Lecture No. 12. Anesthesia. Types and stages of anesthesia

General anesthesia, or anesthesia, is a state of the body that is characterized by a temporary shutdown of a person’s consciousness, his pain sensitivity and reflexes, as well as relaxation of the muscles of the skeletal muscles, caused by the action of narcotic analgesics on the central nervous system. Depending on the routes of administration of narcotic substances into the body, inhalation and non-inhalation anesthesia are distinguished.

1. Theories of anesthesia

Currently, there are no theories of anesthesia that would clearly define the narcotic mechanism of action of anesthetics. Among the available theories of anesthesia, the most significant are the following. Drugs can cause specific changes in all organs and systems. During the period when the body is saturated with a narcotic analgesic, there is a certain staging in the change in consciousness, respiration and blood circulation of the patient. Therefore, there are stages that characterize the depth of anesthesia. These stages manifest themselves especially clearly during ether anesthesia. There are 4 stages:

1) analgesia;

2) excitement;

3) surgical stage, subdivided into 4 levels;

4) stage of awakening.

Stage of analgesia

The patient is conscious, but some lethargy is noted, he is dozing, answers questions in monosyllables. Superficial and pain sensitivity are absent, but as for tactile and thermal sensitivity, they are preserved. In this stage, short-term surgical interventions are performed, such as opening phlegmon, abscesses, diagnostic studies, etc. The stage is short-term, lasting 3-4 minutes.

Excitation stage

In this stage, the centers of the cerebral cortex are inhibited, and the subcortical centers at this time are in a state of excitation. At the same time, the patient's consciousness is completely absent, pronounced motor and speech excitation is noted. Patients begin to scream, make attempts to get up from the operating table. Hyperemia of the skin is noted, the pulse becomes frequent, systolic blood pressure rises. The pupil of the eye becomes wide, but the reaction to light persists, lacrimation is noted. Often there is a cough, increased bronchial secretion, sometimes vomiting. Surgical intervention against the background of excitation cannot be performed. During this period, you should continue to saturate the body with a narcotic to enhance anesthesia. The duration of the stage depends on the general condition of the patient and the experience of the anesthesiologist. Typically, the duration of excitation is 7-15 minutes.

Surgical stage

With the onset of this stage of anesthesia, the patient calms down, breathing becomes calm and even, heart rate and blood pressure approach normal. During this period, surgical interventions are possible. Depending on the depth of anesthesia, 4 levels and stage III of anesthesia are distinguished. First level: the patient is calm, the number of respiratory movements, the number of heartbeats and blood pressure are approaching the initial values. The pupil gradually begins to narrow, its reaction to light is preserved. There is a smooth movement of the eyeballs, an eccentric arrangement. The corneal and pharyngeal-laryngeal reflexes were preserved. Muscle tone is preserved, therefore abdominal operations at this level are not performed. Second level: the movement of the eyeballs is stopped, they are fixed in a central position. The pupils dilate, and their reaction to light weakens. The activity of the corneal and pharyngeal-laryngeal reflexes begins to weaken with a gradual disappearance towards the end of the second level. Respiratory movements are calm and even. Values ​​of arterial pressure and pulse acquire normal values. Muscle tone is reduced, which allows for abdominal operations. Anesthesia, as a rule, is carried out in the period of the first and second levels. The third level is characterized as deep anesthesia. At the same time, the pupils of the eyes are dilated with a reaction to a strong light stimulus.

As for the corneal reflex, it is absent. Complete relaxation of the skeletal muscles develops, including the intercostal muscles. Due to the latter, respiratory movements become superficial or diaphragmatic. The lower jaw sags, as its muscles relax, the root of the tongue sinks and closes the entrance to the larynx. All of the above leads to respiratory arrest. In order to prevent this complication, the lower jaw is brought forward and held in this position. At this level, tachycardia develops, and the pulse becomes small filling and tension. The level of arterial pressure decreases. Carrying out anesthesia at this level is dangerous for the life of the patient. fourth level; the maximum expansion of the pupil with the absence of its reaction to light, the cornea is dull and dry. Given that paralysis of the intercostal muscles develops, breathing becomes superficial and is carried out by movements of the diaphragm. Tachycardia is characteristic, while the pulse becomes threadlike, frequent and difficult to determine in the periphery, blood pressure is sharply reduced or not detected at all. Anesthesia at the fourth level is life-threatening for the patient, as respiratory and circulatory arrest may occur.

Awakening stage

As soon as the introduction of narcotic drugs stops, their concentration in the blood decreases, and the patient goes through all the stages of anesthesia in reverse order, awakening occurs.

2. Preparing the patient for anesthesia

The anesthesiologist takes a direct and often the main role in preparing the patient for anesthesia and surgery. An obligatory moment is the examination of the patient before the operation, but at the same time, not only the underlying disease, for which surgery is to be performed, but also the presence of concomitant diseases, which the anesthesiologist asks in detail, is important. It is necessary to know how the patient was treated for these diseases, the effect of treatment, the duration of treatment, the presence of allergic reactions, the time of the last exacerbation. If the patient undergoes a surgical intervention in a planned manner, then, if necessary, correction of existing concomitant diseases is carried out. Sanitation of the oral cavity is important in the presence of loose and carious teeth, as they can be an additional and undesirable source of infection. The anesthesiologist finds out and evaluates the psychoneurological state of the patient. So, for example, in schizophrenia, the use of hallucinogenic drugs (ketamine) is contraindicated.

Surgery during the period of psychosis is contraindicated. In the presence of a neurological deficit, it is preliminarily corrected. Allergic history is of great importance for the anesthesiologist, for this, intolerance to drugs, as well as food, household chemicals, etc. is specified. If the patient has a aggravated allergic anamnesis, not even to medications, during anesthesia, an allergic reaction can develop up to anaphylactic shock. Therefore, desensitizing agents (diphenhydramine, suprastin) are introduced into premedication in large quantities.

An important point is the presence of a patient in the past operations and anesthesia. It turns out what the anesthesia was and whether there were any complications. Attention is drawn to the somatic condition of the patient: the shape of the face, the shape and type of the chest, the structure and length of the neck, the severity of subcutaneous fat, the presence of edema. All this is necessary in order to choose the right method of anesthesia and drugs. The first rule for preparing a patient for anesthesia during any operation and when using any anesthesia is the cleansing of the gastrointestinal tract (the stomach is washed through the tube, cleansing enemas are performed).

To suppress the psycho-emotional reaction and suppress the activity of the vagus nerve, before surgery, the patient is given medication - premedication. At night, phenazepam is prescribed intramuscularly. Patients with a labile nervous system are prescribed tranquilizers (seduxen, relanium) a day before surgery. 40 minutes before surgery, narcotic analgesics are administered intramuscularly or subcutaneously: 1 ml of a 1-2% solution of promolol or 1 ml of pentozocine (lexir), 2 ml of fentanyl, or 1 ml of 1% morphine. To suppress the function of the vagus nerve and reduce salivation, 0,5 ml of a 0,1% solution of atropine is administered. Immediately before the operation, the oral cavity is examined for the presence of removable teeth and prostheses that are removed.

3. Intravenous anesthesia

The advantages of intravenous general anesthesia are the rapid introduction of the patient into anesthesia. With this type of anesthesia, there is no excitement, and the patient quickly falls asleep. But narcotic drugs that are used for intravenous administration create short-term anesthesia, so they cannot be used in their pure form as mononarcosis for long-term operations. Barbiturates - sodium thiopental and hexenal - are able to quickly induce narcotic sleep, while there is no stage of excitation, and awakening is fast. Clinical pictures of anesthesia conducted by sodium thiopental and hexenal are similar. Geksenal has a less inhibitory effect on the respiratory center. Freshly prepared solutions of barbituric acid derivatives are used. The contents of the vial (1 g of the drug) are dissolved before the onset of anesthesia in 100 ml of isotonic sodium chloride solution (1% solution). The peripheral or central (according to indications) vein is punctured and the prepared solution is slowly injected at a rate of 1 ml for 10-15 s. When the solution was injected in a volume of 3-5 ml, the patient's sensitivity to barbituric acid derivatives is determined within 30 seconds.

If no allergic reaction is noted, then continue the introduction of the drug until the surgical stage of anesthesia. Since the onset of narcotic sleep, with a single injection of anesthetic, the duration of anesthesia is 10-15 minutes. To maintain anesthesia, barbiturates are administered in fractions of 100-200 mg of the drug, up to a total dose of not more than 1 g. During the administration of barbiturates, the nurse keeps a record of the pulse, blood pressure and respiration. The anesthesiologist monitors the state of the pupil, the movement of the eyeballs, the presence of a corneal reflex to determine the level of anesthesia. Anesthesia with barbiturates, especially thiopental-sodium, is characterized by depression of the respiratory center, so the presence of an artificial respiration apparatus is necessary. When respiratory arrest (apnea) occurs, artificial lung ventilation (ALV) is performed using a mask of a breathing apparatus.

Rapid administration of thiopental sodium can lead to a decrease in blood pressure and cardiac depression. In this case, the administration of the drug is stopped. In surgery, anesthesia with barbiturates as mononarcosis is used for short-term operations that do not exceed 20 minutes in duration (for example, opening abscesses, phlegmon, reduction of dislocations, diagnostic manipulations, and repositioning of bone fragments). Derivatives of barbituric acid are also used for induction anesthesia. Viadryl (predion for injection) is used at a dose of 15 mg/kg, with a total dose of 1000 mg on average. Viadryl is mainly used in small doses along with nitrous oxide. In high doses, this drug may cause a decrease in blood pressure. A complication of its use is the development of phlebitis and thrombophlebitis.

In order to prevent their development, it is recommended to administer the drug slowly into the central vein in the form of a 2,5% solution. Viadryl is used for endoscopic examinations as an introductory type of anesthesia. Propanidide (epontol, sombrevin) is available in ampoules of 10 ml of a 5% solution. The dose of the drug is 7-10 mg / kg, administered intravenously, quickly (the entire dose is 500 mg in 30 seconds). Sleep comes immediately - "at the end of the needle." The duration of anesthesia sleep is 5-6 minutes. Awakening is fast, calm. The use of propanidide causes hyperventilation, which occurs immediately after loss of consciousness. Apnea may sometimes occur. In this case, ventilation should be carried out using a breathing apparatus. The negative side is the possibility of hypoxia formation against the background of the drug administration. It is necessary to control blood pressure and pulse. The drug is used for induction anesthesia in outpatient surgical practice for small operations.

Sodium hydroxybutyrate is administered intravenously very slowly. The average dose is 100-150 mg/kg. The drug creates a superficial anesthesia, so it is often used in combination with other narcotic drugs, such as barbiturates - propanidide. It is often used for induction anesthesia.

Ketamine (ketalar) can be used for intravenous and intramuscular administration. The estimated dose of the drug is 2-5 mg / kg. Ketamine can be used for mononarcosis and for induction anesthesia. The drug causes superficial sleep, stimulates the activity of the cardiovascular system (blood pressure rises, pulse quickens). The introduction of the drug is contraindicated in patients with hypertension. Widely used in shock in patients with hypotension. Side effects of ketamine can be unpleasant hallucinations at the end of anesthesia and upon awakening.

4. Inhalation anesthesia

Inhalation anesthesia is carried out with the help of easily evaporating (volatile) liquids - ether, halothane, methoxy-flurane (pentran), trichlorethylene, chloroform or gaseous narcotic substances - nitrous oxide, cyclopropane.

With the endotracheal method of anesthesia, the narcotic substance enters the body from the anesthesia machine through a tube inserted into the trachea. The advantage of the method lies in the fact that it provides free patency of the respiratory tract and can be used in operations on the neck, face, head, eliminates the possibility of aspiration of vomit, blood; reduces the amount of drug used; improves gas exchange by reducing "dead" space.

Endotracheal anesthesia is indicated for major surgical interventions, it is used as a multicomponent anesthesia with muscle relaxants (combined anesthesia). The total use of several drugs in small doses reduces the toxic effects on the body of each of them. Modern mixed anesthesia is used to provide analgesia, turn off consciousness, relaxation. Analgesia and switching off consciousness are carried out by using one or more narcotic substances - inhaled or non-inhaled. Anesthesia is carried out at the first level of the surgical stage. Muscle relaxation, or relaxation, is achieved by the fractional administration of muscle relaxants.

5. Stages of anesthesia

There are three stages of anesthesia.

1. Introduction to anesthesia. Introductory anesthesia can be carried out with any narcotic substance, against which a rather deep anesthetic sleep occurs without a stage of excitation. Mostly, barbiturates, fentanyl in combination with sombrevin, milled with sombrevin are used. Sodium thiopental is also often used. The drugs are used in the form of a 1% solution, they are administered intravenously at a dose of 400-500 mg. Against the background of induction anesthesia, muscle relaxants are administered and tracheal intubation is performed.

2. Maintenance of anesthesia. To maintain general anesthesia, you can use any narcotic that can protect the body from surgical trauma (halothane, cyclopropane, nitrous oxide with oxygen), as well as neuroleptanalgesia. Anesthesia is maintained at the first and second levels of the surgical stage, and to eliminate muscle tension, muscle relaxants are administered, which cause myoplegia of all skeletal muscle groups, including respiratory ones. Therefore, the main condition for the modern combined method of anesthesia is mechanical ventilation, which is carried out by rhythmically squeezing a bag or fur, or using an artificial respiration apparatus.

Recently, the most widespread neuroleptanalgesia. With this method, nitrous oxide with oxygen, fentanyl, droperidol, muscle relaxants are used for anesthesia.

Introductory anesthesia intravenous. Anesthesia is maintained by inhalation of nitrous oxide with oxygen in a ratio of 2: 1, fractional intravenous administration of fentanyl and droperidol 1-2 ml every 15-20 minutes. With increased heart rate, fentanyl is administered, with an increase in blood pressure - droperidol. This type of anesthesia is safer for the patient. Fentanyl enhances pain relief, droperidol suppresses vegetative reactions.

3. Withdrawal from anesthesia. By the end of the operation, the anesthesiologist gradually stops the administration of narcotic substances and muscle relaxants. Consciousness returns to the patient, independent breathing and muscle tone are restored. The criterion for assessing the adequacy of spontaneous breathing are indicators of RO₂, RSO₂, pH. After awakening, restoration of spontaneous breathing and skeletal muscle tone, the anesthesiologist can extubate the patient and transport him for further observation in the recovery room.

6. Methods for monitoring the conduct of anesthesia

During general anesthesia, the main parameters of hemodynamics are constantly determined and evaluated. Measure blood pressure, pulse rate every 10-15 minutes. In persons with diseases of the cardiovascular system, as well as in thoracic operations, it is necessary to constantly monitor the function of the heart muscle.

Electroencephalographic observation can be used to determine the level of anesthesia. To control lung ventilation and metabolic changes during anesthesia and surgery, it is necessary to conduct a study of the acid-base state (RO₂, RSO₂, pH, BE).

During anesthesia, the nurse maintains an anesthetic chart of the patient, in which she necessarily records the main indicators of homeostasis: pulse rate, blood pressure, central venous pressure, respiratory rate, and ventilator parameters. In this map, all stages of anesthesia and surgery are fixed, the doses of narcotic substances and muscle relaxants are indicated. All drugs used during anesthesia are noted, including transfusion media. The time of all stages of the operation and the administration of drugs is recorded. At the end of the operation, the total number of all the means used is indicated, which is also reflected in the anesthesia card. A record is made of all complications during anesthesia and surgery. The anesthesia card is embedded in the medical history.

7. Complications of anesthesia

Complications during anesthesia may occur due to improper anesthesia technique or the effect of anesthetics on vital organs. One such complication is vomiting. At the beginning of the introduction of anesthesia, vomiting may be associated with the nature of the dominant disease (pyloric stenosis, intestinal obstruction) or with the direct effect of the drug on the vomiting center. Against the background of vomiting, aspiration is dangerous - the entry of gastric contents into the trachea and bronchi. Gastric contents that have a pronounced acid reaction, falling on the vocal cords and then penetrating the trachea, can lead to laryngospasm or bronchospasm, resulting in respiratory failure with subsequent hypoxia - this is the so-called Mendelssohn's syndrome, accompanied by cyanosis, bronchospasm, tachycardia.

Dangerous can be regurgitation - passive throwing of gastric contents into the trachea and bronchi. This usually occurs against the background of deep anesthesia using a mask with relaxation of the sphincters and overflow of the stomach or after the introduction of muscle relaxants (before intubation).

Ingestion into the lung during vomiting or regurgitation of acidic gastric contents leads to severe pneumonia, often fatal.

In order to avoid the appearance of vomiting and regurgitation, it is necessary to remove its contents from the stomach with a probe before anesthesia. In patients with peritonitis and intestinal obstruction, the probe is left in the stomach during the entire anesthesia, while a moderate Trendelenburg position is necessary. Before the onset of anesthesia, to prevent regurgitation, you can apply the Selick method - pressure on the cricoid cartilage posteriorly, which causes clamping of the esophagus. If vomiting occurs, it is necessary to quickly remove the gastric contents from the oral cavity with a swab and suction; in case of regurgitation, the gastric contents are removed by suction through a catheter inserted into the trachea and bronchi. Vomiting followed by aspiration can occur not only during anesthesia, but also when the patient wakes up. To prevent aspiration in such cases, it is necessary for the patient to take a horizontal position or the Trendelenburg position, turn his head to the side. The patient should be monitored.

Complications from the respiratory system can occur due to impaired airway patency. This may be due to defects in the anesthesia machine. Before starting anesthesia, it is necessary to check the functioning of the device, its tightness and the permeability of gases through the breathing hoses. Airway obstruction may occur as a result of retraction of the tongue during deep anesthesia (level III of the surgical stage of anesthesia). During anesthesia, solid foreign bodies (teeth, prostheses) can enter the upper respiratory tract. To prevent these complications, it is necessary to advance and support the lower jaw against the background of deep anesthesia. Before anesthesia, the dentures should be removed, the patient's teeth should be examined.

Complications of tracheal intubation performed by direct laryngoscopy can be grouped as follows:

1) damage to the teeth by the laryngoscope blade;

2) damage to the vocal cords;

3) introduction of an endotracheal tube into the esophagus;

4) introduction of an endotracheal tube into the right bronchus;

5) exit of the endotracheal tube from the trachea or bending it.

The described complications can be prevented by a clear knowledge of the intubation technique and control of the position of the endotracheal tube in the trachea above its bifurcation (using auscultation of the lungs).

Complications from the circulatory system. A decrease in blood pressure both during the period of anesthesia and during anesthesia can occur due to the effect of narcotic substances on the activity of the heart or on the vascular-motor center. This happens with an overdose of narcotic substances (often halothane). Hypotension may appear in patients with low BCC with the optimal dosage of narcotic substances. To prevent this complication, it is necessary to fill the BCC deficit before anesthesia, and during the operation, accompanied by blood loss, transfuse blood-substituting solutions and blood.

Heart rhythm disturbances (ventricular tachycardia, extrasystole, ventricular fibrillation) can occur due to a number of reasons:

1) hypoxia and hypercapnia resulting from prolonged intubation or insufficient ventilation during anesthesia;

2) overdose of narcotic substances - barbiturates, halothane;

3) the use of epinephrine against the background of halothane, which increases the sensitivity of halothane to catecholamines.

Electrocardiographic control is needed to determine the heart rhythm. Treatment is carried out depending on the cause of the complication and includes the elimination of hypoxia, a decrease in the dose of the drug, the use of quinine drugs.

Cardiac arrest is the most dangerous complication during anesthesia. The reason for it is most often incorrect control over the patient's condition, errors in the technique of anesthesia, hypoxia, hypercapnia. Treatment consists of immediate cardiopulmonary resuscitation.

Complications from the nervous system.

During general anesthesia, a moderate decrease in body temperature is allowed as a result of the influence of narcotic substances on the central mechanisms of thermoregulation and cooling of the patient in the operating room. The body of patients with hypothermia after anesthesia tries to restore body temperature due to increased metabolism. Against this background, at the end of anesthesia and after it, chills appear, which is observed after halothane anesthesia. To prevent hypothermia, it is necessary to monitor the temperature in the operating room (21-22 ° C), cover the patient, if necessary, infusion therapy, pour solutions warmed to body temperature, and inhale warm, moistened narcotic drugs. Cerebral edema is a consequence of prolonged and deep hypoxia during anesthesia. Treatment should be immediate, it is necessary to follow the principles of dehydration, hyperventilation, local cooling of the brain.

Peripheral nerve damage.

This complication occurs a day or more after anesthesia. Most often, the nerves of the upper and lower extremities and the brachial plexus are damaged. This is the result of an incorrect position of the patient on the operating table (abduction of the arm more than 90° from the body, placing the arm behind the head, fixing the arm to the arc of the operating table, laying the legs on holders without padding). The correct position of the patient on the table eliminates the tension of the nerve trunks. Treatment is carried out by a neuropathologist and a physiotherapist.

Author: Kolesnikova M.A.

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