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LETTERS TO THE EDITOR

New Cuff Design Prevents N₂O Diffusion

Department of Anesthesia William Harvey Hospital Ashford, Kent, UK

To the Editor:

It was interesting to read the article by Nguyen Tu et al. (1) and the comment it generated (2). We 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. The diffusion of O₂ into 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. Recently, we have evaluated pressure changes in a new design tracheal tube cuff, the Portex Soft Seal, (SIMS Portex Ltd, Hythe, UK) during N₂O anaesthesia (3). The new design prevented increases in the intracuff pressure. In 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 Nguyen Tu et al. (1). We believe that using such a cuff prevents tracheal injury caused by the increased intracuff pressure caused by N₂O diffusion and makes the continuous monitoring of the cuff pressure unnecessary.

Footnotes

Dr. H. Nguyen Tu did not wish to respond to this letter.

References

1. Nguyen Tu H, Saidi N, Lieutaud T, et al. Nitrous oxide increases endotracheal cuff pressure and the incidence of tracheal lesions in anesthetized patients. Anesth Analg 1999; 89: 187–90.[Abstract/Free Full Text]
2. Priebe H-J. N₂O and endotracheal cuff pressure. Anesth Analg 2000; 90: 230–1.[Free Full Text]
3. Al-Shaikh B, Jones M, Baldwin F. Evaluation of pressure changes in a new design tracheal tube cuff, the Portex Soft Seal, during nitrous oxide anaesthesia. Br J Anaesth 1999; 83: 805–6.[Abstract/Free Full Text]

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