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:
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
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.
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.
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.