The FM flowmeters are devices for the supply of medical gases with two to six antistatic and graduated tubes and completed with an integrated dosage unit. The body is made of anodized aluminum and the inlet connections for O2, Air and N2O at the bottom of the flowmeter are arranged to be connected to hospital centralized gas plants or to cylinders complete with pressure regulators. The gas feeding unit includes a safety valve automatically blocking the N2O supply when the feeding pressure of O2 drops below the value of approximately 0.4 bar. The mixtures of O2 and N2O can be supplied to the patient through a dosage unit. An incorporated mixing device proportions the N2O in such a way that a minimum of at least 30% of O2 is always present in the gas mixture. At the outlet of the dosage unit, an anesthesia evaporator can be connected or the gas mixture can be supplied directly to the patient through the gas feeding unit. The O2+ flush button can be used for a quick supply of O2 directly at the outlet of the mixture on the gas feeding unit.