Autoregulatory adjustment range of Cuff-Keeper, a new tracheal tube cuff self-regulatory inflator 

Background: 
To prevent endotracheal tube (ETT)-related complications during ventilation, it is recommended to maintain cuff pressure (Pcuff) within range of 20-30 cmH2O. CuffKeeper (CK; Tokukigikenkogyo, Oita, Japan) is designed to control Pcuff only by handling rotary dial without electricity. This study is to investigate the accuracy and the range of automatic adjustment regulation under simulated plastic tracheal model.

Methods: 
Phase 1, CK pump pressure validation analysis;
CK was connected to a pressure transducer (TD) directly. Using pump handle static pressure was given to TD from atmospheric pressure with 4 hPa (≒4 cmH2O) increment stepwise fashion to 60 hPa and compared with the value measured by TD.
Phase 2, CK auto adjustment function test;
A syringe and ETT were connected to the experimental system to validate adjustment function by artificially causing leakage and inflation. We tested 2 cuff shapes and 4 sizes of ETTs with 3 sizes of sheath of syringe as the tracheal model. Once Pcuff was set at 24 hPa, auto adjustment function was tested by inflating and deflating air from the system to determine the effective adjustment limit of leakage and inflation.

Results and discussion: 
1. The values from CK and TD consistently matched. With 30-60 ml of air infusion by a syringe, both CK and TD showed 20-30 hPa which is the appropriate range of Pcuff.
2. We evaluated 8 combinations of ETT size, cuff shape and the tracheal model. Inflation or deflation of 15-18ml air maintained the Pcuff within 20-30 cmH2O and CK showed autoregulatory efficacy of Pcuff at 24 hPa with air inflation/deflation within 2-3ml.
Without CK, Pcuff indicated out-of-range value after inflating or deflating only 1-2ml air (P < 0.01, vs. with CK, paired t-test). These results support potential usefulness of the CK although it is not capable of holding Pcuff strictly at the same pressure. However, its usability when patients cough and move is unclear, which requires further studies to conclude clinical usefulness and limitations of this device.

Conclusion: 
CuffKeeper, which is easily operated with manual handle without electricity, is potentially an effective device for achieving appropriate Pcuff.