Anaesthesia 2015, 70, 591–597
doi:10.1111/anae.12988
Original Article A comparison of fibreoptic-guided tracheal intubation through the AmbuâAura-iTM, the intubating laryngeal mask airway and the i-gelTM: a manikin study* L. J. de Lloyd,1 F. Subash,2 A. R. Wilkes3 and I. Hodzovic1,3 1 Consultant, Department of Anaesthetics, University Hospital of Wales, Cardiff, UK 2 Consultant, Department of Anaesthetics, Royal Gwent Hospital, Newport, UK 3 Senior Lecturer, Cardiff University, Cardiff, UK
Summary We compared the Aura-iTM, intubating laryngeal mask airway and i-gelTM as conduits for fibreoptic-guided tracheal intubation in a manikin. Thirty anaesthetists each performed two tracheal intubations through each device, a total of 180 intubations. The median (IQR [range]) time to complete the first intubation was 40 (31–50 [15–162]) s, 37 (34– 48 [25–75]) s and 28 (22–35 [14–59]) s for the Aura-i, intubating laryngeal mask airway and i-gel, respectively. Tracheal intubation through the i-gel was the quickest (p < 0.01). Resistance to railroading of the tracheal tube over the fibrescope was significantly greater through the Aura-i compared with the intubating laryngeal mask airway and the i-gel (p = 0.001). There were no failures to intubate through the intubating laryngeal mask airway or the i-gel but six intubation attempts through the Aura-i were unsuccessful, in five owing to a railroading failure and in one owing to accidental oesophageal intubation. We conclude that the Aura-i does not perform as well as the intubating laryngeal mask airway or the i-gel as an adjunct for performing fibreoptic-guided tracheal intubation.
.................................................................................................................................................................
Correspondence to: I. Hodzovic Email: [email protected] *Presented in part at the AAGBI Annual Congress, September 2011, Edinburgh, UK. Accepted: 22 November 2014
Introduction In the event of unexpected failure to intubate the trachea during conventional direct laryngoscopy, Plan B of the Difficult Airway Society (DAS) guidelines recommends insertion of the intubating laryngeal mask airway (ILMATM; Intavent Orthofix Ltd, Maidenhead, Berks, UK) or classic laryngeal mask airway (LMA ClassicTM; Intavent Orthofix Ltd) in order to maintain oxygenation and facilitate tracheal intubation using a fibrescope [1]. The Aura-iTM (Ambu Ltd, St Ives, Cambridgeshire, UK ) is a recently developed supraglottic airway device © 2015 The Association of Anaesthetists of Great Britain and Ireland
with integral features designed to facilitate fibreopticguided tracheal intubation. These include an anatomical curvature and wide lumen designed to allow passage of an appropriately sized tracheal tube. Markings within the device are designed to aid navigation of a fibrescope; the first mark indicates when the fibrescope tip should be manipulated in order to view the glottis, while the second mark indicates when the fibrescope tip has been advanced too far. There has been one report of successful fibreoptic-guided tracheal intubation through the Aura-i in adult patients [2], but no 591
Anaesthesia 2015, 70, 591–597
randomised studies comparing it with alternative supraglottic airway devices. The ILMA was designed to provide a superior conduit for tracheal intubation compared with the LMA Classic. It has an anatomically curved rigid airway tube, a metal introducer handle and the bowl of the device contains an ‘epiglottic elevator bar’. Although originally designed to facilitate ‘blind’ tracheal intubation, success is increased by using a fibrescope inserted through the ILMA [3–5] and it may be considered the standard device for fibreoptic-guided tracheal intubation. The i-gelTM (Intersurgical Ltd, Wokingham, Berks, UK) is a single-use disposable supraglottic airway device with a non-inflatable cuff, introduced into clinical practice in the UK in 2007. The i-gel has been evaluated for ease of insertion by novices in both manikins and patients and compares favourably with other supraglottic airway devices [6, 7]. There have been reports of the i-gel’s being used as both an airway rescue device and a conduit for fibreoptic-guided tracheal intubation in predicted difficult airways [8–10]. A manikin study evaluating the i-gel as a means of achieving fibreoptic-guided tracheal intubation showed that intubation was achieved faster and more easily through the i-gel than through the LMA Classic [11]. In a study performed in patients with an anticipated difficult airway, the i-gel compared favourably with the single-use ILMA [12]. We decided to conduct a randomised crossover manikin study to compare the Aura-i, ILMA and i-gel supraglottic airway devices with respect to the time taken to perform successful tracheal tube placement and to determine device preference.
Methods The local Research Ethics Committee were contacted and waived formal ethical review. Anaesthetists with at least one year of experience were invited to take part in the study and written informed consent was obtained from all participants. The Laerdalâ Adult Airway Management Trainer (Laerdal Medical Ltd, Orpington, Kent, UK) was used in this randomised crossover study. The size-4 Aura-i, ILMA and i-gel supraglottic airway devices were inserted by the investigators. The position of the device was then 592
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
standardised by an investigator to ensure that a complete view of the glottis was obtained with the fibrescope when inserted through the device before each intubation attempt was performed. Participants were allowed time to familiarise themselves with the equipment before commencing the study; this included a demonstration by the investigators and at least one successful tracheal intubation by the participant with each device. Each participant performed two tracheal intubations through each supraglottic airway device and the order was randomised using computer-generated software. The first intubation was performed in two timed sections. Time 1 was the time taken from picking up either the fibrescope for the Aura-i and i-gel, or the tracheal tube for the ILMA, until a view of the carina was obtained. Time 2 was the time taken from commencement of railroading the tracheal tube over the fibrescope through the supraglottic airway device until delivery of a breath to the manikin. A second intubation was performed without interruption and was timed from picking up either the fibrescope with a pre-mounted tracheal tube, or the tracheal tube for the ILMA, until delivery of a breath to the manikin. Failure was defined as an intubation time that exceeded 180 s. A 6.0-mm ID reinforced tracheal tube (Mallinckrodt, Hazelwood, MO, USA) was used to intubate through the Aura-i and the i-gel and was pre-mounted on the fibrescope by an investigator with the bevel facing posteriorly [13–15]. For tracheal intubation through the ILMA, a 6.0-mm ID silicone tracheal tube, designed by the manufacturer, was used. The technique used to intubate through the ILMA differed from the other two supraglottic devices: the tracheal tube was inserted into the airway of the ILMA until the elevator bar was lifted, before insertion of the fibrescope. For intubation through the ILMA, timing was therefore started when the participant picked up the tracheal tube. At the end of each intubation attempt, the participant was asked to score the resistance encountered to railroading the tracheal tube over the fibrescope through the supraglottic airway device. A four-point scoring system adopted from Blair et al. [16] was used: 1 = no resistance; 2 = minor resistance; 3 = marked resistance; 4 = passage of tracheal tube not possible. © 2015 The Association of Anaesthetists of Great Britain and Ireland
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
Following completion of the second intubation, the time taken to remove the ILMA was measured. This was from the participant's picking up the tube extension device to delivery of a breath to the manikin through the remaining tracheal tube, after removal of the ILMA. This time was not included in the total intubation time. After completion of the study, participants were asked to state their preferred supraglottic airway device in the event of having to manage an unexpectedly difficult intubation and also whether the integral markings within the lumen of the Aura-i assisted with performing fibreoptic-guided tracheal intubation through the device. The primary outcome measure was tracheal intubation time. A previous study [10] showed a standard deviation for intubation time of 11 s and we considered an important time difference as 10 s or more. For a p value < 0.01 and a power of 99%, we required a sample size of 30. Friedman’s test was used to analyse non-normally distributed interval scale data and ordinal categorical data. Where appropriate, the Wilcoxon signed-rank test was used for post-hoc pairwise analyses. Cochran’s Q test was used to analyse nominal data (successful tracheal intubation). The chi-squared test was used to analyse categorical nominal data (preference for a particular supraglottic airway device). Statistical analysis was performed using SPSS version 20 software (SPSS Inc., Chicago, IL, USA) and a p value < 0.05 was considered statistically significant.
Results Thirty anaesthetists participated in the study: two core trainees, 19 specialist registrars and nine consultants. The median (IQR [range]) number of years of anaes-
Anaesthesia 2015, 70, 591–597
thetic experience was 7 (4–12 [1–22]). No anaesthetist had performed fibreoptic-guided tracheal intubation through the Aura-i previously. Nine anaesthetists had previously performed fibreoptic-guided tracheal intubation through the ILMA and four anaesthetists had performed fibreoptic-guided tracheal intubation through the i-gel. The device used had a significant effect on the times taken to complete the procedures (Table 1). The time to locate the carina with the fibrescope through the selected device (Time 1) was shorter through the i-gel compared with the Aura-i (p = 0.0003) and ILMA (< 0.0001). Time 1 was also shorter with the ILMA than with the Aura-i (p = 0.005). The time to railroad the tracheal tube (Time 2) was shorter with the ILMA than with the Aura-i (p < 0.0001) and i-gel (p = 0.010). Time 2 was also shorter with the i-gel than with the Aura-i (p = 0.014). Total tracheal intubation times for the first and second intubations were shorter with the i-gel than either the Aura-i (p = 0.001 and 0.009, respectively) or the ILMA (p = 0.0002 and < 0.0001, respectively). There was no significant difference in total tracheal intubation time between the Aura-i and the ILMA for either the first or the second intubation (p = 0.60 and 0.40, respectively). Intubation time was shorter for the second, compared with the first, tracheal intubation for all three devices. Resistance to railroading the tracheal tube through the supraglottic airway device into the trachea for the first and second intubations was significantly greater with the Aura-i than with the ILMA (p = 0.009) or the i-gel (p < 0.001). Marked resistance to passage of the tracheal tube through the device (a score of 3) occurred in 16 of 60 (27%) tracheal intubations through the Aura-i, none
Table 1 Intubation times for the Aura-i, ILMA and i-gel. Time 1 was from the start until a view of the carina was obtained; Time 2 was from the start of railroading until delivery of a breath to the manikin. Values are median (IQR [range]).
First intubation (timed sections) Time 1; s Time 2; s Total time; s Second intubation (uninterrupted) Total time; s
Aura-i (n = 30)
ILMA (n = 30)
i-gel (n = 30)
p value*
19 (14–25 [8–60]) 18 (14–27 [7–144])† 40 (31–50 [15–162])†
29 (22–35 [13–48]) 11 (9–14 [6–36]) 37 (34–48 [25–75])
12 (10–15 [6–25]) 14 (11–18 [6–47]) 28 (22–35 [14–59])
< 0.0001 0.001 0.001
32 (25–36 [12–75])
31 (28–41 [20–55])
24 (21–30 [15–37])
0.001
*p values refer to overall effect of device on time (Aura-i vs i-gel vs ILMA). †Failure of railroading in two participants. © 2015 The Association of Anaesthetists of Great Britain and Ireland
593
Anaesthesia 2015, 70, 591–597
through the ILMA and 2 (3%) through the i-gel. Inability to railroad the tracheal tube through the device (a score of 4) occurred in 5 (8%) tracheal intubations through the Aura-i and none through either the ILMA or the i-gel. Two failed during the first intubation attempt and two during the second intubation attempt (all four attempts were abandoned after 180 s); one railroading failure was due to a participant’s not wishing to continue following an attempt that lasted 154 s. Accidental oesophageal intubation occurred after placement of the fibrescope in the trachea in 1 (2%) attempt through the Aura-i, despite a complete view of the glottis via the fibrescope. Successful tracheal intubation was achieved on each attempt through the ILMA and the i-gel (p = 0.002). None of the anaesthetists found the Aura-i’s markings helpful in aiding placement of the fibrescope in the trachea. Twenty-seven anaesthetists (90%) reported not utilising the markings when performing fibreoptic-guided tracheal intubation through the device. Removal of the ILMA over the tracheal tube was timed for 27 of the 30 participating anaesthetists (this time was not measured for the first three participants). The median (IQR [range]) time taken to remove the ILMA was 24.4 (21.6–28.3 [17.4–45.0]) s. The manikin’s lungs could be successfully ventilated through the tracheal tube after removal of the ILMA on each occasion, indicating continued correct placement of the tracheal tube. Five (17%) of the participants preferred the Aura-i, 5 (17%) preferred the ILMA and 19 (63%) preferred the i-gel (p = 0.001). The preference of one participant was not recorded.
Discussion We found that the time for fibreoptic-guided tracheal intubation was significantly shorter through the i-gel than either the Aura-i or the ILMA. Of the three devices assessed, participating anaesthetists stated a preference for the i-gel as a conduit for fibreopticguided tracheal intubation when managing a difficult airway scenario. There were no failures to intubate through either the ILMA or i-gel; however, six of 60 (10%) intubation attempts through the Aura-i were unsuccessful. Of these six unsuccessful intubation 594
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
attempts, five were due to railroading and one was due to oesophageal intubation. The supraglottic airway devices were placed in a standardised manner by the investigators because our aim was not to assess their placement but rather their usefulness as conduits to achieve successful tracheal intubation [17]. The first intubation attempt was divided into two timed sections in order to ascertain when, during the process of tracheal intubation, problems were encountered [10]. We measured intubation times with a different starting point for the ILMA compared with the Aura-i and the i-gel, because the ILMA has the added device-specific requirement to protect the advancing tip of the fibrescope from damage due to collision with the epiglottic elevator bar. We considered that having the tracheal tube preloaded on the fibrescope for the Aura-i and the i-gel reflected the situation in clinical practice, whereas insertion of the tracheal tube to lift the epiglottic bar would normally be performed by the anaesthetist before handling the fibrescope. Our starting points for each device reflected this. The time taken to achieve a view of the carina (Time 1) was shortest through the i-gel. It might be expected that this stage of tracheal intubation would take longer through the ILMA because of the extra step required to lift the epiglottic elevator bar before advancing the fibrescope through the ILMA tracheal tube. The time required to achieve a view of the carina was longer with the Aura-i compared with the i-gel, suggesting that manipulation of the fibrescope into the trachea may have been more difficult through the Aura-i. Time 2 (from the start of railroading until delivery of a breath to the manikin) was significantly longer through the Aura-i than through the i-gel or ILMA, suggesting a particular difficulty encountered when railroading the tracheal tube through the Aura-i. Railroading the ILMA silicone tracheal tube was faster than railroading the Mallinckrodt reinforced tracheal tube used for the other two devices. The tapered soft tip of the ILMA silicone tube appears to facilitate railroading. We found that the overall time to fibreoptic-guided tracheal intubation was significantly shorter through the i-gel than either the Aura-i or the ILMA. Tracheal intubations performed for the second time were shorter than when performed for the first time for all three devices © 2015 The Association of Anaesthetists of Great Britain and Ireland
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
Anaesthesia 2015, 70, 591–597
Aura-i Trachea Oesophagus
ILMA Trachea Oesophagus
i-gel Trachea Oesophagus
Figure 1 Radiographic images of the three supraglottic airway devices with superimposed lines demonstrating the exit trajectory from the lumen of the device. Images on the right side show the devices in situ in the manikin and their relationship to the trachea and oesophagus.
and this may reflect increased familiarity with the equipment for the second intubation. Tracheal intubation was achieved successfully on every attempt through the ILMA and the i-gel but in only 54 of 60 (90%) tracheal attempts through the Aura-i. Of the six failed intubation attempts through the Aura-i, five were due to inability to railroad the tracheal tube over the fibrescope into the trachea within 180 s and one failed intubation attempt occurred when the tracheal tube was railroaded into the oesophagus, despite a complete view of the glottis via the fibrescope. Marked resistance to railroading (a score of 3) occurred in 16 of 60 (27%) attempts through the Aura-i compared with none through the ILMA and 2 of 60 (3%) through the i-gel. Differences in the rates of successful tracheal intubation and ease of railroading may relate to the angle of exit of the fibrescope or tracheal tube from the distal portion of the device because the ILMA and i-gel both have an elevated exit trajectory. The Aura-i, by contrast, has a flatter angle of exit which may result in the fibrescope or tracheal tube’s exiting more posteriorly and heading towards the oesophagus (Fig. 1). The trajectory © 2015 The Association of Anaesthetists of Great Britain and Ireland
of tracheal tube exit from the supraglottic airway device appears to influence the success of tracheal tube placement. In a clinical study using a ‘visualised blind technique’ for tracheal intubation through an i-gel this was frequently unsuccessful because the tracheal tube abutted the posterior structures of the larynx. A more anterior trajectory appears to facilitate successful passage of the tracheal tube into the trachea [18]. There was one accidental oesophageal intubation when using the Aura-i as a conduit for tracheal intubation and this occurred despite successful placement of the fibrescope into the trachea. The most likely cause was the tracheal tube’s passing in the direction of the oesophagus, thus pushing against the mid-segment of the fibrescope and forming a loop [15], which resulted in the fibrescope’s being pulled out of the trachea by the advancing tube and subsequently entering the oesophagus. Regardless of the cause of the difficulty encountered with railroading the tracheal tube through the device and into the trachea, it is significant that difficulty occurred disproportionately more often with the Aura-i, suggesting a particular problem with this device. 595
Anaesthesia 2015, 70, 591–597
Participants expressed a preference for the i-gel over the Aura-i or the ILMA, and the Aura-i and ILMA were preferred in equal measure, despite the findings of this study favouring the ILMA over the Aura-i. This may be because of the simplicity and familiarity of the Aura-i and i-gel compared with the less familiar ILMA [19]. The manufacturer recommends removal of the ILMA after tracheal intubation [20]. Although there were no dislodgements of the tracheal tube with the ILMA in our study, this has occurred in previous clinical studies [21] and may be another reason why the ILMA was not favoured. There are limitations to our study. Firstly, the use of manikin-based studies for evaluation of airway equipment has been criticised [22]. However, we would argue that evaluation of untested devices may be better performed on an appropriate manikin in order to identify devices that do not perform as well as established alternatives [23]. A correctly positioned supraglottic airway device within the airway of an anaesthetised patient will create an air space between the glottis and the bowl of the airway device. The manikin airway, with a supraglottic airway device in situ, will closely replicate this part of a patient’s airway. This assertion is supported by the findings of a human study that reported very similar success rates for fibreoptic-guided tracheal intubation through the ILMA and i-gel to those we found in our manikin study [11]. We are not aware of any randomised studies assessing tracheal intubation through the Aura-i. Secondly, the findings of our study are applicable only in so far as the levels of anaesthetic experience and fibrescope handling skills of our 30 anaesthetists are representative of anaesthetists generally. Thirdly, this technique of tracheal intubation may be used in patients with a difficult airway and our manikin study was not designed to simulate this scenario. However, whilst the actual time to tracheal tube placement with each device may be different in actual patients, the differences between the tested devices are likely to remain the same. We found that the Aura-i did not perform as well as the ILMA or the i-gel as an adjunct for fibreopticguided tracheal intubation and therefore recommend that it is not chosen for this purpose. The Aura-i was associated with a higher failed intubation rate and increased resistance to railroading compared with both the ILMA and the i-gel. 596
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
We conclude that, when used as a conduit for fibreoptic-guided tracheal intubation in a manikin model, the i-gel results in shorter intubation times compared with the Aura-i or the ILMA, and was the preferred device.
Acknowledgements We thank the participants from the University Hospital of Wales. The Aura-i and i-gel devices used in the study were provided free of charge by the manufacturers.
Competing interests No external funding and no competing interests declared.
References 1. Henderson JJ, Popat MT, Latto IP, Pearce AC; Difficult Airway Society. Difficult Airway Society guidelines for management of the unanticipated difficult intubation. Anaesthesia 2004; 59: 675–94. 2. McAleavey F, Michalek P. Aura-i laryngeal mask as a conduit for elective fibreoptic intubation. Anaesthesia 2010; 65: 1151. 3. Pandit JJ, MacLachlan K, Dravid RM, Popat MT. Comparison of times to achieve tracheal intubation with three techniques using the laryngeal or intubating laryngeal mask airway. Anaesthesia 2002; 57: 128–32. 4. Joo HS, Kapoor S, Rose DK, Naik VN. The intubating laryngeal mask airway after induction of general anesthesia versus awake fiberoptic intubation in patients with difficult airways. Anesthesia and Analgesia 2001; 92: 1342–6. 5. Ferson DZ, Rosenblatt WH, Johansen MJ, Osborn I, Ovassapian A. Use of the intubating LMA-Fastrach in 254 patients with difficult-to-manage airways. Anesthesiology 2001; 95: 1175–81. 6. Wharton NM, Gibbison B, Gabbott DA, Haslam GM, Muchatuta N, Cook TM. I-gel insertion by novices in manikins and patients. Anaesthesia 2008; 63: 991–5. 7. Gatward JJ, Cook TM, Seller C, et al. Evaluation of the size 4 i-gel airway in one hundred non-paralysed patients. Anaesthesia 2008; 63: 1124–30. 8. Joshi NA, Baird M, Cook TM. Use of an i-gel for airway rescue. Anaesthesia 2008; 63: 1020–1. 9. Sharma S, Scott S, Rogers R, Popat M. The i-gel airway for ventilation and rescue intubation. Anaesthesia 2007; 62: 419–20. 10. Michalek P, Hodgkinson P, Donaldson W. Fiberoptic intubation through an I-gel supraglottic airway in two patients with predicted difficult airway and intellectual disability. Anesthesia and Analgesia 2008; 106: 1501–4. 11. de Lloyd L, Hodzovic I, Voisey S, Wilkes AR, Latto IP. Comparison of fibrescope guided intubation via the classic laryngeal mask airway and i-gel in a manikin. Anaesthesia 2010; 65: 36–43. 12. Kleine-Brueggeney M, Theiler L, Urwyler N, Vogt A, Greif R. Randomized trial comparing the i-gelTM and Magill tracheal tube with the single-use ILMATM and ILMATM tracheal tube for
© 2015 The Association of Anaesthetists of Great Britain and Ireland
Anaesthesia 2015, 70, 591–597
doi:10.1111/anae.12988
Original Article A comparison of fibreoptic-guided tracheal intubation through the AmbuâAura-iTM, the intubating laryngeal mask airway and the i-gelTM: a manikin study* L. J. de Lloyd,1 F. Subash,2 A. R. Wilkes3 and I. Hodzovic1,3 1 Consultant, Department of Anaesthetics, University Hospital of Wales, Cardiff, UK 2 Consultant, Department of Anaesthetics, Royal Gwent Hospital, Newport, UK 3 Senior Lecturer, Cardiff University, Cardiff, UK
Summary We compared the Aura-iTM, intubating laryngeal mask airway and i-gelTM as conduits for fibreoptic-guided tracheal intubation in a manikin. Thirty anaesthetists each performed two tracheal intubations through each device, a total of 180 intubations. The median (IQR [range]) time to complete the first intubation was 40 (31–50 [15–162]) s, 37 (34– 48 [25–75]) s and 28 (22–35 [14–59]) s for the Aura-i, intubating laryngeal mask airway and i-gel, respectively. Tracheal intubation through the i-gel was the quickest (p < 0.01). Resistance to railroading of the tracheal tube over the fibrescope was significantly greater through the Aura-i compared with the intubating laryngeal mask airway and the i-gel (p = 0.001). There were no failures to intubate through the intubating laryngeal mask airway or the i-gel but six intubation attempts through the Aura-i were unsuccessful, in five owing to a railroading failure and in one owing to accidental oesophageal intubation. We conclude that the Aura-i does not perform as well as the intubating laryngeal mask airway or the i-gel as an adjunct for performing fibreoptic-guided tracheal intubation.
.................................................................................................................................................................
Correspondence to: I. Hodzovic Email: [email protected] *Presented in part at the AAGBI Annual Congress, September 2011, Edinburgh, UK. Accepted: 22 November 2014
Introduction In the event of unexpected failure to intubate the trachea during conventional direct laryngoscopy, Plan B of the Difficult Airway Society (DAS) guidelines recommends insertion of the intubating laryngeal mask airway (ILMATM; Intavent Orthofix Ltd, Maidenhead, Berks, UK) or classic laryngeal mask airway (LMA ClassicTM; Intavent Orthofix Ltd) in order to maintain oxygenation and facilitate tracheal intubation using a fibrescope [1]. The Aura-iTM (Ambu Ltd, St Ives, Cambridgeshire, UK ) is a recently developed supraglottic airway device © 2015 The Association of Anaesthetists of Great Britain and Ireland
with integral features designed to facilitate fibreopticguided tracheal intubation. These include an anatomical curvature and wide lumen designed to allow passage of an appropriately sized tracheal tube. Markings within the device are designed to aid navigation of a fibrescope; the first mark indicates when the fibrescope tip should be manipulated in order to view the glottis, while the second mark indicates when the fibrescope tip has been advanced too far. There has been one report of successful fibreoptic-guided tracheal intubation through the Aura-i in adult patients [2], but no 591
doi:10.1111/anae.12988
Original Article A comparison of fibreoptic-guided tracheal intubation through the AmbuâAura-iTM, the intubating laryngeal mask airway and the i-gelTM: a manikin study* L. J. de Lloyd,1 F. Subash,2 A. R. Wilkes3 and I. Hodzovic1,3 1 Consultant, Department of Anaesthetics, University Hospital of Wales, Cardiff, UK 2 Consultant, Department of Anaesthetics, Royal Gwent Hospital, Newport, UK 3 Senior Lecturer, Cardiff University, Cardiff, UK
Summary We compared the Aura-iTM, intubating laryngeal mask airway and i-gelTM as conduits for fibreoptic-guided tracheal intubation in a manikin. Thirty anaesthetists each performed two tracheal intubations through each device, a total of 180 intubations. The median (IQR [range]) time to complete the first intubation was 40 (31–50 [15–162]) s, 37 (34– 48 [25–75]) s and 28 (22–35 [14–59]) s for the Aura-i, intubating laryngeal mask airway and i-gel, respectively. Tracheal intubation through the i-gel was the quickest (p < 0.01). Resistance to railroading of the tracheal tube over the fibrescope was significantly greater through the Aura-i compared with the intubating laryngeal mask airway and the i-gel (p = 0.001). There were no failures to intubate through the intubating laryngeal mask airway or the i-gel but six intubation attempts through the Aura-i were unsuccessful, in five owing to a railroading failure and in one owing to accidental oesophageal intubation. We conclude that the Aura-i does not perform as well as the intubating laryngeal mask airway or the i-gel as an adjunct for performing fibreoptic-guided tracheal intubation.
.................................................................................................................................................................
Correspondence to: I. Hodzovic Email: [email protected] *Presented in part at the AAGBI Annual Congress, September 2011, Edinburgh, UK. Accepted: 22 November 2014
Introduction In the event of unexpected failure to intubate the trachea during conventional direct laryngoscopy, Plan B of the Difficult Airway Society (DAS) guidelines recommends insertion of the intubating laryngeal mask airway (ILMATM; Intavent Orthofix Ltd, Maidenhead, Berks, UK) or classic laryngeal mask airway (LMA ClassicTM; Intavent Orthofix Ltd) in order to maintain oxygenation and facilitate tracheal intubation using a fibrescope [1]. The Aura-iTM (Ambu Ltd, St Ives, Cambridgeshire, UK ) is a recently developed supraglottic airway device © 2015 The Association of Anaesthetists of Great Britain and Ireland
with integral features designed to facilitate fibreopticguided tracheal intubation. These include an anatomical curvature and wide lumen designed to allow passage of an appropriately sized tracheal tube. Markings within the device are designed to aid navigation of a fibrescope; the first mark indicates when the fibrescope tip should be manipulated in order to view the glottis, while the second mark indicates when the fibrescope tip has been advanced too far. There has been one report of successful fibreoptic-guided tracheal intubation through the Aura-i in adult patients [2], but no 591
Anaesthesia 2015, 70, 591–597
randomised studies comparing it with alternative supraglottic airway devices. The ILMA was designed to provide a superior conduit for tracheal intubation compared with the LMA Classic. It has an anatomically curved rigid airway tube, a metal introducer handle and the bowl of the device contains an ‘epiglottic elevator bar’. Although originally designed to facilitate ‘blind’ tracheal intubation, success is increased by using a fibrescope inserted through the ILMA [3–5] and it may be considered the standard device for fibreoptic-guided tracheal intubation. The i-gelTM (Intersurgical Ltd, Wokingham, Berks, UK) is a single-use disposable supraglottic airway device with a non-inflatable cuff, introduced into clinical practice in the UK in 2007. The i-gel has been evaluated for ease of insertion by novices in both manikins and patients and compares favourably with other supraglottic airway devices [6, 7]. There have been reports of the i-gel’s being used as both an airway rescue device and a conduit for fibreoptic-guided tracheal intubation in predicted difficult airways [8–10]. A manikin study evaluating the i-gel as a means of achieving fibreoptic-guided tracheal intubation showed that intubation was achieved faster and more easily through the i-gel than through the LMA Classic [11]. In a study performed in patients with an anticipated difficult airway, the i-gel compared favourably with the single-use ILMA [12]. We decided to conduct a randomised crossover manikin study to compare the Aura-i, ILMA and i-gel supraglottic airway devices with respect to the time taken to perform successful tracheal tube placement and to determine device preference.
Methods The local Research Ethics Committee were contacted and waived formal ethical review. Anaesthetists with at least one year of experience were invited to take part in the study and written informed consent was obtained from all participants. The Laerdalâ Adult Airway Management Trainer (Laerdal Medical Ltd, Orpington, Kent, UK) was used in this randomised crossover study. The size-4 Aura-i, ILMA and i-gel supraglottic airway devices were inserted by the investigators. The position of the device was then 592
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
standardised by an investigator to ensure that a complete view of the glottis was obtained with the fibrescope when inserted through the device before each intubation attempt was performed. Participants were allowed time to familiarise themselves with the equipment before commencing the study; this included a demonstration by the investigators and at least one successful tracheal intubation by the participant with each device. Each participant performed two tracheal intubations through each supraglottic airway device and the order was randomised using computer-generated software. The first intubation was performed in two timed sections. Time 1 was the time taken from picking up either the fibrescope for the Aura-i and i-gel, or the tracheal tube for the ILMA, until a view of the carina was obtained. Time 2 was the time taken from commencement of railroading the tracheal tube over the fibrescope through the supraglottic airway device until delivery of a breath to the manikin. A second intubation was performed without interruption and was timed from picking up either the fibrescope with a pre-mounted tracheal tube, or the tracheal tube for the ILMA, until delivery of a breath to the manikin. Failure was defined as an intubation time that exceeded 180 s. A 6.0-mm ID reinforced tracheal tube (Mallinckrodt, Hazelwood, MO, USA) was used to intubate through the Aura-i and the i-gel and was pre-mounted on the fibrescope by an investigator with the bevel facing posteriorly [13–15]. For tracheal intubation through the ILMA, a 6.0-mm ID silicone tracheal tube, designed by the manufacturer, was used. The technique used to intubate through the ILMA differed from the other two supraglottic devices: the tracheal tube was inserted into the airway of the ILMA until the elevator bar was lifted, before insertion of the fibrescope. For intubation through the ILMA, timing was therefore started when the participant picked up the tracheal tube. At the end of each intubation attempt, the participant was asked to score the resistance encountered to railroading the tracheal tube over the fibrescope through the supraglottic airway device. A four-point scoring system adopted from Blair et al. [16] was used: 1 = no resistance; 2 = minor resistance; 3 = marked resistance; 4 = passage of tracheal tube not possible. © 2015 The Association of Anaesthetists of Great Britain and Ireland
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
Following completion of the second intubation, the time taken to remove the ILMA was measured. This was from the participant's picking up the tube extension device to delivery of a breath to the manikin through the remaining tracheal tube, after removal of the ILMA. This time was not included in the total intubation time. After completion of the study, participants were asked to state their preferred supraglottic airway device in the event of having to manage an unexpectedly difficult intubation and also whether the integral markings within the lumen of the Aura-i assisted with performing fibreoptic-guided tracheal intubation through the device. The primary outcome measure was tracheal intubation time. A previous study [10] showed a standard deviation for intubation time of 11 s and we considered an important time difference as 10 s or more. For a p value < 0.01 and a power of 99%, we required a sample size of 30. Friedman’s test was used to analyse non-normally distributed interval scale data and ordinal categorical data. Where appropriate, the Wilcoxon signed-rank test was used for post-hoc pairwise analyses. Cochran’s Q test was used to analyse nominal data (successful tracheal intubation). The chi-squared test was used to analyse categorical nominal data (preference for a particular supraglottic airway device). Statistical analysis was performed using SPSS version 20 software (SPSS Inc., Chicago, IL, USA) and a p value < 0.05 was considered statistically significant.
Results Thirty anaesthetists participated in the study: two core trainees, 19 specialist registrars and nine consultants. The median (IQR [range]) number of years of anaes-
Anaesthesia 2015, 70, 591–597
thetic experience was 7 (4–12 [1–22]). No anaesthetist had performed fibreoptic-guided tracheal intubation through the Aura-i previously. Nine anaesthetists had previously performed fibreoptic-guided tracheal intubation through the ILMA and four anaesthetists had performed fibreoptic-guided tracheal intubation through the i-gel. The device used had a significant effect on the times taken to complete the procedures (Table 1). The time to locate the carina with the fibrescope through the selected device (Time 1) was shorter through the i-gel compared with the Aura-i (p = 0.0003) and ILMA (< 0.0001). Time 1 was also shorter with the ILMA than with the Aura-i (p = 0.005). The time to railroad the tracheal tube (Time 2) was shorter with the ILMA than with the Aura-i (p < 0.0001) and i-gel (p = 0.010). Time 2 was also shorter with the i-gel than with the Aura-i (p = 0.014). Total tracheal intubation times for the first and second intubations were shorter with the i-gel than either the Aura-i (p = 0.001 and 0.009, respectively) or the ILMA (p = 0.0002 and < 0.0001, respectively). There was no significant difference in total tracheal intubation time between the Aura-i and the ILMA for either the first or the second intubation (p = 0.60 and 0.40, respectively). Intubation time was shorter for the second, compared with the first, tracheal intubation for all three devices. Resistance to railroading the tracheal tube through the supraglottic airway device into the trachea for the first and second intubations was significantly greater with the Aura-i than with the ILMA (p = 0.009) or the i-gel (p < 0.001). Marked resistance to passage of the tracheal tube through the device (a score of 3) occurred in 16 of 60 (27%) tracheal intubations through the Aura-i, none
Table 1 Intubation times for the Aura-i, ILMA and i-gel. Time 1 was from the start until a view of the carina was obtained; Time 2 was from the start of railroading until delivery of a breath to the manikin. Values are median (IQR [range]).
First intubation (timed sections) Time 1; s Time 2; s Total time; s Second intubation (uninterrupted) Total time; s
Aura-i (n = 30)
ILMA (n = 30)
i-gel (n = 30)
p value*
19 (14–25 [8–60]) 18 (14–27 [7–144])† 40 (31–50 [15–162])†
29 (22–35 [13–48]) 11 (9–14 [6–36]) 37 (34–48 [25–75])
12 (10–15 [6–25]) 14 (11–18 [6–47]) 28 (22–35 [14–59])
< 0.0001 0.001 0.001
32 (25–36 [12–75])
31 (28–41 [20–55])
24 (21–30 [15–37])
0.001
*p values refer to overall effect of device on time (Aura-i vs i-gel vs ILMA). †Failure of railroading in two participants. © 2015 The Association of Anaesthetists of Great Britain and Ireland
593
Anaesthesia 2015, 70, 591–597
through the ILMA and 2 (3%) through the i-gel. Inability to railroad the tracheal tube through the device (a score of 4) occurred in 5 (8%) tracheal intubations through the Aura-i and none through either the ILMA or the i-gel. Two failed during the first intubation attempt and two during the second intubation attempt (all four attempts were abandoned after 180 s); one railroading failure was due to a participant’s not wishing to continue following an attempt that lasted 154 s. Accidental oesophageal intubation occurred after placement of the fibrescope in the trachea in 1 (2%) attempt through the Aura-i, despite a complete view of the glottis via the fibrescope. Successful tracheal intubation was achieved on each attempt through the ILMA and the i-gel (p = 0.002). None of the anaesthetists found the Aura-i’s markings helpful in aiding placement of the fibrescope in the trachea. Twenty-seven anaesthetists (90%) reported not utilising the markings when performing fibreoptic-guided tracheal intubation through the device. Removal of the ILMA over the tracheal tube was timed for 27 of the 30 participating anaesthetists (this time was not measured for the first three participants). The median (IQR [range]) time taken to remove the ILMA was 24.4 (21.6–28.3 [17.4–45.0]) s. The manikin’s lungs could be successfully ventilated through the tracheal tube after removal of the ILMA on each occasion, indicating continued correct placement of the tracheal tube. Five (17%) of the participants preferred the Aura-i, 5 (17%) preferred the ILMA and 19 (63%) preferred the i-gel (p = 0.001). The preference of one participant was not recorded.
Discussion We found that the time for fibreoptic-guided tracheal intubation was significantly shorter through the i-gel than either the Aura-i or the ILMA. Of the three devices assessed, participating anaesthetists stated a preference for the i-gel as a conduit for fibreopticguided tracheal intubation when managing a difficult airway scenario. There were no failures to intubate through either the ILMA or i-gel; however, six of 60 (10%) intubation attempts through the Aura-i were unsuccessful. Of these six unsuccessful intubation 594
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
attempts, five were due to railroading and one was due to oesophageal intubation. The supraglottic airway devices were placed in a standardised manner by the investigators because our aim was not to assess their placement but rather their usefulness as conduits to achieve successful tracheal intubation [17]. The first intubation attempt was divided into two timed sections in order to ascertain when, during the process of tracheal intubation, problems were encountered [10]. We measured intubation times with a different starting point for the ILMA compared with the Aura-i and the i-gel, because the ILMA has the added device-specific requirement to protect the advancing tip of the fibrescope from damage due to collision with the epiglottic elevator bar. We considered that having the tracheal tube preloaded on the fibrescope for the Aura-i and the i-gel reflected the situation in clinical practice, whereas insertion of the tracheal tube to lift the epiglottic bar would normally be performed by the anaesthetist before handling the fibrescope. Our starting points for each device reflected this. The time taken to achieve a view of the carina (Time 1) was shortest through the i-gel. It might be expected that this stage of tracheal intubation would take longer through the ILMA because of the extra step required to lift the epiglottic elevator bar before advancing the fibrescope through the ILMA tracheal tube. The time required to achieve a view of the carina was longer with the Aura-i compared with the i-gel, suggesting that manipulation of the fibrescope into the trachea may have been more difficult through the Aura-i. Time 2 (from the start of railroading until delivery of a breath to the manikin) was significantly longer through the Aura-i than through the i-gel or ILMA, suggesting a particular difficulty encountered when railroading the tracheal tube through the Aura-i. Railroading the ILMA silicone tracheal tube was faster than railroading the Mallinckrodt reinforced tracheal tube used for the other two devices. The tapered soft tip of the ILMA silicone tube appears to facilitate railroading. We found that the overall time to fibreoptic-guided tracheal intubation was significantly shorter through the i-gel than either the Aura-i or the ILMA. Tracheal intubations performed for the second time were shorter than when performed for the first time for all three devices © 2015 The Association of Anaesthetists of Great Britain and Ireland
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
Anaesthesia 2015, 70, 591–597
Aura-i Trachea Oesophagus
ILMA Trachea Oesophagus
i-gel Trachea Oesophagus
Figure 1 Radiographic images of the three supraglottic airway devices with superimposed lines demonstrating the exit trajectory from the lumen of the device. Images on the right side show the devices in situ in the manikin and their relationship to the trachea and oesophagus.
and this may reflect increased familiarity with the equipment for the second intubation. Tracheal intubation was achieved successfully on every attempt through the ILMA and the i-gel but in only 54 of 60 (90%) tracheal attempts through the Aura-i. Of the six failed intubation attempts through the Aura-i, five were due to inability to railroad the tracheal tube over the fibrescope into the trachea within 180 s and one failed intubation attempt occurred when the tracheal tube was railroaded into the oesophagus, despite a complete view of the glottis via the fibrescope. Marked resistance to railroading (a score of 3) occurred in 16 of 60 (27%) attempts through the Aura-i compared with none through the ILMA and 2 of 60 (3%) through the i-gel. Differences in the rates of successful tracheal intubation and ease of railroading may relate to the angle of exit of the fibrescope or tracheal tube from the distal portion of the device because the ILMA and i-gel both have an elevated exit trajectory. The Aura-i, by contrast, has a flatter angle of exit which may result in the fibrescope or tracheal tube’s exiting more posteriorly and heading towards the oesophagus (Fig. 1). The trajectory © 2015 The Association of Anaesthetists of Great Britain and Ireland
of tracheal tube exit from the supraglottic airway device appears to influence the success of tracheal tube placement. In a clinical study using a ‘visualised blind technique’ for tracheal intubation through an i-gel this was frequently unsuccessful because the tracheal tube abutted the posterior structures of the larynx. A more anterior trajectory appears to facilitate successful passage of the tracheal tube into the trachea [18]. There was one accidental oesophageal intubation when using the Aura-i as a conduit for tracheal intubation and this occurred despite successful placement of the fibrescope into the trachea. The most likely cause was the tracheal tube’s passing in the direction of the oesophagus, thus pushing against the mid-segment of the fibrescope and forming a loop [15], which resulted in the fibrescope’s being pulled out of the trachea by the advancing tube and subsequently entering the oesophagus. Regardless of the cause of the difficulty encountered with railroading the tracheal tube through the device and into the trachea, it is significant that difficulty occurred disproportionately more often with the Aura-i, suggesting a particular problem with this device. 595
Anaesthesia 2015, 70, 591–597
Participants expressed a preference for the i-gel over the Aura-i or the ILMA, and the Aura-i and ILMA were preferred in equal measure, despite the findings of this study favouring the ILMA over the Aura-i. This may be because of the simplicity and familiarity of the Aura-i and i-gel compared with the less familiar ILMA [19]. The manufacturer recommends removal of the ILMA after tracheal intubation [20]. Although there were no dislodgements of the tracheal tube with the ILMA in our study, this has occurred in previous clinical studies [21] and may be another reason why the ILMA was not favoured. There are limitations to our study. Firstly, the use of manikin-based studies for evaluation of airway equipment has been criticised [22]. However, we would argue that evaluation of untested devices may be better performed on an appropriate manikin in order to identify devices that do not perform as well as established alternatives [23]. A correctly positioned supraglottic airway device within the airway of an anaesthetised patient will create an air space between the glottis and the bowl of the airway device. The manikin airway, with a supraglottic airway device in situ, will closely replicate this part of a patient’s airway. This assertion is supported by the findings of a human study that reported very similar success rates for fibreoptic-guided tracheal intubation through the ILMA and i-gel to those we found in our manikin study [11]. We are not aware of any randomised studies assessing tracheal intubation through the Aura-i. Secondly, the findings of our study are applicable only in so far as the levels of anaesthetic experience and fibrescope handling skills of our 30 anaesthetists are representative of anaesthetists generally. Thirdly, this technique of tracheal intubation may be used in patients with a difficult airway and our manikin study was not designed to simulate this scenario. However, whilst the actual time to tracheal tube placement with each device may be different in actual patients, the differences between the tested devices are likely to remain the same. We found that the Aura-i did not perform as well as the ILMA or the i-gel as an adjunct for fibreopticguided tracheal intubation and therefore recommend that it is not chosen for this purpose. The Aura-i was associated with a higher failed intubation rate and increased resistance to railroading compared with both the ILMA and the i-gel. 596
de Lloyd et al. | Aura-i vs ILMA vs i-gel in manikins
We conclude that, when used as a conduit for fibreoptic-guided tracheal intubation in a manikin model, the i-gel results in shorter intubation times compared with the Aura-i or the ILMA, and was the preferred device.
Acknowledgements We thank the participants from the University Hospital of Wales. The Aura-i and i-gel devices used in the study were provided free of charge by the manufacturers.
Competing interests No external funding and no competing interests declared.
References 1. Henderson JJ, Popat MT, Latto IP, Pearce AC; Difficult Airway Society. Difficult Airway Society guidelines for management of the unanticipated difficult intubation. Anaesthesia 2004; 59: 675–94. 2. McAleavey F, Michalek P. Aura-i laryngeal mask as a conduit for elective fibreoptic intubation. Anaesthesia 2010; 65: 1151. 3. Pandit JJ, MacLachlan K, Dravid RM, Popat MT. Comparison of times to achieve tracheal intubation with three techniques using the laryngeal or intubating laryngeal mask airway. Anaesthesia 2002; 57: 128–32. 4. Joo HS, Kapoor S, Rose DK, Naik VN. The intubating laryngeal mask airway after induction of general anesthesia versus awake fiberoptic intubation in patients with difficult airways. Anesthesia and Analgesia 2001; 92: 1342–6. 5. Ferson DZ, Rosenblatt WH, Johansen MJ, Osborn I, Ovassapian A. Use of the intubating LMA-Fastrach in 254 patients with difficult-to-manage airways. Anesthesiology 2001; 95: 1175–81. 6. Wharton NM, Gibbison B, Gabbott DA, Haslam GM, Muchatuta N, Cook TM. I-gel insertion by novices in manikins and patients. Anaesthesia 2008; 63: 991–5. 7. Gatward JJ, Cook TM, Seller C, et al. Evaluation of the size 4 i-gel airway in one hundred non-paralysed patients. Anaesthesia 2008; 63: 1124–30. 8. Joshi NA, Baird M, Cook TM. Use of an i-gel for airway rescue. Anaesthesia 2008; 63: 1020–1. 9. Sharma S, Scott S, Rogers R, Popat M. The i-gel airway for ventilation and rescue intubation. Anaesthesia 2007; 62: 419–20. 10. Michalek P, Hodgkinson P, Donaldson W. Fiberoptic intubation through an I-gel supraglottic airway in two patients with predicted difficult airway and intellectual disability. Anesthesia and Analgesia 2008; 106: 1501–4. 11. de Lloyd L, Hodzovic I, Voisey S, Wilkes AR, Latto IP. Comparison of fibrescope guided intubation via the classic laryngeal mask airway and i-gel in a manikin. Anaesthesia 2010; 65: 36–43. 12. Kleine-Brueggeney M, Theiler L, Urwyler N, Vogt A, Greif R. Randomized trial comparing the i-gelTM and Magill tracheal tube with the single-use ILMATM and ILMATM tracheal tube for
© 2015 The Association of Anaesthetists of Great Britain and Ireland
Anaesthesia 2015, 70, 591–597
doi:10.1111/anae.12988
Original Article A comparison of fibreoptic-guided tracheal intubation through the AmbuâAura-iTM, the intubating laryngeal mask airway and the i-gelTM: a manikin study* L. J. de Lloyd,1 F. Subash,2 A. R. Wilkes3 and I. Hodzovic1,3 1 Consultant, Department of Anaesthetics, University Hospital of Wales, Cardiff, UK 2 Consultant, Department of Anaesthetics, Royal Gwent Hospital, Newport, UK 3 Senior Lecturer, Cardiff University, Cardiff, UK
Summary We compared the Aura-iTM, intubating laryngeal mask airway and i-gelTM as conduits for fibreoptic-guided tracheal intubation in a manikin. Thirty anaesthetists each performed two tracheal intubations through each device, a total of 180 intubations. The median (IQR [range]) time to complete the first intubation was 40 (31–50 [15–162]) s, 37 (34– 48 [25–75]) s and 28 (22–35 [14–59]) s for the Aura-i, intubating laryngeal mask airway and i-gel, respectively. Tracheal intubation through the i-gel was the quickest (p < 0.01). Resistance to railroading of the tracheal tube over the fibrescope was significantly greater through the Aura-i compared with the intubating laryngeal mask airway and the i-gel (p = 0.001). There were no failures to intubate through the intubating laryngeal mask airway or the i-gel but six intubation attempts through the Aura-i were unsuccessful, in five owing to a railroading failure and in one owing to accidental oesophageal intubation. We conclude that the Aura-i does not perform as well as the intubating laryngeal mask airway or the i-gel as an adjunct for performing fibreoptic-guided tracheal intubation.
.................................................................................................................................................................
Correspondence to: I. Hodzovic Email: [email protected] *Presented in part at the AAGBI Annual Congress, September 2011, Edinburgh, UK. Accepted: 22 November 2014
Introduction In the event of unexpected failure to intubate the trachea during conventional direct laryngoscopy, Plan B of the Difficult Airway Society (DAS) guidelines recommends insertion of the intubating laryngeal mask airway (ILMATM; Intavent Orthofix Ltd, Maidenhead, Berks, UK) or classic laryngeal mask airway (LMA ClassicTM; Intavent Orthofix Ltd) in order to maintain oxygenation and facilitate tracheal intubation using a fibrescope [1]. The Aura-iTM (Ambu Ltd, St Ives, Cambridgeshire, UK ) is a recently developed supraglottic airway device © 2015 The Association of Anaesthetists of Great Britain and Ireland
with integral features designed to facilitate fibreopticguided tracheal intubation. These include an anatomical curvature and wide lumen designed to allow passage of an appropriately sized tracheal tube. Markings within the device are designed to aid navigation of a fibrescope; the first mark indicates when the fibrescope tip should be manipulated in order to view the glottis, while the second mark indicates when the fibrescope tip has been advanced too far. There has been one report of successful fibreoptic-guided tracheal intubation through the Aura-i in adult patients [2], but no 591
