A 17-year-old woman (AB) presents with a 4-year history of dysphagia. She is unable to eat solids. She also has poor voice with low pitch and stridor at rest and would like these symptoms improved as well.

AB has a complicated airway history. As a neonate she had a congenital right-sided neck lymphatic malformation that was surgically excised and then treated with a sclerosing agent. At 1 month of age, a tracheotomy was performed because of airway obstruction secondary to supraglottic swelling. As a child she had repeated laryngeal procedures with a CO₂ laser. She was decannulated at age 8 after an anterior tracheal augmentation with rib graft.

AB is otherwise well. She is well nourished despite her dysphagia and is an active sportswoman despite her stridor.

Her anesthetic history post-decannulation includes an uneventful laryngeal mask anesthetic for nasal surgery performed last year when she was 16 years old.

Nasal endoscopy reveals an infantile larynx—small with a relatively large, omega-shaped and retroflexed epiglottis. She has a supraglottic stenosis, posterior glottic stenosis secondary to inter-arytenoid scarring, impaired vocal cord motion, circumferential subglottic stenosis, tracheal stenosis, and a pharyngoesophageal stricture (Figure 44–1).

A CT scan confirms supraglottic narrowing at the level of the hyoid bone (0.5 × 1 cm) (Figure 44–2), a transverse diameter across her vocal cords of 1 cm, infraglottic narrowing measuring 1.5 cm in diameter, the transverse diameter of her proximal trachea is 0.8 cm, while her lower trachea and the rest of the airways are widely patent and normal.

AB will need multiple laryngeal procedures under general anesthesia to improve her swallowing, voice, and airway. However, her first priority is to be able to eat better, and she presents for microlaryngoscopy, tracheoscopy, and pharyngoesophageal balloon dilation.

What Is a Congenital Lymphatic Malformation?

Congenital lymphatic malformations are endothelial-lined, lymph-filled cysts caused by an abnormal development in lymphatic channels. Approximately 50% of lymphatic malformations are in the head and neck area, also referred to as cystic hygromas. While fetal cystic hygromas detected by ultrasound before 23 weeks gestation are associated with karyotypic or genetic abnormalities, lymphatic malformations appearing after 30 weeks gestation, as seen in AB’s case, tend to be isolated lesions.

Spontaneous regression of these lesions is rare. Without treatment breathing, swallowing, speech, and cosmesis may be affected. Surgical excision is the mainstay of treatment though in some cases anatomical location or local infiltration may make surgical excision difficult and complete excision impossible. Incompletely excised lesions can recur. Post-surgical sclerosing therapy, laser ablation, or photocoagulation therapies have all been described, with varying degrees of success.

Is This Patient Fit for Anesthesia?

Apart from AB’s airway pathology, she is a fit and well 17-year-old. The challenge will be managing her airway safely while providing an unobstructed surgical field.

Define a Difficult Airway

A difficult airway can be defined as one in which an experienced practitioner anticipates or encounters difficulty with any or all of bag-mask-ventilation, direct or indirect (e.g., video) laryngoscopy and tracheal intubation, extraglottic airway use, or surgical airway.¹

Does AB Have Risk of Difficult Bag-Mask-Ventilation?

AB has normal facial, dental, nasopharyngeal, and oropharyngeal anatomical structures, the ability to prognath, and normal range of neck motion. Bag-mask-ventilation should not be impeded superior to the level of the larynx.

Her stridor has been slow-onset, over years, and is due to known sites of narrowing of relatively rigid structures. Nasendoscopy shows that her supraglottic and subglottic stenosis do not narrow further with pressure changes that occur during the respiratory cycle. AB does not have a history of difficulty breathing during sleep.

If her airway is not instrumented, it is likely that AB will be easy to bag-mask-ventilate. However, if instrumented, laryngeal edema could cause complete airway obstruction preventing successful bag-mask-ventilation.

Does AB Have Risk of Difficult Extraglottic Device Use?

Despite AB’s grossly abnormal larynx, anesthesia with an extraglottic device was performed without difficulty just a few months earlier (a reinforced laryngeal mask airway [LMA^®] size four was used) for nasal surgery. For the proposed surgery, a laryngeal mask would completely obstruct the surgical field however it could be used as a rescue device if required.

What About the Risk of Difficult Intubation?

AB’s larynx would not be difficult to visualize with a direct- or video-laryngoscope, though the retroflexed infantile epiglottis may obstruct the glottic view.

Owing to the glottic and subglottic stenosis, AB’s airway would be a challenge to intubate, if required. The best choice of endotracheal tube would probably be a 4.0-mm ID microlaryngeal tube (MLT). MLTs differ from their pediatric counterparts of the same size by possessing a length long enough to be passed through a surgical laryngoscope and an adult-sized cuff (see Figure 44–3). In AB’s case, an adult-sized cuff would be necessary to seal her adult-sized trachea distal to her subglottic narrowing. The external diameter of a 4.0-mm ID tube is approximately 5.5 mm depending on the manufacturer and may be a concern. AB’s airway is 5.0 mm at its narrowest point. Therefore, endotracheal intubation with the smallest MLT available may cause trauma and swelling with the risk of post-extubation airway obstruction.

Does AB Have Risk of Difficult Front-of-Neck Access?

AB is not keen on any form of front-of-neck access due to the psychological experience of having had a tracheostomy as a child. The surgeons are also reluctant owing to the presence of subglottic stenosis, tracheal stenosis, scar tissue, and previous rib-graft. For these reasons, a tracheotomy would be technically challenging and may have consequences for future surgical options.

What Anesthetic Technique Is Required?

As a general rule, airway management is safest when the patient is awake and able to maintain airway patency, manage their own gas exchange, and protect themselves from aspiration. With this in mind, balloon dilation of AB’s pharyngoesophageal stricture was first attempted in clinic under local anesthesia but was not well tolerated due to pain. She wants further procedures to be performed under general anesthesia.

Total intravenous anesthesia (TIVA) is preferred by most anesthesia practitioners and surgeons for shared airway procedures. TIVA ensures constant anesthetic administration and avoids the risk of inhalation of anesthetic gas by the surgical team when the airway is manipulated. TIVA also permits the use of tubeless oxygenation and ventilation methods, such as apneic oxygenation or narrow-bore ventilating techniques, which best enable exposure of the laryngotracheal surgical field.

In our practice, we administer TIVA using a combination of remifentanil and propofol infusions.

Remifentanil is an ideal drug for TIVA. As a rapid-onset/offset opioid, it is both readily titratable and able to provide smooth intraoperative hemodynamic conditions. By blunting the patient’s drive to breath and their response to surgical stimulation, remifentanil may eliminate the need for muscle relaxants. Unlike other opioids, remifentanil maintains a stable and short context-sensitive half-life and does not accumulate, enabling rapid recovery of respiratory drive and consciousness after prolonged administration. Usual infusion rates are 0.1 to 0.3 mcg·kg⁻¹·min⁻¹.

Which Airway Management Techniques Best Enable Surgical Access to the Airway?

The mainstay methods of airway management (bag-mask-ventilation, extraglottic device use, and endotracheal intubation) would impede the surgeon’s access to the surgical field. In AB’s case, these airway management modalities are not useful during the surgical procedure, but may be useful for bridging oxygenation or rescue airway techniques.

Possible choices of methods for oxygenation and ventilation during suspension laryngoscopy include:

1. 
   

   Techniques involving a cuffed tube in the trachea

   
   
   
   
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     MLTs

     
     
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     tracheostomy tube

   
   
   
   
2. 
   

   Tubeless techniques

   
   
   
   
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     spontaneous ventilation under generation anesthesia

     
     
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     intermittent apnea technique

     
     
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     Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE)²

     
     
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     narrow-bore oxygenation catheters located above the glottis (supraglottic), through the glottis (transglottic), or through the front-of-neck directly into the trachea (transtracheal) may be employed. These small-bore catheters are categorized as either <2 mm³ or <4 mm⁴ in diameter. Oxygen sources attached to narrow-bore catheters can be attached to either pressure-regulated or flow-regulated oxygenation sources

     
     
   • 
     

     extracorporeal membrane oxygenation (ECMO)

   
   

What Are the Benefits of Cuffed Endotracheal Tubes During Airway Surgery?

Cuffed endotracheal tubes, including MLTs and wide-bore tracheostomy tubes, connect to standard anesthesia circuits and ventilators. This enables administration of anesthetic gases and standard positive pressure ventilation techniques. Oxygenation and carbon dioxide clearance will occur via the usual bulk-flow (conventional tidal volume) method of gas exchange with which all anesthesia practitioners are familiar. A cuffed endotracheal tube also protects the airway from soiling with surgical debris or gastric contents, and protects the surgeon from exhaled gases and blood or debris being blown into the surgical field.

What Are the Features of MLTs?

MLTs are endotracheal tubes of narrow internal diameter designed to allow increased view of the surgical field during laryngeal surgery.

MLTs are available in three sizes, with internal diameters of 4.0, 5.0, or 6.0 mm. Unlike pediatric tubes of the same internal diameter, MLTs have an adult-sized cuff, ensuring that the adult trachea can be sealed to facilitate positive pressure ventilation. MLTs are also longer than their pediatric counterparts, which enables insertion into the airway via a surgeon’s suspension laryngoscope if required (see Figures 44–3 and 44–4).

Despite their narrow profile, MLTs will still obscure the posterior glottis and the inter-arytenoid region. Depending on the pathology, the surgeon may have to lift the MLT anteriorly to improve visualization of the posterior larynx. The subglottis and tracheal airway are also obscured by microlaryngoscopy tubes, making them unsuitable for laryngotracheal work. The laryngeal apertures will also move with ventilation.

Could an MLT be Used in AB’s Case?

Physical obstruction by the MLT does not allow assessment of the subglottis and tracheal airway, making them unsuitable for laryngotracheal work and therefore of limited utility in this clinical scenario.

In AB’s case a 4.0-mm ID MLT should be reserved as a possible rescue device.

If endotracheal intubation of AB is required, even with a size 4.0 MLT, formation of a tracheotomy distal to the subglottic stenosis may be necessary to best ensure airway patency post-extubation. This potential outcome should be made explicit both in the patient’s written consent as well as in the discussion of the airway plan prior to initiation of the procedure.

What Are the Advantages of Elective Tracheotomy for Shared Airway Procedures?

Depending on the pathology, a wide-bore tracheostomy tube may be able to provide a cuffed endotracheal tube distal to the surgical field. Although clearly an invasive airway technique, for some patients with complicated airways a tracheotomy is the safest way to manage a shared airway procedure, especially in cases at risk of upper airway obstruction under anesthesia. Some patients with complicated upper airways will have tracheotomies for months or years while their upper airway is being managed and improved.

Could an Elective Tracheotomy be Performed in AB’s Case?

As discussed above, neither AB nor the surgical team are keen on any form of front-of-neck access. In AB’s case, a tracheotomy is best reserved as an undesirable, though possible emergency airway rescue option.

What Are the Advantages and Disadvantages of Tubeless Airway Management for Shared Airway Procedures?

From a surgical perspective, procedures under suspension laryngoscopy are best performed with direct vision of an unimpeded and immobile surgical field. Tubeless airway management techniques facilitate these surgical goals but will require the anesthesia practitioner to be comfortable with:

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  an airway unprotected from aspiration of surgical debris or gastric contents

  
  
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  mechanisms of gas exchange that occur with open-airway oxygenation and ventilation techniques, and

  
  
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  administration of TIVA

Tubeless techniques include:

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  spontaneous ventilation under generation anesthesia

  
  
• 
  

  intermittent apnea technique

  
  
• 
  

  THRIVE²

  
  
• 
  

  narrow-bore oxygenation catheters (in supraglottic, transglottic, or front-of-neck access locations) with either pressure-regulated or flow-regulated oxygenation devices

  
  
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  ECMO⁵

What Are the Advantages and Disadvantages of Spontaneous Ventilation Under General Anesthesia During Suspension Laryngoscopy?

Spontaneous ventilation under general anesthesia for suspension laryngoscopy is a technique more commonly used in children than adults. Successful execution of this technique requires a plane of general anesthesia deep enough to blunt laryngeal reflexes and patient movement to stimuli but also maintain regular respiration.

Anesthetic gas (and oxygen) can be delivered via the side-port of a suspension laryngoscope or via a nasopharyngeal or oropharyngeal catheter. Given that the airway is open, gas scavenging is difficult to achieve and anesthetic and exhaled gases will spill toward the surgeon and contaminate the operating room.

Compared to children, adults have reduced minute ventilation, reduced cardiac index, and larger vessel-poor body mass which slows titration of inhalational anesthetic depth. For these reasons, TIVA may be a better choice than inhalational anesthesia during suspension laryngoscopy. Balancing reliable maintenance of spontaneous respirations with adequate anesthetic depth requires experience with this technique.

The rapid and shallow pattern of spontaneous ventilation achieved under general anesthesia may exaggerate dynamic motion of the vocal cords and laryngeal structures, making precision surgery difficult to execute.

Could AB be Managed with Spontaneous Ventilation?

The exaggerated movement of the laryngeal structures seen during spontaneous ventilation makes this technique unsuitable for AB’s case.

What Is the “Intermittent Apnea Technique” for Shared Airway Surgery?

The intermittent apnea technique involves the induction of anesthesia, administration of neuromuscular blockers, commencement of TIVA, and application of suspension laryngoscopy followed by intubation of the trachea with a small diameter endotracheal tube. This endotracheal tube is used to oxygenate and hyperventilate the patient, before being removed for short periods of time during which the surgical procedure is performed. The duration of tolerated apnea will be determined by oxygen desaturation and hypercarbia.

Provided the airway is held open (i.e., by the surgical laryngoscope), a patient’s apneic window before oxygen desaturation can be considerably extended by continuous flow of oxygen into the nasopharynx or oropharynx, for example, with nasal cannula or a shortened endotracheal tube placed in the hypopharynx. Suggested flow rates of 5 to 15 L·min⁻¹ have been described.⁶ The physiological explanation for this is that oxygen is removed from the alveoli into the blood stream at a faster rate than carbon dioxide travels in the opposite direction. As a consequence, a negative pressure gradient from the lips to the lungs is established, which can be up to 20 cm H₂O pressure. This gradient will continue to draw pharyngeal gas toward the alveoli continuously and oxygenate the patient provided that there is no airway obstruction.⁶

Could AB be Managed with Intermittent Apnea Technique?

As discussed earlier, while endotracheal intubation of AB’s airway may be possible with a small diameter endotracheal tube, doing so risks causing traumatic swelling that could cause post-extubation subglottic obstruction. Repeated intubation would be especially undesirable, therefore the intermittent apnea technique is unsuitable in AB’s case.

What Is OptiFlow/THRIVE?

Warmed, humidified high-flow nasal oxygen has been used for a number of years in critical care environments for spontaneously breathing patients with respiratory failure. These devices reduce heat and moisture loss from the airway, are well tolerated, and enable higher flow oxygen (up to 60 L·min⁻¹).⁷ If the mouth is closed, a small amount of positive end-expiratory pressure (PEEP) can be achieved which can stent open upper airways, help reduce atelectasis, and improve gas exchange.

Recently a commercial transnasal humidified oxygenation system (OptiFlow™, Fisher and Paykel Healthcare Ltd, Panmure, Auckland, New Zealand) has been shown to extend safe apnea time in difficult airway patients having suspension laryngoscopy and complete muscle relaxation.²

Simple high-flow nasal oxygenation does not assist with ventilation in apneic patients and therefore arterial carbon dioxide concentrations will rise at a predictable rate. However, the OptiFlow™ system has been shown to provide some degree of ventilation, as measured by slower rise of carbon dioxide over time.

Fluid modeling at the Fisher and Paykel laboratories has suggested a mechanism for the increased carbon dioxide clearance witnessed during THRIVE. OptiFlow™ runs at very high flow rates (70 L·min⁻¹) that create turbulent flow in the nasopharynx. Cardiac pulsations cause boluses of tracheal gas to be delivered through the cords that are then whisked away by turbulent flow in the pharynx.

Although relatively new, THRIVE certainly is an attractive option for providing adequate oxygenation in a still and unobstructed surgical field.

How Is Oxygenation and Ventilation Achieved via a Narrow-Bore Catheter?

Narrow-bore oxygenation catheters can be placed in supraglottic, transglottic, or transtracheal locations (Figure 44–5).⁸

These catheters require high-pressure oxygenation delivery systems to overcome the increased resistance produced by a narrow internal diameter. Special attention should also to be given to the route of exhalation of gas, as exhalation will not occur through the narrow-bore cannula for most devices. Therefore, an open upper airway is required for passive exhalation. Table 44–1 summarizes the risk of complications associated with the use of these catheters.