Expanding clinical applications of augmented reality laryngoscopy: a need for further exploration and validation
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We write in to response to the comments provided by Orrock and Ward [1] and Inoue et al. [2] on our article [3]. In our preliminary research, we did not conduct a strict randomised controlled trial. Instead, we recruited 15 volunteers to evaluate the comfort, visual satisfaction and overall satisfaction of using different laryngoscopes for tracheal intubation. We acknowledge the difficulty of blinding operators in such studies and the limitations of using models in airway studies, particularly their lack of tissue plasticity. This can affect blade lifting and require the operator to be closer to the model for an appropriate glottic view. Currently, we are conducting a randomised controlled trial to assess the clinical usability and efficacy of the augmented reality laryngoscope. Regarding the concerns about image bias and non-standard tracheal intubation techniques, the positions depicted in our article, although different from those preferred by Orrock and Ward, are used commonly in our clinical practice. A review of relevant recent tracheal intubation videos on the internet revealed similar techniques, suggesting that these variations may be due to individual practice habits [4, 5]. We agree that musculoskeletal strain related to laryngoscopy is a common issue in anaesthesia, and propose a multifaceted approach to mitigate this [6]. This includes standardised training; adopting the head-up (semi-Fowler's) position; using pillows/neck supports for optimal cervical flexion/extension; adjusting the operating table height; and designing novel laryngoscopes and tracheal intubation protocols using artificial intelligence [7, 8]. Inoue et al. have also rightly pointed out the potential influence of practitioner experience on the ergonomics and effectiveness of augmented reality laryngoscopes, a factor our initial study did not address. Novice practitioners tend to exhibit greater forward flexion and head movement during tracheal intubation compared to experts, regardless of the laryngoscope used. This difference is particularly evident when comparing Macintosh and videolaryngoscopes, with novices often requiring more substantial adjustments to achieve an adequate glottic view. However, experienced anaesthetists also exhibit variations in their tracheal intubation techniques due to factors including habit and vision issues. We appreciate the insights and agree that failing to account for operator experience could limit the applicability of our findings. Augmented reality technology may offer greater benefits to less experienced practitioners by providing a more intuitive and visual representation of the laryngeal anatomy. Viewing an enlarged, three-dimensional image of the larynx without adjusting posture could facilitate learning and improve technique among novice anaesthetists. The use of videolaryngoscopes with articulable and rotatable screens is noted. However, during our clinical use of an integrated videolaryngoscope, the screen is not at eye level, requiring downward head movement for adequate visualisation. The screen's size necessitates proximity for clear viewing, highlighting the difference from augmented reality glasses that allow for eye-level operation. Further exploration of the impact of practitioner experience on the use of augmented reality laryngoscopes is essential. Future studies should include a broader range of participants, encompassing both novice and experienced anaesthetists, to comprehensively assess the benefits and challenges of this emerging technology. This will help tailor the design and training protocols for augmented reality laryngoscopes to meet the needs of practitioners at all skill levels. We share the concern about using industrial endoscopes instead of clinically designed devices. In our ongoing research, we are collaborating with manufacturers to develop a clinical grade augmented reality laryngoscope tailored for patient use. Tracheal intubation practices can vary widely across regions; experience levels; clinical settings; and operational constraints. Our goal was not to dismiss the clinical value of direct or videolaryngoscopes but to introduce an innovative augmented reality laryngoscope and compare it with existing tools. We believe our augmented reality laryngoscope represents a novel concept that could revolutionise tracheal intubation practices. We are eager to collaborate with anaesthetists worldwide to create a portable, fully developed head-mounted display system for augmented reality laryngoscopy, enhancing the tracheal intubation experience and safeguarding the wellbeing of both anaesthetists and patients.Keywords:
Laryngoscopes
Summary The effectiveness of two laryngoscopes, the English Macintosh and the Flexiblade (a levering laryngoscope), were compared in a clinical setting. An investigation was carried out in 100 patients admitted for surgery under general anaesthesia, to compare intubation with the Flexiblade or the Macintosh laryngoscope. The patients had two anatomical characteristics that may predict difficult intubation – Mallampati score II and III, and a thyromental distance ≤ 6.5 cm. Patients were randomly allocated to receive intubation with one of the laryngoscopes. The laryngeal view obtained during laryngoscopy, the intubation time, and the need for optimization manoeuvres and assistance required were compared in the two groups. The correlation between intubation time and anatomical characteristics was determined. Only 49 patients had a poor laryngeal view during initial laryngoscopy and required additional facilitating manoeuvres. In these patients, successful intubation time (in seconds) using the Flexiblade was significantly shorter than using the Macintosh laryngoscope (median 14.3 s, IQR 6.3 vs. median 20.8 s, IQR 10.5) (p < 0.01). Assistance and additional manoeuvres were required significantly less frequently in the Flexiblade group (21%) compared to Macintosh group (67%) (p < 0.01). No correlation was found between intubation time, Mallampati scores, thyromental distance, or body weight. We concluded that in patients with an initial poor laryngoscopic view, the Flexiblade may enable faster and easier tracheal intubation.
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We investigated whether the use of two different video laryngoscopes [direct-coupled interface (DCI) video laryngoscope and GlideScope] may improve laryngoscopic view and intubation success compared with the conventional direct Macintosh laryngoscope (direct laryngoscopy) in patients with a predicted difficult airway.One hundred and twenty adult patients undergoing elective minor surgery requiring general anaesthesia and endotracheal intubation presenting with at least one predictor for a difficult airway were enrolled after Institutional Review Board approval and written informed consent was obtained. Repeated laryngoscopy was performed using direct laryngoscope, DCI laryngoscope and GlideScope in a randomized sequence before patients were intubated.Both video laryngoscopes showed significantly better laryngoscopic view (according to Cormack and Lehane classification as modified by Yentis and Lee = C&L) than direct laryngoscope. Laryngoscopic view C&L >or= III was measured in 30% of patients when using direct laryngoscopy, and in only 11% when using the DCI laryngoscope (P < 0.001). The GlideScope enabled significantly better laryngoscopic view (C&L >or= III: 1.6%) than both direct (P < 0.001) and DCI laryngoscopes (P < 0.05). Clinically relevant improvement in the specific 36 patients with insufficient direct view (C&L >or= III) could be achieved significantly more often with the GlideScope (94.4%) than with the DCI laryngoscope (63.8%; P < 0.01). Laryngoscopy time did not differ between instruments [median (range): direct laryngoscope, 13 (5-33) s; DCI laryngoscope, 14 (6-40) s; GlideScope, 13 (5-34) s]. In contrast, tracheal intubation needed significantly more time with both video laryngoscopes [DCI laryngoscope, 27 (17-94) s, P < 0.05 and GlideScope, 33 (18-68) s, P < 0.01] than with the direct laryngoscope [22.5 (12-49) s]. Intubation failed in four cases (10%) using the direct laryngoscope and in one case (2.5%) each using the DCI laryngoscope and the GlideScope.We conclude that the video laryngoscope and GlideScope in particular may be useful instruments in the management of the predicted difficult airway.
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Summary A new laryngoscope has been designed, incorporating an adjustable mirror and a levered tip similar to the McCoy blade, in an attempt to bridge the gulf between simple direct laryngoscopy and fiberoptic laryngoscopy. Manual in‐line neck stabilisation was used to simulate difficult laryngoscopy in 14 anaesthetised patients after full neuromuscular blockade. The best view at laryngoscopy was assessed using a standard Macintosh laryngsocope, a size 3 McCoy laryngoscope and the mirrored laryngoscope. The best laryngeal view obtained in all cases with the Macintosh blade was a grade 3. The mirrored laryngoscope improved this view in 10 cases (71%) compared with five cases (36%) with the McCoy laryngoscope (p = 0.005); in seven cases (50%), the view improved to a grade 1 compared with no cases when the McCoy was used (p = 0.02). We conclude that the mirrored laryngoscope offers considerable advantages over the Macintosh and the McCoy laryngoscopes in simulated difficult laryngoscopy, is simple to use and requires no special training.
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The authors, each with 40 years of experience in laryngology, aim to lay out the general principles and details of a systematic method of direct laryngoscopy for adults, children, and infants. Advances in laryngoscope design and application, advantages of telescopes, use of the operating microscope, and principles of modern anesthesia are highlighted. Particular reference is made to classification of laryngoscopes, advantages of Lindholm laryngoscopes, suspension laryngoscopy, the principles of biopsy, and problems of laryngoscopy. The difficult airway and the obstructed airway are discussed in detail. With the recent renewed interest in investigation and treatment of laryngeal problems and a better understanding of laryngeal physiology and voice production, the future will, no doubt, see new procedures to treat and restore laryngeal function. The fundamentals in this report form a basis for direct laryngoscopy, endolaryngeal microsurgery, laser surgery, and phonosurgery.
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We thank Drs Butchart and Young for their interesting comments on our paper [1], and welcome the opportunity to respond to these comments. We agree with the authors that there is a learning curve with regard to the acquisition of skills with all laryngoscopes, and a decay curve with regard to loss of skills over time. However, these skills appear to be acquired more quickly, and lost less quickly, at least with the Airtraq laryngoscope, when compared with the Macintosh laryngoscope [2, 3]. With regard to our study, the authors are correct in that, while the participants used the devices in random order, the order in which the scenarios were attempted was not randomised. Tracheal intubation attempts with each device were first performed in the easy laryngoscopy scenario, followed by the difficult laryngoscopy scenario. Therefore, it is possible that a learning effect was seen when using the Glidescope laryngoscope. However, this was not seen when testing the other videolaryngoscopes, namely the C-MAC and Airtraq laryngoscopes. We agree that there may be advantages to using videolaryngoscopes that incorporate the Macintosh laryngoscope blade, given its familiarity to anaesthetists, and our results in this study do provide some support for that premise [1]. However, these findings need to be replicated in clinical studies, both of easy and predicted difficult laryngoscopy. In addition, it must be remembered that other videolaryngoscopes that incorporate novel blade curvatures and structures, particularly the Airtraq [4–6] and Pentax laryngoscopes [7–9], have performed well in clinical studies of both easy and difficult laryngoscopy, and hold significant promise as alternatives or backup devices to the Macintosh laryngoscope. We are not aware of the Venner AP Advance laryngoscope, and could find no published data regarding this device. Ultimately, we believe that anaesthetists should be expert in the use of more than one type of laryngoscope, and should not limit themselves to the use of laryngoscopes based on the Macintosh blade. The optimal ‘secondary’ laryngoscope (or ‘primary’ laryngoscope, for that matter) that anaesthetists should use will depend on several issues, and remains an active area of investigation. No external funding and no competing interests declared. Previously posted at the Anaesthesia Correspondence website: http://www.anaesthesiacorrespondence.com.
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The C-MAC comprises a Macintosh blade connected to a video unit. The familiarity of the Macintosh blade, and the ability to use the C-MAC as a direct or indirect laryngoscope, may be advantageous. We wished to compare the C-MAC with Macintosh, Glidescope and Airtraq laryngoscopes in easy and simulated difficult laryngoscopy. Thirty-one experienced anaesthetists performed tracheal intubation in an easy and difficult laryngoscopy scenario. The duration of intubation attempts, success rates, number of intubation attempts and of optimisation manoeuvres, the severity of dental compression, and difficulty of device use were recorded. In easy laryngoscopy, the duration of tracheal intubation attempts were similar with the C-MAC, Macintosh and Airtraq laryngoscopes; the Glidescope performed less well. The C-MAC and Airtraq provided the best glottic views, but the C-MAC was rated as the easiest device to use. In difficult laryngo-scopy the C-MAC demonstrated the shortest tracheal intubation times. The Airtraq provided the best glottic view, with the Macintosh providing the worst view. The C-MAC was the easiest device to use.
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Video laryngoscopes have been introduced in recent years as an alternative choice to facilitate tracheal intubation. Difficulties with tracheal intubation are mostly caused by difficult direct laryngoscopy with impaired view to the vocal cords. Many endoscopic intubation laryngoscopes have been designed to visualize the vocal cords around the corner looking through a proximal viewfinder. Although they are useful devices, they have limitations for doing direct laryngoscopy and are very expensive, hence they are not used for routine tracheal intubation.
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Airway management is one of the greatest anaesthesiologic challenges. Direct laryngoscopy using a standard McIntosh laryngoscope has been the predominant intubation choice for many years. Videolaryngoscopy is becoming a widely accepted airway management technique owing to its potential advantages over direct laryngoscopy including a better view of the larynx, reduced tracheal intubation time and educational value. We present an overview of the currently most used optical and video-assisted laryngoscopes with a special focus on the McGrath Series 5 videolaryngoscope.
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The C-MAC comprises a Macintosh blade connected to a video unit. The familiarity of the Macintosh blade, and the ability to use the C-MAC as a direct or indirect laryngoscope, may be advantageous. We wished to compare the C-MAC with Macintosh, Glidescope and Airtraq laryngoscopes in easy and simulated difficult laryngoscopy. Thirty-one experienced anaesthetists performed tracheal intubation in an easy and difficult laryngoscopy scenario. The duration of intubation attempts, success rates, number of intubation attempts and of optimisation manoeuvres, the severity of dental compression, and difficulty of device use were recorded. In easy laryngoscopy, the duration of tracheal intubation attempts were similar with the C-MAC, Macintosh and Airtraq laryngoscopes; the Glidescope performed less well. The C-MAC and Airtraq provided the best glottic views, but the C-MAC was rated as the easiest device to use. In difficult laryngo-scopy the C-MAC demonstrated the shortest tracheal intubation times. The Airtraq provided the best glottic view, with the Macintosh providing the worst view. The C-MAC was the easiest device to use.
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