With interest, we read the study of Miller and colleagues who investigated the usefulness of the laryngeal tube in spontaneous breathing patients . However, in our opinion, some methodological aspects of the study raise concern. First, the sequential analysis chart is principally reasonable in cases with limited pre-existing or missing data, but in our opinion the results of the study might probably have been modified by the choice of parameters that were used to evaluate the laryngeal tube. Whether other parameters (tidal volume or end-tidal CO2) are more adequate criteria in spontaneous breathing patients should have been discussed. In addition, the 10 s proposed by the authors to distinguish between successful and unsuccessful attempt of placement seems rather short and is not based on study data. Dörges and colleagues report a range between 8 and 28 s (median 21 s) for placement of the laryngeal tube. In their study, no failed attempts to place the laryngeal tube were observed . Unfortunately, the authors do not present data on the time required to insert the airway device. Second, a specific manoeuvre is described and recommended by the manufacturer in case of an insufficient airway. Miller and colleagues reported that the manipulation (pushing the airway in and out to find the ideal position) was partially effective. However, the authors judged the necessity for further manipulations after the initial placement a 'problem' and included this variable in their scoring system.
By allowing five positioning trials before the study, the authors express their intention to minimize the effects of a learning curve on their results. However, despite the clinical experience of the authors, it seems possible that the individual learning curve is not finished after five insertions of a new airway device. Additionally, Genzwuerker and colleagues observed a reduction of the time during the first 10 attempts of laryngeal tube placing by 35% . The time required to insert an airway should be as short as possible for the aim not to endanger the patient by insufficient oxygenation. However, in our opinion it might be necessary to reconsider if the chosen time of 10 s is a marker for the usefulness of this airway device.
As pointed out by Miller and colleagues, secondary dislocation of the airway may be the reason for loss of airway control. To us, it seems worth discussing if the reported cases of secondary dislocation might have been the result of an insufficient level of anaesthesia. The authors assumed that the placement of the laryngeal tube evokes an irritation of laryngeal structures equal to those produced by positioning of the laryngeal mask airway. However, to our knowledge the available data are not sufficient to answer this question finally. Laryngeal irritation resulting on placement of any airway device is alleviated by excluding a 'light' level of anaesthesia. This might as well reduce the risk for secondary dislocation of the device. Unfortunately, the authors did not include in their investigation the documentation of the depth of anaesthesia or a definition of the administered dose of volatile anaesthetics in volume percentage or MAC.
The question if a procedure is in ethical aspects justifiable has to be posed regularly and answered positively. However, one must take into consideration if the scoring system used to compare the devices might have changed the results. Thus, it remains uncertain if the present study is capable of answering this question. To summarize, the development and application of new techniques and devices needs detailed examination and thorough observation. In our opinion, more detailed studies are required to examine if the use of the laryngeal tube is beneficial in patients undergoing anaesthesia.
Klinik für Anästhesiologie; Universitätsklinikum Aachen; Aachen, Germany
1. Miller DM, Youkhana I, Pearce AC. The laryngeal mask and VBM laryngeal tube compared during spontaneous ventilation. A pilot study. Eur J Anaesthesiol
2. Dörges V, Ocker H, Wenzel V, Schmucker P. The laryngeal tube: a new simple airway device. Anesth Analg
3. Genzwuerker H, Hilker T, Hohner E, Kuhnert-Frey B. The laryngeal tube: a new adjunct for airway-management. Prebosp Emerg Care