To the Editor:—
We read with interest the recent article by van Zundert et al. 1regarding a new disposable laryngeal mask, the Soft Seal® LM (Smiths Medical International, Portex Ltd., Hythe, Kent, United Kingdom). We believe that the Soft Seal® LM has a good laryngeal seal while demonstrating satisfactory clinical performance. The authors reported that the cuff of the Soft Seal® LM prevented an increase in intracuff pressure, and intracuff pressure increased only from 60 to 62.8 cm H2O.
However, we obtained different results regarding changes in the intracuff pressure during nitrous oxide anesthesia using the Soft Seal® LM. Anesthesia was maintained with 66% N2O in oxygen and 1.5–3% sevoflurane in spontaneously breathing patients. In six patients, the intracuff pressures increased from 60 to 103 cm H2O (mean value) after 120 min. However, the rates of increase regarding the intracuff pressure were significantly lower than with the LMA-Classic™ (Intavent Orthofix Ltd., Maidenhead, Berkshire, United Kingdom).
On the other hand, we measured the aspirated volume from the cuff to maintain the intracuff pressure at 60 cmH2O during nitrous oxide anesthesia. Twenty patients were assigned to use a size 4 LMA-Classic™ (n = 10) or a size 4 Soft Seal® LM (n = 10). After the intracuff pressure was adjusted to 60 cm H2O, anesthesia was also maintained with 66% N2O in oxygen and sevoflurane during spontaneous breathing. The deflated volume to maintain the intracuff pressure at 60 cm H2O was measured. At 120 min after the initiation of anesthesia, the aspirated volume from the cuff to maintain the intracuff pressure at 60 cm H2O was 7.3 ml in the LMA-Classic™ group and 4.5 ml in the Soft Seal® LM group (P < 0.01).
These results suggest that Soft Seal® LM provided a reduction in nitrous oxide diffusion into the cuff; however, cuff deflation was needed to keep intracuff pressure at 60 cm H2O. We therefore still recommend the careful monitoring of the intracuff pressure during nitrous oxide anesthesia, even when using the Soft Seal® LM.
* Tokai University School of Medicine, Kanagawa, Japan. firstname.lastname@example.org