Difficult intubation remains a problem in approximately 1–2% of the population and the majority of these are associated with limited view at laryngoscopy [1,2]. In such situations, the use of the Eschmann multiple-use introducer (EMUI) (Eschmann Healthcare Tracheal Tube Introducer, SIMS Portex, Hythe, Kent, UK) is a popular and effective choice amongst anaesthetists in the UK [1,3,4]. A recent prospective survey found the EMUI to be considered effective although occasionally several attempts were required prior to achieving successful intubation . The EMUI is not necessarily used routinely elsewhere. In the USA for instance, in a survey of members of the ASA of their practice in managing difficult airway scenarios, less than 5% would use the EMUI .
There are numerous ways to aid intubation; transillumination using a lightwand is a technique that has been shown to be safe and effective in patients with difficult airways [6-9]. Currently this device is not used commonly. The technique uses transillumination of the soft tissues of the anterior surface of the neck in order to accurately locate the tip of the lightwand within the trachea and therefore facilitate blind intubation. Correct placement of the tip of the lightwand produces a characteristic light in the subglottic area. If the tip is wrongly sited, the light is more diffuse. Once placement of the lightwand is achieved the tube can be railroaded over the lightwand into the trachea.
One feature of this technique is that it does not require direct laryngoscopy but provides a visual confirmation of correct placement. However, there is evidence that the combination of direct laryngoscopy with the lightwand may be of use . The main disadvantage is that the successful use of a lightwand requires experience for which there is a steep learning curve in addition to which, the user would need to maintain their skills by regular use of the device [9,10]. The lightwand may also not be as effective in those patients with either anatomical abnormalities to their airway or those with fixed or obese necks .
The Trachlight® (Laerdal Medical Corporation, New York, USA) (Fig. 1) is a lightwand that has already been shown to be effective as an adjunct in the management of simulated difficult intubation . We wanted to compare the Trachlight® with the EMUI which is used as the first choice in the management of difficult intubation in the UK. Previous studies have compared the use of an EMUI with a stylet in difficult intubations and found it to be more effective [11,12], but there are no studies comparing the EMUI with the Trachlight®. The only way to compare the lightwand with the EMUI is with simulated difficult intubation. The effect of simulated difficult intubation on passage of the lightwand is unknown.
We conducted a randomized crossover study, to compare the use of the EMUI with the Trachlight® in patients with simulated difficult intubations. After gaining ethical approval from the Bro Taf Local Research Ethics Committee, we obtained written informed consent from 64 ASA I–II patients who were undergoing elective surgical procedures requiring intubation. Patients were excluded if there was a history of difficult intubation or difficult intubation was anticipated. Pregnant patients and those with known gastro-oesophageal disease were also excluded. Patients were then randomized using a computer generated randomization code (Labview version 2.1; National Instruments Corporation, Austin, Texas, USA), into one of two groups: Group One was intubated using the EMUI first, followed by the Trachlight®; Group Two the reverse. The simulated intubation and subsequent passage of the chosen introducer were performed by a single-handed anaesthetist (KH or RD).
The EMUI used was the re-usable 15 Ch × 60 cm tracheal tube version (Sims Portex, Hythe, UK), each being used up to five times. The EMUI was preformed to a curve prior to insertion. Clicks and/or hold-up were sought to confirm placement but these signs were not formally documented.
The Trachlight® is a battery powered lightwand, comprising three separate parts: the handle, the lightwand and a stylet. The wand in this study was re-usable up to 10 times. The temperature of the light reaches a maximum of 55°C, and after 25 s, the light starts blinking to minimize heat production and the risk of thermal damage to the oropharyngeal mucosa . The use of the Trachlight® involves preloading the chosen tracheal tube onto the lightwand, and ensuring that the light is just proximal to the distal end of the tube. The distal end is preformed into a ‘hockey stick configuration’ and it is then ready for use. A more detailed explanation of use of the Trachlight® can be found elsewhere .
After instituting full monitoring, 100% oxygen was administered for 3 min. Anaesthesia was induced and the patient given a muscle relaxant (of the anaesthetist's choice). Response to a train of four was monitored at the wrist using a peripheral nerve stimulator and, when there were no twitches, direct laryngoscopy was performed. The best laryngoscopic view obtained was classified according to the Modified Cormack and Lehane, i.e. 1 (full view of glottis), 2a (partial view of glottis), 2b (arytenoids or posterior cords only), 3 (epiglottis only) or 4 (neither glottis or epiglottis visible) . The laryngoscope was then lowered to simulate a Grade 3 view. Intubation was attempted using both the EMUI and the Trachlight® in a randomized order, up to 60 s being allowed for each intubation. When the EMUI was used the attempt included the passage of the EMUI and the tracheal tube. If during intubation, it was necessary to remove and reform the device before continuing, this was considered as a second attempt. The total duration of all attempts was limited to 60 s. Anaesthetists were allowed multiple attempts within this time, with reforming of devices allowed at the discretion of the anaesthetist. After each intubation attempt success or failure was confirmed by direct laryngoscopy.
The intubations were performed by either one of two anaesthetists (KH or RD), both of whom had practised with the Trachlight® 15 times prior to starting the study. The cuff of the tracheal tube was not inflated between intubations in order to minimize trauma. Between successive intubations, patients were oxygenated for 1 min.
Any bench study using simulated difficult intubation produces identical test conditions for the items of apparatus that are tested. However in a clinical study using simulated difficult intubation, there is always the potential for introducing observer bias and having slightly different Grade 3 views for the items being investigated. This is unavoidable but this test model is being used with increasing frequency both in vitro and in vivo; it is the only one we have.
Primary outcome was success or failure of intubation within 60 s. Time to achieve intubation was recorded from insertion of the EMUI or lightwand into the patient's mouth until successful intubation, as confirmed with capnography. If repeated attempts were required, these were also included in the time. The need to recurve or reform any device prior to successful placement was noted. Both anaesthetists also rated the ease of intubation with each device on a 10-point scale, ranging from 1 being easy, to 10 being difficult.
Times to intubation were described as mean (SD); ease of intubation as median (interquartile range). Data was analysed using the McNemar test for success or failure, Wilcoxon signed rank sum test for non-parametric data for the time to intubation and the ease of intubation and χ2 -test for number of attempts at intubation. The study had a power of 0.85 of showing significance at the P < 0.05 level, using a projected success rate of 0.8 in the EMUI Group .
A total of 64 patients were recruited. The patient characteristics data are as shown in Table 1. Intubation failed in only one patient of the 64 patients using either technique. Once both devices had been tested, the laryngoscopic view reverted to the best obtainable and this patient was then intubated without difficulty. All other patients were successfully intubated by one or both methods.
The intubation success rates are as shown in Table 2. Using the EMUI, 62 of the 64 attempts (96.8%) were successful, compared to 60 of 64 (93.7%) with the Trachlight®. There was no significant difference between the EMUI and the Trachlight® (P =0.63). Time required to achieve intubation was longer with the Trachlight®, the mean difference being 6 s, which was significant with P < 0.001 (Table 2). The mean time required for intubation on the first attempt with the Trachlight® was 18.4 s compared to 14.4 s with the EMUI.
The spread of individual times to intubation for each device are shown in Figure 2. Within 20 s, 84% had been successfully intubated using the EMUI, compared to 61% using the Trachlight®. Intubation was considered easier with the EMUI (median 1 [1,2] vs. 2 [1-3]) than with the lightwand. This was assessed on a 10-point scale, rated from easy to difficult and the results are shown in Figure 3.
Fifteen of sixty-one patients had a postoperative sore throat, 11 mild, 4 moderate. Two patients were lost to postoperative follow-up due to ITU admission. There were no incidences of dental or obvious mucosal damage.
This data demonstrate that the EMUI is a faster means to intubation than the Trachlight® in simulated difficult intubation, the mean difference between the times being 6 s which did show statistical significance. Despite this, we have demonstrated that, with respect to the primary outcome of success or failure, there is no significant difference between the two devices.
It is questionable whether a significant difference only in the time required to intubate can be considered clinically significant and therefore of relevance to practise. A mean difference of only 6 s is minimal in terms of successful outcome and no episodes of desaturation occurred during the attempts at intubation in this study. Indeed, this difference is probably of little significance, especially when the steep learning curve associated with the use of the Trachlight® is taken into consideration. A study by Ellis and colleagues  in 1986 looking at times to intubation with a lightwand, found that mean time for the first 25 patients was 42 s as compared to 32 s for the subsequent 25. Studies on the Trachlight® itself confirm a need for repeated use to develop and maintain skills [9,16]. The operators in this study had only limited experience with the Trachlight® were therefore still on the learning curve and thus their mean time could show improvement with further use.
Intubation times with the Trachlight® in our study are comparable or better than those in other studies. A similar study looking at intubation using the Trachlight® in simulated difficult laryngoscopy in 300 patients showed a 78% success rate with the average time for the first attempt (mean (SD)) required being 11.8 (2.3) s . This study was performed by anaesthetists well versed in the use of the Trachlight®. Thus our figures of 79.7% for first pass success and a mean (SD) 18.4 (10.1) s for time of first attempt are probably acceptable given the disparity in experience with the device between the two studies. Intubation times with the EMUI in our study were also comparable or better than those in previous publications. A study looking at intubation times using the EMUI in simulated Grade 3 laryngoscopy found a median time of 32 s  compared to a median time of 13 s in our study.
The anaesthetists in this study generally found intubation easier when using the EMUI than when using the Trachlight®. Both anaesthetists routinely use an EMUI within their normal practice to assist in difficult laryngoscopy, therefore any alternative to this procedure is likely to seem harder in comparison, particularly as the Trachlight® requires more than just simple railroading to insert an endotracheal tube. However when considering the speed of intubation this is offset by the fact that the tracheal tube is already loaded on the Trachlight® whereas with the EMUI a few additional seconds are taken up as the tube is loaded after placement of the device in the trachea.
The potential role which the Trachlight® could play in anaesthetic practice needs to be considered. Currently the majority of intubations are performed using direct laryngoscopy alone (2) and that situation is likely to continue. For the small percentage of intubations that require an alternative technique, there are a number of options. In the situation of unexpected difficult intubation, the EMUI is the first choice for UK anaesthetists [1,4,18]. The EMUI is a very simple piece of equipment. It requires no power source and it is readily available in every UK anaesthetic room. It is available in both re-usable and disposable forms; a desirable feature with the necessary move towards single-use equipment. Two clinical signs have been shown to be of use in confirming tracheal placement of the EMUI are the: presence of ‘clicks’ and ‘hold-up’, which in combination, are very sensitive in determining correct position [15,19]. Another advantage of the EMUI is that it';s use is not limited to those patients who are not at risk of regurgitation. It is considered to be the first choice when faced with unexpected difficulties during rapid sequence inductions . The disadvantages are the fact that it can be a blind process, resulting in very rare instances of trauma [21,22]. There have however been concerns regarding sterilization of the EMUI [23,24]. The Association of Anaesthetists has recommended the adoption of single-use items . There is evidence however that some single-use introducers may not be as effective as the EMUI [26,27] and those tested had greater potential for trauma .
The Trachlight® has already been shown to be a useful device for intubation. In experienced hands, it has a high success rate [6,16], and is available as a single-use item. The use of the Trachlight® may reduce the incidence of sore throat postoperatively . The fact that intubation can be achieved without laryngoscopy may lessen cardiovascular stimulation, but studies show conflicting results [29-31]. The main problem for anaesthetists is the need to use the Trachlight® on a regular basis to achieve and maintain skills. The availability of the Trachlight is however limited in the UK and the USA [32,33]. This limits its usefulness and when faced with a difficult intubation, most anaesthetists in the UK will continue to choose the familiar and readily available EMUI as their first choice. In addition, lightwands have been shown to be more difficult to place when cricoid pressure is applied, prolonging the time to intubation . The lightwand may be contra-indicated in the presence of a full stomach as in a darkened room reflux of stomach contents may not be immediately noticed . This seriously limits the applicability of the device. These issues are likely to prove the main deterrent to the use of the Trachlight®, though the device performed well in this study. It seems unlikely however that the EMUI with its ready availability [3,36], high success rate [1,4] and ease of use in will be displaced from anaesthetic practice by the Trachlight® in the foreseeable future.
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