3.3 Closed anesthetic breathing system: 

In a closed anesthetic breathing system (Figure3.6), there is total rebreathing of exhaled gases after absorption of carbon dioxide, and the APL valve or relief valve of the ventilator is closed. A closed system is present when the fresh gas inflow into the circle system (150 to 500 mL/min) satisfies the patient’s metabolic oxygen requirements and replaces anesthetic gases lost by virtue of tissue uptake. 

Advantages of a closed circle anesthetic breathing system over a semiclosed circle anesthetic breathing system include: 

• Maximal humidification and warming of inhaled gases, 
• Less pollution of the surrounding atmosphere with anesthetic gases. 
• Economy in the use of anesthetics 

A disadvantage of a closed circle anesthetic breathing system is an inability to rapidly change the delivered concentration of anesthetic gases and oxygen because of the low fresh gas inflow.