Chapter Outline
Introduction 92
Intubation Devices 92
Retractor-Type Laryngoscopes 93
Rigid Fiberoptic Laryngoscopes 98
Bullard Laryngoscope and UpsherScope 98
Bonfils Intubating Fiberscope 98
Video Laryngoscopes 99
The Storz C-MAC 99
The Glidescope 99
Airtraq Laryngoscope 99
Flexible Fiberoptic Laryngoscopes (Bronchoscopes) 101
Principles and Design 101
Usage 102
Care of the Fiberscope 104
Fiberoptic Intubation 104
Associated Equipment 104
Aids for Intubation/Tube Exchange 106
Bougies and Stylettes 106
Lightwand 107
Trachlight 107
Airway Exchange Catheter 107
Retrograde Intubation 107
Magill Forceps 107
Drug Delivery Systems 108
Introduction
Visualization of the vocal cords for intubation was popularized by Sir Robert Macintosh and Sir Ivan Magill in the early 1940s. It was during the insertion of a Boyle-Davis gag that Macintosh conceived the idea of his laryngoscope, which is still the most popular design in use today and has spawned a wide variety of modifications. It consists of a blade that elevates the lower jaw and tongue, a light source near the tip of the blade to illuminate the larynx, and a handle to apply force to the blade. The handle also contains the power supply (battery) for the light source. The light comes on when the blade, which is hinged on the handle, is opened to the right angle position. Macintosh designed a slightly curved blade ( Figure 7-1 ) with a small bulbous tip that was designed to be inserted anterior to the base of the epiglottis in an adult. The child and infant blades were not designed by him, and he criticized them as being anatomically wrong and unnecessary. Some blades for adults and many of those intended specifically for children or infants tend to be either straight or with a small shallow curve at the tip only. These are designed to be inserted deeper into the pharynx and posterior to the epiglottis and hence the blades are correspondingly longer.
In practice, the term “laryngoscope,” when not further described, is still largely synonymous with the rigid retractor type and more specifically the Macintosh-designed laryngoscope. The term “difficult laryngoscopy” therefore is largely used to describe any situation where only a suboptimal view of the larynx can be obtained with these default devices. For practical usefulness, given the variety of devices now routinely available, this term should always be further defined to describe the circumstances.
Intubation Devices
Intubation devices may be considered under two broad categories:
- 1.
Retractor type, such as the Macintosh laryngoscope, reliant on retracting tissues to create an uninterrupted sight line between the operator and the objective. Fiberoptics may be used in the light source of these types.
- 2.
Fiberoptic laryngoscopes, where a fiberoptic channel transmits the image from the tip of the device to an eyepiece or camera, thus allowing the observer to effectively view around an obstruction. Fiberoptic channels are hence also necessitated for light transmission to the objective. Two types of fiberoptic laryngoscopes can be categorized:
- a.
Rigid fiberoptic laryngoscopes, such as the Upsher and Bonfils, where the fiberoptic viewing channel is rigid and usually encased in metal. This type of device can also force tissues aside and act as a retractor. Accepted wisdom has it that such instruments require less dexterity and expertise to use than their flexible counterparts. Other devices recently introduced include the Airtraq optical laryngoscope and the video laryngoscopes such as the GlideScope, Storz C-MAC, and the McGrath. Some of these are not truly fiberoptic devices―using mirrors or cameras and light sources at their tips instead—but they perform in fundamentally the same way.
- b.
Flexible fiberoptic laryngoscopes. The viewing bundle (plus light transmission bundles and an optional instrument channel) is wrapped in a flexible casing. The instrument can thus be made to follow anatomical spaces and will bend as necessary to negotiate almost any route. The term “flexible fiberoptic bronchoscope” is synonymous in use.
- a.
Retractor-Type Laryngoscopes
Figure 7-2 shows some of the wide variety of blades currently available. The choice of blade for routine use is probably largely a matter of personal preference. One must keep in mind that the technique for laryngoscopy is different for the various designs of blade and differing designs may offer better views of the larynx in a given patient. Most blades are detachable from the handle for ease of cleaning and change of blade size where appropriate. The “hook on” connection for the blade, which allows easy detachment, is very convenient and was developed by Welch Alleyn Ltd. in the early 1950s. Two new standards, ISO 7376/3 (green system) and ISO 7376/1 (red system) have been developed, which allow blades from different manufacturers to be interchangeable, but they have not been universally adopted. In both, the bulb is housed within the handle and light is transmitted through an optical “bundle” to the tip of the blade. Their difference lies in the dimensions of the hinges and the relative positions of the light sources. Prisms and mirrors are sometimes added to these devices to overcome the principal shortcoming of this class of device, namely that the operator’s eye and patient’s larynx must be in a straight line with no interposed tissue. So far, such modifications have not proven popular or lasting.
Features of Modern Laryngoscopes
Figure 7-3 shows a typical instrument with a hook on type Macintosh blade. Some specific points are highlighted next:
- ▪
Detachable blade for interchangeable blade designs and ease of cleaning and sterilization.
- ▪
Light source sited within the handle. Much brighter xenon gas-filled bulbs are used to compensate for light loss during transmission.
- ▪
Light projection via a shaped bundle of glass fibers. The bundle may be manufactured as an integral part of the blade, or may be detachable so that should it become damaged or opaque it may be replaced separately. Fiberoptic bundles are prone to degradation resulting in poor illumination and difficult laryngoscopy.
- ▪
Disposable single-use blades are gaining popularity as an alternative to the costly and damaging process of sterilization of laryngoscope blades. These may be of plastic or even metal design but must not be assumed to perform as well as traditional instruments.
Laryngoscopy
Figure 7-4 shows how correct positioning of the patient’s head with craniocervical extension and lower cervical flexion, the position known as “sniffing the morning air,” allows the laryngoscope to retract the tongue and associated soft tissues into the elastic and distensible area of the floor of the mouth. Such positioning provides an uninterrupted sight line through to the larynx. Poor views of the larynx can be predicted from this model where there is:
- ▪
Inadequate craniocervical movement or jaw opening; reduction in volume of distensible area below floor of mouth as with small receding mandible or following scarring or distortion of the anatomy as from head and neck surgery or radiotherapy; tumors of tongue base or larynx; or swelling of the posterior pharyngeal wall.
The handle of the laryngoscope is used to lift (i.e., force is applied in the direction of the handle rather than using the handle as a lever). Curved blades are designed for the tip to be inserted into the vallecula with the standard Macintosh blade being inserted to the right of the tongue and hence forcing it to the left side, whereas the straight blade may be inserted posterior to the epiglottis and is particularly useful for small children and adults with a large floppy epiglottis. Different laryngoscope blades require different techniques for viewing the larynx, which must be learned to exploit that device. For example, the Henderson blade (Karl Storz, Germany), a modification of the Miller blade, is a long straight bladed design with a “C”-shaped cross section ( Figure 7-5 ) and is intended to be inserted to the right of the tongue with the head turned aside in effectively a “retromolar” fashion. A poor view obtained with one design does not predict a poor view with a different design.
Laryngoscopes
Macintosh Blade
The Macintosh blade is probably the most commonly used blade in adults in the United States. The Macintosh blade is curved to better fit in the mouth and oropharyngeal cavity. There is a small bulbous structure at the tip of the Macintosh blade designed to help lift the larynx ( Figure 7-6 ). In the United States, the Macintosh blade is available in the following sizes: large (Macintosh 4), adult (Macintosh 3½ and 3), child (Macintosh 2), infant (Macintosh 1), and premature (Macintosh 0).
During intubation, the Macintosh blade is traditionally inserted from the right side of the mouth. Then the tongue can be pushed over to the left side of mouth by the blade. The tip of the Macintosh blade is placed in the space between the base of the tongue and the pharyngeal surface of the epiglottis (compared with placement of the Miller blade beneath the laryngeal surface of epiglottis). The laryngoscope with Macintosh blade then can be lifted upwards, which will elevate the larynx and allow visualization of the vocal cords. The use of the Macintosh blade may cause less trauma to the teeth and allow more room for the passage of the endotracheal tube than other blades. The Macintosh blade may also cause less bruising of the epiglottis because the tip of Macintosh blade usually does not come in contact with it.
Even though the Macintosh blade is one of the most commonly used blades, it has some limitations. In the case of a difficult airway, the Macintosh blade may not be able to provide good exposure made possible by the lifting of the epiglottis that can be accomplished with the Miller blade. However, the choice of a laryngoscope is based on the operator’s training and experience.
Miller Blade
The Miller blade is another of the most commonly used blades. As can be seen in Figure 7-7 , the tip of the Miller blade is straight. The size of the Miller blade can be large (Miller 4), adult (Miller 3), child (Miller 1½ and 2), infant (Miller 1), or premature infant (Miller 0 and 00).
Even though the Miller blade is commonly used, the choice of laryngoscope is based on personal preference and experience. Nevertheless, this blade is often used to intubate neonates and infants. The tip of the Miller blade is placed beneath the laryngeal surface of the epiglottis (versus in the space between the base of the tongue and pharyngeal surface of epiglottis if the Macintosh blade is used). Miller blade can potentially provide better exposure of the glottic opening and less frequent need for a stylette during intubation. The limitations of the Miller blade include the possibility of causing more trauma to the teeth and epiglottis than the Macintosh blade, and its insertion may result in less room for the passage of the endotracheal tube.
Macintosh Polio Blade
This variation alters the angle between the blade and the handle and is developed to allow the laryngoscope blade to be more easily inserted into the mouth in patients with abnormal anatomy. The polio blade is essentially a modification of the Macintosh blade. It is also a curved blade, but the angle between the polio blade and the handle is approximately 120 degrees (rather than 90 degrees in the Macintosh blade). This design allows the easier introduction of the blade into the mouth in specific groups of patients ( Figure 7-8 ). The polio blade was originally designed to intubate patients housed in iron lungs. Now it can be used in patients who are using respirators or wearing body jackets, who are obese, have breast hypertrophy, or have restricted neck mobility. The polio blade can facilitate the introduction of the blade into the mouth of these patients. However, this blade does not have all the mechanical advantages of the Macintosh blade. For example, only a small amount of force can be applied when the polio blade is used. Alternatively, a regular Macintosh blade with a “stunted” handle may be used in the special patient populations discussed above. Another device, the Patil-Syracuse handle allows multiple locking positions for the blade attachment point.
Left-Handed Macintosh Blade
The “reversed” Macintosh blade has a flange on the right side in a mirror image of the traditional Macintosh blade. The right-sided flange can help move the tongue to the right side of the mouth when the blade is inserted from the left side of the mouth. Although the reversed Macintosh is held in the right hand, manufacturers still named it a “left-handed” blade, referring to the hand which passes the endotracheal tube.
The left-handed Macintosh blade can be used by left-handed individuals. It can also be used for patients whose anatomy (e.g., lesions on the right side of the tongue, mouth, or face) makes it difficult to insert the Macintosh blade from the right side of the mouth or for patients who need to be intubated while lying on their right side. The left-handed Macintosh blade is inserted from the left side of the mouth and then swept from left to right, creating a space on the left side of the mouth. The left-handed Macintosh blade comes in No. 3 size only. The use of the left-handed laryngoscope blade requires training and practice. A right-handed person (and most experienced left-handed anesthesiologists) would find the device most odd in use.
McCoy Blade
This blade is based on a standard Macintosh blade modified by the insertion of a hinge to give an adjustable tip that is operated by a lever on the handle ( Figure 7-9 ). The blade is inserted in the normal way, and if the view is obscured, the tip can be flexed so that it further elevates the vallecula and epiglottis. Opinion is divided as to its usefulness: although the design has been commercially successful and it is included in many algorithms for airway management, there is little evidence to support its widespread use. The effect on laryngeal view is variable depending on whether the base of tongue and vallecula is already optimally elevated. In difficult direct laryngoscopy, activation of the tip may improve the laryngeal view, where there is a grade 3 Cormack and Lehane view but is unlikely to do so where the epiglottis cannot be seen (grade 4 view). Additionally, the incidence of grade 2 or worse views may be increased compared with a standard Macintosh blade even without activation of the tip.
Soper Blade
The Soper blade is a straight blade that has a shallow vertical portion with a flange facing to the left ( Figure 7-10 ). This blade comes in adult and pediatric sizes, it is generally used to intubate neonates and infants. This blade combines the “Z” section (outward flange) of the Macintosh design with the pattern common to Miller and other straight blades. The broad flat shape makes it easier to restrict the neonate and premature infant’s tongue movement. The tip of Soper blade is placed beneath the laryngeal surface of the epiglottis. Soper blades can be technically difficult to use and can lead to longer intubation times compared with straight blades.
Wisconsin Blade
The Wisconsin blade is a straight blade with a flange that is curved to form two thirds of a circle in cross section ( Figure 7-11 ). The Wisconsin blade can extend slightly toward the distal portion of the blade, therefore increasing the visual field and reducing the possibility of trauma during intubation. Five sizes are available, and the Wisconsin blade is designed primarily for use in infants. After successful exposure of vocal cords by this blade, the endotracheal tube can then be inserted through the circle of the cross section or through the mouth for intubation. The space for the passage of the endotracheal tube can be too narrow when the Wisconsin blade is inserted.
Robertshaw Blade
The Robertshaw blade was originally designed for use in infants and children, but can be also used in adults. It is gently curved over the distal third and is designed to lift the epiglottis indirectly in the manner similar to the Macintosh blade ( Figure 7-12 ). During intubation, the tip of the Robertshaw blade is placed in the space between the base of the tongue and the pharyngeal surface of the epiglottis. Usually, a size 0 Robertshaw blade is used for low-birth-weight babies because the tapered tip of the blade makes it easier to navigate in a small pharynx. The Robertshaw blade allows binocular vision, and therefore the blade can potentially cause less trauma due to better visualization of the anatomy. The Robertshaw blade can be particularly useful in nasotracheal intubation because it provides a better view of the pharynx when Magill forceps are introduced into the mouth.
Seward Blade
The Seward blade has a straight tongue with a curve near the tip, and a small reverse Z-shaped flange ( Figure 7-13 ). The Seward blade is especially useful for nasotracheal intubation because the shape of the Seward blade allows Magill forceps to be introduced into the mouth with a minimum loss of view. It is intended for use in children younger than 5 years old.
Oxford Infant Blade
The Oxford infant blade has a straight tongue that curves up slightly at the tip. This blade has a “U shape” at the proximal end, and the distal part is open. It tapers from a maximum width at the proximal end to the smallest width at the tip ( Figure 7-14 ). It is suitable for premature infants, babies, and children up to the age of 4. There is sufficient overhang on the open side, helping to prevent the lips from obscuring vision. The broad, flat lower surface is useful in a small child with a cleft palate. Similar to the Wisconsin blade, the space between the corner of the mouth and the Oxford infant blade can be narrow, which could make it difficult to insert the endotracheal tube into the mouth.
Rigid Fiberoptic Laryngoscopes
Bullard Laryngoscope and UpsherScope
These two devices have a broadly similar curve to the blade and use fiberoptics to transmit the image from the tip to the eyepiece. They are designed to elevate the jaw without the need for neck extension and for use in patients with limited mouth opening. Physical alignment of the oral, pharyngeal, and laryngeal axes for direct visualization of the glottis is not required, unlike in direct laryngoscopy. Whereas the Bullard ( Figure 7-15 ) uses a fixed stylet to carry the tracheal tube, the UpsherScope ( Figure 7-16 ) has a “C”-shaped cross section, which will transmit a tube of the correct diameter to emerge in the field-of-view of the device.
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