What Is Volatile Anesthetic?

Inhalation anesthesia is a type of volatile liquid or gas that enters the human body through the respiratory tract and exerts anesthesia from shallow to deep anesthesia. It has strong anesthesia functions and high controllability. It is used in general anesthesia and during the maintenance of anesthesia. Occupy a dominant position.

Drug Name: Inhaled anesthetic
Foreign name: AnestheticEther

Dosage: Open drip method is commonly used for inhalation through an anesthesia mask.
Function: anesthesia
Precautions: Physician required

Development of inhaled anesthetics

The earliest (1842) general anesthetics used in surgery were anesthetic ether, nitrous oxide, and chloroform. Anesthesia ether has a clear anesthesia period, is easy to control and has good analgesic and muscle relaxation effects. However, due to the shortcomings of flammable, explosive, unpleasant smell, stimulating the respiratory tract to increase glandular secretion, and prone to accidents, it is now rarely used. Nitrous oxide has the advantages of good analgesic effect and low toxicity, but it has a weak anesthetic effect and is often used in combination with other general anesthetics. Chloroform has been eliminated due to its high toxicity.

In order to overcome the shortcomings of anesthetic ether such as flammable, explosive, and chloroform toxicity, we began to look for other better inhaled anesthetics.

The introduction of halogen courtyards into hydrocarbon and ether molecules can reduce flammability and enhance anesthetic effects, but it increases toxicity. Later, it was discovered that the introduction of fluorine atoms was less toxic than the introduction of other halogen atoms, and thus successively discovered the halothane, enflurane, isoflurane, sevoflurane, desflurane, etc., which had application value. ^[2]

Pharmacokinetics of inhaled anesthetics

Inhalation anesthetic drugs are volatile liquids or gases that enter the human body through the respiratory tract to form anesthetic effects. Drugs include ether, isoflurane, nitrous oxide, etc., which enter the blood through the alveolar artery and follow the blood circulation through the blood-brain barrier. When it reaches the brain and enters the central nervous system, it can block the function of nerve transmission and cause anesthesia.

Inhalation anesthetic

The induction and wake-up time of inhaled anesthetics are determined by lung ventilation, drug concentration in the inhaled gas, and blood / gas distribution coefficient.

The blood / gas distribution coefficient is the ratio of the concentration of the drug in the blood to the concentration of the drug in the inhaled gas. A drug with a large blood / gas distribution coefficient has a large solubility in blood, and the partial pressure of the drug in the blood rises slowly, that is, the blood / gas partial pressure equilibrium state is reached slowly, so the induction time of anesthesia is long.

Increasing the concentration of the drug in the inhaled gas can shorten the induction period.

Lung ventilation and pulmonary blood flow are positively correlated with drug absorption rate.

The minimum alveolar concentration (MAC) refers to the concentration of the drug in the alveolar gas that can make 50% of patients' analgesia disappear under a single atmospheric pressure. The lower the MAC, the stronger the anesthetic effect of the drug. ^[1]

Distribution of inhaled anesthetics

Inhalation anesthetics have a high fat solubility and can easily enter the brain tissue through the blood-brain barrier to play a role. Its speed is proportional to the brain / blood distribution coefficient. The brain / blood distribution coefficient is the ratio of the concentration of the drug in the brain to the concentration of the blood drug. Drugs with large coefficients can easily enter the brain tissue, which enhances the anesthetic effect and shortens the induction period. ^[1]

Elimination of inhaled anesthetics

Inhaled anesthetics are rarely metabolized by the liver or excreted by the kidneys, and are excreted mainly through the respiratory tract in their original form. Therefore, inhaled anesthetics with large alveolar ventilation and low brain / blood and blood / gas distribution coefficients are more likely to be expelled and anesthesia will awaken quickly. ^[1]

Comparison of characteristics of commonly used inhalation anesthetics
drug	Blood / gas distribution coefficient	Brain / blood distribution coefficient	MAC (%)	Induction period	Skeletal muscle relaxation
Enflurane	1.80	1.45	1.68	short	it is good
Isoflurane	1.40	1.60	1.15	short	it is good
Desflurane	0.42	1.30	6.00	short	it is good
Sevoflurane	0.69	1.70	2.05	short	it is good
Nitrous oxide	0.47	1.06	104	short	Very poor

Clinical application of inhaled anesthetics

With the gradual improvement of monitoring technology and the gradual increase in the function of anesthesia mechanisms, low-flow inhalation anesthesia has been valued clinically. Low-flow anesthesia has the disadvantages of hypoxia and increased CO concentration, but the advantages of low cost are also very significant, and the depth of new inhaled anesthetic drugs is easy to control, which is more suitable for low-flow anesthesia.

Desflurane

Although desflurane is more expensive than clinically used isoflurane, desflurane has low fat solubility, rapid anesthesia recovery, and can reduce the residence time in PACU. Desflurane is used for surgery with anesthesia longer than 3 hours. It allows patients to wake up quickly after the operation is completed, and can reduce their costs.

Desflurane can cause hypoxia in children due to reduced blood oxygen saturation, so it is not suitable for anesthesia.

Desflurane has low fat solubility and low solubility, so it can also have a rapid wake-up effect on obese patients, without affecting the wake-up time, and faster than propofol anesthesia. The new desflurane inhalation anesthesia induces smooth, suitable for outpatient surgical anesthesia, can maintain the circulation stability of the patient's body, and the anesthesia cost is low.

Sevoflurane

Sevoflurane, which is more expensive than clinically used isoflurane, is less soluble in blood than isoflurane. Because sevoflurane has similar solubility in muscle tissues as isoflurane, surgery within 90 minutes to 2 hours The intake is almost equal, which can make the recovery time of the patient is similar to that of isoflurane anesthesia.

Because sevoflurane has low fat solubility and low solubility, it can also have a fast wake-up effect on obese patients, without affecting the wake-up time, and faster than propofol anesthesia. The new type of sevoflurane induces smooth anesthesia during inhalation anesthesia, is suitable for outpatient surgical anesthesia, can maintain the circulation stability of the patient's body, and has low anesthesia cost.

Sevoflurane has no irritation response to the airway, fast induction of anesthesia, small circulation interference, rapid recovery after anesthesia, and no need to worry about liver toxicity, so it is more suitable for induction of anesthesia in children.

Halothane

Halothane has no irritation response to the airway, fast induction of anesthesia, small circulation interference, rapid recovery after anesthesia, no need to worry about liver toxicity, so it is more suitable for induction of anesthesia in children.

Halothane is highly fat-soluble, has a more stable concentration in the alveoli than sevoflurane, has better conditions than sevoflurane, and is more commonly used when anaesthesia is performed on children. Emulsification technology has a shorter induction of anesthesia and wake-up time after anesthesia, and enables inhaled anesthetic drugs to be used directly for intravenous injection.

Harm and prevention of inhaled anesthetic fumes

Halide anesthetics can cause damage to the ozone layer, accelerate global warming, and potentially harm the global environment. Less than 5% of inhaled anesthetics are metabolized by patients, and most of them are exhaled in prototype form without any degradation. In addition, abortion, infertility, etc. may occur in exposed people in the anesthetic exhaust gas. As a result, there are growing concerns about the potential harm of anaesthetic exhaust.

A volatile anesthetic is a halide, which is closely related to the chlorofluorocarbons that destroy the ozone layer. It is the main component of the ozone layer. It also causes long-term exposure of ozone-depleting operating room staff to anesthetic gases, especially if they Exhaust gas exposure has a greater impact on occupational health under conditions of gas removal systems. The possible health effects of occupational exposure include fatigue and irritability, headache, liver function, kidney function, abnormal hematopoietic system, and behavior changes. Exposure to anesthetic exhaust gas, especially nitric oxide, is prone to spontaneous abortion, infertility, and birth defects.

With the development of our country's economy and society and people's emphasis on health, monitoring of toxic gases should require various effective measures to reduce the concentration of anesthetic agents in the environment as much as possible to reduce the harm of exhaust gas.