Anesth Analg 2007; 105:1508-1509
© 2007 International Anesthesia Research Society
doi: 10.1213/01.ane.0000282773.64723.63
LETTER TO THE EDITOR
The Conventional LMA®: Benchmark for Assessing Supralaryngeal Airway Efficacy?
Shelley Vamadevan, MBChB, FRCA, DA, DipPEC, and
A. Diba, BM, FRCA
Queen Victoria Hospital, East Grinstead; United Kingdom; shellvam{at}doctors.org.uk
To the Editor:
Lange et al.'s (1) recent comparison of the SLIPATM airway with the conventional LMATM confirms previous results that the SLIPA forms an effective airway (2) and a surprisingly good seal for a rigid airway without an inflatable cuff. Although using the "classic" LMATM as the gold standard for comparative assessments of new supralaryngeal airways is rational (3), this study as reported raises a number of questions.
The investigators inserting the LMA were reported to have at least 3 yr experience with the device, yet no mention was made of their experience with the SLIPA. The conventional LMA is well recognized to have a significant learning curve in the short term (4), medium term (5), and also a long-term one with Brimacombe demonstrating differences in success even beyond 750 insertions (6). With the SLIPA, Hein et al. (2) showed that novices had a 7.5% failure rate compared with none in the experienced user group. We wonder how much of Lange's results from the study can be ascribed to poor size selection of the SLIPA, which in lacking a conformable profile and being available in six sizes may need greater experience in size selection than the LMA.
Their reported 19% incidence of gastric insufflation noted with the SLIPA is strikingly high. This is in contrast to our experience, where we audited the SLIPA in 40 consecutive anesthetized patients who would have been suitable for a laryngeal mask airway. In our group, where the mode of sizes was 51 for females and 55 for males, we achieved mean (sd) seal pressures of 22.4 (4.9) cm H2O but had only one case of gastric insufflation. The disparity could be due to improper anatomical placement of the SLIPA because of inexperience. In addition, inappropriately small sizes lead to a poor seal.
We also take issue with the unsubstantiated statement that "supraglottic airways with higher sealing pressures protect against aspiration." When measuring seal pressures, the airway pressure at which gas leaks from the airway device-patient interface is measured. To comment on protection against aspiration of gastric contents, one would have to measure the pressure at which oropharyngeal matter leaks inwards into the trachea. Seal pressures examine a mechanism that is distinct from the one required to protect against aspiration and they therefore bear no relationship to each other.
As a final point, we note that the abstract and text refer to seal pressures of 24 millimeters of water (mm H2O) for both devices whereas the units in the table are cm H2O. We assume the table is correct.
REFERENCES
- Lange M, Smul T, Zimmermann P, Kohlenberger R, Roewer N, Kehl F. The effectiveness and patient comfort of the novel streamlined pharynx airway liner (SLIPA®) compared with the conventional laryngeal mask airway in ophthalmic surgery. Anesth Analg 2007;104: 431–4[Abstract/Free Full Text]
- Hein C, Plummer J, Owen H. Evaluation of the SLIPA (streamlined liner of the pharynx airway), a single use supraglottic airway device, in 60 anaesthetized patients undergoing minor surgical procedures. Anaesth Intensive Care 2005;33: 756–61[Web of Science][Medline]
- Cook TM. Novel airway devices: spoilt for choice?. Anaesthesia 2003;58:107–110[Web of Science][Medline]
- McCrirrick A, Ramage DT, Pracilio JA, Hickman JA. Experience with the laryngeal mask airway in two hundred patients. Anaesth Intensive Care 1991;19: 256–60[Web of Science][Medline]
- Young TM. The laryngeal mask in dental anaesthesia. Eur J Anaesthesiology 1991; 4:53–9
- Brimacombe J. Analysis of 1500 laryngeal mask uses by one anaesthetist in adults undergoing routine anaesthesia. Anaesthesia 1996;51:76–80[Web of Science][Medline]
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