Module 12
The American Society of Anesthesiologists'
Management of the Difficult Airway Algorithm
and Explanation-Analysis of the Algorithm
The ASA Algorithm on the Management of the Difficult Airway
A side by side comparison of the original
(1993) and updated (2003) Difficult Airway Management Algorithm
is depicted in Figs 1a and 1b. Differences between the two
algorithms are listed in Box 1. The algorithm begins with the
most basic question of whether or not the presence of a
difficult airway is recognized (see
Chapter 8). Obviously, if the
potential for difficulty is recognized, then one can make proper
mental and physical preparation, and the chance of a successful
good outcome is increased, whereas failure to recognize the
potential for difficulty means, by definition, that the actual
difficulty will be unexpected, proper mental and physical
preparation will be minimized, and a chance of a successful good
outcome decreased.
 
Box 1: Differences between 1993 and 2003 ASA Management of
the Difficult Airway Algorithm
1. Difficult ventilation is now listed
first under assessment of the likelihood and clinical impact
of basic management problems. Also, in this same category,
difficult trachestomy was added.
2. To actively pursue opportunities to
deliver supplemental oxygen throughout the process of
difficult airway management was added.
3. When considering the relative
merits and feasibility of basic management choices, awake
intubation versus intubation attempts after induction of
anesthesia should now be considered first before
non-surgical techniques as the initial approach to
intubation.
4. The use of the Laryngeal Mask
Airway (LMA) is incorporated into the algorithum in the
awake limb and after induction of general anesthesia limb in
both the non-emergency and emergency pathways (either as a
ventilatory device or as a conduit for treacheal
intubation).
5. Removed one more intubation attempt.
6. Added the rigid bronchoscope as an
option for emergency non-invasive ventilation.
When performing a proper airway
evaluation, the practitioner should take into account any
patient characteristics that could lead to difficulty in the
performance of: 1) bag-mask ventilation, 2) laryngoscopy, 3)
intubation, and 4) a surgical airway. As mentioned above, the
possibility of difficult mask ventilation (DMV) is now the first
issue addressed in the revised algorithm.
Langeron et al39,
in a recent prospective study of 1,502 patients, made the
following observations: 1) the reported incidence of DMV was 5%
in the general adult population; 2) DMV was reported more
frequently when intubation was difficult; 3) anesthesiologists
did not accurately predict DMV; and 4) five criteria (age>
55yrs, BMI >26kg/m2, lack of teeth, presence of
mustache/beard, history of snoring) were independent risk
factors for DMV, and finally the presence of two of these risk
factors indicated a high likelihood of DMV.
As perioperative physicians,
anesthesiologists should keep these risk factors in mind in
order to optimize the patient’s condition, as some of them can
be reversed. Thus, DMV may possibly be prevented by such simple
precautions as shaving a mustache/beard, or leaving dentures in
place during bag-mask ventilation, and having the patient
worked-up for possible obstructive sleep apnea, if time
permits. These points merit further investigation.
The following plan for routine evaluation
of a patient's airway, assuming that the patient has no obvious
pathologic airway problems, is a reasonable one
(see Chapter 8 for a complete discussion
of preoperative evaluation).
1) Before the initiation of anesthetic care and airway
management in any patient, an airway history should be
conducted, whenever feasible, to detect medical, surgical and
anesthetic factors that may indicate the presence of a difficult
airway. Systemic diseases (e.g., respiratory failure and
coronary artery disease) that might place limits on or require
special attention during awake intubation, such as increased
fraction of inspired oxygen (FiO2) and prevention of
sympathetic nervous system stimulation, respectively, should be
noted. Additionally, examination of previous anesthetic records,
if available in a timely manner, may yield useful information
about airway management.
2) Physical examination of the airway should also be
conducted, whenever feasible, before the initiation of
anesthetic care and airway management in all patients to detect
physical characteristics that may indicate the presence of a
difficult airway. Multiple airway features should be assessed
(Table 1).
a) Patients should be asked to open their mouths as widely
as possible and extend their tongues. The mandibular opening
(measured by ruler, if there is doubt about any limitation) and
pharyngeal anatomy (uvula, tonsillar pillars, etc.) are
observed.
b) The length of the submental space (mandible to hyoid) and
thyromental distance (mandible to thyroid notch) should be noted
(measured by ruler, if there is any doubt).
c) Patients should be viewed from the side to see their
ability to assume the “sniffing” position (flexion of the neck
on chest and extension of the head on the neck). The lateral
view should also reveal any degree of maxillary overbite.
d) The patency of the nostrils.
e) The length and thickness of the neck.
Although each anatomical risk factor
individually has a rather low positive predictive value for
difficult intubation, when combined, the factors can provide a
gestalt for difficult airway management.
Table 1: Components of the Preoperative Airway Physical Examination
Airway Examination Component |
Nonreassuring Findings |
1. Length of upper incisors |
Relatively long |
2. Relation of maxillary and mandibular incisors
during normal jaw closure |
Prominent “overbite” (maxillary incisors anterior to mandibular
incisors) |
3. Relation of maxillary and mandibular incisors
during voluntary protrusion of mandible |
Patient cannot bring mandibular incisor anterior to (in front of)
maxillary incisors |
4. Interincisor distance |
<3cm |
5. Visibility of uvula |
Not visible when tongue is protruded with patient
in sitting poition (e.g., Mallampati class >II) |
6. Shape of palate |
Highly arched or very narrow |
7. Compliance of mandibular space |
Stiff, indurated, occupied by mass, or nonresilient |
8. Thyromental distance |
<3 ordinary finger breadths |
9. Length of neck |
Short |
10. Thickness of neck |
Thick |
11. Range of motion of head and neck |
Patient cannot touch tip of chin to chest or cannot extend neck |
3) Additional evaluation may be indicated in some patients
to characterize the likelihood or nature of the anticipated
airway difficulty. The findings of the airway history and
physical examination may be useful in guiding the selection of
specific diagnostic tests and consultation.31
4) In a few patients,
an “awake-look” using direct laryngoscopy (after
adequate preparation) may be performed in order to further
assess intubation difficulty. If an adequate view is obtained,
endotracheal intubation may be performed followed immediately by
the administration of an intravenous induction agent.
If it is recognized that mask
ventilation or the intubation is going to be difficult because
of the presence of a pathologic factor(s) or a combination of
anatomic factors (large tongue size, small mandibular space, or
restricted atlanto-occipital extension), airway patency should
be secured and guaranteed (usually by intubation) while the
patient remains awake.
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