Abstract: A safety system for use in a breathing system of an anesthesia apparatus including a gas supply circuit and re-breathing or counter lung circuit. The safety system includes pneumatically operated switches, battery-powered monitoring circuitry and alarm circuitry. The alarm circuitry is coupled to the monitoring circuitry to provide an alarm signal in the event that gas pressure in the breathing circuit exceeds a threshold level for a predetermined period of time, irrespective of the mode of operation of the apparatus. The pneumatically operated switches are arranged to minimize battery drainage during operation.

Abstract: In anesthesia apparatus for supplying oxygen and an anesthesia gas through respective flow control valves to a patient breathing circuit a low oxygen flow alarm system is provided. The alarm system includes a restrictor in the pipeline of the oxygen flow control valve and a restrictor in the pipeline of the anesthesia gas flow control valve. A differential pressure sensing unit including a diaphragm assembly responsive to the pressure in the oxygen pipeline and another diaphragm assembly responsive to the pressure in the anesthesia gas pipeline is coupled to the restrictor pipelines. The diaphragm assemblies are opposed to each other and coupled together by a displaceable linkage. Electrical switch means are provided coupled to the linkage to provide an alarm signal when the linkage has been moved to a predetermined position indicating that the oxygen concentration has dropped below a predetermined value. The differential pressure sensing unit includes spring biasing means.