John C. Sakles
Ross B Rodgers
Introduction
Most intubating laryngoscopes that achieve an image of the glottic entrance without requiring direct line of sight use video or fiberoptic technology. These technologies are expensive and thus raise the overall cost of the device. Combinations of mirrors, prisms, or lenses, which allow one to “see around the corner” of the airway, can transmit the glottic image to the operator's eye at a much lower expense. This chapter reviews two recently released optically enhanced laryngoscopes.
Devices
Airtraq
Device Components
The Airtraq optical laryngoscope is a single-unit, plastic, disposable laryngoscope that does not require a direct line of sight of the glottic structures for intubation (Fig. 15-1). The Airtraq uses a series of mirrors, prisms, and lenses to provide the operator a magnified and enhanced image of the airway through an optical channel. The Airtraq has an endotracheal tube (ETT) channel alongside the optical channel where the operator preloads the ETT prior to intubation. The device is currently available in two sizes, small and regular, and a pediatric size is under development. The small Airtraq requires 16 mm of mouth opening and accommodates ETT sizes from 6.0 to 7.5 mm, and the regular Airtraq requires 18 mm of mouth opening and accommodates ETT sizes from 7.0 to 8.5 mm internal diameter. The device is powered by three disposable AAA batteries that provide approximately 90 minutes of operating time. The Airtraq is turned on by pressing a button located on top of the device. The illumination is derived from a low-heat light-emitting diode (LED), and the device contains a heat monitoring unit that prevents the Airtraq from reaching temperatures that could harm the patient. The rubber eyepiece, which is connected to the optical channel, can be removed to allow attachment of an optional video composite system that can transmit the optical image via video cable or wirelessly using a 2.4-GHz receiver to an external monitor. The shelf-life of the Airtraq is approximately 2 years. The device cannot be cleaned or sterilized and will not function properly if either is attempted.
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Figure 15-1 • Airtraq Optical Laryngoscope. Note the black rubber eyepiece atop the viewing channel and grey endotracheal tube guide (top: small size, bottom: regular size). |
Use of Device
The Airtraq requires little setup time and is self-contained within its protective packaging. The Airtraq's antifogging mechanism requires the device be turned on for approximately 30 seconds to maximize this benefit. The LED will flash when the device is turned on and become constant when the heating element has reached the appropriate antifog temperature and the device is therefore ready for use. The ETT should be lightly lubricated and preloaded into the ETT channel. Also, the anterior surface of the Airtraq blade, which will come in contact with the tongue, can be lubricated to help facilitate passing the device around the tongue. The Airtraq should be placed into the mouth using a midline approach. Gentle traction is applied to the tongue, if necessary, to ensure that the tongue is not pushed into the hypopharynx. As the Airtraq is advanced, the operator visualizes the epiglottis through the optical channel and continues to move the device forward into the vallecula. At this time, the Airtraq is lifted in the vertical plane to elevate the epiglottis and align the vocal cords within the center of the optical field (Fig. 15-2). The ETT is slowly advanced through the vocal cords, and then disengaged from the device and the Airtraq is removed. If the ETT is obstructed by the epiglottis or arytenoids, the entire device must be manipulated to better align the ETT position with the glottic entrance. The Airtraq can be pulled back slightly and rotated within the horizontal plane to help align the glottic structures. Alternatively, the epiglottis can be lifted directly by the Airtraq blade via a straight blade approach to appropriately align the glottic structures. However, this technique can somewhat distort the anatomy and is not the recommended approach.
If the proprietary composite video system is used, then the rubber optical eyepiece is removed and the video adaptor is snapped onto the Airtraq prior to insertion. The operator then visualizes the entire procedure on the external monitor. This approach allows the operator to maintain a safe distance from the patient and provides a larger view of the anatomical structures.
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Figure 15-2 • Clinical use of Airtraq optical laryngoscope using optional video camera adaptor with glottic view inset in the right lower corner. As can be seen, the endotracheal tube is approaching the vocal cords from the right side of the image. |
Summary
The Airtraq is an inexpensive and lightweight device that provides an alternative approach to emergency airway management. The quality of the optics is substantially less than the video laryngoscopes but provides a clear and reasonable image of the glottis. The operator must learn to manipulate the device instead of the ETT for proper intubation. This technique may feel somewhat uncomfortable to the operator who is used to adjusting the ETT instead of the device for proper ETT placement. The antifog technology provides adequate clarity during the intubation process and is an added benefit for a low-cost device. The camera attachment greatly enhances the image and allows the operator to remain at a safe distance from the patient. Overall, the Airtraq is reasonably easy to learn and use within the emergency setting.
TruView EVO
Device Components
The TruView EVO consists of a conventional laryngoscope handle that houses two C batteries and an attached laryngoscope blade with several unique features (Fig. 15-3). First, the EVO blade has a straight proximal portion with a steep angulation of the distal end. On the straight portion of the blade, there is a channel that houses the view tube, which consists of a prism and lens providing 42 degrees of light refraction. The design of the eyepiece allows the operator to view the glottic structures at a distance of 2 feet from the device. At this distance, the image seen by the operator is actual size. In addition, the eyepiece will accept all universal 32-mm endoscopic camera heads. This feature allows the operator to perform the intubation while viewing the procedure on an external monitor. This configuration also allows others to view the intubation and can be used for instruction during the procedure, or the intubation can be recorded for teaching after the intubation. The manufacturer also distributes a digital camera with a 2.5-in. LCD and video capabilities that attaches directly to the view tube eyepiece. The EVO blade incorporates an oxygen port that can be attached to standard medical tubing, and oxygen can be delivered at 10 L/minute. The flow of oxygen is directed in front of the distal portion of the optical system to potentially help keep the lens clear of contamination and reduce fogging. In addition, insufflation of oxygen can allow the operator slightly more time for intubation by reducing patient hypoxia. Currently, there are two sizes of the EVO, adult and small adult. Each is designed to attach to a conventional laryngoscope handle or a fiberoptic green-line handle. The manufacturer also offers the OptiShape stylet, which can be used to facilitate correct direction of the ETT during intubation.
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Figure 15-3 • TruView EVO optical laryngoscope connected to a standard green-line fiberoptic handle. |
Use of Device
The setup time for the EVO is minimal. The view tube is secured to the blade with the view tube button located in the up position. Antifog solution can be applied to the distal portion of the view tube lens to minimize fogging. Oxygen tubing is connected to the oxygen port, and oxygen flow is set to 10 L/minute. The operator then conforms the ETT with stylet to a shape comparable to that of the EVO blade. Alternatively, the operator can use the OptiShape, a specially designed stylet that exactly corresponds to the EVO blade. The OptiShape has a locking device to prevent the stylet from advancing past the ETT. As opposed to standard laryngoscopy, the operator places the EVO blade into the patient's mouth using a midline approach. The blade should be inserted until the handle is approximately 2 to 3 cm from the patient's lips. Very little or no neck extension is required. The operator then looks through the eyepiece at a comfortable standing position. In most circumstances, the glottic structures are visualized; however, adjustments may be required to obtain the best possible view for intubation. Due to the limited field of view and the necessity for perfect alignment of the operator's line of sight with the eyepiece, it may be difficult to gain visualization of the glottic inlet. Connecting the device to a standard camera adaptor and external video monitor alleviates the previous difficulty, but results in a smaller glottic image (Fig. 15-4). The ETT is then inserted at the right corner of the patient's mouth in the horizontal plane and rotated 90 degrees toward the midline during advancement into the hypopharynx, bringing the tip of the ETT into view at the laryngeal inlet. The ETT is then advanced through the vocal cords, and the device is removed from the patient's mouth.
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Figure 15-4 • Clinical use of TruView EVO with optional camera attachment and oxygen delivery at 10 L per minute. The insert in the right lower corner shows the glottic inlet surrounded by reflection within the metal eyepiece. Notice the V-shaped clearing of the upper portion of the lens provided by the oxygen flow that is surrounded by fogging. This view is similar to that shown when the operator looks through the optical channel. |
Summary
The TruView EVO is a newly developed and promising optical laryngoscope that allows the operator to see and intubate the larynx with less applied vertical force and without having a direct line of sight. Although the device appears similar to a standard laryngoscope, the technique is quite different due to the requirement of standing away from the patient and directing the ETT toward structures that are visualized through the viewing port, rather than directly in the line of sight. The decreased field of view may also increase the difficulty to navigate toward the glottic structures. Overall, the EVO provides an alternative to direct laryngoscopy, especially for patients with a known anterior airway or cervical spine injury, by allowing the operator to perform intubation without direct line of sight.
Conclusion
These two devices both capitalize on optics to improve glottic view without requiring a direct line of sight from outside the patient's mouth, and so share many of the advantages of the more expensive video and fiberoptic systems. Although the two devices appear to perform well in limited testing, there are no published studies of their use in emergency or difficult airway situations. As we acquire further knowledge and experience related to these devices, their strengths, limitations, and role in emergency airway management will become better elucidated.
Evidence
1. Is the Airtraq device easy to learn? There are currently no literature-based evaluations for the Airtraq device for emergency patients. Studies in elective anesthesia patients show significant promise, however. In a study of 60 elective anesthesia patients, the Airtraq was compared to direct laryngoscopy using a MacIntosh blade. All patients in the Airtraq group and all but one in the Macintosh group were intubated on the first attempt, but the intubations were scored as more difficult in the MacIntosh group. Time to intubation did not differ between the groups. Anesthetists rated the Airtraq easier to use than the Macintosh laryngoscope (mean scores of 1.2 vs. 2.0 on a 0–10 visual analog scale) (1). The same investigators, in a subsequent study, evaluated the Airtraq versus the MacIntosh laryngoscope in 40 elective surgical patients with manual inline stabilization (2). The Airtraq provided superior laryngeal views and shorter intubation times, and was rated as easier to use by anesthesiologists who had used both instruments.
2. What is the role of the EVO in emergency intubations? There are currently no literature-based evaluations for the TruView EVO for emergency patients. There are several studies for routine intubations and case series of patients with difficult airways within a controlled setting. Further research is needed to evaluate the utility of this device for intubation of emergency department patients.
References
1. Maharaj CH, O'Croinin D, Curley G, et al. A comparison of tracheal intubation using the Airtraq or the Macintosh laryngoscope in routine airway management: a randomised, controlled clinical trial. Anaesthesia 2006;61:1093–1099.
2. Maharaj CH, Buckley E, Harte BH, et al. Endotracheal intubation in patients with cervical spine immobilization: a comparison of Macintosh and Airtraq laryngoscopes. Anesthesiology 2007;107:53–59.
