We are grateful for the opportunity to respond to the comments of Drs Schultz and Buhre on our investigation of the laryngeal tube (LT) in spontaneously breathing patients. The objective of our study was to investigate whether the LT was equivalent to the laryngeal mask (LM) for spontaneous ventilation. At the time of the study, the LT was marketed as a highly satisfactory airway device with little supporting evidence that this fact was true. Indeed, there appeared to be no data from its use in patients breathing spontaneously. The LT and LM are both reusable, supraglottic airway devices and it is reasonable to compare them for equivalence. The fact that Dörges and colleagues  had no failures in inserting the device with a median placement time of 21s is irrelevant to the objectives of our study. Their study incorporated only controlled ventilation and each placement of the LT was assisted by means of fibreoscopy. Ten seconds is usually ample time for the routine successful 'blind' insertion of the LM, but we accept this may be too short a period for the 'blind' insertion of the LT. However, it should be pointed out that there was no great difficulty encountered with the initial insertion of the device into the airway. Furthermore, the device failed primarily because of our inability to obtain a satisfactory airway and not because of prolonged initial insertion times. Evaluating the airway from the point of view of tidal volume and end-tidal CO2 is indeed useful in spontaneous ventilation, but our main problem was to establish a satisfactory airway first, an essential prerequisite. We agree with the comments, also stated in the discussion, that five uses probably provide an insufficient learning curve for this device. However, by the end of the study, we cannot say that we had mastered the use of the device and had, in fact, failed to establish any learning curve. This is quite dissimilar to the learning curve of the LM.
Unless the LT is more stimulatory than the LM, and we were not given this impression during the study, then the suggestion that the secondary dislocation related to a light plane of anaesthesia is unlikely. Light planes of anaesthesia are more likely to be implicated in the failure of the device on induction and initial insertion than intraoperatively. We believe that the most likely explanation for the intraoperative loss of a satisfactory airway is the diffusion of nitrous oxide into the lower cuff. It is possible that this problem will be less common with the latest version of the LT where both cuffs are inflated via one pilot tube, thereby allowing the transfer of gas between the cuffs when volume increases.
We believe that our study addressed the question of equivalence. A study to define the maximum success rate that could be achieved using the LT would have a different methodology. Better results may be achievable but have not yet been published. We stand by our conclusion that the LT version we evaluated is not equivalent to the LM for use in spontaneous ventilation. Our experience was that it was unsatisfactory as an airway for spontaneous ventilation.
D. M. Miller
A. C. Pearce
Guy's Hospital; London, UK
1. Dörges V, Ocker H, Wenzel V, Schmucker P. The laryngeal tube: a new simple airway device. Anesth Analg