The commonly used methods of general anesthesia in clinical practice are inhalation anesthesia, intravenous anesthesia and combined anesthesia. The implementation of general anesthesia can be divided into several steps, such as pre-anesthetic treatment, induction of anesthesia, maintenance of anesthesia and recovery from anesthesia.
1. Inhalation anesthesia
(1) Inhalation anesthesia is a method of general anesthesia in which volatile anesthetics or anesthetic gases are absorbed into the bloodstream by the anesthesia machine through the respiratory system and inhibit the central nervous system. In the history of anesthesia, inhalation anesthesia is the earliest application of anesthesia, ether is widely known as inhalation anesthetics, but because of its unstable and flammable and explosive properties, the modern operating room more need for electric knife and other equipment, which may lead to the explosion of ether, and is now abandoned for clinical use. Inhalation anesthesia has developed into the main method of general anesthesia. Inhalation anesthetics in the body metabolism, decomposition, most of the original form from the lungs out of the body, so inhalation anesthesia has a high degree of controllability, safety and effectiveness.
Based on the way of contact between respiratory gas and air, the degree of repeated inhalation, and the presence or absence of carbon dioxide absorption device, inhalation anesthesia can be divided into four kinds of open, semi-open, semi-tightly closed, and tightly closed method. According to the amount of fresh gas flow is divided into low-flow anesthesia, minimum-flow anesthesia and tight-circuit anesthesia.
(2) the implementation of inhalation general anesthesia ① preanesthesia treatment mainly includes the patient's physical and psychological preparation, preanesthesia assessment, selection of anesthesia methods, and the preparation and inspection of the corresponding equipment, as well as reasonable preanesthetic medication. In addition, according to the characteristics of inhalation anesthesia induction itself, we should do a good job of explaining to the patient and preparing the respiratory tract. Induction can be divided into slow induction with increasing concentration and fast induction with high concentration. Simple inhalation anesthesia induction is suitable for children who are not suitable for intravenous anesthesia and not easy to keep the vein open, difficult airway and laryngeal mask intubation, etc. It is not suitable for those who are alcoholic or strong. Slow induction method is to use the left hand to fix the mask on the patient's mouth and nose, the right hand gently hold the airbag, after inhaling oxygen to remove nitrogen, open the volatile canister to start to give a low concentration of inhalation anesthetics. Halothane is the best choice of anesthetic, but other inhalational anesthetics are also available. If necessary, an oropharyngeal or nasopharyngeal ventilation catheter can be inserted to maintain the usual airway while the patient's response to stimulation is detected, and if the response disappears, the surgeon can be notified to prepare for surgery. Venous dilatation after the onset of anesthesia should be established as early as possible. This slow induction method with increasing concentrations allows for a smoother induction of anesthesia, but the prolonged induction time increases the possibility of accidents during the period of arousal and the patient is susceptible to noncooperation.
High-concentration fast induction method is the first inhalation of pure oxygen 6L/min denitrogenation by mask for 3 minutes, then inhalation of high-concentration anesthetics, let the patient take a deep breath for many times after the disappearance of consciousness and then switch to inhalation of medium-concentration anesthetics until the surgical anesthesia period. Feasible tracheal intubation, implementation of assisted or controlled breathing.
In the clinic, there are many patients will ask whether the inhalation induction is like the film and television works of gauze covering the mouth and nose to cause the disappearance of consciousness, in fact, the clinical application of inhalation anesthetics will not be so fast-acting, and need a special closed instrument to be able to store in the open environment is easy to volatilize. After the completion of anesthesia induction, the maintenance phase of anesthesia is entered. During this period, it should meet the requirements of surgery, maintain the patients' painlessness, unconsciousness, muscle relaxation and normal organ function, inhibit the stress response, maintain the balance of water, electrolytes and acid-base, and replenish the blood loss in time. At present, low-flow inhalation anesthesia is the main method of maintaining anesthesia. The depth of anesthesia should be adjusted intraoperatively according to the characteristics of surgery, preoperative medication and the patient's response to anesthesia and surgical stimuli. Changing the depth of anesthesia without altering the patient's minute ventilation is achieved primarily by adjusting the volatile tank opening concentration and increasing the fresh air flow. Inhaled anesthetics produce weak inotropic effects on their own, and intravenous administration of inotropic agents is often necessary to obtain perfect inotropy to meet the demands of major surgery to avoid circulatory depression caused by increasing inhalation concentrations alone in an attempt to augment inotropic effects. Volatile anesthetics can significantly enhance the nerve-blocking effect of nondepolarizing muscarinic agents, and the dosage of muscarinic agents can be reduced when the two are combined. ④ Awakening and Recovery The process of awakening in patients with inhalation anesthesia is the opposite of the induction process and can be viewed as a washout process of inhaled anesthetics. Due to the low flow rate of the gas in the circuit, it is impossible to wash out the anesthetic rapidly, so the volatile tank should be closed earlier at the end of the operation than in high-flow anesthesia. At the end of the entire surgical operation, high-flow pure oxygen is used to rapidly wash out the patient and any residual anesthetic from the circuit. When the concentration of inhaled anesthetic in the alveoli drops to 0.4 MAC (minimum alveolar air effective concentration), approximately 95% of patients are able to open their eyes as directed by the physician. The cleaner the inhalational anesthetic is washed out, the better it is for a smooth awakening process and the patient's recovery. Excessive residuals may not only lead to irritability and vomiting, but may even inhibit wakefulness and respiration. When washing out the inhalational anesthetics, some painkillers can be given intravenously to increase the patient's tolerance to the tracheal tube, in order to facilitate the early discharge of the inhalational drugs, and also to reduce the stress reaction during extubation.
2. Intravenous anesthesia
(1) Intravenous general anesthesia refers to the method of generating general anesthesia by injecting one or several kinds of drugs into the central nervous system via vein and acting on the central nervous system through blood circulation. According to the different ways of drug administration, intravenous anesthesia can be divided into single-administration method, split-administration method and continuous-administration method. Due to some of its own 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 potent and short-acting intravenous anesthetics and the introduction of computerized intravenous automatic drug delivery system, intravenous anesthesia has been greatly improved and developed.
Based on the different modes of drug delivery, intravenous anesthesia can be divided into single infusion, fractionated infusion, continuous infusion, and target-controlled infusion (TCI).
(2) Implementation of intravenous general anesthesia ①Pre-anesthetic treatment is the same as other general anesthesia, mainly including the patient's physical and psychological preparation, pre-anesthesia assessment, selection of anesthesia methods, and the preparation and inspection of the corresponding equipment, as well as reasonable pre-anesthetic medication. ②Induction of anesthesiaThe induction of intravenous anesthesia is more comfortable and suitable for most routine anesthesia situations (including inhalational general anesthesia), which is especially suitable for patients who need rapid induction. This can be achieved using a single intravenous injection of anesthetic drugs, or the induction of intravenous anesthesia can be accomplished using the TCI technique. Of the various stimuli produced by surgical anesthesia, tracheal intubation is higher than in general surgery, and thus the blood concentration required for induction of anesthesia may be greater than that required for intraoperative maintenance of anesthesia. The first dose of sedation can be calculated based on the loading dose formula CTVd peak effect, taking into account the patient's actual condition. The anesthesiologist should also be familiar with the peak effect times of the drugs used, which is important for induction of anesthesia. When utilizing TCI techniques for intravenous induction, care should be taken to select the appropriate target concentration based on the patient's individual condition. The time required for the patient to lose consciousness during induction decreases with increasing target concentration.
The use of intravenous anesthesia to implement the induction of anesthesia should also be aware of some of the characteristics of intravenous anesthesia itself. First, the principle of individualization should be emphasized. The selection and dosage of drugs should be adjusted according to the patient's specific situation, such as weight, age, circulatory status, preoperative medication and so on. Secondly, the dosage of drugs for elderly patients or patients with slow circulation time (such as shock, hypovolemia and cardiovascular disease) should be reduced, and the injection should be at a slow speed, while the changes in the cardiovascular system should be closely monitored. Finally, the injection of some anesthetics at the time of induction may cause local pain, and the preoperative or pre-induction administration of opioids or the injection of intravenous general anesthetics mixed with lidocaine can reduce the occurrence of pain. (iii) Anesthesia maintenance Maintaining the patient's anesthesia using continuous intravenous drops or pumping of anesthetics needs to include two doses, that is, the dose of drug eliminated from the central compartment plus the dose of drug transported to the peripheral compartments. Adjusting the rate of infusion of intravenous anesthetics according to the intensity of the surgical stimulus and the specifics of each patient can also provide relatively reasonable anesthetic maintenance blood concentrations. Using the TCI technique, the above objectives can be achieved more precisely and easily by target concentration setting. It should be noted, however, that since the injury stimulus is not invariable intraoperatively, the appropriate target concentration should be selected on a case-by-case basis (size of the procedure, degree of stimulation, and patient response, etc.). It should also be emphasized that it is much more effective to actively adjust the target concentration in advance to accommodate an impending strong stimulus than to wait until an injurious stimulus occurs before passively adjusting it.
Combination of drugs should be emphasized in the maintenance of anesthesia. A well-established anesthesia should achieve at least loss of consciousness, complete analgesia, muscle relaxation, and suppression of autonomic reflexes, provided that the patient's vital signs are stable. In order to achieve these four purposes, it is obvious that relying on a certain type of anesthetics is not feasible, which requires the combined use of anesthetics. Perfect intravenous general anesthesia mainly involves three major classes of drugs: first, intravenous general anesthetics, such as isoproterenol, imipramine, etc., which can make the patient fall asleep, consciousness disappears, and there is no memory of the surgical process; second, narcotic analgesics, such as fentanyl, dulcolax, and other opioid drugs, which can reduce pain and inhibit the stress response; and third, skeletal muscle relaxants, such as depolarizing muscarinic drug succinylcholine and non-depolarizing muscarinic drug Vecuronium bromide, pancuronium bromide, and other drugs. drugs such as vecuronium bromide and pancuronium bromide can relax the muscles and provide a good surgical field of vision, but a ventilator is needed to control breathing. ④ After anesthesia is restored to intravenous anesthesia, the patient's awakening time is closely related to the concentration of anesthetic drugs in the central compartment (plasma). For single-injection drugs, the decrease in blood concentration depends mainly on the distribution half-life and clearance half-life of the drug. For single-infusion administration of drugs in equivalent doses, the order of rapidity of recovery is: isoproterenol, etomidate, sodium thiopental, imipramine, and ketamine. In the case of longer continuous infusions of anesthetic drugs, the rate of decline in blood concentration depends not only on the distribution half-life and clearance half-life, but also on the sluggishness of its peripheral compartments. In addition to being rapid, a good recovery should be free of side effects and have adequate analgesia remaining. Isoproterenol has the fewest side effects during recovery. After ketamine and etomidate anesthesia, agitation is common during the awakening period; imipramine reduces these side effects better but makes recovery delayed. Haloperidol may increase the incidence of nightmares. Patient agitation during recovery should first rule out hypoxia, carbon dioxide accumulation, wound pain, and residual muscarinic medication; if inhalational anesthetics were used consideration should also be given to the thoroughness of their washout.
3. Compound anesthesia
Current clinical anesthesia is the simultaneous or sequential use of several different anesthetic drugs or techniques to obtain general anesthesia. This simultaneous or sequential application of two or more general anesthetic drugs or anesthetic techniques to achieve analgesia, amnesia, muscle relaxation, autonomic reflex inhibition and maintenance of stable vital signs of the anesthesia method, called balanced anesthesia. Balanced anesthesia emphasizes the combination of drugs, which 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 plays a very important role in improving the quality of anesthesia, ensuring patient safety and reducing medical costs in many aspects, and is an anesthesia concept that meets China's national conditions.
Static-absorption compound anesthesia is a typical representative of balanced anesthesia, the patient at the same time or successively implement intravenous general anesthesia and inhalation general anesthesia technology of anesthesia method is called intravenous - inhalation compound anesthesia technology, referred to as static-absorption compound anesthesia. Its methods are various, such as intravenous anesthesia induction, inhalation anesthesia maintenance; or inhalation anesthesia induction, intravenous anesthesia maintenance; or static-absorption compound induction, static-absorption compound maintenance. Since intravenous anesthesia has fast effect and smooth induction, and inhalation anesthesia is easy to manage and the depth of anesthesia is easy to control, therefore, inhalation anesthesia or static-absorption compound anesthesia maintenance after intravenous anesthesia induction occupies a major position in clinical anesthesia work. Intravenous anesthesia induction and inhalation anesthesia maintenance 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 kinds of general anesthesia, there are basic anesthesia, supervised anesthesia and other general anesthesia techniques, their degree of anesthesia is different, but there is no obvious difference in essence. Now clinically carried out more and more painless examination / treatment techniques, such as painless gastroscopy, painless abortion, etc., which is in fact a general anesthesia techniques, giving intravenous anesthetics (propofol commonly used) and analgesic drugs, to achieve the state of the patient to fall asleep and painless, but most of the short operation, most of them do not need to be intubated to control respiratory control, but there is a risk of respiratory depression, malinstitutionalized pneumonia, and so on.