Identification of the Difficult and Failed Airway

Introduction

Although both difficult and failed airways are discussed in this chapter, the two concepts are distinct. A difficult airway is one in which identifiable anatomical attributes predict technical difficulty with securing the airway. A failed airway is one for which the chosen technique has failed, and rescue must be undertaken. Obviously, there is much overlap, but it is important to keep the two notions distinct.

In addition, one can think about airway difficulty in two categories: an anatomically difficult airway and a physiologically difficult airway. The former presents anatomical or logistical barriers to successful airwaymanagement, whereas the latter requires the operator to optimize overall patient management in the context of critically low oxygen saturation, blood pressure, or metabolic derangement, such as severe metabolic acidosis. This chapter focuses on the anatomical issues related to airway management, and the term “difficult airway,” throughout this manual, refers to airways with anatomical or logistical difficulties for airway management. Chapter 32 discusses the approach to the physiologically compromised patient, whichsome authors refer to as a physiologicallydifficult airway.

A difficult airway is one for which a preintubation examination identifies physical attributes that are likelyto make laryngoscopy, intubation, bag-maskventilation(BMV), the use of an extraglottic device (e.g., laryngeal mask airway [LMA]), or surgical airway management more difficult than would be the case in an ordinary patient without those attributes. Identification of a difficult airway is a key component of the approach to airway management for anypatient and is a keybranchpoint onthe mainairwayalgorithm(see Chapter 3). The key reason for this is that, depending on the degree of predicted difficulty, one should not administer a neuromuscular blocking medication to a patient unless one has a measure of confidence that gas exchange can be maintained if laryngoscopy and intubation fail. Accordingly, if an anatomically difficult airway is identified, the difficult airway algorithm is used.

A failed airway situation occurs when a provider has embarked on a certain course of airway management (e.g., rapid sequence intubation[RSI]) and has identified that intubationby that method is not goingto succeed, requiringthe immediate initiationof a rescue sequence (the failed airway algorithm, see Chapter 3). Certainly, in retrospect, a failed airway can be called a difficult airway because it has proven to be difficult or impossible to intubate, but the terms “failed airway” and “difficult airway” must be kept distinct because they represent different situations, require different approaches, and arise at different points in the airway management timeline. One way of thinkingabout this is that the difficult airway is something one anticipates and plans for; the failed airway is something one experiences (particularly if one did not assess for, and anticipate, a difficultyairway).

Airways that are difficult to manage are fairly common in emergency practice. Difficult direct laryngoscopy (DL), defined as a grade III or grade IV laryngoscopic view, occurs in approximately 10% of all adult emergency intubations. The incidence is drastically lower when a video laryngoscope is used (see Chapter 14 Video Laryngoscopy). However, the incidence of overall intubation failure is quite low, that is, less than 1%. Intubation failure can occur in a setting where the patient can be oxygenated by an alternative method, such as by BMV or using an EGD, or in a setting where the patient can be neither intubated nor oxygenated. The incidence of the “can’t intubate, can’t oxygenate” (CICO) situation in preselected operating room intubations is rare, estimated to occur once in 5,000 to 20,000 intubations. The true incidence is unknown in emergency intubations, but it is likely substantially more common, given patient acuity, lack of preselection, and a higher rate of difficult airway markers. Rescue cricothyrotomy most often happens in the setting of a can’t oxygenate failed airway, but its incidence has declined with the advent of video laryngoscopy (VL) and various rescue devices. Based on large registry data of adult intubations, rescue surgical airways occur in 0.3% to 0.5% of all encounters. This chapter explores the concepts of the failed and the difficult airway in the setting of emergency intubation. Recognizing the difficult airway in advance and executing an appropriate and thoughtful plan, guided by the difficult airway algorithm (see Chapter 3), will minimize the likelihood that airway management will fail. Furthermore, recognizing the failed airway promptly allows use of the failed airwayalgorithmto guide selectionof a rescue approach.

THE FAILED AIRWAY

Afailed airwayexists whenanyof the followingconditions is met:

  1. Failure to maintain acceptable oxygen saturation during or after one or more failed laryngoscopic attempts (CICO) or
  2. Three failed attempts at orotracheal intubation by an experienced intubator, even when oxygensaturationcanbe maintained or
  3. The single “best attempt” at intubationfails inthe “Forced to Act” situation(see below).

Clinically, the failed airway presents itself in two ways, dictating the urgency created by the situation:

  1. Can’t Intubate, Can’t Oxygenate: There is not sufficient time to evaluate or attempt a series of rescue options, and the airway must be secured immediately because of an inabilityto maintainoxygensaturationbyBMVor withanEGD.
  2. Can’t Intubate, Can Oxygenate: There is time to evaluate and execute various options because the patient is oxygenated.

The most important way to avoid airway management failure is to identify in advance those patients for whom difficulty can be anticipated with intubation, BMV, insertion of an EGD, or cricothyrotomy. In the “Forced to Act” scenario, airway difficulty is apparent, but the clinical conditions (e.g., combative, hypoxic, rapidly deteriorating patient) force the operator’s hand, requiring administration of RSI drugs in an attempt to create the best possible circumstances for tracheal intubation, with immediate progression to failed airway management if that one best attempt is not successful (see Chapter 3).

THE DIFFICULT AIRWAY

According to the main emergency airway management algorithm, RSI is the method of choice for any non-crash airway when airway management difficulty is not anticipated. This requires a reliable and reproducible method for identifying the difficult airway. This evaluation must be expeditious, easyto remember, and complete.

Inclinical practice, the difficult airwayhas four dimensions:

  1. Difficult laryngoscopy
  2. Difficult BMV
  3. Difficult EGD
  4. Difficult cricothyrotomy

A distinct evaluation is required for difficult laryngoscopy, difficult BMV, difficult EGD, and difficult surgical airway management, and each evaluation must be applied to each patient before airwaymanagement is undertaken(Fig. 2-1).

Difficult Laryngoscopy: LEMON

The concept of difficult laryngoscopyand intubationis inextricablylinked to poor glottic view; the less adequate the glottic view, the more challengingthe intubation. This concept, developed during an era when almost all intubations were done by DL, appears to hold true even in the era of VL. Nearly all research relating certain patient characteristics to difficult or impossible intubation is based on studies of DL. VL is much less affected than DL by the presence or number of difficult airway attributes. With the exception of severely reduced mouth opening such that the device is unable to be inserted or sudden unanticipated device failure, it is rare for VLto yield a Cormack and Lehane grade III (or worse) glottic view. VLaccomplishes this independently of the need to align the various airway axes, as must occur during DL (see Chapters 13 and 14). Difficult laryngoscopy and intubation are uncommon, even rare, when certain video laryngoscopes are used. It follows that evidence-based guidelines for prediction of difficult VL may be challenging, or even impossible, to develop. Pending further information, however, we recommend performing a difficult laryngoscopy assessment, using the LEMON mnemonic, on all patients for whom intubation is planned, including for planned VL.

Cormack and Lehane introduced the most widely used system of categorizing the degree of visualization of the larynx during laryngoscopy, in which an ideal laryngoscopic view is designated grade 1 and the worst possible view, grade 4 (## Fig. 2-2## ). Cormack–Lehane (C–L) view grade 3 (only the epiglottis is visible) and grade 4 (no glottic structures are visible) are highly correlated with difficult or failed intubation. C–Lgrade 1 (visualization of virtually the entire glottic aperture) and grade 2 (visualization of the posterior portion of the cords or the arytenoids) are not typically associated with difficult intubation. The C–Lgrading systemdoes not differentiate precisely the degree to which the laryngeal aperture is visible during laryngoscopy: A grade 2 view may reveal little of the vocal cords, or none at all if only the arytenoids are visible. This led to adoption of a grade 2a/2b system, wherein a 2a shows any portion of the cords and a 2b shows only the arytenoids. Grade 2a airways perform comparably to those scored as grade 1, whereas grade 2b airways behave more like grade 3 airways. Grade 2b accounts for only about 20% of grade 2 views. However, when a grade 2b view occurs, two-thirds of patients are difficult to intubate, whereas only about 4% of patients withgrade 2a views are characterized as difficult intubations. Agrade 1 view reveals virtually the entire glottis and is associated withnearlyuniversal intubationsuccess.

Despite scores of clinical studies, no evidence to date has identified a full-proof set of patient attributes that, when absent, always predicts successful laryngoscopy and, when present, indicates certain intubation failure. In the absence of a proven and validated system that is capable of predicting intubation difficulty with 100% sensitivity and specificity, it is important to develop an approach that will enable a clinician to quickly and simply identify those patients who might be difficult to intubate so an appropriate plan can be made using the difficult airway algorithm. In other words, when asking the question, “Does this patient’s airway warrant using the difficult airway algorithm, or is it appropriate and safe to proceed directly to RSI?,” we value sensitivity (i.e., identifying all those who might be difficult) more thanspecificity(i.e., always beingcorrect whenidentifyinga patient as difficult).

The mnemonic LEMON is a useful guide to identify as many of the risks as possible as quickly and reliably as possible to meet the demands of an emergency situation. The elements of the mnemonic are assembled from an analysis of the difficult airway prediction instruments in the anesthesia, emergency medicine, and critical care literature. The mnemonic, which we developed for The Difficult Airway Course and the first edition of this book, has been externally validated in ED patients. The modified LEMON (all aspects of LEMON except the Mallampati score and thyromental distance) has undergone additional external validation and been found to have very high negative predictive value for both conventional and video laryngoscopy. LEMON has now been adopted as a recommended airway assessment tool in Advanced Trauma Life Support (ATLS). The mnemonic is as follows:

L—## Look externally: Although a gestalt of difficult intubation is not particularly sensitive (meaning that many difficult airways are not readily apparent externally), it is quite specific, meaning that if the airway looks difficult, it probably is. Most of the litany of physical features associated with difficult laryngoscopy and intubation (e.g., small mandible, large tongue, large teeth, and short neck) are accounted for by the remaining elements of LEMON and so do not need to be specifically recalled or sought, which can

be a difficult memory challenge in a critical situation. The external look specified here is for the “feeling” that the airway will be difficult. This feeling may be driven by a specific finding, such as external evidence of lower facial disruption and bleeding that might make intubation difficult, or it might be the ill-defined composite impression of the patient, such as the obese, agitated patient with a short neck and small mouth, whose airway appears formidable even before any formal evaluation (the rest of the LEMON attributes) is undertaken. This “gestalt” of the patient is influenced by patient attributes, the setting, and clinicianexpertise and experience, and likelyis as valid for VLas for DL.

E—## Evaluate 3-3-2: This step is an amalgamation of the much-studied geometric

considerations that relate mouth opening and the size of the mandible to the position of the larynx in the neck in terms of likelihood of successful visualization of the glottis by DL. This concept originally was identified with “thyromental distance,” but has become more sophisticated over time. The thyromental distance is the hypotenuse of a right triangle, the two legs being the anteroposterior dimension of the mandibular space, and the interval between the chin–neck junction (roughly the position of the hyoid bone indicating the posterior limit of the tongue) and the top of the larynx, indicated by the thyroid notch. The 3-3-2 evaluation is derived from studies of the geometrical requirements for successful DL, that is, the abilityof the operator to create a direct line of sight fromoutside the mouth to the glottis. It is not known whether it has any value in predicting difficult VL, for which no straight line of sight is required. The premises of the 3-3-2 evaluationare as follows:

The first “3,” therefore, assesses mouth opening. A normal patient can open his or her mouthsufficientlyto accommodate three of his or her ownfingers betweenthe upper and lower incisors (## Fig. 2-3A## ). In reality, this is an approximate measurement as it would be unusual to ask an acutely ill or injured patient to stick three fingers in his or her mouth. If a patient is able to comply, ask if he or she can open the mouth as wide as possible. This will give a meaningful sense of whether the patient is able to open fully, partially, or not at all. The second “3” evaluates the length of the mandibular space by ensuring the patient’s ability to accommodate three of his or her own fingers between the tip of the mentum and chin–neck junction (hyoid bone) (## Fig. 2-3B## ). The “2” assesses the position of the glottis in relation to the base of the tongue. The space between the chin–neck junction (hyoid bone) and the thyroid notch should accommodate two of the patient’s fingers (## Fig. 2-3C## ). Thus, in the 3-3-2 rule, the first 3 assesses the adequacy of oral access, and the second 3 addresses the dimensions of the mandibular space to accommodate the tongue on DL. The ability to accommodate significantly more than or less than three fingers is associated with greater degrees of difficulty in visualizing the larynx at laryngoscopy: The former because the length of the oral axis is elongated, and the latter because the mandibular space may be too small to accommodate the tongue, requiring it to remain in the oral cavity or move posteriorly, obscuring the view of the glottis. Encroachment on the submandibular space by infiltrative conditions (e.g., Ludwig angina) is identified during this evaluation. The final 2 identifies the location of the larynx in relation to the base of the tongue. If significantly more than two fingers are accommodated, meaning the

larynx is distant fromthe base of the tongue, it may be difficult to reach or visualize the glottis on DL, particularly if a smaller blade size is used initially. Fewer than two fingers may mean that the larynx is tucked up under the base of the tongue and may be difficult to expose. This conditionis oftenimpreciselycalled an“anterior larynx.”

M—## Mallampati score: Mallampati determined that the degree to which the posterior

oropharyngeal structures are visible when the mouth is fully open and the tongue is extruded reflects the relationships among mouth opening, the size of the tongue, and the size of the oral pharynx, which defines access through the oral cavity for intubation, and that these relationships are associated with intubation difficulty. Mallampati’s classic assessment requires that the patient sit upright, open the mouth as widely as possible, and protrude the tongue as far as possible without phonating. ## Figure 2-4## depicts how the scale is constructed. Class I and class II patients have low intubation failure rates; so the importance withrespect to the decisionwhether to use neuromuscular blockade rests with those in classes III and IV, particularly class IV, where intubation failure rates may exceed 10%. By itself, the scale is neither sensitive nor specific; however, when used in conjunction with the other difficult airway assessments, it provides valuable information

about access to the glottis through the oral cavity. In the emergency situation, it frequently is not possible to have the patient sit up or to follow instructions. Therefore, often only a crude Mallampati measure is possible, obtained by examining the supine, obtunded patient’s mouth with a tongue blade and light, or by using a lighted laryngoscope blade as a tongue depressor on the anterior half of the tongue to gain an appreciation of how much mouth opening is present (at least in the preparalyzed state) and the relationship between the size of the tongue and that of the oral cavity. Although not validated in the supine position using this approach, there is no reason to expect that the assessment would be significantly less reliable than the original method with the patient sitting and performing the maneuver actively. The laryngoscope or tongue blade should not be inserted too deeply because this may incite a gag reflex and can place a supine and compromised patient at riskfor vomitingand aspiration.

the pillars are not visible. In class III, only a minimalportion of the oropharyngealwallis visible, and in class IV, the tongue is pressed against the hard palate.

O—## Obstruction/Obesity: Upper airway obstruction is a marker for difficult laryngoscopy. The four cardinal signs of upper airway obstruction are muffled voice (hot potato voice), difficulty swallowing secretions (because of either pain or obstruction), stridor, and a sensation of dyspnea. The first two signs do not ordinarily herald imminent total upper airway obstruction in adults, but critical obstruction is much more imminent when the sensation of dyspnea occurs. Stridor is a particularly ominous sign. The presence of stridor is generally considered to indicate that the airway has been reduced to <50% of its normal caliber, or to a diameter of 4.5 mmor less. The management of patients with upper airway obstruction is discussed in Chapter 36. Although it is controversial whether obesity per se is an independent marker for difficult laryngoscopy or whether obesity

simply is associated with various difficult airway attributes, such as high Mallampati

score or failure of the 3-3-2 rule, obese patients frequently have poor glottic views by DL

or VL, and obesity, initself, should be considered to portend difficult laryngoscopy. ## N—## Neck mobility: The ability to position the head and neck is one of the key factors in

achieving the best possible view of the larynx by DL. Cervical spine immobilization for

trauma, by itself, may not create a degree of difficulty that ultimately leads one to avoid

RSI after applying the thought processes of the difficult airway algorithm. However,

cervical spine immobilization will make intubation more difficult and will compound the

effects of other identified difficult airway markers. In addition, intrinsic cervical spine

immobility, as in cases of ankylosing spondylitis or rheumatoid arthritis, can make

intubation by DLextremely difficult or impossible and should be considered a much more

serious issue than the ubiquitous cervical collar (which mandates inline manual

immobilization). VLrequires much less (or no) head extension, depending on blade shape,

and provides a glottic view superior to that by DLwhen head extension or neck flexion is

restricted. Other devices, such as the Airtraq or the Shikani optical stylet, discussed

elsewhere inthis manual, also mayrequire less cervical spine movement thanDLalthough

image size and clarityare far inferior to that obtained withVL.

Difficult BMV: ROMAN##

Chapter 9 highlights the importance of BMV in airway management, particularly as a rescue maneuver when orotracheal intubation has failed. The airway manager must be confident that oxygenation with a BMV or EGD is feasible before neuromuscular blockers are administered whether or not laryngoscopyis thought to be successful.

The validated indicators of difficult BMV from various clinical studies can be easily recalled for rapid use inthe emergencysettingbyusingthe mnemonic ROMAN.

R—## Radiation/Restriction: Recent evidence suggests that radiation treatment to the neck is

one of the strongest predictors of difficult and failed maskventilation. Restrictionrefers to patients whose lungs and thoraces are resistant to ventilation and require high-ventilation pressures. These patients are primarily suffering from reactive airways disease with mediumand small airways obstruction (asthma and chronic obstructive pulmonary disease [COPD]) and those with pulmonary edema, acute respiratory distress syndrome (ARDS), advanced pneumonia, or any other condition that reduces pulmonary compliance or increases airwayresistance to BMV.

O—## Obesity/Obstruction/Obstructive sleep apnea: We often refer to this as the “triple O” because all three attributes are important, and they are often linked (e.g., obesity with obstructive sleep apnea [OSA]). Patients who are obese (body mass index [BMI] >26 kg

per m2) are often difficult to ventilate adequately by bag and mask. Women in third- trimester gestation are also a prototype for this problem because of their increased body mass and the resistance to diaphragmatic excursion caused by the gravid uterus. Pregnant or obese patients also desaturate more quickly, making the bag ventilation difficulty of even greater import (see Chapters 37 and 40). Difficulty bagging the obese patient is not

caused solelybythe weight of the chest and abdominal walls but also the resistance bythe abdominal contents to diaphragmatic excursion. Obese patients also have redundant tissues, creating resistance to airflow in the upper airway. This explains the recent association with OSA and difficult mask ventilation. Similarly, obstruction caused by angioedema, Ludwig angina, upper airway abscesses, epiglottitis, and other similar conditions will make BMVmore difficult. Ingeneral, soft tissue lesions (e.g., angioedema, croup, and epiglottis) are amenable to bag-and-mask rescue if obstruction occurs, but not with 100% certainty. Similarly, laryngospasm can usually be overcome with good bag- and-mask technique. In contrast, firm, immobile lesions such as hematomas, cancers, and foreignbodies are less amenable to rescue byBMV, whichis unlikelyto provide adequate ventilationor oxygenationif total obstructionarises inthis context.

M—## Mask Seal/Mallampati/Male sex: Bushy beards, blood or debris on the face, or a

disruption of lower facial continuity are the most common examples of conditions that may make an adequate mask seal difficult. Some experts recommend smearing a substance, suchas KYjelly, onthe beard as a remedyto this problem, althoughthis action may simply make a bad situation worse in that the entire face may become too slippery to hold the mask in place. Both male sex and a Mallampati class 3 or 4 (see earlier) airway also appear to be independent predictors of difficult BMV.

A—## Age: Age older than 55 years is associated with a higher risk of difficult BMV, perhaps

because of a loss of muscle and tissue tone in the upper airway. The age is not a precise cutoff, and some judgment canbe applied withrespect to whether the patient has relatively elastic (young) or inelastic (aged) tissue.

N—## No teeth: An adequate mask seal may be difficult in the edentulous patient because the

face may not adequately support the mask. An option is to leave dentures (if available) in situ for BMV and remove them for intubation. Alternatively, gauze dressings may be inserted into the cheek areas through the mouth to puff them out in an attempt to improve the seal. Another technique for limiting mask leak involves rolling the lower lip down toward the chinand usingthe inner mucosal surface as a contact point for the bottomof the mask(See Chapter 9).

Difficult EGD: RODS##

In the emergency setting, extraglottic airway devices have emerged as credible first-line devices for ventilation and oxygenation, instead of the traditional bag and mask; as alternatives to tracheal intubation in some patient circumstances (especially out of hospital); and as valuable rescue devices.

Studies have identified factors that predict difficulty in placing an EGD and providing adequate gas exchange. These canbe assessed usingthe mnemonic RODS.

R—## Restriction: The restriction referred to here is similar to that for the ROMAN mnemonic, that is, “restricted” lung capacity with intrinsic resistance to ventilation fromprimary lung

or tracheal/bronchial pathology. VentilationwithanEGD maybe difficult or impossible in the face of substantial increases in airway resistance (e.g., asthma) or decreases in pulmonary compliance (e.g., pulmonary edema), although often the EGD is more effective

at ventilation than is a bag and mask. In addition, restricted mouth opening will affect

EGD insertion or make it impossible. Adequate mouth opening is required for insertion of

the EGD. This requirement varies, depending on the particular EGD to be used. Recent

operating room(OR) data have also identified restricted cervical spine mobility as a risk

for difficult EGD use, likelybecause placement canbe more challenginginthese patients. ## O—## Obstruction/Obesity: If there is upper airway obstruction in the pharynx, at the level of

the larynxor glottis, or below the vocal cords, anEGD maybe impossible to insert or seat

properly in order to achieve ventilation and oxygenation. In some circumstances, it will

not bypass the obstruction at all. Obesity creates two challenges to oxygenation using an

EGD. First, redundant tissues in the pharynx may make placement and seating of the

device more difficult. Usually, this is not a significant problem. More importantly, obese

patients require higher ventilation pressures, largely because of the weight of the chest

wall and abdominal contents. The former causes resistance to ventilationbyincreasingthe pressures required to expand the chest, and the latter causes resistance to ventilation by increasing the pressures required to cause the diaphragm to descend. Depending on the EGD chosen and positioning of the patient (it is better to attempt ventilation with the patient 30° head up or in reverse Trendelenberg position), ventilation resistance may exceed the ability of the EGD to seal and deliver the necessary pressures. More

information on leak pressures for the variety of EGDs in circulation can be found in Chapters 10, 11, and 29.

D—## Disrupted or Distorted airway: The key question here is “If I insert this EGD into the

pharynx of this patient, will the device be able to seat itself and seal properly within relativelynormal anatomy?” For example, fixed flexiondeformityof the spine, penetrating neck injury with hematoma, epiglottitis, and pharyngeal abscess each may distort the anatomysufficientlyto prevent proper positioningof the device.

S—## Short thyromental distance: A small mandibular space, as assessed by the patient’s

thyromental distance, may indicate that the tongue resides less in the mandibular fossa and more in the oral cavity. This can obstruct and complicate EGD insertion and has been stronglyassociated withdifficult EGD use.

Difficult Cricothyrotomy: SMART##

There are no absolute contraindications to performing an emergency cricothyrotomy in adults (see Chapter 19). However, some conditions maymake it difficult or impossible to performthe procedure, making it important to identify those conditions in advance and allow consideration of alternatives rather than assuming or hoping that cricothyrotomy, if necessary, will be successful as a rescue technique. The mnemonic SMART is used to quickly assess the patient for features that may indicate that a cricothyrotomy might be difficult. A part of patient assessment using this mnemonic, which occurs during the “A” step, is to perform a physical examination of the neck, identifying the landmarks and any barriers to the procedure. The SMART mnemonic is applied as follows:

S—## Surgery (recent or remote): The anatomymaybe subtlyor obviouslydistorted, makingthe airway landmarks difficult to identify. Scarring may fuse tissue planes and make the

procedure more difficult. Recent surgery may have associated edema or bleeding, complicatingperformance of the procedure.

M—## Mass: A hematoma (postoperative or traumatic), abscess, or any other mass in the

pathway of the cricothyrotomy may make the procedure technically difficult, and requires the operator to meticulously locate the landmarks, which may be out of the midline, or obscured.

A—## Access/Anatomy: Obesity makes surgical access challenging, as it is often difficult to

identify landmarks. Similar challenges are presented by subcutaneous emphysema, soft tissue infection, or edema. A patient with a short neck or overlying mandibular pannus presents challenges with both identification of landmarks and access to perform the procedure. Extraneous devices, suchas a cervical immobilizationcollar, or a halothoracic brace also mayimpede access.

R—## Radiation (and other deformity or scarring): Past radiation therapy may distort and scar

tissues, making the procedure difficult and often causing tissues that are normally discrete to bond together, distortingtissue planes and relationships.

T—## Tumor: Tumor, either inside the airway (beware of the chronically hoarse patient) or

encroaching on the airway, may present difficulty, both from access and bleeding perspectives.

SUMMARY##

some degree of difficulty after a bedside assessment, the decision to use neuromuscular blocking agents (NMBAs) is a complex one that takes into account the degree of difficulty, the urgency for tube placement, available difficult airway tools, especially VL, and one’s own skill and experience. Basically, to use NMBA, the operator must be confident that oxygenation can be maintained, and that intubation is likely to be successful, usingthe planned approach. See Chapter 3 for further details.

NMBAs.

EVIDENCE##

>14,000 patients.1 For obese patients, the incidence of difficult intubation certainly is higher, but how much of this is caused by obesity alone, and how much is a product of the presence of various difficult airway markers, such as a poor Mallampati score, is not clear. The Intubation Difficulty Score (IDS) considers the numbers of operators, devices, attempts, the C–L score, vocal cord position (abducted or not), and whether

excessive lifting force or external manipulation is required.2 In one study of 129 lean and 134 obese patients, using an IDS of five or greater as the definition of difficult intubation (a relatively high bar), investigators identified difficult intubation in 2.2% of

leanpatients and 15.5% of obese patients.3 Only1% of 663 patients inone Britishstudy had grade III glottic views, but 6.5% had grade IIb views (only arytenoids visible), and

2/3 of these were difficult to intubate.4 In Reed’s validation study of the LEMON mnemonic, 11/156 (7%) of patients had C–Lgrade III glottic views, and only 2/156 had

grade IV views.5 The largest emergency department series is from the National Emergency Airway Registry (NEAR) project. Glottic view is highly dependent on the type of laryngoscope chosen. Multiple ED studies have shownthat glottic view is better

with both the C-MAC and GlideScope compared to DL.6–8 In an analysis of 198 video macintosh intubations (V-MAC), a grade I or II glottic view was obtained in 97% of encounters when the video screen was used, but in only 78% of encounters when the V-

MAC was used as a direct laryngoscope.7 In a single-center prospective evaluation of 750 ED intubations over a 2-year period, during which 255 intubations were performed with a C-MAC and the rest with a conventional laryngoscope, the C-MAC yielded

grade I/II views in94% of cases compared with83% for DL.8 In the multicenter NEAR II study, reporting on 8,937 intubations from 1997 to 2002, the first chosen method ultimately was not successful in approximately 5% of intubations. Overall airway management success was >99%, and surgical airways were performed on 1.7% of trauma patients and approximately 1% of all cases.9 In a subset of almost 8,000 of the NEAR II patients, approximately 50% of rescues from failed attempts involved use of RSI after failure of intubation attempts without neuromuscular blockade.10 In NEAR III, an analysis of 17,583 adult intubations from 2002 to 2012 showed that 17% of all encounters required more than one attempt before successful intubation. Ultimate intubation success was 99.5%. Rescue cricothyrotomy, a surgical airway performed after at least one intubation attempt, was lower than previously reported, occurring in

0.3% of cases and was performed twice as oftenintrauma patients.11

relevant thyromental distance that predicts difficultydepends onthe size of the patient.13 This reinforces the notion of using the patient’s own fingers as a size guide for thyromental distance, but also for the other two dimensions of the 3-3-2 rule. Hyomental distance has also been used, but seems less reliable, causing researchers to explore the value of repeated measurements and ratios involving different head and neck

positions.14 The eponymous Mallampati evaluation has been validated multiple times. The modified Mallampati score, the four-category method that is most familiar, was found highly reliable in a comprehensive meta-analysis of 42 studies, but the authors emphasize, as do we, that the test is important, but not sufficient in evaluating the

difficult airway.1 One study suggested that the Mallampati evaluation gains specificity (from 70% to 80%) without loss of sensitivity if it is performed with the head in

extension, but this studyinvolved only60 patients, and performingthe Mallampati, even in the neutral position, is challenging enough before emergency intubation, so we do not

recommend head extension.15 Interference with DLby upper airway obstruction is self- evident. Obesity is uniformly identified as a difficult airway marker, but, remarkably, controversy persists regarding whether obesity, per se, indicates difficult laryngoscopy, or whether obese patients simply have a greater incidence of having other difficult

airway markers, such as higher Mallampati scores.16 An opposing view suggests that, although a higher Mallampati score is associated with difficult intubation in obese patients, other traditional predictors of difficult intubation do not account for the high

incidence and degree of difficulty in obese patients.3 The only two studies to compare obese and lean patients head to head found a similar fivefold increase in intubation difficulty for obese patients (about 15% vs. about 3% of lean patients), but one study

concluded that BMI was important, whereas the other concluded the opposite.17

Langeron et al.,18 where a 5% incidence of difficult BMV occurred in 1,502 patients. They identified five independent predictors of difficult BMV: presence of a beard, high BMI, age > 55 years, edentulousness, and a history of snoring. Subsequent studies by other investigators were much larger. Kheterpal et al. used a graded definition of difficult BMV in their study of >22,000 patients. They divided difficult BMV into four classes, ranging from routine and easy (class I) to impossible (class IV). Class III difficulty was defined as inadequate, “unstable,” or requiring two providers. They identified class III (difficult) BMV in 313/22,600 (1.4%) and class IV (impossible) in 37 (0.16%) patients. Multivariate analysis was used to identify independent predictors of difficult BMV: presence of a beard, high BMI, age > 57 years, Mallampati class III or IV, limited jaw protrusion, and snoring. Snoring and thyromental distance < 6 cm

were independent predictors of impossible BMV.19 Subsequently, the same researchers studied 53,041 patients over a 4-year period. Independent predictors of impossible BMV included the following: presence of a beard, male sex, neck radiation changes, Mallampati class III or IV, and sleep apnea, with neck radiation having the strongest

association of failed mask ventilation.20 These studies, combined with others, and with our collective experience, are the foundation for the ROMAN mnemonic. Interestingly, Mallampati class did not fare well as a predictor of difficult BMV in Lee’s meta- analysis of 42 studies with >34,000 patients, although it did quite well for difficult

intubation.1 Nevertheless, we believe that Mallampati is a worthy consideration with respect to difficult BMV, as it helps the operator to understand the extent to which the

tongue might impede ventilation. Conditions that create resistance to ventilation, suchas reactive airways disease and COPD, and those associated with a decrease in

pulmonary compliance, such as ARDS or pulmonary edema, understandably make ventilation with a bag and mask more difficult. Why were these attributes not identified

conditions were too ill to be included in any such studies. Nonetheless, we are confident inincludingthis concept inthe “R” of ROMAN.

previously to affect rescue mask ventilation.21 As such, this mnemonic really represents our expert consensus rather than an assessment of high-quality evidence. The requirement for minimal mouth opening sufficient to insert the device is self-evident. Obesity and obstruction will interfere with EGD use in similar fashion to their interference with BMV. Devices vary in their utility in various patients, however, and some may be better suited for obese patients than others. One study compared 50 morbidlyobese patients with50 leanpatients and identified no increase indifficultyfor

either ventilationor intubationwiththe intubatingLMA.22 Distorted anatomy is our own concept, based on the fact that each of these devices is designed to “seat” into normal humananatomy, giventhat the right size of device is selected.

few as 2% of patients.12 In one study of prehospital intubations, difficult airway predictors such as obesity and cervical immobility were present in 13% and 50% of

failed airways, respectively.23 In anesthesia practice, using a definition of difficult intubation as two failed attempts despite optimal laryngeal manipulation, one study

found only 0.9% unexpected difficult intubations among >11,000 patients.24 Investigators did not report C–L scores, however. In elective anesthesia practice, difficult airway patients often are “selected out” and managed by modified anesthetic technique, such as awake flexible endoscopic intubation. The safety of performing preintubation assessment is reinforced by this practice, however, as difficult and failed BMV and intubation in this population generally are unexpected because of the prescreening, and so probably reasonably predict unexpected (i.e., not detected by preintubation assessment of difficulty) similar events during emergency intubation. In one study of almost 23,000 patients, only about 1.6% had difficult BMV, and only

0.37% or 1/300 had a combinationof difficult BMVand difficult intubation.19

not have any reason to believe that the 3-3-2 rule applies, particularly with hyper- curved video laryngoscopes. In one study comparing the C-MAC video laryngoscope with DLin ED intubations, the aggregate effect of multiple difficult airway markers had a significant impact on first past success with DL but not with VL. Comparing first attempt success between patients without difficult airway markers with those that had three or more, the first attempt success for DL decreased from 88% to 75% but

decreased only by 5% for VL (99% to 93%).8 Mallampati is not nearly as important, because the video viewer onmost video laryngoscopes is positioned beyond the tongue, thus eliminating the tongue from consideration. Mallampati assesses mouth opening, also, however, as does the first “3” of the 3-3-2 rule, and mouth opening remains important for VL, although much less so. Only one study has attempted to identify attributes associated with difficult VL, in this case the GlideScope, and it is difficult to put much weight on any conclusions because 400/400 patients had C–L class I or II

views.25 The evidence for superiority of VL over conventional laryngoscopy is presented inChapter 14.

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