What is a self-contained breathing apparatus

Anesthetic system

1 definition

A Anesthetic system is part of the anesthesia machine. As part of general anesthesia, it enables regulated ventilation as well as the supply and disposal of breathing air, oxygen and anesthetic gases.

2 forms

There are 4 different forms of anesthetic systems, whereby a basic distinction is made between non-rebreathing systems and rebreathing systems.

2.1 Non-rebreathing systems

2.1.1 Open system

With the open system, the patient breathes in and out of the room or ambient air, there is no separation of inspiration and expiration. The Schimmelbusch mask is known as a classic system. A mask-shaped wire body, which is covered with gauze, is placed on the patient's face. Chloroform or ether was dripped onto these and evaporated so that the patient was anesthetized by inhalation anesthesia. The process of open systems and that of the Schimmelbusch mask is only of historical importance today.

2.1.2 Semi-open system

With this system, the patient receives fresh gas from the anesthetic system during inspiration. Expiration takes place in the environment, no gas is returned. As an example, the basic principle of a ventilation bag works that of a half-open system. Some ventilators also use this mode of operation. With this system it must be ensured that the minute volume of the patient is not exceeded. Furthermore, when using volatile anesthetics, an anesthetic gas suction device should be used to avoid pollution of the environment (personal protection). In general, the process is considered uneconomical, since no gases are returned in this system either and large amounts of fresh gas are required.

2.2 rebreathing systems

2.2.1 Semi-closed system

Semi-closed systems are currently (2014) the most widely used anesthetic systems. The inspiration and expiration take place here in the so-called circular part of the anesthetic system. The patient receives fresh gas and, if necessary, volatile anesthetics from the inspiratory leg. Both ventilation hoses are connected to the patient by a Y-piece. During expiration, the exhaled CO is absorbed2 in soda lime. At the same time, the air you breathe is humidified. The rebreathing of gas is prevented by valves, they specify a flow direction in the system. During expiration, part of the breathing air is released into the anesthetic gas suction through a pressure relief valve. In general, this process can be viewed as a very economical process. During anesthesia, only 0.5 - 1.0 liters of fresh oxygen are required per minute (low flow).

2.2.2 Closed system

The closed system works essentially like the semi-closed system based on a circle part. While a small excess of gas is always lost in semi-closed systems, the closed system prevents gases from being lost. Very small amounts of fresh gas are required, which correspond to the amounts of oxygen required by the patient per minute: 0.2-0.5 liters of fresh gas consumption per minute. While closed systems are unbeatably cheap in terms of fresh gas consumption, their overall economic efficiency is questionable. The acquisition and maintenance costs are correspondingly higher than those for a semi-closed system and put the advantages of this system into perspective from an economic point of view.