impair mask ventilation and subsequent endotracheal intubation attempts, thereby creating a CICV situation. Therefore, it is imperative that the anesthesiologist makes his or her optimal-best attempt at laryngoscopy as early as possible, under the best circumstances, which is usually the first or second attempt. If the optimal-best attempt fails twice, an alternative plan should be activated as the next step, so that no further risk is incurred from additional attempts without likely benefit.

An optimal-best attempt at conventional laryngoscopy is defined as having the following characteristics ^34,³⁵:

1. Performed by a reasonably proficient anesthesiologist with at least 3 years of experience (Rationale: If such an experienced anesthesiologist is having difficulty in visualizing the glottis, no other anesthesiologist or surgeon needs to or should attempt the same maneuver)

2. With the patient in the optimal “sniffing” position (Rationale: No attempt is wasted because the position was suboptimal; slight flexion of the neck on the head and severe extension of the head on the neck aligns the oral, pharyngeal, and laryngeal axes into a straight line; positioning devices are necessary in the obese patient [Fig. 10-2])

3. Using the appropriate type and length of blade (Rationale: Macintosh-type blades work best in patients with little upper airway room, and Miller-type blades are ideal for patients who have small mandibular space, anterior larynx, large incisors, or a long, floppy epiglottis). Based on most recent literature, a rigid video laryngoscope should be considered at least for the second attempt, if immediately available.

4. Using the appropriate blade length (Rationale: Patients’ airways vary in size, and optimal fit of the blade to the airway allows the best possible pressure application to lift the epiglottis directly or indirectly)

5. Having a low threshold for using optimal external laryngeal manipulation (OELM) or backward upward rightward pressure (BURP) (Fig. 10-3) (Rationale: Both maneuvers can frequently improve the laryngoscopic view by at least one entire grade and should be an inherent part of laryngoscopy and an instinctive reflex response to a poor laryngoscopic view)

Figure 10-2 Troop Elevation Pillow with additional foam head rest.

(Courtesy of Mercury Medical, Clearwater, FL.)

Figure 10-3 Determining optimal external manipulation (OELM) with the free (right) hand. OELM should be an inherent part of laryngoscopy and is performed when the laryngoscopic view is poor. Ninety percent of the time, the best view is obtained by pressing over the thyroid cartilage (T, hand position 1) or the cricoid cartilage (C, position 2); pressing over the hyoid bone (H, position 3) may also be effective.

With this definition and no other confounding factors, an optimal-best attempt at laryngoscopy may be achieved on the first attempt, and no more than three attempts should be required (e.g., wrong blade, wrong length).

C Definition of Optimal-Best Attempt at Conventional Mask Ventilation

If the patient cannot be intubated, gas exchange is dependent on mask ventilation. If the patient cannot be ventilated by mask, a CICV situation exists, and immediate resuscitation maneuvers must be instituted. Because each of the acceptable responses to a CICV situation has its own risks, the decision to abandon mask ventilation should be made after the anesthesiologist has made an optimal-best attempt at mask ventilation.

An optimal-best attempt at conventional mask ventilation is defined as having the following characteristics ^34,³⁵:

1. Performed by a reasonably proficient anesthesiologist with at least 3 years of experience (Rationale: as above)

2. With the patient in the optimal sniffing position (Rationale: as above)

3. Using two-person BMV with the most proficient anesthesiologist holding the mask and the less proficient anesthesiologist squeezing the bag (Fig. 10-4) (Rationale: Usually this leads to a far better mask seal, better jaw thrust, and therefore higher tidal volume than can be achieved with one person in a difficult-to-mask patient)

4. Using appropriately sized oropharyngeal or nasopharyngeal airway devices that have been inserted correctly (Rationale: This provides a canal for airflow through the soft tissue of the upper airway; establishes and improves tidal volume)

Figure 10-4 Optimal mask ventilation. Left, Two-person effort when second person knows how to perform jaw thrust; right, two-person effort when second person can only squeeze the reservoir bag.

If mask ventilation is very poor or nonexistent, even with a vigorous two-person effort in the presence of large artificial airways, this constitutes a classic CICV scenario, and the team needs to start potentially life-saving plan B (see Fig. 10-1).

D Options for the CICV Scenario

Both the LMA and the Combitube have been shown to work well to rescue airway emergencies.^17,^36,³⁷ The ASA DAA does not dictate the order of preference of these devices in the CICV situation, but the following considerations must be taken into account: (1) the anesthesiologist’s own experience and level of comfort in the use of these methods, (2) the availability of these devices, (3) the type of airway obstruction (upper versus lower), and (4) the benefits and risks involved.

The ProSeal LMA usually forms a better seal than the LMA-Classic and provides improved protection against aspiration.³⁸^–⁴⁸ When properly positioned, the Combitube allows ventilation with a higher seal pressure than the LMA-Classic, protects against regurgitation,⁴⁹ and allows further attempts at intubation while the esophageal cuff protects the airway.⁵⁰ The Combitube has been successfully used in difficult intubation and CICV situations,^49,⁵¹^–⁵⁵ including ventilation failure with an LMA.⁵⁶

Both the LMA and the Combitube are supraglottic ventilatory devices (Fig. 10-5). They cannot solve a truly glottic problem (e.g., spasm, massive edema, tumor, abscess) or a subglottic problem.³⁷ If an obstacle is suspected to exist in the glottic or subglottic area, the ventilatory mechanism (e.g., ETT, TTJV, rigid ventilating bronchoscope, surgical airway) needs to be positioned below the level of the lesion. The ASA DAA does not discriminate between the obstructed and the unobstructed airway, and this is a critical weakness of the algorithm.

Figure 10-5 The laryngeal mask airway (left) and the Combitube (right) are supraglottic ventilatory devices.

E Determinants of the Use of Muscle Relaxants for Difficult Airway Management

Muscle relaxants have different characteristics regarding time of onset and duration that significantly determine their advantages and disadvantages in the context of airway management (Table 10-2). The key elements in the choice of a nondepolarizing muscle relaxant are whether mask ventilation will be adequate and what rescue plan has been determined. For instance, with the induction of general anesthesia in an uncooperative patient who has a DA, the anesthesiologist should consider the relative merits of preservation of spontaneous ventilation versus use of muscle relaxants. Alternatively, if a small dose of succinylcholine (0.5 to 0.75 mg/kg) is used, good intubating conditions can be achieved within 75 seconds for about 60 seconds, allowing an early-awaken option if the ETT cannot be placed. In contrast, use of succinylcholine during DA management may not be the best choice if mask ventilation is considered possible and the alternative plan of action is FOB.⁵

TABLE 10-2 Advantages and Disadvantages of Muscle Relaxants with Different Durations of Action

Muscle Relaxant	Advantages	Disadvantages
Succinylcholine	Permits the awaken option at the earliest time possible	A period of poor ventilation (spontaneous or with positive pressure) may occur as the drug wears off Does not permit a smooth transition to plan B (e.g., use of a fiberoptic bronchoscope) and so on
Nondepolarizing	Permits a smooth transition to plan B and so on, provided mask ventilation is adequate	Does not allow awaken option at an early time

Moreover, endotracheal intubation can be successfully accomplished without the use of any muscle relaxant, and this option should be considered in certain situations.^57,⁵⁸ Another consideration is that in most patients, prior administration of a small dose of a nondepolarizing neuromuscular blocker may slightly diminish the duration of action of succinylcholine,⁵⁹ and therefore the time to spontaneous recovery of airway reflexes may be shortened.

Experts are debating whether a second dose of succinylcholine should be provided during a cannot-intubate situation when the patient resumes spontaneous ventilation. We believe that this practice is appropriate if the chance of successful endotracheal intubation is high (i.e., a fairly good laryngoscopic grade at the initial attempt) and laryngoscopy is difficult because of incomplete paralysis. A second dose of succinylcholine may also be appropriate when mask ventilation is possible, the laryngoscopist is highly skilled, and a simple change in either the patient’s position or the type of laryngoscope is necessary for final success. Glycopyrrolate at a dose of 0.2 to 0.4 mg should be administered in conjunction with the repeated dose of succinylcholine in order to prevent a bradycardic response.

F Summary

In summary, the ASA DAA has worked well over the past decade. In fact, there has been a very dramatic decrease (30% to 40%) in the number of respiratory-related malpractice lawsuits, brain damage, and deaths attributable to anesthesia since 1990 (Fig. 10-6).⁶⁰ However, a number of issues have emerged that indicate that the algorithm can be improved, as discussed earlier. Consideration of these issues should make the algorithm still more clinically specific and functional. Nonetheless, the DAA provides excellent guidelines for anesthesiologists in their clinical decision-making for patients with DAs. Successful management in these cases is key to reducing the risk of anesthesia-related morbidity and mortality.

Figure 10-6 A, The incidence of respiratory system damaging events as a proportion of all claims in the database for each 5-year period (N = 3282). **P ≤ 0.01 between 1975 and 1990+ time periods. B, Claims for death and brain damage as a proportion of all claims in the database for each 5-year time period (N = 3282). **P ≤ 0.01. (In both A and B, N does not equal the sum of n because there are some claims in the database for which the date is before 1975 or unknown.)

(From Cheney FW: Committee on Professional Liability: Overview. ASA Newsletter 58:7–10, 1994.)

V Introduction of A New comprehensive Airway Algorithm

Based on the reasoning presented to this point, currently available evidence from the literature, and a plethora of clinical experience, we created a new and comprehensive algorithm for airway management with the intent of improving patient safety during the perioperative period. This new airway algorithm includes several subalgorithms that address the various potential clinical scenarios and suggest clear procedures and readily available equipment to solve the problem.

Most recently we incorporated the use of video laryngoscopy into the new comprehensive airway algorithm based on new evidence that strongly supports its role either as primary device or as first rescue device during the management of a difficult airway.^12,¹³

The main algorithm comprises all the necessary information for routine airway management. It is supplemented with four subalgorithms (A through D) that describe maneuvers and instruments necessary to solve various DA scenarios and are organized in an escalating manner according to the immediate threat of the respective scenario. In addition, a fifth subalgorithm (E) suggests a standardized approach for extubation of these patients.

• Subalgorithm A = cannot ventilate, cannot intubate (CICV)

• Subalgorithm B = can ventilate but cannot intubate via laryngoscopy

• Subalgorithm C = ventilation established through a subglottic airway, further management options

• Subalgorithm D = surgical airway management

• Subalgorithm E = extubation of a patient with a known or suspected DA

Extubation of these patients carries significant risks and requires a systematic approach. To our knowledge, this new airway algorithm is the only algorithm that provides a specific paradigm to address extubation of the patient with a DA.

A The Main Algorithm

This algorithm (Fig. 10-7) is intended for and limited to elective surgery in the operating room and does not include airway trauma and crash intubations. As with the ASA algorithm, the crux of management of the DA lies in its recognition (Box 10-5). If difficulties are anticipated, surgery under regional anesthesia may be considered. However, there are anesthetic, surgical, and patient factors that may render the option of regional anesthesia for surgery inappropriate (Box 10-6). If regional anesthesia is considered appropriate and successful anesthesia is achieved, then surgery may proceed. However, if regional anesthesia fails, then the option for an awake airway technique or inhalation induction should be considered. Similarly, if regional anesthesia is not an appropriate option for surgery, then the performance of an awake intubation or inhalation induction is recommended.

Figure 10-7 The main algorithm for airway management. BMV, Bag-mask ventilation; GA, general anesthesia; RA, regional anesthesia.

(Courtesy of Ansgar Brambrink, MD, and Carin Hagberg, MD.)

Box 10-5 Individual Predictors of Difficult Airway Management *

History

Congenital/acquired syndromes, malignancy, trauma, or disease states affecting the airway (e.g., diabetes, obstructive sleep apnea)

Recent difficult intubation

Prior surgery involving the larynx or neck

^* Includes predictors of difficult mask ventilation, difficult laryngoscopy, difficult intubation, and surgical airway.

Box 10-6 Factors Influencing the Choice of Regional Anesthesia (RA) in Patients with a Difficult Airway (DA)

Anesthesiologist

Expertise in both RA and DA management

Enough preoperative time to perform RA technique

Appropriate RA technique for surgical procedure

Prepared for alternative plans for DA management

Surgical Procedure

Nonemergent

Appropriate duration

Patient position allows airway access during surgery

Procedure can be interrupted

Limited or moderate blood loss

Support

Equipment, including a DA cart with specialized devices and airway adjuncts

Staff (additional experienced anesthesiologists and operating room nurses)

The choice of awake versus asleep spontaneous ventilation depends on the experience of the anesthesiologist and the patient’s level of cooperation. In general, the awake technique is the safest technique. However, in some patients (e.g., children; mentally retarded or incapacitated patients; aggressive, intoxicated, or delirious patients), an awake technique may not be possible. Additionally, in patients with cervical spine pathology who are at risk for neurologic injury, extreme caution should be exercised during an awake technique, and precautions should be undertaken to prevent any cervical movement.

Failure of an awake technique usually falls into three categories: oversedation, obscuration of vision (by blood or secretions), and technical difficulties. If the patient is oversedated, airway issues may become complicated. If optimal attempts at BMV are successful, then Pathway B may be followed. However, if optimal attempts at BMV fail, the anesthesiologist should quickly proceed to Pathway A. If difficulty occurs with any of the awake fiberoptic techniques as a result of blood, mucus, or secretions such that adequate visualization is not possible, a blind technique may be considered (see “Bloody Airways.”) Additionally, more invasive techniques, such as a surgical airway or retrograde intubation may be performed.

1 The Nonpredicted Difficult Airway

Although projected difficulties with airway management may not be present, making an optimal-best attempt at ventilation and intubation is paramount. First, even the best airway assessment will not detect 100% of DAs, as is evident from the literature. Second, the optimal-best attempt allows the anesthesiologist to follow the algorithm quickly and appropriately. Third, when the first attempt is the optimal-best attempt, this allows a greater margin of safety before patient decompensation begins. Fourth, making the first attempt the optimal-best attempt minimizes repeated attempts at airway manipulation, which may lead to greater morbidity. Therefore, the algorithm emphasizes proper positioning and the use of external laryngeal pressure even in patients without predicted airway difficulty.

After proper positioning, preoxygenation, and induction of general anesthesia, adequacy of BMV should be assessed. (An exception may be made for patients who undergo a rapid-sequence induction). If BMV is deemed adequate, intermediate- or long-acting muscle relaxants can be given to aid direct laryngoscopy. Liberal use of external laryngeal manipulation to optimize the laryngoscopist’s view of the glottic opening is recommended. If BMV is inadequate despite optimal positioning and placement of an oropharyngeal or nasopharyngeal airway, then the “emergency situation,” Pathway A, should be followed.

If direct laryngoscopy is successful, then surgery may proceed. However, if direct laryngoscopy is unsuccessful and BMV is adequate, then the “elective measures,” Pathway B, should be followed. In performing a rapid-sequence induction, a short-acting muscle relaxant is usually given after induction of general anesthesia without checking BMV adequacy; therefore, if the anesthesiologist fails to intubate after induction, he or she should proceed directly to Pathway B and continue along the algorithm based on the initial laryngoscopic view.

2 New Algorithm Pathways

a Pathway A

The CICV scenario is an emergency situation in which the optimal-best attempt at ventilation and intubation has failed (Fig. 10-8). If muscle relaxants have not been administered, then one further laryngoscopy attempt, preferably using a video laryngoscope if available, or a conventional direct laryngoscope.^12,¹³ without muscle relaxation can be made (preferably by another experienced anesthesiologist). If tracheal intubation fails, assistance should be summoned. Thereafter, the algorithm alerts the anesthesiologist to the difference in airway management with respect to the possibility of a fixed obstruction (e.g., tumor, vocal cord paralysis) at or below the cords.

Figure 10-8 Pathway A: cannot ventilate, cannot intubate. DL, Direct laryngoscopy; ETT, endotracheal tube; ILMA, intubating laryngeal mask airway; SGA, supraglottic airway; VL, video laryngoscopy.

If the patient has no known obstruction at or below the cords, a supraglottic airway (SGA) may help establish ventilation. If ventilation is inadequate via an SGA, then a surgical airway (Pathway D) should be performed. If an SGA does establish adequate ventilation, then Pathway C is recommended, in which endotracheal intubation is performed with an SGA in place.

If the patient has a known fixed obstruction at or below the cords, then use of an SGA would be inappropriate. Ventilation attempts with an SGA would most likely be unsuccessful. If awakening the patient is a valid option, an awake intubation technique should be performed. If awakening the patient is not an option, an intubating stylet in combination with a video laryngoscope or a rigid bronchoscope should be used. These devices, unlike an SGA, allow the provider to establish a conduit beyond the obstructed area. Again, if these approaches are unsuccessful, rapid progression to a surgical airway via Pathway D is advised.

b Pathway B

Pathway B (Fig. 10-9) is derived from a situation where oxygenation and ventilation are adequate but a definitive airway has not been established. After calling for assistance and repeating laryngoscopy, using a video laryngoscope, if available, the management is divided based on the grade of glottic view. If a Cormack-Lehane grade 2B or 3 laryngoscopic view is visualized, an intubating stylet, or special laryngoscopic blade or video laryngoscope can be helpful. If this is successful, surgery may proceed. However, if the attempt is not successful, then adequacy of BMV must be reassessed, especially if BMV has not been attempted previously (i.e., rapid-sequence induction). If BMV is adequate, then further elective measures may be considered. If a grade 4 laryngoscopic view is observed, a retrograde technique may be considered or the anesthesiologist may proceed directly to SGA or ILMA, depending on the availability of equipment and the expertise of the anesthesiologist. However, if BMV is inadequate, then it is likely inappropriate to perform a fiberoptic intubation (FOI) or retrograde intubation. Instead, the anesthesiologist should recognize this as an emergent situation and immediately attempt SGA or ILMA.

Figure 10-9 Pathway B: can ventilate, but cannot intubate via laryngoscopy. FOI, Fiberoptic intubation; ILMA, intubating laryngeal mask airway; SGA, supraglottic airway; VL, video laryngoscopy.

c Pathway C

Pathway C (Fig. 10-10) represents a situation in which the patient is anesthetized and oxygenation and ventilation are adequate via an SGA. The decision to intubate depends on the answer to the question, “Is endotracheal intubation necessary for the surgical procedure?” If the answer is “No,” surgery may continue with an SGA. If the answer is “Yes,” FOI through the SGA with an Aintree Intubation Catheter (Cook Critical Care, Bloomington, IN) may be performed. Alternatively, if an ILMA or CTrach (LMA International, Singapore) was inserted as the SGA, intubation via these devices is appropriate. However, if intubation attempts fail, it would be appropriate to awaken the patient and perform an awake intubation.

Figure 10-10 Pathway C: ventilation established through a subglottic airway, further management options. FOI, Fiberoptic intubation; SGA, supraglottic airway.

d Pathway D

In Pathway D (Fig. 10-11), all attempts to oxygenate and ventilate the patient have been unsuccessful. A surgical airway is crucial, and in patients older than 6 years of age, the cricothyroid membrane (CTM) remains the window to the airway. However, if the patient is younger than 6 years old, the CTM is not well developed, and TTJV or the performance of a surgical tracheostomy is advised.

Figure 10-11 Pathway D: surgical airway management.

e Pathway E

After a secure airway has been established, there will come a time when extubation is necessary. Consultants of the ASA Task Force on Management of the Difficult Airway,⁵ as well as the Canadian Airway Focus Group, recommended a preformulated strategy for extubation of the DA.⁶¹ Extubation strategies are discussed in detail in Chapter 50. Extubation strategies for the DA include, but are not limited to, bronchoscopic examination under general anesthesia through an SGA, substitution of an ETT with an SGA, and extubation over a TE.

Pathway E (Fig. 10-12) is an extubation algorithm in which a TE used is for patients who underwent multiple attempts at direct laryngoscopy or for whom alternative rescue devices were used. It should also be used for patients with a known or suspected DA who have undergone successful intubation. If the patient has met the extubation criteria (Box 10-7), one of the aforementioned extubation strategies can be used. A TE may be placed and the ETT removed over it, leaving the TE in the trachea. If ventilatory parameters and oxygenation are adequate, the TE can then be removed, provided there is no evidence of laryngeal edema or respiratory difficulty. The length of time for which these catheters are left in place is most commonly 30 to 60 minutes, although durations as long as 72 hours have been reported in the literature. Clinical judgment should be used according to the particular situation.