The composition and function of anesthesia machine:

The anesthesia machine delivers the anesthetic into the patient's alveoli through a mechanical circuit, forming a partial pressure of the anesthetic gas. After it diffuses into the blood, it directly inhibits the central nervous system, thereby producing the effect of general anesthesia.
This article mainly introduces the composition and function of anesthesia machine
1. Gas supply and control loop system Since the anesthesia machine requires a large amount of oxygen to operate, it is usually obtained from the hospital's central gas supply system or oxygen cylinder. Each gas entering the circuit from the cylinder passes through a filter, a one-way breather valve, and a regulator that reduces the pressure to the appropriate operating pressure for the anesthesia machine. The central air supply system does not require a regulator as the gas has been reduced to around 4kg. The suitable working pressure of the anesthesia machine is 3-6 kg. Most anesthesia machines have an oxygen source failure alarm system. If the oxygen pressure drops below 2.8 kg, the machine will reduce or cut off the flow of other gases and activate the alarm. ​
The flow rate of each gas in a continuous flow device is controlled and displayed by a flow meter. Flow meters can be mechanical or electronic sensors with LCD. After the gas passes through the control valve and flow meter, it enters the low-pressure circuit, passes through the evaporator if necessary, and is then supplied to the patient. In a good anesthesia machine, the flow control mechanisms of laughing gas and oxygen should be linked, so that the ratio of oxygen to laughing gas will never drop to the minimum value (0.25L/min). 2. Breathing and ventilation circuit system
Most anesthesia machines provide a continuous flow of circulating oxygen and anesthetic gases, called a circulation system. In this type of anesthesia machine, there are two main types of breathing circuits, closed and semi-closed. In a closed breathing circuit, all the gas exhaled by the patient returns to the circulatory system after removing CO2. In the semi-closed style, part of the patient's exhaled air enters the circulatory system and part is discharged from the circulatory system. In the circulatory system, the supply flow rate of fresh gas below 1L/min is called low-flow anesthesia, and the fresh gas flow rate below 0.5L/min is called minimum-flow anesthesia. ​
Manual ventilation requires the operator to continuously manually squeeze the air storage bag to allow the patient to breathe. During a long-term operation, the operator is not only very tired, but also affects other work. Therefore, automatic ventilators are commonly used to mechanically allow the patient to breathe. The ventilator forces the anesthetic mixture into the patient's circuit and respiratory system, accepting the patient's exhaled gas and fresh gas. The anesthesiologist can adjust parameters such as tidal volume, respiratory rate, inhalation-to-exhalation ratio, and minute ventilation according to the patient's condition. Adjust ventilation to meet patient needs. ​
3. Clear the system
Also known as the carbon dioxide absorption system, it consists of 1-2 CO2 absorption tanks filled with soda lime or barium lime. Its main function is to remove CO2 from the patient's exhaled gas. ​
4. Monitoring and alarm system The anesthesia machine has a set of monitoring-related devices according to different configurations, such as monitoring the airway, physiological aspects, anesthetic gas concentration, and monitoring that can indirectly reflect the patient's anesthesia depth and muscle relaxation. The monitoring system of most anesthesia machines is only equipped with a basic monitoring device as the system platform. The monitoring content includes: airway pressure, inhaled tidal volume, minute ventilation, respiratory rate and related alarm systems. Other required monitors can be purchased separately and added to the system. In addition, the anesthesia workstation needs to be equipped with an anesthesia information management system. This system can receive, analyze, and store information related to anesthesia clinical and administrative management, automatically collect monitor information, and automatically generate anesthesia records. The anesthesia machine is structurally composed of the following parts: frame, external circuit, ventilator, and monitoring system. ​
The anesthesia machine is composed of four main subsystems in terms of working principle: gas supply and control loop system, breathing and ventilation loop system, removal system, and a set of system functions and breathing circuit monitors. Some anesthesia machines also have monitors and alarms to indicate the values and changes of certain physiological variables and parameters related to cardiopulmonary function or the concentration of gases and anesthetics in the respiratory mixture. Usually manufacturers only provide a small number of monitoring and alarm combinations for standard products. ​

The following mainly explains the composition and function of the anesthesia machine from the working principle:

1. Gas supply and control loop system Since the anesthesia machine requires a large amount of oxygen to operate, it is usually obtained from the hospital's central gas supply system or oxygen cylinder. Each gas entering the circuit from the cylinder passes through a filter, a one-way breather valve, and a regulator that reduces the pressure to the appropriate operating pressure for the anesthesia machine. The central air supply system does not require a regulator as the gas has been reduced to around 4kg. The suitable working pressure of the anesthesia machine is 3-6 kg. Most anesthesia machines have an oxygen source failure alarm system. If the oxygen pressure drops below 2.8 kg, the machine will reduce or cut off the flow of other gases and activate the alarm. ​

The flow rate of each gas in a continuous flow device is controlled and displayed by a flow meter. Flow meters can be mechanical or electronic sensors with LCD. After the gas passes through the control valve and flow meter, it enters the low-pressure circuit, passes through the evaporator if necessary, and is then supplied to the patient. In a good anesthesia machine, the flow control mechanisms of laughing gas and oxygen should be linked, so that the ratio of oxygen to laughing gas will never drop to the minimum value (0.25L/min).
​
2. Breathing and ventilation circuit system
Most anesthesia machines provide a continuous flow of circulating oxygen and anesthetic gases, called a circulation system. In this type of anesthesia machine, there are two main types of breathing circuits, closed and semi-closed. In a closed breathing circuit, all the gas exhaled by the patient returns to the circulatory system after removing CO2. In the semi-closed style, part of the patient's exhaled air enters the circulatory system and part is discharged from the circulatory system. In the circulatory system, the supply flow rate of fresh gas below 1L/min is called low-flow anesthesia, and the fresh gas flow rate below 0.5L/min is called minimum-flow anesthesia. ​
Manual ventilation requires the operator to continuously manually squeeze the air storage bag to allow the patient to breathe. During a long-term operation, the operator is not only very tired, but also affects other work. Therefore, automatic ventilators are commonly used to mechanically allow the patient to breathe. The ventilator forces the anesthetic mixture into the patient's circuit and respiratory system, accepting the patient's exhaled gas and fresh gas. The anesthesiologist can adjust parameters such as tidal volume, respiratory rate, inhalation-to-exhalation ratio, and minute ventilation according to the patient's condition. Adjust ventilation to meet patient needs.
​
3. Clear the system
Also known as the carbon dioxide absorption system, it consists of 1-2 CO2 absorption tanks filled with soda lime or barium lime. Its main function is to remove CO2 from the patient's exhaled gas.
​
4. Monitoring and alarm system
The anesthesia machine has a set of monitoring-related devices according to different configurations, such as monitoring the airway, physiological aspects, anesthetic gas concentration, and monitoring that can indirectly reflect the patient's anesthesia depth and muscle relaxation. The monitoring system of most anesthesia machines is only equipped with a basic monitoring device as the system platform. The monitoring content includes: airway pressure, inhaled tidal volume, minute ventilation, respiratory rate and related alarm systems. Other required monitors can be purchased separately and added to the system. In addition, the anesthesia workstation needs to be equipped with an anesthesia information management system. This system can receive, analyze, and store information related to anesthesia clinical and administrative management, automatically collect monitor information, and automatically generate anesthesia records.