Abstract: A gas pressure generator for a ventilator includes a variable volume container provided with an inlet connectable to a fresh gas supply and an outlet connectable to a respiration circuit of the ventilator and a driving fluid-actuated piston having a shaft with a piston head for transmitting the force to the variable volume container at one end and an opposite end, at which the force is generated, being moveable in a driving fluid chamber so to reduce the volume of the container to maintain a substantially constant output pressure of contained fresh gas. The driving fluid is maintained at a substantially constant pressure with the piston shaft and the chamber relatively dimensioned such that the percentage volume change within the chamber as the shaft moves therein is no greater than an allowable percentage variation in the output pressure of the fresh gas.

Abstract: An apparatus for the administration of a respiratory gas and at least one anaesthetic to a living being, in which apparatus the anaesthetic is vaporized in a vaporizing unit and is entrained in respiratory gas, acquires a safer and more accurate control of the anaesthetic concentration level by means of a regulating valve which controls the flow of respiratory gas through the vaporizing unit and in that a regulating device controls the regulating valve with such accuracy that a preselected concentration of vaporized anaesthetic in the respiratory gas is substantially fully maintained. To further increase the control of the apparatus it may also be provided with a feedback system for both the anaesthetic concentration level and the total flow.