Airway Emergencies

When one is faced with airway emergencies, critical action within a limited time frame is of paramount importance. Accordingly, it is essential that healthcare providers who find themselves in this situation be capable not only of rapidly assessing the patient but also of simultaneously implementing appropriate interventions. The goal is to optimize oxygenation and ventilation while minimizing the risk of complications.

Several professional societies, including the UK Difficult Airway Society (DAS) ^[1] and the American Society of Anesthesiologists (ASA), ^[2] have created difficult airway algorithms to help guide clinicians with airway management.

Key components to consider include the following:

• Understanding of the urgency and indication for intubation
• Optimization of the method of airway management
• Use of ideal pharmacologic agents on the basis of the patient's hemodynamic status and the technique planned
• Preparation for an alternate plan in the event of failure of the primary technique planned, coupled with the capacity for quick execution of the backup technique - It is prudent to remember that maintaining oxygenation is key; one can continue oxygenating the patient without attempting to instrument the airway repeatedly, which can drastically reduce the chances of being able to intubate thereafter

A difficult airway is one for which a preintubation examination identifies attributes that are likely to make laryngoscopy, intubation, bag-mask ventilation (BMV), the use of a supraglottic device, or surgical airway management more difficult than would be the case for a normal airway. Early identification of a difficult airway ^[3] is a key component of the approach to airway management for any patient and is a key branch point on airway algorithms. ^{[1, 2, 4]}

A failed airway occurs when a provider has embarked on a certain course of airway management (eg, rapid sequence intubation/induction [RSI]) and has determined that intubation by that method will not succeed and that immediate initiation of a rescue sequence must be implemented.

Airway difficulties may be encountered in numerous scenarios, including head and neck trauma, traumatic airway injury, morbid obesity with or without respiratory distress, thermal injury, upper-airway pathology (eg, Ludwig angina), and term pregnancy (to name only a few examples).

Various mnemonic guides to suggest airway difficulties have been suggested. One is the LEMON score, which includes the following elements ^[5] :

• L - Look externally
• E - Evaluate the 3-3-2 rule
• M - Mallampati classification
• O - Obstruction?
• N - Neck mobility

A simple approach to assessing predictors of a difficult airway may be summarized in the acronym HAVNO, as follows ^[6] :

• H - History (including previous airway problems)
• A - Anatomy (features of the face, mouth, and teeth suggesting that intubation may prove difficult)
• V - Visual clues (eg, trauma, obesity, facial hair, and age)
• N - Neck mobility and accessibility (including the presence of in-line stabilization)
• O - Opening of the mouth (an opening smaller than 3 fingerbreadths suggests potential difficulty with intubation)

Another pertinent consideration in dealing with airway emergencies is the ability to preoxygenate effectively in a timely fashion. The risk of worsening airway injuries (eg, turning a partial tear of the larynx into a total one) through injudicious airway instrumentation must be avoided. Whereas RSI is the norm in emergency intubations, it is important to consider hemodynamic perturbations when selecting the drugs to be used. Optimization of cardiopulmonary status (with fluids, blood products, vasoactive drugs, etc) may have to be concurrently performed before and during induction.

A key point in managing the unanticipated difficult airway is the importance of maximizing the safe apnea oxygenation time by providing optimal preoxygenation. It is the failure to oxygenate that leads to hypoxia and the lack of sufficient time to secure an airway.

Routine methods of preoxygenation are inadequate for many different reasons, including increased ventilation-perfusion (V/Q) mismatch and, sometimes, a leak around the mask (to name only two). In select circumstances, it may be wise to consider noninvasive positive-pressure ventilation (PPV), when this is permissible, or a high-flow nasal cannula (HFNC). HFNCs have proved to be useful adjuncts during intubation attempts by safely extending the duration of apnea and reducing episodes of desaturation.

While instrumenting the airway, one must bear in mind the "vortex." It can sometimes be all too easy to fixate on trying to intubate, while making the situation worse in the meantime. 

Trauma

In preparing to manage the traumatic airway, it is helpful to follow an ABC (airway, breathing, circulation) approach in addition to considering other airway algorithms. The following questions should be asked: 

• Is there airway injury?
• Is there traumatic brain injury (TBI)?
• Is there cervical spine (C-spine) injury?
• Is there circulatory instability?

Video laryngoscopy appears to be the best approach for the majority of at-risk blunt trauma patients requiring cervical immobilization: It achieves better views of the glottis in less time, and it leads to higher intubation success rates. In patients with severe or unstable C-spine injuries, the use of flexible endoscopic approaches to reduce the amount of cervical displacement should be considered—provided that the requisite time, equipment, and expertise are available.

Upper-airway obstruction

Signs that suggest early intervention should be implemented include the following:

• Change in voice (muffled)
• Stridor (suggests 50% reduction in airway caliber)
• Difficulty in swallowing secretions and dyspnea

Intervening early in certain circumstances will prevent the situation from deteriorating into a "cannot intubate, cannot ventilate" (CICV) scenario.

In most instances, unless the patient is in crisis or deteriorating rapidly, awake examination using a flexible endoscope is the best approach. The endoscopic examination allows both assessment of the airway and, if indicated, intubation. Alternatively, providing topical anesthesia of the airway and using an awake video laryngoscope may be feasible in certain circumstances. 

It is worthwhile to mark the cricothyroid membrane ultraonographically in conjunction with preparing to secure the airway. This facilitates identification of the membrane under duress and reduces the time needed to perform a cricothyrotomy (either with a Seldinger technique or via a surgical approach).

Morbid obesity

Morbid obesity is an independent predictor of a difficult airway. The Fourth National Audit Project (NAP4) documented complications of airway management and showed that obesity was a factor in nearly half the airway management complications that led to harm. ^{[7, 8]} The main effects of obesity on airway management are as follows:

• Rapid desaturation - Secondary to a decreased functional residual capacity (FRC) and increased oxygen consumption
• Difficult mask ventilation resulting in an increased risk of obstruction - Secondary to excess pharyngeal adipose tissue and increased resistance from the weight of the chest wall and the mass of abdominal contents limiting diaphragmatic excursion
• Difficult laryngoscopy, intubation, and cricothyrotomy

Technical tips

Positioning obese individuals in the upright ramp position (eg, with the Rapid Airway Management Positioner [RAMP] system) helps offload adipose tissue off the chest and reduce the pressure exerted by abdominal contents on the lungs. Video laryngoscopy is preferred in this subset of patients. In the absence of a video laryngoscope, a short-handled laryngoscope may be needed to deal with the enlarged breast tissue that may impede the maneuvering of the laryngoscope.

Because of the increased soft tissue and easy collapsibility of the upper airway, BMV is tricky in these patients. Early use of adjuncts such as oral and nasal airways and the application of two-handed technique (jaw thrust, mask seal) must be considered should mask ventilation be necessary between intubation attempts.

An intubating laryngeal mask airway (LMA) or an LMA ProSeal Airway (Teleflex, Athlone, Ireland) should be available as a rescue measure in the event of an inability to ventilate. The intubating LMA can be used as a conduit with a Braintree catheter for intubation. Using a device to provide continuous positive airway pressure (CPAP; either an HFNC or a nasal mask with CPAP) can help splint open the upper airway during an asleep fiberoptic attempt and thus can provide supplementary oxygenation.

Clinical scenario

A 62-year-old woman is brought to the emergency department (ED) with increasing swelling of her tongue after she begins taking a newly added antihypertensive agent (an angiotensin-receptor blocker [ARB]). The swelling of her tongue and pharynx is causing her some dyspnea.

No oropharyngeal structures are seen on inspection, and neck mobility is normal. The patient can protrude her lower jaw, and her mouth opening is approximately 3.5 cm (2 fingerbreadths). Her tongue is severely swollen and protrudes from her mouth. Arterial oxygen saturation (SaO₂) is 93% on room air, heart rate (HR) is 100 beats/min, and respiratory rate (RR) is 22 breaths/min.

This clinical picture is consistent with ARB-induced angioedema.

Resolution

Initial steps in this setting would include delivery of oxygen via a nonrebreather mask (NRB) and administration of intravenous (IV) steroids and racemic nebulized epinephrine.

A decision to secure the airway was made: it was an attempt at intubation in the operating room (OR) with difficult airway equipment available. A backup airway plan, including surgical airway access performed by an otorhinolaryngologic surgeon, was in place.

The airway underwent topical anesthesia with nebulized lidocaine (4%), and the nose was prepared with phenylephrine nasal drops and numbed with 4% lidocaine topical. Glycopyrrolate 200 μg IV was administered. After adequate topical anesthesia, the patient was kept sitting up at a 45º angle, and fiberoptic intubation (FOB) was initiated. An oxygen mask with a one-way valve was used to provide oxygenation while nasal intubation was being attempted.

A spray-as-you-go technique, in which local anesthetic was instilled through the working channel of the FOB, was employed as the cords were visualized. A gentle jaw thrust was administered to open up the space needed to visualize the glottic opening. A size 6.0 endotracheal tube (ETT) was passed with ease after visualization of tracheal rings was confirmed. The FOB scope provided the inherent benefit of allowing visualization of structures during passage through the airway landmarks.

Adjuncts to use in this scenario would include fresh frozen plasma (FFP), C1 esterase inhibitor, and tranexamic acid, depending on institutional availability.

Clinical scenario

A 32-year-old man with a past history significant for asthma and previous neck surgery presents to the ED in severe respiratory distress. Physical examination reveals a scar in the neck that is likely to be due to previous cricothyrotomy, tracheostomy, or both. Respiratory examination reveals increased work of breathing with retractions and stridor. The patient is tachycardic, with a stable BP and a peripheral oxygen saturation (SpO₂) of 91% on an NRB. Despite the use of nebulized bronchodilators, IV steroids, and nebulized racemic epinephrine, his respiratory status deteriorates and is now complicated by agitation.

Resolution

This scenario illustrates the importance of recognizing the limitations of traditional routes of intubation.

An attempt at awake FOB was unsuccessful because of the patient's agitation. His neck was prepared for an awake tracheostomy. Either IV ketamine or IV dexmedetomidine could be used to maintain spontaneous respirations. The caveats to using ketamine include the already heightened sympathetic tone causing tachycardia and the increased secretions in the airway that can impede attempts at awake fiberoptic techniques.

A rigid bronchoscope was prepared. The view through the bronchoscope showed subglottic narrowing. Ventilation resumed through the side lumen of the bronchoscope. A bougie was then passed through the bronchoscope; this allowed successful placement of a size 6.0 ETT. 

Clinical scenario

A middle-aged woman is brought to the ED after being extricated from a house fire. According to bystanders, the building was on fire for at least 30 minutes before the patient could be rescued and brought outside.

At presentation, the patient’s RR is 32 breaths/min, her HR is 112 beats/min, her blood pressure (BP) is 111/68 mm Hg, and her SpO2 is 87% on an NRB. On examination, she has areas of burned skin over her upper neck and lower face. Oral examination reveals some soot in the oropharynx. Airway examination reveals no change in voice or stridor; however, wheezing can be heard throughout all lung fields.

Resolution

Because acute airway obstruction can occur within minutes of smoke inhalation, patients with facial burns, burns over a large body surface area (BSA), soot in the nose or mouth, or signs or symptoms of inhalation injury (eg, stridor, hoarseness, wheezing, or dysphagia) should be considered for prophylactic intubation. ^[9] Waiting until the condition progresses can lead to an intubation that is procedurally more difficult.

While bronchodilators were administered, an HFNC was applied to optimize preoxygenation. Although direct laryngoscopy and video might have been successful, a desire to explore the lower airway led to topical anesthesia and thus the opportunity for fiberoptic intubation. A combined video laryngoscopic–oral fiberoptic approach was undertaken. The video laryngoscope helped displace the swollen tongue gently, and the fiberoptic scope was passed into the supraglottic area using this guide. Subsequent passage of the fiberoptic scope through the cords facilitated evaluation of injury to structures around the glottic area. The patient was intubated with a size 7.5 ETT.

An oral fiberoptic approach is preferable in burn patients with airway injury in that it enables the intensive care unit (ICU) team to perform bronchoscopy through an ETT tube of adequate caliber, as opposed to a narrower-caliber ET tube such as might be needed with the nasal approach.

Clinical scenario

A 44-year-old man is scheduled for a total knee replacement. The patient is 5 ft 6 in. (~1.7 m) tall and weighs 250 lb (~114 kg). His body mass index (BMI) is 40 kg/m². He has requested general anesthesia for the surgical procedure.

Upon entry to the OR, the patient is placed in the supine position. RSI is performed after monitors are placed. Oral laryngoscopy with a MAC 3 blade is attempted, revealing a grade 4 view (no identifiable laryngeal anatomy). Mask ventilation with an oral airway is then attempted and proves very difficult, resulting in high positive inspiratory pressures. Oral laryngoscopy is attempted first with a MAC 4 blade and then with a Miller 2 blade. The difficult airway cart, an intubating LMA, and additional assistance are requested.

After several minutes of unsuccessful airway management, a general surgeon arrives. As the surgeon attempts a difficult tracheotomy, the patient goes into arrest, and further resuscitation efforts fail.

Resolution

This unfortunate patient outcome was potentially preventable. This case raises several important learning points, including the following:

• First, positioning is critical in the obese patient - The head and neck must be elevated about the chest and abdomen, not just to relieve the pressure of the abdomen on the diaphragm but also to align all parts of the airway for a grade 1 view with laryngoscopy
• Second, all backup plans should not only be thought out before induction but also be kept immediately available and ready for implementation - As soon as it is clear that the first attempt is not going as planned, the backup plan should be resorted to immediately
• Finally, with each subsequent attempt, something different about the strategy should be attempted - One should never simply repeat exactly the same approach hoping for a different result