1 Huddersfield, UK, 2 Cairns, Australia and 3 Innsbruck, Austria
LMA® is the property of Intavent Limited.
EditorI was interested to read the case report by Brimacombe and colleagues1 listing the features of the LMA ProSealTM together with the insertion problems ascribed to its bulky nature. The recently introduced Airway Management Device (AMDTM) was designed to address the same shortcomings associated with the LMA ClassicTM, whilst allowing easy and less traumatic insertion.2 3
The mechanical closure described by Brimacombe is explained in detail,1 and corroborates a similar phenomenon seen when using a pre-production prototype in an early stage of the development of the AMDTM. Before the development of the arrow-head shape of the currently available device, the anteroposterior diameter of the inflated lower cuff with its unique central drainage channel was some 50% greater. Over-enthusiastic insertion and inflation of this cuff beyond its optimal position resulted in near complete airway obstruction, presumably of similar aetiology (i.e. forward displacement of the glottic inlet). As stated, the application of cricoid pressure with the classic LMA simulates the same conditions.4
The less bulky nature of the AMDTM should not cause such compression opposite the glottic inlet. The slim anteroposterior profile of the lower cuff, when inflated before insertion, greatly reduces the risk of inadvertent intrusion beyond the oesophageal sphincter. The upper cuff, designed to elevate the tongue and lift the epiglottis clear of the laryngeal inlet, in a fashion similar to laryngoscopy, ensures an unobstructed airway whilst maintaining access to the oesophagus.
M. J. ONeil
Huddersfield, UK
EditorWe would like to thank Dr ONeil for confirming our observation of mechanical cord closure.1 It would seem that this is a potential problem with any extraglottic airway device forming a seal in the hypopharynx, and as such is also likely to occur with the Laryngeal Tube AirwayTM5 and Pharyngeal Airway ExpressTM6 devices, which are very similar to the Airway Management Device or AMDTM. However, we feel it is somewhat premature for Dr ONeil to claim, on design grounds alone, that the AMDTM cannot cause mechanical cord closure and yet form an effective seal with the hypopharynx. In its resting state the hypopharynx is usually closed (as readily observed during gastroscopy). Any device occupying the hypopharynx sufficiently to form a seal must open it and push the glottis anteriorly. In a percentage of patients with unfavourable anatomy, this will inevitably cause glottic compression. In our original report, we stated that the incidence of mechanical cord closure with the ProSealTM was 0.4% (4/915).1 Our latest figure from ongoing data collection is 0.3% (19/6321). We consider that the incidence of mechanical cord closure for the Laryngeal Tube AirwayTM, Pharyngeal Airway ExpressTM and AMDTM will be similar once sufficient data has been collected.
J. Brimacombe1
C. Richardson1
C. Keller2
S. Donald1
1Cairns, Australia
2Innsbruck, Austria
References
1 Brimacombe J, Richardson C, Keller C, Donald S. Mechanical closure of the vocal cords with the ProSealTM laryngeal mask airway. Br J Anaesth 2002; 88: 2967
2 ONeil MJ. Development and evaluation of the AMDTM including comparison with LMA in spontaneously breathing anaesthetized patients. Todays Anaesthesist 2001; 16: 98103
3 Cook TM, Gupta K, Gabbott DA, Nolan JP. An evaluation of the airway management device. Anaesthesia 2001; 56: 16[ISI][Medline]
4 Brimacombe J, Berry A. Mechanical airway obstruction following cricoid pressure with the laryngeal mask airway. Anesth Analg 2001; 78: 6045
5 Brimacombe J, Keller C, Brimacombe L. A comparison of the laryngeal mask airway ProSealTM and the laryngeal tube airway in paralyzed anesthetized adult patients undergoing pressure-controlled ventilation. Anesth Analg 2002; 95: 7706
6 Voyagis GS, Iatrou C, Dimitriou V. Safety of the new pharyngeal airway (PAXexpress) as a ventilatory device. Preliminary data. Eur J Anaesthesiol 2002; 19: A143