Anesth Analg 2004;99:1560-1563
© 2004 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000133916.10017.6D
GENERAL ARTICLES
The Laryngeal Mask Airway UniqueTM versus the Soft SealTM Laryngeal Mask: A Randomized, Crossover Study in Paralyzed, Anesthetized Patients
Joseph Brimacombe, MD*,
Achim von Goedecke, MD
,
Christian Keller, MD,
Lawrence Brimacombe, MB ChB*, and
Moira Brimacombe, MB ChB*
*Department of Anaesthesia and Intensive Care, James Cook University, Cairns Base Hospital, The Esplanade, Australia; and
Department of Anaesthesia and Intensive Care Medicine, Leopold-Franzens University, Innsbruck, Austria
Address correspondence and reprint requests to Joseph Brimacombe, MD, Department of Anesthesia and Intensive Care, Cairns Base Hospital, The Esplanade, Cairns 4870, Australia. Address e-mail to jbrimaco{at}bigpond.net.au
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Abstract
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We tested the hypothesis that ease of insertion, oropharyngeal leak pressure, fiberoptic position, ease of ventilation, and mucosal trauma are different for the Soft SealTM laryngeal mask airway (SSLM) and the laryngeal mask airway UniqueTM (LMA-U). Ninety paralyzed, anesthetized adult patients (ASA I–II; 18–80 yr old) were studied. Both devices were inserted into each patient in random order. Oropharyngeal leak pressure and fiberoptic position were determined during cuff inflation from 0–40 mL in 10-mL increments and at an intracuff pressure of 60 cm H2O. Ease of ventilation was determined by controlling ventilation for 10 min at 8 and 12-mL/kg tidal volume and recording hemoglobin oxygen saturation, end-tidal CO2, leak fraction, peak airway pressure, and the presence or absence of gastric insufflation. Mucosal trauma was determined by examining the first randomized device for the presence of visible and occult blood. Insertion time was shorter (P = 0.0001) and fewer attempts were required (P = 0.005) for the LMA-U. There were no failed uses of either device. Oropharyngeal leak pressures were similar, but fiberoptic position was superior with the LMA-U (P 
0.0003). There were no differences in hemoglobin oxygen saturation, end-tidal CO2, leak fraction, or peak airway pressure at either tidal volume. Gastric insufflation was not detected in either group at either tidal volume. The frequency of visible (P = 0.009) and occult blood (P = 0.0001) was less with the LMA-U. We conclude that the LMA-U is superior to the SSLM in terms of ease of insertion, fiberoptic position, and mucosal trauma, but similar in terms of oropharyngeal leak pressure and ease of ventilation.
IMPLICATIONS: The laryngeal mask airway Unique TM is superior to the Soft Seal TM laryngeal mask in terms of ease of insertion, fiberoptic position, and mucosal trauma but similar in terms of oropharyngeal leak pressure and ease of ventilation.
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Introduction
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The Soft SealTM laryngeal mask airway (SSLM; Portex Ltd, Hyathe, United Kingdom) is a new single-use, plastic laryngeal mask airway similar to the single-use, plastic laryngeal mask airway UniqueTM (LMA-U; Intavent, Henley-on-Thames, United Kingdom), but it has a deeper bowl, a blunter distal cuff, a wider airway tube fused to a larger portion of the bowl, an integral inflation line, and no mask aperture bars (Fig. 1). The LMA-U has a similar clinical performance to the ClassicTM LMA (1,2), but there are no published data about the SSLM. The differences in design suggest that the clinical performance of the SSLM will differ from the LMA-U. In a randomized, crossover study, we tested the hypothesis that ease of insertion, oropharyngeal leak pressure, fiberoptic position, ease of ventilation, and mucosal trauma are different for the SSLM and LMA-U.
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Figure 1. The Soft SealTM (SSLM; top) and UniqueTM (LMA-U; bottom) laryngeal mask airways (A). View of the bowl of the SSLM (B) and LMA-U (C), illustrating the lack of mask aperture bars for the SSLM.
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Methods
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We studied 90 consecutive patients (ASA I–II; 18–80 yr old) undergoing routine superficial or peripheral surgery in a crossover fashion. Ethical committee approval and written informed consent were obtained. Patients were excluded from the trial if they had a known or predicted difficult airway, mouth opening <2.0 cm, a body mass index >35 kg/m2, or were at risk of aspiration of gastric contents. In 45 patients, the LMA-U was inserted first, and in the other 45 patients, the SSLM was inserted first. Randomization was by opening a sealed envelope. The ventilator and anesthesia circuit were tested for leaks before use by connecting them to an artificial lung and recording the difference between inspired and expired tidal volume over 20 breaths at similar tidal volumes to those used in patients.
Anesthesia was induced with fentanyl 1 µg/kg and midazolam 0.05 mg/kg, followed by propofol 2.5 mg/kg. Maintenance was with O2 and sevoflurane 1%–2%. Neuromuscular blockade was achieved with vecuronium 0.1 mg/kg. Patients were ventilated via a face mask for 3–5 min. The LMAs were used in strict accordance with their respective manufacturer’s recommendations and inserted by two users (45 patients each) with experience using both devices (50–300 uses with each of the study devices and 1500–10,000 insertions of other LMA devices). A size 4 LMA was used for women and a size 5 for men. The cuff was inflated with air until an effective airway was obtained or the maximum recommended volume reached (30 mL for size 4, and 40 mL for size 5). Both devices were fixed by taping the tube over the chin. The number of insertion attempts was recorded. A failed attempt was defined as removal of the device from the mouth. Three attempts were allowed before device use was considered a failure. The time between picking up the LMA and obtaining an effective airway was recorded, as in a previous study of the LMA-U (3). An effective airway was judged by an expired tidal volume of 8 mL/kg. If an effective airway could not be achieved, one attempt with the other device was allowed. Measurements were made with the head and neck in the neutral position and the occiput on a firm pillow 7 cm in height.
Oropharyngeal leak pressure and fiberoptic position were determined at 0–40 mL of cuff volume in 10-mL increments and at an intracuff pressure of 60 cm H2O using a digital manometer (Mallinckrodt Medical, Athlone, Ireland) (4). Oropharyngeal leak pressure was determined by closing the expiratory valve of the circle system at a fixed gas flow of 3 L/min and noting the airway pressure (maximum allowed was 40 cm H2O) at which equilibrium was reached (4). Fiberoptic position of the airway tube was determined by passing a fiberoptic scope through the airway tube to a position 1 cm proximal to the end of the tube and scoring the view (5).
Ease of ventilation was determined by setting the intracuff pressure to 60 cm H2O, controlling ventilation for 10 min at 8 and 12 mL/kg tidal volume, a respiratory rate of 12 breaths/min and a inspiratory:expiratory ratio of 1:2, and recording hemoglobin oxygen saturation, end-tidal CO2, inspired and expired tidal volume (using a pneumotachograph connected directly to the proximal end of the airway tube), peak airway pressure, and the presence or absence of gastric insufflation (6). Trained observers collected data during the last 10 breaths of the 10-min period, and the average values were taken. Leak fraction was calculated by subtracting the expired from the inspired tidal volume and dividing by the inspired tidal volume. Measurements were made during the maintenance phase of anesthesia with the patient in the supine position. The alternative randomized device was then inserted and data collection repeated. The first randomized device was examined for the presence of visible and occult blood. Occult blood was determined by rinsing the LMA in a fixed volume of water and using a dipstick (7).
The primary variables tested were insertion success rates and times, efficacy of seal, fiberoptic position, ease of ventilation, the presence or absence of gastric insufflation, and mucosal trauma. Sample size was based on previous studies of the LMA-U (1,2) and a pilot study of 30 patients with the SSLM and was selected to detect a projected difference of 20% between the groups with respect to all the primary variables for a type I error of 0.05 and a power of 0.95. The distribution of data was determined using Kolmogorov-Smirnov analysis (8). Patients were excluded from the analysis of insertion time if more than one attempt was required. Statistical analysis was with paired t-test, Friedman two-way analysis of variance, and 
2 test. Significance was taken as P < 0.05.
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Results
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The mean ± SD (range) for age, height, and weight was 47 ± 15 yr (19–77 yr), 172 ± 11 cm (148–197 cm), and 77 ± 18 kg (42–120 kg), respectively. The men:women ratio was 46:44. The ASA I:II ratio was 49:41. Ventilator and circuit leaks were always <1 mL at the pre-use test. The comparative data are presented in Table 1. The data were normally distributed. Insertion time was shorter (P = 0.0001) and fewer attempts were required (P = 0.005) for the LMA-U. There were no failed uses of either device. Oropharyngeal leak pressures were similar, but fiberoptic position was superior, with the LMA-U (P 0.0003). There were no differences in hemoglobin oxygen saturation, end-tidal CO2, leak fraction, or peak airway pressure at either tidal volume. Gastric insufflation was not detected in either group at either tidal volume. The frequency of visible (P = 0.009) and occult blood (P = 0.0001) was less with the LMA-U. There were no adverse events. There were no differences in performance between users.
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Discussion
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The SSLM is more difficult to insert than the LMA-U. This is probably related to its wider, stiffer tube and bulkier cuff, restricting intraoral manipulation and resulting in greater impaction at the back of the mouth and more malpositioning. We consider that the 10% difference in first attempt insertion success is clinically important, but the five-second difference in insertion time is not. The LMA-U would be preferable to the SSLM in situations where avoiding multiple insertion attempts is critical, such as for airway rescue.
Fiberoptic position is inferior for the SSLM over the range of cuff volumes. This is probably related to the bulkier cuff, which collides more frequently with the epiglottis during insertion and causes it to fold over, as reported for the ClassicTM LMA when inserted with the cuff inflated (9). It is probably unrelated to the absence of mask aperture bars because there is evidence from the Classic LMATM that the fiberoptic position is uninfluenced by the presence or absence of mask aperture bars (10). Perhaps the passage of instruments into the respiratory tract will be more difficult with the SSLM, and therefore, it will be less useful as an airway intubator.
There was more mucosal trauma with the SSLM. This probably reflects the greater difficulty with insertion rather than mucosal hypoperfusion because mucosal pressures are similar between the devices (11). We speculate that postoperative pharyngolaryngeal morbidity will be more frequent for the SSLM because there is some evidence that the frequency of mucosal trauma (12,13) and sore throat (14) are increased after multiple insertion attempts with the ClassicTM LMA. No data about postoperative pharyngolaryngeal morbidity were collected in this study because both devices were inserted into each patient.
Ease of ventilation was similar at both ventilatory settings, suggesting that the inferior fiberoptic position of the SSLM does not impede its performance as a ventilatory device. Most studies show little or no correlation between fiberoptic position and function for LMA devices (15). Insertion success rates, oropharyngeal leak pressure, fiberoptic position, and frequency of bloodstaining for the LMA-U were similar to previous studies (1,2).
Our study has three limitations. First, two experienced users inserted the devices, and the results may not be applicable to less experienced personnel. However, there is some evidence that performance using the LMA-U is similar for experienced and inexperienced personnel (2). Second, although the level of experience with each device was similar, it is possible that the experience with other LMA devices favored the LMA-U because it is more like the ClassicTM LMA than the SSLM. Third, the study was unblinded and partially sponsored by the manufacturer of one of the devices (LMA-U), both possible sources of bias.
We conclude that the LMA-U is superior to the SSLM in terms of ease of insertion, fiberoptic position, and mucosal trauma but similar in terms of oropharyngeal leak pressure and ease of ventilation.
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Footnotes
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Dr Brimacombe has previously worked as a consultant for the Laryngeal Mask Company and Mallincrodt Medical. Dr Keller has previously worked as a consultant for the Laryngeal Mask Company. This project was partially sponsored by the Laryngeal Mask Company, who manufacture the laryngeal mask airway UniqueTM. Neither the Laryngeal Mask Company nor Dr Brain (the inventor) were involved in the design of the study, data analysis, or manuscript preparation.
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References
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- Verghese C, Berlet J, Kapila A, Pollard R. A clinical assessment of the single use laryngeal mask airway the LMA-UNIQUETM. Br J Anaesth 1998; 80: 677–9.[Abstract/Free Full Text]
- Brimacombe J, Keller C, Morris R, Mecklem D. A comparison of the disposable versus the reusable laryngeal mask airway in paralyzed adult patients. Anesth Analg 1998; 87: 921–4.[Abstract/Free Full Text]
- Brimacombe J, Keller C. Insertion of the LMA-UniqueTM with and without digital intraoral manipulation by inexperienced personnel after manikin-only training. J Emerg Med 2004; 26: 1–5.[Web of Science][Medline]
- Keller C, Brimacombe J, Keller K, Morris R. A comparison of four methods for assessing airway sealing pressure with the laryngeal mask airway in adult patients. Br J Anaesth 1999; 82: 286–7.[Abstract/Free Full Text]
- Keller C, Brimacombe J, Puehringer F. A fibreoptic scoring system to assess the position of laryngeal mask airway devices: interobserver variability and a comparison between the standard, flexible and intubating laryngeal mask airways. Anasthesiol Intensivmed Notfallmed Schmerzther 2000; 35: 692–4.[Web of Science][Medline]
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- Parker MR, Day CJ. Visible and occult blood contamination of laryngeal mask airways and tracheal tubes used in adult anaesthesia. Anaesthesia 2000; 55: 388–90.[Web of Science][Medline]
- Gaddis GM, Gaddis ML. Introduction to biostatistics. V. Statistical inference techniques for hypothesis testing with nonparametric data. Ann Emerg Med 1990; 19: 1054–9.[Web of Science][Medline]
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- Keller C, Brimacombe J, Moriggl B, et al. In cadavers, directly measured mucosal pressures, oropharyngeal leak pressure and fibreoptic position are similar for the UniqueTM and Soft SealTM laryngeal mask airway devices. Can J Anaesth. In press.
- St Claire Logan A, Morris P. Complications following use of the laryngeal mask airway in children. Paediatr Anaesth 1993; 3: 297–300.
- Keller C, Sparr HJ, Brimacombe J. Laryngeal mask lubrication: a comparative study of saline versus 2% lignocaine gel with cuff pressure control. Anaesthesia 1997; 52: 592–6.[Web of Science][Medline]
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- Brimacombe J. Anatomy. In: Laryngeal mask anesthesia: principles and practice. 2nd ed. London: WB Saunders, 2004.
Accepted for publication May 13, 2004.
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Abstract
Introduction
