In Reply:— We thank Osborn et al. for starting an interesting debate about the use of new supraglottic devices in clinical practice without solid evidence on their performance.
As described earlier for the Laryngeal Mask Airway ProSeal ™ (LMA-P ™),1we reported an unexpected acute airway obstruction caused by the Laryngeal Mask Airway Supreme ™ (LMA-S ™), which ultimately was interpreted as a medial displacement of the laryngeal inlet by the mask itself, leading to airway obstruction, stridor, and ventilation difficulty.2
The patient's head was in the neutral position without head flexion and slightly elevated, as recommended. His height was 1.78 m, he weighed 95.6 kg (body mass index 30.2 kg/m2). Based on the patient's characteristics and the recommendation in the LMA-S ™ instruction manual, the LMA-S ™ size 5 was the correct one. We acknowledge other suggestions regarding how to choose the right size of an LMA-S ™.
In 2003, Stix et al. described malposition of the LMA-P ™ indicated by the depth of the bite block.3Whether this applies to the LMA-S ™ with its different construction as well is speculative, and we cannot comment on that. In our case, the bite block did not remain outside of the mouth.
We also cannot judge whether an LMA-S ™ size 4 would have changed the airway problem. Our report was not intended to show all possibilities how to resolve airway obstructions with the use of an LMA ™, but rather to point out that such obstruction may happen.
Osborn et al. mention that the cuff volume of the size 5 LMA-S ™ should not exceed 45 ml. We completely agree that overinflation needs to be avoided carefully in any cuffed supraglottic airway device. Besides airway obstruction, it might also cause nerve damage.4Clinical observation in the operating room showed us that even 45 ml often results in high cuff pressures. The cuff volume in the patient presented was well below 45 ml, leading to a cuff pressure of 60 cm H2O.
Our clinical practice with the LMA-P ™ includes the described methods to detect malposition. Whether these also apply to the LMA-S ™ needs to be proven. In the case described, we had the luxury of having a fiberoptic bronchoscope immediately available to directly visualize the reason for the airway obstruction.
We disagree that previously published findings regarding the performance of the LMA-P ™ should automatically apply to the LMA-S ™, as Osborn et al. imply. The LMA-S ™ should not be confused with the LMA-P ™. It is not a single-use LMA-P ™ because substantial details are designed and constructed in a different way to overcome weaknesses of other LMAs ™, as the producers of the LMA-S ™ promote their device. The LMA-S ™'s clinical performance can only be evaluated in clinical trials. First published comparisons with a reasonable sample size between the LMA-P ™ and LMA-S ™5showed clinically important differences in the seal pressure between both devices.
We affirm our statement that acute airway obstruction of LMAs ™ can occur at any time, and backup strategies for the failure of the backup device LMA ™ have to be considered.
*University Hospital Bern, Bern, Switzerland. lorenz.theiler@insel.ch
