Diffusion of nitrous oxide through endotracheal tube cuffs

During general anesthesia using nitrous oxide (N₂O), N₂O diffuses into the tracheal tube cuff and increases cuff pressure, potentially causing tissue damage in the trachea. However, the permeability of the tube cuff to N₂O flowing into the cuff is unknown. Here, we examined decrease in cuff pressure and N₂O permeability of the tracheal tube cuff. Two tracheal tubes, i.e., Portex Blue Line Profile, Soft-Seal Cuff (SPN) and Mallinckrodt Nasal RAE Tracheal Tube Cuffed, Murphy Eye (MRN), were examined. Six gas samples (air, oxygen, 70% N₂O in oxygen, 50% N₂O in oxygen, 30% N₂O in oxygen, and a mixture of 60% N₂O in oxygen to air [4:3]) were prepared and used to inflate both cuffs at a pressure of 30 cmH₂O. Cuff pressures were recorded at every 5 min. After inflation with air, cuff pressures reached 26.8 ± 1.9 and 30.0 cmH₂O for MRN and SPN, respectively, within 60 min. Inflation with 70% N₂O dramatically decreased cuff pressures (3.2 ± 0.4 and 5.2 ± 1.1 cmH₂O, respectively). The rate of pressure decrease was dependent on the concentration of N₂O and was more rapid for MRN than SPN. Inflation with the mixture gas decreased the pressure to 14.8 ± 2.7 and 17.4 ± 3.8 cmH₂O for MRN and SPN, respectively, within 60 min. Here, we provided the first analysis of deflating cuff pressures, which may help to predict patterns for cuff pressure deflation in clinical practice. This study model may be beneficial for the study of ventilator-associated pneumonia.