Division of Anesthesiology, Critical Care and Pain Medicine
The University of Texas MD Anderson Cancer Center
Executive Director 2009-Present, Society for Airway Management
Editor’s note: A key of all abbreviations and acronyms appears at the end of this article.
Management of the difficult airway remains one of the most relevant and challenging clinical situations encountered by anesthesia practitioners, as major adverse consequences can occur if the airway is not secured in a timely fashion. This edition of “Current Concepts in the Management of the Difficult Airway” marks the 15th anniversary of this review of airway devices and techniques that are currently available to manage both routine and difficult airways, regardless of setting.
Alternative Airway Devices
A common factor preventing successful tracheal intubation is the inability to visualize the vocal cords during the performance of DL. Many devices and techniques are now available to circumvent the problems typically encountered with a difficult airway using conventional DL.
Advances in ET design have been made to facilitate both passage of the ET, such as the Parker Flex-Tip (Salter Labs), and tracheal intubation in narrowed airways, such as the Tritube (Ventinova Medical BV) and the Shiley Microlaryngeal ET (Medtronic). Several ET guides have been used to aid in intubation or extubation, including both reusable/disposable and solid/hollow introducers, stylets, and tube exchangers (Table 1).
Lighted stylets, when used alone, are a blind technique of intubation, as they rely on transillumination of the tissues of the anterior neck to demonstrate the location of the ET. These devices can be used with either DL or VL to allow direct visualization of the airway (Table 2).
Viewing Optical Stylets
Viewing optical stylets provide a view from the tip of the ET. Whereas the view from a VL is at the end of the laryngoscope, viewing optical stylets provide a view from the tip of the ET for steering the ET through the cords. The stylet size for this device allows it to be placed within an ET as an inde-pendent instrument, or as an adjunct to VL or DL. Additionally, some can be used to place an ET through intubating supraglottic ventilatory devices for visualization of ET placement through the SGA (Table 2). As an alternative to a viewing optical stylet placed inside the ET tip, the VivaSight-SL (ETView, Ambu) is a single-use ET with an integrated camera at the tip of the tube to provide a view for steering the ET through the cords. When in place, it pro-vides continuous real-time monitoring of tube position.
Video-assisted techniques have become pervasive in various surgical disciplines, as well as in anesthesiology. As more VLs are introduced into clinical practice, and as airway managers become more skillful with the technique of video-assisted laryngoscopy, it could well become standard procedure for patients with known or suspected difficult airways. It also may become the standard for routine intubations as the equipment and users’ skills improve and the cost of the devices decreases, with the potential for important savings in time and decreased morbidity in patients. It is beyond the scope of this review to discuss all of the laryngoscopes that have been manufactured; thus, only some of the most recently developed blades are described (Table 3).
Indirect Rigid Fiber-Optic Laryngoscopes
These laryngoscopes were designed to facilitate tracheal intubation in the same population that would be considered for flexible fiber-optic bronchoscopy, such as patients with limited mouth opening or neck movement. Relative to the flexible FOBs, they are more rugged in design, control soft tissue better, allow for better management of secretions, are more portable (with the exception of the new portable FOBs), and are not as costly. Intubation can be performed via the nasal or oral route and can be accomplished in awake or anesthetized patients (Table 4).
Supraglottic Ventilatory Devices
The LMA (Laryngeal Mask Airway; Teleflex) is the single most important development in airway devices in the past 25 years. Since its introduction into clinical practice, it has been used in more than 300 million patients worldwide. Other supraglottic ventilatory devices are available for routine or rescue situations. The most recently developed supraglottic ventilatory devices have a gastric channel or are intended to be used as a conduit for fiber-optic–guided intubation (Table 5).
Special Airway Techniques
For managing patients in whom a difficult airway is suspected or anticipated, securing the airway before induction of general anesthesia adds to the safety of anesthesia and helps minimize the possibility of major complications, including hypoxic brain damage and death. To perform awake intubation, the patient must be adequately prepared for the procedure. Good topical anesthesia is essential to obtund airway reflexes and can be provided by various topical agents and administrative devices (Table 6). Other relatively new devices can be used to best position patients and maintain an open airway during awake intubation (Table 7).
Atomizing devices currently available for delivering topical anesthesia to nasal, oral, pharyngeal, laryngeal, and tracheal tissues include the DeVilbiss Model 15-RD Glass Atomizer (DeVilbiss Healthcare), the LMA MADgic (Teleflex) atomizer, and the LMA MADgic Airway (Teleflex). Although any technique of tracheal intubation can be performed under topical anesthesia, flexible fiber-optic intubation is most commonly used.
Flexible Fiber-Optic Intubation
Flexible fiber-optic intubation is a very reliable approach to difficult airway management and assessment. It has a more universal application than any other technique. It can be used orally or nasally for both upper and lower airway problems and when access to the airway is limited, as well as in patients of any age and in any position.
Technological advances—including improved optics, battery-powered light sources, better aspiration capabilities, increased angulation capabilities, and improved reprocessing procedures—have been developed. The Airway Mobilescope (MAF; Olympus) is a portable, flexible endoscope with expanded viewing and recording capability, incorporating a monitor, LED light source, battery, and recording device in a single unit. Also available is the Ambu aScope 3, a disposable, sterile, portable, flexible endoscope with a fully functional suction/working channel.
Rescue techniques, such as DL and placing a retrograde guidewire through the suction channel, may be performed if the glottic opening cannot be located with the scope, or if blood or secretions are present. Insufflation of oxygen or jet ventilation through the suction channel may provide oxygen throughout the procedure, and allow additional time when difficulty arises in passing the ET into the trachea.
Retrograde intubation (Table 6) is an excellent technique for securing a difficult airway either alone or in conjunction with other airway techniques. Every anesthesia care provider should be skilled in employing this simple, straightforward technique. It is especially useful in patients with limited neck mobility that is associated with cervical spine pathology or in those who have suffered airway trauma. Cook Medical has 2 retrograde intubation sets: a 6.0 Fr for placing tubes at least 2.5 mm ID, and a 14.0 Fr for placing tubes at least 5.0 mm ID.
Transtracheal Jet Ventilation (TTJV) and Small–Gauge Lumen Ventilation
TTJV is a well-accepted method for securing ventilation in rigid and interventional bronchoscopy, and there are several commercial manual jet ventilation devices available (Table 6). The Enk Oxygen Flow Modulator (Cook Medical) can be used when jet ventilation is appropriate but not available. An MRI Conditional 3.0 Tesla manual jet ventilator (Anesthesia Associates, AincA) also is now available to enable TTJV in the MRI suite for both planned and emergency procedures (Table 6). The Ventrain (Ventinova Medical B.V.) is a single-use ventilation device specifically designed for difficult or obstructed airway situations, allowing ventilation through small–gauge lumens. Ventrain is not a traditional jet ventilator: Its ventilation is not based on a continuous high pressure to induce inspiration; instead it is based on a continuous and bidirectional gas flow, inducing both inspiration and expiration. Thus, Ventrain not only supplies oxygen during the inspiration phase, but also actively removes gas from the lungs with Expiratory Ventilation Assistance (EVA). Ventrain enables adequate ventilation through small–gauge lumen catheters, as well as in situations when the airway is obstructed (Table 6).
Cricothyrotomy (Table 8), a lifesaving procedure, is the final option for “cannot-intubate, cannot-ventilate” patients according to all airway algorithms, whether they concern prehospital, ED, ICU, or surgical patients. In adults, needle cricothyrotomy should be performed with catheters at least 4 cm and no more than 14 cm in length. A 6.0 Fr reinforced fluorinated ethylene propylene Emergency Transtracheal Airway Catheter (Cook Medical) has been designed as a kink-resistant catheter for this purpose. Percutaneous cricothyrotomy involves using the Seldinger technique to gain access to the cricothyroid membrane. Subsequent dilation of the tract permits passage of the emergency airway catheter. Surgical cricothyrotomy is performed by making incisions through the cricothyroid membrane using a scalpel, followed by the insertion of an ET. This is the most rapid technique and should be used when equipment for the less invasive techniques is unavailable and speed is particularly important.
Tracheostomy (Table 9) establishes transcutaneous access to the trachea below the level of the cricoid cartilage. Emergency tracheostomy may be necessary when acute airway loss occurs in children under the age of 10 years or those whose cricothyroid space is considered too small for cannulation, as well as in individuals whose laryngeal anatomy has been distorted by the presence of pathologic lesions or infection.
Percutaneous dilatational tracheostomy is the most commonly performed tracheostomy technique, yet it is still considered invasive and can cause trauma to the tracheal wall. Translaryngeal tracheostomy, a newer tracheostomy technique, is considered safe and cost-effective, and can be performed at the bedside. It may be beneficial in patients who are coagulopathic. Surgical tracheostomy is more invasive, and should be performed on an elective basis and in a sterile environment.
Most airway problems can be solved with relatively simple devices and techniques, but clinical judgment born of experience is crucial to their application. As with any intubation technique, practice and routine use will improve performance and may reduce the likelihood of complications. Each airway device has unique properties that may be advantageous in certain situations, yet limiting in others. Specific airway management techniques are greatly influenced by individual disease and anatomy, and successful management may require combinations of devices and techniques.
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