Consider Pre-existing Difficult Airway

A fundamental rule of airway management is to ensure caution when considering the paralysis of a patient who is expected to be a difficult or impossible intubation, unless the clinician has a specific plan to address a failed airway. Further, the ability to adequately mask ventilate should be considered when determining the type and method of airway intervention.

Trauma Immobilization

The physical process of trauma immobilization with a cervical collar and backboard can significantly limit access to the airway and the anterior neck. A properly placed collar limits mouth opening and intentionally prevents repositioning of the head and neck. If time allows, patients should be log rolled off a backboard, and providers should remove the cervical collar and utilize inline stabilization during intubation attempts.

Mechanical Distortion of the Airway and Contiguous Structures

Direct trauma; previous surgery; or cancers to the face, larynx, or thorax can alter the normal anatomical relationships of the airway structures and can significantly increase the difficulty of the intubation.

Closed Head Injury

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  Changes in hemodynamics, oxygenation, and ventilation should be minimized in an attempt to maintain adequate cerebral perfusion pressure (CPP).

  
  
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  CPP = MAP – ICP, where ICP is intracranial pressure and MAP is mean arterial pressure.

  
  
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  Laryngoscopy causes an increase in ICP secondary to its resultant hypertension.

  
  
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  The goal during intubation is to minimize the two main contributors to increased ICP – patient position and hypoventilation (Box 2.3).

  
  
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  Obtain a focused neurologic examination prior to intubation and the administration of sedatives and paralytics in an effort to guide further care.

  
  
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  Opiates, such as Fentanyl, may be given two-to-three minutes prior to intubation in an effort to blunt the sympathetic response.

  
  
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  Ketamine, etomidate, or propofol can be used as an induction agent.

  
  
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  Ketamine increases cerebral blood flow and counters systemic hypotension. Evidence suggests that it does not elevate ICP.

  
  
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  Although propofol can be used, it should be used with caution and with reduced doses in patients who are hemodynamically unstable.

Maxillofacial Trauma

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  Facial trauma can significantly distort normal anatomy, and injuries can range in severity from minimal to severe.

  
  
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  In cases where airway obstruction is either present or imminent, immediate decisive action is required. Alternatively, some patients initially present with minor respiratory difficulty, but pose a significant risk of rapid deterioration.

  
  
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  A few moments should be taken to plan an effective strategy to safely intervene without resulting in further harm.

  
  
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  Expectant management or delayed decision-making may force a cricothyrotomy.

  
  
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  Preparation including arrangements for back up plans significantly increases the chances of successfully securing the airway.

  
  
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  The patient’s neck should immediately be prepped for a surgical airway in the event of a likely difficult airway or failed intubation.

  
  
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  There is an associated cervical spine injury in up to 5% of patients with maxillofacial trauma and neurologic injury in up to 36%.^{2, 3}

  
  
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  If there is no concern for C-spine injury, place the patient in an upright position to allow blood and secretions to drain. Check the oropharyngeal anatomy and ensure jaw mobility.

  
  
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  RSI is the initial method of choice – if not possible or contraindicated then a surgical airway should be performed (Box 2.4).

Direct Airway Trauma

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  Important signs or symptoms of airway involvement include dyspnea, cyanosis, subcutaneous emphysema, hoarseness, and air bubbling through the wound site (Box 2.5).

  
  
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  Penetrating trauma has a high degree of morbidity and mortality; in fact, the overall mortality is as high as 11%,⁴ with up to 40% of patients requiring emergent intubation.^{5, 6}

  
  
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  Zone I – between the clavicles and cricoid cartilage – is the least common neck injury, but the most likely to require emergent airway management due to the close proximity of major pulmonary and vascular structures.⁵

  
  
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  Tracheobronchial injury occurs in approximately 10–20% of patients with penetrating trauma to the neck.^7–10

  
  
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  Indications for intubation in the setting of penetrating trauma include acute respiratory distress, airway compromise from blood or secretions, extensive subcutaneous emphysema, tracheal shift, or altered mental status.¹¹

  
  
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  Gunshot wound to the anterior neck is also an indication for early intubation in order to prevent obstruction from an expanding hematoma.¹²

  
  
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  A stab wound to the anterior neck is an indication for early intubation only if there is evidence of vascular or direct airway trauma.¹³

  
  
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  Orotracheal intubation with RSI is the technique of choice in penetrating neck trauma¹²; however, administration of paralytics may result in an obstructed airway due to the relaxation of a damaged airway segment.

  
  
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  An awake airway evaluation or an awake intubation can be performed under sedation and topical anesthesia. Ketamine has been suggested as a good induction agent to use in this setting without paralytics.¹⁴

  
  
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  Occasionally the entrance wound provides a direct communication between the anterior neck and the trachea – in this case, it may be easier to intubate directly through the wound.

  
  
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  Blunt trauma to the neck is frequently more complicated as it is associated with a high incidence of C-spine injuries. Specifically, up to 50% of blunt airway trauma patients have concurrent C-spine injuries.¹⁵

  
  
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  In terms of securing the airway in patients with blunt neck trauma, there are essentially three initial methods of choice: RSI, awake intubation, and awake fiberoptic intubation. The exception occurs in a laryngeal fracture, in which emergent tracheostomy is the best first maneuver.

Cervical Spine Injury

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  All trauma patients who present with cervical spine precautions should be assumed to have a cervical spine injury until proven otherwise (Box 2.6).

  
  
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  The two initial methods of choice for securing the airway are oral intubation with RSI or awake fiberoptic intubation.

  
  
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  When performing RSI, the anterior portion of the collar should be removed to allow for manual in-line axial head and neck stabilization (MILS).

  
  
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  MILS has been shown to immobilize the c-spine better in the setting of endotracheal intubation than the c-collar alone.¹⁶

  
  
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  However, MILS can make intubation attempts difficult, and it may not reduce the risk of cervical spine movment.^{17, 18}

  
  
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  Consider airway adjuncts such as using video assisted laryngoscopy to improve the chance of success while maintaining MILS.

Thoracic Trauma

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  Thoracic trauma may present difficulties when it causes a distortion of the trachea from its normal midline position (Box 2.7).

  
  
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  Occasionally a large pneumothorax can cause significant subcutaneous emphysema tracking into the neck, which can interfere with the ability to identify the trachea and/or cricothyroid membrane.

  
  
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  Pneumothorax, hemothorax, or significant trauma to the lung (pulmonary contusion) can inhibit the ability to adequately pre-oxygenate the patient prior to the intubation.

  
  
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  A pneumothorax should be treated prior to intubation if possible.

Burns

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  Upper airway edema is progressive over 24–36 hours after the burn; therefore, it is advisable to secure an airway earlier rather than later (Box 2.8).

  
  
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  Because burn injuries develop over hours, it is often is reasonable to consult a burn specialist prior to securing an airway when appropriate.

  
  
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  If transport is needed to a burn center, particularly a prolonged transport, consider a secure airway with intubation prior to transfer.

  
  
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  Indications for intubation include: Stridor or hoarseness, known inhalation of toxic fumes, and increased work of breathing. Nasopharyngoscopy by the treating clinician or an ENT consultant can help to look for evidence of burns or edema of the posterior pharyngeal or glottis structures. If no burns to these structures are discovered and the patient remains stable, intubation can be withheld. Remember, however, that this is a dynamic situation. Any change with respect to the patient’s work of breathing or stridor should prompt another nasopharyngoscopic evaluation or definitive airway management with intubation.

  
  
• 
  

  Standard oral endotracheal intubation with RSI is the initial method of choice to secure the airway when no obvious obstruction is visualized.

  
  
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  If concerned about obstruction, “an awake look” should be performed under sedation and topical anesthetics.

  
  
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  Because of the incidence of upper airway edema, there should be a low threshold for moving to fiberoptic intubation or cricothyrotomy.

P – Plan B

The first P in this series refers to the predetermined plan for dealing with a difficult or failed orotracheal intubation. A complicated situation can rapidly become a disaster if no pre-implemented plan is in place to mitigate unanticipated difficulty. An emergency airway cart, containing difficult intubation equipment, can keep all needed tools readily available. See Box 2.10 for an example emergency airway cart.

P – Predict a Difficult Intubation

A thorough evaluation of the patient prior to attempts at laryngoscopy can help to predict a difficult intubation. The LEMON law can be used as a tool for airway evaluation. The description below adds “S” for saturation.

By discussing out loud your primary plan, your plan B, and the conditions which will mandate an emergent cricothyrotomy, it will make it easier to move to cricothyrotomy if indicated.

M – Mallampati

The Mallampati classification was developed to correlate a simple visual inspection of the patient’s pharynx with the ability to obtain direct visualization of the larynx. Airways are designated as Class I, II, III, or IV. Mallampati classes roughly correlate with the Cormack and Lehane direct laryngoscopic views, graded as 1, 2, 3, and 4 (Figure 2.1).

Figure 2.1 Mallampati classification

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  Mallampati Class I: No difficulty: Soft palate, uvula, fauces, pillars visible

  
  
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  Mallampati Class II: No difficulty: Soft palate, uvula, fauces visible

  
  
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  Mallampati Class III: Moderate difficulty: Soft palate, base of uvula visible

  
  
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  Mallampati Class IV: Major difficulty: Hard palate only visible

(by Jmarchn (Own work), reproduced under CC BY-SA 3.0; https://creativecommons.org/licenses/by-sa/3.0)

P – Prepare

Preparation includes the following:

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  Remove dentures.

  
  
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  Bring the difficult airway cart to the bedside.

  
  
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  Have the chosen intubation method set up.

  
  
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  Verify the integrity of the balloon on the ET tube.

  
  
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  Have suction ready at the bedside. When preparing suction, it is useful to have two suction options available. A standard Yankauer tip works well for loose secretions but does not adequately aspirate larger food pieces.

  
  
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  Verify the integrity of IV access.

  
  
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  Have color-change capnography and/or end-tidal CO₂ device ready.

P – Preoxygenate

As early as possible the patient should be placed on high flow oxygen, as close to 100% FiO₂ as possible (Figure 2.2). A typical NRB mask with oxygen reservoir can only provide an FiO₂ in the mid 60% range. The FiO₂ can be substantially raised by placing a nasal cannula set at 15 LPM on the patient during the preoxygenation period. A full 15 LPM can be effectively delivered via a standard cannula.²² A non-rebreather mask with a reservoir is then added over the nasal cannula and set at the absolute maximum possible setting. This means that the oxygen flow knob will be turned until it will not turn any further. During the intubation procedure, the mask is removed, but the nasal cannula is left in place during intubation. Passive oxygenation, also known as apneic oxygenation, provides real oxygen delivery to the patient and can help maintain saturations above 90% for an extended period of time.^{22, 23} Patients should be positioned sitting up during pre-oxygenation, as patients will have less ventilation/perfusion mismatch compared to lying flat.

Figure 2.2 Preoxygenation

(Photos: Colin Kaide)

P – Position

Many trauma patients present in a c-collar (Figure 2.3). After collar removal, the c-spine should be maintained with manual in-line stabilization. If the patient’s c-spine can be cleared, the patient should be placed such that the head is elevated off the bed by a few inches (approximately four inches). The head is subsequently extended on the neck so that the face is parallel to the ceiling, while the earlobe is aligned with the sternal notch.²² This maximizes the alignment of the oral axis, pharyngeal axis, and the glottis axis. Except in the pediatric patient, placing the pillow or towel roll beneath the shoulders to force hyperextension of the neck without elevating the head is not helpful, and should be avoided.

Figure 2.3 Positioning (Photos: Colin Kaide)

Proper positioning with earlobe in line with sternal notch and face parallel to the floor (used with permission, courtesy of Colin Kaide)

Proper positioning with earlobe in line with sternal notch and face parallel to the floor using multiple blankets

Incorrect positioning with earlobe not in line with sternal notch and neck hyperextended

(used with permission, courtesy of Colin Kaide)

P – Put to Sleep

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  Induction agents are given simultaneously to or in rapid succession with paralytic agents (Table 2.1).

  
  
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  Cricoid pressure (Sellick’s Maneuver) is no longer recommended routinely. It has no proven benefits and can potentially make intubation more difficult.²⁴

  
  
• 
  

  Avoid ventilating the patient until reoxygenation is required, as indicated by oxygen saturation falling below 90%.

P – Paralyze

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  Depolarizing agents such as succinylcholine act at the ACh receptor and act to initially cause depolarization of the motor endplate and induce contraction, manifesting clinically as fasciculations (Table 2.2).

  
  
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  Subsequently, the receptor is blocked by the succinylcholine, preventing ACh from binding and producing further contraction. The paralysis lasts until succinylcholine is degraded by acetylcholinesterase.

  
  
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  Non-depolarizing agents such as vecuronium and rocuronium competitively inhibit the ACh receptor, occupying it and then exiting the site. These agents are removed from the neuromuscular junction and broken down in the liver. Their duration and onset of action are generally longer than succinylcholine. Vecuronium is not ideal for RSI and is best used for ongoing paralysis.

P – Pass the Tube

One technique which has been described to facilitate direct visualization of an anterior larynx is called “BURP” (Backward-Upward-Rightward-Pressure).^{25, 26} The assistant applies pressure to the thyroid cartilage, first backward (toward the table), then upward (toward the head), and finally rightward. The adult larynx should be displaced backward so as to abut the vertebrae, 0.5–2 cm to the right and about 2 cm cephalad. Meanwhile, the intubator attempts direct visualization of the larynx.

External Laryngeal Manipulation (ELM) achieves the same backward, upward, and rightward airway repositioning as does “BURP,” however the pressure is applied by the intubator with his or her right hand.^{27, 28} This allows the intubator to visualize the effects of the manipulations and adjust the pressure accordingly. The final position of the larynx can be held by the assistant, freeing the intubator’s right hand to complete the procedure (Figure 2.4).

Figure 2.4 External laryngeal manipulation

(Photo: Colin Kaide)

The GlideScope

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  Unlike with a conventional laryngoscope, the GlideScope blade is inserted in the middle of the tongue without a sweeping motion.

  
  
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  Owing to the steep curvature of the blade, the cords can be easily seen, even in an anterior airway.

  
  
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  Occasionally, the cords and tube can be seen, but difficulty arises in trying to pass the tube through the opening. Passage of the tube can be made easier by using the rigid GlideScope stylet.

The C-MAC

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  Conceptually similar to the GlideScope, but the C-MAC uses a blade configured much like a conventional Macintosh blade, whereas the glidescope blade has a more hyperacute angle.

  
  
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  The CMAC can be used to perform DL, with the back-up of having a video view of the cords.

  
  
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  One study suggested that the C-MAC and GlideScope both provided good views of the cords, however use of the C-MAC resulted in faster times to passage of the tube successfully through the cords.²⁹