Anesthesia machines can be divided into the following major sub-systems based on their working principles: gas supply systems, control circuit systems, respiratory and ventilation circuit systems, and removal systems, as well as a set of system functions and respiratory circuit monitors. Some anesthesia machines also have monitors and alarms to facilitate the display of the values and changes in certain physiological variables and parameters related to the concentration of anesthetic and other gases in the cardiopulmonary function or breathing mixture.
The following is an explanation of the constitution of the anesthesia machine and its functions in terms of working principles.
1. Gas supply and control loop system
The anesthesia machine needs a lot of oxygen when working. It is usually obtained from the hospital's central air supply system or oxygen cylinder. Every gas from the cylinder input loop must pass through the filter, one-way vent valve and regulator, and the regulator can The pressure is reduced to the appropriate working pressure of the anesthesia machine. The central gas supply system does not need a regulator because the gas has dropped to about 4 kg, and the 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 below 2.8 kg, the machine will reduce or cut off the flow of other gases and activate the alarm.
The flow of each gas in the continuous flow device is controlled by the flow meter and displayed by the flow meter. The flow meter can be mechanical or it can be an electronic sensor with LCD. After the gas passes through the control valve and the flow meter, , into the low pressure circuit, if necessary, through the evaporation tank, and then to the patient. A good anesthetic machine, Laugh and Oxygen flow control mechanism should be linked, and only then the ratio of oxygen and nitrous oxide will never be reduced to a minimum (0.25 L/min).
2. Breathing and ventilating circuit system
Most anesthesia machines provide continuous flow of circulating oxygen and anesthetic gases called circulatory systems. In this kind of anesthesia machine, there are two main breathing circuits, closed and semi-closed.
In the closed breathing circuit, the gas exhaled by the patient is returned to the circulatory system after the carbon dioxide is removed. In the semi-closed type, the gas exhaled by the patient enters the circulatory system and part of the circulatory system is discharged. In the circulatory system, the supply flow of fresh gas is less than 1L/min 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 manually squeeze the storage balloon to breathe the patient. When the surgery is performed for a long time, the operator is not only very tired, but also affects other tasks. Therefore, an automatic ventilator is commonly used to mechanically allow the patient to breathe. The ventilator forces the anesthetic gas mixture into the patient circuit and respiratory system and receives the patient's expired gas and fresh gas. The anesthesiologist can adjust the parameters such as tidal volume, respiratory rate, inhalation and breathing ratio, and minute ventilation according to the patient's condition, and adjust the ventilation mode to meet the various needs of the patient.
3, clear the system
The scavenging system of the anesthesia machine is also called the carbon dioxide absorption system. It consists of 1-2 carbon dioxide absorption tanks. The tank contains sodium lime or limulus lime. The main function is to remove the carbon dioxide from the exhaled gas of the patient.
4, monitoring and alarm system
The anesthesia machine has a set of monitoring-related devices according to different configurations, such as monitoring airway, physiological aspects, concentration of anesthetic gas, and monitoring that can indirectly reflect the depth of anesthesia and muscle relaxation.
Most monitoring systems for anesthesia machines have only one platform with a basic monitoring device as the system. Monitoring includes: airway pressure, suction tidal volume, minute ventilation, respiratory frequency, and related alarm systems. The other monitoring instruments can be purchased separately and added to the anesthesia system.
In addition, the anesthesia machine workstation also needs to be equipped with an anesthesia information management system. The anesthesia information management system can receive, analyze and store information related to clinical and administrative management of anesthesia, automatically collect information of the monitor and automatically generate an anesthesia record sheet.