The Complexity of Tracheal Intubation Using Rigid Fiberoptic Laryngoscopy (WuScope)

Abstract

There are many strategies for managing the airway in patients with anatomic risk factors of difficult intubation [1]. The WuScope (Pentax Precision Instruments, Orangeburg, NY) is a new fiberoptic laryngoscope system that combines a tubular rigid blade and a flexible fiberscope to facilitate placement of the endotracheal tube (ETT) [2]. The anatomically shaped rigid blade consists of a main blade and bivalve element that forms a tubular exoskeleton that provides a built-in passageway through which the ETT can be advanced through the glottic opening without the need for an intubating stylet or head extension. The purpose of this observational study was to characterize the complexity of intubation difficulty encountered during the initial use of the fiberoptic laryngoscope device (WuScope) in a tertiary care, level 1 trauma hospital. Methods The study was approved by the our institutional review board. Informed consent was not required. Anesthetics and techniques were at the discretion of the anesthesiologist, not dictated by protocol. Airway examinations and intubations were performed by or under the direction of two certified anesthesiologists (CES, TS), each of whom had performed at least two WuScope intubations before the study after viewing the instructional video, reading the manual, and practicing the technique on a mannequin. Airway information collected included history of difficult intubation, Mallampati classification, thyromental distance (<6.5 cm or >or=to6.5 cm), mouth opening (<3.5 cm or >or=to3.5 cm), cervical spine mobility (normal, slightly limited, or none), and other factors predictive of intubation difficulty, such as anteriorly protruding incisors. The technique of fiberoptic laryngoscopy was as follows: after assembly of the WuScope device, application of antifog to fiberscope tip, and suitable anesthesia, the rigid blade was introduced into the patient's mouth at the midline (Figure 1A). The handle was rotated toward the operator, and the main blade was advanced until the epiglottis and larynx came into view (Figure 1B). The ETT was then advanced by the operator through the glottis and into the trachea (Figure 2). A suction catheter inside the ETT was used to remove secretions and as a guide for ensuring proper alignment of the ETT and glottic opening. The intubation process was displayed on a color video monitor using a camera connector with a focusing ring that attached to the fiberscope, or was viewed directly through the fiberscope if the video monitor was not available. Illumination was provided by a fiberoptic light source. Adult-size blades were used for female and male patients weighing <70 kg. Otherwise, large adult blades were used. For nasotracheal intubation, the bivalve element was excluded.Figure 1: The WuScope is introduced into the patient's mouth at the midline. Manual in-line axial stabilization is applied by an assistant (A). The handle is then rotated toward the operator (B), and the main blade is advanced until the epiglottis and larynx come into view.Figure 2: As the handle is rotated toward the operator, first the epiglottis (A), then the larynx (B) come into view. The ETT is advanced by the operator through the glottis and into the trachea (C and D).The Intubation Difficulty Scale (IDS) score was recorded by an independent observer (JL, ABP) after each intubation [3]. The IDS is based on seven variables associated with difficult intubation: number of supplementary attempts, number of supplementary operators, number of alternative techniques, Cormack grade, subjective lifting force, laryngeal manipulation, and vocal cord position (Appendix 1 (Table 4)). The scoring of each variable represents a divergence from an ideal intubation-i.e., one performed by the first operator on the first attempt with full visualization of the vocal cords.Table 4: Appendix 1 Intubation Difficulty Scale (IDS)aTime to glottic exposure was from the moment the rigid blade touched the patient to the moment the glottis was seen. Time to intubation was from the moment the blade touched the patient until the ETT was visualized entering the glottis and cuff inflation. In the case of unsuccessful glottic visualization, the time continued to run until a successful intubation was performed as confirmed by sustained presence of end-tidal CO2 on the capnogram. Nonparametric statistical analyses were used for comparisons between the IDS scores and time to visualize the glottis and complete the intubation. P < 0.05 was considered statistically significant. Results Forty-five patients had normal airways, and 24 had factors predictive of difficult intubation (Table 1 and Table 2). The ages ranged from 12 to 92 yr. Manual in-line axial stabilization of the neck was used in 12 patients with known or suspected cervical spine instability, and 2 patients had halo traction for C1 and/or C2 instability. Sixty-six patients had orotracheal intubation, and three patients had nasotracheal intubation.Table 1: Patient DataTable 2: Predictive Factors of Intubation Difficulty in 24 PatientsAn IDS value of 0 (ideal intubation) occurred in 38 of 45 patients (84%) without predictive factors of intubation difficulty and in 17 of 24 patients (71%) with predictive factors of intubation difficulty (Figure 3). No trauma to the lips or teeth was noted. No new neurologic deficits occurred. Reasons for IDS score >or=to1 are shown in Table 3. A Cormack grade 1 view and successful intubation were obtained in 97% of patients by the second attempt. Only two patients had an IDS value >or=to5. One patient had sustained blunt trauma from a motor vehicle accident and had cervical spine instability. Glottic visualization with the fiberoptic device was not possible because of blood and secretions in the airway, and the trachea was intubated orally on the third attempt using direct laryngoscopy and threading the ETT over a gum-elastic bougie (IDS score 5). The other patient had a submandibular abscess extending across the midline and a limited mouth opening. Only the epiglottis could be visualized with the WuScope, despite two attempts. A third attempt with conventional direct laryngoscopy revealed a grade 4 view despite optimal sniff position, external laryngeal pressure, and extra lifting force. The patient's trachea was intubated on the fourth attempt by using a nasotracheal tube threaded over a flexible fiberscope (IDS score 11).Figure 3: Frequency histogram of the distribution of the Intubation Difficulty Scale (IDS) scores in patients with and without predictive factors of intubation difficulty.Table 3: Median Time to Tracheal Intubation and Reasons for Intubation Difficulty Scale (IDS) Score >or=to1There was a significant relation between IDS score and time to glottic exposure and intubation (P < 0.0002, Kruskal-Wallis test). In patients with an IDS score of 0, the median (25th-75th percentiles) time for glottic exposure was 16 s (14-30 s), and time to intubation was 38 s (25-57 s). In patients with an IDS score >or=to1, time for glottic exposure was 55 s (30-114 s), and time to intubation was 103 s (56-146 s). Discussion In this study, we demonstrated that fiberoptic laryngoscopy using the WuScope was associated with relatively easy glottic exposure and tracheal intubation, even in patients with anatomic factors that would normally prevent adequate visualization of the vocal cords. The WuScope had been previously used in approximately 300 adult patients to facilitate oral and nasal tracheal intubation, including 48 cases of difficult intubation [2]. No failures were reported in the initial series, despite the large number of patients with Mallampati airway classification 3 and 4, and other instances of difficult intubation, such as failed conventional direct laryngoscopy, receding jaw, short mandibular ramus, history of difficult intubation, caudal larynx, limited mobility of the temporomandibular joint, and small atlantooccipital gap [2,4]. Reported advantages of the WuScope were an oropharyngeal airway-shaped blade to allow glottic visualization without the need for head extension, tongue lifting, or forceful jaw opening; modified handle-to-blade angle (110[degree sign]) for easy entry into the oropharynx; a tubular blade structure to protect the fiberscope from secretions, blood, and/or redundant soft tissue; a built-in ETT passageway through which the ETT can be advanced without a stylet; and a bivalve element that can be excluded to allow the use of the device for nasotracheal intubation [2]. Another advantage of the WuScope is that, unlike flexible fiberoptic endoscopes, one can continuously view the ETT as it advances through the glottic opening into the trachea. In the present study, there were no requirements for external laryngeal manipulation, extra lifting force, patient repositioning, or stylet when using the WuScope. Rather, small adjustments were often required to align the ETT with the glottis before advancing the ETT. This was done by manipulating the tubular blade sideways or advancing, withdrawing, or lifting the blade slightly. Other minor difficulties were also encountered in the present study. Fogging of the fiberscope was overcome by removing the WuScope and gently wiping the tip of the fiberscope with an alcohol pad and applying more antifog solution. Secretions in the airway could often be removed by applying continuous suction through a 14F or 18F catheter placed just beyond the distal tip of the ETT. Softening the ETT in warm water before inserting it through the tubular passageway obviated the need for external lubrication of the ETT and eliminated the problem of ETT cuff tear. Although we have found the WuScope laryngoscope to be extremely useful in patients with anatomical predictors of difficult intubation, its limitations include a high initial cost ($9800 for the blades, handle, flexible fiberscope, and extender), the introduction of new cleaning and disinfecting routines, the cost of repairing the fiberscope, the requirement for learning and mastering new skills, the requirement for a fiberoptic light source, blood in the airway, and the time required to assemble and disassemble the device. Complications from rigid laryngoscopy are also possible, and a 20-mm mouth opening is minimally required to insert and maneuver the device. We are grateful to Frederic Adnet, MD, PhD, for reviewing the manuscript; Joan F. Hagen, BA, and Alfred C. Pinchak, MD, PE, PhD, for assistance with statistical analyses; and Tom Roach and Ken Rick for their support.