Diffusion of nitrous oxide through endotracheal tube cuffs

Nitrous oxide (N2O) is an inhalational anesthetic that is frequently used for general anesthesia. While N2O is not sufficient for maintaining general anesthesia if used alone, when used in combination with a volatile inhalation agent, N2O decreases the minimum alveolar concentration (MAC) of the volatile inhalational agent, thereby reducing the amount of the agent required during longer procedures [1]. However, N2O increases the intracuff pressure of the tracheal tube due to diffusion of N2O into the cuff during general anesthesia [2]. Intracuff pressure increases steadily and reaches a level high enough to impede the microcirculation in the tracheal mucosa within 1 h [3,4], which may cause damage to the tracheal tissue. This represents a major complication of N2O use. In anesthesia using N2O, it is thought that the N2O concentration in the tube cuff is close to the N2O concentration prescribed for the patient. Usually, at the end surgery, administration of N2O is stopped, and the patient is given 100% oxygen or air. Subsequently, the patient recovers from anesthesia and is moved to the intensive care unit. In such cases, the N2O that flowed into the cuff will be transferred to outside of the cuff, which may cause a decrease in cuff pressure. This decrease in cuff pressure may then trigger ventilator-associated pneumonia (VAP) [5]. However, few studies have examined the decrease in cuff pressure associated with N2O administration. Therefore, in this study, we examined the decrease in cuff pressure caused by the flow of N2O into the cuff. Materials and Methods