The rediffusion system. Limitation of nitrous oxide increases the cuff pressure of endotracheal tubes

There is an increase in endotracheal tube-cuff volume and pressure due to nitrous oxide diffusion into the cuff during anaesthesia. A rise of the cuff pressure up to 100 mm Hg (high volume-low pressure cuffs!) within only two hours is nothing out of the ordinary. The inspiratory nitrous oxide concentration influences the cuff pressure rises. The rate of pressure rise depends on the diffusion constant of the cuff material for nitrous oxide, on the cuff wall thickness, and on the difference of nitrous oxide concentration between cuff and trachea or tracheal tissue. An innovation of the blocking system--we call it the Rediffusion System--reduces the nitrous oxide-induced rise of cuff pressure even during long lasting endotracheal anaesthesia with a high FIN2O. The principle of the Rediffusion System is the enlargement of the pilot balloon in order to improve its diffusion capacity for nitrous oxide. In this way a rediffusion into the air is enabled for that nitrous oxide that diffused into the blocking system through the cuff wall. In endotracheal tubes with a Rediffusion System, cuff pressure never exceeds capillary perfusion pressure of the tracheal mucosa. In our in vitro-experiments we found an increase of cuff pressure from 14.2 +/- 0.5 mm Hg to only 27.3 +/- 1.9 mm Hg within six hours (FIN2O = 0.66). Within 150 minutes of endotracheal anaesthesia (FIN2O = 0.66) cuff pressure rose from 14.6 +/- 0.5 mm Hg to only 21.5 +/- 3.6 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)