GENERAL ARTICLES;TECHNOLOGY, COMPUTING, AND SIMULATION: Research Report
Difficulty is often encountered during oral tracheal tube exchange with a tube exchanger (TE) after one-lung anesthesia or long-duration endotracheal intubation in an intensive care unit. Many studies have reported that obstruction of the tube at the arytenoid cartilage or right vocal cord was the main reason for the difficulty (1–6). During fiberoptic intubation, the design of the tracheal tube and the diameter of the fiberscope influence the passing ability of the tube. The purpose of this study was to compare the ease of passage of two different tubes through the glottis during introducer-guided intubation. One tube was a conventional polyvinyl chloride tube with a standard bevel with the leading edge at the side, and the other was a newly designed tube with a hemispherical bevel and the leading edge in the midline. In addition, we investigated the effects of introducer thickness on the passage of each tube.
After institutional approval and informed consent from each of the 92 patients included in the study were obtained, patients (ASA physical status I–II) scheduled for elective surgery under general anesthesia were included in this study. Uncooperative patients and patients with pulmonary diseases, cervical spine fracture, or tumors and polyps in the upper airway were excluded from the study. The patients were randomly divided into 4 groups: 2.5F (n = 25), 5F (n = 23), 2.5P (n = 21), and 5P (n = 23). In groups 2.5F and 5F, a Flex-Tip™ (10.0-mm outer diameter [OD]; Parker Medical, Englewood, CO) was used. In groups 2.5P and 5P, a Profile™ (10.3-mm OD; SIMS Portex Inc., Kent, UK) was used. In groups 2.5F and 2.5P, a TE of 2.5-mm OD was used. In groups 5F and 5P, a TE of 5.0-mm OD was used.
Routine monitoring was performed, and standard anesthesia protocol was followed. Patients breathed for 3 min. Anesthesia was induced with 2 mg/kg of propofol and 2 μg/kg of fentanyl. Paralysis was induced by the administration of 0.1 mg/kg of vecuronium. Ventilation of the lungs with 100% oxygen and 3% sevoflurane via a face mask was established and continued for 3 min. The TE was then inserted into the trachea by using a direct laryngoscope. The TE and the tracheal tube were covered with a large blue cloth, such that they could not be distinguished from one another; at that time, the observer was not with the patient. After the TE was inserted, the observer was allowed into the operating room. After the laryngoscope was removed, the tracheal tube was gently railroaded over the TE into the trachea. The difficulty of tube passage was assessed by a blinded observer and graded with a four-point scale (1, no difficulty passing the tube; 2, obstruction while passing the tube, relieved by withdrawal and a 90° counterclockwise rotation; 3, obstruction necessitating more than one manipulation or external laryngeal manipulation; 4, direct laryngoscope was required). In all cases, one anesthesiologist (HM) intubated, and observation was performed by only one anesthesiologist (TK). Statistical comparisons of the demographic data were performed by analysis of variance followed by the Scheffé test. Statistical comparisons of the obtained data were performed with the Kruskal-Wallis test. Bonferroni’s correction to the Mann-Whitney ranked sum test was used to distinguish differences among groups. A probability value of <0.01 was considered to be statistically significant. The statistical data analysis was performed with StatView 5.0 (Abacus Concepts Inc., Berkeley, CA).
There were no significant differences among the four groups in terms of age, height, or weight (Table 1). The difficulties experienced while passing the tube, and the results, are shown in (Fig. 1). The P value of the Kruskal-Wallis test was <0.0001. The newly designed tube was inserted more smoothly than was the conventional tube when the 2.5-mm-OD TE was used (P < 0.01). No differences were observed between the newly designed tube and the conventional tube when the 5.0-mm-OD TE was used (P = 0.114). The thicker TE allowed smooth passage of the conventional tube into the trachea (P < 0.01). However, the difficulty of leading the newly designed tube into the trachea was not dependent on whether or not the thicker TE was used (P = 0.92). Moreover, neither airway trauma nor hypoxemia was observed with any of the tubes.
When the tubes were exchanged by using the TE, patients were usually deeply sedated, and the lungs were not ventilated. Hypoxia was probably caused in cases in which a relatively long period of time was required to exchange the tube. Repeated attempts to pass the tube through the glottis may in some cases lead to damage of the vocal cords or to bleeding of the upper airway. Reducing the tube impingement at the upper airway is important to pass the tracheal tube smoothly into the trachea. To close the tip of the tube bevel to the introducer reduces the possibilities of tube striking and hanging up on arytenoid cartilage or right vocal cord. The following three methods of filling the gap may be available to reduce tube impingement. 1) A thicker TE may be used; Hakala and Randell (7) demonstrated that a fiberscope with a thicker insertion cord is more suitable for orotracheal fiberoptic intubation because it is more likely to fill the space between the tube and the fiberscope, which would in turn reduce the incidence of impingement of the tube. 2) A thinner (smaller OD) tracheal tube may be used; Nicholas and Marsh (8) used a pediatric tube to decrease the incidence of difficult fiberoptic intubation by decreasing the distance between the fiberscope and the tube. However, using a much thinner tube to fill the gap is not practical. 3) The tube tip can be bent toward the introducer or the leading edge may be initiated at the center of the tube; for fiberoptic intubation, Jones et al. (9) used a prototype tube without a bevel that tapered conically. When this tube was positioned on the fiberscope, the gap between the leading edge of the tube and the OD of the fiberscope was minimized. Because of the minimized gap, the prototype tube did not catch on the larynx or elsewhere in the upper airway, and smooth passage into the trachea was thus enabled.
Greer et al. (10) concluded that during fiberoptic intubation, an intubating laryngeal mask airway tube with a hemispherical bevel with the leading edge in the midline could be passed into the trachea more smoothly than a conventional tube with the standard bevel design. Because the edge of this newly designed tube began at the center of the tube, the gap between the TE and the leading edge was narrow, even in cases in which a thinner TE was used. However, with conventional tube use, using a thinner TE will render the gap larger (Fig. 2).
Passage of the tube was often obstructed by the arytenoid cartilage and the right vocal cord during gum elastic bougie-guided intubation (1–6). Cossham (2) and Dogra et al. (11) observed that a counterclockwise rotation of 90° facilitated the passage of the tube through the upper airway because the bevel could slide more easily over the arytenoid cartilage. The bevel of the conventional tube leads at the right side. When the tube is rotated 90° counterclockwise, the bevel assumes an upright position. The bevel of the newly designed tube leads at the upper side, such that the same effect can be achieved as that of rotating the conventional tube 90° counterclockwise, provided that the newly designed tube is not rotated. The position of the bevel enabled the newly designed tube to pass smoothly over the TE (Fig. 3). In this study, 8 patients receiving the newly designed tube required 90° counterclockwise rotation to pass the tube. This result seems not to correspond to the hypothesis. Tubes were railroaded blindly. When the bougie was at the center of the glottic inlet, the newly designed tube would railroad smoothly. In some cases, the bougie might not be at the center of the glottic inlet. When the bougie was shifted to the right or left vocal cord, the tube would be obstructed. With a 90° counterclockwise rotation, the newly designed tube would slide over the obstacle.
Combining the methods described here would provide the greatest passing ability of the tube through the glottis. However, for various reasons, some of these methods cannot be implemented in clinical practice. For example, after one-lung anesthesia, when we exchanged the double-lumen tube for an oral tracheal tube, a thicker TE was not applicable, because the inner diameter of the double-lumen tube was very narrow and the thicker TE could not pass through it. In this trial, the newly designed tube was passed into the glottis more smoothly than was the conventional tube, even when a 2.5-mm-OD TE was used. In addition, the passing ability of the newly designed tube might not be dependent on whether a thin or a thick TE was used (according to power analysis, it will require >350 cases to confirm this hypothesis).
Murashima et al. (12) mentioned that a softer tube tip will also allow a poorly directed bevel to curve back toward the glottic inlet and should reduce the risk of impaction against the anterior tracheal wall. In theory, a better-directed, softer bevel should produce less trauma. The tip of the newly designed tube is very soft. It might contribute to smooth passage of the new tube. The newly designed tube appears to be preferable.
The limitations of this study were the following. 1) The observer was blinded to the tip and OD of the tracheal tube by the use of a blue cloth, but the anesthesiologist who intubated the tube was not blinded. 2) We used a large cloth, but the thickness of the TE was not completely blinded to the observer.
In conclusion, when we exchanged the tracheal tube by using a TE, it was necessary to fill the gap between the leading edge of the tracheal tube and the TE to reduce the incidence of impingement of the tube. In situations such as those occurring after one-lung anesthesia, when use of a thicker TE is not applicable, this newly designed taper-tipped tube with the leading edge in the midline may be considered as an adjunct to oral tracheal tube exchange, using a thinner TE as the guide for tracheal intubation.
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© 2003 International Anesthesia Research Society
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