Architecture and composition system of pet respiratory anesthesia machine
The machine structure of respiratory anesthesia is basically composed of an oxygen supply system, a respiratory anesthesia machine, a breathing circuit system, an end-tidal carbon dioxide monitoring system, and an exhaust gas recovery system. If it is matched with an automatic breathing system, it can provide intermittent positive pressure ventilation (IPPV). Generally speaking, thoracotomy, pneumonia, myasthenia gravis... and other anesthesia where animals cannot ventilate normally will require intermittent positive pressure ventilation (IPPV) using an automatic breathing system. Most surgical anesthesia does not require the use of intermittent positive pressure ventilation (IPPV). Automatic breathing system's (not even recommended).
At present, the commonly used respiratory anesthesia machines in veterinary clinics mainly include semi-automatic respiratory anesthesia machines with medical specifications and small animal specifications, and fully automatic respiratory anesthesia machines combined with gas anesthesia machines and automatic ventilators. It is only used in surgeries that require an automatic ventilator, and general anesthesia is still a traditional semi-automatic breathing anesthesia machine.
1. Oxygen supply system
Oxygen supply system
There are two main types of oxygen supply systems: Cylinder or Liquid Tank. Connecting the oxygen cylinder directly to the anesthesia machine as the source of oxygen supply is the easiest way, but due to the limited oxygen storage, it is necessary to check and supplement oxygen frequently. Liquid cylinders are mainly used in the central oxygen supply system. They are used in hospitals with high demand. Although the cost of setting up a central system is higher, the unit cost of oxygen is lower than that of steel cylinders, which can save costs in the long run.
Oxygen pressure reducing valve
The pressure reducing valve can keep the gas entering the anesthesia machine at a low and stable pressure (usually 310-345 kPa, 45-50 psi), so that the anesthesia machine is not affected by the high pressure of the oxygen cylinder. Some anesthesia machines do not have a pressure reducing valve, and a pressure reducing valve needs to be connected to the oxygen cylinder to achieve the pressure reduction effect (the pressure valve must be manually adjusted to 45-50 psi).
1. Respiratory anesthesia machine
The important devices of the respiratory anesthesia machine are: oxygen flow control valve, anesthetic gas vaporizer, air outlet and pressure gauge, emergency oxygen button.
Oxygen flow control valve
The oxygen flow control valve is composed of an oxygen flow meter and a rotary control knob. In the anesthesia machine of human and medical specifications, there may be a flow control valve of nitrous oxide (N2O) at the same time. This control valve is basically used less in veterinarians. The unit of the oxygen flow meter is liters of gas per minute, and its flow rate is approximately equal to the gas volume at the outlet of the anesthesia machine, and the set volume varies according to the selected breathing circuit.
Anesthetic gas vaporizer
At present, most of the vaporizers used by veterinarians are the third-generation vaporizers. There are slight differences according to different brands, but most of them recommend that they need to be calibrated and cleaned once every two to three years, and the air flow should be higher than 500 ml/min to ensure Accuracy, the minimum accurate concentration is 0.5%. The newest veterinarians are the fifth and sixth generation vaporizers. Generally, it is recommended to calibrate and clean once every five years. The air flow rate must be higher than 300 ml/min to ensure the accuracy, and the minimum accurate concentration is 0.2%.
The vaporizer plays an extremely important role in respiratory anesthesia, but it is often overlooked by us. When we find that the stability of respiratory anesthesia is problematic (with isoflurane as respiratory anesthesia, usually at an anesthesia concentration of 2% (scale 2%) ) below to maintain anesthesia), if there is no abnormality in the pipeline inspection, it should be considered whether the vaporizer has lost its accuracy due to years of calibration and cleaning.
Air outlet and pressure gauge
The air outlet can be connected with the breathing circuit to form a circuit system (mask, non-circulating circuit, circulating circuit). Excessive pressure causes damage to the alveoli.
emergency oxygen button
The emergency oxygen button can make oxygen enter the circuit system without going through the vaporizer. The outlet flow rate is about 30-70 liters/min, and the pressure is 45-50 psi (the same pressure as the oxygen pressure reducing valve). It is usually used for rapid supply of oxygen. when used. When using it, you need to pay attention to whether the breathing bag is loose. If the breathing bag is too full, the rapid increase in the amount of gas may cause the alveolar pressure to be too high and rupture.
1. The breathing circuit system
The breathing circuit system can be divided into three categories: mask type, non-circulating circuit, and circulatory circuit. Different breathing circuits have their own advantages and disadvantages, and an appropriate circuit system should be selected according to the size of the animal during anesthesia.
face mask
The mask is connected to the breathing pipeline as a pipeline for providing the breathing anesthetic gas for the sick animals, which is the mask type anesthesia. It is usually used to induce anesthesia, and a small number of small animals (such as birds, mice, etc.) that cannot be intubated can also use a mask to maintain anesthesia.
Mask-type anesthesia is open breathing because it cannot be tightly sealed with the animal's respiratory tract (unless a laryngeal mask tube is used), and the anesthesia exhaust gas is easily polluted into the environment and affects the operator. When using a mask for anesthesia, the animal's mouth and nose should be as close as possible to the mask and close to the air outlet, because the space between the connection between the breathing tube and the mask and the animal's mouth and nose is a dead space for breathing. Respiratory dead space is due to the fact that the exhaust gas exhaled by the animal cannot be effectively removed, resulting in re-breathing still inhaling part of the previously discharged exhaust gas. Excessive respiratory dead space will reduce the ventilation rate of anesthetized animals, resulting in unstable and low anesthesia. Blood oxygen and carbon dioxide are too high.
circular loop
The breathing circuit design of the circulating circuit allows the gas exhaled by the animal to return to the breathing circuit through the carbon dioxide absorption tank. It is the most commonly used circuit for respiratory anesthesia at present. Since the gas exhaled by the animal can be reused, it can effectively save the amount of anesthetic gas; the carbon dioxide in the exhaled gas combined with the soda lime in the absorption bottle will generate heat energy and water vapor, providing additional heat for anesthetized animals, which can slow down the hypothermia. The occurrence of body temperature.
acyclic loop
The breathing circuit design of the non-circulating circuit allows the gas exhaled by the animal to be directly discharged without returning to the breathing circuit. Flush away, so every breath the animal takes is inhaling fresh anesthetic gas. The breathing tube has many designs. Compared with the breathing tube design of the circulating circuit, the non-circulating circuit does not use a carbon dioxide absorption tank, so the gas inhaled by the animal is a gas with zero humidity and the same temperature as the room temperature, which is easier. There is a problem of hypothermia, but also because there is no carbon dioxide absorption tank in the pipeline, the breathing gas resistance is small.
