Brand and size matter when choosing a syringe to relieve pressure in a tracheal tube cuff.

We studied the use of an inline syringe as a pressure relief valve for tracheal tube cuffs during exposure to nitrous oxide to see if the technique works. Bench testing was done to determine the stick and slip characteristics of syringes of different brands and sizes. Cuffs were inflated with 20 mL of air, producing a cuff pressure of 100-120 mm Hg. Then the plunger of the syringe was allowed to passively rebound to a steady pressure at which the plunger stopped ("stick pressure"). After several minutes, pressure in the syringe was forcibly increased with a second syringe until the plunger started moving again ("slip pressure"). Stick pressure varied from 18 to 82 mm Hg depending on the brand and size of syringe used. Slip pressures exceeded stick pressures by 20-120 mm Hg. Cuff pressure increased in a linear fashion during nitrous oxide exposure, and no syringe demonstrated automatic pressure reduction. We conclude that a syringe attached to the pilot balloon connector can be used to control tracheal tube cuff pressure during nitrous oxide anesthesia. However, not all syringes are suitable for this purpose: large syringes are better than small syringes, and the Terumo brand is more suitable than BD or Monoject. The system does not work automatically, and intermittent compression of the syringe plunger to overcome static friction is required to avoid overdistension.