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Approach to the difficult airway in adults for emergency medicine and critical care

Approach to the difficult airway in adults for emergency medicine and critical care
Literature review current through: May 2024.
This topic last updated: Dec 05, 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 for emergency medicine" and "Emergency airway management in children: Unique pediatric considerations" and "Rapid sequence intubation (RSI) in children for emergency medicine: 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 management in adults" and "Videolaryngoscopes and optical stylets for airway management for anesthesia in adults")

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.

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 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.)

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 in adults for emergency medicine and critical care".)

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 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 (VL), 83 percent for direct laryngoscopy (DL), and 90 percent with the C-MAC VL [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 airway management in adults for emergency medicine and critical care".)

Effect of increasing video laryngoscopy use — The increasing use of 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 DL. 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 VL 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 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 VL. 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) in adults".)

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 DL 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 DL [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.

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, DL is difficult or impossible because of the angles that have to be negotiated to permit visualization.

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 DL.

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 DL. In general, Mallampati class I or II predicts easy laryngoscopy, class III predicts difficulty, and class IV predicts extreme difficulty.

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 DL 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 DL 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 DL 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 DL view [44,45]. Proper positioning for DL 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 VL is less common compared with 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.

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 DL, where they are detrimental [53].

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 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 (VL) 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 laryngoscope or a VL 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 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 techniques' 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.

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 (SpO2) 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 SpO2 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

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 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).

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 SpO2 ≥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 SpO2 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 SpO2 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 in adults for emergency medicine and critical care", 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 SpO2, 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 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:

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?

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 techniques' 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). 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 in adults for emergency medicine and critical care", section on 'Physiologic 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 in adults for emergency medicine and critical care", section on 'Physiologic optimization'.)

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 'Awake techniques' 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.

Awake techniques — "Awake" is an imprecise term that encompasses the techniques in a spontaneously breathing, fully conscious, or lightly to moderately sedated patient. 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. The intubation is most commonly performed using a flexible intubating scope or a VL and is facilitated by topical anesthesia (and occasionally a nerve block) and sedation. The awake tracheal intubation (ATI) procedure is discussed separately. (See "Awake tracheal intubation".)

Awake airway examination — The ATI procedure is distinct from an “awake look,” which refers to a flexible nasopharyngolaryngoscopy airway examination performed in a patient unlikely to need tracheal intubation (eg, new onset voice hoarseness, to exclude adult epiglottitis or airway edema/foreign body). This procedure does not require sedation, and the endotracheal tube is not loaded over the top of the flexible scope. If tracheal intubation is ultimately required, airway visualization during the awake airway examination may identify barriers that preclude supraglottic intubation and mandate a surgical airway (eg, cricothyrotomy) or may identify a straightforward upper airway amenable to RSI and laryngoscopy. The following outlines our approach to the awake airway examination:

Apply a topical nasal vasoconstrictor (eg, oxymetazoline 0.05% two sprays) to reduce the risk of bleeding and enlarge the caliber of the nasal passages.

Spray 4% aqueous lidocaine through the nasal chamber of a laryngo-tracheal mucosal atomization device.

Place a soft 7-0 nasal trumpet lubricated with lidocaine ointment or gel.

Insert a flexible nasopharyngoscope or bronchoscope that is ≤4 mm wide and advance to visualize glottic structures.

Decision to perform awake intubation — The decision to perform ATI ultimately depends upon the clinical circumstances, likelihood of deterioration, and the judgment of the airway operator. We prefer an ATI technique instead of an awake airway examination if the clinician suspects that it is likely a tracheal tube will need to be delivered during the airway examination (eg, Ludwig’s angina).

ATI contraindications – ATI is contraindicated in a patient who refuses despite explanation of the benefits and risks of the procedure. ATI is generally not appropriate in a “forced to act” scenario since it requires more time and preparation (eg, administration of airway anesthesia) compared with RSI; in the presence of excessive airway bleeding or secretions, which may obscure the view of a flexible intubating scope and may complicate administration of topical anesthesia; in a patient with a local anesthetic allergy; and in an uncooperative or agitated patient. (See 'Operator forced to act' above.)

Potential ATI indications – Clinicians may choose to perform ATI instead of RSI for many indications/scenarios that would benefit from the patient breathing spontaneously and maintaining airway protective reflexes during the intubation attempt, such as the following:

Anticipated difficult airway anatomy – These patients (table 1 and picture 1) may benefit from an awake airway examination and/or ATI. If the oral approach is not available (eg, patient cannot open mouth or there is known large obstructing airway pathology), then ATI with a flexible intubating scope via the nasal route is clearly the preferred approach. (See 'Identifying the anatomically difficult airway' above.)

Predicted difficulty with face mask or supraglottic airway (SGA) ventilation – These patients (table 2 and table 4) are at risk for a failed airway with RSI. (See 'Difficult bag-mask ventilation' above.)

Presence of high-risk physiology – Patients with difficulty preoxygenating due to high intrapulmonary shunt or low functional residual capacity and/or high oxygen demand may benefit from ATI. In patients with physiologic derangements that increase the risk of peri-intubation cardiovascular collapse (eg, severe metabolic acidosis, hypotension, or right ventricular failure), ATI may be the preferable initial approach. These patients will not tolerate a brief period of apnea without developing hypoxia. (See 'High-risk physiology present' above.)

Predicted difficulty with emergency surgical airway access – ATI may be preferable in patients with predicted difficult emergency surgical airway access (table 3). In these patients, it is preferable to avoid airway management that creates a “cannot intubate/cannot oxygenate” (CICO) situation that necessitates rescue with emergency surgical airway access. (See "Approach to the failed airway in adults for emergency medicine and critical care".)

Choice of ATI approach – The ATI approach (ie, flexible intubating scope versus VL) should be based on available equipment, patient tolerance, and predicted likelihood for success. If a flexible intubating scope is unavailable, then ATI should be performed with VL but will likely require a deeper degree of sedation compared with ATI with a flexible intubating scope. (See "Awake tracheal intubation".)

Awake intubation attempt unsuccessful or awake airway examination precludes RSI — If the awake airway examination identifies that RSI is not advisable and/or the tracheal tube cannot be delivered during ATI (eg, glottis cannot be visualized), several airway management options remain, provided an adequate SpO2 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 VL will likely achieve a glottic view superior to that of a standard laryngoscope, enabling intubation. A fiberoptic or video intubating stylet may also be used. (See "Devices for difficult airway management in adults for emergency medicine and critical care".)

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:

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")

SOCIETY GUIDELINE LINKS — 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 [SpO2] >92 percent). (See 'The difficult airway algorithm' above.)

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 SpO2 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".)

Awake tracheal intubation – In a patient who needs airway management with anticipated difficult airway anatomy, predicted difficulty with BVM or supraglottic airway ventilation, physiologic derangements that increase the risk of peri-intubation cardiovascular collapse, or predicted difficulty with emergency surgical airway access, we suggest performing awake tracheal intubation instead of RSI (Grade 2C). These patients would benefit from breathing spontaneously and maintaining airway protective reflexes during the intubation attempt. (See 'Awake techniques' above.)

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

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