The effect of nitrous oxide on laryngeal mask cuff pressure. In vitro and in vivo studies.

We have studied the effect of nitrous oxide on the cuff pressure of a laryngeal mask both in vitro and in vivo. In laboratory tests, we showed that nitrous oxide and carbon dioxide diffuse across the cuff wall much more rapidly than nitrogen and oxygen. Differing partial pressures of these gases across the cuff wall therefore give rise to changes in volume and pressure within the cuff. We then studied 18 patients undergoing general anaesthesia with nitrous oxide, and found a consistent and linear increase in cuff pressure in all patients. After 30 min, the mean pressure had increased by 30 mmHg, and there was approximately 10% nitrous oxide in the cuff. It is difficult to relate these findings to pressure on pharyngeal structures, but methods of limiting the rise in intracuff pressure are discussed.