Nitrous oxide diffusion into tracheal tube cuffs – efficacy of a new prototype cuff pressure release valve

Abstract

The aim of this study was to evaluate the performance of a new cuff pressure release valve (CPRV), in which the release pressure can be adjusted from 10 to 25 cmH2O, particularly intended to control pressure in paediatric cuffed tracheal tubes and to avoid cuff hyperinflation caused by N2O diffusion. In vitro: the PRV was set to 10, 15, 20 or 25 cmH2O release pressure and connected to a cuffed tube placed into a box flushed with 66% N2O in O2. The cuff pressure was monitored with and without CPRV for 60 min. Experiments were performed four times using two different CPRVs. In vivo: with Institutional Review Board approval, CPRV was studied in 50 children undergoing general anaesthesia with tracheal intubation and standardized anaesthesia technique (including 66% N2O in O2) and ventilator settings. Patients were randomized into two groups (with and without CPRV). The cuff pressure baseline was 20 cmH2O and CPRV was set to 25 cmH2O. If the cuff pressure exceeded 25 cmH2O, it was manually released to 20 cmH2O. The numbers of deflations in both groups were noted and compared by Mann-Whitney U-test (P<0.05). In vitro: the cuff pressure exceeded 50 cmH2O after 60 min without CPRV, but did not exceed the settings with CPRV. In vivo: there was no need to manually deflate the cuff in the CPRV group but, in every patient in the control group, three (two to seven) deflating manoeuvres were required within the first hour of anaesthesia (P<0.0001). The CPRV allows reliable cuff pressure release at various pressure levels and reliably prevents cuff pressure increases caused by N2O.