Background: The Brandt tracheal tube keeps cuff pressure constant during anaesthesia, but the mechanisms have not been examined. We assessed volume, pressure and gas concentration in the cuff and pilot balloon using the Brandt system.
Methods: The pressure in an air-filled cuff of the Brandt system (Mallinckrodt Brandt tracheal tube, n = 60) was recorded during anaesthesia with 67% nitrous oxide; gas volume and concentration in cuffs and balloons were measured for up to 12 h from the start of anaesthesia. The volume change of each gas was calculated to assess its contribution to the cuff pressure. We also measured cuff compliance in vitro.
Results: Cuff pressure increased slightly during anaesthesia (P < 0.05). The nitrous oxide concentration increased to 47.7 (8.2)% (mean (SD)) in the cuff and to 2.2 (0.9)% in the pilot balloon. The nitrous oxide volume in the cuff and pilot balloon increased by approximately 2 ml during the first 4 h of anaesthesia. The carbon dioxide volume increased slightly, and nitrogen and oxygen did not change significantly. The compliance of the Brandt tube cuff was six times greater than that of a standard tube cuff (Mallinckrodt Hi-Contour tracheal tube).
Conclusions: The Brandt tracheal tube maintains stable cuff pressure during nitrous oxide anaesthesia because of a highly compliant balloon. The concentration gradient of nitrous oxide between the cuff and pilot balloon also contributes to the stable-cuff pressure because the high nitrous oxide concentration in the cuff reduces nitrous oxide influx.