Chapter 6. Context-Sensitive Airway Management

A 50-year-old man is in the waiting room of the emergency department (ED) awaiting evaluation for several days of hematuria. He has a remote history of prostate cancer. Suddenly, the man falls to the floor, becomes unresponsive, and has a generalized, tonic-clonic seizure. The emergency physician and paramedic on duty are summoned by the triage nurse. Intravenous (IV) access is established and the seizure is halted with multiple doses of intravenous lorazepam totaling 12 mg. Unfortunately, the patient is extremely somnolent and the emergency physician is concerned that he is at risk for airway obstruction, apnea, and aspiration. The decision to intubate the trachea is made.

The obtunded patient is positioned on a stretcher and monitors are applied. Evaluation of airway anatomy and ease of intubation reveal no significant predictors of difficulty. The physician elects to proceed with a rapid-sequence intubation (RSI). Direct laryngoscopy using a Macintosh #3 blade proves difficult, with two failed attempts by the physician. Bag-mask-ventilation (BMV) is performed between attempts and the patient's oxygen saturation never falls below 95%. On the third attempt, direct laryngoscopic intubation is successful with the aid of an Eschmann Tracheal Introducer (commonly known as the gum-elastic bougie) after establishing a partial (Cormack/Lehane Grade 2) view of the glottis.

The patient is sedated and transported to the CT scanner. CT scan is unremarkable. Collateral history reveals a history of heavy alcohol abuse, although the patient had recently decided to "quit drinking" and had been abstinent for 48 hours. A presumed diagnosis of alcohol withdrawal seizure is made and sedation is weaned. Three hours postintubation, the patient is noted to be awake, cooperative, and increasingly agitated by the tracheal tube. Extubation is performed without incident and supplemental oxygen is applied by facemask. Several minutes later the bedside nurse summons the physician as the patient is having increasing difficulty in breathing with labored, noisy respirations. Moments later, the patient loses consciousness and becomes apneic and cyanotic.

The emergency physician immediately attempts tracheal intubation via direct laryngoscopy but fails due to a completely obstructed upper airway secondary to a massive tongue hematoma. The hematoma is presumed to be as a result of his earlier seizure. Help is summoned and a Code Blue is called.

The fundamental goals of airway management are the maintenance of adequate ventilation, oxygenation, and protection from aspiration of foreign materials. In the majority of clinical settings, these three goals are achieved in tandem, usually via orotracheal intubation using a conventional laryngoscope. As the location, skill set of the practitioner, and the devices available (ie, the "context") change, the practitioner must be prepared to modify his or her approach and employ different techniques as appropriate. The provision of oxygenation, by whatever method possible, is ultimately the task that takes precedence over all others, particularly in emergency situations.

6.2.1 What Is Context-Sensitive Airway Management?

The concept of "context-sensitive" airway management represents a paradigm shift in the approach to airway management. The skilled practitioner will be less focused on specific devices and techniques, and more aware of the context presented by each patient encounter—and how that context may influence the approach to the preservation of gas exchange.

The "context defining" questions can be conceptualized as the "who, what, where, when, why, and how" unique to each and every airway management encounter. These questions, or situational modifiers, influence the decision making of a skilled airway practitioner. In a more pragmatic sense, examples of these context defining factors might include: availability of equipment, the expertise of assistance, the skill set and personal experience of the practitioner, and the environment in which the patient encounter occurs. Additionally, individual patient factors, such as anatomy and physiology, acuity of the situation, and the distinction between cooperative and uncooperative patients all modify the context of the airway management encounter and must be considered in order to best approach the airway in a context-sensitive fashion.

6.2.2 Does the Context of the Case Presented Suggest Which Technique Should Be Used to Provide Ventilation and Oxygenation to an Unconscious, Apneic Patient?

This case demonstrates how airway management by nature, is context-sensitive. "Who, what, when, where, why, and how" are all context-defining questions that affect the way the airway is best approached and managed. In this case, an airway successfully managed in one way, is unmanageable by the same team in a similar environment a short time later. This is owing to altered airway anatomy, that is, the context has changed and alternate methods of ventilation, oxygenation, and airway protection must be considered.

Traditionally, great emphasis has been placed on the provision of bag-mask-ventilation (BMV) as an initial approach to the unconscious and apneic patient. Indeed, among the four domains of airway management (BMV, extra-glottic devices, tracheal intubation, and surgical airway), BMV has been the most common initial maneuver employed by most airway practitioners. Unfortunately, mounting evidence and opinion suggests that BMV is a difficult skill to master, particularly in the hands of nonexpert practitioners.1-4 In many cases, BMV is performed poorly with ineffective oxygenation and ventilation, and gastric insufflation the end result. As extraglottic devices (EGDs) continue to improve in quality and ease of use, many experts agree that the placement of an EGD ought to supplant BMV as the initial technique of choice for the airway management of an unconscious and apneic patient, particularly by nonexpert airway practitioners.5

Clearly, no single device or technique can be relied upon as the sole modality for airway management by any practitioner. The choice of device and technique depends on the context of the situation. The second airway management encounter in the case presented is likely to result in impossible BMV and failure of any oral intubation approach. The practitioner would be well advised to consider nasal route options (blind nasal intubation, nasal bronchoscopic intubation, and nasal intubation using a lightwand [Trachlight™]) while at the same time preparing for surgical options, such as cricothyrotomy.

6.2.3 How Has Increasing Appreciation of the Context-Sensitive Nature of Airway Management Guided Technological Advances Leading to Improved Airway Management Tools?

Technological advances over the past two decades have dramatically improved the quality and clinical utility of many airway management tools, including:

1. The manufacturing and marketing of newer and improved EGDs for use in a variety of situations.6,7 Gone are the days where the LMA-Classic™ was the only, or even the preferred, EGD for use in difficult or failed airways. The airway practitioner now has to choose among devices that serve as tracheal intubation conduits in addition to those that have been shown to be effective rescue devices in situations where intubation is not possible.8

2. Advances in video resolution and LCD monitor technology, combined with high-quality color fidelity and optics have led to the development of several video-camera endoscopic-based devices. These include the Glidescope® (Verathon Medical, Bothell WA), the Video Macintosh Intubating Laryngoscope System (VMS, K. Storz Endoscopy Co., Culver City, CA), the LMA CTrach™, and the McGrath® Video Laryngoscope (Aircraft Medical, Edinburgh, UK). These devices remain subject to limitations due to fogging, and obscuration of glottic visualization in the presence of blood, vomitus, or secretions. Their utility is questionable in these contexts (see Chapter 10). Nonetheless, video laryngoscopy continues to be an evolving field with intriguing possibilities in the absence of bodily fluids that may obscure their optics.

3. Improved portability of sophisticated airway management devices, coupled with the introduction of disposable variants, has broadened their utility. Devices are becoming more lightweight, portable, and robust in construction. Battery-powered endoscopes and compact video laryngoscopes, such as the McGrath® and the Glidescope® Ranger Video Laryngoscopes, can be carried to the patient regardless of location and irrespective of external power sources or large video displays.

4. Enhanced light intensity of some airway instruments. The transillumination technique employed by lightwand devices, such as the Trachlight™, is substantially improved with the use of high-intensity bulbs.9 Adequate transillumination is often possible under ambient lighting conditions, obviating the need to dim the lights or darken the room when these devices are being used. One study involving 950 patients demonstrated that nearly 88% of Trachlight™ intubations were effectively accomplished under ambient light with or without simple shading of the neck.10

6.2.4 In What Contexts Are Blind Intubating Techniques Indicated?

Over the years, direct laryngoscopic intubation has been shown to be an effective and safe technique that is relatively easy to perform. It has become the standard method of tracheal intubation in operating rooms, intensive care units, emergency departments, and in the field. Unfortunately, even in the hands of experienced laryngoscopists, the rapid and accurate placement of an endotracheal tube (ETT) remains a significant challenge in some patients. This is particularly true in unprepared patients, or those requiring emergency tracheal intubation. In these contexts, a blind or nonvisual technique may be more successful.

Alternative intubation techniques, such as flexible bronchoscopic intubation, have gained a measure of popularity over the past several decades. While effective and reliable, this technique requires expensive equipment, and special skill and training. Additionally, bronchoscopic intubation can be difficult in emergency situations in which unprepared or uncooperative patients may have copious secretions, blood or vomitus in the oropharynx, or airway. One large study involving more than 1600 fiberoptic intubations recorded a success rate of approximately 94%.11

Because of the difficulties posed by laryngoscopic intubation under direct vision, particularly under emergency conditions, the search for other techniques has led to the development of blind techniques using a variety of devices. During the last few decades, intubating guides and light-guided intubation using the principle of transillumination have proven to be effective, safe, and simple.

6.2.5 Would It Not Be Safer to Place a Tracheal Tube Using a Technique that Is under Direct Vision?

One would anticipate that the placement of an endotracheal tube (ETT) into the trachea under direct vision using a laryngoscope ought to be safer and achieve higher success rates than nonvisual techniques. Such is not the case; success and complication rates are not substantially different with blind techniques performed by skilled practitioners,10 as elaborated below. Furthermore, the technique of direct vision can be very difficult or even impossible because of distorted anatomy or the patient's disease—as illustrated in the preceding case study. However, several contextual factors do influence the success rates and safety of indirect laryngoscopic intubation including the inability to visualize the passage of the ETT through the glottic opening and the presence of blood, secretions, and vomitus.

Many practitioners fail to understand that after having placed the flexible bronchoscope into the trachea under indirect vision, the actual passage of the ETT over the bronchoscope is done blindly employing the scope as a guide. In other words, during bronchoscopic intubation, after advancing the tip of the bronchoscope into the trachea, the bronchoscope functions only as a stylet to guide the ETT into the trachea similar to that of an Eschmann introducer. The use of advanced airway devices to enable continuous glottic visualization during endotracheal tube exchange has recently been reviewed.12 This intriguing application of these devices may be applied to primary intubation to further increase the safety of blind intubation techniques, although further research is required.

Many other procedures performed in medicine are in fact blind techniques including the placement of pulmonary arterial catheters, arterial cannulae, epidural catheters, and femoral nerve sheath catheters. All of these procedures demand placement blindly under the guidance of anatomical landmarks, and physiological responses.

Blind intubating techniques have been shown to be effective and safe, and in the absence of abnormalities of the upper airway, these techniques are acceptable methods of airway management when employed in the appropriate contexts.

6.3.1 Which of the EGDs Has Been Shown to Provide Better Ventilation and Oxygenation and in What Contexts?

Implicit to any discussion about airway management tools and techniques is the realization that the best instrument for the situation depends entirely on the context, or the situational modifiers. Unfortunately, there is no 'one size fits all' device.

The context affects a variety of issues when one contemplates the use of an EGD. These include: patient anatomy and predicted ease of insertion, full-stomach precautions and the need for airway protection from aspiration, need for positive-pressure ventilation, and the presence or absence of airway-obstructing pathology. These are just a few of the situational modifiers which define the context of EGD use in airway management.

In general, EGDs are best reserved for fasted patients at low risk of aspiration, and those with acceptable airways resistance and pulmonary compliance should positive-pressure ventilation be desired. However, EGDs are invaluable rescue devices in the case of unexpected airway management difficulty or failure. They have proven to be valuable as primary airway management devices in EMS. In these situations, placement of an EGD with intubation capabilities and a parallel lumen for gastroesophageal venting may be advisable. In clinical practice, the actual device is less important than the thoughtful consideration of all contextual factors. In the opinion of the authors, the EGDs currently available which best fulfill these objectives are the LMA-Supreme™ (nonintubating EGD), the LMA-Fastrach™ (intubating EGD), and the King LTS-D™.

6.3.2 What Extraglottic Devices (EGDs) Should I Incorporate into My Practice?

The most thoroughly studied EGDs currently in use are the laryngeal mask airway and the Combitube™. Many competing designs and variations of these devices have been released to market and are in use worldwide. We now have the option of using intubating LMAs as well as alternatives to the Combitube™, such as the King Laryngeal Tube Airway (King LT™, King Systems) which are placed blindly into the oropharynx and seated in the hypopharynx, directing respiratory gases into the trachea. In addition, a new generation of disposable, single-use EGDs has entered the marketplace, including the Ambu LMA (Ambu USA), the Streamlined Liner of the Pharynx (SLIPA, SLIPA Medical Inc), and the i-Gel (Intersurgical Ltd).

Of particular use in the difficult or failed airway scenario are the various models of intubating LMAs such as the LMA-Fastrach™ and Cook Intubating LMA (ILMA). Intubating LMA systems are fundamentally designed to permit the practitioner to ventilate the patient and to provide a conduit for tracheal intubation. This may be accomplished using a flexible bronchoscope, a lightwand, or even by blind insertion. In the author's institution, an intubating LMA (LMA-Fastrach™) is kept in each anesthesia machine with the intention of immediate availability in the event of a failed airway or an airway emergency where other methods of preserving oxygenation have failed unexpectedly.

The final consideration of note when deciding on the best EGDs to purchase and implement in one's institution is the differentiation between disposable and reusable devices. Several high-quality disposable EGDs are now on the market. These were developed partially in response to concerns of potential transmission of prion-based infection disease, such as Creutzfeldt-Jakob disease. Disposable devices, such as the LMA-Supreme™, may be best suited to use in the pre-hospital context where a reusable device requiring sterilization may be discarded or lost. Environmental concerns with the routine use, disposable devices are worth noting.

6.3.3 What Tracheal Intubation Techniques Should I Incorporate into My Practice?

Recalling the principles of context-sensitive airway management, it is apparent that an expert practitioner should be comfortable with several techniques of tracheal intubation, including visual and nonvisual methods.

For most practitioners involved in airway management, tracheal intubation equates to direct laryngoscopy. It is true that the conventional laryngoscope, with interchangeable curved and straight blades, is likely the tool with the greatest recognition and use worldwide. Expertise with the use of this tool is an essential skill for any airway practitioner. In addition, all practitioners should become familiar with the use of an Eschmann introducer. This device should be kept readily at hand wherever airway management and direct laryngoscopy may be required. This includes: the operating room, emergency department, intensive care unit, and in crash-carts throughout the hospital.

Beyond direct laryngoscopy the best tracheal intubation tools for an individual's practice depends on the context of that practice. Specifically, what types of patients do you routinely expect to see? Does your institution deal with "difficult" airway situations on a regular basis? How will budgetary constraints dictate which tools may or may not be available for purchase?

While it is not possible to mandate a standard list of devices, it is reasonable to ensure access to a complementary armamentarium of tools to confront the challenges that might arise. This should include: laryngoscopes with curve and straight blades, the Eschmann introducer, a flexible bronchoscope, a video laryngoscope, such as the Glidescope®, Storz VMAC or McGrath®, and a nonvisual technique, such as a lightwand (Trachlight™). The remaining devices available should be considered on a case-by-case basis. Certainly a surgical airway kit, such as the Melker percutaneous cricothyrotomy kit (Cook Medical), is mandatory in all areas where airway management may occur.

There is a staggering array of airway management tools and techniques available today. For the average practitioner, it is unrealistic to expect to be proficient with all devices. However, to be an efficient and safe practitioner in a field where airway management is an expectation, one must be familiar with a number of airway management tools and techniques in order to be prepared for the inevitable challenges.

6.4.1 What Is the Most Appropriate Airway Management Tool for an Unconscious Patient?

The simple answer to this question is: Whichever device restores ventilation and oxygenation promptly! A subsidiary concern is that the device protects against gastric insufflation and aspiration. These goals suggest that tracheal intubation is the most-desired solution, most commonly achieved through direct laryngoscopy.

However, in reality, the context will define the 'best' way to manage an airway. In the example given at the beginning of this chapter, direct laryngoscopy, and indeed any conventional approach to tracheal intubation may be impossible. In this case, resorting to a surgical airway as the primary method of airway management may be the only viable option to establish oxygenation and ventilation.

Classically, individuals charged with emergency airway management have learned that BMV ought to be the initial airway management strategy in the unconscious patient. This paradigm may be shifting, particularly as evidence supporting the ease of use and effectiveness of EGDs in the hands of those who infrequently manage the airway mounts. EGDs and BMV have similar drawbacks in that they leave the patient with an unprotected airway in terms of aspiration risk, and the ability to administer effective positive-pressure ventilation is variable. Overall, it is the authors' opinion that EGDs should be taught to rescue personnel because the authors believe that they are more effective than BMV in most cases. EGDs should also be familiar to all other airway practitioners for primary use in appropriate patients, or as rescue devices in the setting of an intubation failure.

6.4.2 How Would You Manage This Patient If This Patient Is Awake, Cyanotic, and Uncooperative?

The situation (context) has changed. The management of the uncooperative patient will be covered in detail in Chapter 39. In this case, the practitioner is faced with the unenviable decision as to whether or not to induce anesthesia with or without muscle relaxation in the face of a potentially difficult airway. In other words, should a rapid-sequence induction/intubation (RSI) be preformed?

There is no simple answer to this question. In short, it is always desirable to have a controlled situation to permit examination and evaluation of the patient's anatomy prior to the induction of anesthesia or the start of an airway management procedure. Due to patient factors, this may not always be possible. In this context, one must judge whether maneuvers or interventions to correct the patient's cyanosis without invasive intervention are likely to succeed. These include administration of supplemental oxygen or simple airway maneuvers, such as a chin lift or jaw thrust. If these are unlikely to succeed, or are impossible due to the underlying pathology or the behavior of the patient, an RSI may be the only course of action while preparing for an immediate surgical airway in the event of failure (double setup). In this circumstance, calling for help, meticulous preparation for the primary plan, and preparation for several backup plans is critical.

6.4.3 What Other Factors Influence the Selection of an Airway Management Tool?

Successful context-sensitive airway management depends on the interplay between three general categories of situational modifiers. Each modifier demands a "who, what, where, when, why, and how" analysis. Consider the following:

1. Practitioner factors. These are factors unique to each airway practitioner and include, but are not limited to: degree of expertise, past experiences, ability to rapidly assess the needs of the situation, and the ability to modify or adapt one's approach to a dynamic and variable situation. In general, the skilled practitioner will be able to quickly assess a given airway management situation and select the most appropriate technique from his or her personal arsenal of skills.

2. Patient factors. These factors are those unique to each individual patient including, but not limited to: degree of cooperation, anatomical features pertinent to airway management (eg, a parturient), size of the patient (children or morbidly obese patients), medical comorbidities and past medical/surgical history, full stomach considerations, presence of bodily fluids such as blood or vomitus in the airway, lung compliance, and the anticipated need for aggressive positive-pressure ventilation. In general, the patient factors are "what the patient brings to the table." They refer to things the practitioner may be able to modify. Patient factors must be considered for each individual for an airway management plan to be crafted that is best suited to that individual. There is no one size fits all in airway management!

3. Situational factors. This category refers to factors that are unique to the particular situation in which the airway must be managed. Situational factors include, but are not limited to: location of the encounter (pre-hospital vs emergency department vs intensive care unit vs operating room, etc), urgency (elective vs emergency situations), availability of skilled assistants, the airway management tools and equipment available, presence of confounding/complicating factors such as C-spine immobilization collars, and availability of expert backup in the event of difficulty. The situational factors present in the environment where one practices may be modifiable to some extent. For example, a practitioner can petition the hospital to purchase an airway management tool not currently available or advocate for higher standards of airway management training for pre-hospital care personnel.

The aim of this chapter is to introduce the concept of context-sensitive airway management, and to serve as an introduction to a few of the general classes of airway management tools and techniques available. The most fundamental dilemma facing the practitioner wishing to improve their difficult or failed airway management skills is making logical, evidence-based, and clinically appropriate management decisions. The case at the beginning of this chapter is based on an encounter at the author's institution. It was used as an example of the principles involved in context-sensitive airway management.

This case presented an airway managed initially in a conventional way (direct laryngoscopy together with an Eschmann introducer) that subsequently became unmanageable due to dynamic situational factors. In the case described, an emergency cricothyrotomy in the trauma bay was successful. The patient made an unremarkable recovery from this life-threatening episode.

Gaining familiarity and experience with a variety of airway management techniques and devices will best equip the practitioner for these inevitable and challenging situations. At the very least, a competent practitioner should be facile with the techniques of bag-mask-ventilation, direct laryngoscopy and tracheal intubation, placement of an extraglottic device, and performance of an emergency cricothyrotomy. In addition, all practitioners should have predetermined plans "A," "B," and "C" when approaching any airway situation. The rare but extremely important can't intubate, can't ventilate situation must be routinely considered. Under these circumstances, placement of a rescue device (eg, LMA, Intubating LMA, Combitube™, or King LT™) should be performed while concurrently preparing for a surgical airway.