General anaesthesia is a pharmacologically induced, temporary and reversible coma state, which consists of muscle relaxation. This is obtained by administering some drugs to the patient. Anaesthesia aims to temporarily induce the total loss of consciousness, with the suppression of all kinds of sensitivities; its major application concerns surgery. The right dosing and mixing of gases depend on precision. The doctor needs high precision to control the patient’s respiratory rate. The requested flow is very high at very low pressure.