The invention concerns a device (20) for determining the period of consumption of a gas by a patient comprising an internal gas passage (25) with a gas inlet (21) and a gas outlet (22), adjustment means (23) for adjusting a desired gas consumption period (Tflxé), display means (24) for displaying at least the desired gas consumption period (Tfixé), means for determining the gas consumption period (5, 6) designed to measure the total gas consumption period (Tconso) during which gas is flowing in said internal gas passage (25), from the gas inlet (21) to the gas outlet (22), information processing means (9) capable of and designed to compare the total gas consumption period (Tconso) determined by the means for determining the gas consumption period (5, 6) with the desired gas consumption period (Tfixé), and flow interruption means designed to stop any flow of gas in said gas passage when the information processing means determine that the total gas consumption period (Tconso) is greater than or equal to the desired gas consumption period (Tfixé).
