What Is General Anesthesia?

General anesthesia is referred to as general anesthesia. It refers to the inhalation of anesthetic, intravenous or intramuscular injection into the body, which results in temporary suppression of the central nervous system. Clinical manifestations include disappearance of consciousness, disappearance of general pain, forgetting, reflex inhibition and skeletal muscle relaxation. The degree of inhibition on the central nervous system is related to the concentration of drugs in the blood and can be controlled and regulated. This inhibition is completely reversible. When the drug is metabolized or excreted from the body, the patient's mind and various reflexes gradually recover.

Basic Information

English name

general anesthesia

Visiting department

Department of Anesthesiology

General anesthesia drugs

Inhaled anesthetic

Nitrous oxide, halothane, enflurane, isoflurane, sevoflurane, desflurane, etc .;

2. Intravenous anesthetic drugs

Barbiturates (sodium thiopental, phenobarbital, etc.), opioids (morphine, fentanyl, alfentanil, sofentanil, ramifentanil, etc.), propofol, droperidol Lido, benzodiazepines (diazepam, midazolam, etc.), ketamine, etomidate, etc .;

3. Muscle relaxant

Non-depolarizing muscle relaxants (tuberculosis poison, pancuronium, atracurium, vecuronium, etc.), depolarizing muscle relaxants (such as succinylcholine).

General anesthesia method

General anesthesia methods commonly used clinically include inhalation anesthesia, intravenous anesthesia, and combined anesthesia. The implementation of general anesthesia can be divided into several steps such as pre-anaesthesia treatment, induction of anesthesia, maintenance of anesthesia and recovery of anesthesia.

Inhalation anesthesia

(1) Inhalation anesthesia refers to a general anesthesia method in which volatile anesthetics or anesthetic gases are absorbed into the blood by the anesthesia machine through the respiratory system to suppress the central nervous system. Inhalation anesthesia is the earliest anesthesia method used in the history of anesthesia. Ether is a widely known inhalation anesthetic. However, due to its unstable and flammable and explosive characteristics, modern operating theatres often require equipment such as electrosurgical tools, which may cause explosion , Now clinically deprecated. Inhalation anesthesia has evolved as the main method for general anesthesia. Inhalation anesthesia has less metabolism and decomposition in the body, and most of it is excreted from the lungs in its original form. Therefore, inhalation anesthesia has high controllability, safety and effectiveness.

Inhalation anesthesia can be divided into four methods: open method, semi-open method, semi-closed method and closed method according to the contact mode of breathing gas and air, the degree of repeated inhalation and the presence or absence of carbon dioxide absorption devices. According to the size of fresh air flow, it is divided into low flow anesthesia, minimum flow anesthesia and closed circuit anesthesia.

(2) Implementation of inhalation general anesthesia Pre-anaesthesia treatment mainly includes patient physical and psychological preparation, pre-anaesthesia evaluation, selection of anesthesia method, preparation and inspection of corresponding equipment, and reasonable pre-anaesthesia medication. In addition, according to the characteristics of induction of inhalation anesthesia, patients should be prepared for interpretation and preparation on the respiratory tract. Induction is divided into increasing concentration slow induction method and high concentration fast induction method. Simple inhalation anesthesia induction is suitable for children who are not suitable for intravenous anesthesia and difficult to keep the veins open, difficult airways, and laryngeal mask intubation. It is not suitable for alcoholics and strong physiques. The slow induction method is to fix the mask to the patient's snout with the left hand, hold the airbag lightly with the right hand, open the volatilizer after inhaling oxygen and nitrogen, and start to give a low concentration of inhaled anesthetic. The best choice of anesthetic is halothane. Other inhalable anesthetics can also be used. Oropharyngeal or nasopharyngeal ventilation catheters can be inserted if necessary to maintain the airway normally, while the patient's response to the stimulus is detected, and if the response disappears, the surgeon can be notified to prepare for surgery. After the anesthesia begins, the veins should dilate and the venous channels should be established as early as possible. This slowly increasing concentration method can make the induction of anesthesia more stable, but the prolongation of the induction time increases the possibility of accidents during the excitement period, and patients are prone to mismatches.

The high-concentration fast induction method is to use a mask to inhale pure oxygen at 6L / min for 3 minutes, then inhale the high-concentration anesthesia, let the patient take a deep breath and lose his consciousness several times before switching to a medium-concentration anesthetic until the surgical anesthesia period. Tracheal intubation may be performed to assist or control breathing.

In clinical practice, many patients will ask whether the induction of inhalation is like the gauze covering the mouth and nose in film and television works, which leads to the disappearance of consciousness. In fact, the clinically used inhalation anesthetic does not take effect so quickly, and it needs a special sealed device to store it. Environment is volatile. After the induction of maintenance anesthesia is completed, the maintenance phase of anesthesia is entered. During this period, the surgical requirements should be met, and the patient should be painless, unconscious, with muscle relaxation and normal organ function. The stress response is suppressed, water, electrolytes and acid-base balance are maintained, and blood loss is promptly replenished. Low flow inhalation anesthesia is currently the main method of maintaining anesthesia. The depth of anesthesia should be adjusted during the operation according to the characteristics of the operation, the pre-operative medication situation and the patient's response to anesthesia and surgical stimulation. Without changing the minute ventilation of the patient, changing the depth of anesthesia is mainly achieved by adjusting the opening concentration of the volatilizer and increasing the fresh air flow. Inhalation anesthetics can produce a weak muscle relaxant. In order to obtain a perfect muscle relaxant for major surgery, it is often necessary to administer a muscle relaxant intravenously to avoid circulation inhibition caused by simply increasing the inhalation concentration to enhance the muscle relaxant effect. Volatile anesthetics can significantly enhance the nerve block effect of non-depolarizing muscle relaxants, and when used in combination, can reduce the amount of muscle relaxants. Wake up and recovery of patients with inhaled anesthesia. The wake up process is opposite to the induction process, which can be regarded as the washing out process of inhaled anesthesia. Due to the low flow of gas in the circuit, the anesthetic cannot be washed out quickly, so the volatilizer should be closed earlier than the high flow anesthesia at the end of the operation. After the entire operation, high-flow pure oxygen is used to quickly flush the patient and the residual anesthetic in the circuit. When the concentration of inhaled anesthetic in the alveoli dropped to 0.4MAC (the lowest effective alveolar gas concentration), about 95% of the patients were able to open their eyes as instructed by the doctor. The cleaner the inhaled anesthetic is, the better it is for the smoothness of the recovery process and the recovery of the patient. Excessive residues may not only cause the patient to be irritable, vomiting, or even inhibit the awake condition and breathing. When washing out the inhaled anesthetic, certain painkillers can be given intravenously to increase the patient's tolerance to the tracheal tube to facilitate the early discharge of the inhaled medicine and reduce the stress response when extubation.

2. Intravenous anesthesia

(1) Intravenous general anesthesia refers to a method of injecting one or several drugs through a vein and acting on the central nervous system through blood circulation to produce general anesthesia. According to the different administration methods, intravenous anesthesia can be divided into single administration, divided administration and continuous administration. Due to some of its limitations, the use of intravenous general anesthesia was once restricted. However, since the 1980s, with the continuous improvement of clinical pharmacology research methods, the development of new powerful and short-acting intravenous anesthetics and the advent of computerized automatic intravenous drug delivery systems have greatly improved intravenous anesthesia. And development.

According to different administration methods, intravenous anesthesia can be divided into single injection, divided injection, continuous injection and target-controlled infusion (TCI).

(2) Implementation of intravenous general anesthesia The pre-anaesthesia treatment is the same as other general anesthesia, mainly including the patient's physical and psychological preparation, pre-anaesthesia evaluation, selection of anesthesia methods, preparation and inspection of corresponding equipment, and reasonable pre-anaesthesia medication . Induction of anesthesia Induction of intravenous anesthesia is more comfortable and suitable for most routine anesthesia situations (including inhalation general anesthesia), which is especially suitable for patients who need rapid induction. It can be achieved by a single intravenous injection of anesthesia drugs, or TCI technology can be used to complete the induction of intravenous anesthesia. Among the various stimuli produced by surgical anesthesia, tracheal intubation is higher than that of ordinary surgery, so the blood drug concentration required for induction of anesthesia may be greater than the blood drug concentration required for intraoperative anesthesia maintenance. The first dose of intravenous injection can be calculated according to the CTVd peak effect of the loading dose formula, and the actual situation of the patient should also be taken into account. The anesthesiologist should also be familiar with the peak-effect time of the drug used, which is important for induction of anesthesia. When using TCI technology to implement intravenous induction, care should be taken to select an appropriate target concentration according to the individual situation of the patient. The time required for the patient to lose consciousness during induction decreases with increasing target concentration.

When using intravenous anesthesia for induction of anesthesia, some characteristics of intravenous anesthesia itself should be noted. The principle of individualization should be emphasized first. The choice and dosage of the drug should be adjusted according to the specific conditions of the patient, such as weight, age, circulation status, preoperative medication, etc. Secondly, for elderly patients or patients with slower circulation time (such as shock, hypovolemia, and cardiovascular disease), the dosage should be reduced, and the injection should be slow, and the changes of the cardiovascular system should be closely monitored. Finally, the injection of some anaesthetics during induction may cause local pain, and the administration of opioids or intravenous general anesthesia injected before surgery or before induction can reduce the incidence of pain. Anesthesia maintenance The continuous anesthesia intravenous infusion or pumping to maintain the patient's anesthesia needs to include two doses, namely the dose of the drug eliminated from the central chamber, and the dose of the drug transferred to the peripheral chamber. Adjusting the infusion rate of intravenous anesthesia according to the intensity of the surgical stimulus and the specific conditions of each patient can also provide a relatively reasonable anesthesia to maintain blood concentration. By using the TCI technology, through the setting of the target concentration, the above purpose can be achieved more accurately and conveniently. However, it should be noted that because the injury stimulus is not static during the operation, the appropriate target concentration should be selected according to the specific situation (the size of the operation, the degree of stimulation, and the response of the patient, etc.). In addition, it should be emphasized that it is much better to actively adjust the target concentration in advance to adapt to the upcoming strong stimulus than to passively adjust the effect after noxious stimuli appear.

Combination medication should be emphasized when maintaining anesthesia. Under the premise of ensuring stable vital signs of patients, perfect anesthesia should at least eliminate consciousness, complete analgesia, muscle relaxation and inhibition of autonomic reflex. In order to achieve these four objectives, it is obvious that certain types of anesthetics will not work. This requires the combined use of anesthetics. Complete intravenous general anesthesia mainly involves three major classes of drugs: first, intravenous general anesthesia drugs, such as propofol and midazolam, which can make patients fall asleep, lose consciousness, and have no memory of the surgical process; Pain medicines, such as fentanyl, dulandine, and other opioids, can reduce pain and suppress stress; third, skeletal muscle relaxants, such as depolarizing muscle relaxant succinylcholine and non-depolarizing muscle relaxant vitamins Sulfabromide and pancuronium bromide can relax muscles and provide a good surgical field, but need a ventilator to control breathing. After intravenous anesthesia recovery , the patient's wake-up time is closely related to the concentration of anesthetic in the central chamber (plasma). For a single injection of a drug, the decrease in its blood concentration depends mainly on the distribution half-life and elimination half-life of the drug. A single injection was administered at the equivalent dose, and the order of recovery was: propofol, etomidate, thiopental sodium, midazolam, and ketamine. For long-term continuous infusion of narcotic drugs, the speed of blood drug concentration decline depends not only on the distribution half-life and clearance half-life, but also on whether the peripheral chamber is dull. In addition to good recovery, there should be no side effects and sufficient analgesic effects. Propofol has the fewest side effects during recovery. After ketamine and etomidate anesthesia, agitation often occurs during the wake period. Midazolam can better reduce these side effects, but delays recovery. Haloperidine may increase the incidence of nightmares. Patients with restlessness during the recovery period should first rule out hypoxia, carbon dioxide accumulation, wound pain, and residual muscle relaxants; if inhaled anesthetics are used, they should also be considered for thorough washing out.

3. Compound Anesthesia

At present, several different anesthetic drugs or techniques are used simultaneously or successively in clinical anesthesia to obtain general anesthesia. This kind of anesthesia method that simultaneously or successively uses two or more kinds of general anesthetic drugs or anesthesia techniques to achieve analgesia, forgetting, muscle loosening, autonomic reflex suppression, and maintaining vital signs stability is called balanced anesthesia. Balanced anesthesia emphasizes combined use. Combined use can not only maximize the pharmacological effects of each type of drug, but also reduce the dosage and side effects of each drug. This method has played a very important role in improving the quality of anesthesia, ensuring the safety of patients, and reducing medical costs. It is in line with China's national anesthesia concept.

Static anesthesia combined anesthesia is a typical representative of balanced anesthesia. Anesthesia methods that use intravenous general anesthesia and inhalation general anesthesia for patients at the same time or in succession are called intravenous-inhalation combined anesthesia, referred to as static combined anesthesia. There are various methods, such as induction of intravenous anesthesia and maintenance of inhalation anesthesia; induction of inhalation anesthesia and maintenance of intravenous anesthesia; Intravenous anesthesia has fast onset and smooth induction, while inhalation anesthesia is easy to manage and the depth of anesthesia is easy to control. Therefore, inhalation anesthesia or static inhalation combined anesthesia is used to maintain the main position in clinical anesthesia. Induction of intravenous anesthesia and maintenance of inhaled anesthesia fully demonstrate the advantages of intravenous anesthesia and inhalation anesthesia, which is the sublimation of anesthesia technology to the art of anesthesia.

In addition to the above three types of general anesthesia, there are general anesthesia techniques such as basic anesthesia and guardian anesthesia. They have different degrees of anesthesia, but there is no significant difference in essence. There are more and more clinically performed painless examination / treatment techniques, such as painless gastroscopy, painless human flow, etc. This is actually a general anesthesia technique, given intravenous anesthetic (commonly used with propofol) and analgesics Patients fall asleep and painless, but most of them are short operations, and most do not require intubation to control breathing, but there are risks such as respiratory depression and aspiration pneumonia.

Serious complications during general anesthesia

During the clinical operation, the anesthesiologist's thinking mode is between that of the surgeon and the physician. The ultimate goal is to minimize or reduce the patient's fear of surgery and pain and safety during the perioperative period. The anesthesiologist is the protector of the safety of the patient during the operation.

Anesthesiologists need to use a variety of drugs to maintain a certain state of anesthesia, but also to ensure the safety of patients throughout the operation and provide safe and painless surgical conditions. But patients, surgeries, and other conditions vary widely, and there may still be some unexpected situations, some of which are likely to endanger life.

1. Reflux, aspiration, and aspiration pneumonia

Vomiting or reflux under anesthesia may cause serious consequences, aspiration of gastric contents, and even acute respiratory obstruction and other serious complications in the lungs, is one of the important causes of death in patients with general anesthesia. The extent to which aspiration occurs in patients with acute lung injury is directly related to the physico-chemical properties of the aspiration of the stomach contents (such as pH, fat fragments and their size) and volume, as well as bacterial contamination.

The clinical manifestations of aspiration include acute respiratory obstruction, Mendelson syndrome, aspiration atelectasis and aspiration pneumonia. Preventing aspiration is mainly to take measures against the causes of aspiration and lung damage:

(1) Reduce the content of the stomach and increase the pH of gastric juice;

(2) Reduce the intragastric pressure below the lower esophageal sphincter resistance;

(3) Protecting the airways, especially when the protective reflections of the airways disappear or weaken. The key to the management of aspiration is to find and take effective measures in time to prevent airway obstruction and suffocation and reduce acute lung injury. Specific measures include reconstruction of the airways, bronchial irrigation, correction of hypoxemia, hormones, bronchoscopy, antibiotics, and other supportive therapies.

In order to reduce the possibility of reflux and aspiration, surgical patients often need to fast water before surgery, usually fasting for 6 to 8 hours, drinking for 4 hours, children can be controlled within 2 hours.

2. restlessness

During the recovery period of general anesthesia, most patients showed drowsiness, quietness or mild disorientation, and their brain function gradually returned to normal. However, some patients still experienced large emotional fluctuations, manifested as uncontrollable crying and irritability (restlessness) disturbed. Apart from the preoperative and intraoperative medication, the appearance of restlessness may be an important factor causing restlessness.

3. Delayed wake-up after general anesthesia

After general anesthesia is stopped, patients generally get awake within 60 to 90 minutes, and they can recover command movements, orientation ability, and preoperative memory. If the consciousness is still not clear beyond this time limit, the wake up after general anesthesia can be considered delayed. Common causes of delayed wake-up after general anesthesia include prolonged drug action time, advanced age, systemic metabolic disease in patients, and damage to the central nervous system.

4. Postoperative nausea and vomiting

Postoperative nausea and vomiting (PONV) are very common problems after general anesthesia, causing discomfort to patients and affecting rest. The incidence rate is 20% to 30%. Previously related medical history, the relative incidence of women and inhaled anesthesia is high. The risk factors are:

(1) Patients with predisposing factors such as early pregnancy, diabetes and anxiety;

(2) Increased stomach capacity

(3) Anesthesia drugs and methods General anesthesia is more common than regional anesthesia; the drugs used are nitrous oxide, ketamine and neostigmine;

(4) Surgery sites and methods of ovarian and cervical dilatation, laparoscopic surgery, strabismus correction, and middle ear surgery are more common;

(5) opioids, hypotension, and plenty of water should be used for pain after surgery. Gastrointestinal decompression catheter stimulation also often causes vomiting. The use of drugs is only considered for patients who have a tendency to develop PONV, and preventive medication is generally not required. The main drugs are butyrylbenzenes, phenothiazines, gastrokinetic drugs, anticholinergics, antihistamines, serotonin antagonists, and so on.

4. Bronchial spasm

Acute bronchospasm can occur during anesthesia and after surgery, manifested by spasmodic contraction of bronchial smooth muscles, narrowing of the airways, sudden increase in airway resistance, exhaled dyspnea, causing severe hypoxia and CO ₂ accumulation. If it is not immediately relieved, because the patient cannot perform effective ventilation, not only hemodynamic changes, but even arrhythmia and cardiac arrest occur.

The causes of bronchospasm include airway hyperresponsiveness, nerve reflexes related to anesthesia surgery, local stimulation such as tracheal intubation, application of excitatory vagus nerves, increase of airway secretions to promote histamine release, muscle relaxants Or other drugs. Among them, local stimulation such as tracheal intubation is the most common cause of airway spasm during induction of anesthesia. Patients with a history of chronic respiratory inflammation, smoking, or bronchial asthma have a higher incidence. Avoid using drugs that can induce bronchospasm during anesthesia. Local anesthesia is selected for complete anesthesia of the throat and trachea surface to block airway reflexes and prevent bronchospasm caused by irritation of the airway. Management of bronchospasm includes: clarifying the causes and eliminating irritants; deep anesthesia caused by too shallow anesthesia; inhaling oxygen in a mask, assisting or controlling breathing if necessary; intravenous infusion of corticosteroids, aminophylline It may be better to apply two drugs at the same time.

5. Hypoxemia and hypoventilation

Respiratory complications are still one of the main reasons for delaying postoperative recovery after general anesthesia and threatening the safety of patients. The most common cause of airway obstruction after general anesthesia is obstruction of the pharynx due to incomplete recovery of the mind and fall of the tongue; laryngeal obstruction can be caused by laryngospasm or direct airway damage. The most effective technique for the posterior fall of the tongue is that the patient's head is tilted back while the mandible and the lower incisor are biting on the upper incisor. Make appropriate adjustments according to the patient's different positions to achieve a complete airway. If the above procedure fails to release the obstruction, it should be placed in the nasopharyngeal or oropharyngeal airway. However, when it is placed in the pharyngeal airway, it may induce nausea, vomiting, and even laryngeal spasm, so it should be closely observed. Very few patients require reintubation.

1. Hypoxemia is not only a common complication after general anesthesia, but also can lead to serious consequences, even coma and death. Factors that are prone to cause hypoxemia after anesthesia are:

(1) The patient's age is> 65 years;

(2) Patients who are overweight, such as> 100kg;

(3) Patients undergoing general anesthesia are more likely to occur than regional anesthesia;

(4) Anesthesia time> 4 hours;

(5) The effect of abdominal surgery on breathing is more significant in the chest, and the effect of limb surgery is relatively slight;

(6) Drugs for anesthesia: If benzodiazepines and opioids are used together, the effect of anaesthesia induced by thiopental sodium on respiration is more significant than that of propofol.

2. Hypoventilation refers to an increase in PaCO ₂ caused by decreased alveolar ventilation. The reasons for hypoventilation after surgery are:

(1) weakening of central respiratory drive;

(2) Insufficient recovery of respiratory muscle function;

(3) Increased CO ₂ production in the body;

(4) Affected by acute or chronic diseases of the respiratory system.

6. Acute atelectasis

Acute atelectasis refers to the sudden collapse of the lung segment, lobe, or side of the patient, which causes loss of ventilation. Acute atelectasis is one of the serious complications after surgery, especially after general anesthesia. Large-scale acute atelectasis can cause death due to severe hypoxia due to insufficient compensation of respiratory function.

Risk factors for acute atelectasis: perioperative patients with acute respiratory infections; acute or chronic obstruction of the respiratory tract, the most common cause after surgery is airway blocked by viscous secretions; chronic bronchitis; smoking; obesity; Elderly patients have small lung volumes, such as non-obstructive pulmonary disease, thoracic deformities, or respiratory muscle disorders or limitations due to muscle, neuromuscular, and neurological disorders;

7. Hypoventilation syndrome

Patients with central or obstructive sleep-apnea syndrome.

Risk factors for atelectasis after surgery include:

(1) There are many secretions in the respiratory tract, and drainage or drainage is not smooth;

(2) Patients undergoing major surgery on the chest or upper abdomen;

(3) Pain in surgical incision;

(4) Improper application of analgesics;

(5) Use drugs that inhibit the central nervous system.

8. Hypertension

During the recovery period of general anesthesia, as the role of anesthetics subsides, pain and discomfort, as well as sputum suction and stimulation of the removal of the endotracheal tube are very likely to cause hypertension. Especially those with a previous history of hypertension, which usually begin within 30 minutes after the operation. If antihypertensive drugs are abruptly stopped before surgery, the occurrence of hypertension is even more severe. The causes of hypertension include: pain, hypoxemia and hypercapnia, intraoperative fluid overload and improper application of booster drugs, stimulation of sputum suction, and other such as postoperative chills, urinary retention of the bladder Highly inflated and so on.

9. Cerebrovascular accident

Patients previously had cerebrovascular disease, and during anesthesia (perioperative period), accidental stroke occurred, about 80% of which was due to insufficient cerebral blood supply (or too little blood flow), which is called deficiency. Bloody strokes, the other 20% are hemorrhagic strokes (such as cerebral hemorrhage and subarachnoid hemorrhage). The scope of stroke can be focal, multifocal, or diffuse, reflecting the impaired brain function caused by pathological changes in one or more blood vessels. Old age (over 65 years), hypertension, diabetes, abducent vascular disease, and heart disease (coronary heart disease and atrial fibrillation, etc.) are all high-risk factors for cerebrovascular accidents during the perioperative period.

During general anesthesia, because the patient is sleeping, the monitoring of the patient's consciousness and muscle strength is affected, and the occurrence of stroke may not be detected in time.

10. Malignant fever

Malignant hyperthermia (MH) is an abnormally high metabolic state of skeletal muscle induced by inhalation of a strong volatile anesthetic and succinylcholine, exhaled CO ₂ and sudden increase in body temperature, tachycardia, and myoglobinuria. MH is more common in Caucasians, but has been reported in different races, indicating that MH is not racially specific. The incidence of MH in children (1/15000) is significantly higher than that in adults (1/50000). Children are more likely to be under 10 years of age, and more men than women. MH is more common in congenital diseases such as idiopathic scoliosis, strabismus, ptosis, umbilical hernia, and inguinal hernia. It has also been reported in other surgical diseases. MH is currently considered to be a subclinical myopathy with familial inheritance. The clinical manifestations of MH can be divided into burst type (22%), masseter spasm type (22%) and abortion type (57%). Burst type is the most severe, manifested by sudden occurrence of hypercapnia and hyperkalemia, tachyarrhythmia, severe hypoxia and acidosis, and rapid rise in body temperature, which can reach 45 ° C to 46 ° C. Most patients die from intractable arrhythmias and circulatory failure within hours.

References

1.Zhuang Xinliang, Zeng Yinming, Chen Bozhen Modern Anesthesiology Third Edition People's Medical Publishing House 2010936-1041.

2. Guo Xiangyang, Luo Ailun, Chinese Journal of Anesthesiology of Malignant Fever 2001, 21 (10): 604-606.

3. Wu Xinmin, Luo Ailun, Tian Yuke, and other expert opinions on prevention and treatment of postoperative nausea and vomiting (2012) Journal of Clinical Anesthesiology 2012, 28 (4): 413-416.