The anaesthetist has available a number of tools and techniques for management of difficult airways. The choices made for an individual patient will depend on whether the difficult airway was anticipated, the skill base of the anaesthetist and the particular features that render the airway difficult. On occasion an anaesthetist may be faced with a rapidly deteriorating situation where they have been ‘drafted in’ to retrieve a situation such as a severe facial trauma in the emergency department or swollen tongue with anaphylaxis.
The GlideScope® (Saturn Biomedical System Inc, Burnaby, British Columbia, Canada) is a new video laryngoscope, which may be a useful tool in difficult airways, however, published data in patients is limited [1,2] being in the form of case reports and short series. The paucity of data reflects the difficulty of studying rare, severe events in a comparative manner. Simulators offer the ability to consistently reproduce rare or adverse events without fear of patient harm and thus are particularly well suited to the evaluation of equipment that may be useful in these circumstances.
The GlideScope (Fig. 1) is a unique laryngoscope with a video camera built into its blade; it also comes with its own light source and liquid crystal display (LCD) on a mobile stand. The laryngoscope is a reusable device made of a resilient plastic material that can withstand repeated cold sterilization. It is recommended that a 60° angled stylet is used with the tracheal tube following the angle of the blade. When the tracheal tube is in the glottis the stylet needs to be withdrawn 2–3 cm prior to advancing it further into the trachea.
The GlideScope is designed to facilitate tracheal intubation by displaying an unobstructed view of the patient's glottis on its monitor (GlideScope Product information), showing cord visualization and tracheal tube placement.
The aim of our study was to determine whether the GlideScope improved the view at laryngoscopy and ease of ‘intubation’ when used on an Airman™, a Laerdal difficult airway simulator. Also it was to discover whether anaesthetists thought the GlideScope would be useful in clinical practice if faced with one of these scenarios.
Thirty anaesthetists from our department in Christchurch hospital were recruited for the study. Anaesthetic grade and previous experience of the GlideScope were recorded.
A description and demonstration of the GlideScope was first given to the anaesthetist using the standard product training manikin but no formal tuition was given. Anaesthetists were allowed a short practice with the GlideScope using the product training manikin until they were comfortable with its use prior to going onto the difficult airway simulator.
The Airman™ simulator (Laerdal Medical Ltd, Kent, UK) is a difficult airway manikin consisting of a head and torso unit with pneumatically actuated airway states. The four base states are normal, pharyngeal obstruction, cervical rigidity and tongue oedema. The manikin produces a high level of difficulty in even the individual pathological base states and using combinations it is possible to render the manikin unintubatable.
The four base modes of the AirMan manikin were used: normal, pharyngeal obstruction, cervical rigidity and tongue oedema. The subject was asked to insert either a bougie or a stylet (pre-angled to 60°) through the vocal cords first using a standard metal size 3 Macintosh laryngoscope then the GlideScope. We accepted the passage of a bougie or stylet through the larynx into the trachea as a surrogate for successful passage of a tracheal tube. We found when planning the study that adhesion between the plastic of the tracheal tube and the plastic of the manikin's oropharynx introduced an additional level of difficulty into already difficult scenarios.
There were no time restrictions but the anaesthetists were encouraged to treat the manikin as a real patient. The correct position of the bougie or stylet was checked by the investigator after each scenario.
Participants were asked to state the best view obtained with both the Macintosh and the GlideScope according to our scoring system (a modified version of the Cormack and Lehane scoring system). This was chosen to standardize the exact view seen (Fig. 2).
Ease of ‘intubation’ as judged by the anaesthetist was also recorded on a 5-point rating scale: 1 very easy, 2 easy, 3 moderate, 4 difficult, 5 impossible. After each scenario the anaesthetist was asked ‘If this scenario occurred in real life, do you think the GlideScope would be a useful tool to have available?’
Unfortunately the manikin's tongue broke during the 12th volunteer meaning that the tongue was unable to swell up for the ‘tongue oedema’ scenario. A new part was obtained, fitted and the study was completed.
The 30 anaesthetists consisted of 13 Registrars (>6 months in anaesthesia) 2 Senior Registrars and 15 Consultants. Only two participants had seen the GlideScope being used in clinical practice previously. The results of the view obtained and ease for the Macintosh and GlideScope are shown in Table 1 for each of the four scenarios.
Specialist statistical advice was sought and two approaches were taken to analysing the data. The sign test simply looks at whether the GlideScope improved or worsened the view or ease when compared to the Macintosh for each of the scenarios (Table 2). In the pharyngeal obstruction scenario 43% (n = 13, P = 0.02) of anaesthetists had an improvement in the view with the GlideScope compared to the Macintosh blade. In the other scenarios no statistically significant results were obtained in view or ease.
Applying the t-test shows the average improvement in view with the GlideScope compared to the Macintosh and the 95% confidence intervals (CI) (Fig. 3). An improvement in view with the GlideScope was seen in the pharyngeal obstruction scenario (average 0.5, P = 0.006), all the scenarios grouped together (average 0.4, P = 0.004) and the tongue oedema before the manikin broke (average 1.8, P = 0.003). The improvement in view with the GlideScope was lost after the manikin was mended.
After their experience with the manikin, 93% of participants thought the GlideScope would be a useful tool to have available if faced with one or more of the studied scenarios in their own clinical practice.
The GlideScope has been shown to improve the view in 23 out of 50 patients as compared to the Macintosh blade in ‘normal airways’ . In a recent study using a human being patient simulator, anaesthetists found it faster and easier to intubate with the GlideScope compared to the Macintosh blade in the Grade 3 (difficult) laryngoscopy scenario . The GlideScope product information makes claims to be the answer to the difficult airway and resolve ‘airway anxiety’.
We used simulation to allow comparative study of the GlideScope and Macintosh laryngoscopes in extremely challenging scenarios. It is unlikely that a clinical study of this nature would be feasible by virtue of the relative infrequency of these events clinically and the ethical difficulties in these acute situations. Our study demonstrated that for the pharyngeal obstruction scenario and the pooled abnormal airway scenarios the GlideScope offered a statistically significant (P < 0.05) improvement in view of at least one grade in our scoring system. Our study failed to demonstrate any improvement in ease of intubation despite these instances of an improved view. This failure of improved view to translate into greater ease may reflect the need to acquire skill in manipulating instruments under ‘indirect’ vision. This is similar to the new skills required of a surgeon when embarking on laparoscopic surgery compared with conventional open surgery, and would support the regular use of these sorts of airway tools to ensure skilled use in an emergency. In planning the study we had chosen to use a stylet or bougie to avoid the additional difficulties introduced by plastic on plastic adhesion between the tracheal tube and the manikin. However, we are aware that placing a bougie or stylet has its limitations in being a true surrogate for intubation with a tracheal tube.
Another perspective arises if one considers our study data as a series of case reports or anecdotal reports from colleagues in a department. It can then be seen that when approaching a case with tongue oedema, on canvassing colleagues or reviewing case reports, approximately 20% would report a worse view with the GlideScope, 40% an equivalent view and 40% an improved view. On the basis of this statistically non-significant result one might still conclude that having the GlideScope available for use when managing the scenario reasonable. This reflects the fact that clinical judgement considers balance of probability and makes decisions in light of general evidence as applied to the individual case at hand. It also recognizes that no airway management technique is a panacea and that plans may evolve with a changing clinical scenario. Therefore, the highly positive response to the statement ‘If this scenario occurred in real life do you think the GlideScope would be a useful tool to have available?’ It could be argued that this response is likely to be encountered as most anaesthetists have a ‘kitchen sink’ approach to the difficult airway, and would be likely to welcome any addition to the airway armamentarium. The distinction of the GlideScope would lie in its ability to be used as a first line device with potential for improving view (as demonstrated in part by our data) as opposed to, for example, a transcricoid puncture device which would have a high potential success rate but would generally be regarded as a last resort. Video laryngoscopes have been suggested in recent difficult airway guidelines as an alternative technique in difficult intubations .
The subset of tongue data from before the equipment failure shows a highly significant benefit from the GlideScope on the basis of the t-test. This is not maintained after the repairs. While disappointing from the point of view of our study it raises an interesting point with regard to this type of study. Manikins are manufactured items and therefore would be considered likely to be homogenous. Indeed, a study could be designed using multiple manikins to allow high throughput or multiple study locations, in the belief that the results between manikins could be strictly comparable. Our misfortune demonstrates that manikins may need to be considered in some respects as variable as patients and thus trials should be based on a single manikin, over relatively short study period.
The lack of randomization of order of the study is also a potential area of criticism of our study. This effect would likely manifest as the subjects learning the scenario during their first exposure with the Macintosh and then applying this during their attempt with the GlideScope. The decision not to randomize was deliberate as we wished to base our study on likely real life usage of the equipment. Therefore, it is likely that in a difficult scenario, laryngoscopy would have been initially attempted with a Macintosh blade before trying the GlideScope. If the ambition of simulation is to mimic a real world event then incorporating the real world learning effect of an attempted laryngoscopy (if it exists) is reasonable.
The flexible fibrescope is often seen as the gold standard for the predicted difficult intubation . Interestingly the GlideScope has recently been described as an alternative in the awake intubation [7,8]. This may appeal to for those without fibre optic skills looking for another alternative. The GlideScope is easy to learn and use . It has an antifogging device, is able to deal with secretions (GlideScope Product information) and is robust and hence less susceptible to damage. One of the limitations of the GlideScope here is that the patient needs to be able to open their mouth, the GlideScope being 1.8 cm at its maximal width. Its use has been described in a patient with only 2.5 cm mouth opening .
The GlideScope provides an excellent picture of the glottis along with visualization on the vocal cords and passage of the tracheal tube through them. This could be useful in teaching junior anaesthetists, medical students and paramedics removing the ‘look over my shoulder’ method. Once a good view with the GlideScope is obtained such things as cord relaxation, correct insertion of the tracheal tube, etc. could be demonstrated. It has been suggested that the ‘video display should be standard with teaching intubation techniques’ . However, as has been mentioned, skill with tracheal tube placement under direct vision might not automatically translate into skill when using an indirect video scope system.
In conclusion, the GlideScope improved the view in one of three difficult airway situations when used by anaesthetists with no formal training in its use. No single airway device offers a solution to all scenarios. However, we consider that the GlideScope is a useful addition to the range of difficult airway devices available.
Work was carried out at Christchurch Hospital, Christchurch, New Zealand. We would like to thank Dr J.E. Wells, Biostatistician, Christchurch School of Medicine; Mrs D. Salisbury, Bamford & Co. Ltd., for the loan of the GlideScope and Mr J. McMurray, Laerdal for the loan of the manikin.
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