Module 12
The American Society of Anesthesiologists'
Management
of the Difficult Airway Algorithm
and Explanation-Analysis of the Algorithm
Problems with the ASA Algorithm
and Likely Future Directions
DEFINITION OF OPTIMAL-BEST ATTEMPT AT
CONVENTIONAL LARYNGOSCOPY
Difficulty in performing endotracheal
intubation is the end result of difficulty in performing
laryngoscopy, which depends on the operator’s level of
expertise, patient characteristics, and circumstances. The
problem with multiple repeated attempts at conventional
laryngoscopy is the creation of laryngeal edema and bleeding,
which will impair mask ventilation and subsequent endotracheal
intubation attempts, thereby creating a CICV situation.
Thus, it is imperative that the anesthesiologist makes his/her
optimal-best attempt at laryngoscopy as early as possible, and,
if that fails, an alternative plan should be activated so that
no further risk, without likely benefit, will be incurred.
What is an optimal-best attempt at
conventional laryngoscopy?8
First, a reasonably experienced anesthesiologist who has had at
least 3 full years of experience, should perform the
laryngoscopy. If an experienced anesthesiologist is having
difficult visualizing the glottis, he/she should not ask or
allow other anesthesiologists or ENT surgeons to attempt the
same maneuver.
Second, the patient should always be in an
optimal “sniffing” position (slight flexion of the neck on the
head and severe extension of the head on the neck),8
which aligns the oral, pharyngeal, and laryngeal axis into more
of a straight line. In some patients (such as the obese)
obtaining an optimal “sniffing” position takes a great deal of
work (Fig. 4), such as placing pillows and blankets under the
scapula, shoulders, nape of the neck, and head, which is
difficult when anesthesia and paralysis have made the patient a
massive (dead) weight. Positioning the obese patient can
be easily accomplished with a new positioning device, the Troop
Elevation Pillow (Mercury Medical, Clearwater, FL) (Figure 5).
Thus, an endotracheal intubation attempt should not be wasted
because of failure to have the patient in an optimal “sniffing”
position prior to the induction of general anesthesia.
Third, if the laryngoscopic grade is
either II (arytenoids only), III (epiglottis only), or IV (soft
palate only), then optimal external laryngeal manipulation
(OELM) or backwards, upwards,
rightward pressure (BURP) should be
used (Fig. 6).6,8
Neither OELM nor BURP is cricoid pressure (Fig. 6) and can be
achieved in 5-10secs.6
Such maneuvers very frequently can 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.6
Thus, an endotracheal intubation attempt should not be wasted
because of failure to use these maneuvers.
Fourth, the proper function of both a
Macintosh and Miller blade is dependent on using an appropriate
length of blade. In order to life the epiglottis out of the line
of sight, the Macintosh blade must be long enough to put tension
on the glossoepiglottic ligament, and the Miller blade must be
long enough to trap the epiglottis against the tongue. Thus, in
some patients, it may be appropriate to change the length of the
blade one time in order to obtain proper blade function.
Fifth, in some patients, a Macintosh blade
may provide a superior view or intubating conditions than a
Miller blade, and vice versa. A Macintosh blade is generally
regarded as a better blade whenever there is little upper airway
room to pass the ET (e.g., small narrow mouth, palate,
oropharynx), and a Miller blade is generally regarded as a
better blade in patients who have a small mandibular space
(anterior larynx), large incisors, or a long, floppy epiglottis.
In summary, an optimal-best attempt at laryngoscopy can be
defined as: (1) a reasonably experienced (at least 3 full recent
years) laryngoscopist; (2) use of optimal “sniffing” position;
(3) use of OLEM or BURP; (4) change of length or type of blade
one time. With this definition, and with no other
confounding considerations, optimal-best attempt at laryngoscopy
may be achieved on the first attempt and should not take more
than a maximum of 3 attempts. Thus, difficult endotracheal
intubation may be readily apparent to a reasonably experienced
intubationist on the very first attempt and therefore be both
number of attempts and time independent. A more logical
definition would be based on optimal-best attempt laryngoscopic
view and periglottic and subglottic pathology and retain number
of attempts and time of attempt as maximal boundary airway
conditions.
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