To the Editor:—

It was interesting to read the article by Combes et al.  1We fully agree with the authors that, during N2O anaesthesia, the main cause for the increase in intracuff pressure, when filled with air, is the diffusion of N2O into the cuff. Other factors, such as the diffusion of O2into the cuff and the warming of gases inside the cuff, play a small role in the increase in the intracuff pressure. Various factors affect the rate of diffusion of N2O, including the difference in partial pressure of N2O inside and outside the cuff, the area available for diffusion, and the cuff material. We have evaluated pressure changes in a new design endotracheal tube cuff, the Portex Soft Seal (Portex Ltd., Hythe, United Kingdom) during N2O anesthesia. 2The new design prevented increases in the intracuff pressure and remained stable throughout the procedure with pressure changes similar to those in the saline group observed by Combes et al.  1In the Portex Soft Seal tube cuff, the plasticizer added to soften the polyvinyl chloride makes the cuff much less permeable to N2O despite having a thickness of 0.06 mm, which is very similar to the Mallinckrodt Lo-Contour (Athlone, Ireland) used by Combes et al.  1We agree with the authors that filling the cuff with saline is not recommended in routine clinical practice as the cuff is not designed to be filled with saline. We believe that using the Portex Soft Seal cuff prevents tracheal injury caused by the increased intracuff pressure due to N2O diffusion and makes filling the cuff with saline and monitoring the cuff pressure throughout the anesthetic course unnecessary.

Combes X, Schauvliege F, Peyrouset O, Motamed C, Kirov K, Dhonneur G, Duvaldestin PI: Intracuff pressure and tracheal morbidity: Influence of filling cuff with saline during nitrous oxide anesthesia. A nesthesiology 2001; 95: 1120–4
Al-Shaikh B, Jones M, Baldwin F: Evaluation of pressure changes in a new design tracheal cuff, the Porex Soft Seal, during nitrous oxide anaesthesia. Br J Anaesth 1999; 83: 805–6