Letters to the Editor: Letters & Announcements
We thank Drs. Al-Shaikh and Van Zundert for their interest in our article and for providing additional information about the performance of the Soft Seal laryngeal mask (SSLM). We will respond to each of their points in turn.
First, we inserted both the Unique laryngeal mask airway (LMA-U) and the SSLM with the cuff fully deflated. At the time we conducted our research (early 2003) the manufacturer did not recommend insertion with the cuff partially inflated and we were unaware of the research suggesting that the atmospheric pressure technique was best or that using a size 3 for females and size 4 for males was a useful strategy with the SSLM. These factors may well account for the improved performance detected by Al-Shaikh and Van Zundert; however, we would recommend using a size 4 for females and size 5 for males when positive pressure ventilation is required, as larger sizes form better seals, at least with reusable laryngeal mask airways (1).
Second, Al-Shaikh and Van Zundert are incorrect when they state that an oropharyngeal leak pressure >20 cm H2O was achieved in all patients with the SSLM at all cuff volumes other than with the cuff fully deflated. If the authors had taken a more careful look at the range of values rather than the mean values, they would have noticed that this was only achieved at the maximum recommended volume of 40 mL. We do not consider an oropharyngeal leak pressure of 20 cm H2O to be a reliable test of correct anatomic position, as it provides little information about the position of the distal cuff, which is critical to safety.
Third, the level of experience with each device was similar, with an average of 85 insertions with the LMA-U and 98 insertions with the SSLM. Perhaps the extensive previous experience with other LMA devices favored insertion of the LMA-U.
Fourth, we speculated that the SSLM may be less effective than the LMA-U as an airway intubator on the basis of its poor fiberoptic position. This speculation still holds as there are no data comparing the SSLM and LMA-U as airway intubators.
Fifth, Al-Shaikh and Van Zundert attempt to rubbish the differences in insertion success and fiberoptic position found in our patient study by referring to a cadaver study where we found no differences (2). This is an unreasonable comment to make, as the patient study was powered to examine these variables (90 subjects) whereas the cadaver study was not (10 subjects). In fact the cadaver study hinted that there was a difference for fiberoptic position, but a P value < 0.05 was not reached.
Finally, we look forward to the publication of further studies comparing the SSLM and LMA-U, as the jury is still out as to which device, if any, is superior. In our view, neither matches the performance of the ProSeal LMA, which should be the extraglottic device of choice in most clinical situations (3).
J. Brimacombe, MD, FRCA
Department of Anaesthesia and Intensive Care
James Cook University; Cairns Base Hospital
C. Keller, MD, MSc
Department of Anaesthesia and Intensive Care Medicine
1. Asai T, Brimacombe J. Review article: Cuff volume and size selection with the laryngeal mask airway. Anaesthesia 2000;55:1179–84.
2. Keller C, Brimacombe J, Moriggl B, et al. In cadavers, directly measured mucosal pressures, oropharyngeal leak pressure and fibreoptic position are similar for the Unique™ and Soft Seal™ laryngeal mask airway devices. Can J Anaesth 2004;51:834–7.
3. Brimacombe J. ProSeal LMA for ventilation and airway protection. In: Laryngeal mask anesthesia. Principles and practice. London: WB Saunders, 2003:505–38.