[Pressure changes in the pneumoballoon of several endotracheal tubes after the administration of nitrous oxide]

We compare the degree of nitrous oxide diffusion in three types of endotracheal tubes available in the market, by means of continuous monitoring of the pressure attained at the pneumoballoon. Among the systems designed to impede or to minimize nitrous oxide diffusion, we have used in this study the so called "rediffusion system". When the endotracheal tube possesses this system, the pressure attained at the pneumoballoon remained constant throughout the study period (23.2 +/- 0.53 mmHg at time zero vs 24.2 +/- 0.66 mmHg 50 min after administration of protoxide). In contrast, endotracheal tubes without "rediffusion system" showed a statistically significant increase (p less than 0.05) of pneumoballoon pressure (25.2 +/- 2.43 mmHg and 26.7 +/- 1.01 mmHg at time zero vs 45.2 +/- 3.12 and 44.3 +/- 2.41 mmHg 50 min after protoxide administration in the two other types of endotracheal tubes). We believe that during anesthesia with nitrous oxide the pneumoballoon pressure should be monitored or systems that avoid diffusion of this inhalational agent should be inserted. Our results indicate that endotracheal tubes equiped with "rediffusion system" are effective in impeding diffusion of the inhalational agents.