Summary

In study session III you have learnt

• The function of anesthetic breathing systems is to deliver oxygen and anesthetic gases to the patient and to eliminate carbon dioxide.
• Anesthetic breathing systems are classified as open, semiopen, semiclosed, and closed according to the presence or absence of gas reservoir bag in the circuit, rebreathing of exhaled gases, means to chemically neutralize exhaled carbon dioxide, unidirectional valves and fresh gas inflow rate
• The Mapleson F (Jackson-Rees) is a semi open system T-piece arrangement with a reservoir bag and an adjustable pressure-limiting overflow valve on the distal end of the gas reservoir bag. Fresh gas flow equal to two to three times the patient's minute ventilation is recommended to prevent rebreathing of exhaled gases. It is popular in pediatrics
• The Bain circuit is a semi open breathing system in which the fresh gas supply tube runs coaxially inside the corrugated expiratory tubing. The Bain circuit may be used for both spontaneous and controlled ventilation.
• The circle system is the most popular anesthetic breathing circuit. The circle system essential components are arranged in a circular manner. Components of the circle system consists of (1) a fresh gas inlet, (2) inspiratory and expiratory unidirectional check valves, (3) inspiratory and expiratory corrugated tubing, (4) a Y-piece connector, (5) an adjustable pressure-limiting (APL) valve, also referred to as an overflow or pop-off valve, (6) a reservoir bag, (7) a canister containing carbon dioxide absorbent, (8) a bag/vent selector switch, and (9) a mechanical anesthesia ventilator.
• In a closed anesthetic breathing system, there is total rebreathing of exhaled gases after absorption of carbon dioxide and the APL valve or relief valve of the ventilator is closed. 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 and economy in the use of anesthetics
• Open and semiopen breathing systems eliminate carbon dioxide by venting all exhaled gases to the atmosphere. Semiclosed and closed breathing systems eliminate carbon dioxide by chemical neutralization. Chemical neutralization is accomplished by directing the exhaled gases through a carbon dioxide absorber, which consists of a canister (usually transparent) containing carbon dioxide absorbent granule.
• Efficiency of carbon dioxide neutralization: is influenced by the size of the carbon dioxide granules and the presence or absence of channeling in the carbon dioxide canister. Absorbent efficiency increases as absorbent granule size decreases because the total surface area coming in contact with carbon dioxide increases.
• Scavenging is the collection and subsequent removal of vented gases from the operating room. The excess gas comes from either the APL valve if the bag/vent selector switch is set to bag or from the ventilator relief valve if the bag/vent selector switch is set to vent.
• All components of the anesthesia machine, gas source, delivery system need to be visually inspected daily. An anesthesia delivery system that has been appropriately tested will allow for the correct flow of the anesthetic gas mixtures through the system. Thus allowing the removal of CO2 from the exhaled gases before the patient inhales. Also the proper removal of waste gases will ensure a safe work environment for the hospital staff.