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LETTER TO THE EDITOR

Comparison Between the PLA Cobra^TM and the Laryngeal Mask Airway Unique^TM: Choice of Laryngeal Mask Airway Unique Size

Department of Anesthesiology; Bnai-Zion Medical Center; Haifa, Israel (Gaitini) Department of Anesthesiology; Vanderbilt University Medical Center; Member, Anesthesia Medical Group; Centennial Medical Center; Nashville, Tennesse; luis.gaitini{at}b-zion.org.il (Alfery)

In Response:

Drs. Timmermann and Crozier raise a valid question (1): are our results (2) incorrect due to selecting the wrong size of Laryngeal Mask Airway (LMA) Unique? This raises the broader question of "what size LMA Unique is appropriate?" We believe this question is best answered by combining manufacturer’s guidelines, individual patient characteristics, and the experience of the practitioner using the device.

As Drs. Timmermann and Crozier observe, the guidelines given for the LMA Unique are inconsistent in men weighing <70 kg and women weighing <50 kg or >70 kg. The manufacturer further states that the guidelines should be used "only as an approximate guide. Clinical judgment based on many patient factors, including patient anatomy and physiology as well as weight, should be used in selecting an LMA airway size" (3).

The published clinical studies of the LMA Unique offer little agreement as to proper sizing. Verghese et al. (4) studied patients who received either a size 4 or 5, but did not explain how the sizes where chosen. Brimacombe et al. (5,6) used size 4 for women and size 5 for men, noting that they found gender-based guidelines more helpful than weight-based guidelines. However, Brimacombe (7) also states in his textbook on LMAs that "clinical judgment should be used at all times when selecting the size." In an evaluation of the LMA Unique versus the SoftSeal airway Cook et al. (8) used size 5 for all males, size 4 for all females over 50 kg, and size 3 for females between 40 and 50 kg. A similar evaluation done by Paech et al. (9) used size 3 for females weighing 50–70 kg, size 4 for females weighing >70 kg, and size 4 for all males, with size 5 not used at all. Clearly, there is no consensus among experienced investigators, nor even the manufacturer, as to the correct size LMA Unique to be used in any given patient.

The new ASTM (previously called American Standard and Test Materials) standards adopted by the Supralaryngeal Airway Task Group addresses the issue of proper sizing of supraglottic devices. The Task Group agreed that manufacturer sizing recommendations were inadequate and that "the necessity for expert clinical judgment in selecting the size of a supralaryngeal airway remains" (Paul Dryden, ProMedic, Indianapolis, IN—Member of Supralaryngeal Airway Task Group— personal communication).

With experience totaling more than 100 LMA Unique insertions and more than 1000 insertions of the LMA Classic, we chose to use primarily weight-based guidelines. Clinical judgment was part of the decision, and that judgment resulted in more frequent use of size 4. We believe that clinical judgment is warranted, the size selection was appropriate, and our results are correct.

Footnotes

Conflict of interest: Dr. Alfery is the inventor of the CobraPLA and receives royalties on sales.

REFERENCES

1. Timmermann A, Crozier TA. Comparison between the PLA Cobra^TM and the Laryngeal Mask Airway Unique^TM: choice of Laryngeal Mask Airway Unique size. Anesth Analg 2007;104:457.[Free Full Text]
2. Gaitini L, Yanovski B, Somri M, et al. A comparison between the PLA Cobra and the Laryngeal Mask Airway Unique during spontaneous ventilation: a randomized prospective study. Anesth Analg 2006;102:631–6.[Abstract/Free Full Text]
3. How do I select the correct size of LMA airway? Under Products/LMA—Unique area of LMA North America website: lmana.com.
4. Verghese C, Berlet J, Kapila A, Pollard R. Clinical assessment of the single use laryngeal mask airway—the LMA unique. Br J Anaesth 1998;80:677–9.[Abstract/Free Full Text]
5. Brimacombe J, Keller C. Insertion of the LMA-Unique with and without digital intraoral manipulation by inexperienced personnel after maniken-only training. J Emerg Med 2004;26:1–5.[Web of Science][Medline]
6. Brimacombe J, von Goedecke A, Keller C, et al. The laryngeal mask airway Unique versus the Soft Seal laryngeal mask: a randomized crossover study in paralyzed, anesthetized patients. Anesth Analg 2004; 99:1560–3.[Abstract/Free Full Text]
7. Brimacombe J. Pre-anesthesia phase: size selection. In: Brimacombe J, ed. Laryngeal mask anesthesia. 2nd ed. Philadelphia: WB Saunders, 2005:179.
8. Cook TM, Trumpelmann P, Beringer R, Stedeford J. A randomized comparison of the Portex Softseal laryngeal mask airway with the LMA-Unique during anesthesia. Anaesthesia 2005;60:1218–25.[Web of Science][Medline]
9. Paech MJ, Tweedie O, Stannard K, et al. Randomized, crossover comparison of the single-use SoftSeal and the LMA Unique laryngeal mask airways. Anaesthesia 2005;60:354–9.[Web of Science][Medline]

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