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Directly measured mucosal pressures produced by the i-gelTM and laryngeal mask airway SupremeTM in paralysed anaesthetised patients
Article first published online: 11 FEB 2012
Anaesthesia © 2012 The Association of Anaesthetists of Great Britain and Ireland
Volume 67, Issue 4, pages 407–410, April 2012
How to Cite
Eschertzhuber, S., Brimacombe, J., Kaufmann, M., Keller, C. and Tiefenthaler, W. (2012), Directly measured mucosal pressures produced by the i-gelTM and laryngeal mask airway SupremeTM in paralysed anaesthetised patients. Anaesthesia, 67: 407–410. doi: 10.1111/j.1365-2044.2011.07024.x
- Issue published online: 12 MAR 2012
- Article first published online: 11 FEB 2012
- Accepted: 27 November 2011
The i-gelTM and LMA SupremeTM are extraglottic airway devices with non-inflatable and inflatable cuffs, respectively. We hypothesised that directly measured mucosal pressures would differ between these devices in anesthetised paralysed patients. Thirty patients were randomly allocated to receive one of these two devices. Four pressure sensors were attached to all airway devices used to measure mucosal pressure at the base of the tongue, the distal oropharynx, the hypopharynx and the pyriform fossa. At these four places, median (IQR [range]) i-gel mucosal pressures were 8.0 (2.7–10.7 [0–26.7]), 5.0 (2.7–7 [1.0–37.3]), 9.3 (2.7–13.3 [0–22.7] and 8.0 (2.7–10.7 [0–25.3]) cmH2O, respectively, and for the LMA Supreme, these were 5.0 (0.5–8.0 [0–33]), 4.0 (1.3–9.3 [0–24]), 10.7 (4–17.3 [0–26.7]) and 8.0 (0–10.7 [0–36]) cmH2O, respectively. Mucosal pressures were low and similar for both devices. The LMA Supreme mucosal pressures were higher in the hypopharynx than in the distal oropharynx (p = 0.04) and base of the tongue (p = 0.011). There were no pressure differences between the locations for the i-gel.
The i-gelTM (Intersurgical Ltd., Wokingham, Berkshire, UK) is a single-use extraglottic airway device with a non-inflatable cuff made from a medical-grade thermoplastic elastomer. The Laryngeal Mask Airway (LMA) SupremeTM (The Laryngeal Mask Company, St. Helier, Jersey, UK) is a single-use extraglottic airway device with an inflatable cuff made from a medical grade plastic [1–4]. We postulated that these structural differences might influence the way each cuff interacts with the pharyngeal mucosa with implications for ischaemic airway injury. We test the hypothesis that directly measured mucosal pressure differs between the i-gel and LMA Supreme in paralysed anesthetised patients.
With Ethikkommission der Medizinischen Universität Innsbruck Local Research Ethics Committee permission and written informed consent, 30 female patients, of ASA physical status 1–2, aged 20–70 years, were randomly allocated (http://www.randomizer.org) to receive either the i-gel or LMA Supreme for airway management. Patients were excluded if they had a known or predicted difficult airway, a body mass index greater than 35 kg.m−2, or were at risk of aspiration.
Mucosal pressures were measured directly using four 1.2-mm diameter strain gauge silicone microchip sensors (Codman® MicroSensorTM; Johnson and Johnson Medical Ltd, Raynham, MA, USA) attached to the external surface of the devices with clear adhesive dressing 0.45 μm thick (TegadermTM, 3M, Ont., Canada), as previously described [5–7]. The sensors were fully covered with lubricant jelly and applied to mucosal areas corresponding to the following locations: (A) anterior base of cuff to base of tongue; (B) posterior tube todistal oropharynx; (C) posterior tip of cuff to hypopharynx; and (D) anterior middle part of cuff side to pyriform fossa (Fig. 1). The sensing elements of sensors were orientated towards the mucosal surfaces. The position and orientation of all the sensors were checked in vitro before and after use in each patient [5–7].
Pre-medication was with midazolam 0.05–0.1 mg.kg−1 orally one hour pre-operatively. Anaesthesia was in the supine position with the patient’s head and neck in the neutral position. Following the application of routine monitoring, standardised general anaesthesia was given using fentanyl 2–4 μg.kg−1, propofol 2.5–3.0 mg.kg−1 and neuromuscular blockade with rocuronium 0.4 mg.kg−1. The patient’s lungs were ventilated via a facemask for 3 min and then the airway device (size 4 for both devices) was inserted using a guided technique with a well-lubricated 60-cm long, 12-Fr gastric tube . Both devices were fixed by taping tube over the chin. The intracuff pressure of the LMA Supreme was set at 60 cmH2O using a digital manometer (Mallinckrodt Medical, Athlone, Ireland). Maintenance of anaesthesia was with remifentanil 0.1–0.3 μg.kg−1.min−1 and propofol 75–125 μg.kg−1.min−1 in 33% oxygen in air. The patient’s lungs were ventilated at an inspired tidal volume of 10 ml.kg−1, a respiratory rate of 10 breath.min−1 and an inspiratory:expiratory ratio of 1:1.
An observer blinded to the airway device recorded oropharyngeal leak pressure 5 min after insertion and mucosal pressures every 5 min from 10 min after insertion. Oropharyngeal leak pressure was measured by closing the expiratory valve of the circle system at a fixed gas flow of 3 l.min−1, and noting the airway pressure at which the dial on the aneroid manometer reached equilibrium . The airway device was inspected for blood staining at removal. Any adverse events were documented.
Sample size was selected to detect a projected difference of 25% between the groups with respect to directly measured mucosal pressure for a type-1 error of 0.05 and a power of 0.9. The power analysis was based on data from a pilot study of four patients in which directly measured mucosal pressure at the anterior middle part of the cuff side (pyriform fossa) was measured with the i-gel and a previous study of directly measured mucosal pressure with the LMA Classic . The distribution of data was determined using Kolmogorov–Smirnov analysis . Statistical analysis was performed with paired t-test, chi-squared test and ANOVA. Significance was taken as p < 0.05.
Patients’ characteristics and doses of anaesthetic agents used are presented in Table 1. There were no differences in insertion success or oropharyngeal leak pressures between groups (Table 1). The position and orientation of the sensors were unchanged before and after use.
|i-gel(n = 15)||LMA Supreme(n = 15)|
|Age; years||40 (17)||45 (14)|
|Height; cm||167 (6)||166 (4)|
|Weight; kg||62 (9)||64 (10)|
|Fentanyl; mg||0.2 (0.04)||0.2 (0.03)|
|Propofol; mg||194 (28)||183 (24)|
|Propofol; mg.kg−1.h−1||6.3 (1.4)||6.3 (1.1)|
|Remifentanil; μg kg−1.min−1||0.17 (0.05)||0.15 (0.06)|
|First attempt||15 (100%)||15 (100%)|
|Overall||15 (100%)||15 (100%)|
|Oropharyngeal leak pressure; cmH2O||27.3 (7.5)||26.5 (6.8)|
|Mucosal pressures; cmH2O|
|(A) Base of tongue||8.0 (2.7–10.7 [0–26.7])||5.0 (0.5–8.0 [0–33])*|
|(B) Distal oropharynx||5.0 (2.7–7 [1.0–37.3])||4.0 (1.3–9.3 [0–24])†|
|(C) Hypopharynx||9.3 (2.7–13.3 [0–22.7])||10.7 (4–17.3 [0–26.7])|
|(D) Pyriform fossa||8.0 (2.7–10.7 [0–25.3])||8.0 (0–10.7 [0–36])|
Directly measured mucosal pressures were low and not different between devices with the maximum value never exceeding 40 cmH2O (Table 1). For the i-gel, there were no differences in mucosal pressure between locations. For the LMA Supreme, mucosal pressures were higher in the hypopharynx than in the distal oropharynx and base of tongue. Oropharyngeal leak pressure was higher than directly measured mucosal pressure on 99% (177/180) of occasions for the i-gel and on 96% (172/180) of occasions for the LMA Supreme. Blood staining was detected in 13% (2/15) of uses of the i-gel and 0% (0/15) of uses of the LMA Supreme. There were no adverse events.
Directly measured mucosal pressures have not previously been documented for the i-gel and LMA Supreme. Mucosal pressures were similar for the i-gel and LMA Supreme. The values measured are similar to the LMA Classic and LMA ProSeal , but lower than the cuffed oropharyngeal airway , the laryngeal tube airway , the intubating LMA  and oesophageal tracheal combitube . Mucosal pressures were low for both the i-gel and LMA Supreme. Pharyngeal perfusion pressure is approximately 40 cmH2O  and as no measurement exceeded this value for either device, the frequency of mucosal ischaemic injury is also likely to be low.
Mucosal pressures were slightly higher in the hypopharynx for the LMA Supreme, but there were no differences among locations for the i-gel. This suggests subtle differences in the way each device interacts with the surrounding mucosa. Efficacy of seal with both the respiratory and gastrointestinal tracts is probably related to matching shape at low volumes and mucosal pressure at high volumes. Oropharyngeal leak pressure was higher than directly measured mucosal pressure on 99% of occasions for the i-gel and on 96% of occasions for the LMA Supreme. This suggests that for both devices, matching shape is the primary mechanism of seal.
Our study has several limitations. First, we studied paralysed, anesthetised, females undergoing ventilation using size-4 devices, and our data may not apply in other situations. Mucosal pressures differ slightly between males and females ; however, neuromuscular blockade and mode of ventilation do not influence mucosal pressure . Secondly, we inflated the cuff of the LMA Supreme to 60 cmH2O, as recommended by the manufacturer. As mucosal pressure increases with intracuff pressure, it is likely that mucosal pressures would have been lower for the LMA Supreme than the i-gel at lower intracuff pressures and higher at higher intracuff pressures. Finally, our study was not sufficiently powered to provide information about the efficacy of seal or airway injury.
No external funding or competing interests declared.
- 4The laryngeal mask airway Supreme – a single use laryngeal mask airway with an oesophageal vent. A randomised, cross-over study with the laryngeal mask airway ProSeal in paralysed, anaesthetised patients. Anaesthesia 2009; 64: 79–83., , , .
- 10Der Kolmogoroff-Smirnov-Test für die Güte der Anpassung. Angewandte Statistik. Anwendung statistischer Methoden. Berlin: Springer Verlag, 1992: 426–30..