Local anesthetics, classification. Local anesthetics. Classification. Mechanism and conditions of action. Requirements for local anesthetics. The meaning of their use with adrenomimetics Means for infiltration anesthesia

Anesthesia (Greek an - denial, anesthesia - sensation) - the destruction or cessation of all types of sensitivity, of which the loss of pain sensitivity is of particular importance - analgesia (Greek an - denial, algos - pain).

The loss of sensitivity can be general, due to a violation of the function of the central nervous system, and local (local), - the cessation of the flow of impulses into the central nervous system from receptors that perceive irritation in a particular area of ​​the body.

There are several types of local anesthesia:

superficial, or terminal, anesthesia - an anesthetic is applied to the surface of the mucous membrane, where it blocks the endings of sensory nerves; in addition, the anesthetic can be applied to the wound, ulcerative surface;

Infiltration anesthesia - the skin and deeper tissues are sequentially “impregnated” with an anesthetic solution, through which the surgical incision will pass; while the anesthetic blocks the nerve fibers, as well as the endings of sensory nerves;

conduction, or regional (regional), anesthesia - the anesthetic is injected along the nerve; there is a block in the conduction of excitation along the nerve fibers, which is accompanied by a loss of sensitivity in the area innervated by them.

Varieties of conduction anesthesia are spinal anesthesia, in which the anesthetic is injected subarachnoidly, and epidural (epidural) anesthesia - the anesthetic is injected into the space above the hard shell of the spinal cord.

In these variants, the anesthetic acts on the anterior and posterior roots of the spinal cord.

Pharmacological agents that can temporarily desensitize afferent nerves or block conduction along the nerves at the site of their application, without depressing the central nervous system, are called local anesthetics or local anesthetics.

The mechanism of action of local anesthetics:

1. Under their action, the activity of the mediator acetylcholine decreases and its effect on cholinergic receptors is weakened.

2. The cell membrane stabilizes, its permeability to sodium ions decreases, i.e. they are blockers of sodium channels. This prevents the formation of an action potential and, consequently, the conduction of impulses.

3. The breathing of the nervous tissue is weakened, its excitability is reduced.

4. Anticholinergic, ganglioblocking and desensitizing action is manifested.

Requirements for anesthetics:

1. Must have a high selectivity of action.

2. Should not have a negative effect (irritating, etc.) either on the nerve elements or on the surrounding tissues.

3. Must have a short latency period.

4. Must be highly effective in various types of local anesthesia.

5. Must have a certain duration of action (convenient for a variety of manipulations).

6. Should not dilate blood vessels.

7. Low toxicity and minimal side effects.

8. Water solubility and stability.

Classification of local anesthetics

According to their chemical structure, they are divided into:

1. Esters of various aromatic acids - benzoic, PABA, para-aminosalicylic - novocaine, cocaine, anesthesin, dicaine;

2. anilides of the same acids - trimekain, ksikain, sovkain.

From the point of view of practical application, anesthetics are divided into the following groups:

1. Means used for surface anesthesia.

Cocaine, dicaine, anesthesin, pyromecaine.

2. Means used primarily for infiltration and conduction anesthesia.

Novocaine, trimecaine, bupivacaine.

3. An agent used for all types of anesthesia.

Lidocaine.

The use of a number of drugs only for surface anesthesia is explained by the fact that they are either quite toxic (cocaine, dicaine) or poorly soluble in water (anesthesin).

Anesthetics in the tissues are rapidly destroyed, but when administered in large doses, they can be absorbed and act toxic.

Poisoning with anesthetics is characterized by anxiety, the appearance of clonic convulsions, disruption of the heart and breathing, and a drop in blood pressure. After excitation, depression of the central nervous system, collapse and respiratory arrest occurs. As a first aid for anesthetic poisoning, it is recommended to use a short-acting barbiturate when CNS is excited. With the onset of depression - artificial respiration with the introduction of oxygen, the use of ephedrine, substances that stimulate respiration and the cardiovascular system.

The first anesthetic used in medical practice was cocaine - alkaloid of the plant Erythroxylon coca (growing in South America) (In 1879, the Russian scientist V.K. Anrep discovered the anesthetic properties of cocaine alkaloid and suggested using it in medical practice for local anesthesia.

cocaine hydrochloride

cocaine hydrochloridum.

Salt of cocaine alkaloid.

Colorless needles or white crystalline powder with a bitter taste.

Causes a feeling of numbness in the tongue. Easily soluble in water.

Release form - powder, 2% solution in 1 ml ampoules.

The action develops in 3 - 5 minutes, and lasts 30 - 60 minutes. Easily penetrates through mucous membranes, wounds and skin ulcers, well absorbed into the surrounding tissues after subcutaneous injection. It is not absorbed through intact skin.

The use of cocaine is limited by its high toxicity and is mainly used for superficial anesthesia.

With a resorptive effect, cocaine has a predominantly stimulating effect on the central nervous system. The functional state of the cerebral cortex is changing. There are euphoria, anxiety, psychomotor agitation, the feeling of fatigue, hunger decreases, hallucinations are possible.

If the dose of cocaine is large enough, then the excitation of the central nervous system is replaced by its oppression; death occurs from oppression of the vital centers of the medulla oblongata (mainly the center of respiration).

Anestezin

White crystalline powder, slightly bitter taste, causes a transient feeling of numbness in the tongue. Slightly soluble in water.

Release form - powder, tablets of 0.3 g; 5% ointment.

One of the earliest synthetic compounds used as local anesthetics (1890).

It is an active surface local anesthetic. Due to the low solubility in water, it is not used parenterally. It is widely used in the form of ointments, powders, and other dosage forms for urticaria, skin diseases accompanied by itching, as well as for pain relief of wound and ulcer surfaces, for burns of the esophagus and stomach, vomiting, spastic conditions of the stomach and intestines, ulcerative processes in the stomach and 12 - duodenal ulcer, with cracks in the udder teats.

apply 5 - 10% ointments or powders and finished drugs (Menovazin, Amprovizol).

Novocaine(procaine hydrochloride).

Its synthesis was carried out in 1905.

Colorless crystals or odorless white crystalline powder. Easily soluble in water.

Release form - powder, 0.25% and 0.5% solutions in ampoules of 1; 2; 5; 10 and 20 ml.

1% and 2% solutions 1; 2; 5 and 10 ml;

0.25% and 0.5% sterile solutions in vials of 200 and 400 ml;

5% and 10% ointment, suppositories 0.1 g.

It has a fairly pronounced anesthetic activity, but is inferior in this respect to other drugs.

The duration of infiltration anesthesia is 30 minutes - 1 hour. The big advantage of novocaine is its low toxicity. It does not pass well through the mucous membranes, therefore it is rarely used for superficial anesthesia. Novocaine, unlike cocaine, does not constrict blood vessels. Their tone does not change or decreases to a small extent, therefore adrenomimetics (for example, adrenaline) are often added to novocaine solutions. By narrowing the vessels and slowing down the absorption of novocaine, adrenomimetics enhance and prolong its anesthetic effect, and also reduce its toxicity.

In addition to the anesthetic effect, novocaine, when absorbed and directly injected into the bloodstream, has a general effect on the body: it reduces the formation of acetylcholine and lowers the sensitivity of peripheral cholinergic receptors, has a blocking effect on the autonomic ganglia, reduces spasms of smooth muscles, reduces the excitability of the heart muscle and motor areas of the cerebral cortex.

In the body, it is relatively quickly hydrolyzed, forming para-aminobenzoic acid and diethylaminoethanol.

It is excreted in the urine unchanged and in the form of its decay products.

Application.

For infiltration anesthesia, 0.25 - 0.5% solutions are used; for anesthesia according to the method of A.V. Vishnevsky (tight creeping infiltrate) 0.125 - 0.25% solutions; for conduction anesthesia - 1 - 2% solutions; for the spinal - 5% solution.

Intradermal injections of 0.25 - 0.5% solution are recommended for circular and paravertebral blockade in eczema, neurodermatitis, sciatica.

In connection with the ability of the drug to reduce the excitability of the heart muscle, it is sometimes prescribed for atrial fibrillation (in / in a 0.25% solution).

Candles (rectal) are used as a local anesthetic and antispasmodic for spasms of the smooth muscles of the intestine.

Novocain (5 - 10% solutions) is also used using the electrophoresis method. To dissolve antibiotics.

It is well tolerated but may cause side effects and should be used with caution in all routes of administration.

The highest single doses of novocaine: horses 2.5 g; cattle 2 g; small cattle and pigs 0.5 - 0.75 g; dogs 0.5 g

Decain

White or white with a yellow tint crystalline powder, soluble in water.

Release form - powder.

Exceeds the local anesthetic action of cocaine and novocaine. It is 2 times more toxic than cocaine and 10 times more novocaine.

Anesthesia occurs in 1-5 minutes. and lasts 20 - 50 minutes.

Used for surface anesthesia in ophthalmology in 0.5 - 1% solutions for the removal of foreign bodies, eye operations, in otorhinolaryngology during surgical interventions (0.5 - 1.5% solutions).

Since it dilates the vessels, to prolong the action and reduce absorption, add 1 drop of a 0.1% solution of adrenaline hydrochloride to 5 ml of dicaine solution.

The highest single dose for anesthesia of the mucous membranes of the upper respiratory tract should not exceed 6 ml of a 1.5% solution for small animals.

Trimecain

Trimecain. White crystalline powder, highly soluble in water.

2-3 times more active than novocaine, but somewhat more toxic. It acts longer than novocaine (2 - 4 hours).

The fabric is not irritating.

It has a depressing effect on the cerebral cortex and on the ascending reticular formation of the brain stem. It has a sedative, hypnotic, anticonvulsant effect.

Used for infiltration anesthesia in the form of 0.25%; 0.5%; 1% solutions; for conduction anesthesia in the form of 1 - 2% solution. To enhance and lengthen local anesthesia, adrenaline is added at the rate of 3 drops of a 0.1% solution per 5 ml of anesthesin.

Xicain

White or slightly yellowish crystalline powder, highly soluble in water.

Release form - powder; one % ; 2%; 5% solutions.

Possesses high local anesthetic activity of long action.

It acts faster, stronger and longer than novocaine. Does not reduce the antimicrobial action of sulfonamides, unlike novocaine and anesthesin.

Used for all types of local anesthesia in surgical, gynecological, ophthalmic and orthopedic practice in the form of 0.25% - 5% solutions.

For conduction anesthesia, 1-3 drops of a 0.1% solution of adrenaline hydrochloride per 10 ml of anesthetic are added to the solution.

In addition to surgery, drugs for pain relief are used in cosmetology, dentistry and other industries. There are several types of painkillers, general and local action. Depending on the desired effect and scope, a specific type of anesthesia is selected.

Classification

Drugs that reduce the sensitivity of nerve fibers and inhibit the excitation passing through them are called anesthetics. Painkillers according to the mechanism of action are divided into two groups: local and general. The first is classified according to the chemical structure and type of anesthesia. General painkillers (anesthesia) are divided into single-component (simple) and multi-component (combined).

Types of anesthetics

General anesthetics can be in the form of volatile liquids or gases that are inhaled through a mask along with oxygen. Other general anesthetics are administered intravenously. Classification of local anesthetics by type:

1. Surface. The substance is applied to the surface of the mucosa or skin, reducing the sensitivity of a particular area.
2. Conduction, spinal. It consists in the inhibition of sensitivity passing along the nerve fiber at a distance from the place of manipulation.
3. Infiltration. The skin and tissues are impregnated with an anesthetic solution using intra- and subcutaneous injections.

General

Anesthesia has four stages:

• Superficial - sensitivity disappears, pain is not felt, but reflexes of internal organs and skeletal muscles remain.
• Easy - almost all reflexes disappear, skeletal muscles relax, surgeons can perform simple superficial operations.
• Full - all systems and reflexes are blocked, except for blood circulation throughout the body, so doctors can perform operations of any complexity.
• Super deep - all reflexes are blocked, the muscles of smooth and skeletal muscles are completely relaxed.

Depending on how anesthetics are introduced into the human body, general anesthesia can be:

1. Inhalation. Immersion in sleep occurs with the help of ethers, vapors, gases.
2. parenteral. The body is administered intramuscularly or intravenously. This species has subspecies:

• classical intravenous administration (preservation of breathing, moderate muscle relaxation);
• ataralgesia (surface anesthesia);
• neuroleptanalgesia (lethargy and drowsiness);
• combined anesthesia.

Local

Local anesthetics cause a temporary loss of sensation in a certain area due to the blockade of pain receptors. Indications for local anesthesia may be small operations on soft tissues, the refusal of general anesthesia, the age of patients. According to the chemical structure, the group of drugs is divided into two forms: esters of aromatic acids and substituted amides. Their main representatives are Novocaine and Lidocaine.

Mechanism of action of anesthetics

Inhalation anesthetics for general anesthesia block receptors, which causes not only pain relief, but also sleep (sedation). Local anesthetics vary in strength. In accordance with the severity and duration, they are divided into groups:

• short-term weak effect (Novocain from 30 to 90 minutes);
• moderate duration and strength (Lidocaine 90 minutes);
• great duration and strength (Bupivacaine, Dicaine 180-600 minutes).

The intensity, duration and onset of local anesthesia increases with increasing doses of drugs. Reduces toxicity and increases the duration of anesthesia by 2 times by adding adrenaline to the anesthetic solution, the total dose of which should not exceed 0.5 mg. In addition to the main action, local pain relief drugs enter the bloodstream, which leads to the development of a toxic effect on the body.

Inhalation anesthesia

It is used for general anesthesia for surgical intervention of varying complexity. During the action of inhalation anesthesia, a person sleeps, blood circulation and breathing slow down, so everything that happens is inaccessible to consciousness. Anesthesia is carried out using a mask through which a drug is injected that blocks the central nervous system.

More often, one anesthetic is used (mononarcosis), but sometimes doctors use a combination with two or more components in the composition. Means for inhalation anesthesia are divided into two groups: gaseous and vaporous. The former include nitrous oxide and cyclopropane. Vapor preparations:

• Fluorotan;
• Chloroform;
• Trichlorethylene;
• Ether;
• Penotran (Methoxyflurane).

Conduction anesthesia

It is characterized by the introduction of a drug into the tissues located around the nerve trunk. Sometimes injections are made into the nerve itself. For manipulation, a warm solution of Novocain is used. Local conduction anesthesia is performed with a sharp needle sharpened at an angle of 45 or 60 degrees. The drug chosen by the doctor is administered very slowly so as not to damage the tissues and the nerve. The anesthetic liquid is distributed in a fan-like fashion.

Conduction anesthesia is often used in dentistry. Such anesthesia can immediately affect a group of teeth. This type of anesthesia has become widespread during operations on the ankle, Achilles tendon, and foot.

Infiltration anesthesia

Another type of local anesthesia, characterized by the introduction of a solution into the periosteum, under the skin or under the mucous membrane. The method has found wide application in various fields of surgery. There are two types of infiltration anesthesia:

1. Direct anesthesia. The needle is inserted into the manipulation area. It is mainly used in facial surgery.
2. Indirect anesthesia. The drug is injected into the deep layers of tissues for anesthesia of the adjacent area. This method is widely used in dentistry.

Surface anesthesia

A popular type of local anesthesia is superficial (application, terminal). To carry it out, you only need to lubricate the skin or mucous membranes with a special agent. Terminal anesthesia relieves pain sensitivity in a small area of ​​the body. During anesthesia, the patient is conscious.

Application anesthetic is a salvation for people who cannot tolerate pain. Preparations of various forms are used: ointments, gels, sprays, aerosols, injections. Indications for the use of surface anesthesia are:

• installation of a venous or urinary catheter;
• cosmetic procedures;
• piercing;
• tattoos;
• treatment of ulcers;
• measurement of eye pressure;
• removal of foreign bodies;
• simple procedures on the cornea;
• painful manipulations in the mouth.

Drugs with anesthetics

The specialist chooses a drug for blockade of nerve endings, depending on the patient's condition and the area of ​​anesthesia. Lidocaine is more often used, as it has a wide spectrum of action. Other popular drugs for local anesthesia:

1. Novocaine. The least toxic drug that does not affect blood vessels. To narrow their lumen, adrenaline or another adrenomimetic is added to it. After that, the duration of action of Novocain increases and the toxicity of the drug decreases.
2. Artikain. They are used for various methods of anesthesia: spinal, conduction, infiltration. The analgesic effect of the drug lasts about 4 hours. Often used in obstetric practice.
3. Markain. Produces the longest effect - about 8 hours. It is superior in activity to Lidocaine. Used for epidural, conduction or infiltration anesthesia.

Contraindications and side effects

For any type of anesthesia, there is one main contraindication - allergic reactions manifested by the body in the form of itching, urticaria, Quincke's edema, anaphylactic shock. It is undesirable to administer anesthetics during pregnancy and lactation. All anesthetic manipulations during this period are carried out only in case of vital necessity. Prohibition for the introduction of inhalation anesthesia are chronic diseases in the stage of decompensation. For local anesthesia, a contraindication is children's age and the patient's mental illness.

During anesthesia (general) there is a risk of side effects. The patient may stop cardiac activity or be depressed breathing with an overdose of pain medication. After intravenous or inhalation anesthesia, a person is sometimes worried about general weakness, increased motor activity, and hallucinations.

Video

Local anesthetics (from the Greek. anesthesia- pain, sensation, and an- negative prefix) reduce the sensitivity of the endings of the afferent nerve fibers, and / or inhibit the conduction of excitation along the nerve fibers. At the same time, they primarily disrupt the conduction of excitation along sensory nerve fibers, but they can also inhibit the conduction of impulses along motor fibers. Local anesthetics first of all eliminate pain sensitivity, then temperature and other types of sensitivity (tactile sensitivity is eliminated last). Due to the predominant inhibitory effect of local anesthetics on pain receptors and sensitive nerve fibers, they are used for local anesthesia (local anesthesia).

The mechanism of action of local anesthetics is associated with the blockade of voltage-dependent sodium channels of cell membranes of sensitive nerve fibers. Local anesthetics (weak bases) in a non-ionized form penetrate the cell membrane into the axon and are ionized there. Ionized molecules of the substance interact with specific binding sites on sodium channels on the inside of the membrane and, by blocking sodium channels, prevent Na + from entering the cell and depolarizing the membrane. As a result, the generation of the action potential and the propagation of impulses along the nerve fiber are disturbed. The action of local anesthetics is reversible (after inactivation of the substance, the function of sensory nerve endings and nerve fibers is fully restored).

Since local anesthetics are weak bases, the degree of their penetration through the membrane depends on the pH of the medium (the lower the pH value, the greater part of the substance is in the ionized form and does not penetrate into the axon). Therefore, the effectiveness of local anesthetics is reduced in an acidic environment (in an environment with low pH values), in particular, with tissue inflammation.

Most local anesthetics are based on an aromatic structure (lipophilic fragment) connected via ether or amide bonds (intermediate chain) to an amino group (hydrophilic fragment). For the manifestation of a local anesthetic effect, an optimal ratio between the lipophilic and hydrophilic fragments of the molecule is necessary. The nature of the intermediate aliphatic chain is important for the duration of action of the substance. Since ester bonds are more easily hydrolysed, esters (procaine) have a shorter duration of action than amides (lidocaine).

Depending on the method of application of local anesthetics, the following main types of local anesthesia are distinguished.

superficial(terminal) anesthesia. When applied to the surface of the mucous membrane, the substance blocks the sensitive nerve endings (terminals) located in the mucous membrane, as a result of which it loses sensitivity. Local anesthetics can have the same effect when applied to wound, ulcerative surfaces. For terminal anesthesia, substances are used that easily penetrate the epithelium of the mucous membranes and, therefore, reach sensitive nerve endings. With terminal anesthesia, pain sensitivity is first lost, and then the sensation of cold, heat, and, finally, tactile sensitivity.

Terminal anesthesia is used in eye practice to anesthetize the conjunctiva and cornea during diagnostic or surgical interventions, in otolaryngology - during operations in the nasal cavity, in the pharynx, larynx, as well as during tracheal intubation, bronchoscopy, cystoscopy, etc. This method of anesthesia is also used to eliminate pain from burns, stomach ulcers.

Local anesthetics can be partially absorbed from the mucous membranes and have a resorptive toxic effect. To reduce the absorption of substances into the blood, and, consequently, to reduce the risk of resorptive effects, as well as to prolong the local anesthetic effect, vasoconstrictive substances (adrenaline) are added to solutions of local anesthetics.

Conduction anesthesia. With the introduction of a local anesthetic into the tissue surrounding the nerve, which contains sensitive nerve fibers, a block occurs in the conduction of excitation along the sensitive nerve fibers. As a result, there is a loss of sensitivity (primarily pain) in the area innervated by these nerve fibers. When exposed to a mixed nerve, the conduction of impulses is blocked first along the sensitive, and then along the motor fibers of the nerve. Motor fibers have a larger diameter, so local anesthetics diffuse into the fibers of these nerves more slowly, thus motor fibers are more resistant to local anesthetics. Conduction anesthesia is used for anesthesia during surgical operations, including in dental practice.

The closer to the central nervous system is the site of injection of local anesthetic, the wider the area of ​​anesthesia. The maximum area of ​​anesthesia is obtained by the action of a local anesthetic substance on the roots of the spinal cord. Varieties of conduction anesthesia, in which the substance acts on the anterior and posterior roots of the spinal cord, is epidural(epidural) anesthesia and spinal anesthesia.

In epidural anesthesia, a local anesthetic is injected into the space above the dura mater of the spinal cord. Spinal anesthesia is performed by injecting a local anesthetic solution into the cerebrospinal fluid at the level of the lumbar spinal cord. In this case, there is a blockade of the conduction of impulses along the sensitive fibers entering the lumbosacral spinal cord, which leads to the development of anesthesia of the lower extremities and lower body (including internal organs). Spinal anesthesia is used for pain relief during surgical operations (usually on the pelvic organs and lower extremities).

Infiltration anesthesia- a widespread method of local anesthesia, which is obtained by layer-by-layer impregnation of tissues in the area

surgery with a local anesthetic solution. In this case, the substance acts both on sensitive nerve endings and on sensitive nerve fibers that are located in infiltrated tissues. For infiltration anesthesia, solutions of local anesthetics of low concentration (0.25-0.5%) in large quantities (200-500 ml) are used, which are injected into tissues (skin, subcutaneous tissue, muscles, tissues of internal organs) under pressure.

Infiltration anesthesia is used in operations on internal organs and many other types of surgical interventions. Dissolve anesthetics in hypotonic (0.6%) or isotonic (0.9%) sodium chloride solution.

Since local anesthetics, when injected into tissues, can be absorbed into the blood and enter the systemic circulation, low-toxic substances should be used during conduction and infiltration anesthesia. To reduce the resorptive effect and lengthen the effect of local anesthetics, vasoconstrictive substances (for example, adrenaline) are added to their solutions.

For conduction, spinal and infiltration anesthesia, only sterile solutions of local anesthetics are used. Therefore, only such local anesthetic substances are suitable for these types of anesthesia, which are sufficiently soluble in water and are not destroyed during sterilization. To increase solubility and stability, local anesthetics are available in the form of salts (hydrochlorides).

Currently, in medical practice, many local anesthetic substances are used with varying degrees of activity and different durations of action. According to their use in clinical practice, local anesthetics are divided into:

1) funds used only for surface anesthesia: cocaine, tetracaine (Dicaine), benzocaine (Anestezin), bumecaine (Pyromecaine);

2) funds used mainly for infiltration and conduction anesthesia: proc and n (Novocaine), trimecaine, bupivacaine (Mar-caine), mepivacaine (Isocaine), articaine (Ultracaine);

3) means used for all types of anesthesia: lidocaine (Xycaine).
According to the chemical structure, local anesthetics can be divided into

into two groups:

Esters: cocaine, tetracaine, benzocaine, procaine.

Substituted acid amides: lidocaine, trimecaine, bupivacaine, mepivacaine, bumecaine, articaine.

Amides are not hydrolyzed under the influence of esterases in blood plasma and tissues, therefore, the substances of this group have a longer local anesthetic effect than esters.

Anesthetics (local anesthetics)- (from the Greek. sthesis - pain, sensation, an - the prefix of denial) a group of drugs that have the ability to weaken the sensitivity of the endings of afferent nerve fibers and / or inhibit the conduction of excitation along afferent nerve fibers.

Local anesthetics They are classified according to two important features: according to the chemical structure and according to the type of anesthesia they cause.

Esters of aromatic acids:

Substituted aromatic acid amides:

• Lidocaine;
• Trimecain;
• Bupivacaine;
• Articain;
• Bumekain and others.

It should be noted that local anesthesia can be of several types. So, they distinguish superficial (terminal), infiltration and conduction anesthesia. All these types of anesthesia, regardless of their characteristics, are due to the local action of drugs, therefore, they do not depend on the dose, but on the effective concentration of the anesthetic.

Superficial (terminal anesthesia) is characterized by a decrease in the sensitivity of nerve endings on the surface of the mucous membrane, wound or ulcerative surface and is achieved by applying an anesthetic to the surface of the skin or mucous membranes in a certain concentration.

With infiltration anesthesia there is a sequential impregnation of the skin and deeper tissues with the anesthetic solution, through which the surgical incision will pass.

Conduction anesthesia is determined by the suppression of sensitivity along the afferent nerve fiber. This type of anesthesia includes several special cases, namely:

• spinal anesthesia- conduction anesthesia at the level of the spinal cord;
• epidural (epidural) anesthesia - conduction anesthesia in the space above the dura mater.

Most anesthetics are selective for one or another type of local anesthesia. Therefore, these drugs are classified depending on the type of anesthesia they cause.

Classification of local anesthetics according to the type of anesthesia they cause

Means for terminal (surface) anesthesia:

• Benzocaine;
• Tetracaine;
• Bumecain.

Means for infiltration anesthesia:

Means for conduction anesthesia:

• Trimecain;
• Articain;
• Bupivacaine (mainly for spinal anesthesia), etc.

Means for all types of local anesthesia:

• Lidocaine.

Origin of electrical phenomena in tissues

To understand the mechanism of action of local anesthetics, it is necessary to recall the electrophysiology of a pain impulse in the cells of afferent nerve fibers. At rest, cells have an electrical charge, and the inner side of their membrane is negatively charged and has a value of -70-90 mV. This charge is called resting potential (RP). It is caused by an uneven distribution of sodium and potassium ions outside and inside the cell, with more sodium on the outside of the membrane, and potassium on the inside. In addition, there are sodium and potassium channels on the cell membrane, through which the corresponding ions are transported through the membrane during the occurrence of electrical phenomena in tissues. At the same time, sodium channels work “from outside to inside”, and potassium channels work the other way around. Finally, an important element of cell electrophysiology is the membrane enzyme Na7K+-AT Phase, which is involved in the normal distribution of electrolytes.

During excitation (irritation), an action potential (AP) is formed. Due to the energy of the stimulus, Na + ions enter the cell through slow sodium channels (pores in the membrane), providing an increase in the membrane charge to a level of -40:-50 mV, which is called the critical level of depolarization (CDL). With such a charge of the membrane, potential-dependent fast sodium channels open, sodium rushes into the cell like an avalanche, the membrane charge rises sharply, and depolarization of the cell membrane occurs, during which it becomes negatively charged from the outside, and positively charged from the inside.

In this case, a pain impulse is transmitted along the nerve fibers. Then the cell seeks to return the negative charge, the phase of repolarization begins (restoration of the resting potential), which is due to the release of K+ ions from the cell. This leads to the fact that the charge of the membrane is restored to its original level. However, at this moment, the distribution of ions outside and inside the cell does not correspond to normal: there is a lot of potassium outside, and sodium inside. Na + / K + -ATOa3a is activated on the cell membrane, which transfers 3 Na + ions from the cell to the outside and returns 2 K + ions to the inside, restoring the physiological ratio of electrolytes on the cell membrane.

Mechanism of action, local anesthetics

The principal mechanism of the anesthetic action of local anesthetics is that they competitively block fast potential-dependent sodium channels on the membrane of nerve cells, thereby disrupting the flow of sodium ions into the cell, and as a result, depolarization and excitation of the nerve cell.

It is important to understand that anesthetics cause blockade of sodium channels only from the inside of the membrane, having penetrated into the cell. In this regard, the pH of the tissue medium into which the anesthetic is injected is of decisive importance for the occurrence of the anesthetic effect, since the degree of ionization of the anesthetic molecule depends on this parameter.

Recall that only non-ionized lipophilic substances can overcome the membrane barrier and get inside the cell. Due to the fact that almost all local anesthetics are basic compounds in their chemical structure, they acquire lipophilicity only in a slightly alkaline or neutral environment, and in an acidic environment a hydrogen proton is attached to the tertiary nitrogen atom, the substances are ionized and become hydrophilic. As a result of this modification, they lose their ability to pass through membranes, and therefore are not able to block sodium channels. It is this feature of anesthetics that explains the lack of their action in an acidic environment during inflammation, purulent wounds, etc.

It should also be noted that in order to increase the effectiveness of anesthesia and reduce its systemic toxicity, the appointment of anesthetics requires a combination with vasoconstrictors (norepinephrine, epinephrine, and other a-agonists).

The fact is that with the narrowing of the blood vessels in the area of ​​​​administration of the anesthetic, its absorption into the general bloodstream decreases. As a result, a larger amount of the active substance remains at the site of implication (therefore, efficiency increases) and a smaller amount of it spreads throughout the body (toxicity decreases).

Pharmacological characteristics of individual local anesthetics

Some representatives of the group of local anesthetics have a number of important individual characteristics, in connection with which we will give the necessary characterization of these properties. Needless to say, this does not concern the principle mechanism of local anesthetic action. It is the same for all drugs in the group under consideration.

— highly active and low-toxic anesthetic. However, it is practically insoluble in water (solubility is 1 g per 2500 liters of H20), which does not allow its use in injectable dosage forms. Therefore, it is used only for terminal anesthesia. It is applied topically and internally.

locally(in the form of ointments, pastes, powders, rectal suppositories, alcohol solutions) - with acute inflammation of the middle ear, skin diseases accompanied by itching, hemorrhoids, etc. Inside (in the form of powders and tablets) - with and peptic ulcer of the stomach and duodenum.

- the first anesthetic used in medicine. The anesthetic properties of cocaine were discovered back in 1879 by a Russian doctor, pharmacologist and physiologist Vasily Konstantinovich Anrep (1852-1918). Cocaine is an alkaloid from the South American tree Erythroxylon Coca.

Currently, the use of cocaine hydrochloride in medicine is very limited, because, in addition to a pronounced local anesthetic activity, the drug has a resorptive effect, which is manifested by a strong psychostimulating effect due to the ability to inhibit the reuptake of monoamines in the central nervous system - norepinephrine and serotonin - and block monoamine oxidase (MAO ). As a result, the level of norepinephrine and serotonin in the structures of the brain increases significantly, which leads to a powerful excitation of the cortex. There is euphoria, anxiety, psychomotor agitation, the feeling of fatigue and hunger decreases, etc. With chronic use of cocaine, a mental drug addiction develops, called cocainism.

Sympathomimetic effects of cocaine manifests itself in the periphery, and therefore the use of this drug does not require combination with vasoconstrictors.

Given the above, cocaine hydrochloride is used in medicine only in ophthalmic practice for surface anesthesia (in the form of eye drops and ointment).

- highly effective, but extremely toxic anesthetic. It is 10-12 times more potent than cocaine, but 2-5 times more toxic. Therefore, tetracaine is used only for terminal anesthesia in ophthalmic practice.

During resorption, it can cause various side effects, so a combination with vasoconstrictors is required. Cases are described when a gross violation of the protocol for prescribing this drug (injection by mistake) led to death.

- a widely used anesthetic with moderate anesthetic activity. Along with the main action, it has a number of resorptive effects that have found their application in medicine.

After entering the general circulation, procaine penetrates the central nervous system, where it has a moderate inhibitory effect on the cortex and subcortical structures, including the centers of the medulla oblongata: the n.vagus centers and the vasomotor center. In addition, on the periphery, procaine blocks the autonomic ganglia. The cumulative consequence of such effects is the weakening of the parasympathetic and sympathetic innervation of the internal organs. Given the above, procaine can be useful in hypertension, circulatory spasm, as well as peptic ulcer of the stomach and duodenum (duodenal ulcer).

- a universal anesthetic suitable for all types of local anesthesia. At the same time, the duration of anesthesia caused by it is significantly higher than that of procaine. This is explained by the fact that procaine, being an ester, is exposed to esterases in tissues and blood (enzymes that cleave the ester bond). Lidocaine, on the other hand, belongs to the group of substituted amides, and therefore there is no target for deesterification in its structure.

In addition, an important pharmacological property of lidocaine is the antiarrhythmic effect associated with the blockade of sodium channels in cardiomyocytes.

Means used primarily for infiltrative and conduction anesthesia

Novocaine- is one of the least toxic local anesthetics, its effect lasts from 30 minutes to an hour. Novocaine does not penetrate well through the mucous membranes, and therefore its use for surface anesthesia is limited (only in ENT practice, its 10% alcohol solution is used). Novocaine does not affect the vessels, therefore, to narrow them, some adrenomimetic (for example, adrenaline) is added to novocaine. At the same time, adrenaline prolongs the action of novocaine and reduces its toxicity. The resorptive effect of novocaine is expressed in the inhibition of visceral and somatic reflexes, the development of hypotension and antiarrhythmic action.

For infiltration anesthesia, novocaine is used in low concentrations (0.25-0.5%) and in large volumes (hundreds of ml). For conduction anesthesia, the volume of the anesthetic solution is significantly less, but its concentration increases (1.2% in a volume of 5, 10, 20 ml). Novocaine is used for the most part for intramuscular injections, often in cases where the injected drug is painful. Here, in controlled proportions, the drug and novocaine are diluted in a syringe and injected to the patient.

· Trimecain surpasses novocaine in duration of action by 3-4 times. Trimecaine is somewhat less toxic than novocaine and does not irritate tissues. The general effect on the body is a depressant effect on the cerebral cortex, as well as a sedative, hypnotic and anticonvulsant effect. When administered intravenously, trimecaine has an antiarrhythmic effect.

Application area

Conduction anesthesia - 1% and 2% solutions

Infiltration anesthesia - 0.25% and 0.5% solutions

Means used for all types of anesthesia

Lidocaine has analgesic power, 2.5 times greater than that of novocaine. Lidocaine in combination with adrenaline acts for 2-4 hours. Its toxicity is almost the same as that of novocaine. The local anesthetic does not irritate the surrounding tissues. When administered intravenously, lidocaine has an antiarrhythmic effect.

Application area

Application (surface anesthesia) - 10% spray

Infiltration anesthesia - 0.125%, 0.25%, 0.5% solutions

Conductive anesthesia - 1%, 2% solutions

Dikain is a strong local anesthetic. In terms of activity, it significantly exceeds Novocaine and cocaine, but it has a high toxicity, exceeding the toxicity of cocaine by 2 times and Novocaine by 10 times, which requires caution when using the drug. Well absorbed through the mucous membranes.

Application area

Anesthesia of the oral mucosa - 0.25-1% solutions

Superficial anesthesia - 1% and 2% solutions

Classification of bleeding.

Bleeding (haemorrhagia) is the outflow of blood from a blood vessel into the external environment or cavities and tissues of the body.

Looks like a bleeding vessel.

1. Arterial.

2. Venous.

3. Arteriovenous.

4. Capillary.

5. Parenchymal.

According to the clinical picture.

1. External (blood from the vessel enters the external environment).

2. Internal (blood leaking from the vessel is located in the tissues (with hemorrhages, hematomas), hollow organs or body cavities).

3. Hidden (without a clear clinical picture).

For internal bleeding, there is an additional classification.

1. Leaks of blood in the tissue:

1) hemorrhages in the tissues (blood flows into the tissues in such a way that they cannot be separated morphologically. The so-called impregnation occurs);

2) subcutaneous (bruising);

3) submucosal;

4) subarachnoid;

5) subserous.

2. Hematomas (massive outflow of blood into the tissues). They can be removed with a puncture.

According to the morphological picture.

1. Interstitial (blood spreads through interstitial spaces).

2. Interstitial (blood outflow occurs with tissue destruction and cavity formation).

According to clinical manifestations.

1. Pulsating hematomas (in case of communication between the hematoma cavity and the arterial trunk).

2. Non-pulsating hematomas.

Allocate also intracavitary bleeding.

1. Blood outflows into the natural cavities of the body:

1) abdominal (hemoperitoneum);

2) the cavity of the heart bag (hemopericardium);

3) pleural cavity (hemothorax);

4) joint cavity (hemarthrosis).

2. Blood outflows into hollow organs: gastrointestinal tract (GIT), urinary tract, etc.

The rate of bleeding.

1. Acute (from large vessels, a large amount of blood is lost within minutes).

2. Acute (within an hour).

3. Subacute (during the day).

4. Chronic (within weeks, months, years).

By the time of occurrence.

1. Primary.