The ASA Difficult Airway Algorithm: Analysis and Presentation of a New Algorithm

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Chapter 10 The ASA Difficult Airway Algorithm

Analysis and Presentation of a New Algorithm*

I Introduction

There is strong evidence that successful airway management in the perioperative environment depends on specific strategies. Suggested strategies from various subfields of medicine are now being linked together to form more comprehensive treatment plans or algorithms. The classic flow charts of this nature are the resuscitation algorithms that provide evidence-based guidance during cardiopulmonary resuscitation worldwide.

The purpose of the Algorithm on the Management of the Difficult Airway (DAA), published by the American Society of Anesthesiologists (ASA), is to facilitate management of the difficult airway (DA) and to reduce the likelihood of adverse outcomes. The principal adverse outcomes associated with the DA include (but are not limited to) death, brain injury, cardiopulmonary arrest, unnecessary tracheostomy, airway trauma, and damage to teeth.

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.

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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.)

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):

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 literature3 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:

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

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 literature1214 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.

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:

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 patient1,15 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 oxygen11; (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,

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