1. Introduction Many types of supraglottic airway device have been used as a conduit for tracheal intubation. The technique may be useful in difficult airway scenarios and the likelihood of success increases if fibreoptic guidance is used. In this randomised cross-over manikin study of a simulated difficult intubation, 26 anaesthetists attempted to intubate the trachea using two techniques: a fibreoptic-guided technique using an Aintree Intubating Catheter (AIC) via an LMA Classic TM (cLMA), and a fibreoptic-guided technique via an Intubating Laryngeal Mask Airway (ILMA). We hypothesised that intubation success rate would be higher using the former technique than with the latter. If correct, use of the cLMA would appear to be preferable to use of the ILMA when faced with a failed intubation. Introduction Many types of supraglottic airway device have been used as a conduit for tracheal intubation. The technique may be useful in difficult airway scenarios and the likelihood of success increases if fibreoptic guidance is used. In this randomised cross-over manikin study of a simulated difficult intubation, 26 anaesthetists attempted to intubate the trachea using two techniques: a fibreoptic-guided technique using an Aintree Intubating Catheter (AIC) via an LMA Classic TM (cLMA), and a fibreoptic-guided technique via an Intubating Laryngeal Mask Airway (ILMA). We hypothesised that intubation success rate would be higher using the former technique than with the latter. If correct, use of the cLMA would appear to be preferable to use of the ILMA when faced with a failed intubation. Methods The Local Research Ethics Committee waived the need for formal approval for this study. Prior to participant involvement a size three cLMA was positioned in an Airsim airway manikin (Trucorp Ltd, Belfast, UK), and a size three ILMA was positioned in an identical manikin. In both cases the larynx of the manikin was lifted anteriorly and laterally by tube ties, to simulate a difficult airway. Care was taken to ensure that the anatomical relationship between the airway device and the larynx was identical in each manikin (see Figure 2). After being shown written and video instruction, the participants attempted to intubate the trachea of each manikin. Successful intubation was the primary endpoint and these data were evaluated using the Sign test. Timings were also recorded, and analysed using paired t-tests. Methods The Local Research Ethics Committee waived the need for formal approval for this study. Prior to participant involvement a size three cLMA was positioned in an Airsim airway manikin (Trucorp Ltd, Belfast, UK), and a size three ILMA was positioned in an identical manikin. In both cases the larynx of the manikin was lifted anteriorly and laterally by tube ties, to simulate a difficult airway. Care was taken to ensure that the anatomical relationship between the airway device and the larynx was identical in each manikin (see Figure 2). After being shown written and video instruction, the participants attempted to intubate the trachea of each manikin. Successful intubation was the primary endpoint and these data were evaluated using the Sign test. Timings were also recorded, and analysed using paired t-tests. Acknowledgements The authors would like to thank Michael Phillips for his help with the statistical methods employed, and LMA PacMed for supplying the manikins. Acknowledgements The authors would like to thank Michael Phillips for his help with the statistical methods employed, and LMA PacMed for supplying the manikins. Results The median (IQR [range]) number of years experience in anaesthesia of the participants was 6 (3.5-8.75 [0- 18]) years. Two participants had no experience with fibreoptic intubation, eight described their experience as minimal, thirteen as moderate, and three as extensive. Participants’ prior experience in the use of the two intubating techniques examined is outlined in the table below: Table 1. Number of times participants had performed the two intubating techniques, prior to the study. Values are numbers (proportion) Results The median (IQR [range]) number of years experience in anaesthesia of the participants was 6 (3.5-8.75 [0- 18]) years. Two participants had no experience with fibreoptic intubation, eight described their experience as minimal, thirteen as moderate, and three as extensive. Participants’ prior experience in the use of the two intubating techniques examined is outlined in the table below: Table 1. Number of times participants had performed the two intubating techniques, prior to the study. Values are numbers (proportion) Ferson et al. have reported use of the ILMA in 48 FO-guided intubations, in patients with airway distortion 3. All these were successful at the first attempt, however the operators were experienced in the use of the ILMA This expertise may help to explain Ferson’s high success rates, and the low success rates with the same technique in our study. A FO-guided technique needs to be easy to perform despite minimal prior exposure. Proficiency in the use of the ILMA may require 20 attempts 4, whereas safe use of the cLMA + AIC technique can be achieved with considerably less experience 5,6. A.M.B. Heard, 1 D.A. Lacquiere, 2 and R.H. Riley. 1 1 Department of Anaesthesia and Pain Medicine, Royal Perth Hospital, Perth, Australia 2 Department of Anaesthesia, Taunton and Somerset NHS Foundation Trust, Taunton, UK References 1McNeillis NJD, Timberlake C, Avidan MS, Sarang K, Choyce A, Radcliffe JJ. Fibreoptic views through the laryngeal mask and the intubating laryngeal mask. European Journal of Anaesthesiology 2001; 18: 471–5. 2Keller C, Brimacombe J. Pharyngeal mucosal pressures, airway sealing pressures, and fibreoptic position with the intubating versus the standard laryngeal mask airway. Anesthesiology 1990; 90: 1001–6. 3Ferson D, Rosenblatt W, Johansen M, Osborn I, Ovassapian O. Use of the intubating LMA-Fastrach in 254 patients with difficult-to-manage airways. Anesthesiology 2001: 95: 1175-81Scott, E.C. 2005. 4Chan YW, Kong CF, Kong CS, Hwang NC, Ip-yam PC. The intubating laryngeal mask (ILMA): initial experience in Singapore. British Journal of Anaesthesia 1998; 81:610–11 5Atherton DPL, O’Sullivan E, Lowe D, Charters P. A ventilation-exchange bougie for fibreoptic intubations with the laryngeal mask airway. Anaesthesia 1996; 51: 1123-6 6Higgs A, Clark E, Premraj K. Low-skill fibreoptic intubation: use of the Aintree Catheter with the Classic LMA. Anaesthesia 2005; 60: 915–20 7Hodzovic I, Wilkes AR, Gataure P, Latto IP. Survey of experience with the more advanced components of the 2004 Difficult Airway Society guidelines. Anaesthesia 2005; 60: 834A References 1McNeillis NJD, Timberlake C, Avidan MS, Sarang K, Choyce A, Radcliffe JJ. Fibreoptic views through the laryngeal mask and the intubating laryngeal mask. European Journal of Anaesthesiology 2001; 18: 471–5. 2Keller C, Brimacombe J. Pharyngeal mucosal pressures, airway sealing pressures, and fibreoptic position with the intubating versus the standard laryngeal mask airway. Anesthesiology 1990; 90: 1001–6. 3Ferson D, Rosenblatt W, Johansen M, Osborn I, Ovassapian O. Use of the intubating LMA-Fastrach in 254 patients with difficult-to-manage airways. Anesthesiology 2001: 95: 1175-81Scott, E.C. 2005. 4Chan YW, Kong CF, Kong CS, Hwang NC, Ip-yam PC. The intubating laryngeal mask (ILMA): initial experience in Singapore. British Journal of Anaesthesia 1998; 81:610–11 5Atherton DPL, O’Sullivan E, Lowe D, Charters P. A ventilation-exchange bougie for fibreoptic intubations with the laryngeal mask airway. Anaesthesia 1996; 51: 1123-6 6Higgs A, Clark E, Premraj K. Low-skill fibreoptic intubation: use of the Aintree Catheter with the Classic LMA. Anaesthesia 2005; 60: 915–20 7Hodzovic I, Wilkes AR, Gataure P, Latto IP. Survey of experience with the more advanced components of the 2004 Difficult Airway Society guidelines. Anaesthesia 2005; 60: 834A Figure 1. Manikin with tube ties looped around the larynx to simulate a difficult airway We have shown that FO-guided tracheal intubation can be achieved more often and faster using an AIC via a cLMA than using an ILMA, in the simulated difficult airway. Even in this scenario the technique appears easy to perform by those with limited experience. Given the familiarity most anaesthetists have with the cLMA and the limited experience they have with the ILMA 7 we suggest most anaesthetists, when facing a possible airway crisis, consider using the cLMA as the first choice conduit for oxygenation and subsequent FO- guided intubation, if conventional intubation techniques have failed. Why is the cLMA + AIC technique superior? In 18 of the 21 failures to intubate in the ILMA group, the vocal cords were never reached with the fibrescope. This suggests that the primary reason for the superiority of the cLMA technique is that it is easier to locate the larynx with a fibrescope from the end of the cLMA than from the end of the ILMA, when there is abnormal perilaryngeal anatomy. In the case of the ILMA, the fibrescope (or rather, the tracheal tube that surrounds it) has to lift, and thus pass beyond the EEB, before the larynx is revealed. In normal airways, with good ILMA positioning, this is not a problem, and may be advantageous, as the EEB lifts the epiglottis out of the way. However in the difficult airway it may not be possible to position the EEB directly beneath the epiglottis, and so the EEB itself may distort the perilaryngeal anatomy as it is lifted. Moreover if the larynx is anterior and/or distorted, a ‘wide-angled’ view of the larynx is desirable. The need to pass beyond the EEB reduces the angle available, thus limiting the ability of the operator to locate the vocal cords. Why is the cLMA + AIC technique superior? In 18 of the 21 failures to intubate in the ILMA group, the vocal cords were never reached with the fibrescope. This suggests that the primary reason for the superiority of the cLMA technique is that it is easier to locate the larynx with a fibrescope from the end of the cLMA than from the end of the ILMA, when there is abnormal perilaryngeal anatomy. In the case of the ILMA, the fibrescope (or rather, the tracheal tube that surrounds it) has to lift, and thus pass beyond the EEB, before the larynx is revealed. In normal airways, with good ILMA positioning, this is not a problem, and may be advantageous, as the EEB lifts the epiglottis out of the way. However in the difficult airway it may not be possible to position the EEB directly beneath the epiglottis, and so the EEB itself may distort the perilaryngeal anatomy as it is lifted. Moreover if the larynx is anterior and/or distorted, a ‘wide-angled’ view of the larynx is desirable. The need to pass beyond the EEB reduces the angle available, thus limiting the ability of the operator to locate the vocal cords. Comparison of fibreoptic-guided intubation through the ILMA versus fibreoptic-guided intubation using the LMA Classic plus the Aintree Intubating Catheter: a manikin study in a simulated difficult airway Discussion We found that in a simulated difficult intubation, FO-guided intubation can be achieved more quickly and reliably using a cLMA with an AIC, than using an ILMA. We suspect most anaesthetists would choose a cLMA over an ILMA to oxygenate the patient when faced with an airway crisis, because of the cLMA’s ubiquity and the familiarity anaesthetists have with its use. Our findings of increased speed and, more importantly, success of tracheal intubation if a cLMA is chosen, represent another reason to select a cLMA in this situation. Discussion We found that in a simulated difficult intubation, FO-guided intubation can be achieved more quickly and reliably using a cLMA with an AIC, than using an ILMA. We suspect most anaesthetists would choose a cLMA over an ILMA to oxygenate the patient when faced with an airway crisis, because of the cLMA’s ubiquity and the familiarity anaesthetists have with its use. Our findings of increased speed and, more importantly, success of tracheal intubation if a cLMA is chosen, represent another reason to select a cLMA in this situation. Intubation was completed successfully in all 26 cases using the AIC with cLMA technique, and in five cases using the ILMA technique (p<0.0001). The former technique also proved quicker (mean [95% CI]) in terms of: 1. Time taken in seconds to reach the vocal cords with the fibrescope (17.8 [15.0-21.2] versus 81.9 [50.7-132.5], p = 0.0008) 2. Time until a device was railroaded into the trachea (40.7 [35.9-46.2] versus 91.0 [49.7-166.4] p = 0.01) 3. Time to first ventilation (89.8 [81.5- 99.1] versus 113.5 [69.6-185.3], p = 0.0038). Intubation was completed successfully in all 26 cases using the AIC with cLMA technique, and in five cases using the ILMA technique (p<0.0001). The former technique also proved quicker (mean [95% CI]) in terms of: 1. Time taken in seconds to reach the vocal cords with the fibrescope (17.8 [15.0-21.2] versus 81.9 [50.7-132.5], p = 0.0008) 2. Time until a device was railroaded into the trachea (40.7 [35.9-46.2] versus 91.0 [49.7-166.4] p = 0.01) 3. Time to first ventilation (89.8 [81.5- 99.1] versus 113.5 [69.6-185.3], p = 0.0038). (a) (b) Figure 2. (a) Endoscopic view via the cLMA. (b) Endoscopic view via the ILMA (epiglottic elevating bar removed) Are our findings supported by the literature? Other authors have also reported inferior fibreoptic positioning of the ILMA compared to the cLMA. Like us, McNeillis et al. blame the increased depth of insertion of the bronchoscope, necessary to lift the EEB 1. Keller and Brimacombe suggest that the fixed length of the airway tube of the ILMA may be responsible 2. However we controlled for this by ensuring that the distance between the point at which the bronchoscope emerged from the airway tube and the vocal cords was identical in the two manikins. Figure 3. The need to pass the fibreoptic bronchoscope beyond the Epiglottic Elevating Bar of the ILMA reduces the angle available to view the larynx. (a) view via the cLMA. (b) view via the ILMA.