The anesthesia machine is composed of four main sub-systems in terms of working principle: gas supply and control circuit system, breathing and ventilation circuit system, purge system, and a set of system functions and breathing circuit monitors. Some anesthesia machines also have some monitors and alarms to point out the values and changes of certain physiological variables and parameters related to the cardiopulmonary function or the gas and anesthetic concentration in the breathing mixture. Generally, manufacturers only provide less 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
As the anesthesia machine needs a lot of oxygen when it works, it is usually obtained from the hospital's central gas supply system or oxygen cylinders. Each gas input from the cylinder to the circuit must pass through a filter, a one-way vent valve and a regulator. The regulator can reduce the pressure to the appropriate working pressure of the anesthesia machine. The central gas supply system does not require a regulator, because the gas has dropped to about 4 kg. 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 is lower than 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 the continuous flow device is controlled by a flow meter and displayed by the flow meter. The flow meter can be mechanical or an electronic sensor with LCD. After the gas passes through the control valve and the flow meter, it enters the low-pressure circuit, if necessary, it passes through the vaporizer and then is supplied to the patient. For a good anesthesia machine, the flow control mechanism of laughing gas and oxygen should be linked, only in this way the ratio of oxygen to laughing gas will never drop to the minimum (0.25L/min).
2. breathing and ventilation circuit system
Most anesthesia machines can provide a continuous flow of oxygen and anesthetic gas, which is called the circulatory system. In this type of anesthesia machine, there are two main types of breathing circuits, a closed type and a semi-closed type. In a closed breathing circuit, all the gas exhaled by the patient returns to the circulatory system after removing CO2. In the semi-closed mode, part of the gas exhaled by the patient enters the circulatory system and partly exits the circulatory system. In the circulatory system, the supply flow of fresh gas below 1L/min is called low flow anesthesia, and the flow of fresh gas below 0.5L/min is called minimum flow anesthesia.
Manual ventilation requires the operator to continuously manually squeeze the airbag to make the patient breathe. During a long time operation, the operator is not only very tired, but also affects other tasks. Therefore, automatic ventilators are often used to mechanically allow the patient to breathe. The ventilator forces the mixed gas of anesthesia into the patient's circuit and breathing system, and accepts the gas and fresh gas exhaled by the patient. The anesthesiologist can adjust parameters such as tidal volume, respiratory rate, inspiratory-expiratory ratio, and minute ventilation according to the patient's condition. Adjust the ventilation method to meet the various needs of the patient.
3.Cleaning system
Cleaning system, also known as carbon dioxide absorption system, is composed of 1-2 CO2 absorption tanks. The tanks are filled with soda lime or barium lime. The main function is to remove CO2 from the patient's exhaled air.
4. Monitoring and alarm system
The anesthesia machine has a set of monitoring-related devices according to different configurations, such as monitoring the airway, physiology, anesthetic gas concentration, and monitoring that can indirectly reflect the patient's anesthesia depth and muscle relaxation.
Most of the monitoring systems of anesthesia machines are equipped with a basic monitoring device as a platform for the system. The monitoring content includes: airway pressure, inhaled tidal volume, minute ventilation, respiratory rate, and related alarm systems. Other monitoring required can be purchased separately and added to the system.
In addition, the anesthesia workstation needs to be equipped with an anesthesia information management system, which can receive, analyze, and store information related to the clinical and administrative management of anesthesia, automatically collect information from the monitor, and automatically generate an anesthesia record sheet. The anesthesia machine is structurally composed of the following parts: frame, external circuit, ventilator, and monitoring system.
