Intubation through the LMA-Supreme[TM]: a pilot study of two techniques in a manikin.
The primary goal of our study was to examine the ease of performing AIC-assisted and AECS-assisted intubations through the sLMA as well as to compare operator preferences for one technique over the other. Secondary aims were to compare the time required to perform the LMA exchange with each technique and record any failures.
MATERIALS AND METHODS
The University of Wisconsin Health Sciences Institutional Review Board exempted our study from scientific review. Written informed consent was obtained from all participants. Twenty senior anaesthesia trainees and staff experienced in fibreoptic-aided intubation through a LMA were invited and agreed to participate in the study.
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All intubations were performed on an Airsim[TM] airway manikin (Trucorp, Belfast, Ireland) through a #4 sLMA with a 15 mm bronchoscope adapter attached using a 4.29 mm outer diameter (OD) fibreoptic endoscope (FOS, Pentax Fiberscope FB-13V, Pentax Medical Company, Montvale, NJ, USA). Prior to their use, the manikin, the airway channel of the sLMA and the airway exchange catheters were pretreated with surgical grade silicone spray. Repeated flipping of a coin randomised the order in which each technique was performed. Prior to each study procedure, the sLMA was placed by one of the investigators (AMJ, ECL) and a full view of the vocal cords was confirmed through the eyepiece of the FOS. For the AECS-assisted technique, the operator passed the FOS via the LMA through the vocal cords and into the trachea. A 140 cm, unmarked, polytetrafluoroethylene coated, 0.35 mm diameter Amplatz guide wire was then passed through the injection port of the FOS and advanced through the working channel until it could be visualised within the trachea beyond the tip of the scope. The FOS was gradually removed with the guidewire under direct visualisation to assure that the wire remained in the same relative position within the trachea. After the FOS was removed, a 70 cm, 14 Fr (4.7 mm OD) airway exchange catheter, with guide markings every centimetre, was passed over the guidewire through the adapter into the trachea. The LMA was deflated and removed keeping both the guidewire and airway exchange catheter in the same relative position (6). For the AIC-assisted technique, the 56 cm, 19 Fr (6.27 mm OD) catheter was preloaded onto the FOS by an investigator before it was handed to the participant. The operator passed the FOS/AIC via the LMA through the vocal cords and into the trachea and the FOS was gradually removed to assure that the AIC remained in position. The LMA was deflated and removed, keeping the AIC in the same relative position7. For all procedures, timing was started when the FOS was handed to the participant and stopped when the LMA had been withdrawn over the airway exchange catheter and its position within the trachea confirmed. Tracheal position was confirmed by palpation of the airway exchange catheter within the trachea of the manikin. Participants were instructed to guide the FOS below the epiglottic fins rather than above them until the vocal cords could be seen. Inability to manipulate the FOS or exchange catheter into the trachea through the LMA or inadvertent removal of the exchange catheter from the trachea during LMA removal was considered a failure. After each intubation, the participant was asked to rate the ease of the technique during intubation of the trachea and during removal of the LMA over the exchange catheter as: 1 = easy, no resistance, 2 = slightly difficult, minor resistance, 3 = moderately difficult, moderate resistance and 4 = severe difficulty, severe resistance. Additionally, participants were asked to identify which LMA they preferred and why they preferred it.
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Grading of the ease of each technique and intubation times were compared using the MannWhitney U-test. Device preferences were compared by [chi square] testing. Unless otherwise noted, data is presented as mean (SD) or median (interquartile range [range]). Statistical significance is defined by a two-sided P value <0.05. Statistical analysis was performed using Prism 5.0a (GraphPad Software, Inc., La Jolla, CA, USA).
Each participant performed one intubation each with the AIC and the AECS through the sLMA. Twenty intubations utilising each technique were performed. The overall rating for passing the FOS during AECS into the trachea through the sLMA was 1 (1 to 1 [1 to 2]) and for the FOS/AIC was 2 (1 to 3 [1 to 4]), P=0.0001. The median rating for passage of the airway exchange catheter included in the AECS through the sLMA was 1 (1 to 1 [1 to 2]). Removal of the sLMA over the airway exchange catheter was rated 1 (1 to 1 [1 to 2]) for the airway exchange catheter of the AECS and 1 (1 to 2 [1 to 2]) for the AIC, P=0.03. Of the 20 participants, 10 (50%) preferred the AIC and 10 (50%) the AECS techniques. Participants who preferred the AECS stated they had better control of the FOS, making it easier to manipulate into the trachea (6) or that less resistance was encountered upon advancing the exchange catheter over the wire, through the LMA (4). Participants who preferred the AIC stated the technique involved fewer steps and was faster (7), that the catheter was stiffer and felt less likely to dislodge from the airway during the exchange (2) or both (1). The time to completion was 54 (21) seconds for the AIC and 98 (23) for the AECS, P <0.0001. There was no difference in failure rate between the two techniques (two failures with the AIC and none with the AECS, P=0.48). In one case, the AIC was dislodged from the trachea during LMA removal and in one case the FOS/AIC could not be manoeuvred past the vocal cords.
The main findings of our study are that performing fibreoptic-aided tracheal intubation using the AECS was subjectively easier than the AIC through an sLMA. This was true for both intubation of the trachea with the FOS through the sLMA and removal of the sLMA over the exchange catheter. However, our objective data (the time from placing the FOS into the LMA to LMA removal over the airway exchange catheter) supports the use of AIC-assisted intubation through the sLMA. In addition, half of our participants preferred the AIC-assisted to AECS-assisted intubation, citing fewer steps and faster performance as the reason.
Although the precise dimension of the airway space of the sLMA is unpublished, passing lubricated, uncuffed paediatric tracheal tubes of increasing OD into the airway space of a #4 sLMA indicates that it is [less than or equal to] 6.9 mm (a 5 mm inner diameter [ID] tube is tight, but passable) with the ID of the space bounded by the epiglottic fins even smaller. The relative stiffness of the 6.27 mm OD AIC may explain why some have found it difficult to manipulate through the sLMA and have advised the use of the pLMA instead (8). Our findings agree with this observation. The AECS utilises a smaller 4.62 mm OD exchange catheter, which makes it less likely to encounter resistance while passing through the airway space and underneath the epiglottic fins of the sLMA. Supporting this assertion, 17/20 (85%) participants encountered no resistance and 3/20 (15%) encountered minor resistance to passage of the AECS exchange catheter through the sLMA. Furthermore, successful clinical experience of the AECS technique through the sLMA has been reported (5).
An alternative technique to those used in our study has been reported (9). Mathes and colleagues evaluated two techniques alternating a paediatric gum elastic bougie and a nasogastric tube. In one technique, the bougie was passed down the right side of the airway space by one operator while another operator passed a paediatric FOS down the left side to direct placement of the bougie into the trachea. After the bougie was successfully placed in the trachea, the sLMA and the FOS were removed, leaving the bougie in the same relative position over which a tracheal tube was placed. Oesophageal intubation occurred in two of four patients,
however. In the second technique, the FOS was loaded with a modified nasogastric tube and guided into the trachea. The FOS was then removed and a bougie introduced into the nasogastric tube for stabilisation. The LMA was then exchanged for a tracheal tube. This was successful in all four patients in whom it was attempted. Compared with the techniques evaluated in our study, this technique is cumbersome, requires more than one operator, utilises equipment not designed specifically for the task and may not be readily available in an emergency.
Our study has limitations. The number of participants in our study was small. The finding that 5% (1/20) of AIC-assisted intubations encountered severe resistance to advancement resulting in an inability to guide the FOS/AIC into the trachea and intubation failure, deserves further study. Further, all of the participants in our study had considerable experience with fibreoptic-aided intubation. Thus, our findings cannot be generalised to less experienced operators. We acknowledge that in clinical practice the same individual would place the LMA and then proceed to attempt to pass the fibrescope. However, we wanted to test participant's ability to intubate through the LMA and not their ability to insert a LMA into a manikin. Other manikin studies have used similar methodology (10). Given that clinical studies have already documented insertion success rates and excellent views of the vocal cords after insertion of the sLMA (11), data regarding ease of insertion and laryngeal views through the sLMA after placement by a study participant in a manikin would add nothing to our general knowledge. Also, our primary study endpoint (removal of the LMA over the exchange catheter) stopped short of the penultimate clinical endpoint (confirmed tracheal intubation) in that our study procedure omitted railroading of the tracheal tube over the airway exchange catheter. Insofar as prior studies have documented the clinical efficacy of AIC7, (10,13) and AECS-assisted intubations (6,12), we are dubious that the time required to railroad the tube over the exchange catheter would have been so disparate between techniques as to change our results and that subjective opinions about the ease of railroading a tracheal tube over an exchange catheter would have been superfluous. We acknowledge, however, that the nearly 45 second difference we report between the AIC and AECS techniques, although statistically significant, may be clinically irrelevant. This question can only be answered by a properly conducted clinical trial. Lastly, the reader should be aware of differences between the exchange catheters used in our study that bear clinical relevance. The AIC has an ID of 4.7 mm, which limits the size of bronchoscope over which it can be placed. Regular and smaller adult scopes are too large. Furthermore, the 19 Fr size only accommodates tracheal tubes [greater than or equal to] 7 mm ID. In cases of a narrowed glottis, tracheal stenosis, in children or adolescents, this technique may be inadequate. In contrast, the guide wire of the AECS fits through the working channel of regular adult, small adult, double-lumen and paediatric bronchoscopes and the 14 Fr exchange catheter will accommodate tracheal tubes as small as 5 mm ID.
When intubating through an LMA, passage of the FOS into the trachea is not the only important factor that determines the ultimate success of tracheal intubation. For example, resistance to removal of the LMA over the exchange catheter may result in dislodgment of the exchange catheter from the trachea and intubation failure. Thus, we believe subjective data regarding the ease of removal of the sLMA over the airway exchange catheter is an important addition to our knowledge about this device.
Reusable laryngeal masks are being gradually phased out in favour of single-use disposable devices at our institution. Outside the hospital, in our local and surrounding communities, emergency medical services have incorporated the sLMA or disposable LMA-Fastrach[TM] into their difficult airway algorithms. As these devices become more ubiquitous, anaesthetists will no doubt encounter patients in whom a sLMA has been successfully placed and will be confronted with an all too common conundrum; what do I do now? He/she who removes a functional airway from a patient does so at his/her own peril. This is particularly true if the LMA was placed as a 'rescue' device after repeated airway manipulation, which could result in a 'can't intubate/can't ventilate' scenario. Therefore, our intention was primarily to document whether one or both of the techniques we describe could be adequately performed through the sLMA given the design differences between it and other commonly used LMAs. It is our hope that this will aid clinicians in decision making when presented with an sLMA already in place and in need of exchange for a tracheal tube or if fibreoptic-guided tracheal tube placement using the sLMA as the conduit is chosen as a primary means of airway management. Our report should not be interpreted however, as an endorsement for placing a sLMA as the primary conduit for tracheal intubation when devices specifically designed for this task (e.g. LMA-Fastrach[TM]) and operators experienced in its use are available. Furthermore, the reader is cautioned that our results cannot be extended to a size #3 sLMA. Using the methodology described above, the ID of the airway space of the #3 sLMA appears to be [less than or equal to] 6.2 mm (a 4.5 mm ID tube is tight, but passable), making passage of an AIC difficult or impossible.
In summary, experienced operators can perform both AIC-assisted and AECS-assisted intubations through the sLMA. The larger OD of the AIC results in greater resistance to passage through the sLMA and removal of the sLMA over the catheter compared with the AECS. However, because one less step is required to intubate with the AIC compared to the AECS, it can be performed faster. Clinicians should choose their preferred technique based on the size of sLMA, their clinical experience and the availability of necessary equipment.
We gratefully acknowledge the staff and senior resident class of the Department of Anesthesiology, University of Wisconsin School of Medicine and Public Health for their participation. Without it, this study would not be possible.
CONFLICT OF INTEREST
The authors acknowledge a departmental association with Dr George Arndt, the inventor of the Arndt Airway Catheter Exchange Set. The authors received no assistance in any way from Dr Arndt or Cook Critical Care for the performance of this study or preparation of the manuscript.
The airway manikin and equipment for the study was provided solely by intramural departmental funding.
Accepted for publication on June 21, 2009.
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Address for correspondence: Dr A. M. Joffe, 600 Highland Ave, B6/319, CSC, Madison, WI 53792, USA.
A. M. JOFFE *, E. C. LIEW ([dagger])
Department of Anesthesiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
* D.O., Clinical Assistant Professor, Anesthesiology.
([dagger]) M.D., F.R.C.A., Clinical Assistant Professor, Anesthesiology.
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|Author:||Joffe, A.M.; Liew, E.C.|
|Publication:||Anaesthesia and Intensive Care|
|Date:||Jan 1, 2010|
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