The participants were briefly informed that there was an unconscious and already very cyanosed patient lying on the floor, needing urgent tracheal intubation. Movement of the manikin was not allowed, so the only option to perform tracheal intubation was the use of the ‘ice pick-position’.15
The devices used to perform tracheal intubation in this scenario were Macintosh #3 laryngoscope for direct laryngoscopy (reference method); Airtraq Size 3 (Prodol SA, Madrid, Spain); Ambu Pentax Airway Scope (Ambu, Copenhagen, Denmark); Storz C-MAC with a Macintosh 3 blade (Storz Medical, Tuttlingen, Germany); McGrath Series5 (Airway Medical, Glasgow, UK); and GlideScope Ranger with GLV 3 Stat blade (Verathon Medical, Bothell, USA).
A lubricated Mallinckrodt 7.0 mm internal diameter tracheal tube was used for all intubation attempts. To facilitate intubation, a preformed semi-rigid tube guide was already inserted into the tracheal tube in all attempts made with the Storz C-MAC, McGrath Series5 and Macintosh laryngoscopes. The GlideRite rigid stilette was used in all attempts with the GlideScope (as recommended by the manufacturer). The Ambu Pentax AirwayScope and the Airtraq have tube guidance channels and these devices were used without any additional tube guides (as recommended by the manufacturer).
Each participant used all devices in a randomly assigned order. Device assignment was implemented by means of carefully shuffled sealed opaque envelopes for each participant, to make sure that there was no learning effect in the course of the study. All devices were provided ‘ready to use’ (i.e. the devices were switched ‘on’ and the correct blade was attached to the device, where applicable) and all necessary items (resuscitation bag, lubricated tube – with inserted stilette if applicable – and 5-ml syringe to inflate the cuff) were within reach.
The Cormack and Lehane grading (best obtainable view of the glottis as reported by the participant) was used to classify visualisation of the glottis.16 To achieve secure tracheal intubation with visualisation of the tube passing through the vocal cords, a view of the glottis corresponding to a Cormack and Lehane grade I (>50% of the vocal cords visible) or II (<50% or vocal cords or only posterior tips of arytenoids visible) is usually required.
The primary end-point was time from first device contact until the first successful ventilation (detected by a positive signal of inflation of the manikin's lungs or – if unsuccessful – stomach). Secondary end-points were the success of the intubation attempt (i.e. tracheal or oesophageal tube position) and the time until a sufficient view of the glottis was obtained.
A sample size of 20 was found sufficient to detect effect sizes (δ/σ) of 0.6 to 0.7 with about 80% power at a two-sided significance level of 5% (paired t-test). Statistical analysis was performed with SPSS (IBM SPSS 20.0, IBM Corp., New York, USA). The Wilcoxon signed-rank test was used to compare the times needed for glottic view and first ventilation. Success rates for tracheal intubation were compared using the McNemar test. P values of less than 0.05 were deemed statistically significant.
Twenty anaesthesiologists (13 men and seven women, mean age: 31.1 ± 3.7 years) with a mean experience in anaesthesiology of 5.1 ± 3.9 years served as participants in this study. All participants were experienced and regularly involved in ground and helicopter-based out-of-hospital emergency medical service missions.
A good view of the glottis (Cormack and Lehane grade I or II) was achieved by all participants with all devices. It was achieved most rapidly (mean ± SD) with the GlideScope (8.5 ± 4.7 s), followed by the Storz C-MAC (11.3 ± 7.3 s), Airtraq (12.8 ± 7.7 s), Macintosh (14.5 ± 20.4 s), Pentax AWS (17.3 ± 12.3 s) and McGrath Series5 (19.6 ± 18.7 s). Evaluation with the Wilcoxon signed-rank test revealed no statistically significant differences between the devices and the reference method (Fig. 3).
The time to first ventilation with the reference method, the standard Macintosh laryngoscope, was 36.1 ± 13.4 s. The use of the Airtraq achieved the fastest time to first ventilation (31.0 ± 14.7 s; n.s.); the Pentax AWS (44.8 ± 31.9 s; n.s.) and Storz C-Mac (49.7 ± 31.1 s; n.s.) achieved comparable times. The use of the McGrath Series5 (54.8 ± 31.5 s, P = 0.023) and GlideScope Ranger (61.0 ± 45.0 s, P = 0.01) led to significantly longer times until first ventilation was achieved (Fig. 4).
Despite a good view of the glottic structures and the vocal cords, attempts to place the tracheal tube in the trachea were unsuccessful in one attempt with the Airtraq and Pentax AWS devices, in two attempts with the Storz C-MAC and GlideScope Ranger and in three attempts with the McGrath Series5 (all n.s.), whereas this never occurred with the Macintosh laryngoscope.
Unrecognised misplacement of the tube into the oesophagus occurred with the Pentax AWS and Storz C-MAC (each n = 1), Macintosh (n = 2) and McGrath Series5 (n = 4), whereas it did not occur with the Airtraq or GlideScope Ranger.
When comparing overall intubation success (Fig. 5), the McNemar test revealed a significantly higher rate of successfully placed tracheal tubes with the Airtraq than with the McGrath Series5 (P = 0.031).
All failed intubation attempts are marked with red dots in Fig. 4. The same participants (who later proved to be unsuccessful) have also been marked with a red dot in Fig. 3, when they reported to have a sufficient view of the glottis to perform tracheal intubation.
Conventional tracheal intubation using direct laryngoscopy is a skill that requires continuous practice and is quite difficult to learn.4 Therefore, a large number of successfully performed intubation attempts is usually required.17 Additional regular training to maintain these skills during daily routine is also essential.4,18 Because a misplaced tracheal tube can have deleterious consequences for the patient,19,20 there is a need for high quality airway management to ensure patient safety. Tracheal intubation with video laryngoscopes is a skill that can be achieved much more rapidly, with higher success rates even for untrained or inexperienced users,10,21 which makes it particularly interesting for emergency medicine. In addition, the time needed to achieve ventilation of the lungs through a secured airway must be kept as short as possible. Usually, the available time for securing the airway by tracheal intubation is limited by a decrease in arterial oxygen saturation to a critical level. Even with adequate preoxygenation, time is limited to a maximum of 3 to 5 min before critical (i.e. life-threatening) desaturation occurs.22
Verification of the correct tube position by auscultation is not sufficient,23 especially in the noisy environment often surrounding medical emergencies. In addition to the obligatory detection of expiratory carbon dioxide by capnography,24 visual observation of the tracheal tube passing through the vocal cords is considered a safe sign of correct tracheal intubation.25 Visibility of the anatomy of the glottis and vocal cords is usually essential for tracheal intubation. In the airway manikin used, a Cormack and Lehane grade I view can be achieved in the standard position by a laryngoscopist of average experience. When using three of the video laryngoscopes, the vocal cords could be visualised more rapidly than when using the reference method, but two achieved the view more slowly. However, the differences in time are not statistically significant. In this study, all participants reported that they were able to achieve good views of the glottis and vocal cords with all devices. Consequently, all participants should have been able to visualise the tracheal tube passing through the vocal cords, resulting in all tracheal tubes being inserted correctly. It may thus be assumed that other factors have a significant impact on the success of tracheal intubation. Difficulties in introducing a tracheal tube despite a good view of the anatomical structures have been reported with video laryngoscopes.9,26
Ventilation of the manikin was achieved most rapidly when using the indirect Airtraq laryngoscope, followed by the reference method using direct laryngoscopy with the Macintosh blade. The use of the GlideScope Ranger and McGrath Series5 laryngoscopes led to significantly longer times until first ventilation. This difference was not present at the time of obtaining a view of the glottis and the handling of the devices may have been disadvantageous in this scenario.
When using video laryngoscopes, some of the participants were unable to insert the tracheal tube between the vocal cords or advance it into the trachea. This occurred once with the Airtraq and Pentax, twice with the Storz C-MAC and GlideScope Ranger and three times with the McGrath Series5, but never occurred when using direct laryngoscopy. However, our results were not statistically significant, and larger trials are needed to clarify the importance of this finding.
Unrecognised oesophageal misplacement of the tracheal tube did not occur when using the Airtraq and GlideScope Ranger, but occurred once with the Pentax AWS and Storz C-MAC laryngoscopes, twice with direct laryngoscopy (the reference method) and four times with the McGrath Series 5. This is a surprising finding, as an experienced anaesthesiologist should be able to insert the tracheal tube into the trachea when obtaining a good view of the glottis. In this scenario, we believe that this may represent a strong influence of the position and the lack of experience in handling of the devices.
Although there are studies that describe the ice-pick position as advantageous over other intubation positions in out-of-hospital emergency medicine,8 several difficulties of this technique became obvious in our study. In contrast to the standard position for laryngoscopy, the laryngoscope has to be held in the right hand and the tube is inserted with the left hand. This is very awkward if not regularly practised. Furthermore, the image of the video screen of the video laryngoscopes appears mirror-inverted, which has to be considered when introducing the tube.13 Turning the screen upside down is not possible in some devices (Airtraq, Pentax AWS, or McGrath) and this may have contributed to the failure of tube placement despite a good glottic view in a number of participants in the present study.
Even highly trained and experienced participants were unable to achieve a 100% success rate using some laryngoscopes. In contrast, overall failure rates (including impossibility to insert the tube and unrecognised oesophageal placement) were alarmingly high. In cases when access to the head from above is not possible, alternative airways such as supraglottic airway devices (e.g. laryngeal mask or laryngeal tube) must be considered as a first-line airway device for the inexperienced and must be available as an immediate second-line airway in case of failed tracheal intubation by emergency medicine providers.27–29
Influence of laryngoscope type
In this study, two different types of video laryngoscope were used. Some laryngoscopes (GlideScope Ranger, McGrath and Storz C-MAC) are used like a conventional Macintosh laryngoscope, whereas others (Pentax AWS and Airtraq) require a different kind of handling.
Pentax AWS and Airtraq have a guidance channel for the tracheal tube, which is integrated in the blade for laryngoscopy. The tracheal tube should be preinserted into the guidance channel before starting laryngoscopy. After visualisation of the vocal cords, the tube needs only to be advanced forwards and will then pass through the vocal cords.
When compared with video laryngoscopes with a conventional blade, the devices with a guidance channel required longer times before the glottic structures could be visualised. Although not statistically significant, the time needed for first successful ventilation was fastest with the Airtraq and comparable with the Pentax AWS. Taken together, the time from view to successful ventilation through the successfully placed tracheal tube was shortest with the two devices with the tube guidance channel. The failure rates in devices with a guidance channel were lowest of all (Airtraq) or comparable with the reference method (Pentax AWS). Taken together, in this specific setting, the use of devices with a guidance channel seems to offer advantages over devices that require conventional tube handling. To speculate, it might be possible that eliminating the mirror-inverted visibility by using video laryngoscopes with a guidance channel improves time to successful ventilation as well as success rate and reduces the number of unrecognised oesophageal tube positions.
There are several limitations that apply to the present study. First, the study was performed in a manikin and not in patients. Although it would be very helpful to gather data for patients, the present study design with randomisation of intubation devices would not be feasible for a clinical trial. Second, experienced anaesthesiologists/emergency physicians performed intubation in the present study. Therefore, the results may not be applicable to less experienced physicians. Third, the airway manikin used was equipped with a standard airway and had no difficult airway. Fourth, although the sample size was statistically sufficient for analysis, larger clinical studies seem to be required to validate our results.
In this manikin study with anaesthesiologists experienced in out-of-hospital emergency medicine, we were able to show that video laryngoscopes did not facilitate tracheal intubation in a faster or more secure way than conventional laryngoscopy in the ice-pick position. The use of the Airtraq and GlideScope Ranger video laryngoscopes was associated with no unrecognised oesophageal intubation in contrast to all other devices used in this study. Despite the high acceptance of video laryngoscopes in cases of difficult intubations within a hospital, video laryngoscopes did not improve the overall success rate of tracheal intubation in this scenario.
Assistance with the study: none declared.
Financial support and sponsorship: this work was supported by the Department of Anaesthesiology and Intensive Care Medicine, University Hospital of Cologne, Germany. There was no financial support by any of the companies mentioned in this study or any external partners. JH has received travel expenses from Ambu GmbH, Germany, and The Surgical Company BV, The Netherlands, during the last 5 years. The other authors do not have any conflict of interest to declare.
Conflicts of interest: all devices used were provided free of charge by the manufacturers or distributors, and were returned after the study. The sole role of the manufacturers was to provide the devices until the end of the study. There was no other assistance, financial support or sponsorship by any of the companies. None of the companies was involved in designing, planning or execution of the study, in analysis of the study data or in writing of the manuscript. The authors alone are responsible for the content and writing of this article.
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