Die Larynxmaske - aktueller Stellenwert in der Anästhesiologie

The Laryngeal Mask - its Importance in Anaesthesia

The invention of the laryngeal mask by Dr. Archibald Brain in 1981 and its development for clinical use have greatly increased the technical possibilities for airway management in anaesthesia. Parallel to its triumphant advance throughout the world, starting from England in 1988, and its clinical introduction in Germany in 1990, interest in this instrument has increased continuously. Thanks to Brain’s inventiveness, we now have a whole range of instruments called laryngeal masks which differ with respect to indication, operation and comfort. It is no surprise that the indication spectrum for laryngeal masks has also steadily increased and now goes clearly beyond its being an alternative to the face mask. This is especially true for its application in place of the tracheal tube, including controlled ventilation [1 - 4].

This inevitably leads to discussion of the safety of laryngeal masks in comparison with the tracheal tube, especially the risk of aspiration, with the notable exception of the intubation laryngeal mask (LMA Fasttrach®; since 1997) which has its firm place in the management of difficult airway and, in any case, was designed for intubation. A meta analysis carried out in 1995 and a retrospective analysis made in 1996 show that for the LMA classic® an incidence of 1 - 5 per 10,000 applications can be estimated regarding aspiration complications [5, 6]. Using these data, A. Rieger (Neuwied) initially claims in his overview article that as far as aspiration is concerned the risk in using a laryngeal mask (we are still talking about the original LMA classic®) is comparable to that of a face mask or tracheal tube [7]. This significant claim, however, was not accepted without criticism or comment, and in particular legitimate questions were raised concerning statistical assessments in these frequency areas [8]. Rieger also clearly points to the limitations of the laryngeal mask. In addition to the well-known contraindication in patients with stomach content per se, the increased risk of aspiration due to malpositions or in connection with insufficient narcosis depth is also given detailed attention. The latter can facilitate regurgitation when a swallowing reflex with choking occurs, but can also cause a laryngeal airway obstruction, which can be mistaken for a malposition of the laryngeal mask. Forced ventilation manoeuvres then increase the likelihood of regurgitation as a result of possible stomach insufflation. Anaesthesia using the laryngeal mask is therefore more sophisticated when no tube pushes the vocal cords apart. Should aspiration occur, it is unimportant how often this happens; the only question that poses itself is whether this could have been avoided by intubation.

This must not lead, however, to an underestimation of the value of the laryngeal mask in the anaesthesiological repertoire. It must be seen as equally detrimental to withhold from a patient the benefit of the laryngeal mask-when assessing the individual risk of an upcoming anaesthesia-as this does not arise by far solely from the danger of possible aspiration. The advantages over the tracheal tube, which authors praise at great length regarding all the subject areas mentioned here, speak for themselves. The much-sought-after ”gold standard” of airway safety in anaesthesia lies more and more in selecting a procedure which suits each individual patient according to the kind of operation, the existing risks and the circumstances of the operation. In this selection process, the laryngeal mask and the tracheal tube should not be seen as rival but as complementary tools. A major precondition for a balanced concept of airway management is, of course, extensive practice with the methods. To be considered as experienced in using the laryngeal mask (”expert level”), an anaesthetist should have applied this airway device between 700 and 1000 times. This is certainly required for such indications where the operation site competes with the airway (e. g. ENT, eye, mouth, jaw, face and neck operations). Rieger estimates that, under these prerequisites and given the availability of the new LMA Proseal®, up to 60 % of anaesthetic procedures can be successfully carried out using the laryngeal mask. According to J. R. Brimacombe, 80 % of all general anaesthetics at James Cook University Hospital in Cairns (Australia) are done using the laryngeal mask, with the LMA Proseal® being used in 50 % of the cases [9].

The development of the LMA Proseal® is a further step to raise the safety of laryngeal mask use. Of special importance is the fact that this instrument has a higher impermeability of 6 - 15 cm H₂O compared with the LMA classic® at lower mucosal pressure, whereby the impermeability of the laryngeal mask is increased to pressure values of 30 cm H₂O - and can be improved considerably more (to mean value 34 cm H₂O) by anteflexion of the head. As far as a possible regurgitation is concerned, an easy-to-perform stomach probe can reduce the potential danger of aspiration, with the possibility of draining the oesophagus and stomach, and give an important indication as to the correct position of the LMA Proseal®. In a cadaver model a correctly positioned LMA Proseal® opposes regurgitation with pressures of over 40 cm H₂O [10, 11]. Under these preconditions the application for controlled ventilation seems clearly safer. In principle it is thus possible to extend the indication area, as is already done in some centres [9, 12, 13]. This, however, should remain the domain of the experienced anaesthetist, and further proof is required to prevent a good concept for airway safety from falling unnecessarily into disrepute through expanding the spectrum too quickly. This is true, for example, for upper abdomen operations, especially with increased intra-abdominal pressure, obesity, or in patients with lower compliance of lungs and thorax. This also means promoting relevant investigations and studies and also treating them with greater goodwill and objectivity than has sometimes been the case recently, even though in the meantime reports of aspirations due to malpositions while using LMA Proseal® have appeared [8, 14, 15, 16]. We should not lose sight of realities, since - and this is worth mentioning again - intubation, too, has its inherent risks, including aspiration, which are amplified by both A. Rieger and F. K. Pühringer and C. Rex (Reutlingen) [7, 17, 18].

Accordingly, this review of the position of the laryngeal mask in anaesthesia seems all the more justified. Following A. Rieger’s overview article, F. K. Pühringer et al. address in their article above all the importance of muscle relaxants when using the laryngeal mask [17]. They stress that for most applications with sufficient anaesthetic there is no need for relaxing. While accepting that care is always necessary when using relaxants, they consider individual and indication-supported application of short-acting substances in low doses to be safe and effective. This is also true for their use in treating a laryngospasm (beware: malposition must be excluded !).

In his article K. Goldmann (Marburg) presents the importance and indications of the laryngeal mask in pediatric anaesthesia [19]. He explains that in cases in which intubation is not necessary the laryngeal mask is a less invasive instrument and a firm component of modern anaesthesia management in children. He points explicitly to the absolute necessity of good anaesthesia management, which is assumed given the training and experience of the anaesthetist in child anaesthesia in general and with the laryngeal mask in particular. Finally, K. Goldmann pays tribute to the potential new possibilities of the paediatric LMA Proseal®, which recently became available.

An indication for the laryngeal mask, which has meanwhile become a domain - its use in ENT operations - is addressed by C. Rex et al. [18]. Here another type of laryngeal mask is used, the LMA Flexible®, which is strengthened with a wire spiral. This also has a not insignificant position in pediatric anaesthesia. A major point in the presentation of Rex et al. is again discussion of the risk of aspiration. According to current data, nothing speaks against using the laryngeal mask at least as regards such operations as adeno-/tonsillectomy. Indeed, clear arguments in favour of the laryngeal mask over the tracheal tube are less airway irritation during chronic infections that frequently occur in childhood, fewer traumatic applications and a general dispensing with muscle relaxants. In addition to the required abilities of the anaesthetist, cooperation with the surgeon is here essential.

Another topic given far too little attention is taken up by R. Gottschall (Jena) in his article on the status of the laryngeal mask as a valuable instrument for fibre-optic bronchological investigations and operations [20]. Fibre-bronchoscopy is not just an important means for checking the position of the laryngeal mask. As an alternative to intubation for all age groups, the laryngeal mask is a very advantageous instrument for airway safety if anaesthesia is required in fibre-optic bronchoscopy. The combination of laryngeal mask and relevant fibre-bronchoscope has a lower calibre conflict, which greatly facilitates ventilation of the lungs. Furthermore, assessments and manipulations in the larynx and trachea region are much easier. Another advantage is that in some cases laryngo-bronchoscopies with rigid tubes can be replaced.

The final contribution by K. Wiedemann et al. (Heidelberg) concentrates on an important application of laryngeal masks, that of difficult airway. Here emergency care is given the attention it deserves [21]. The authors show that a considerably higher safety potential for patients exists by including the laryngeal mask in the very differentiated procedure of managing difficult airway situations. In particular, the authors look more closely at the problem of difficult airway situations in thoracic operations. The detailed presentation of the procedure impresses and draws attention to difficult subglottic airway conditions, which are not so rare in thoracic surgery. The article also describes the use of the laryngeal mask as an integral part of airway management and of ventilation during operations on the main airways or during lung separation.

All the articles written for this mini-symposium leave no doubt that the concept of the laryngeal mask has attained a firm place in anaesthesia. In our opinion, this is one of the outstanding developments in anaesthesia in the last few years.

Literatur

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