Dr Miller and colleagues reported that insertion of the laryngeal tube and ventilation through it were frequently difficult or unsatisfactory, particularly when they were inexperienced with its use . They also reported that airway obstruction often occurred during anaesthesia in patients who were breathing spontaneously .
The laryngeal tube, which is designed to provide a patent airway during either spontaneous breathing or controlled ventilation, consists of an airway tube with a balloon cuff (proximal cuff) at the middle part of the tube and a smaller balloon (distal) cuff attached to the tip. The proximal cuff provides a seal by forming a plug in the upper pharynx and the distal cuff seals the oesophageal inlet . The design of the laryngeal tube has been changed a few times to improve its effectiveness: the original device (Type 1) had two pilot tubes to inflate the two cuffs. Several improvements had been added to the next version (Type 2), and the major change was that the two cuffs could be inflated via a single pilot tube. Finally, the current device has a longer distal airway aperture.
Miller and colleagues used the Type 1 device. There have been two other clinical reports of the use of the Type 1 laryngeal tube [2,3]. In one study, insertion of the laryngeal tube was successful at the first attempt and a patent airway was obtained in all of 30 patients , and in the other study insertion and ventilation of the lungs were successful at the first attempt in 47 of 50 patients . Later, we reported a preliminary use of the Type 2 laryngeal tube in 10 patients in whom controlled ventilation was used . In all 10 patients, the laryngeal tube provided a patent airway during the entire course of anaesthesia without necessitating adjusting the position of the device or the patient's head and neck . These results contradict those of Miller and colleagues, in which even controlled ventilation was often unsatisfactory.
Miller and colleagues cast doubt on the efficacy of the laryngeal tube by stating that '(is) it ethically justifiable to use a device such as the laryngeal tube that requires more extensive training than is shown here?' and that 'the point of the sequential analysis is to limit the extent of investigations, which are obviously not beneficial to patients' . Our impression is contradictory, and we have found that insertion of the laryngeal tube is generally easy even for inexperienced personnel. To prove this point, we asked five anaesthetists to insert the device and attempt to ventilate patients' lungs through it. Each anaesthetist, who had had no experience of its use and to whom one of us demonstrated the method of insertion once before the trial, attempted to place the device in five patients. In 23 of 25 patients, it was possible to insert the laryngeal tube and to ventilate through it adequately at the first attempt.
At the moment, there have been no reports of the use of the laryngeal tube during spontaneous breathing other than that of Miller and colleagues. Nevertheless, in patients in whom lung ventilation was controlled, placement of and ventilation through the laryngeal tube were usually successful in three papers [2-4], but often unsatisfactory in Miller and colleagues' study. Therefore, it seems too early to conclude that the device is not satisfactory for management of the airway during spontaneous breathing.
Department of Anaesthesia; Matsue Red Cross Hospital; Shimane, Japan
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. Asai T, Murao K, Shingu K. Efficacy of the laryngeal tube during intermittent positive pressure ventilation. Anaesthesia
3. Dorges V, Ocker H, Wenzel V, Schmucker P. The laryngeal tube: a new simple airway device. Anesth Analg
4. Asai T, Kawashima A, Hidaka I, Kawachi S. Laryngeal tube: its use during controlled ventilation. Masui