General anesthesia is a pharmacologically induced, temporary and reversible coma state, which consists of muscle relaxation. These are obtained by administering to the patient some drugs. The aim of anesthesia is to temporarily induce the total loss of consciousness, with the suppression of all kinds of sensitivities; its major applications concern surgery. The right dosing and mixing gasses depends on the precision. The doctor need high precision to control the patient’s respiratory rate . The requested flow is very high at a very low pressure.