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Summary

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

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.

Methods

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

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].

image

Figure 1.  Location of the mucosal pressure sensors (corresponding mucosal area) on a schematic laryngeal mask airway. (A) anterior base of cuff (base of tongue); (B) posterior tube (distal oropharynx); (C) posterior tip of cuff (hypopharynx); (D) anterior middle part of cuff side (pyriform fossa).

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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 [8]. 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 [9]. 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 [6]. The distribution of data was determined using Kolmogorov–Smirnov analysis [10]. Statistical analysis was performed with paired t-test, chi-squared test and ANOVA. Significance was taken as p < 0.05.

Results

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

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.

Table 1.   Patients’ characteristics, doses of anaesthetic induction and maintenance agents, insertion success, oropharyngeal leak pressure and directly measured pharyngeal mucosal pressures with the i-gel or LMA Supreme. Values are mean (SD), number/number (proportion) or median (IQR [range]).
 i-gel(n = 15)LMA Supreme(n = 15)
  1. *p = 0.011 base of tongue compared with hypopharynx in the same group.

  2. †p = 0.04 distal oropharynx compared with hypopharynx in the same group.

Age; years40 (17)45 (14)
Height; cm167 (6)166 (4)
Weight; kg62 (9)64 (10)
ASA 1/212/312/3
Fentanyl; mg0.2 (0.04)0.2 (0.03)
Propofol; mg194 (28)183 (24)
Propofol; mg.kg−1.h−16.3 (1.4)6.3 (1.1)
Remifentanil; μg kg−1.min−10.17 (0.05)0.15 (0.06)
Insertion success
 First attempt15 (100%)15 (100%)
 Second attempt00
 Overall15 (100%)15 (100%)
Oropharyngeal leak pressure; cmH2O27.3 (7.5)26.5 (6.8)
Mucosal pressures; cmH2O
 (A) Base of tongue8.0 (2.7–10.7 [0–26.7])5.0 (0.5–8.0 [0–33])*
 (B) Distal oropharynx5.0 (2.7–7 [1.0–37.3])4.0 (1.3–9.3 [0–24])†
 (C) Hypopharynx9.3 (2.7–13.3 [0–22.7])10.7 (4–17.3 [0–26.7])
 (D) Pyriform fossa8.0 (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.

Discussion

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

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 [6], but lower than the cuffed oropharyngeal airway [11], the laryngeal tube airway [12], the intubating LMA [13] and oesophageal tracheal combitube [14]. Mucosal pressures were low for both the i-gel and LMA Supreme. Pharyngeal perfusion pressure is approximately 40 cmH2O [15] 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 [16]; however, neuromuscular blockade and mode of ventilation do not influence mucosal pressure [17]. 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.

Competing interests

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References

No external funding or competing interests declared.

References

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Competing interests
  7. References
  • 1
    Garcia-Aguado R, Vinoles J, Brimacombe J, Vivo M, Lopez-Estudillo R, Ayala G. Suction catheter guided insertion of the ProSeal laryngeal mask airway is superior to the digital technique. Canadian Journal of Anesthesia 2006; 53: 398403.
  • 2
    Janakiraman C, Chethan DB, Wilkes AR, Stacey MR, Goodwin N. A randomised crossover trial comparing the i-gel supraglottic airway and classic laryngeal mask airway. Anaesthesia 2009; 64: 6748.
  • 3
    Theiler LG, Kleine-Brueggeney M, Kaiser D, et al. Crossover comparison of the laryngeal mask supreme and the i-gel in simulated difficult airway scenario in anesthetized patients. Anesthesiology 2009; 111: 5562.
  • 4
    Eschertzhuber S, Brimacombe J, Hohlrieder M, Keller C. The 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: 7983.
  • 5
    Brimacombe J, Keller C, Giampalmo M, Sparr HJ, Berry A. Direct measurement of mucosal pressures exerted by cuff and non-cuff portions of tracheal tubes with different cuff volumes and head and neck positions. British Journal of Anaesthesia 1999; 82: 70811.
  • 6
    Keller C, Brimacombe J. Mucosal pressure and oropharyngeal leak pressure with the Proseal versus the classic laryngeal mask airway. British Journal of Anaesthesia 2000; 85: 2626.
  • 7
    Horisberger T, Gerber S, Bernet V, Weiss M. Measurement of tracheal wall pressure: a comparison of three different in vitro techniques. Anaesthesia 2008; 63: 41822.
  • 8
    Brimacombe J, Keller C, Vosoba JuddD. Gum elastic bougie-guided insertion of the ProSealTM laryngeal mask airway is superior to the digital and introducer tool techniques. Anesthesiology 2004; 100: 259.
  • 9
    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. British Journal of Anaesthesia 1999; 82: 2867.
  • 10
    Sachs L. Der Kolmogoroff-Smirnov-Test für die Güte der Anpassung. Angewandte Statistik. Anwendung statistischer Methoden. Berlin: Springer Verlag, 1992: 42630.
  • 11
    Keller C, Brimacombe J. Mucosal pressures from the cuffed oropharyngeal airway vs the laryngeal mask airway. British Journal of Anaesthesia 1999; 82: 9224.
  • 12
    Keller C, Brimacombe J. Pharyngeal mucosal pressures with the laryngeal tube airway versus ProSeal laryngeal mask airway. Anaesthesiologie Intensivmedizin Notfallmedizin Schmerztherapie 2003; 38: 3936.
  • 13
    Keller C, Brimacombe J. Pharyngeal mucosal pressures, airway sealing pressures and fiberoptic position with the intubating versus the standard laryngeal mask airway. Anesthesiology 1999; 90: 10016.
  • 14
    Keller C, Brimacombe J, Boehler M, Loeckinger A, Puehringer F. The influence of cuff volume and anatomic location on pharyngeal, esophageal and tracheal mucosal pressures with the esophageal tracheal combitube. Anesthesiology 2002; 96: 10747.
  • 15
    Brimacombe J, Keller C, Puehringer F. Pharyngeal mucosal pressure and perfusion. A fiberoptic evaluation of the posterior pharynx in anesthetized adult patients with a modified cuffed oropharyngeal airway. Anesthesiology 1999; 91: 16615.
  • 16
    Brimacombe J, Keller C. Laryngeal mask airway size selection in males and females: ease of insertion, oropharyngeal leak pressure, pharyngeal mucosal pressures and anatomical position. British Journal of Anaesthesia 1999; 82: 7037.
  • 17
    Keller C, Brimacombe J. Influence of neuromuscular block, mode of ventilation and respiratory cycle on pharyngeal mucosal pressures with the laryngeal mask airway. British Journal of Anaesthesia 1999; 83: 4802.