The LMA CTrach TM, a new laryngeal mask airway for endotracheal intubation under vision: evaluation in 100 patients

Transcription

1 British Journal of Anaesthesia 96 (3): (2006) doi: /bja/ael001 Advance Access publication January 16, 2006 The LMA CTrach TM, a new laryngeal mask airway for endotracheal intubation under vision: evaluation in 100 patients E. H. C. Liu 12 *, R. W. L. Goy 2 and F. G. Chen 12 1 Department of Anaesthesia, Yong Loo Lin School of Medicine, National University of Singapore and 2 Department of Anaesthesia, National University Hospital, 5 Lower Kent Ridge Road, Singapore *Corresponding author. analiue@nus.edu.sg Background. The LMA CTrach TM is a new laryngeal mask system consisting of an LMA CTrach TM Airway with integrated fibreoptic channels, and a detachable LMA CTrach TM Viewer. This system enables viewing of the larynx and aids endotracheal intubation through a laryngeal mask airway. Method. We used and evaluated this system in 100 adult patients undergoing general anaesthesia for elective surgery. Our primary outcomes were the success rates of LMA CTrach TM Airway insertion and endotracheal intubation with this system. Results. We were able to insert the LMA CTrach TM Airway in and to ventilate all 100 patients. We were successful in endotracheal intubation, either under vision or blind, in 96 patients. We were able to view the larynx in 84 patients, but the quality of the best view obtained was very variable. The median (inter quartile range) time for the complete intubation process was 166 ( ) s. The system allowed nearly continuous ventilation and oxygenation during the process. Conclusions. The LMA CTrach TM system has potential advantages over the LMA Fastrach TM system, including the ability to align the LMA outlet with the larynx and a high first intubation attempt success rate. However, it was difficult to view the larynx with the LMA CTrach TM compared with direct laryngoscopy, and expectations must be moderated. Br J Anaesth 2006; 96: Keywords: equipment, laryngeal masks; equipment, LMA CTrach TM ; intubation, endotracheal Accepted for publication: December 12, 2005 The LMA CTrach TM system (The Laryngeal Mask Company, Singapore) is a new system for airway management and endotracheal intubation. Based on the Intubating Laryngeal Mask Airway (LMA Fastrach TM ) system, this new system comprises a LMA CTrach TM Airway and a detachable liquid crystal display LMA CTrach TM Viewer. This system enables viewing of the larynx and the process of endotracheal intubation through the laryngeal mask airway. The LMA CTrach TM system is indicated as a device for achieving and maintaining an airway in both anticipated and unexpected difficult intubation situations. We evaluated the success rates of insertion of the LMA CTrach TM Airway, of viewing the larynx and of endotracheal intubation with this new system in 100 adult patients. Methods The LMA CTrach TM system The LMA CTrach TM system is shown in Figure 1. The LMA CTrach TM Airway (CTrach) has two in-built fibreoptic channels, one to convey light from and the other to convey the image to the viewer. This fibreoptic system is sealed and robust, and the CTrach can be autoclaved. The CTrach has an epiglottis elevating bar, which elevates the epiglottis during passage of the endotracheal tube (ETT) through the CTrach into the larynx. This bar has an aperture through which the anatomy anterior to the bar is viewed. The CTrach s shape is based on magnetic resonance imaging of the human airway, to enable a close fit with the oropharyngeal curve and optimal alignment with the laryngeal inlet. The magnetic latch connection at the top of the CTrach connects the detachable LMA CTrach TM Viewer securely to the CTrach airway, ensuring correct alignment of the fibreoptic channels to the viewer. The viewer has a high resolution 86 mm LCD colour display. It provides the light source, and has keys for adjusting the image gain, brightness and colour. It has a thumbwheel for adjusting the focus and a rechargeable battery for up to 30 min of continuous use. A charger cradle for recharging the viewer is included in the system. Ó The Board of Management and Trustees of the British Journal of Anaesthesia All rights reserved. For Permissions, please journals.permissions@oxfordjournals.org

2 Evaluation of the LMA CTrach TM Fig 1 The LMA CTrach TM system comprising the liquid crystal display LMA CTrach TM Viewer connected to the LMA CTrach TM Airway. Patients We obtained institutional review board approval, and written informed consent from all patients for this study. We recruited 100 adult patients, yr of age and ASA I III physiological status, who required general anaesthesia with endotracheal intubation for elective surgery. Patients who were pregnant, non-fasted, morbidly obese, had gastrooesophageal reflux, delayed gastric emptying or severe respiratory disease, were excluded. Preparation We chose the CTrach size according to the patients body weight, following the manufacturer s recommendations. We used flexible, cuffed, wire reinforced silicone Fastrach ETTs (The Laryngeal Mask Company, Singapore) for all patients. A size 3 CTrach and 7 mm inner diameter ETT were used for patients with body weight <50 kg. A size 4 CTrach and 7.5 mm ETT were used for patients kg, and a size 5 CTrach and 8 mm ETT were used for patients >70 kg. Before the insertion of the CTrach, the viewer was attached to the CTrach and focused by obtaining a sharp image of a sheet of text held 1 cm in front of the fibreoptic channel port. The viewer was then detached. Only the posterior surface of the CTrach was lubricated, to prevent obscuring of the fibreoptic channel port. Anaesthesia and airway management After preoxygenating the patients, we induced general anaesthesia with propofol mg kg 1, and maintained anaesthesia with isoflurane at expiratory concentrations of 1 1.5%. We tested face-mask ventilation before inducing muscle relaxation with atracurium 0.5 mg kg 1. Two investigators (E.H.C.L., R.W.L.G.) carried out all the CTrach procedures. These two investigators were experienced with the Fastrach and had carried out at least 10 successful endotracheal intubations with the CTrach system before this evaluation. Before the CTrach procedure, a separate anaesthetist with at least 5 yr of experience performed direct laryngoscopy using a Macintosh laryngoscope. The patient s occiput was supported on a silicone jelly doughnut of 4 cm height. The sniffing position with neck flexion and head extension was used. The anaesthetist graded the laryngeal view using the modified Cormack and Lehane grading, 1 without revealing this grade to the investigator carrying out the CTrach procedure. The head and neck were then placed in neutral posture. We inserted the CTrach with minimal neck movement in all patients, without the viewer attached. We inflated the CTrach cuff, and then checked ventilation with the CTrach. If necessary, we manipulated the CTrach to obtain the least resistance to ventilation and minimal leak. Once satisfactory ventilation was achieved, we attached the viewer to the CTrach to obtain a view of the larynx. Ventilation via the CTrach was maintained throughout this time. If we could not view the larynx, we manipulated the CTrach to try to obtain a view. At a minimum, we aimed to see the vocal cords and laryngeal inlet in the centre of the viewer. After obtaining the best possible view, we passed the ETT through the CTrach into the trachea under vision and confirmed correct intubation by chest auscultation and capnography. We then detached the viewer, removed the ETT connector, deflated the CTrach cuff, and removed the CTrach over the ETT with the aid of a stabilizer rod. The ETT connector was then replaced and connected to the anaesthesia circuit for continued ventilation, the ETT was securely taped, and surgical preparation commenced. We permitted a maximum of three attempts at insertion of the CTrach to achieve adequate ventilation, a maximum of 3 min to achieve a view of the larynx after attaching the viewer, and a maximum of three attempts at endotracheal intubation. We carried out blind endotracheal intubation via the CTrach if we were unable to obtain a view of the larynx. Intubation with the CTrach was abandoned after three failed attempts and carried out using a Macintosh laryngoscope. Data and analysis Our primary outcome measures were the success rate of CTrach insertion and ventilation, and of endotracheal intubation with this system. We recorded the success rate of viewing the larynx, the quality of the best laryngeal view obtained, the number of attempts at CTrach insertion and number of attempts at endotracheal intubation. The times required for achieving ventilation with the CTrach, for obtaining a view of the larynx, and for the complete process from insertion of the CTrach to the completion of endotracheal intubation and the removal of the CTrach, were recorded. Means and standard deviation were used to describe parametric data, medians and interquartile ranges to describe non-parametric data, and rates and percentages 397

3 Liu et al. for success rates and nominal data. The Pearson coefficient was used to assess correlation between direct laryngoscopy grade and the success of obtaining a view of the larynx with the CTrach, and correlation between laryngoscopy grade and success of intubation with the CTrach. Results The patients had a mean age of 44.2 (21 80) yr, mean weight of 66.0 (13.5) kg and a mean BMI of 24.7 (4.6) kg m 2. There were 47 male and 53 female patients. There were 67, 29 and 4 patients of ASA status I, II and III, respectively. There were 33, 41, 23 and 3 patients with Mallampati class I, II, III and IV airways, respectively. Anaesthesia was uncomplicated in all patients. We successfully inserted the CTrach at the first attempt in all 100 patients and were able to ventilate all 100 patients with the CTrach. We were able to view the larynx in 84 patients. We were initially unable to distinguish any structures after attaching the viewer in 40 of these 84 patients. We tried manipulations including partial withdrawal and reinsertion of the CTrach, passage of a suction catheter (without suction) through the CTrach, applying suction to this catheter, rotation of the CTrach, jaw thrust and tongue traction and were then able to view the larynx in 24 of these 40 patients. We were simply unable to view the larynx in 16 patients after 3 min. Water vapour condensation obscured the image in 21 patients and we corrected this problem with ventilation and suction. We succeeded in endotracheal intubation using the CTrach in 96 patients overall. In the 84 patients where we obtained a view of the larynx, we successfully intubated the trachea in 83 (98.8%) of these patients at the first attempt. In the remaining patient, the larynx could only be seen on the far left of the viewer display. We were unable to centralize the image and to align the CTrach with the larynx despite several manipulations. We were unable to direct the ETT into the trachea after three attempts and carried out conventional intubation using a Macintosh laryngoscope. In the 16 patients in whom we could not view the larynx, we carried out blind intubation in 14 patients and were successful in 13 patients (92.9%) at the first attempt. We failed in one patient despite three attempts in this patient and good ventilation with the CTrach, and had to use conventional laryngoscopy. In the remaining 2 of these 16 patients, we did not attempt blind intubation via the CTrach and used conventional laryngoscopy directly. This was because we were unable to achieve a good seal with the CTrach and needed high fresh gas flows for ventilation. The times for CTrach insertion, visualization of the larynx, and intubation are shown in Table 1. The ease of laryngeal visualization, quality of the view and number of attempts for intubation are shown in Table 2. An example of a good view of the larynx, and the intubation process are shown in Figure 2A D. Table 1 Timings for CTrach insertion, visualization and endotracheal intubation. Times are median (inter quartile range) [range] in seconds Procedure Insertion of CTrach and successful ventilation Time to achieve view of larynx after attachment of LCD viewer Time for successful intubation, measured from the beginning of ETT insertion to confirmation of successful intubation after the removal of the CTrach conduit Time for the complete process of CTrach insertion and endotracheal intubation Time (s) 26, (20 33), [10 300] 65, (30 141), [5 218] 55, (48 65), [22 525] 166, ( ), [70 605] Table 2 Ease of viewing the larynx and quality of the best laryngeal view obtained (N=100). Quality of view: good view able to see detailed laryngeal structure; acceptable able to distinguish arytenoids and laryngeal inlet; poor able to see laryngeal inlet but unable to distinguish other features. Intubation attempts: each pass of the ETT was counted as one attempt Number Success of viewing the larynx 84 Ease of obtaining view Easy 52 Difficult 32 Impossible 16 Quality of best laryngeal view where visible N=84 Good 28 Acceptable 28 Poor 28 Attempts at intubation where attempted via the CTrach N=98 One 96 Two 0 Three 2 Direct laryngoscopy was difficult (Grade 3) in nine patients. The factors contributing to difficulty included receding chin, poor dentition, and limited head and neck movement. Using the CTrach, we could see the larynx and intubation process in eight (88.9%) of these patients. The direct laryngoscopy grading, success rate of viewing the larynx and success rate of intubation via the CTrach are cross-tabulated in Table 3. There was no correlation between direct laryngoscopy grading and success of obtaining a view of the larynx (Pearson coefficient 0.16, P=0.11). There was no correlation between direct laryngoscopy grading and success of intubation (Pearson coefficient 0.09, P=0.38). Discussion Our evaluation showed high success rates of CTrach insertion, of ventilation with the CTrach, and endotracheal intubation with the CTrach, all with minimal neck movement. Although ventilation was not optimal in two patients, there was no difficulty maintaining good oxygenation. In contrast, our success at viewing the larynx and the quality of the best possible views were very variable. In nearly all 398

4 Evaluation of the LMA CTrach TM A B C D Fig 2 (A) View of the larynx seen on the LMA CTrach TM Viewer. (B) Lifting of the epiglottis elevator bar as the ETT is advanced through the LMA CTrach TM Airway. (C) ETT approaching the laryngeal inlet. (D) ETT inserted into the larynx. Table 3 Laryngoscopy grade and success of visualization and intubation. *Intubation failed in one patient after three attempts. Intubation not attempted in one patient as unable to optimize ventilation with the CTrach. y Unable to centralize larynx view in one patient, intubation failed after three attempts. x Intubation not attempted in one patient as unable to optimize ventilation with the CTrach Laryngoscopy grade Number of patients Ease of viewing the larynx with the CTrach system Easy Difficult Impossible Intubation success (57.6%) 18 (30.5%) 7 (11.9%)* 57 (96.6%) 2a (50%) 5 (25%) 5 (25%) 20 (100%) 2b 12 6 (50%) 3 (25%) y 3 (25%) 11 (91.7%) (22.2%) 6 (66.6%) 1 (11.1%) x 8 (88.9%) 4 0 patients where we could view the larynx, endotracheal intubation was successful at the first attempt. The difficulty of conventional laryngoscopy did not seem to influence the success of ventilation, viewing the larynx and intubation via the CTrach. One limitation is that we studied a general elective surgical patient population for this initial evaluation, and there were only nine patients with Grade 3 laryngoscopy. The CTrach system is indicated for difficult airway management, hence evaluation specifically in difficult airway patients is required. Our study also lacked a standardized protocol for managing failure to view the larynx, and did not include changing the size of the CTrach airway if ventilation was successful. Finally, all our patients had atracurium, and we are unable to assess the ease and success of visualization in unparalysed patients. While we could achieve a patent airway and ventilation with the CTrach in all patients, this is only a small study. The CTrach can be inserted without muscle relaxation and we advise testing ventilation after insertion of the CTrach before using neuromuscular blocking agents in patients with difficult airways. The CTrach has similar advantages as the Fastrach when compared with airway management with a Macintosh laryngoscope. The CTrach enables nearly continuous ventilation and oxygenation of the patient during the intubation process. Similar to the Fastrach, the CTrach is designed to enable endotracheal intubation with minimal distortion of the airway. 23 In contrast, conventional tracheal intubation requires alignment of the oral, pharyngeal and laryngeal axes, which is not always possible or easy, causing difficulty in up to 3% of patients and failure in up to 2%

5 Liu et al. The CTrach may also be useful in establishing an airway in difficult to ventilate, difficult to intubate scenarios, and may be left in place to maintain an airway if intubation through it fails. Compared with the Fastrach, the CTrach s advantage is that it can be manipulated and aligned with the larynx under vision. In the patients where the larynx could be seen, our 98.9% first attempt success rate for endotracheal intubation compares favourably with the 79.8% first attempt success rate in a large analysis of the Fastrach. 6 Despite easy insertion of and optimal ventilation via the Fastrach, alignment with the larynx may still be suboptimal. In evaluating the Fastrach with a fibreoptic bronchoscope, Kapila and colleagues 7 showed that the number of blind intubation attempts increased with worsening alignment of the Fastrach with the larynx. A study comparing blind and fibreoptic guided intubation via the Fastrach showed a higher success rate with fibreoptic guidance. 8 The CTrach system can enable detection of mal-alignment and epiglottic obstruction, and can guide manipulations to correct these problems before attempting intubation. This suggests that it may be worth the effort to obtain a view of the larynx with the CTrach, in order to reduce the number of intubation attempts, interruption of ventilation and trauma, compared with multiple blind attempts. The CTrach is also less cumbersome than using a fibreoptic bronchoscope through a Fastrach. Finally, the ability to see the intubation process may help in teaching intubation through a laryngeal mask conduit. Our main problems with the CTrach were the unpredictable success of obtaining a view and the variable quality of the larynx images. The failure to obtain a satisfactory view of the larynx in a significant proportion of patients will reduce the CTrach s clinical value, although the CTrach can be used similarly to the Fastrach for blind intubation. We are unable to identify the factors that lead to poor views of or failure to view the larynx. In patients where no feature could be distinguished, it was unclear if this was attributable to the epiglottis or arytenoids or a displaced epiglottis elevating bar abutting against the fibreoptic channel outlet. Minor lateral displacement of this flexible bar can completely obstruct the view. There was no single manipulation that could assure a successful view. Further evaluation of this system is required to diagnose the causes of such failure and to formulate corrective protocols. In conclusion, in this evaluation, it was easier to obtain good views of the larynx with direct laryngoscopy than with the CTrach. The LMA CTrach TM system may have a role in difficult airway management by facilitating ventilation and enabling viewing of endotracheal intubation through a laryngeal mask device. But we must moderate our expectations of the quality of laryngeal views. Acknowledgements We thank The Laryngeal Mask Company (Singapore) Private Limited, our colleagues in the Department of Anaesthesia and the anaesthesia nurses of the Operation Theatres Department, National University Hospital, for their help with this study. References 1 Yentis SM, Lee DJ. Evaluation of an improved scoring system for the grading of direct laryngoscopy. Anaesthesia 1998; 53: Brain AI, Verghese C, Addy EV, Kapila A. The intubating laryngeal mask. I: Development of a new device for intubation of the trachea. Br J Anaesth 1997; 79: Brain AI, Verghese C, Addy EV, Kapila A, Brimacombe J. The intubating laryngeal mask. II: A preliminary clinical report of a new means of intubating the trachea. Br J Anaesth 1997; 79: Davies JM, Weeks S, Crone LA, Pavlin E. Difficult intubation in the parturient. Can J Anaesth 1989; 36: Samsoon GL, Young JR. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42: Baskett PJ, Parr MJ, Nolan JP. The intubating laryngeal mask. Results of a multicentre trial with experience of 500 cases. Anaesthesia 1998; 53: Kapila A, Addy EV, Verghese C, Brain AI. The intubating laryngeal mask airway: an initial assessment of performance. Br J Anaesth 1997; 79: Langeron O, Semjen F, Bourgain JL, Marsac A, Cros AM. Comparison of the intubating laryngeal mask airway with the fiberoptic intubation in anticipated difficult airway management. Anesthesiology 2001; 94: