Difficult Airway and Its Management

Abstract

In the emergency unit, there may not be enough time for proper airway evaluation of a patient with respiratory distress. However, albeit fast, evaluation of head and neck mobility, lower jaw position, condition of teeth, mouth opening, mouth anatomy, and jaw-thyroid distance can contribute significantly to the correct management of the process. Based on these results, a decision can be made on how to manage the airway and how to proceed. If there is a finding of a difficult airway, a call for help should not be delayed. Ready-to-use “emergency airway management kit” is important. Determining whether the condition is a “difficult airway” is important because the “anticipated difficult airway” and “unanticipated difficult airway” approaches are different. There are numerous options for providing respiratory support to patients, and conservative approaches should be prioritized. Definitely, in addition to respiratory support with bag-masks, supraglottic airway devices, endotracheal tubes, and tracheostomy approach may also be processed without delay, in case of need. The aim of all procedures is to provide the patient with oxygen, which is indispensable for life. It should not be forgotten to avoid oxygen neglection during selecting the method, which requires least interventions and guarantees airway security. Consequently, in semi-urgent states, a more detailed evaluation of the patient is more appropriate.

1. Introduction

Secured airway is the cornerstone of effective resuscitation at life-threating states. Emergency practitioners are at the frontline for resuscitation of complex situations when airway management is far different from that in elective conditions. The shortage of time for decision-making and diagnosing the pathologic state also contributes to management failure.

It is important for practitioners to be aware and prepared for complicated intubation situations to reduce unpleasant outcomes and to provide high-quality healthcare. This chapter is aimed to discuss difficult airway prediction and the most used airway management devices and offers easy-to-understand descriptions of instrumentation techniques. Among the predictive difficult airway parameters, this chapter covers a brief explanation of ultrasound guided methods to foresee the airway complexity. The manuscript also contains revised guidelines for difficult airway management, accepted worldwide, and includes suggestions for specific complicated airway circumstances. We hope this chapter’s content would be helpful for airway managers in complicated circumstances and beneficial to improve the outcomes.

2. Definitions

Difficult airway (DA) is one of the most frightening situations, which may possibly be faced by practitioners in emergency, intensive care departments, and operating rooms. Inability to secure airway increases mortality associated with hypoxic brain injury and cardiopulmonary arrest. The core definition of DA was adopted by The American Society of Anesthesiologists (ASA) as the clinical situation in which a conventionally trained anesthesiologist has trouble with face mask ventilation of the upper airway, difficulty with tracheal intubation, or both [1]. Both these definitions may be uncovered and classified further into separate variations. Here, we encounter the most common variations of difficult airway conditions.

2.1 Difficult face mask ventilation

Authors define this condition as the inability of an experienced specialist (intensivist or anesthesiologist) to maintain oxygen saturation above 90% with a 100% FiO2 face mask [2]. The condition occurs generally as a consequence of inadequate mask seal, excessive gas leak (both are seen mainly in patients with complicated face anatomy, obesity, age over 65, “no teeth,” and beard and/or mustache), or excessive resistance to gas inflow and outflow (seen in cases with “stiff lungs” or foreign body in the airways).

2.2 Difficult supraglottic airway ventilation

Difficult supraglottic airway ventilation is defined the same as difficult face mask ventilation and occurs in the same circumstances.

2.3 Difficult supraglottic airway placement

Difficult supraglottic airway placement encounters the inability to place supraglottic device after multiple attempts in the presence or absence of tracheal pathology.

2.4 Difficult tracheal intubation

Difficult tracheal intubation is a state of unsuccessful tracheal tube placement after three or more attempts or time elapse more than 10 minutes spent to perform tracheal tube placement by due to presence or absence of tracheal pathology. Difficult tracheal intubation (orotracheal, nasotracheal, or transtracheal) may occur as the consequence of difficult laryngoscopy (inability to visualize any portion of vocal cords after multiple attempts) or failed intubation (incorrect placement of the intubation tube after multiple attempts).

2.5 Difficult surgical transtracheal intubation

Difficult surgical transtracheal intubation covers the terms of unsuccessful cricothyrotomy or tracheotomy after multiple attempts processed by skilled practitioner [2, 3].

3. Prediction

Proper physical examination and medical history of a patients may provide clues for prediction of DA. It is important for practitioners to be aware and prepared for complicated intubation situations to reduce unpleasant outcomes and to provide high-quality healthcare. Depending on whether the cases are predicted to be difficult or not, airways are classified into anticipated and unanticipated. As a common rule, not all anticipated difficult airways appear problematic at performance. Emergency department practitioners do not generally have enough time for detailed physical examination of a patient with the risk of respiratory collapse. However, a quick look on patient’s overall appearance may be profitable. Examination in elective circumstances starts with head and neck assessment and includes:

3.1 The jaw opening

In general, it is about 4 cm, which could be easily measured by three finger breadths between upper and lower incisors. The jaw opening lesser that three fingers is considered as limited mouth opening and complicates laryngoscope blade positioning in the mouth.

3.2 Size of the tongue

It is usually examined during the evaluation of Mallampati score. Extremely large tongues in contrast to mouth diameter are also predisposed to DA.

3.3 Abnormal teeth or lack of teeth

Incomplete frontal dentition, presence of loose teeth or prosthesis, inappropriate prognation (inability to protrude the mandible so that the lower incisors are anterior to the upper incisors), and too prominent upper incisors.

3.4 Abnormal congenital or acquired mandibular anatomy

Micrognathia (small size of mandible) and retrognathia (abnormally posterior location of mandible compared to maxilla) are two main structural abnormalities of mandibular shape, which are predisposed to DA. These rare conditions occur 1 in 1500 live births worldwide [4, 5] and are generally associated with inborn genetic errors, for instance, Pierre Robin sequence, Treacher Collins syndrome, branchio-oculo-facial syndrome, cri du chat syndrome, trisomy 13 and trisomy 18, and so on [6]. Acquired mandibular or maxilla pathologies are commonly associated with maxillofacial traumas and burns.

3.5 Head and neck mobility

Cervical range of motion decreases with age. Cervical spine arthritis, ankylosing spondylitis, previous cervical surgery, and neck collar presence due to traumatic accident may lead to restricted neck extension, which complicates the positioning of head for successful intubation.

3.6 Neck circumference

Normal values are <37 cm in males and < 34 cm in females. Obesity, thyroid gland diseases, obstructive sleep apnea syndrome, and pregnancy are among the most common reasons of increased neck circumference.

3.7 Presence of facial hair, beard

The presence of beard or moustache predisposes to difficulties with mask sealing during ventilation and air leak through facial hair.

3.8 Mallampati classification

It was described in 1985 as a test to predict difficult laryngoscopy and involves the assessment of how far the tongue size restricts pharyngeal view.

• Class I: Tonsillar pillars, uvula, and hard and soft palates are easily visualized.

• Class II: Partial uvula and soft palate are visualized.

• Class III: Only the soft palate is visualized.

• Class IV: No uvula or soft palate is visualized.

3.9 Cormack-Lehane (CL) score

It was described in 1984. This score, unfortunately, has little correlation with Mallampati score, so it is impossible to predict the CL grade by simple physical examination of the patient. CL is assessed only after direct laryngoscopy has been proceeded and is expressed as the degree of glottis aperture visualization. The updated CL description is as follows:

• Grade 1: A full view of glottis including arytenoid cartilages, vocal cords, and epiglottis.

• Grade 2a: Only posterior laryngeal aperture is visualized and includes part of vocal cords, arytenoids, and epiglottis.

• Grade 2b: Posterior aperture and vocal cords are not visualized; only arytenoids are defined.

• Grade 3: Only epiglottis is visualized (no vocal cords, no arytenoids).

• Grade 4: No glottis structure is visualized (no epiglottis, no vocal cords, no arytenoids).

Both Mallampati and CL scores > 3 are considered as difficult laryngoscopy and intubation circumstances and require difficult airway preparation.

3.10 Upper lip bite test (ULBT)

Sensitivity of ULBT in prediction of DA is more than 70%. Specificity for ULBT is >85% [7]. Upper lip bite test evaluates mandibular movement, which is important during tongue root elevation with laryngoscope blade. To measure the mandibular joint mobility, the patients are asked to bite their upper lip with lower incisors as high as they can [8].

• Class I: Lower incisors can bite above the vermilion border of the upper lip.

• Class II: Lower incisors cannot reach vermillion border.

• Class III: Lower incisor cannot bite upper lip.

3.11 Thyromental distance

It is the distance between thyroid notch and chin tip. Normal range is fluctuative, depending on the age and gender, but measurements <6.5 cm (3 finger breadths) indicate anticipated DA.

3.12 Hyomental distance

It is the distance between hyoid bone and chin tip. Normal range is equal or more than 4 cm (2 finger breadths). Distance less than two fingers is predisposed to DA.

3.13 3-3-2 rule

It is a simple tool for difficult intubation prediction, which combines three distinct measurements: three finger breadths between upper and lower incisors, three finger breadths between thyroid notch and chin, and two finger breadths between hyoid cartilage and chin. The distances should not be measured in head-extended position!

3.14 LEMON

It is an abbreviation of another difficult intubation prediction tool, which is extremely useful and quick. The higher the score, the harder is the intubation. This method was first developed by Scottish emergency department practitioners after evaluating data from patients diagnosed with anticipated difficult airways, between June 2002 and September 2003 [9].

L-look externally:
facial trauma	1 point
large incisors	1 point
beard or mustache	1 point
large tongue	1 point
E-evaluate the 3-3-2 rule:
interincisor distance 3 finger breadths	1 point
thyromental distance 3 finger breadths	1 point
hyomental distance 2 finger breadths	1 point
M-Mallampati score > 3	1 point.
O-obstruction (may be quickly suspected if stridor is present)/obesity	1 point
N-neck mobility (asking the patient for cervical extension and flexion/presence of collar or any other evident neck immobility feature)	1 point

3.15 Six features have been identified as likely to cause difficulty with bag mask ventilation (BMV)

• Presence of beard

• Lack of teeth

• Age > 55

• BMI > 30

• History of snoring

• Inability to protrude mandible

3.16 MOANS

The potential DA predictive features were further incorporated into MOANS mnemonic by American Emergency Airway Course:

• M-mask seal (ineffective due to presence of beard, blood, trauma)

• O-obesity/obstruction

• A-age

• N-no teeth

• S-stiff lungs

No single tool or assessment method was identified as consistently being more predictive than another, and multivariate measures intended to predict difficult airway were too few and diverse among the studies to determine a common list of predictors [3]. Experience confirms that a better way to judge on the severity of airway difficulty of a patient is to interpret the anatomical and physiological features in combination, naturally in the presence of sufficient time interval.

4. Using ultrasound guidance (USG) for evaluation

Even after using multiple clinical screening tests, a significant incidence of unanticipated difficult laryngoscopy (1–8%) has been observed [10]. In addition, the clinical assessment tools play a limited role in unconscious and uncooperative individuals [11]. So, in addition to general data, based on facial features, anatomical landmarks, and measurements, we would like to share a brief overview of measurements obtained from ultrasonography inspection of a patient. There are plenty of distance measurements between significant head and neck landmarks that provide foresight concerning the degree of being at loss of airway management. Ultrasound usage in all departments and among practitioners has become extremely widespread, and there seems to be no obstacle for emergency doctors to evaluate several features in elective circumstances. According to the 2022 ASA Practice Guideline Difficult Airway Management, measuring the skin-to-hyoid distance, skin-to-epiglottis distance, and tongue volume by USG is the simplest, fastest, and most sufficient way to decide whether the airway is complicated or not.

4.1 Skin-to-epiglottis distance (DSE)

In the absence of front neck adipose tissue, this distance is the same as skin-to-thyrohyoid membrane distance (DST). This distance is the most predictive and trusted among USG measurements. The distance may be measured in parasagittal or mid-transverse plane. Is also measured with linear probe placed sagittal (Figure 1) or transversely (Figure 2) over the midway between hyoid bone and thyroid cartilage (at the level of the epiglottis). Epiglottis is identified as a curvilinear hypoechoic structure with a bright posterior air mucosal interface and hyperechoic pre-epiglottic space. It is important to mention that this distance shows variations in men and women, so there is no clearly defined value. According to Guan et al. [12], a cutoff value of 2.36 cm was optimized for DSE and proved to be more powerful predictive value than other USG indicators for predicting a difficult laryngoscopy. This research points on high sensitivity of 95% and specificity of 95% of DSE as an independent predictive feature. Pinto et al. [13] evaluated the use of the USG measured distance from the skin to epiglottis in the transverse plane and demonstrated that a cutoff value of 2.75 cm was effective for classifying easy versus difficult laryngoscopies. Falcetta et al. [14] also measured this same distance and found that a cutoff value of 2.54 cm was the most effective. The larynx is usually higher in males than in females; on the other hand, laryngoscopy during intubation leads to manual elevation of epiglottis, and consequently, the distance measured prior to instrumentation now becomes shorter. To abolish doubts on eligibility and accuracy of DSE measurement, the parasagittal measurement is recommended, as it avoids the effect of a high larynx and can clearly visualize the adjoining relationship with the various larynx structures. Another research on DSE, conducted by Chabbra et al. [15] in 2022, defines the cutoff value of > 1.67 cm to predict difficult laryngoscopy (the study encounters measurements in mid-transverse plane at the level of vocal cords) but with lower sensitivity (64.71%) and specificity (78.45%). Resuming all the mentioned above, the approximate cutoff >2.36 cm is strongly associated with CL > grade 3 during parasagittal measurements; a cutoff >1.67 cm is suspicious of CL > grade 2 during transverse measurements.

Figure 1.

Parasagittal USG view of DSE. Blue star: hyoid bone, red star: thyroid cartilage, green star: thyrohyoid membrane, yellow star: tongue root, white arrow: epiglottis, blue arrow: DSE. Copyright belongs to the authors.

Figure 2.

Transverse USG view of DSE. Green star: pre-epiglottic space, white stars: sternocleidomastoid muscles, black star: epiglottis, blue star: glottis, black arrow: DSE. Copyright belongs to the authors.

4.2 Skin-to-hyoid distance (DSH)

It is measured by placing the linear high-frequency US probe transversely over the hyoid cartilage. The hyoid cartilage is visualized as a curved echogenic lining with posterior acoustic shadow (Figure 3). According to Wu et al. [16], the distance more than 1.28 cm predicts a difficult laryngoscopy.

Figure 3.

Transverse US view of DSH. Black star: Epiglottis, blue arrow: Hyoid bone, green arrow: DSH. Copyright belongs to the authors.

4.3 Tongue volume

It is measured by a low-frequency convex probe with the patient in supine position with head extended, mouth closed, and tongue slightly touching the incisors (Figure 4). The probe is placed under the chin in the median sagittal plane and adjusted to obtain the entire tongue outline clearly on the screen. The maximal vertical dimension from the tongue surface to the skin is measured as the tongue thickness. Although no clear data on cutoff value of tongue thickness exists, significant study was conducted by Andruskiewicz’s et al. [17], and tongue volumes >12 cm show correlation with difficult laryngoscopy and difficult intubation.

Figure 4.

Tongue volume USG measurement. Black star: tongue, black arrow: tongue volume, blue star: hyoid bone. Copyright belongs to the authors.

5. Preparation and equipment

The main goal during management of anticipated or unanticipated difficult airway cases is to provide sufficient oxygenation. Time losses on decision-making, unsuccessful attempts, or equipment supply should not cause an interruption in the oxygen supply to the tissues. Remember, the goal is to provide ventilation, for example, inflow and outflow of fresh gas in order to sustain tissue metabolism. It is not exactly intubation or any other invasive airway access that saves the lives. As it is known, oxygenation is of vital importance. In cases when laryngoscopy and endotracheal intubation seems difficult, and BMV provides necessary oxygenation, it is wiser to simply ventilate the victim in spite of losing time on unsuccessful intubation attempts. If DA is known or strongly suspected:

• Ensure the presence of difficult airway cart or emergency trolley with difficult airway equipment.

• Call for help as soon as possible. Do not struggle on DA or pursue intubation rather than calling for assistance or maintaining oxygenation.

• Airway management should be performed by the most skilled practitioner in the field.

• Make sure to provide the most proper position that will ease instrumentation and ventilation.

• Capnography should be used wherever airway performance is undertaken to confirm correct airway device placement. If there is CO2 in the exhaled air, the endotracheal tube (ETT) is in the trachea, and capnography is considered the “gold standard” in this respect. Do not forget: “no Trace=wrong Place” [18].

• Strictly administer supplemental oxygen before initiating airway management, and keep delivering whenever feasible throughout the whole process.

• If CICO (“can’t intubate can’t oxygenate”-the situation when failed intubation is compounded by the inability to maintain adequate oxygen saturation with BMV) diagnosed, surgical airway must be performed immediately.

Where difficult airways are anticipated, management includes the following basic attitudes and interventions:

5.1 Airway maneuvers

The most commonly used airway manipulation is backward-upward rightward pressure (BURP) adjustment on the larynx, performed externally by repositioning thyroid cartilage, and the best laryngeal view is obtained to assist intubation. Another maneuver is external cricoid pressure (Sellick maneuver), used for proper visualization of vocal cords. Appropriate head and neck position is also important for successful airway management. The aim of Sniffing position, which is broadly used among anesthesiologists and emergency practitioners, is to bring the laryngeal and pharyngeal axes as close as possible to the oral axis. The position is easily given after placement of 10 cm pillow under patient’s occipital bone and involves cervical flexion and head extension. The “jaw thrust chin lift” is a principal and extremely trusted maneuver practiced among anesthesiologist. The simultaneous chin protrusion and elevation, achieved by mandibular angle manipulation with dominant single hand or both hands, mostly requires a second person and improves BMV in almost all cases.

5.2 Noninvasive airway management devices

In case of anticipated DA, it is important to adequately preoxygenate the patient, to earn extra time during airway management attempts. Preoxygenation increases oxygen reserves (saturation of forced reserve lung capacity is especially important in pediatric cases, who are extremely predisposed to desaturation after even subtle apnea period) and delays the onset of hypoxia, and this way allows time for rescue instrumentations. In anesthesiology practice, we prefer the term denitrogenation as a synonym for preoxygenation, as not only oxygen reserve is fulfilled but also nitrogen present in the residual and reserve lung volumes is replaced with oxygen. Classically, preoxygenation is considered as 3–5 minutes of FiO2 = 100% patient ventilation at the tidal volumes. This time lag is enough to remove nitrogen from respiratory system. The ASA suggests other versions of preoxygenation. In a case of spontaneously breathing patient (preoxygenation prior to awake intubation), 4–12 breaths at forced vital capacity in 1 minute or shortest time lag with FiO2 = 100% is enough to avoid desaturation. If FiO2 is possible to be measured (in cases of emergency room air BMV), 3 minutes of oxygen administration to reach an end-tidal oxygen concentration of 0.90 or higher (EtO2 > 0.9) is considered an appropriate preoxygenation [3]. The duration of apnea without desaturation can also be prolonged by passive oxygenation (which means the patient shows no spontaneous breathing) during the apneic period. This issue is called apneic oxygenation and can be achieved by administering up to 15 L/min oxygen through nasal cannula [2]. High-flow ventilation devices are used for this purpose and are widely administered for awake intubation, which will be described later. Any healthcare practitioner should be familiar with the basic equipment required for airway management:

5.2.1 Rigid laryngoscopic blades

Macintosh (curved) and Miller (straight) blades are available in sizes from neonatal (No. 0) to large adult (No. 4). The aim of a blade is to remove oral anatomical structures to provide the vision of the glottis. Levering of blades (using shorter or longer blade during intubation attempts) has shown to rise the intubation success rate [3]. As a common rule, straight blades are used for infant intubation, while curved blades are more practicable for adult and pediatric instrumentations.

5.2.2 Adjuncts

Bougies are rubber, elastic, 50–60 cm long wires with 30 degrees angulated tips. They are usually indicated in cases of CL grade 3–4, and the practitioner inserts the bougie just below the epiglottis without seeing the vocal cords. After that, endotracheal tube is inserted over the bougie. Some of them may have lumen and fenestrated tips, so oxygenation may be allowed while providing necessary airway manipulation resources or conducting surgical airway. Some of these devices are equipped with a video or fiber-optic display element at the distal end. Light wands allow the practitioner to view the glottis from outside the mouth; at the same time, the progression of the device through the vocal cords results in light transillumination in the midline of the neck, which confirms proper positioning.

5.2.3 Supraglottic airway devices (SAD)

Laryngeal Mask airways, or so-called LMAs, were first described in 1983 by Archie Brain [2] and are considered one of the milestones of airway management. Additionally, SAD¹ is indicated for CL grade 3–4 cases and difficult BMV situations. Being placed blindly, none of SADs directly intubate the patient but seal around and above the glottis. Thus, they carry the risk of aspiration. Another disadvantage of using LMA is its instability and displacement risk during transportation, even if accurately secured and fixed. The diversity of LMA modifications is now present. Intubating laryngeal mask airway (ILMA), or so-called FASTRACH, has a handle and is used for blind intubations. The sealing mechanism is the same as for classic LMA, whereas FASTRACH has its own special endotracheal tube. Despite blind insertion of the tube, proper tracheal intubation rates are extremely high. The Air-Q Intubating Laryngeal Airway (ILA) was first introduced by Daniel Cook in 2005. It is available in distinct sizes, in both disposable and reusable forms. The only difference from FASTRACH is the absence of a handle. A special intubation tube is inserted, as in the case of ILMA, blindly through the Air-Q. I-Gel LMA is different from mentioned devices in the way its hypopharyngeal part (the part that seals onto the larynx) has a preshaped soft thermoplastic elastomer and has no inflatable cuff, so easier insertion and less trauma is encountered. Except this advantages, I-Gels have gastric channel for aspiration. Recommended insertion depth and size, correlated with weight, are shown on the outer surface of the device.

5.2.4 Retroglottic airway devices (RAD)

Combitube is a double lumen tube, advocated for blind intubations. The tube has two separate lumens: one for esophageal intubation, with single pore at its tip (clear) and another, with multiple fenestrations on both sides, for air entrance into supraglottic area (blue). Esophageal lumen is inflated with 10–15 ml of air and the supraglottic one with 80–100 ml of air. This device is not used in pediatric patients and is present only in two sizes. 37F size is appropriate for patients <170 cm height, and 41F is indicated for patients >170 cm height. The recommended maximum duration for Combitube persistence in the airway is 8 hours. In some cases, blind insertion of Combitube may accidentally intubate trachea, which is not fatal but even beneficial. In this case, just inflating the cuff of the esophageal lumen is enough, just as with ETTs. However, the cases of tracheal intubation with Combitube should definitely be recognized, as the cuff inflation with 10–15 is hazardous for tracheal wall. Separate ventilation of every lumen in combination with midaxillary line lung auscultation is the simplest way to differentiate whether esophagus or trachea is intubated. If respiratory sounds are achieved during ventilation through esophageal lumen (clear one), tracheal intubation should be suspected.

5.2.5 King laryngeal tube (King LT)

It differs from Combitube by having a single pilot balloon for both cuff inflations. This device also has two lumens, both ending up in two apertures: the shorter one beveled anteriorly and the longer one beveled posteriorly. The posteriorly beveled tip of the longer lumen escapes tracheal insertion. This tip should enter esophagus with its smaller cuff preventing regurgitation. Beveled tip allows aspiration catheter insertion through the device and gastric matter aspiration if needed. The shorter lumen has no side fenestrations (in contrast to Combitube), and its anteriorly beveled tip remains just superior to glottis, thus providing laryngopharyngeal ventilation. Esophageal lumen cuff (the smaller one) is inflated inside the esophagus, while the larger supraglottic cuff separates pharynx from larynx just beneath the root of the tongue. As mentioned, both cuffs are inflated by single pilot balloon with 60–100 ml of air, depending on the device size. The size and required air inflation volumes are indicated on the outer side of the tube and accord to patients’ height. King LT maximum airway persistence period is the same as for Combitube and is also not recommended for use in children.

The contraindications for Combitube and King LT include obstructive masses or foreign bodies in laryngopharynx, known lesions of esophagus and larynx (as cuff inflation may lead to perforation) and patients with preserved gag reflex. In contrast to supraglottic devices, these ones reduce the risk of airway aspiration and regurgitation.

5.2.6 Videolaryngoscopes

These are preferred in cases when direct laryngoscopy does not provide necessary visualization of glottis. It has more angled blades, a camera built into the blade tip, and a screen. The screen is located on the handle in some and as a separate unit in others. The more angulated blade curvature, in combination with localization of optic camera on the tip of the videolaryngoscope blade, improves the view of glottis aperture. Besides this, ETT insertion and progression in patients with micrognathia or incomplete mouth opening is comforted, as tube passage through the airway is visualized from outside the mouth. Videolaryngoscopes improve Cormack-Lehane views of the larynx by one to two grades [19]. This device should be preferred as first—to pass in high aspiration risk patients. There are two types of videolaryngoscopes: channeled-guided (examples include Airtraq, King Vision, and Pentax) and non-channeled-guided (Glidescope, C-MAC, and McGrath). The difference is that channeled ones are more angulated at the curvature and also have a conduit for ETT guidance (which is beneficial in patients with immobile cervical spine) [19].

5.2.7 Fiberoptic (FBO) intubation and awake airway management

Visualization of airway passage is possible with a flexible endoscope with an optic fiber inside it. The tip of the device is manipulated by a handle from outside the airway. The endotracheal tube is seated along the scope. After proper glottis visualization, the ETT is forwarded to the trachea; then, the fiber optic guide is removed. Insertion of fiberscope may be through nostrils (inferior concha) or through the oral cavity. This technique is appropriate for awake or mildly sedated patients. The reason for this is necessity of tongue and airway wall tonus to be preserved, as fiberscope advancement through collapsed airway restricts reaching the trachea. Awake patient intubation is a complicated but, at the same time, a very safe method to be tracked at elective anticipated difficult airway circumstances. This method is of little practice in emergency departments but anyway deserves a brief discussion. The indications for awake fiberoptic airway intubation include: patients with previously recorded difficult intubation or difficult ventilation history (known CICO cases), predicted difficult airways due to inability to access pre-cricoid or pre-thyroid region, known aspiration risk, and cervical spine immobility.

At the other end, definite contraindications are present:

• Impending airway obstruction (epiglottitis or any other upper airway infection or abscess that may rupture or progress).

• Blood, infection or fragile tumoral tissue in the upper airways (due to potential contamination of lower airways).

• Patient refusal or uncooperative patient.

• Penetrating eye injuries.

• Fractured skull base (accidental fiberoptic device insertion into brain).

• Absence of skilled practitioner.

An important step in the preparation for awake intubation is topical anesthesia. Topical anesthesia can be provided either through surface analgesia or using appropriate nerve blocks [20]. The average dose necessary for topical anesthesia is 8–9 mg/kg lignocaine. It is important to anesthetize oral cavity (or nasal cavity in cases of nasal intubation), pharynx, and larynx. Lignocaine sprays for oral cavity and swabs lubricated with lignocaine for nasal cavity require 5–10 minutes for the top numbness to be achieved. Pharynx is anesthetizes by introducing lignocaine swabs into palatoglossal and palatopharyngeal folds or, simply, by asking the patient to gargle 2% viscous lignocaine. To anesthetize the laryngeal region, injection of lignocaine through cricothyroid membrane in caudad orientation at the end of patient’s deep inspiration. This approach causes cough reflex, which ultimately improves the dispersion of local anesthetic. It is important to provide oxygen supply (the most preferred method is high-flow oxygen cannula) during the whole process of topicalization and fiberoscope advancement. The performer may also use the “spray and go” technique: when local anesthetic is injected through fiberoscope’s suction canal and oxygen supply is attached to the canal simultaneously. This provides both, oxygenation and topicalization. Successful topicalization may not always be achieved and, besides, takes a little longer time, so practitioners prefer to combine local anesthetic infiltration with light sedation, without neuromuscular blocker addition, as mentioned above, to secure airway tonus for scope fibers progression.

5.3 Invasive airway management techniques

5.3.1 Retrograde wire-guided intubation

This technique includes endotracheal tube progression along a wire, inserted retrograde from the larynx up to the oral cavity. The approach may be considered in cases of oral, pharyngeal, or laryngeal tumors (impossibility of glottis visualization); patients with stiff laryngeal wall (unable to be elevated with laryngoscope blade); unsuccessful intubation attempts; patients with immobile cervical spine due to variety of reasons (ankylosing spondylitis, cervical collar etc.); and especially patients with maxillofacial trauma and burns. A 16–20 G needle is used to puncture the cricothyroid membrane. Care should be taken to avoid thyroid gland, cricothyroid artery, and posterior laryngeal wall damage during puncture. The needle is initially approached 90 degrees to the skin, and negative pressure applied by the syringe. Air rush into the syringe informs that needle is inside the larynx, and at this step, the needle should be redirected 45 degrees cephalad. The guide-wires incorporated into central vein catheterization kits are most commonly used for retrograde intubation. The guide wire is introduced through the needle until it appears out of the mouth or nostrils. Endotracheal intubation tube exchanger (ETT exchanger) is then advanced upon the guide wire, until resistance is felt as anterior laryngeal wall is contacted. At this step, the cephalad end of the guide is exerted with simultaneous advance of ETT exchanger, which consequently passes through vocal cords. The next step is the progression of appropriate sized intubation tube along the exchanger and final drawing out of the ETT exchanger. Do not hesitate BMV, passive oxygenation, or high-flow nasal cannula ventilation of the patient during retrograde airway management! In the case of absence of ETT exchanger, intubation tube may be simply advanced through wire guide, but this method carries risk of tube dislodgement into esophagus or tube clinging at any level throughout the passageway (as the guide wire is too thin to properly route the tube, bigger than self-diameter).

5.3.2 Front-of-neck percutaneous needle cricothyrotomy

The technique resembles the retrograde intubation, except the guide wire is protruded downward into the trachea instead of upwards. Ready kits are present to perform cricothyrotomy. The main goal is to perform a tiny longitudinal incision on the cricothyroid membrane. Then, a needle is inserted into the airway through the incision (again with a negative pressure syringe, and stop advancing as air fills the syringe). The kit needle usually has a plastic catheter over it. Taking care not to puncture the opposite laryngeal wall, the needle is then removed with simultaneous pushing the catheter in caudad direction. A guide wire is introduced; then, the plastic apparatus is removed. Special dilatator present in the kit is slid along the guide with rotational manipulations, again, with care not to harm the opposite wall. After the dilatator is removed, the cannula is introduced through the guide, and the guide finally removed. Both retrograde intubation and cricothyrotomy (as well as tracheotomy) necessitate immobility of thyroid cartilage and laryngeal structures during needle insertion. This is best achieved by fixating the thyroid cartilage with nondominant hand in the following matter: the thumb and middle finger grasp the thyroid cartilage at both sides, thus stabilizing it and preventing movement. Index finger is placed on the cricothyroid membrane, exactly at the point where the needle is inserted (this fixation method is called laryngeal handshake).

5.3.3 Front-of-neck scalpel cricothyrotomy

This method is preferred in cases when no crycothyrotomy kit is available. Depending on whether the cricothyroid membrane is palpable or not (cases of irradiated neck, when the tough front neck tissues are impossible to differentiate), two methods are described in literature. If cricothyroid membrane is easily identified by laryngeal handshake motion, a transverse 4 cm incision is made; blind finger dissection of subcutaneous tissues is performed until the cricothyroid membrane is palpated or visualized. Then, another horizontal incision is made over the membrane itself. Finger palpation of cricoid cartilage and tracheal lumen, together with the incised aperture dilatation, assists the bougie (or 6.0 mm ETT tube) insertion in caudad orientation at the depth less than 10 cm (carina is reached at that depth). Then, the 6.0 mm ETT is slid along the bougie into the airways. If cricothyroid membrane is not palpated properly, a vertical incision is preferred. It may extend upward until mandibula or downward untıl sternum in order to anatomically define the membrane.

5.3.4 Front-of-neck percutaneous tracheostomy

Out of scope of emergency airway management.

6. Guidelines

The steps, which should be followed in cases of difficult airway, were described by American Association of Anesthesiology (ASA) and Difficult Airway Society (DAS) [21]. First DAS guideline was adopted in 2015, and the recommendations are repeatedly updated and revised. Here, we submit 2022 difficult intubation guideline, as the simplest way to decide on which action to choose (Figures 5 and 6).

Figure 5.

Reproduced from “Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults” C. Frerk, V. S. Mitchell, A. F. McNarry, C. Mendonca, R. Bhagrath, A. Patel, E. P. O’Sullivan, N. M. Woodall, and I. Ahmad, Difficult Airway Society.

Figure 6.

Reproduced from “Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults” C. Frerk, V. S. Mitchell, A. F. McNarry, C. Mendonca, R. Bhagrath, A. Patel, E. P. O’Sullivan, N. M. Woodall, and I. Ahmad, Difficult Airway Society.

During Plan A, if the laryngoscopy is unsuccessful, return back to ventilation and suggest which maneuvers may challenge your laryngoscopy. Reposition patient’s head, administer paralytic drug (in cases when vocal cords are visible, but intubation is made impossible due to their closed state), use external maneuvers, discussed above, and try laryngoscopy again. A max of 3 laryngoscopies may be attempted by the same practitioner; then, the practitioner should be replaced and is permitted only 1 (max 2) attempt, as further instrumentation may lead to airway damage and even harder intubation conditions. If intubation is considered impossible after Plan A, the practitioner should proceed to Plan B and use the supraglottic device. In case of successful Plan B, the patient may be left with SAD, or the trachea may be intubated through the SAD. ILMA and ILA are most commonly used intubating suraglottic devices and are discussed above. There is still another method allowing ETT placement into trachea through SAD. A modified Bailey’s maneuver may also be employed. The manipulation is described by incorporation of fiberoptic FASTRACH or Air-Q and then sliding the ETT (or ETT exchanger tube) into trachea under direct glottis visualization.

If Plan B has also failed, the patient should be started on ventilation again and woken up. If BMV is also unsuccessful, then switch to Plan C and perform immediate cricothyrotomy without delay.

7. Difficult airway management in special cases

• Obese patients are prone to airway wall collapse that restricts BMV. Any obese patient should be suspected to have difficult ventilation and difficult intubation. It is recommended to have a ready-to-use videolaryngoscope and employ it after the first unsuccessful intubation attempt. Do not forget that ramped head position (achieved by raising the patient’s head with multiple pillows, to bring the external ear meatus on the same line with the sternum) alleviates laryngoscopy. At the other end, increased abdominal pressure and reduced lung reserve volume prone the patient to quick desaturation and high risk of aspiration. It is advantageous to ventilate the patient in Trendelenburg position, both to avoid aspiration and to sustain effective preoxygenation. Obese individuals pose difficulty at cricothyrotomy too. Due to excessive front neck fat tissue, identification of cricothyroid membrane is harder. Besides, the cricothyrotomy tube is usually too short to be advanced into the trachea, so scalpel—bougie technique and ETT insertion are preferred.

• Blunt or penetrating head and neck traumas, as well as blunt and penetrating direct airway traumas, burns are serious life threating conditions with concomitant difficult airway status. Neck fractures restrict cervical mobility and acute bleeding harden laryngoscopy; presence of burns leads to tissue swelling, and hematomas provide extra obstruction, all of which complicate airway device insertion. In such cases, it is of vital importance to diagnose if the airway obstruction is impending and manage airway protection before total failure occurs. In cases with visible tracheal laceration, take precautions to prevent tracheal retraction into airway. For this purpose, the trachea may be grasped wıth a clamp and immediate front-of-neck tracheotomy, and ETT placement should be performed. If there is no visible laceration of trachea, the practitioner should diagnose if the obstruction of airway is above or beneath the larynx. For cases with up-to-larynx obstruction and damage, steps for front-of-neck techniques are the only options. For cases with down-the-larynx obstruction or damage ‘double setup’ (simultaneous preparation for oral intubation and cricothyrotomy) or, even, ‘triple setup’ (simultaneous preparation for oral intubation, nonsurgical rescue device, and cricothyrotomy).

• Angioedema is another common difficult airway scenario faced in emergency departments. The goal is to evaluate how far the patient’s airway is swelled. When diagnosing the patient, pay attention to uvula involvement. Asking the patient to pronounce his/her name may provide a concept about vocal cord involvement. İf both uvula and vocal cords are suspected to be swelled, awake fiberoptic intubation is the approach of choice. The chance for direct laryngoscope or videolaryngoscope intubation is extremely low. İf the patient admits with respiratory arrest, front-of-neck approach (may be combined with laryngoscopy attempt) should be undertaken immediately.

8. Conclusion

Although this chapter aimed to cover every single detail concerning difficult airway and its management, we still must mention that the final decision and approach is the practitioner’s decision. İn reality, the practitioners face very complicated situations and usually are obligated to manage combination of difficult airway contexts, so the outcome is greatly influenced by the experience of the healthcare professional at the injured one’s head.

Abbreviations

ASA	American Society of Anesthesiology
BMV	Bag mask ventilation
BURP	Backward-upward-rightward-pressure
CICO	Cannot intubate cannot oxygenate
CL	Cormack-Lehane
DA	Difficult airway
DAS	Difficult Airway Society
DSE	Skin-to-epiglottis distance
DSH	Skin-to-hyoid distance
DST	Skin-to-thyrohyoid membrane distance
ETT	Endotracheal tube
FBO	Fiberoptic
ILA	İntubating laryngeal airway
ILMA	İntubating laryngeal mask device
King LT	King laryngeal tube
LMA	Laryngeal mask airway
RAD	Retroglottic airway device
SAD	Supraglottic airway device
ULBT	Upper lip bite test
US	Ultrasound
USG	Ultrasound guidance