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R. H. Kelley et al.
Table 16.2
to Class 4 airway in the Modied Mallampati Scoring system. Created by Dr. Sullivan
Modied Mallampati Scoring
Class 1 Ye s Yes Full Yes
Class 2 Ye s Yes Partial No
Class 3 Ye s No Base No
Class 4 No No No No
Graphical representation of the important anatomic features differentiating a Class 1
Visible
Soft palate Fauces Uvula Tonsillar pillars
Mallampati Scoring
Despite being more than 40years old, it is still widely used. Modied Mallampati
scoring [13, 14] allows for quick evaluation of the anatomy of the mouth and oropharynx. The patient is instructed to extend their neck and protrude their tongue to
their maximum ability. The anatomy is then classied into class 1–4 based on visible structures (Table16.2).
Ultrasound
Several upper airway ultrasound (UA-US) index tests have been cited in the literature including the following: DSE, distance from skin to epiglottis; DSHB, distance
from skin to hyoid bone; DSVC, distance from skin to vocal cords; E-VC, distance
from the epiglottis to the midpoint of distance between the vocal cords.
Distance from skin to epiglottis (DSE) seems accurate to predict difcult laryngoscopy based on 10 studies considering 1812 patients [15]. DSE is assessed using
a linear probe placed in a transverse plane and measuring the thickness of the preepiglottic space at the midline, with higher values of DSE having a signicant association with difcult intubation. The positive predictive value ranged from 30.26%
to 49.4% while the negative predictive value ranged from 94.61% to 97.53%. Due
to the low prevalence of patients with difcult airway in the target population, a
negative test represents a probability of an easy laryngoscopy being about 95%–97%.
It may help to rule out the probability of a true difcult laryngoscopy in a selected
population with uncertain difcult airways based on clinical assessment. However,
further studies needed with better standardization of US assessment to limit
heterogeneity.
Physiologic Difcult Airway
In addition to the anatomic features described above, there are physiologic features
which may contribute to difcult airway management. Physiologic derangements
include hypoxemia, hypotension, severe metabolic acidosis, and right ventricular
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failure, which increase the risk of cardiovascular collapse from airway management
due to transition to positive pressure ventilation, and/or difculty with optimizing
gas exchange [16]. Additional physiologic considerations include the presence of a
full stomach, increasing education and aspiration risk.
257
Obesity
Obesity is a signicant predictor of airway difculty due a combination of anatomic
and physiologic factors listed above. In addition to the anatomic factors listed above,
physiologically, patients with obesity have reduced functional capacity, resulting in
a decrease in the duration of apnea before desaturation [16]. Patients with obesity
twice as likely to have severe airway complications as those who are not obese [2].
Patients with body mass index great above 40 are four times more likely to have a
severe complication.
Airway Management
According to the 2022 Difcult Airway Algorithm, prior to attempting intubation,
the clinician managing the airway should choose either an awake or post-induction
airway strategy. Any one factor alone, including assessed difculty with intubation, ventilation, or aspiration or desaturation risk, may be clinically important
enough to warrant an awake intubation. Patients with a suspected difcult laryngoscopy and at least one additional risk factor including suspected difcult face
mask/supraglottic airway, increased risk of aspiration or increased risk of rapid
desaturation should undergo awake intubation [4]. Throughout the algorithm there
is repeated emphasis on limiting attempts alternating and optimizing techniques
and avoiding task xation and maintaining an awareness of the passage of time,
this is likely due to known human factors which contribute to failed airways as
discussed below.
Pre-Oxygenation
ASA guidelines emphasize optimization of oxygenation prior to and in between
intubation attempts through low- or high-ow nasal cannula and elevated head position throughout procedure [4]. Pre-oxygenation followed by apneic oxygenation is
an effective maneuver for prolonging safe apnea time. Apnea time is the time before
oxygen desaturation. Apneic oxygenation traditionally is provided using low-ow
nasal oxygen at ow rates up to 15L/min while the patient is apneic [17, 18]. It is
effective in prolonging apnea time before desaturation prior to intubation. Preoxygenation is recommended to be performed in all patients undergoing anesthesia
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R. H. Kelley et al.
although there is special emphasis on pre-oxygenation if there is an anticipated
interruption of O2 delivery such as before and during awake beroptic intubation [17].
In patients with morbid obesity, it has been shown that high-ow nasal oxygenation compared to conventional oxygenation provides longer safe apnea time by
40% (76s) and higher minimum SpO2 during anesthesia induction [19, 20].
In critically ill patients with acute hypoxic respiratory failure, pre-oxygenation
with non-invasive or high-ow oxygen therapy did not change the risk of severe
hypoxemia [21].
Face Mask Ventilation
Face mask ventilation is a maneuver associated with airway management that is
often overlooked. In an unanticipated difcult airway scenario, face mask ventilation can be used as a rescue maneuver between tracheal intubation attempts or
while pursuing surgical options. Additionally difculty with face mask ventilation
can be an important indicator as 25% of patients who are difcult face mask ventilation are difcult to intubate [9]. Effective face mask ventilation can be conrmed
by the following: rise in chest, capnographic tracing and increase in oxygen saturation. There are four classications of face mask ventilation [20], described in
Table16.3.
Troubleshooting aids in face mask ventilation include oropharyngeal or nasopharyngeal airway, modied two-handed ventilation with exaggerated jaw life.
Jaw- thrust and chin life maneuvers are performed to keep the airway open [22].
Direct Laryngoscopy
When difculty is encountered during a direct laryngoscopy, a changing the operator or changing to video laryngoscopy for a second or third attempt should always
Table 16.3 Graphical representation of qualities differentiating Grade 1 to Grade 4 face mask
ventilation. Created by Dr. Sullivan
Face mask ventilation
Grade Description
1 Easy one-provider ventilation achieved
2 Possible with oral airway or other adjuvant
3 Difcult; inadequate, unstable, or requiring additional providers
4 Impossible
be considered [23].
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Video Laryngoscopy
Video laryngoscopy overcomes the requirement to align the anatomic axes by using
a camera attached near the tip of the laryngoscope blade to capture a live image that
is projected on a portable monitor [24]. There are now numerous devices that can be
utilized for video laryngoscopy. The rst attempt and overall success rate for tracheal intubation via video laryngoscopy is often higher compared to direct layrngoscopy [25]. Success rate of tracheal intubation with video laryngoscope is
97.1%–99.6% overall and 95.8%–100% when a difcult airway is suspected [26,
27]. A 2016 Cochrane review comparing video laryngoscopy with direct laryngos-
copy concluded that video laryngoscopy may reduce the number of failed tracheal
intubations, particularly among patients with a difcult airway [28]. However, there
was insufcient evidence that the use of a video laryngoscope reduces the number
of tracheal intubation attempts or the incidence of hypoxia or respiratory complications. This may be due to a lack of evidence that the use of a video laryngoscope
affects the time required for tracheal intubation.
The presence of blood in the airway, airway edema, cervical immobility and
obesity are associated with increased odds of rst attempt failure with video laryngoscopy in an ICU [24].
Awake Intubation
Awake intubation techniques include tracheal intubation with the aid of a exible
bronchoscope, video laryngoscopy, direct laryngoscopy, combined techniques and
retrograde wire-aided intubation [4]. Awake tracheal intubation has a high success
rate and a favorable safety prole; however, it is often considered underutilized in
anticipated difcult airway management [29].
Tracheal intubation while the patient is awake involves applying topical airway
anesthesia and securing the airway, with or without the use of sedation [29]. Ideally,
the patient is sufciently conscious and breathing spontaneously. Otherwise, a
patient’s responsiveness to stimuli, airway reexes, and ability to maintain spontaneous ventilation is impaired by deep sedation [30]. Unfortunately both excessive
sedation and inadequate sedation can increase the difculty of bronchoscopic intubation [31]. Poorly managed sedation during “awake” intubation was a contributing
factor noted in the NAP4 study [2].
Awake beroptic intubation is highly reliable with a low number of complications and a success rate ranging from 88% to 100% depending on operator experience [32]. There have been a wide variety of medications described in the literature
for use during “awake” beroptic intubation including benzodiazepines, opioids
(fentanyl, remifentanil), propofol, dexmedetomidine, and ketamine [32–34].
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Surgical Airway
In a patient with either an anticipated or an unanticipated difcult airway, the situation may arise where a surgical airway may become the only option to secure the
airway. Available options include open, percutaneous or needle cricothyroidotomy
or open tracheostomy. The time available to the proceduralist may guide decision making.
The “Three-Step Emergency Cricothyroidotomy,” as described by the military, is
where a scalpel is used to incise the skin vertically supercial to the cricothyroid
membrane, the non-dominant nger is used to palpate the membrane, quickly following with a horizontal incision through the cricothyroid membrane. An elastic
bougie is then inserted into the trachea, allowing for placement of an endotracheal
tube over the bougie and into the airway before removal of the bougie and ination
of the endotracheal tube cuff [35]. This method is now frequently referred to as the
“scalpel, nger, bougie” technique.
Percutaneous cricothyroidotomy involves palpation of the cricothyroid membrane, followed by insertion of a needle through the cricothyroid membrane and
into the trachea. Using the Seldinger technique, a wire is then advanced through the
needle that then allows for the placement of an emergency airway tube through the
cricothyroid membrane [36].
Needle cricothyroidotomy allows for emergency oxygenation by placing a large
bore IV cannula (typically 14g) through the cricothyroid membrane. Once in place,
oxygen can be administered via a three-way stop cock or jet ventilation to allow for
oxygenation. Needle cricothyroidotomy generally does not allow for adequate carbon dioxide management and a more denitive airway should be pursued to ensure
proper ventilation [36].
In some situations, the decision may be made to perform a surgical tracheotomy,
rather than a cricothyroidotomy. This can be performed asleep or awake based on
the situation. The procedural description is beyond the scope of this chapter. The
entire team should be in communication to ensure the best decision is made given
the circumstances.
In 2019, DeVore etal. published a systematic review that found that, overall, the
rate of complications for both cricothyrotomy and tracheotomy was comparable.
The most frequent early complications were failure to obtain an airway (1.6%) and
hemorrhage (5.6%). Airway stenosis was the most common long-term complication
(0.22%–7.0%). They concluded that both approaches present similar risks and management should depend on clinician experience and patient characteristics [37].
Extubation ofDifcult Airway
An overlooked aspect of airway management, the post-operative course and extubation period is critical when considering the overall picture of managing the difcult
airway. Joffe etal. point out that “only one article regarding extubation is published
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261
for every 36 regarding tracheal intubation [5].” A number of factors play into the
decision of when, where, and how to extubate the patient with a known (or unknown)
difcult airway; these include factors associated with the surgical procedure itself,
as well as the patient’s own anatomy and physiology.
Mechanical ventilation carries time-dependent risks, with complications like
ventilator-associated pneumonia, barotrauma, non-pulmonary complications like
hypotension, acute kidney injury, and gastric stress ulcers, as well as overall mortality increasing as time on the ventilator increases [38]. Timely and efcient strategies
toward extubation remains the best preventative measure in preventing these complications [39].
General Extubation Criteria
Anesthesiologists employ a number of criteria when deciding whether or not a
patient is ready to extubate in the operating room. These criteria can be applied
broadly to every patient undergoing mechanical ventilation, whether immediately
postoperatively in the operating room, in the post-anesthesia care unit (PACU), or in
the intensive care setting. Safely dictating the timing of extubation in difcult airway
patients is a critical aspect of ensuring successful liberation from the ventilator [39].
When considering extubation, several broad criteria must rst be applied to
assess the patient’s level of readiness for liberation from mechanical ventilatory
support. These criteria can be best summed up by the acronym “MOVE”: mental
status, oxygenation, ventilation, and expectoration [40]. These criteria are summarized in Table16.4.
Mental status is traditionally assessed by asking the patient to perform simple
commands, such as hand squeeze, sustained head lift, and deep inspiratory effort.
The Glasgow Coma Scale has been shown to be a reliable scoring system for prediction of extubation success, with higher scores indicating a higher likelihood of success [41–43]; studies have shown, however, that patients with GCS <8 can safely be
extubated if the clinical picture allows [44]. Required support of oxygenation and
ventilation should be minimized prior to attempted extubation; while these factors
can be optimized via the use of non-invasive measures such as high-ow nasal
Table 16.4 Graphical representation of the MOVE criteria used to support potential for successful
extubation. Created by Dr. Sullivan
“MOVE” criteria for extubation
Criteria Indicator of successful extubation
Mental status Glascow coma scale ≥8
Oxygenation FiO2 ≤50%, PEEP ≤8; PaO2/FiO2 ratio >150
Ventilation Rapid shallow breathing index (RSBI) >105
Expectoration Subjective; thin/scant secretions, strong cough/gag reex
a
Patients with GCS <8 should be considered for extubation depending on the rest of the clini-
cal picture
a
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cannula and non-invasive positive pressure ventilation, patients with PaO2/FiO2
ratios less than 150, as well as those requiring FiO2 greater than 0.50 and PEEP
greater than 8cmH2O to maintain adequate oxygenation, are poor candidates for
extubation [39]. Rapid shallow breathing index (RSBI) greater than 105 breaths/
min/L has shown high sensitivity (97%) for predicting patients who will pass spontaneous breathing trial, but only moderate specicity (65%), conferring no benet
to survival and no reduction in extubation failure or tracheostomy while prolonging
the weaning process [45]. Assessment of airway secretions (qualitative and quantitative) and the patient’s ability to clear them remains subjective but should be taken
into consideration on a case-by-case basis [43].
Additional criteria to consider when deciding whether a patient is ready for spontaneous breathing trial and extubation are numerous and vary widely based on the
clinical picture. Patients who are likely to return to the operating room for additional
procedures under general anesthesia within 24h should not be extubated, as repeated
airway instrumentation for intubation increases the risk of airway trauma and
edema. Cardiovascular instability requiring escalating measures of support is generally accepted to be a relative contraindication for extubation, though extubation can
be considered if support is minimal and there are no other contraindications to
removal of mechanical ventilatory support [40].
In patients who have had a prolonged course on the ventilator, or those who have
undergone repeated instrumentation of the airway (prior failed extubation, repeated
intubation for surgical procedures, head/neck surgery, etc.), additional assessment
of the airway may be necessary prior to extubation. The cuff-leak test can be performed using qualitative and quantitative means to assess the airway for laryngeal
edema that could cause post-extubation stridor. Qualitatively, the test is performed
by listening for a leak with a stethoscope over the upper trachea when the balloon is
deated. To assess for a cuff-leak quantitatively, the patient should be placed on
volume-control ventilation, and the balloon deated. The difference between
inspired and expired tidal volume is then measured (V
cutoff points are subject to some debate; ΔV
[44] of the V
have been suggested as a positive cuff leak. In patients with no cuff-
Tinsp
of 10% [46], 12% [45], and 15.5%
T
Tinsp
−V
=ΔVT). Quantitative
Texp
leak on assessment prior to planned extubation, a four-dose course of corticosteroids prior to extubation has been supported by recent meta-analyses and societal
guidelines [46, 47].
Timing ofExtubation
In addition to the criteria listed above, consideration must be given to both the timing
and the setting of withdrawal of mechanical ventilatory support. The operating room
is a highly controlled environment, with ample support staff and equipment available
in the event of a catastrophic failure. The intensive care unit has the potential to be a
far less-supported setting, requiring logistical preparation when considering the
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extubation of a difcult airway. Multiple factors specic to the postoperative patient
make this period a high-risk stage in the patient’s care; pharmacologically, use and
timing of neuromuscular blockers and opioids play an important role in extubationreadiness. Surgical factors including uid balance, patient positioning (i.e., prolonged steep head-down positioning), and location of surgical site (head/neck
surgery) also increase the likelihood of difculty with liberation from mechanical
ventilatory support.
When considering extubation of the difcult airway in the intensive care setting,
preparation is critical to ensure the highest chance of success. It is our opinion that
a team-based approach including physicians from all necessary teams (critical care,
anesthesiology, surgery, and ENT as indicated), nursing, respiratory therapy, and
pharmacy ensures the best likelihood of a positive outcome. Equipment should be
made available to progress down the difcult airway algorithm (outlined above)
should failure be imminent. This includes video laryngoscope, beroptic bronchoscope, laryngeal mask airway, bougie introducers, as well as equipment for cardiopulmonary resuscitation [46]. It may also be advisable to have tracheostomy or
cricothyrotomy kits (as well as personnel trained in their usage) available at bedside
in case of surgical airway emergency.
The use of post-extubation ventilatory support should be discussed and prepared
ahead of time whenever possible. Evidence has shown that non-invasive positive
pressure ventilation has utility in preventing re-intubation in select high-risk patient
groups, including those with COPD and other causes of hypercapnia [48, 49].
High- ow oxygen has also shown benet in this regard in subsets of patients with
hypoxemic respiratory failure [49, 50].
263
Human Factors andTeam Approach toDifcult
Airway Management
Human Factors Associated withDifcult Airways
Signicant advances have been made in airway management over recent years. A
2018 study of greater than 400,000 anesthetics found that rates of difcult and failed
tracheal intubation decreased fourfold between 2002 and 2015 [51]. Despite this
improvement, outcomes associated with difcult tracheal intubation remain poor
[5]. There is considerable evidence that a lack of adequate planning for intubation
difculty or failure contributes to patient harm [2, 4, 5]. In the NAP4 study, 40% of
serious airway complications were attributed to human factors such as poor situational awareness. In the 2019 claims analysis a judgment error described as perseveration was noted in 25% of claims. Perseveration is dened as consistent
application of airway management technique or tool in three or more attempts without deviation or change, or the return to a technique or tool that was previously
unsuccessful [5].
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Team Approach
Literature around team-based approaches to difcult airway management started
with the Difcult Airway Response Team (DART) at Hopkins [52] has expanded to
numerous hospital systems since. In their decade review of their DART program,
Mark etal. reported responding to over 1000 events in a 10-year time period with
no resultant adult airway related adverse events or morbidity [53]. This approach is
now frequently included in literature describing of airway management in critical
illness [54]. While typically used for emergency airway management in the emergency room, inpatient oor and intensive care unit, some hospitals mobilize their
airway response teams for intraoperative activations as well. Knowing the resources
available at your institution is a vital part of perioperative difcult airway
management.
Summary
Care for the patient in the perioperative period involves both surgical and sedation/
anesthetic risk assessment. Any patient receiving moderate sedation or anesthesia
care must have their airway evaluated to assess the potential for difcult airway
management. A focused history and physical examination, looking for visible characteristics that predict difcult airway, is vital. Preparation to optimize physiologic
reserve, including pre-oxygenation, pairs with basic and advanced airway skills,
such as face mask ventilation and Direct/Video Laryngoscopy, to manage the airway in normal circumstances. In the event of an anticipated difcult airway, a beroptic intubation may be pre-determined; however, an unanticipated difcult airway
may put the surgical team in a position to proceed with surgical airway management. Extubation is a frequently overlooked aspect of airway management in the
perioperative period but is nonetheless an important consideration. Communication
is key between members of the perioperative team in any potential scenario to provide the safest care possible to the patient.
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