REVIEW
Recent developments in the management
of the difficult airway
T. Ezri1, A. Izakson2, Y. Ginosar3
Head, Department of Anesthesia, Wolfson Medical Center, Holon, Associate Professor of Anesthesiology Tel Aviv University, Israel; Outcomes Research
Consortium, Cleveland OH, USA
2
Head, Department of Anesthesia, Rebecca Sief Medical Center, Zefad, Instructor of Anesthesiology, Tel Aviv University, Israel,
3
Director of the Mother and Child Anesthesia Center, Department of Anesthesiology and Critical Care Medicine, Senior Lecturer of Anesthesiology, Hadassah
Hebrew University Medical Center, Jerusalem, Israel
1
The difficult airway is so much a challenge mainly for the un-experienced anesthetist, that it deserves a privileged position in the training program of the residents. Enhanced awareness of the importance of through preoperative airway assessment as routine practice,
implementation of airway management algorithms and the introduction of new airway devices are corner stones for a good outcome.
The aim of these steps is to diminish the consequences of encountering a difficult airway, that is, to avoid failed intubation and thus
brain failure or other complications of hypoxia. The review highlights recent developments in the management of the difficult airway,
by no means intending to substitute clinical teaching or comprehensive airway management courses. Difficult intubation can lead to
failure to intubate and if associated to difficult mask ventilation or to the worst nightmare- failed mask ventilation - bare the risk of
ending up with unwanted outcomes. Therefore, the authors present the predictors of difficult intubation, introducing the Class zero
airways, previously described by the same team. A floppy epiglottis might hamper mask ventilation even to this novel described class
of patients. New devices and recommended positions for intubation are updated; ways to assess depth of intubation are exposed.
The conclusion states how far we are from ideally managing the difficult airways despite novel technology. The opening to learning,
exercising, being prepared with alternatives and providing proper equipment while getting experience are the ways to improve our
performances and the patients’ final outcome.
Introduction
During the last three decades, significant progress has been
made in the perioperative management of the difficult airway. This period has been marked by 1) a greater awareness
of the importance of thorough preoperative airway assessment as routine practice, 2) careful preoperative airway
preparation in patients suspected to have a difficult airway,
3) the implementation of airway management algorithms
and 4) the introduction of new airway devices. Of these
devices, the laryngeal mask airway (LMA) and the fiberoptic bronchoscope (FOB) have made the most impact on
modern airway management. Emerging technologies for
video-assisted laryngoscopy (VAL) are currently gaining
popularity and are likely to similarly impact airway management algorithms in the near future.
The aim of these steps is to avoid the consequences of perioperative airway mishaps. Failed intubation should not
lead to brain injury or death and data will be presented to
suggest that there has indeed been a decrease in perioperative morbidity and mortality associated with the perioperative management of the difficult airway .
The purpose of this review is to emphasize recent developments in the management of the difficult airway. This review is not intended to be a substitute for clinical teaching
or comprehensive airway management courses. There are
some important differences in management of the airway
in pregnant women and in infants which is beyond the
scope of this review, although further reviews will be published on these issues in the near future.
Why is management of the difficult airway still
a problem?
Failed intubation still causes brain injury and death. In the
ASA closed claims study among general surgical patients, failed airway management was implicated in over 6% of the
cases of anesthesia-related severe brain injury or death; this
rose to 18% in obstetric patients [1, 2]. These numbers are
a concern, as recent years have seen advances in strategies
for managing difficult airways. Anesthesia manpower shortages often stretch available resources, so adequate time and
manpower may not be allocated for preoperative assessment.
Indeed, approximately half of cases of difficult intubations
are unpredicted before the induction of anesthesia [3].
Furthermore, the pattern of anesthesia-related morbidity
and mortality is continually changing. Even though airway
management complications during anesthesia induction
are decreasing, they are increasing during emergence from
anesthesia, particularly following extubation of the trachea
[2]. Finally, the co-morbities of surgical patients are steadily increasing (including increasing surgery at the extremes
of age and body size with the associated increase in risk
factors for airway management problems.
Thirty or more years ago, most cases of anesthesia-related
mortality and severe brain damage were associated with the
aspiration of gastric contents either with or without failure
of airway management on intubation. In the last two decades, however, most anesthesia-related mortality has been
linked to obesity, to the failure to recognize and adequately manage critical illnesses and to the failure to adopt an
Recent developments in the management of the difficult airway
147
Table I. Incidence of difficult airway in general surgical and obstetric population, both in obese and non-obese patients
General surgery
Obstetrics
Difficult intubation
Failed intubation
Difficult mask ventilation
Failed mask ventilation
Non-obese 2.2%
Obese 15,5%
Non-obese 0.3%
Obese 1%
Non-obese 5%
Obese ?
Non-obese 0.01%
Obese ???
Non-obese 3.3-7.9%
Obese 35%
Non-obese 0.4%
Obese ???
Non-obese ???
Obese ???
Non-obese 0.025%
Obese ???
adequate extubation strategy for patients who where already difficult to intubate at the beginning of surgery.
Unfortunately, failure of airway management remains a serious problem and its incidence is far from negligible.
Incidence of difficult airway
The incidence of difficult/failed intubation and difficult/
failed ventilation [4-10] is summarized in table I.
Understanding the airway problem
Airway management problem-solving depends on the
anatomic or pathophysiologic mechanism of the difficult
airway which can be classified as supraglottic, glottic-epiglottic or subglottic mechanisms.
Greenland [11, 12] recently described a new model to explain normal and difficult laryngoscopy and tracheal intubation. The interdependence between each laryngoscopy
step and an eventual pathological change that might appear at each point is emphasized. The understanding of
this complex model may help resolve three important airway issues:
f Finding a reliable airway assessment tool.
f Understanding the mechanisms of successful or failed
laryngoscopy and intubation.
f Predicting the use of a specific airway device for a specific problem or scenario.
Predictors of difficult intubation
Predicting a difficult airway and proceeding with the correct airway management approach undoubtedly saves lives.
Mallampati described a frequently used predictor of difficult
intubation, the Mallampati class [13, 14]. However, when
used alone, the Mallampati score is a weak predictor for
Fig. 1. Class zero airway (Reproduced with permission from Wolters
Kluwer Health, license number 2440560983330)
difficult intubation despite the popularity of the test. It also
does not make any prediction about the ease or difficulty of
mask ventilation. For example, Ezri et al [15, 16] described
a “class zero” airway, not included in the Mallampati classes where the epiglottis is visible through direct inspection
of the oral cavity (Fig. 1). Although the authors found all
those patients to be easy to intubate, the presence of a large,
highly situated, floppy epiglottis might hamper mask ventilation in patients who received muscle relaxation.
When compared to the Mallampati classes, another easily
applicable test, the “upper lip bite” test, showed significantly higher specificity and accuracy in predicting difficult intubation [17].
With the “upper lip bite” test a class I is considered if
thelower incisors biting the upper lip, make the mucosa of
the upper lip totally invisible, a class II if the same biting
maneuver reveals a partially visible mucosa and a class III if
the lower incisors fail to bite the upper lip.
To achieve greater predictive value for difficult intubation,
the Mallampati score should be combined with other assessments such as those included in the Wilson score [18]
(patient’s weight, neck extension, mouth opening, receding jaw) A recently described modified Mallampati class
is Mallampati with extended craniocervical junction [19].
The authors of this article found that a high “Extended
Mallampati Score” along with a diagnosis of diabetes mellitus are reliable predictors of difficult laryngoscopy in the
morbidly obese patients. This study also supports previous
findings that a high patient’s body mass index by itself is
not a reliable predictor of difficult laryngoscopy or intubation [20]. Similarly, in a study of 91,332 consecutive patients scheduled for direct laryngoscopy (national anesthesia
database in Denmark), Lundstrøm et al [21] demonstrated
that a high body mass index (BMI) is a poor predictor for
difficult or failed tracheal intubation and that a neck circumference (measured at the level of the thyroid cartilage) greater than 40 cm is a better predictor than the BMI.
Thus, it seems reasonable that the pattern of fat distribution rather than the BMI per se is important in forecasting
a difficult intubation.
A frequently neglected preoperative measurement that may
help predict a difficult airway is the mentohyoid distance.
Recently, Huh et al [22] have shown that a ratio between
mentohyoid distance in full neck extension and that in neutral position may be a good predictor of difficult laryngoscopy if this ratio is less than 1.2.
This ratio reflects mobility of the occipito-atlanto-axial
complex and may explain failed laryngoscopy in patients
with apparently normal airways. In such cases, optimal vi-
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sualization of the glottis might require maximal head extension during laryngoscopy.
Airway management devices and techniques
Devices for airway management can be arbitrarily classified
into intubation devices (laryngoscopes, tracheal tubes, retrograde intubation kits, light wands, gum elastic bougie,
tube exchangers, etc), ventilation devices (facemasks, pharyngeal airways, supraglottic devices, transtracheal needle
jet ventilation devices, etc), surgical airways (cricothyroidotomy, percutaneous dilatational tracheostomy and formal tracheostomy) and devices serving other purposes such
as CO2 detectors, patient positioning devices, etc. As stated
above, this review will focus primarily on recently developed airway devices.
In regard to supraglottic devices, Brimacombe [23] has challenged this terminology and proposed to call them extraglottic devices considering that they may actually be positioned
below the level of glottis although still extraglottic (they do
not pass the vocal cords). New extraglottic airway devices
have been described at a rate of one per year for the last 25
yr, increasing to two per year since the turn of the century.
However, it is not clear whether they add significant improvements compared to the laryngeal mask airway.
Examples of such recently developed devices are laryngeal
tubes with drainage tube, EasyTube, SLIPA, I-gel, etc. The
LMAs, have come with ProSeal pediatric sizes, disposable
intubating LMAs (Fastrach) and the new, disposible LMASupreme (Fig. 2).
The LMA Supreme combines design features promoting
easy insertion available with the Fastrach, with the presence of a draining tube available with the ProSeal LMA. It is
supplied in three sizes: 3,4 and 5. Timmermann [24] et al
Fig. 2. LMA supreme
studied the performance of size 4 LMA Supreme in 100
women. They reported easy insertion, optimal laryngeal fit
and low airway morbidity.
Positive pressure mask ventilation may be both ineffective
and hazardous in obese patients with failed intubation. In
such cases, aspiration of gastric contents is an imminent
risk. Goldmann et al [25], prospectively studied the process of airway management with the ProSeal LMA in 2114
adult surgical patients (some of whom were morbidly obese). They found a 99% insertion success rate within three
attempts and a mean airway leak pressure of 28 cmH2O.
Endotracheal intubation was required in only 3.2% of cases. Ventilation was adequately controlled in 98% of cases.
There were 3.3% clinically “relevant” adverse events. 12
patients had some regurgitation that was witnessed through the drain tube, but none had any signs of aspiration.
The authors concluded that ProSeal is a valuable ventilation device even in morbidly obese patients with a difficult
airway and that the draining tube was useful in preventing
the aspiration of gastric contents into the patients’ lungs.
Video-laryngoscopy
This relatively new laryngoscopy technique is become increasingly popular. It enables an clear view of the larynx,
even with anatomically distorted airways. It combines either a standard or nonstandard laryngoscope blade or stylet
with a built-in video camera and a view screen. Videolaryngoscopy may increase the success rate of intubation in
anesthetized patients with unexpected difficult airways and
is also a valuable teaching tool. Videolaryngoscopy may be
performed with optic stylets (Shikani, Levitan, Foley, SensaScope, etc), C-Trach (video-LMA – Fig. 3), Airtrach (the
first completely disposable laryngoscope – Fig. 4) and with
the videolaryngoscopes (Glidescope – Fig 5, Storz, McGrath, Pentax Airway Scope, ViewMax Laryngoscope, Airway
Cam, Parker TrachView, Weiss Macintosh Laryngoscope,
Video camera attachment to True View, Bullard and Upsher Laryngoscopes, etc).
Fig. 3.
C-Trach
Recent developments in the management of the difficult airway
Fig. 6.
149
The “ramped” position for intubation
In this figure, the Troop Elevation Pillow (Mercury Medical) is used to keep the
patient’s head above the shoulders and keep the external auditory meatus and
the sternal notch in the same horizontal plan. Folded towels can be used for the
same purpose.
Fig. 4. Airtrach
The Glidescope has a video camera embedded into a plastic laryngoscope blade, while the blade bends 60 degrees
at the mid-line allowing an unobstructed laryngeal view. A
Light Emitting Diode (LED) mounted beside the camera
provides illumination. A limitation in using the Glidescope is sometimes difficult manipulation of the endotracheal
tube through the vocal cords which can typically be overcome by using a dedicated, pre-curved tube stylet. In our
experience it is an airway tool that is both easy to use and
teach and has a wide clinical utility including in critical
care units, delivery suites and emergency departments.
As these novel laryngoscopic techniques are still new, there
may not yet be adequate data to judge their role in difficult
airway algorithms. Mihai [26] et al performed a meta-analysis of 15 randomized controlled trials and 42 case series
Fig. 5. Glidescope
and showed no compelling evidence to support the superiority of these tools over direct laryngoscopy. Our opinion
is that videolaryngoscopy does have potential to facilitate
intubation in difficult airway management and save lives
but we await the results of larger ongoing studies.
Positioning of the patient for intubation and
mask ventilation
The “sniff ” position is widely considered the ideal position
for intubation since it bring together the three upper airway axes: the oral pharyngeal and laryngeal, thus, improving the laryngoscopic view. However, in obese patients,
this positioning may not be adequate to enable the best
possible laryngoscopic view. Head elevation beyond the
sniffing position by raising the back and shoulders (“ramped” position – Fig. 6) facilitates alignment of the pharyngeal, laryngeal, and oral axis of the airway during difficult
laryngoscopy, especially in obesity. A rule in attaining the
ramped position is to to keep the patient’s head above his
shoulders and to keep the external auditory meatus and the
sternal notch in the same horizontal plan [27]. Collins et al
[28] found that the “ramped” position improved the laryngeal view when compared to a standard “sniff ” position.
Rao et al [29] proposed that a “ramped” patient’s position
obtained by either changes in the operating table position
or by placing blankets or other devices under the patient’s
head and shoulders produced similar laryngoscopic views.
Patient positioning: against manual in-line stabilization?
Manual in-line stabilization (MILS) is considered a mandatory for safe intubation of patients with suspected cervical spine injury. In a recent study, Santoni et al [30] have
challenged this by showing in a study performed on a cadaveric model that MILS not only increased the rate of failed intubation but also caused a worsening of the cervical
spine subluxation. This is attributed to the fact that MILS
doubled the force that must be applied during laryngoscopy. The authors propose that under these circumstances, if
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gum-elastic bougie, while the others’ approach is more
complex and mostly based on algorithms [33]. Airway
management algorithms are very helpful, provided they
are simple and scenario-oriented. A detailed presentation
of airway management algorithms is beyond the scope of
this review.
Difficult extubation
Airway management related morbidity and mortality is
increasing during and following extubation. The patient
with a difficult intubation still poses a problem at the end
of surgery and, if reintubation is necessary, it may be even
more difficult than the original procedure.
Fig. 7. Calculation of endotracheal tube insertion depth by topographic measurements (Reproduced with permission from Elsevier,
license number 2440570605330)
time permits, awake fiberoptic intubation is recommended
and if there is no time, intubation with a fiberoptic stylet
may be a reasonable choice.
Depth of insertion of endotracheal tubes
Many methods have been described to ensure a correct
depth of the endotracheal tube and to avoid accidental
endobronchial intubation (too deep) or accidental extubation (too superficial). However, all these methods may
sometimes fail.
Evron et al [31] proposed that this failure of the classical
methods is caused by anthropomorphic differences between the patients (some have long necks, others short necks).
The authors found that a formula based on topographic
measurements to be very reliable in establishing the correct depth of endotracheal tube insertion. Fig. 7 shows the
correct depth in cm may be calculated by adding two distances: the distance from the right oral commissure to the
right mandibular angle plus the distance between the right
mandibular angle to the mid-manubrial line. Irrespective
of the method chosen, confirmation of tube placement by
auscultation is mandatory and may be supplemented by
chext Xray or fiberoptic bronchoscopy if warranted.
Oral vs. nasal fiberoptic intubation?
The authors opinion is that in most cases, oral fiberoptic
intubation is preferred to nasal fiberoptic intubation since
is less traumatic, better tolerated by an awake patient and
does not carry the risk of sinusitis if the tube will be kept
in place for a longer period of time. The risks of epistaxis
(which may both further complicate the airway and obstruct visualization through a FOB) are greater in obstetric
(particularly preeclamptic) patients and in coagulopathies.
Management approaches to difficult airway
Some airway experts [32] tend to use a minimal number
of devices such as the intubating laryngeal mask and the
Various techniques of extubation in previously difficult-tointubate patients have been described [34] including extubation with the aid of a fiberoptic bronchoscope, extubation over a ventilating tube exchanger (such as the Cook
airway exchanger catheter), replacement of the endotracheal tube with an LMA, etc.
Sugammadex
Sugammadex, is a new antidote of non-depolarizing muscular blocking agents. A recent Cochrane report [35] summarizing 18 randomized controlled trials demonstrated its
safety and efficacy. It has a potentially crucial role in managing patients who have received non-depolarizing muscle
relaxation (either rocuronium or vecuronium) and who
cannot be intubated or ventilated. Although approved for
use in Europe, so far it has not been approved by the FDA
in the USA.
Airway management tips
f If you suspect an airway difficulty, believe it will be
difficult.
f Never give muscle relaxants before you are sure you
can ventilate the lungs.
f Remember the two/three hand-bag ventilation technique.
f Keep track of time during attempted intubation.
f If you believe the patient needs tracheostomy, do not
delay its performing it until the patient’s heart arrests!
f Have a low threshold to call for an ENT surgeon.
Conclusions
This short introduction into the complex topic of difficult airway management tried to emphasize that we are far
from being able to cope will all the difficulties. So, how
could we perform better?
Learning and getting experience, having appropriate equipment and knowing how to use it, learning and practicing
surgical airways and always being prepared with alternatives (using simple algorithms) will enable us to further
reduce the morbidity and mortality attributable to airway
management difficulties.
Recent developments in the management of the difficult airway
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