Swift Conversion from Laryngoscopic to Fiberoptic Intubation with a New, Handy Fiberoptic Stylet

Because it is difficult to accurately predict a difficult airway during a preoperative evaluation, unexpected difficult airway cases occur. Several classification and scoring methods have been proposed to predict the difficult airway, but the accuracy of these methods has not always been satisfactory. For example, Calder et al. [1] reported that the available tests have a sensitivity of approximately 50%. Benumof [2] noted that unexpected airway difficulty often occurs and that better routine predictors of airway difficulty are needed. Fiberoptic endotracheal intubation is a reliable approach for difficult airway management. In many institutes, however, fiberoptic devices are prepared on request only, when anesthesiologists or emergency physicians recognize that the airway of a patient will be difficult to intubate using routine approaches (e.g., a direct laryngoscopic approach). Such decisions are often made only after the induction of anesthesia, and the delay in setting up the equipment can lead to fatal sequelae, especially when ventilation via a mask is difficult. In addition, special training is necessary to operate the flexible fiberscope efficiently in emergency settings [3]. Handy fiberoptic stylets have a malleable shaft that accommodates a bundle of optic fibers. The viewing window is set on the top of the shaft, and a light source is set on one side (Figure 1). Because of the compact design, a physician acting alone can operate this device without difficulty. When the physician determines that the airway is easy to intubate by direct laryngoscopic viewing, a tracheal tube can be advanced through the vocal cords according to standard procedures. When the physician determines that the airway will be difficult to intubate using a direct laryngoscopic approach, he or she can then view the vocal cords through the eyepiece on the top of the stylet. Only a few seconds are required to make the change in approach. Further, no special training is required to use this device. This is the first fiberoptic device to work without cables and to function simultaneously as a stylet and as a fiberscope. In this study, we examined the usefulness of the fiberoptic stylet in clinical settings.Figure 1: Fiberoptic stylet 482 mm in length and 160 g in weight. The malleable shaft was 395 mm in length and 5.4 mm in diameter. The light source housing was attached to the main body at the base of the eyepiece. A tracheal tube stopper was attached to the proximal end of the shaft. The stylet can be inserted into tracheal tube, which has an internal diameter wider than 6.5 mm.Methods A custom model fiberoptic stylet was tailor-made by Machida Instrument Inc. (Tokyo, Japan). The stylet was 482 mm long and weighed 160 g. The malleable shaft was 395 mm long and 5.4 mm in diameter. The viewing angle was 80[degree sign], and the optical focus was 5-50 mm. The light source housing was attached to the main body at the base of the eyepiece. To allow the tracheal tube to be properly held in place, a tracheal tube stopper was attached to the proximal end of the shaft. Before using this system, approval of the local ethics committee and informed consent from all patients were obtained. No patient was undergoing emergency surgery. In a preoperative examination, the anatomy of the upper airway was classified according to Mallampati's criteria [4]. Data were obtained consecutively over 3 mo, and intubation time was measured in the first 18 patients with airways graded Cormack's I or II and in 16 patients with airways graded III or IV. Anesthesia was induced by using 2 mg/kg propofol, and muscle relaxation was accomplished by using 0.15 mg/kg vecuronium. Tracheal tubes set on the fiberoptic stylet in advance (Mallincklodt; Aethelone, Ireland) were 7.0-8.5 mm in diameter. After relaxing the muscles, a Macintosh direct laryngoscope was inserted through the mouth, and visualization of the vocal cords was attempted according to standard procedures. The final view obtained by the direct laryngoscope was classified according to Cormack's criteria [5]. When direct visualization was possible by direct laryngoscope (Cormack's grade I or II), tracheal intubation was completed according to standard procedures. When direct visualization was impossible by direct laryngoscope (Cormack's grade III or IV), the tracheal tube set on the fiberoptic stylet was inserted beyond the tongue along the blade of the laryngoscope. Next, viewing of the vocal cords was attempted, again through the eyepiece. The location of the vocal cords was determined by moving the top of the tracheal tube. When the vocal cords were aligned with the center of the field of view, the tube was inserted through the vocal cords until the tracheal cartilage rings were observed through the eyepiece. Patients with airways grade III or IV were subdivided into IIIa, IIIb, and IVa according to the first view through the fiberoptic stylet (Table 1). In patients with grade IIIb airways, in whom no distance was observed between the epiglottis and the posterior wall of the pharynx, movement and rotation of the top of the stylet and lifting the jaw further using the laryngoscope were required to visualize the vocal cords.Table 1: Patient DemographicsData are expressed as mean +/- SD. The data obtained from the patients with grade I, II, and IIIa airways were statistically analyzed by using one-way analysis of variance with Scheffe's post hoc test. Results Patient demographics were not different among groups (Table 1). In patients with grade I and II airways, the intubation time using a fiberoptic stylet was 28 +/- 9 s. The duration of the fiberoptic stylet intubation in patients with grade IIIa airways (30 +/- 8 s) was not significantly longer than that in patients with grade I or II airways. Only three patients with grade IIIb and one patient with grade IVa airways were studied. Patients with grade IIIa, IIIb, and IVa airways are listed in Table 2. Patient 1 underwent surgery twice in 3 mo. In the first operation, it took 89 s to intubate the patient's trachea using McCoy's direct laryngoscope. In the second operation, it took 40 s to intubate the patient's trachea using the fiberoptic stylet. Patient 6 underwent a tracheostomy at a different hospital due to a difficult airway. Patients 10 and 11 were determined by a separate anesthesiologist to have difficult airways that could not be intubated using a direct laryngoscopic approach. In Patient 14, the curb of the stylet was not appropriate for intubation on the first attempt. After a readjustment of the curb of the shaft, intubation was completed within 19 s.Table 2: Patients with Grade III and IV AirwaysDiscussion In the present study, we demonstrated that intubation time using a fiberoptic stylet is approximately 20-30 seconds, almost the same duration required for routine direct laryngoscopic intubation, even in patients with grade IIIa airways. The delay in grade IIIb airway patients may be due to the time required to insert the tube with the stylet beyond the epiglottis, given that there is no distance between the epiglottis and the posterior wall of the pharynx. However, the delay was only 30 seconds, and because it takes a significant amount of time to prepare the bulky fiberoptic system, this delay seems to be acceptable. At no point in this study was there a patient in whom intubation was impossible when using this fiberoptic stylet. However, as was practically demonstrated in several cases, the tracheas of most patients with grade III and IV airways were extremely difficult or impossible to intubate using a routine direct laryngoscopic approach. Therefore, the fiberoptic stylet seems to offer a useful means of reducing the risk of fatal airway trouble. Vacanti and Roberts [6] reported that simultaneous use of a stylet and a flexible fiberscope was useful for difficult airway intubation. They noted that a certain stiffness of the stylet was necessary for proper airway management. Fiberoptic stylets have a dual function as both a stylet and a fiberscope. With this device, anesthetists need not insert both the stylet and the fiberscope into the narrow internal space of a tracheal tube. Using a fiberoptic stylet, a physician can control the direction of the tube with one hand while using the other hand for jaw lifting by a direct laryngoscope. In most of the present cases, the anesthetists concluded that jaw lifting using a direct laryngoscope was extremely useful for improving viewing and allowing for a swift insertion of the tracheal tube (Figure 2). For extremely difficult cases, a combination of McCoy's direct laryngoscope and a fiberoptic stylet should be considered as an option. In Patient 15 (Table 2), an anesthetist experienced difficulty in performing the intubation with the fiberoptic stylet and had to replace the tracheal tube with a narrower one. At this point, intubation could be completed without difficulty. Even when performing an intubation using a fiberoptic stylet, the size of the tracheal tube seems to be critical in some cases.Figure 2: Intubation by fiberoptic stylet (a direct laryngoscope is used for jaw lifting). Using a fiberoptic stylet, a physician can control the direction of the tube with one hand while using the other hand for jaw lifting by a direct laryngoscope. The jaw lifting was extremely useful for improving viewing and allowing for a swift insertion of the tracheal tube.