Concentration effect: refers to the positive correlation between the inhalation concentration and the concentration of the alveolar anesthetic. The higher the inhalation concentration, the faster it enters the alveoli, the faster the alveolar anesthetic concentration PA rises, and the faster the anesthetic partial pressure Pa in the blood rises. To shorten the induction period of anesthesia, a higher concentration should be inhaled at the beginning of anesthesia.

Second gas effect: When high-concentration gas and low-concentration gas are inhaled at the same time, the alveolar concentration and blood concentration of the low-concentration gas (second gas) increase faster than when the same low-concentration gas is used alone. --Concentration effect, incremental effect.

Reflects the effectiveness of inhaled anesthetics---the greater the MAC value, the smaller the anesthetic effectiveness

Determine the depth of inhalation anesthesia

1. Half-awake alveolar air concentration (MACawake50): The alveolar air inhalation anesthetic concentration when 50% of patients can open their eyes in response to a simple command is approximately (1/4~1/3 MAC) 2. 95% effective dose (MAC95): The alveolar air inhalation anesthetic concentration when 95% of people are exposed to noxious stimulation and do not move, is about 1.3 MAC, which is equivalent to ED95 3. Half of the endotracheal intubation alveolar air concentration (MAC EI50): 1.5 MAC 4. MACBAR: alveolar air inhalation anesthetic concentration that blocks autonomic nervous response: 1.7 MAC

Factors that reduce the MAC of inhaled anesthetics (more sensitive to inhaled anesthetics): age↑, hypothermia, concomitant medications, pregnancy, central nervous system hypotonicity, acute heavy drinking

Factors that increase the MAC of inhaled anesthetics (not sensitive to inhaled anesthetics): age, elevated body temperature, drugs that excite the central nervous system, chronic alcoholism, and central nervous system hypertonicity

Respiratory depression - dose dependent

Inhibits bronchial smooth muscle contraction, effective for asthma patients

Airway irritation - positive correlation with inhaled concentration

On ischemic pulmonary vasoconstriction (HPV): animal experiments-inhaled anesthetics inhibit ischemic pulmonary vasoconstriction in a dose-dependent manner

Dose-related effects on blood pressure, heart rate and peripheral vascular resistance--inhibition of myocardial contractility

Arrhythmogenic effect---halothane causes ventricular premature

Coronary arteries--Isoflurane has a strong dilation effect on coronary arteries

Cerebral blood flow↑

Brain metabolic rate↓

intracranial pressure↑

Electroencephalogram - suppression, but desflurane or isoflurane has no such effect, so it is suitable for neurosurgery anesthesia

Liver blood flow↓

liver function

Renal blood flow, glomerular filtration rate and urine output↓

nephrotoxicity

PKC-activated, ATP-sensitive potassium channel

ischemia reperfusion injury

Inhibit inflammatory response

Central Nervous System

circulatory system

respiratory system

liver

Kidney---little impact

Advantages: rapid induction, non-irritating, quick recovery, easy to control the depth of anesthesia

Indications: Can be used by all patients who require general anesthesia

Disadvantages: unstable in the presence of soda lime

Contraindications: ①Those who have liver damage after using inhaled general anesthesia within 1 month; ② If you or your family members are allergic to halogenated anesthetics or have malignant hyperthermia; ③Use with caution in those with poor liver and kidney function.

Nausea and vomiting (3.67%) Arrhythmia (2.79%) Hypotension (2.71%)

Central Nervous System

circulatory system

respiratory system

Little effect on liver function

No significant impact on kidneys

advantage

shortcoming

Except for a slightly pungent odor, the physical and chemical properties are close to ideal properties.

There is little biological transformation in the body, and almost all of it is exhaled from the lungs in its original form.

anesthetic potency

Central Nervous System

circulatory system

respiratory system

No obvious damage to liver and kidneys

Advantages and indications

Disadvantages and contraindications

advantage: ① The least toxic inhalation anesthetic, nitrous oxide is not toxic as long as there is no lack of oxygen; ②Anesthesia induction and recovery are rapid; ③Strong analgesic effect; ④No irritation to airway mucosa; ⑤Non-flammable.

Indications: ① Combined with other inhaled anesthetics and muscle relaxants, it can be used for anesthesia in various surgeries; ② It has little impact on circulatory function and can be used for severe shock or critically ill patients; ③Labor analgesia.

Convulsive spikes are the brain wave characteristics of deep anesthesia and are more likely to be induced when PaCO2 is low.

Moderate analgesic effect, suitable for patients with myasthenia gravis

People with epilepsy and increased intracranial pressure should generally not use it.

Adverse reactions: 1. Inhibit breathing and circulation 2. Central excitement 3. Liver damage: Reports of liver necrosis caused by repeated use. 4. Renal damage: Mild suppression, recovery occurs more than 2 hours after stopping the drug. Use with caution in patients with severe renal impairment.

Liver damage-halothane-related hepatitis