Endotracheal intubation, the insertion of a breathing tube into the trachea of a patient, is life saving for many patients in emergency wards, trauma units, and intensive care units. It is frequently an essential part of airway management during general anesthesia. Difficulty performing this procedure quickly and safely remains an important problem in spite of all available equipment and techniques.1 “Difficult intubation” is at best stressful to those involved and is at worst life threatening to the patient.
Any device that makes the procedure of endotracheal intubation easier, and in particular, one that decreases the number of difficult intubations, will be welcomed and sought after by anesthesiologists, intensivists, and all who care for emergency or trauma patients.
The proposed laryngoscope is a new laryngoscope blade that is designed to expose the larynx better than currently marketed blades. It is simple, robust, and has one moving part: an extensible distal portion of the blade. It can be used with standard laryngoscope handles and connectors. It is durable, and easily cleaned and sterilized.
Most important, it is easy and intuitive to use. No training in new techniques is required. All of the operator’s experience using standard blades is directly applicable to its use.
Intubating laryngoscopes fall into two classes. The first kind is designed to displace the tongue, thus allowing direct visualization of the larynx. The proposed laryngoscope is of this type. The advantages of direct visualization laryngoscopes include simplicity and ease of use. They are used in the majority of intubations, both elective and emergency.
The other class of laryngoscopes depends on fiberoptic imaging to visualize the larynx. Examples are the Bullard laryngoscope, the WuScope, and fiberoptic bronchoscopes and stylets. These have the advantage of allowing intubation in some otherwise difficult or impossible cases, but are more expensive, more complex, and require specialized training and experience.
The laryngoscope described here was developed because of the need for a direct laryngoscope that would make intubation easier for a wider range of patients, and that would decrease the number of unexpected difficult intubations.
X-ray images of laryngoscope blade insertions during laryngoscopy (in patients who were easy or difficult to intubate) have demonstrated the importance of the space behind the mandible and in front of the blade.2, 3 This is the “forward space”, and represents the available space into which the tongue can be displaced at the level of greatest restriction. Maximizing the forward space is important because elevation of the epiglottis depends on blade tip-hyoid bone contact, which is obstructed by the compression of soft tissue (mainly tongue) between the blade and the mandible.
The eyeline, or line of sight, passes from the tip of the upper incisor teeth, along a tangent to the laryngoscope blade, and on to the larynx. If the curvature of the blade is too great, the line of sight will be such that the larynx is not visible. Any laryngoscope blade therefore represents a compromise between the forward space and the eyeline deviation. The invention of the proposed laryngoscope resulted from successful efforts to optimize this compromise.
Figure 1 is a schematic illustration of new blade (in red) superimposed on a fixed curve blade (in blue). Both blades are shown in position for laryngoscopy. The green line is the eyeline, and is in this case identical for both blades. The forward space between the mandible and the blade is, however, significantly larger for the new laryngoscope blade. The improvement in the forward space is indicated in red.
At the time of laryngoscopy, the laryngoscope blade is inserted into the mouth and advanced into the vallecula (between the base of the tongue and the epiglottis). The handle is then lifted at right angles to the blade, causing the distal tip (T) of the blade to elevate the hyoid bone. The resulting traction on the hyoepliglottic ligament then lifts and rotates the epiglottis to expose the larynx to view.4, 5 In this position, the proximal portion of the lingual surface of the blade nearly contacts the lower incisor teeth (at point L). In order to position the blade correctly, it must be advanced or retracted (inward or outward) under direct vision after the initial insertion.
The shape of the proposed blade has been carefully designed (by extensive computer modelling) to optimize both the forward space and the line of sight. However, it can be seen (Figure 1) that if the blue blade were to be moved in or out, the apex (A) of the blade would move to a different position. One or both of the eyeline and the forward space would then be altered such that visualization of the larynx would become more difficult. This is a serious limitation of any fixed shape design, and is the reason that currently available blades can be improved upon.
Figure 2 illustrates how the design of the new laryngoscope solves this problem. The distal portion of the blade (beyond the apex A) is extensible, and can be lengthened or shortened in order to bring the apex A into the best position for the individual patient. This simple mechanism allows the blade’s depth of insertion to be adjusted without interfering with the ability to see the larynx.
If the blade is inserted to a different depth, the length of the portion of the blade between the apex (A) and the tracheal tip (T) can be increased or decreased in proportion to the change in the distance from the lower teeth (L) to the apex. Note from Figure 2 that the triangles L1-A1-T1 and L2-A2-T2 are similar triangles: although they differ in size, they have the same shape. This is what allows the apex of the blade to be positioned in the same best position relative to the anatomy of the patient’s oral cavity and pharynx.
Figure 2 illustrates the concept of the laryngoscope: a blade with a proximal portion (LA), an apex (A), and a distal portion (AT). The distal portion (AT) is extensible, having a sliding part such that the length from A to T can be adjusted. The overall shape (concavity) of the blade is determined by the angle (a) at the apex (A). Calculations of the best angle “a” at the apex of the blade using computer models of differing patient anatomies show that it is remarkably insensitive to anatomical variations such as under bite or over bite, or to the depth of the larynx.
Any practical embodiment of the invention must incorporate a means to control the sliding part of the blade. Figure 3 illustrates an artist’s concept of the laryngoscope. This drawing gives a good idea of the overall appearance and operation of the Blade, but it is not intended to constrain or limit further development. The illustration shows a preferred embodiment in which the distal portion of the blade slides in or out, moved by a locking control knob and a flat push bar. The push bar lies against the left (flange) side of the blade, and is shaped so as to remain within the width of the web of the blade throughout its range of movement. The light source as illustrated is a white LED that moves with the sliding portion of the blade. This gives a very bright light that is angled for ideal illumination of the larynx regardless of the length of the distal blade.
The proposed laryngoscope can be used with standard laryngoscope handles and connecting brackets. A prototype has been used to intubate a small number of patients. The extensible blade functions as intended, and improve the visualisation of the larynx.
A very important feature of the laryngoscope is that its method of use is the same as for a standard fixed laryngoscope blade. The only new aspect, the adjustment of the extensible portion of the blade, is intuitively similar to the adjustments to the position of the tip of the blade that are required in any case. Thus the operator can bring to bear, and make use of, all experience previously gained with other blades. This can be expected to result in a high comfort level and a short learning curve.
The patient is positioned as for direct laryngoscopy with a standard blade. An initial adjustment is made to the length of the blade, based on an assessment of the patient’s size and appearance. The blade is then inserted into the mouth to a depth estimated to place the tip of the blade in the vallecula between the base of the tongue and the epiglottis. It is then lifted up in a direction at right angles to the long axis of the blade. If the tip is not positioned in the vallecula, the upward pressure is relaxed and the blade is moved in or out as required. Similarly, if the apex of the blade is not positioned to provide a good view of the larynx, the distal part of the blade is extended or retracted as required to improve the exposure. Once the opening to the larynx is visualized, the endotracheal tube is inserted to complete the procedure.
Exposure of the larynx as described above is typical of the use of a curved laryngoscope blade (such as the Macintosh blade). In some circumstances, it is useful to use a straight blade (or longer curved blade) to lift the epiglottis directly. The proposed laryngoscope was developed as an improvement on the curved blade, but it can be used in the manner of a straight blade simply by further extending the distal portion.
Every operating room, emergency department, and intensive care unit in the world must have the equipment required for laryngoscopy and endotracheal intubation. There is an important market for a better, safer, and more convenient laryngoscope blade.
Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of the same made within the spirit and scope of the invention discussed without departing from such spirit and scope, it is intended that all matter contained in the discussion and description, as well as in the accompanying specification and figures shall be interpreted as illustrative only and not in a limiting sense.