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• W2146298977 abstract "Since the introduction of the Macintosh blade, several attempts have been made to modify and improve laryngoscopes, but the fundamental technique of laryngoscopy has remained unchanged. The basic principle has always been to align the three axes – oral, pharyngeal and laryngeal – to obtain a straight line of view. Attempts at adapting new imaging techniques for laryngoscopy were also made over the years. Higgins and colleagues first described a direct laryngoscopy video system, the Airway Cam [1]. It consisted of a headframe-mounted miniature camera, connected to a video monitor. More specialised rigid indirect laryngoscopes, such as the Bullard and Wuscope, were also introduced, but achieved limited success [2, 3]. This was mainly because of little demonstrable advantage in managing the difficult airway, high initial costs and lack of a shared view. With further improvements, it became possible to produce video chips that could link directly to displays without the need for bulky optical cameras. This led to the introduction of a range of videolaryngoscopes that allow anaesthetists literally to ‘see around corners’. The design and technology are continuing to evolve, with portable versions and miniature camera systems suitable for neonatal use now becoming available [4]. Videolaryngoscopes resemble a traditional laryngoscope, but have a video chip embedded in the blade. The video chip transmits magnified images to a display screen where they can be seen and recorded. The fundamental difference is that the laryngeal view is generated indirectly with a videocamera focused at the laryngeal inlet, and alignment of the oral, pharyngeal and laryngeal axes (i.e. a line of sight) is not essential to view the glottis. Videolaryngoscopes differ from optical laryngoscopes such as the Airtraq, which do not have a videocamera, and in which the image is generated by a series of optical lenses and prisms. The image can be displayed on a remote screen or on a monitor attached to the laryngoscope itself. When performing laryngoscopy, the first step is to determine whether one can see the vocal cords and in that respect, videolaryngoscopes certainly fulfil their promise. There is a large amount of data, from both normal and simulated difficult airways in patients, demonstrating that videolaryngoscopes consistently give a better view of the larynx than conventional direct laryngoscopes [5–8]. This is because the image is captured using a camera with a wide-angled lens positioned close to the vocal cords [9]. A better view is often assumed to facilitate intubation; however, with videolaryngoscopes, there is evidence that insertion of the tracheal tube through the vocal cords may be difficult despite the improved view. Several factors contribute to this. The distal parts of the blades of the Glidescope and McGrath, and the D-blade of the C-MAC laryngoscope – a Macintosh laryngoscope with an integrated videocamera – are angulated with a sharp anterior deflection. This focuses the camera towards the larynx, giving a better view of an anterior or high larynx. This view does not reflect the difficulty encountered while advancing the tube, when the acute anterior curve in the oropharynx has to be negotiated to reach the vocal cords. Also, oropharyngeal tissues do not need to be retracted and compressed to achieve a straight line of sight; this may limit the airspace available for manipulating the tracheal tube. In addition, videolaryngoscopy requires a degree of hand–eye coordination and practice is needed to develop the skill needed for advancing the tracheal tube while viewing the monitor. These problems are being addressed by both manufacturers and investigators, and pre-shaped stylets that match the distal curve of the blade and direct the tube anteriorly are now available [10, 11]. In videolaryngoscopes with an integrated tube channel, the tracheal tube is placed in a slot adjacent to the camera and after a good view is achieved, theoretically, the tube then has merely to be advanced further to reach the glottis. It is plausible that this could make directing the tracheal tube easier, although there is very limited evidence to support this assumption. On analysing the evidence on videolaryngoscopy, one of the principal problems is the lack of a specific evaluation system based on difficulty in inserting the tracheal tube. Some studies have used the Cormack and Lehane grade, or its modifications, as a primary endpoint for comparison. A poor view has been validated as a marker for difficult intubation using conventional laryngoscopes, but does not necessarily reflect the degree of difficulty in intubation using videolaryngoscopes, where the main problem lies in directing the tracheal tube [12]. This can also be assessed using surrogate markers such as the number of attempts required, the need for intubation aids and the time required, but their definition has also been variable. In addition, some of the laryngoscopes have been modified in the short time that they have been available, invalidating some of the earlier results. Moreover, a large amount of evidence comes from manikin studies or small heterogeneous clinical trials, where very few of the recruited patients presented any genuine difficulty in intubation [13, 14]. So, is videolaryngoscopy useful in managing the difficult airway? Does it work when direct laryngoscopy fails and when fibreoptic intubation is not possible? Videolaryngoscopes are robust, easy to use and the set-up time is minimal. This will certainly be of advantage when direct laryngoscopy presents unexpected difficulty. It will also be ideal for managing difficult airways in remote locations, where skilled assistance or specialised equipment such as fibrescopes is not always available. The recent 4th National Audit Project (NAP4) reiterated that repeated attempts at intubation using the same technique risks causing further complications [15]. Case reports suggest that videolaryngoscopes are useful in rescuing failed direct laryngoscopy in both adults and children [16, 17]. What about patients with pre-existing risk factors for difficulty? The evidence here is limited and comes primarily from case reports and retrospective analysis [18–24]. Prospective randomised controlled trials provide the most robust methodology to a research question. However, difficulty in both predicting and recruiting patients with difficult airways, and ethical issues in conducting trials in patients with known difficulty, present significant challenges. In children, using videolaryngoscopy is a particularly attractive solution because awake intubation may not be feasible, fibreoptic endoscopy is more difficult and the high oxygen demand limits the time available for intubation. There is some evidence from case reports describing successful use of videolaryngoscopes in known paediatric difficult airways, including in neonates [21–23]. In a large retrospective study, Aziz et al. evaluated the effectiveness of the Glidescope in adults with predicted difficult laryngoscopy [24]. Patients were identified as potentially difficult direct laryngoscopic intubations if they had a thyromental distance < 6 cm, mouth opening < 3 cm, pre-existing neck pathology (from mass, surgical scar or radiotherapy), morbid obesity, Mallampati score 3 and 4 or limited neck extension. They found the Glidescope to be successful as a primary device in 98% (1712/1755) of cases and as a rescue device in 94% (224/239) of cases of failed direct laryngoscopy [24]. Interestingly, in 28/60 patients in whom the Glidescope failed, intubation was achieved using direct laryngoscopy. The strongest predictors of failure using the Glidescope were presence of airway pathology from previous surgery, local mass and scarring following radiotherapy, suggesting that videolaryngoscopes might not make intubation any easier in severe upper airway distortion caused by malignancy or extensive oropharyngeal infection. Furthermore, although the camera is enclosed, it is still possible that active bleeding and copious secretions may obscure the view, with implications in airway trauma and bleeding. Similarly, videolaryngoscopy will clearly not be useful if mouth opening is very limited, as an interdental gap of at least 18–20 mm is required to insert even the narrow blades. There is convincing evidence that with cervical immobilisation, videolaryngoscopy results in consistently superior views of the larynx. In a randomised control trial of 120 patients with cervical spine immobilisation, Malik et al. found that both the Airway Scope and the Glidescope provided better laryngeal exposure and reduced the need for optimisation manoeuvres compared with the Macintosh laryngoscope [25]. However, perhaps as view alone does not necessarily correlate with ease of intubation, the time required for intubation was longer. In contrast, other studies have shown that the time needed for intubation with the Airway Scope is comparable to, or even shorter than, that using the Macintosh laryngoscope. This has been attributed to shorter time needed for laryngeal exposure [26, 27]. Theoretically, aligning the three axes by neck flexion and atlanto-occipital extension is not required for laryngeal exposure. This would support using videolaryngoscopes in cervical spine injury. However, the available evidence gives conflicting results with regard to the degree of movement seen. On fluoroscopic analysis in patients with manual in-line stabilisation, Maruyama et al. found a significant decrease in movement at the occiput-C1, C1-2 and C3-4 levels with the Airway Scope compared with the Macintosh laryngoscope [28]. In two small prospective studies in patients with normal airways and with no cervical spine pathology, the movement of the cervical spine with the Glidescope was not significantly different at the occiput-C2 level compared with the Macintosh laryngoscope, although it was reduced by 50% at the C2-5 level [29, 30]. Interestingly, the Lo-Pro Glidescope, a low-profile modification of the Glidescope designed to give more space in the oropharynx, produced greater cervical spine movement than fibreoptic intubation in patients without cervical spine immobilisation [31]. In summary, cervical spine movement is generally less when videolaryngoscopes are used and the laryngeal view is also improved. In the absence of data suggesting improved neurological outcome with any one particular technique, we can only conclude that videolaryngoscopy is a potential alternative solution when the fibreoptic option is not possible. One of the most significant advantages of videolaryngoscopy is the improvement in teaching and training. Studies have shown that for novice trainees, the learning curve for direct laryngoscopy does not plateau above a 90% success rate until a mean of 57 attempts, and even after this, there is an 18% failure rate in difficult cases [32, 33]. In recent years, with restricted working hours and widespread use of supraglottic devices, the opportunities available for teaching tracheal intubation have markedly reduced. One of the main problems in teaching laryngoscopy is the lack of a shared view. Video-assisted teaching has been shown to be particularly useful in the verbal-cognitive stage of learning [34, 35]. Videotechnology allows both the instructor and the trainee to view the airway anatomy simultaneously and the trainer can then demonstrate the intubation process at the same time. Most trainees achieve acceptable proficiency in normal patients with traditional teaching. Nevertheless, teaching using videocamera systems allows critical appraisal of the technique and effective feedback that can greatly assist in the acquisition of the good skills necessary when dealing with a difficult or pathological airway. In a prospective trial, using video-assisted instruction for teaching novices with the C-MAC laryngoscope, 69% of intubation attempts were successful when video-assisted instruction was used, whereas 55% were successful using traditional training [36]. This implies that videolaryngoscopy could potentially shift the learning curve to the left [36, 37]. Videoimaging also improves the identification of anatomical structures by novice trainees and any unusual anatomy is much better appreciated with the enlarged image on the monitor [38]. Operating theatre personnel are more engaged and the anaesthesia assistant can also simultaneously see how best to optimise the view, should external laryngeal manipulation be needed. Learning is also helped by recording the procedure for critical analysis later. In paediatric anaesthesia, it is even more difficult to obtain a shared view and therefore images displayed on a remote screen are particularly useful. The 2010 curriculum for the Certificate of Completion of Training in Anaesthesia of the Royal College of Anaesthetists requires that senior trainees in airway management should be able to: ‘discuss and demonstrate the use of novel methods of laryngoscopy. This includes videolaryngoscopes’ [39]. The curriculum does not mention any specific videolaryngoscope. A recent North American survey suggests that videolaryngoscopes are widely used for training residents; a similar audit in our region showed that trainees had very limited exposure and experience of using them [40]. More than eight videolaryngoscopes are commercially available; these differ in their ease of use and function. Purchase of equipment in most anaesthetic departments is governed partially by the acquisition costs and also by individual preferences, with equipment rarely purchased primarily for teaching [41, 42]. With the continued introduction of more videolaryngoscopes – two were introduced in the last year alone – it is important to reach consensus and decide which devices we will be teaching our trainees to use. Benchmarking standards that define competence and proficiency will also need to be established. So, while there are clear benefits in teaching, the place of videolaryngoscopy in the whole range of difficult airway problems has not yet been fully explored. Direct laryngoscopy is likely to remain our primary skill, and fibreoptic intubation the principal technique for managing a difficult airway. However, videolaryngoscopes, with their relatively short learning curve, could potentially bridge the gap between these two established techniques. Videolaryngoscopes do not currently figure in any of the difficult airway algorithms; however, preliminary reports describe a promising role in failed laryngoscopy and possibly as a primary technique in certain presentations. Researchers have so far focused on examining the differences from direct laryngoscopes, improvement in teaching and use in normal airways. We now need to move to the next phase and fully evaluate their clinical use in difficult airways, using prospective studies or by collating observational data. The risk of failure and markers that predict difficulty in intubation using videolaryngoscopes also need to be identified. Finally, new videolaryngoscopes with very similar design features are being introduced, often with limited clinical evidence to support their use – some do not have a single clinical trial to demonstrate their effectiveness. It is vital to compare the relative effectiveness and safety of the available videolaryngoscopes. This will enable us to define the clinical role and limitations of each device and help the clinician to make clear choices at a time of rapid developments in airway management techniques. Only then can this emerging technique make the leap from being another new toy in the hands of a few enthusiasts to being used in everyday clinical practice by the majority of anaesthetists. No external funding and competing interests declared." @default.
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• W2146298977 title "Laryngoscopy: time to shed fresh light?" @default.
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