Comparison of the i-gel and the LMA-Unique laryngeal mask airway in patients with mild to moderate obesity during elective short-term surgery

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1 doi:1.1111/j x ORIGINAL ARTICLE Comparison of the i-gel and the LMA-Unique laryngeal mask airway in patients with mild to moderate obesity during elective short-term surgery U. Weber, 1 R. Oguz, 1 L. A. Potura, 1 O. Kimberger, 2 A. Kober 2 and E. Tschernko 1 1 Resident, 2 Professor, Department of Anesthesiology, General Intensive Care and Pain Control, Medical University of Vienna, Vienna, Austria Summary The aim of our study was to compare leakage pressure, ease and time of insertion of the i-gel and the LMA-Unique laryngeal mask airway in patients with mild to moderate obesity during elective short-term surgery. In this prospective, randomised crossover trial, we included patients with a body mass index (BMI) > 25 and < 35 kg.m )2, and, age > 18 years, undergoing elective surgery in the supine position with an expected duration of surgery < 2 h. Leakage pressures, insertion difficulty, time and number of insertion attempts were evaluated. We included 5 patients consisting of 29 mildly (BMI > 25 and < 3 kg.mg )2 ) and 21 moderately (BMI > 3 and < 35 kg.mg )2 ) obese patients. Mean (SD) leakage pressures were 23.7 (9.2) cmh 2 O (i-gel) and 17.4 (7.) cmh 2 O (LMA-Unique) (p <.1). Subgroup analyses showed leakage pressures of 22.2 (9.4) cmh 2 O (i-gel) and 17.5 (7.5) cmh 2 O (LMA-Unique) (p =.13) in the mild subgroup, and 25.7 (8.6) cmh 2 O (i-gel) and 17. (6.2) cmh 2 O (LMA-Unique) (p <.1), in the moderate subgroup. Insertion of the i-gel was associated with significantly higher leakage pressures compared with the LMA-Unique in mildly and moderately obese patients.... Correspondence to: Dr Ulrike Weber ulrike.weber@meduniwien.ac.at Accepted: 25 January 211 Introduction Supraglottic airway devices are routinely used for short-term elective surgery, and have shown to be safe and effective in spontaneously breathing patients and in patients undergoing pressure-controlled ventilation [1 4]. Recently, the i-gel (Intersurgical Ltd, Wokingham, Berkshire, UK), a novel supraglottic airway device, has been introduced into clinical routine anaesthesia. The i-gel has a non-inflatable, gel-like cuff, that is made of a thermoplastic elastomer (styrene ethylene butadyiene styrene) and is claimed to conform and fit to the perilaryngeal anatomy, providing a reliable perilaryngeal seal. This enables easier positioning and insertion and a better seal compared with laryngeal mask airways (LMAs) with inflatable cuffs [2,5 1]. The i-gel incorporates a drainage tube to prevent gastric inflation, that allows insertion of a gastric tube. A recent study also confirms its use for rescue intubation [11]. There have already been several studies comparing the i-gel with other supraglottic airway devices (LMA- Unique (Intavent Orthofix, Maidenhead, Berkshire, UK), classic LMA) in lean patients. These studies show that the i-gel may be used with higher ventilation pressures due to its better seal compared with other supraglottic airway devices [2, 3, 7]. We speculated that this technical feature may be especially beneficial in patients with mild to moderate obesity during shortterm elective surgery, when supraglottic airway devices are frequently used, and where an optimal fit of the airway device and high leakage pressures are important. The LMA-Unique is one of the most widely used supraglottic airway devices in clinical routine Anaesthesia Ó 211 The Association of Anaesthetists of Great Britain and Ireland 481

2 U. Weber et al. Æ Comparison of i-gel and LMA-Unique Anaesthesia, 211, 66, pages anaesthesia and represents a classical laryngeal mask airway with an inflatable cuff. Therefore, we decided to compare leakage pressure, ease and time of insertion of the i-gel with those of the LMA-Unique in patients with mild to moderate obesity during elective shortterm surgery. Leakage pressure was defined as the primary outcome, and ease and time of insertion of the supraglottic airway devices were defined as secondary outcomes. Methods This prospective randomised crossover clinical study was conducted at the Department of Anaesthesiology, General Intensive Care and Pain Control at the Medical University of Vienna, Austria. Institutional Review Board approval was obtained from the Medical University of Vienna and the University Hospital of Vienna. Written informed consent was obtained from all patients the day before planned surgery. Patients requiring trauma surgery on the upper and the lower limb were recruited for the study during a time period from October 29 to February 21. Inclusion criteria were age over 18 years, elective surgery in the supine position with an expected duration of < 2 h, body mass index (BMI) of > 25 and > 35 kg.m )2, and ASA physical status 1 3. Exclusion criteria were known or predicted difficult airway, mouth opening < 2.5 cm, presence of any significant acute or chronic lung disease, pathology of the neck or upper respiratory tract, increased risk of aspiration (hiatus hernia, gastro-oesophageal reflux, full stomach), pregnancy and refusal to participate. The patients were randomly allocated to one of two groups; in one group, the i-gel was inserted first, thereafter the airway was switched to the LMA- Unique. In the second group, the LMA-Unique was inserted first and thereafter the airway was switched to the i-gel. The patients were assigned to one of the two groups using a randomisation code that was computer generated using a specially written excel spreadsheet randomisation programme (Microsoft, Redmond, WA, USA) to ensure a balanced design. Therefore, sequentially numbered sealed opaque envelopes naming the airway device to be inserted first were used, and opened shortly before induction of anaesthesia. All patients received premedication with oral midazolam.1 mg.kg )1, 3 min before induction of anaesthesia. In the operating room, intravenous access was secured and routine monitoring was established using ECG, non-invasive blood pressure and oxygen saturation (Dräger Infinity Delta; Dräger Medical AG&Co.KGoA, Lübeck, Germany). After preoxygenation with 1% oxygen for 3 min, anaesthesia was induced with intravenous fentanyl 1 lg.kg )1 and 1% propofol 3 5 mg.kg )1 [12, 13]. On loss of verbal contact and eyelash reflex [14], the anaesthetist checked if ventilation via facemask was possible, and then inserted the first airway device according to the manufacturers instructions. We followed a weightbased algorithm recommended by the manufacturer: i-gel size 3 for patients weighing < 5 kg, size 4 for patients weighing 5 9 kg and size 5 for patients weighing > 9 kg; LMA-Unique size 3 for patients weighing < 5 kg, size 4 for patients weighing 5 7 kg and size 5 for patients > 7 kg. The intracuff pressure of the LMA-Unique was adjusted and maintained to a pressure of cmh 2 O using a digital cuff pressure manometer (Mallinckrodt Medical, Athlone, Ireland) [15]. We used 2% lidocaine gel as a lubricant for both airway devices; this was put on the tip and the posterior surface of the device. After successful placement of the i-gel, a gastric tube (sterile stomach tube; 14-G, 11-cm, Unomedical Holding A S, Birkeroed, Denmark) was inserted via the gastric tube channel of the i-gel. Insertion of the airway devices was performed by two users with experience of > 1 LMA insertions and > 5 i-gel insertions, who were trained on the protocol. Anaesthesia was subsequently maintained with sevoflurane, to a MAC of 1.. Additional fentanyl 1 lg.kg )1 was given as clinically needed during anaesthesia. Successful placement of the airway device and ventilation was assessed by gently squeezing the reservoir bag, by bilateral chest auscultation, and by observing end-tidal CO 2 waveforms and movements of the chest wall. Insertion time of the airway device, number of insertion attempts and difficulty of insertion were documented. Insertion time was defined as from picking up the airway device until the presence of a square wave pattern on the capnograph. A failed attempt was defined as removal and re-insertion of the device. Three attempts at insertion were allowed before the device was considered inappropriate. The difficulty of insertion was graded as easy = 1, moderate = 2, difficult = 3 and impossible = 4. Values for heart rate, blood pressure and oxygen saturation were noted before induction (T1), after induction during mask ventilation (T2), after insertion 482 Anaesthesia Ó 211 The Association of Anaesthetists of Great Britain and Ireland

3 U. Weber et al. Æ Comparison of i-gel and LMA-Unique of the first airway device (T3), before (T4) and after (T5) of the insertion of the second airway device. Once a clear airway was secured, patients lungs were ventilated using pressure-controlled ventilation with a rate of 12 breaths.min )1, an inspiratory-toexpiratory ratio of 1:2, a F I O 2 of 5% and a PEEP of 3 cmh 2 O (Dräger Primus; Dräger Medical AG&- Co.KGoA). Thereafter, airway leak tests were performed as follows. First, the fresh gas flow was adjusted to 3 l.min )1 ; for test 1 (audible noise), the adjustable pressure limiting valve of the circle system was completely closed and then the minimal airway pressure was measured at which an audible gas leak occurred using a stethoscope placed just lateral to the thyroid cartilage. Airway pressures were not allowed to exceed cmh 2 O. This test was used as described by Keller et al. in a study comparing four different methods of assessing airway sealing pressure, and was used in similar studies comparing the i-gel with other airway devices [3, 8, 15]. For test 2 (pressurecontrolled-ventilation-test), patients lungs were ventilated using pressure-controlled ventilation as described above and then inspiratory pressure (Pinsp) was changed. Ventilation was performed starting with a very low Pinsp (8 cmh 2 O) that was elevated every 1 breaths by 1 cmh 2 O until a maximum tidal volume of 1 ml.kg )1.min )1 was reached. The test was then stopped. At occurrence of an audible leak fraction, Pinsp, peak pressure and tidal volume were noted. After these tests, the first airway device was removed and the second was inserted using the same algorithms as in the first device. After completing the study, anaesthesia was maintained until the end of surgery, using the second airway device. Adverse events, including S p O 2 < 9% during induction of anaesthesia and insertion of the airway device, aspiration during induction or blood on the airway device when removed, were noted for each device. Sample size calculation was based on the data of previous studies that compared the LMA-Unique with the i-gel in lean patients [2, 7, 8]. A difference of 3 cmh 2 O was considered clinically significant; the typical SD of previous studies was 5 cmh 2 O leakage pressure. Accordingly, a sample size of 43 (per BMI group) was calculated with an alpha error of.5, a power of % and an estimated drop-out rate of 15% (paired t-test). Paired t-tests were used for comparison of leakage and insertion time, and the sign test was used for comparison of number of insertion attempts and difficulty. A value of p <.5 was considered significant; SPSS 15. (SPSS Inc., Chicago, IL, USA) was used for all calculations. Results We included 5 patients in this study. Patients characteristics are listed in Table 1. We included 37 patients with an ASA of 1, 1 patients with an ASA of 2 and three patients with an ASA of 3. We observed 34 patients with a Malampati score of 1, 14 with a score of 2, one patient with a score of 3 and one patient with a score of 4. Figures 1 and 2 show heart rate and blood pressure measurements at the five predefined time points. Our study population consisted of 29 patients with mild (BMI > 25 and < 3 kg.mg )2 ) and 21 with moderate (BMI > 3 and < 35 kg.mg )2 ) obesity. We divided the study population into these two subgroups to evaluate whether the difference in leak pressure was more pronounced with increasing weight. Leak Table 1 Patient s characteristics. Values are mean (SD) or number. n=5 Age; years.7 (16.2) M:F 29:21 BMI; kg.m )2 29. (2.8) Mouth opening; cm 5.7 (1.1) Thyromental distance; cm 8.5 (1.5) Sternomental distance; cm 14.4 (3.5) Duration of operation; h 1.2 (.8) Blood pressure (mmhg) Time points Figure 1 Mean heart rate (grey) and mean arterial pressure (black) at five predefined time points when the i-gel was inserted first. T1: before induction; T2: after induction during mask ventilation; T3: after insertion of the first airway device, before insertion of the second device; T5: after insertion of the second airway device. Error bars are SD Heart rate (beats.min 1 ) Anaesthesia Ó 211 The Association of Anaesthetists of Great Britain and Ireland 483

4 U. Weber et al. Æ Comparison of i-gel and LMA-Unique Anaesthesia, 211, 66, pages Blood pressure (mmhg) Time points Figure 2 Mean heart rate (grey) and mean arterial pressure (black) at five predefined time points when the LMA-Unique was inserted first T1 : before induction; T2: after induction during mask ventilation; T3: after insertion of the first airway device, before insertion of the airway device; T5: after insertion of the second device. Error bars are SD. pressures in the audible-test (test 1) for the whole population, as well as for the two subgroups, are shown in Table 2. Furthermore, we analysed data of the pressurecontrolled-ventilation-test (test 2). In this test, we noted the tidal volume at which we detected an audible leak. This test was limited to a tidal volume of 1 ml.kg )1 to avoid volutrauma. This limit was reached in 46% (23 patients) of the i-gel group, and in 28% (15 patients) in the LMA-Unique group (Table 3). Table 4 shows insertion time, attempts and success rates of both airway devices. One patient s lungs could not be ventilated after three attempts of i-gel insertion but with LMA-Unique insertion a clear airway was established after two insertion attempts. This patient had a Malampati score of 4. The one patient with Malampati score of 3 needed two insertion attempts with the LMA-Unique and three insertion attempts with the i-gel until a clear airway could be established. We observed no adverse events. After removal of the airway devices, we noted blood on both devices in one Table 2 Leakage test (audible noise). Values are mean (SD). i-gel LMA-Unique p value All patients (n = 5) Leakage; cmh 2 O 23.7 (9.2) 17.4 (6.9).1 Mild obesity (n = 29) Leakage; cmh 2 O 22.2 (9.4) 17.5 (7.5).13 Moderate obesity (n = 21) Leakage; cmh 2 O 25.7 (8.6) 17. (6.2) Heart rate (beats.min 1 ) Table 3 Pressure-controlled-ventilation-test (test 2). The test was terminated when no leak occurred even with a tidal volume of 1 ml.kg )1. Values are number (proportion). Tidal volume* ml.kg )1 patient (2%). In this patient, the LMA-Unique was inserted as the first device. There were no cases of aspiration. Discussion i-gel (n = 5) LMA-Unique (n = 5) 5 12 (24%) 18 (36%) 6 4 (8%) 5 (1%) 7 1 (2%) 2 (4%) 8 2 (4%) 4 (8%) 9 2 (4%) 1 (2%) 1 6 (12%) 5 (1%) Test terminated 23 (46%) 15 (3%) *At which an audible leak was detected Table 4 Insertion of the airway devices. Values are mean (SD) or number (proportion). Characteristic i-gel (n = 5) LMA-Unique (n = 5) p value Insertion time; s 18.3 (6.5) 24.4 (7.7).1 Attempts 1 46 (92%) 46 (92%) 2 2 (4%) 4 (8%) 3 2 (4%) Difficulty Very easy 41 (82%) 37 (74%).782 Moderate 4 (8%) 12 (24%) Difficult 4 (8%) 1 (2%) Impossible 1 (2%) (%) Success 49 (98%) 5 (1%) In our study, we observed significantly higher leakage pressures (23.7 cmh 2 O vs 17.4 cmh 2 O) in the i-gel compared with the LMA-Unique in patients with mild to moderate obesity during elective short term surgery. In patients with a BMI > 3 kg.m )2, this difference was even more pronounced (25.7 cmh 2 O vs 17. cmh 2 O). Similar studies in lean patients comparing the i-gel with the LMA-Unique or the classic LMA also showed that leak pressures were higher with the i-gel than with the other airway devices [2, 7, 8]. However, only one of these studies demonstrated a significant difference 484 Anaesthesia Ó 211 The Association of Anaesthetists of Great Britain and Ireland

5 U. Weber et al. Æ Comparison of i-gel and LMA-Unique (i-gel mean airway leak pressure: 29 cmh 2 O vs LMA- Unique: 18 cmh 2 O) [2]. Insertion difficulties occurred in five out of 5 (1%) patients in the i-gel group, and in one out of 5 (2%) patients in the LMA-Unique group (p =.782). This may be a result of the size of the i-gel, which is comparably bigger than the LMA-Unique, and has a thicker proximal end with an integral bite block. This is especially the case in patients with reduced mouth opening and Malampati scores of 3 4. In our population, we observed four patients with a Malampati score of three or more. Insertion difficulty and insertion attempts were predominantly higher in these patients, especially with the i-gel. In contrast, several studies have shown that the i-gel was rapidly and easily inserted, in both manikins and patients, by novice users such as medical students and non-anaesthetist physicians [5, 6, 9]. Studies comparing insertion times and ease of insertion of the i-gel and the LMA-Unique in lean patients have shown that not only was the insertion time lower with the i-gel, but also ease of insertion was slightly better with the i-gel [2, 8]. The i-gel showed significantly shorter mean insertion times than the LMA-Unique (18.3 s vs 24.4 s). We considered this difference as statistically significant but not of clinical significance. Insertion time is usually shorter when insertion is easier and has to be evaluated together with insertion difficulty. In our study, we observed no case of aspiration and one case of blood on the airway device after removal (2%), when the LMA-Unique was inserted as the first device. A recent study evaluating the i-gel showed an incidence of 1% of visible blood on the i-gel after removal in one hundred patients undergoing anaesthesia, which conforms to our data [16]. We decided to compare the i-gel with the LMA- Unique, a LMA with an inflatable cuff that does not hold a drainage tube mechanism as the i-gel does. The LMA-Unique was chosen despite this basic difference because it is one of the most common supraglottic airway devices used in clinical anaesthesia. Therefore, it is of clinical interest to evaluate differences in leakage pressure and difficulty of insertion in these devices. One limitation of the study is that we did not assess sore throat and dysphagia after anaesthesia because this trial was conducted as a crossover trial, and so there was no possibility to compare both airway devices. Previous studies showed that the i-gel resulted in a lower incidence of throat and neck complaints than that of other LMAs [17]. Injuries of the perilaryngeal area and the trachea are feared conditions after intubation [18, 19]. The most frequent sites of airway injury after intubation in closed claims analysis are injuries to the larynx (33%). Injuries of the oesophagus and the trachea are frequently associated with difficult intubation. Most laryngeal injuries (85%) in closed claims analysis are associated with short-term and routine tracheal intubation. Most cases of laryngeal damage have been reported to be caused by abrasion of the mucosa by movement of the tracheal tube [18]. To date, comparable studies for LMAs and other supraglottic airway devices are not available. Trials comparing intubation and supraglottic airway device insertion demonstrate that sore throat, dysphagia and also haemodynamic changes during intubation occur more often in intubation than in supraglottic airway device insertion [1, 2 24]. An updated report of the American Society of Anesthesiologists Task Force on Management of the Difficult Airway has reviewed sore throat complaints after difficult airway in intubation and in LMA insertion: the incidence of sore throat was 2 41% after intubation and 1% after LMA insertion [24]. Intubation is known to be more difficult in obese patients [25, 26]. Closed claims analysis shows that obesity, difficult intubation and intubation by inexperienced personnel are risk factors for severe airway injuries and pharyngooesophageal perforation [18]. Therefore, upper airway devices may be used for the management of the difficult airway [11, 24, 27, 28] or may be a simple alternative to intubation in short-term elective surgery in the supine position. Another limiting factor is that we did not use the fibre-optic scope to determine the anatomical position of the airway devices in relation to the vocal cords, as it has been shown that anatomical findings do not correlate with clinical consequences [29]. Finally, using an additional person blinded to the study for measuring the leaks of the airway devices during ventilation would have improved this study setting, and therefore this is a limitation. Our study has demonstrated that the i-gel has significantly higher leak pressures compared with the LMA-Unique in mildly to moderately obese patients. There was no significant difference in ease of insertion between the airway devices, although we observed slightly lower scores for difficulty of insertion with the LMA-Unique, and statistically significantly shorter insertion times with the i-gel. The i-gel can be used with higher ventilatory pressures than the LMA-Unique, and may therefore be Anaesthesia Ó 211 The Association of Anaesthetists of Great Britain and Ireland 485

6 U. Weber et al. Æ Comparison of i-gel and LMA-Unique Anaesthesia, 211, 66, pages used as a safe and effective alternative supraglottic airway device in patients with mild to moderate obesity with mouth opening < 4 cm, during elective surgery of short duration in the supine position. Acknowledgements No external funding or competing interests declared. The work was solely supported from departmental sources (Medical University of Vienna, Vienna, Austria). References 1 Joshi GP, Inagaki Y, White PF, et al. Use of the laryngeal mask airway as an alternative to the tracheal tube during ambulatory anesthesia. Anesthesia and Analgesia 1997; 85: Francksen H, Renner J, Hanss R, Scholz J, Doerges V, Bein B. A comparison of the i-gel with the LMA- Unique in non-paralysed anaesthetised adult patients. Anaesthesia 29; 64: Uppal V, Fletcher G, Kinsella J. Comparison of the i-gel with the cuffed tracheal tube during pressure-controlled ventilation. British Journal of Anaesthesia 29; 12: Brimacombe J. Analysis of 15 laryngeal mask uses by one anaesthetist in adults undergoing routine anaesthesia. Anaesthesia 1996; 51: Bamgbade OA, Macnab W, Khalaf WM. Evaluation of the i-gel airway in 3 patients. European Journal of Anaesthesiology 28; 25: Jackson KM, Cook T. Evaluation of four airway training manikins as patient simulators for the insertion of eight types of supraglottic airway devices. Anaesthesia 27; 62: Janakiraman C, Chethan D, Wilkes AR, Stacey MR, Goodwin N. A randomised crossover trial comparing the i-gel supraglottic airway and classic laryngeal mask airway. Anaesthesia 29; 64: Uppal V, Gangaiah S, Fletcher G, Kinsella J. Randomized crossover comparison between the i-gel and the LMA-Unique in anaesthetized, paralysed adults. British Journal of Anaesthesia 29; 13: Wharton NM, Gibbison B, Gabbott DA, Haslam GM, Muchatuta N, Cook TM. I-gel insertion by novices in manikins and patients. Anaesthesia 28; 63: Intersurgical Ltd. I-gel User Guide. lib/docs/userguides/i-gel_user_guide_englishpdf.21 (accessed ). 11 Sharma S, Scott S, Rogers R, Popat M. The i-gel airway for ventilation and rescue intubation. Anaesthesia 27; 62: Tanaka M, Nishikawa T. Propofol requirement for insertion of cuffed oropharyngeal airway versus laryngeal mask airway with and without fentanyl: a dose-finding study. British Journal of Anaesthesia 23; 9: Yumura J, Koukita Y, Fukuda K, Kaneko Y, Ichinohe T. Low dose of fentanyl reduces predicted effect-site concentration of propofol for flexible laryngeal mask airway insertion. Journal of Anesthesia 29; 23: Drage MP, Nunez J, Vaughan RS, Asai T. Jaw thrusting as a clinical test to assess the adequate depth of anaesthesia for insertion of the laryngeal mask. Anaesthesia 1996; 51: Keller C, Brimacombe J, Keller K, Morris R. Comparison of four methods for assessing airway sealing pressure with the laryngeal mask airway in adult patients. British Journal of Anaesthesia 1999; 82: Gatward JJ, Cook T, Seller C, et al. Evaluation of the size 4 i-gel airway in one hundred non-paralysed patients. Anaesthesia 28; 63: Keijzer C, Buitelaar D, Efthymiou KM, et al. A comparison of postoperative throat and neck complaints after the use of the i-gel and the La Premiere disposable laryngeal mask: a double-blinded, randomized, controlled trial. Anesthesia and Analgesia 29; 19: Domino KB, Posner K, Caplan RA, Cheney FW. Airway injury during anesthesia: a closed claims analysis. Anesthesiology 1999; 91: Kambic V, Radsel Z. Intubation lesions of the larynx. British Journal of Anaesthesia 1978; 5: Oczenski W, Krenn H, Dahaba AA, et al. Complications following the use of the combitube, tracheal tube and laryngeal mask airway. Anaesthesia 1999; 54: Higgins PP, Chung F, Mezei G. Postoperative sore throat after ambulatory surgery. British Journal of Anaesthesia 22; 88: Cork RC, Depa R, Standen JR. Prospective comparison of use of the laryngeal mask and endotracheal tube for ambulatory surgery. Anesthesia and Analgesia 1994; 79: McHardy FE, Chung F. Postoperative sore throat: cause, prevention and treatment. Anaesthesia 1999; 54: Airway. American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 23; 98: Gonzalez H, Minville V, Delanoue K, Mazerolles M, Concina D, Fourcade O. The importance of increased neck circumference to intubation difficulties in obese patients. Anesthesia and Analgesia 28; 16: Lavi R, Sega l D, Ziser A. Predicting difficult airways using the intubation difficulty scale: a study comparing 486 Anaesthesia Ó 211 The Association of Anaesthetists of Great Britain and Ireland

7 U. Weber et al. Æ Comparison of i-gel and LMA-Unique obese and non-obese patients. Journal of Clinical Anesthesia 29; 21: Warner KJ, Sharar S, Copass MK, Bulger EM. Prehospital management of the difficult airway: a prospective cohort study. Journal of Emergency Medicine 29; 36: Joshi NA, Baird M, Cook TM. Use of an i-gel for airway rescue. Anaesthesia 28; 63: van Zundert A, Brimacombe J, Kamphuis R, Haanschoten M. The anatomical position of three extraglottic airway devices in patients with clear airways. Anaesthesia 26; 61: Anaesthesia Ó 211 The Association of Anaesthetists of Great Britain and Ireland 487