airway.pdf

Approach to the difficult airway in adults for
emergency medicine and critical care
Author: Calvin A Brown, III, MD, FAAEM
Section Editor: Ron M Walls, MD, FRCPC, FAAEM
Deputy Editor: Michael Ganetsky, MD
Contributor Disclosures
All topics are updated as new evidence becomes available and our peer review process is
complete.
Literature review current through: Feb 2023. | This topic last updated: Feb 21, 2023.
INTRODUCTION
Determining the presence of a difficult airway is a critical step in planning
tracheal intubation. This topic review will discuss the incidence, assessment,
and management of the difficult airway in adults outside of the operating
room. Other aspects of airway management, including pediatric airway
management, are discussed separately.
For pediatric airway management: (see "The difficult pediatric airway"
and "Emergency airway management in children: Unique pediatric
considerations" and "Rapid sequence intubation (RSI) outside the
operating room in children: Approach" and "Basic airway management in
children" and "Supraglottic airway devices in children with difficult
airways")
●
For basic and advanced adult airway management: (see "Basic airway
management in adults" and "Direct laryngoscopy and endotracheal
intubation in adults" and "Extraglottic devices for emergency airway
●

DETERMINING THE PROPER APPROACH TO AIRWAY
MANAGEMENT
Most emergency department (ED) endotracheal intubations are performed on
an emergency basis (ie, intubation cannot be significantly delayed or
avoided). The universal emergency airway management algorithm provides
the recommended approach to emergency intubation ( algorithm 1 and
algorithm 2) [1]. This approach is based on several key assessments of the
patient prior to intubation.
management in adults" and "Video laryngoscopes and optical stylets for
airway management for anesthesia in adults")
Cardiac arrest airway? – The first assessment is to determine if the
patient has a "cardiac arrest" airway (ie, presenting in cardiac arrest,
agonal or absent respirations with absent or near absent circulation, or
when chest compressions have begun). If so, the cardiac arrest airway
algorithm is used ( algorithm 3) [1].
●
Anatomic difficulty? – If the patient does not have a cardiac arrest
airway, the next step is to determine if the patient represents an
anatomically difficult airway. This requires assessment of specific patient
attributes to predict the likelihood of difficulty in performing any of the
major procedures in airway management: direct laryngoscopy and
intubation, bag-mask ventilation (BMV), surgical airway management,
and ventilation using an extraglottic airway. (See 'Identifying the
anatomically difficult airway' below.)
●
High-risk physiology? – A critically ill patient can be at higher risk of
apnea intolerance, hemodynamic instability, or cardiovascular collapse
with rapid sequence intubation (RSI), positive pressure ventilation, or
●

RSI is the recommended method for managing the airway in a patient with
spontaneous circulation who is felt to not have an anatomically difficult
airway and does not have high-risk physiological derangements. (See "Rapid
sequence intubation for adults outside the operating room".)
INCIDENCE
Incidence of difficult intubation and first-attempt success — The precise
incidence of difficult intubation in the emergency department (ED) is
unknown. A difficult ED intubation can be defined as one that requires
multiple attempts, multiple operators, multiple devices, excessive lifting force,
external laryngeal manipulation, or performance with an inadequate glottic
view. However, there are various ways of defining what constitutes a "difficult
airway" or "difficult intubation." Conclusively determining that an intubation
was difficult can only happen after the procedure is completed. How
predictive the bedside assessment is for actual intubation difficulty varies
based on these definitions.
The third phase of the multicenter National Emergency Airway Registry (NEAR
III) project analyzed over 17,500 ED intubations and found that, in
approximately 3 percent of cases, the airway was ultimately secured by a
both; some authors call this the "physiologically difficult airway" which
independently increases patient morbidity and mortality following
emergency airway management [2,3]. Such physiologic derangements
include refractory hypoxemia, hypotension, shock, severe metabolic
acidosis, severe lung disease, and right ventricular failure. Administration
of induction medications and neuromuscular blocking agents (NMBAs)
make the apneic phase of RSI intolerable to a patient with hypoxemia or
severe metabolic acidosis and creates a risk for circulatory collapse in a
patient with hypotension. (See 'High-risk physiology present' below.)

means other than the first method chosen [4]. Approximately 0.5 percent of
cases required a surgical airway, with 75 percent of these performed as a
rescue after failure of another method. Using these data and incorporating
the success rate on first pass, use of a tracheal tube introducer ("bougie") or
flexible intubating scopes (ie, fiberoptics) and cricothyrotomy rate, one would
estimate the incidence of a difficult-to-manage airway in the ED to be
approximately 10 to 15 percent. The incidence of intubation requiring more
than two attempts or oxygen saturation falling below 93 percent (regardless
of the numbers of attempts), is estimated to be in the 3 to 5 percent range.
Overall failure, meaning that no airway was secured, was reported rarely, and
data regarding whether hypoxic injury or other severe airway-related injury
occurred were incomplete. In a single-center study, the incidence of
anticipated airway difficulty based on bedside assessment and clinician
gestalt was much higher, with nearly 50 percent of ED intubations falling into
that category, although assessments varied by clinician expertise and
experience [5]. A retrospective study of emergency intubations performed by
anesthesiologists outside the operating room reported that 351 of 3423
intubations (10.3 percent) were difficult (Cormack-Lehane grade 3 or 4)
( figure 1) [6].
Analysis of the NEAR data found that PGY-3 and PGY-4 residents in
emergency medicine perform most intubations at academic hospitals, with
first-attempt success rates of 80 percent when using the GlideScope video
laryngoscope, 83 percent for direct laryngoscopy, and 90 percent with the C-
MAC video laryngoscope [7]. Fewer than 2 percent of intubations required
more than three attempts. Ninety-seven percent of intubations by residents
beyond the level of intern were successfully performed by the first operator.
(See "Devices for difficult emergency airway management in adults outside
the operating room".)

Effect of increasing video laryngoscopy use — The increasing use of video
laryngoscopy (VL) and other advanced airway tools is changing traditional
concepts of airway difficulty. Historically, intubation difficulty has been
defined based on the relative ease or difficulty of obtaining an adequate view
of the glottis using a direct laryngoscope. The Cormack-Lehane scale is the
standard gauge for such airway difficulty ( figure 1) [8]. In the NEAR III
study, VL use increased from less than 2 percent in 2002 to 2004 to almost 30
percent after 2008 [7], and NEAR data from 2016 through 2018 show that VL
are now used as the first device in nearly two-thirds of all ED intubations [7].
Many of the anatomic challenges that confront clinicians using conventional
laryngoscopes are mitigated or eliminated with video-enhanced devices.
When intubation by laryngoscopy is the selected method for emergency
airway management, a video laryngoscope should be used, whenever
possible, for the first intubation attempt, especially if a difficult airway is
anticipated. In a sub-group analysis of a 2022 meta-analysis (42 trials, 4100
patients), in patients with predicted, known, or simulated difficult airways, VL
reduced the rate of failed intubation as compared with direct laryngoscopy
(DL) (4.5 versus 10.2 percent, relative risk [RR] 0.32, 95% CI 0.23-0.44) [9].
Analysis of the NEAR VII dataset, comprising more than 11,000 adult
intubations performed during 2016 and 2017, found VL to be superior to DL
[7]. Multivariable regression analysis, controlling for confounders of first-
attempt success, found that intubators were two to three times more likely to
achieve first-attempt success using a VL compared with DL that was
“optimized” by laryngeal manipulation, ramped patient positioning, tracheal
tube introducer (ie, bougie) use, or any combination of the three.
Conventional laryngoscopes are still favored by some clinicians, and
challenging DL can be improved by laryngeal manipulation, proper patient
positioning, and a tracheal tube introducer. However, emergency medicine
clinical studies heavily favor the use of VL, and we recommend clinicians

become proficient with VL and use it whenever possible. DL continues to play
an important role in hospitals without access to video equipment and in rare
clinical situations (eg, a massively hemorrhaging upper airway without access
to large-bore suction). For such settings, DL remains an important alternative
to DL. Of note, MacIntosh blade type VLs can be used either as a VL or as a
DL, so are well suited to training, skill retention, and rescue use when the
video camera becomes occluded by extensive upper airway soiling.
Incidence of difficult bag-mask ventilation — Difficult bag-mask ventilation
(BMV) has been studied extensively in the operating room but is challenging
to assess in other settings [10-16]. Overall, although definitions vary among
studies, the incidence of difficult BMV is universally low, and true failed BMV is
rare.
Researchers in one prospective, observational study of 1502 operating room
patients defined difficult BMV as the inability of a single clinician to maintain
oxygen saturation above 92 percent or provide adequate ventilation. They
found BMV to be difficult in about 5 percent of patients and impossible in
only a single patient [10]. Subsequent, larger studies found difficult BMV to
occur in approximately 3 percent of patients, with the lower incidence
possibly due to exclusion of some patients who would have been difficult to
ventilate [11,17,18]. In a cluster randomized trial of pre-assessment for
difficult BMV involving 94,006 patients in 26 Danish anesthesia departments,
researchers reported an incidence of unpredicted difficult BMV below 1
percent in both the intervention group, in which potential BMV difficulty was
assessed using 11 explicit criteria (0.91 percent); and the control group, in
which assessment was left to the anesthesiologist's discretion (0.88 percent)
[16].
Among the selected patients studied in the operating room, the combined
inability to intubate and inability to perform BMV occurs in only 1 in 5000 to 1

in 10,000 patients [19]. This likely represents a reasonable estimate of the
incidence of unexpected difficulty in the ED (ie, patients without identifiable
characteristics associated with difficulty but for whom intubation and BMV
are difficult). This observation underscores the safety of an approach to
airway management that includes a preintubation assessment for difficult
intubation and difficult BMV. In the absence of markers of difficult intubation
or difficult BMV, the clinician will rarely encounter a patient who is both
impossible to intubate and impossible to ventilate with a bag-mask. (See
"Basic airway management in adults", section on 'Bag-mask ventilation'.)
Incidence of difficult cricothyrotomy — The incidence of difficult surgical
cricothyrotomy in the ED, where the procedure is most often performed, or in
the operating room is not known. Cricothyrotomy is not a technically difficult
procedure in most patients, but infrequency of performance, time pressure
during the procedure, lack of regular training, and the anxiety accompanying
airway failure undoubtedly contribute to any difficulty encountered.
Several case series of emergency surgical cricothyrotomies have reported
success rates approaching 100 percent with complication rates of 5 to 14
percent. Difficulty related to the procedure, including cases requiring
excessive time to secure the airway, is not properly captured in these
retrospective series [20,21]. (See "Emergency cricothyrotomy
(cricothyroidotomy)".)
Incidence of difficult extraglottic airways — Extraglottic airways are most
often used as rescue devices in the ED. These include the supraglottic airways
(ie, laryngeal mask airways) designed to sit just above the glottis; and the
retroglottic airways, designed to be inserted into the esophagus, and which
provide proximal (oropharyngeal) and distal (esophageal) seals to permit
"side-stream" ventilation (eg, Combitube, King LT Airway, EasyTube, and
others).

The incidence of difficult insertion is not known for most of these devices.
Disposable and reusable laryngeal mask airway devices have been shown to
permit effective ventilation in 92 and 97 percent, respectively, of anesthetized
patients [22]. Emergency medical technicians (EMTs) have used the
Combitube in the prehospital setting, obtaining ventilation rates ranging
from 79 to 95 percent [23-25]. One retrospective review of 162 patients
managed by EMTs reported a success rate of only 70 percent with a 27
percent complication rate using the Combitube [26]. In a single-center
registry of 14,480 elective operating room cases managed with either an iGel
or LMA, the rate of initial difficult ventilation was 0.5 percent; however, 60
percent were corrected with either repositioning or re-insertion. Overall,
successful placement and ventilation occurred in 99.8 percent of all cases
[27].
Success rates for extraglottic airways used in the ED are unknown. Analysis of
data from the NEAR registry showed that extraglottic airways were seldom
used as rescue devices and never as a primary airway in 7712 ED patients
[28]. Patients with disrupted upper airway anatomy are poor candidates for a
supraglottic or extraglottic airway device, as both rely on creating a seal
between an inflatable cuff and the patient's mucosa.
IDENTIFYING THE ANATOMICALLY DIFFICULT AIRWAY
Failure to identify, in advance, characteristics associated with difficult
intubation or ventilation is one of the leading causes of failed airways in the
operating room [29,30]. This concept likely extends to emergency airway
management outside the operating room. Difficult airway assessment
requires determination of the potential for difficulty with bag-mask
ventilation (BMV), laryngoscopy and intubation, cricothyrotomy, and
extraglottic airway insertion.

The LEMON assessment for difficult intubation — The LEMON assessment
uses a series of physical evaluations to determine whether difficult
laryngoscopy and intubation is anticipated. The assessment was developed
for direct laryngoscopy and is most applicable to that technique, but we
recommend its use when VL is planned as well because it identifies features
that make laryngoscopy, whether direct or video, more difficult than when
those features are not present (see 'Difficult video laryngoscopy' below). Each
step is described:
L: Look externally — This refers to the clinician's general impression that
the airway will be difficult. Does the patient have abnormal facies or body
habitus, unusual anatomy, or facial trauma [31-33], any of which can be
expected to create difficulty? A general impression of airway difficulty is
reasonably specific but not particularly sensitive. If an operator observes the
patient and anticipates difficulty, that assessment likely is correct. Conversely,
absence of obvious external markers of airway difficulty does not ensure
success.
E: Evaluate (3-3-2 rule) — The size of the mandible, the distance between
the mentum and the hyoid bone, and the extent of mouth opening are all
important geometric determinants of the success of direct laryngoscopy
[34,35]. These relationships are represented by the 3-3-2 rule ( picture 1)
[36,37]. The rule describes three measurements found in normal patients (ie,
patients in whom difficult laryngoscopy is not expected).
3: This assessment indicates the ease of access to the airway. A normal
patient can open their mouth sufficiently to permit three of their own
fingers to be placed between the incisors. Adequate mouth opening
facilitates both insertion of the laryngoscope and obtaining a direct view
of the glottis.
●

Variations in patient size are accommodated by using the patient's fingers as
the standard for measurement. Since the emergency department (ED) patient
is often uncooperative or unable to perform the required steps, size is
estimated by comparing the examiner's fingers with the patient's. The
examiner's fingers are then used to estimate the proportions involved. Failure
to achieve these three dimensions predicts difficulty visualizing the glottis
during direct laryngoscopy.
M: Mallampati score — The Mallampati classification is a simple scoring
system to help predict difficult intubation ( figure 2) [38,39]. It has been
prospectively validated in several studies, although not as a solitary (ie,
sufficient) predictor of difficult intubation [40,41]. The Mallampati score is
best used as one part of a global airway assessment [42,43].
The Mallampati class, ranging from I to IV, relates the amount of mouth
opening to the size of the tongue and provides an estimate of space for oral
intubation by direct laryngoscopy. In general, Mallampati class I or II predicts
easy laryngoscopy, class III predicts difficulty, and class IV predicts extreme
difficulty.
3: This assessment provides an estimate of the volume of the
submandibular space. A normal patient is able to place three of their
fingers along the floor of the mandible between the mentum and the
neck/mandible junction (near the hyoid bone).
●
2: This assessment identifies the location of the larynx relative to the
base of the tongue. A normal patient is able to place two fingers in the
superior laryngeal notch (ie, the space between the superior notch of the
thyroid cartilage and the neck/mandible junction, near the hyoid bone). If
the larynx is too high in the neck, direct laryngoscopy is difficult or
impossible because of the angles that have to be negotiated to permit
visualization.
●

Many ED patients are unable to cooperate with a Mallampati assessment. In
such cases, the examiner should gently open the mouth, if possible, and use
a direct laryngoscope blade in the manner of a conventional tongue blade to
assess the size of the tongue compared with that of the oropharynx. If this
assessment reveals a large tongue-to-oropharynx ratio or it cannot be done,
the clinician should assume that direct laryngoscopy will be difficult.
O: Obstruction/obesity — The presence of upper airway obstruction
interferes with both laryngoscopy and intubation. A supraglottic mass or
infection, trauma with hematoma, injury with disruption of the upper airway,
and vocal cord masses (eg, tumor), among other conditions, can obstruct the
view of the glottis, block access for tube insertion by narrowing the airway, or
both. The redundant tissues in the upper airway of the obese patient make
visualization of the glottis by direct laryngoscopy more difficult, and an
oversize laryngoscope blade may be required.
N: Neck mobility — Ideally, the patient is placed in the sniffing position for
intubation. The sniffing position is achieved by flexing the neck forward on
the body (thoracic spine) and elevating the head. Thus, decreased cervical
spine mobility compromises the direct laryngoscopic view [44,45]. Proper
positioning for direct laryngoscopy is discussed in detail separately. (See
"Direct laryngoscopy and endotracheal intubation in adults", section on
'Positioning the patient'.)
Medical conditions such as psoriatic or rheumatoid arthritis, ankylosing
spondylitis, or simply the degenerative joint disease that accompanies aging
can greatly reduce neck mobility. In uncooperative, non-trauma patients,
neck mobility can be assessed by passively extending the neck.
Blunt trauma patients require in-line stabilization of the cervical spine during
intubation, which also limits glottic view. Most trauma patients, although
identified as difficult airways because they require in-line cervical spine

stabilization, can nonetheless be intubated successfully orally, unless other
difficult airway markers are present.
Multiple studies have attempted to identify patient characteristics predictive
of difficult laryngoscopy and intubation [35,42]. Not all markers of difficulty
are applicable to ED patients, and many are too complex or require evaluation
(eg, magnetic resonance imaging [MRI]) that is not feasible in the emergency
situation. The LEMON mnemonic described above ( table 1) was developed
by researchers in emergency airway management [36,37]. A prospective
observational study of 156 patients undergoing intubation in the ED found
that the LEMON evaluation accurately stratified patients according to the risk
of difficult intubation [46]. A subsequent large registry study performed in
Japanese EDs evaluated the benefit of a "modified" LEMON assessment (ie,
LEMON without Mallampati classification or measurement of thyromental
distance) and discovered its most impactful feature was its ability to rule out
difficulty [47]. They found that when patients were completely LEMON
negative, difficulty was rarely encountered (negative predictive value of 98
percent). Subsequently, the LEMON mnemonic was adopted by the American
College of Surgeons' Advanced Trauma Life Support course.
Difficult video laryngoscopy — Difficult intubation using video
laryngoscopes (VL) is less common compared with direct laryngoscopes (DL).
Thus, assessment tools for predicting difficult VL are incomplete. The LEMON
mnemonic applies to DL, not to VL, although some of the attributes (eg,
obesity) are likely to have some validity for VL as well.
Although mnemonics encompassing both DL and VL have been developed,
the criteria are broad and do not provide the clinician with specific guidance
for accurate identification [48]. Research to date has identified the upper lip
bite test (ULBT) as one predictor of difficult VL. In a systematic review of 27
studies involving over 18,000 patients, the ULBT showed high specificity and

high negative predictive value [49]. The ULBT is performed by having the
patient extend their jaw and cover the upper lip with their lower incisors. If
the patient can fully cover their upper lip with their lower incisors, difficult
laryngoscopy is unlikely; if the patient cannot reach their upper lip, difficulty is
significantly more likely. (See "Airway management for induction of general
anesthesia", section on 'Airway examination'.)
It will continue to be challenging to develop a reliable set of predictors of
difficult intubation using a VL as these instruments almost universally provide
grade 1 or 2 views (400/400 grade 1 or 2 in one study of the GlideScope [50]
and 60/60 in a study using the Storz C-MAC [51]). In addition, differences in
blade shape (hyper-angulated, like the GlideScope, versus standard
geometry, like the C-MAC) mean that any set of patient characteristics might
have different effects on intubation success based solely on the design of the
device.
Difficult bag-mask ventilation — Assessment for difficult BMV is performed
immediately after the LEMON evaluation for difficult intubation. The LEMON
evaluation and BMV technique are reviewed separately. (See 'The LEMON
assessment for difficult intubation' above and "Basic airway management in
adults", section on 'Bag-mask ventilation'.)
Difficult BMV has been studied in anesthesia populations, and the incidence
appears to be low. (See 'Incidence of difficult bag-mask ventilation' above.)
The predictors of difficult BMV are summarized by the mnemonic ROMAN
( table 2) and discussed immediately below [10,11,16,17,37,52].
There is no clear correlation between each individual attribute and the degree
of difficulty, but assessment of all the attributes helps to determine whether
difficulty is likely [16]. If no markers are present, BMV is unlikely to be difficult.

However, while uncommon, difficult BMV does occur, and clinicians who
perform airway management must be prepared.
R: Radiation/restriction – Head and neck radiation is strongly associated
with difficult rescue mask ventilation, likely due to reduced pliability of
upper airway soft tissue. Restriction is used to connote restriction of
forward gas flow (ie, from the bag and mask apparatus into the patient's
lungs) and resistance to ventilation that occurs in conditions that increase
the required inspiratory pressure to ventilate the lungs, and includes
asthma, chronic obstructive pulmonary disease (COPD), pulmonary
edema, widespread infiltrates, and any other condition that decreases
pulmonary compliance.
●
O: Obstruction/obesity/obstructive sleep apnea – Obstruction of the
upper airway, although not widely studied, will make BMV more difficult,
as increased pressures will be required to ensure that gas flows past the
obstruction in both directions. Obesity (body mass index [BMI] >26) is an
independent marker of difficult BMV. Redundant upper airway tissue and
the combination of chest wall weight and resistance from abdominal
contents all impede airflow. Late third trimester pregnancy is a surrogate
for obesity with respect to BMV as it creates many of the same problems.
Placing the bed at an angle with the head higher than the feet (ie, reverse
Trendelenburg) may reduce impedance to airflow from abdominal
weight. (See "Airway management in the morbidly obese patient for
emergency medicine and critical care".)
●
M: Mask seal/Mallampati/male – Mask seal requires reasonably normal
anatomy, absence of facial hair, lack of interfering substances (such as
excessive vomitus or bleeding), and the ability to apply pressure to the
face with the mask. Poor Mallampati classification and male sex are
associated with challenging mask ventilation as well.
●

Difficult cricothyrotomy — Assessment for difficult cricothyrotomy is
performed after the LEMON evaluation for difficult intubation and the
ROMAN evaluation for difficult BMV.
Difficult cricothyrotomy is caused by difficult access to the anterior neck,
inability to identify landmarks, distortion of the anatomy, or abnormalities of
the tissues; and can be assessed using the mnemonic SMART ( table 3) [37].
Evaluation for difficult cricothyrotomy requires palpating the structures
overlying the larynx, identifying the cricothyroid membrane, and identifying
potential problems with surgical access. Identification of the cricothyroid
membrane is more difficult in the obese and in women [54]. Compared with
bedside ultrasound, many commonly used palpation techniques for
identifying the cricothyroid membrane are only marginally accurate (46 to 62
percent) [55].
Difficult extraglottic airway placement — Placement of a rescue device (eg,
laryngeal mask airway) can be difficult if mouth opening is limited, if the
airway is disrupted or distorted (eg, by swelling), or if debris such as teeth or
A: Age – In one study, age >55 years was a marker of difficult BMV [10].
The general loss of elasticity of tissues and the increased incidence of
restrictive or obstructive pulmonary disease most likely make ventilation
more difficult. Fifty-five years is not a distinct cutoff, but as patients age
or appear to be physiologically aged, it is reasonable to assume that BMV
difficulty will increase.
●
N: No teeth – Edentulousness creates difficulty with BMV. Teeth provide
a framework against which the mask sits and support the cheeks,
enhancing mask seal. If a patient has dentures, they should be left in situ
during BMV, where they are of benefit, then removed for direct
laryngoscopy, where they are detrimental [53].
●

bone fragments are present ( table 4). Increased airway resistance can
prevent effective ventilation via an extraglottic airway.
THE DIFFICULT AIRWAY ALGORITHM
When a difficult airway is identified using the LEMON, ROMAN, or other
bedside criteria, the difficult airway algorithm is used ( algorithm 4).
Predictors of airway difficulty when using a video laryngoscope remain to be
fully defined; pending that, it is reasonable to apply the same principles of
airway assessment and decision-making, regardless of whether a traditional
direct or a video laryngoscope will be used.
Key questions guiding the approach — Although the difficult airway
algorithm appears complex, it is really a series of simple questions:
Is oxygenation adequate? – If oxygen saturation is falling despite
oxygenation maneuvers, this is a failed airway, even before any
intubation attempt, and the failed airway algorithm should be used
( algorithm 5).
●
Is a "forced-to-act" scenario present? – If there is rapid dynamic airway
deterioration (eg, anaphylaxis, combative hypoxic patient who cannot be
re-oxygenated), rapid sequence intubation (RSI) is likely the best initial
technique despite anatomic challenges.
●
Are significant anatomic barriers identified? – RSI may be
contraindicated when significant anatomic barriers are present, and
laryngoscopy is predicted to fail. Minor anatomic challenges may still
reasonably allow for RSI.
●
Are there physiologic derangements that render the patient
intolerant to apnea or at risk of peri-intubation cardiovascular
●

Applying the algorithm — Before initiating the steps in the difficult airway
algorithm, the first action is to obtain any necessary assistance (personnel,
equipment, airway devices) at the earliest opportunity ( algorithm 4). As this
is being done, the stepwise management of the difficult airway can proceed.
Adequate oxyhemoglobin saturation (SpO ) allows the clinician time to plan
and implement a stepwise approach to airway management. If, at any time
during the evaluation or management of the difficult airway, the SpO cannot
be maintained ≥92 percent, or at least held stable in a viable range, the
difficult airway becomes a failed airway, and the failed airway algorithm is
followed ( algorithm 5). (See "Approach to the failed airway in adults for
emergency medicine and critical care".)
Operator forced to act
collapse? – In a patient with refractory hypoxemia or hemodynamic
instability, the pharmacologic effects of RSI agents, exacerbated by the
negative pre-load effects of positive pressure ventilation may result in
cardiac arrest or circulatory collapse even when intubation is
straightforward. This concern favors the decision to attempt an awake
intubation instead of moving forward with RSI.
Is RSI unreasonable for either anatomic or physiologic reasons? In
this case, an awake technique is the preferred approach. (See 'Awake
technique' below.)
●
Is there still sufficient time (ie, oxygenation is adequate and airway
is not deteriorating)? – If so, a number of alternatives remain. If not, the
situation represents a failed airway.
●
2
2
Immediate RSI — In the face of precipitous airway deterioration,
especially with a patient who is agitated and unable to cooperate or a
patient with rapidly progressing airway swelling, immediate
●

administration of an induction agent and neuromuscular blocking agent
(NMBA) may be indicated, even though the airway is identified to be
difficult. In such a situation, patient conditions force the operator to act
immediately to forestall deterioration to respiratory arrest or complete
airway obstruction.
As an example, consider a morbidly obese patient with severe status
asthmaticus, who is combative and fatigued, with oxygen saturations
falling into the upper 80s despite maximal therapy, including high-flow
oxygen (if it can be kept in place). In such circumstances, a prompt
decision to give RSI drugs and create the best possible situation for a
single best attempt at tracheal intubation, whether by laryngoscopy or
surgical airway, often is preferable to considering other (likely impossible)
approaches as the patient progresses toward respiratory arrest and
death. If this single best attempt is not successful, a failed airway is
present, and the operator proceeds to the failed airway algorithm.
As another example, consider a patient with rapidly worsening airway
swelling due to anaphylaxis. In such a patient, the rate of decline
precludes the standard approach to partial airway obstruction (ie, awake
intubation with sedation, topical anesthesia, and flexible nasal or oral
laryngoscopy) as the time required for the procedure would result in
complete airway obstruction.
Delayed sequence intubation — An alternative approach, termed
"delayed sequence intubation" (DSI), has been advocated for use in the
"forced to act" category of patients who are agitated or uncooperative, as
described above. Proponents of DSI recommend administration of
intravenous ketamine sufficient to gain control of the patient to permit
pre-oxygenation, followed by administration of an intubating dose of an
NMBA. Although DSI has been recommended on podcasts and in
●

Dropping oxygen saturations (ie, no time) — If the operator is not initially
forced to act but oxygenation is dropping or inadequate (defined as the
inability to maintain SpO ≥92 percent, as measured by a pulse oximeter),
then attempt to improve it with supplemental oxygen, bag-mask ventilation
(BMV), or assisted ventilation. If there is insufficient time to plan a methodical
approach to the airway because adequate SpO cannot be maintained, the
airway is considered to be a failed airway ( algorithm 5). The combination of
an anticipated difficult intubation and inability to maintain SpO at adequate
levels is a surrogate for the "can't intubate, can't ventilate" failed airway. (See
"Approach to the failed airway in adults for emergency medicine and critical
care".)
Techniques for maximizing oxygenation for intubation are discussed
separately. (See "Rapid sequence intubation for adults outside the operating
room", section on 'Preoxygenation'.)
A patient with chronically low but stable oxygenation might be considered to
have adequate oxygenation at a lower threshold value, but the risk of rapid
desaturation is much higher [58].
Candidate for neuromuscular blockade — In a patient with adequate
SpO , the clinician has time to plan the approach to airway management and
determine if the patient is a candidate for RSI with an NMBA. Many difficult
educational presentations, formal assessment of the technique is limited
to case series and retrospective studies [56,57]. In a retrospective, single-
center, before–and-after study, the use of ketamine prior to RSI as part of
a multi-interventional "no desaturation" bundle for out-of-hospital
tracheal intubation led to lower rates of peri-intubation hypoxia [57]. No
increase in adverse events occurred in the ketamine bundle group.
Pending further study, we do not feel there is sufficient evidence at
present to support routine use of DSI in the emergency department (ED).
2
2
2
2

airways are managed using NMBA/RSI. The presence of a difficult airway does
not preclude use of NMBA/RSI but requires the operator to ask four key
questions:
RSI is not a prudent option if the operator is not confident the patient can be
ventilated adequately with a bag and mask or an extraglottic device, in which
case an awake technique is advised. Even if BMV is deemed possible, RSI is
not advisable unless the clinician believes oral intubation will likely be
successful. (See 'Awake technique' below.)
Often, a "triple setup" is used when RSI is planned in the setting of a
potentially difficult airway. The triple setup implies a primary intubating plan
is in place followed by a non-surgical rescue device (eg, an extraglottic
device), and lastly a surgical rescue plan, most often an open surgical bougie-
assisted cricothyrotomy. These rescue options are identified and readied
before beginning the intubation sequence.
High-risk physiology present — In a patient with physiologic
derangements that increase the risk of hypoxemic injury or peri-intubation
cardiovascular collapse, longer-than-anticipated laryngoscopy may place the
patient in danger. RSI can still be performed (following the universal
emergency airway algorithm) if the clinician believes laryngoscopy and
reoxygenation can be successful and severely compromised physiology does
not preclude the use of RSI medications ( algorithm 1 and algorithm 2).
Am I confident I can perform gas exchange and oxygenate the patient
using a bag and mask or an extraglottic device?
●
Am I confident I can view the glottis and intubate?
●
Is the patient at risk of severe hypoxemia before RSI medications create
adequate intubating conditions and a tracheal tube can be placed?
●
Is the patient at high risk for circulatory collapse following administration
of RSI medications and application of positive intrathoracic pressure?
●

The following are specific physiologic derangements and strategies to
address them that are part of the "physiologically difficult airway":
Hypoxemia – In a patient who is at risk for rapid oxygen desaturation, a
race emerges between the onset of paralysis caused by the
neuromuscular blocking agent, the clinician's efficiency placing the
tracheal tube and providing supplemental oxygen, and the patient's
descent along their oxyhemoglobin desaturation curve [2]. If the clinician
cannot rapidly establish tracheal intubation, the patient is at risk for
cardiac arrest and anoxic brain injury, even if return of circulation is
obtained. Methods for reducing the risks associated with hypoxia are
discussed separately ( table 5). (See "Rapid sequence intubation for
adults outside the operating room", section on 'Preintubation
optimization'.)
●
Hypotension – Induction agents cause variable degrees of myocardial
depression and vasoplegia, partly due to loss of sympathetic tone. A
patient who presents in shock or with profound refractory hypotension
may be dependent on sympathetic drive and remaining myocardial
function to maintain perfusion. Induction agent-induced vasodilation and
myocardial depression (coupled with pre-load reduction caused by
positive pressure ventilation) may result in complete loss of circulation
within minutes of RSI. Patients in shock have a six-fold increased risk of
peri-intubation cardiac arrest following RSI [59]. Therefore, when time
allows, we recommend hemodynamic optimization (ie, isotonic fluids,
blood, vasopressors) before RSI is undertaken. Methods for reducing the
risks associated with hypotension are discussed separately ( table 6).
(See "Rapid sequence intubation for adults outside the operating room",
section on 'Preintubation optimization'.)
●

Avoiding neuromuscular blockade
Awake technique — "Awake" is an imprecise term that connotes the
techniques necessary to undertake direct examination of the upper airway in
a spontaneously breathing, fully conscious (or lightly sedated) patient. The
Metabolic acidosis – A patient with a severe metabolic acidosis (eg,
diabetic ketoacidosis, salicylate toxicity) is at risk for worsening their
acidosis once the respiratory compensation is removed after NMBA. This
can also result in peri-intubation cardiac arrest. Prevention strategies
include initiating treatment of the underlying etiology of the acidosis and,
if significant acidosis is still suspected peri-intubation, then performing
intubation with an awake technique to avoid the period of apnea that
occurs during RSI. (See 'Avoiding neuromuscular blockade' below.)
●
Right ventricular failure – The right ventricle (RV) is a low pressure, high
capacitance chamber with less cardiac muscle mass and contractile force
than the left ventricle. Conditions that increase RV afterload can have a
profound impact on RV function. These include primary pulmonary
hypertension, pulmonary embolism, chronic obstructive pulmonary
disease, and any condition resulting in hypoxic pulmonary
vasoconstriction. While positive pressure ventilation can improve left
ventricular performance, it often degrades RV function. When intubating
a patient with suspected RV failure, if RSI must take place, it is critically
important to maintain oxygenation (ie, use of apneic oxygen), perfusion
(through use of fluids and vasopressors), and hemodynamic stability
(choosing a hemodynamically neutral induction agent, such as
etomidate). An awake intubation is the preferred method if advanced
right heart failure is suspected since the patient can maintain
spontaneous respirations and a sedative or induction agent can be given
in a low dose or avoided altogether.
●

examination is facilitated by light to moderate sedation and topical
anesthesia, using a direct or video laryngoscope or a flexible endoscope. The
term is imprecise because it refers to several different approaches, having
only in common that each is done while the patient is breathing on their own
and, although technically awake, is sedated as for a painful procedure to
permit laryngoscopy.
The patient receives light to moderate procedural sedation and topical
anesthesia (depending upon their clinical condition) to permit laryngoscopy
with intubation occurring if indicated. The laryngoscopy may identify barriers
that preclude oral intubation and mandate cricothyrotomy or, conversely,
may identify a straightforward upper airway amenable to RSI. The patient
may simply be inspected, and a decision made to proceed with an intubation
plan, or may be intubated during the awake look depending upon the
circumstances, likelihood of deterioration, and the judgment of the operator.
Approaches if awake technique unsuccessful — If the awake
examination identifies that RSI is not advisable, and the patient cannot be
intubated during laryngoscopy (eg, glottis cannot be visualized during awake
look), several airway management options remain, provided an adequate
SpO is maintained. The goal with the difficult airway, as with any emergency
intubation, is to place a cuffed endotracheal tube in the trachea. Various
devices can be used to accomplish this end.
An intubating laryngeal mask airway (ILMA) ( picture 2) may be placed, then
an endotracheal tube passed through it. A common approach is to load an
endotracheal tube over top of a flexible intubating scope (ie, fiberoptic
device). The flexible scope is navigated into the airway using the ILMA device
as a conduit to the laryngeal inlet, with the scope acting as an intubation
guide over which the endotracheal tube can be advanced into place. A video
laryngoscope will likely achieve a glottic view superior to that of a standard
2

laryngoscope, enabling intubation. A fiberoptic or video intubating stylet may
also be used. (See "Devices for difficult emergency airway management in
adults outside the operating room".)
Primary cricothyrotomy (ie, cricothyrotomy as a planned airway intervention,
rather than a rescue) may be indicated if there is limited oral access (eg,
restricted mouth opening or profound glottic swelling) or the supraglottic
region of the airway is anatomically disrupted. Blind nasotracheal intubation
may rarely have a role but is best reserved for situations in which no other
device is available or felt to be appropriate (eg, massive hemorrhage
obscuring vision).
SPECIAL POPULATIONS
Emergency airway management in selected adult populations is summarized
in the table ( table 7) and discussed separately:
SOCIETY GUIDELINE LINKS
Elevated ICP (see "Airway management in the patient with elevated ICP
for emergency medicine and critical care")
●
Acute severe asthma (see "Airway management in acute severe asthma
for emergency medicine and critical care")
●
Direct airway trauma (see "Airway management in the adult with direct
airway trauma for emergency medicine and critical care")
●
Patient with obesity (see "Airway management in the morbidly obese
patient for emergency medicine and critical care")
●
Older adult patient (see "Airway management in the geriatric patient for
emergency medicine and critical care")
●

Links to society and government-sponsored guidelines from selected
countries and regions around the world are provided separately. (See "Society
guideline links: Airway management in adults".)
SUMMARY AND RECOMMENDATIONS
Determine proper airway approach – Unless it is not possible because
of patient status (eg, combative) or urgency of the required airway
intervention, the clinician preparing to perform rapid sequence
intubation (RSI) should conduct an airway assessment to determine the
difficulty of intubation, bag-mask ventilation (BMV), extraglottic device
(EGD) placement, and cricothyrotomy. Impaired physiology (eg, hypoxia,
metabolic acidosis, hemodynamic instability) should also be considered
in airway management decision-making ( table 5 and table 6). (See
'Determining the proper approach to airway management' above.)
●
Importance of planning – Failure to recognize and plan for a difficult
intubation is a leading factor contributing to a failed airway and poor
patient outcomes. (See 'Identifying the anatomically difficult airway'
above.)
●
Predicting the difficult airway – Attributes predictive of difficult direct
laryngoscopy and intubation can be identified using the LEMON
mnemonic: Look, Evaluate (3-3-2), Mallampati, Obstruction/obesity, Neck
mobility ( table 1). (See 'The LEMON assessment for difficult intubation'
above.)
●
Predicting difficult bag-mask ventilation – Difficult BMV can be
predicted using the ROMAN mnemonic: Radiation or restriction,
Obstruction/obesity/obstructive sleep apnea, Mask
●

seal/Mallampati/male, Age over 55, No teeth ( table 2). (See 'Difficult
bag-mask ventilation' above.)
Difficult airway algorithm – The difficult airway is managed according
to the difficult airway algorithm ( algorithm 4). The key determinations
are whether the operator is "forced to act" and, if not, whether the
patient's oxygenation is adequate (ie, oxyhemoglobin saturation [SpO ]
>92 percent). (See 'The difficult airway algorithm' above.)
●
2
Obtain assistance and equipment – The first action is to obtain all
necessary assistance (personnel, equipment, airway devices).
•
If "forced to act" situation (eg, imminent airway obstruction) – In a
"forced to act" situation, we suggest proceeding immediately with
administration of RSI drugs (Grade 2C), even if intubation is
anticipated to be difficult. Use of a video laryngoscope rather than a
direct laryngoscope is preferred in these cases. (See 'Applying the
algorithm' above and 'Effect of increasing video laryngoscopy use'
above and "Overview of advanced airway management in adults for
emergency medicine and critical care", section on 'Choice of
laryngoscopy technique'.)
•
Improve oxygenation – If the operator is not forced to act, but
oxygenation is inadequate, attempts are made to improve it with
supplemental oxygen or BMV.
•
If adequate SpO cannot be maintained – In the case of inadequate
oxygen saturation, the airway is considered to be a failed airway and is
managed accordingly ( algorithm 5). (See "Approach to the failed
airway in adults for emergency medicine and critical care".)
• 2
Awake intubation – In a patient with an anticipated difficult intubation
and concerns about whether the patient can be successfully ventilated
●

ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledge Michael
Murphy, MD, who contributed to earlier versions of this topic review.
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