How the respiratory anesthesia machine works

The respiratory anesthesia machine is a semi-open anesthesia device. It includes anesthesia evaporation tanks, flow meters, folding bellows ventilators, breathing circuits, corrugated pipelines and other major components.

1) Evaporator
Inhalational general anesthetic drugs are volatile liquids at normal temperature and pressure. This type of liquid medicine can only be used clinically. This requires an evaporator to evaporate the liquid drug into a usable gas anesthetic. Gas anesthetics enter the human body with breathing to achieve the purpose and effect of general anesthesia.
According to the principle of motion, the number of collisions and the speed of movement of molecules will increase. When the internal energy of some molecules increases to overcome the intermolecular interactions, the molecules that make up the adsorbed material separate into a vaporization process. In a sealed container, the liquid vaporization of substances does not proceed unconditionally. It is subject to the dual influence and negation of pressure and temperature within the container.
When the temperature is constant and the number continues to increase, a pressure will be generated in the container that increases with the increase in the number of molecules. When the molecules in the liquid are affected by the pressure in the container, the adsorbed molecules in the liquid cannot turn into gas molecules, thus reaching a relative equilibrium state. That is, the gas concentration is relatively balanced. The following temperature acts to absorb the evaporation temperature.
When the pressure is constant, as the substance continues to vaporize, the temperature of the liquid medicine will gradually decrease and the evaporation rate will slow down. When the gas concentration drops to 1, the gas concentration molecules are relatively balanced. Its evaporation process will continue until a new equilibrium is reached.
The other category is called vaporizers for certain medications. The liquid surface evaporator passes a certain amount of gas through the space above the container containing volatile anesthetic drugs to the evaporation chamber. It is usually a mixture of oxygen and laughing gas, also called a carrier. When this part of the gas flows through the evaporation chamber, it will become a gas containing absorbed anesthetic vapor, anesthetic gas with a safe concentration required clinically.
notes:
1. Bubble evaporator
The evaporator changes the concentration of anesthetic gas through a concentration adjustment knob. Go to copper plate 4. There are many small holes on the copper plate. When these gas holes emerge, a large number of bubbles will be generated in the medical solution, thereby bringing out the anesthetic gas from the water tank. As the anesthetic solution continues to evaporate, the temperature will decrease and the evaporation rate will slow down. That is, the concentration of anesthetic gas in a bubbling evaporator is difficult to control.

The evaporator changes the concentration of anesthetic gas through a concentration adjustment knob. Go to copper plate 4. There are many small holes on the copper plate. When these gas holes emerge, a large number of bubbles will be generated in the medical solution, thereby bringing out the anesthetic gas from the water tank. As the anesthetic solution continues to evaporate, the temperature will decrease and the evaporation rate will slow down. That is, the concentration of anesthetic gas in a bubbling evaporator is difficult to control.

2. Suction evaporator
The suction evaporator is an ether evaporator. Its core made of cotton is soaked in the ether liquid. Through the siphon principle of the cotton core, a certain concentration of steam is maintained above the anesthetic liquid level. The switch adjusts the switch. It is the same as the bubble evaporator. As the liquid medicine continues to evaporate, the surrounding temperature decreases and the anesthetic gas concentration is difficult to control.

3. Direct heat source evaporator
This kind of evaporator uses the high specific heat and good heat transfer characteristics of copper to absorb the heat in the environment to heat the liquid for evaporation. Temperature-air flow compensation type evaporators are currently used, as shown in Figure 2-3. The anesthesia smoke of -5 years is exported through the airway 4, mixed with the main air flow to form an anesthetic gas with a stable concentration and sent to the patient.
When the ambient temperature decreases due to the continuous evaporation of the medical solution, the bronze plate made of two different thermal expansion coefficients will automatically adjust to the flow rate of the medical liquid gas, so that the concentration of the input anesthetic gas can be stabilized.
CO2 absorber
C02 adopts two absorption forms: back-and-forth and circulation. Its structure is mostly round, made of transparent plastic, and ranges in size from (1200 to 2400) ml. Absorber type built-in type 4 to 8 mesh lime (300 to 2200) g, gas gap in (200 to 2000) ml. It is divided into upper and lower parts for use in series. When the soda lime in the upper layer is bleached (usually pink), the upper and lower layers are exchanged. When using soda lime, be sure to call it powder. In addition, when canning, be sure to fill the absorption tank to minimize the carbon dioxide gas content.
oxygen protection valve
During inhalation general anesthesia, oxygen is a nutrient for the patient's tissue cells and brain. Oxygen is vital to patients. If there is a lack of oxygen, the patient will suffer from drug poisoning or even suffocate to death. Once there is no oxygen, other gases will occur because the piston is not exposed to the laughing gas, which reaches the circulation loop through the thimble.
Pressure reducing valve
The pressure reducing valves currently used are all series pressure reducing valves. The pressure of 15MPa in the high-pressure valve cylinder is adjusted by the pressure reducing valve to a constant pressure of about 0.3MPa for use by the anesthesia machine.
The gas from the high-pressure bottle 2 enters the high-pressure chamber, and the elastic force of the spring is transferred to the valve 10 through the membrane 6 through the adjusting screw 4, creating a small gap to reduce the pressure, and then is sent to the low-pressure chamber 8 words.

Air source breathing circuit system evaporator anesthesia respirator

(1) Air source
It mainly refers to the gas storage equipment that supplies oxygen and nitrous oxide (N 2 O), including compressed oxygen in cylinders and loaded nitrous oxide, or a central supply 343~392kPa (3.5~4kgf)/cm 2 ) rapid oxygenation valve.

(2) Evaporator
Evaporator device. Evaporators are drug-specific, such as enflurane evaporator, isoflurane evaporator, etc. The evaporator is usually placed outside the breathing loop and has an independent bypass air supply system. When the evaporator is opened, the bypass rapid vapor passes through the evaporation chamber, and the inhaled anesthetic vapor mixes with the main vapor and enters the loop, making the inhalation concentration more stable. However, when the evaporator is used, the anesthetic drugs in the road may be inhaled without passing through the evaporator, thereby reducing the inhalation concentration.

(3) Respiratory loop system
The fresh gas and inhaled anesthetic tube are delivered to the patient's respiratory tract through the breathing loop system, so that the patient's exhaled gas is inhaled into the respiratory tract.
notes:
1. There is no re-inhalation of exhaled CO 2 when exposed to the atmosphere.
2. In semi-closed or semi-open type, the gas exhaled and inhaled by the patient is partially controlled by the respiratory control of the anesthesia device. There is an expiration valve in the loop, but no CO 2 absorber. During exhalation, the exhalation valve stabilizes the escape of exhaled gas, which depends on the resistance of the valve and the size of the fresh gas flow rate. Fresh gas flow, outgoing gas (including CO 2 and anesthetic gas)) enters the breathing chamber, and CO 2 can be repeated when replenishing. 1% of CO 2 can be discharged into the atmosphere, and the CO 2 that is repeatedly inhaled is lower than the 1% bottle, which is called half Open.
3. CO 2 absorber. After the respiratory gas absorbs CO 2 through the CO 2 absorber, part or all of it is used for the patient's respiratory management, to install assisted or controlled breathing; it not only significantly reduces anesthetic drugs, but also reduces environmental pollution; it can maintain the temperature of the inhaled gas and respiratory enhancement.

(4) Anesthesia respirator
A respirator may be used to control the patient's breathing during anesthesia. Respirators can be divided into fixed volume type and fixed pressure type. They can set or adjust tidal volume (V T ) or minute ventilation (MV), or airway pressure, respiratory frequency, inhalation:exhalation time ratio (I:E ) and other respiratory parameters. Some equipment is set with positive end-expiratory pressure (PEEP), and can set alarm limits for inspired oxygen concentration, minute ventilation and airway pressure to ensure the safety of anesthesia.
The anesthesia machine is structurally composed of the following parts: pumping, external circuit, ventilator monitoring, and system.
The anesthesia machine is composed of four main subsystems in terms of working principle: gas collection 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 parameters and parameters related to cardiopulmonary function or the concentration of gases and anesthetics in the respiratory mixture. Usually manufacturers only provide clear monitoring and alarm combinations for matching products.
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