Read more about pain relief during operations.

Local anesthesia is used to numb sensations in a specific part of the body. This prevents pain during surgical procedures.

An anesthetic is applied to the part of the body that is undergoing surgery.

Can be used for sedation, which calms the patient and reduces stress levels. Together, they allow the surgeon to perform the procedure without pain or distress.

Local anesthesia does not last long, so it is mainly used for small outpatient procedures where the patient can leave the clinic the same day.

What is local anesthesia

The main distinguishing feature of local anesthesia is that the person remains conscious during its effect. This type of anesthesia acts on receptors that are located below chest level. In addition to complete anesthesia, local anesthesia eliminates other tactile sensations, including temperature, pressure on tissue, or stretching.

Local anesthesia is possible in the following areas:

• on the surface of the mucous membranes of various organs - trachea, larynx, bladder, bronchi, and so on;
• in the thickness of tissue - bone, muscle or soft;
• in the direction of the nerve root extending beyond the boundaries of the spinal cord membrane.
• in impulse-conducting nerve cells of the spinal cord.

The main goal of local anesthesia is to block the occurrence of impulses and their transmission while maintaining consciousness.

Intravenous anesthesia

This type of anesthesia refers to non-inhalation types of anesthesia, which are characterized by a long-lasting effect and a greater depth of effect compared to inhalation anesthesia. Intravenous anesthesia can be performed using the following drugs:

• Thiopental, Recofol, Oxybutyrate and Propofol - classic pain relief
• Fentathyl with diphenhydramine - neuroleptanalgesia, which can be carried out on spontaneous breathing or combined with artificial ventilation
• Sibazon with Fentathyl is ataralgesia, which provides superficial, gentle anesthesia and can be carried out with other types of anesthesia.

This type of anesthesia is used to remove abscesses and phlegmons that occur with complications; it is also possible to treat small benign tumors if their removal under general anesthesia is not possible.

Types of local anesthesia

In medicine, there are the following types of anesthesia, differing in some characteristics and scope of application:

• terminal;
• infiltration;
• regional;
• intravascular.

Each type has a list of indications and contraindications that must be taken into account when conducting them.

Terminal anesthesia

This type is also known as topical or surface anesthesia. The main areas of application are dentistry, gastroenterology and proctology. Terminal local anesthesia (anesthesia) differs from other types in the method of administration: anesthetics in the form of a spray, gel or ointment are applied to the surface of the skin or mucous membranes.

In proctology, local anesthetic gels and sprays (Katetdzhel, Lidochlor, Lidocaine, etc.) are used during proctological examinations and diagnostic procedures: rectal examination, anoscopy, sigmoidoscopy. The examination becomes virtually painless. Also, local anesthesia in proctologists is used during certain medical procedures: latex ligation of hemorrhoids, sclerotherapy of hemorrhoids, infrared coagulation of internal hemorrhoids, as well as biopsy from the rectum.

Infiltration anesthesia

It is used in dentistry and surgery, and involves the introduction of special solutions into soft tissues. The result of the procedure, in addition to a pronounced anesthetic effect, is an increase in pressure in the tissues, and, as a result, a narrowing of the blood vessels in them.

Regional anesthesia

This type involves the introduction of an anesthetic near large nerve fibers and their plexuses, resulting in pain relief in localized areas. It is divided into the following types of local anesthesia:

• conduction, with the introduction of drugs near the trunk of a peripheral nerve or nerve plexus;
• spinal, with the introduction of drugs into the space between the membranes of the spinal cord and “turns off” pain receptors over a large area of ​​the body;
• epidural anesthesia, with the introduction of drugs into the space between the spinal cord and the walls of the spinal canal through a special catheter.

Intravascular anesthesia

It is used mainly for surgical interventions on the extremities. Administration of drugs is possible only with the application of a hemostatic tourniquet. The anesthetic is injected into a blood vessel located near the nerve responsible for the sensitivity of the limb in the area below the injection site.

In recent years, due to the emergence of more effective local anesthetics, the number of proctological operations performed using local anesthetics has increased significantly. In addition, our specialists have developed a method of combined anesthesia - a combination of local anesthesia and intravenous anesthesia. This significantly reduces the toxicity of general anesthesia and reduces the severity of pain in the postoperative period, which allows the patient to recover faster after surgery.

Most often, when performing proctological operations (hemorrhoidectomy, excision of anal fissures, small pararectal fistulas, rectal polyps), pararectal blockade, as well as spinal anesthesia, are used.

Inhalation anesthesia

This is the most commonly used type of anesthesia, which is characterized by ease of implementation, relatively easy control and short duration of action, which is important for minor surgical interventions. Inhalation anesthesia is the administration of drugs through a mask, which ensures their entry into the organs of the respiratory system. Most often, Narcotan, nitrous oxide, Trilene, Ftorotan and Etran are used for this type of anesthesia. There is a certain problem - to achieve the desired result, it is necessary that the effect of anesthesia be deep, and this is fraught with serious complications. Therefore, this type of anesthesia is most often used in pediatric surgery. Children under anesthesia administered by inhalation feel excellent, they do not experience respiratory dysfunction, and complications are extremely rare.

Preparations for local anesthesia

The following drugs are used to provide local anesthesia:

• Novocaine;
• Dicaine;
• Lidocaine;
• Trimecaine;
• Bupivacaine;
• Naropin;
• Ultracaine.

Each of them is effective when carrying out a certain type of anesthesia. Thus, Novocaine Dicaine and Lidocaine are more often used when it is necessary to anesthetize the skin and mucous membranes, while more powerful drugs, such as Naropin and Bupivacaine, are used for spinal and epidural anesthesia.

Benefit

Local anesthesia provides pain relief for dental surgery and other outpatient procedures.

Local anesthesia is used when:

• the operation is minor and does not require general or regional anesthesia
• the procedure can be performed quickly and the patient does not have to stay overnight
• the operation does not require muscle relaxation or loss of consciousness of the patient

Examples include dental surgery, removal of warts, moles or cataracts, and biopsy.

Indications for local anesthesia

All methods of local anesthesia have the same list of indications, and are used if necessary to numb a specific area for a short time (up to an hour and a half). It is recommended to use them:

• for performing surgical non-abdominal interventions or small abdominal operations, the duration of which does not exceed 60-90 minutes;
• with intolerance to general anesthesia;
• if the patient is in a weakened state;
• if it is necessary to carry out diagnostic procedures against the background of severe pain;
• if the patient refuses general anesthesia;
• in elderly patients;
• when general anesthesia cannot be used.

Endotracheal anesthesia

One of the most commonly used methods of anesthesia when performing complex surgical interventions is endotracheal anesthesia, which involves immersing the body in a state of deep narcotic (medicinal) sleep. At the same time, the muscles completely relax, and the patient does not breathe independently. To achieve the desired state, doctors carry out a set of measures for the patient:

1. Tracheal intubation is the insertion of an endotracheal tube into the lumen of the trachea, which is needed to provide artificial ventilation of the lungs.
2. Intravenous administration of narcotic anesthetics, sedatives and tranquilizers.
3. Administration of muscle relaxants – they block neuromuscular transmission.
4. Artificial ventilation.

The quality of endotracheal anesthesia depends not only on the experience of the anesthesiologist, but also on how correctly the patient’s condition is monitored. It is imperative to monitor blood pressure, pulse, and oxygen saturation.

Possible complications when using local anesthesia

The use of local anesthetics carries certain risks, which include several types of complications:

• damage to the central nervous system and conduction system of the heart;
• damage to spinal tissue, nerve roots and spinal cord membranes;
• suppuration at the site of anesthetic injection;
• allergic reactions.

In most cases, the listed problems arise when the anesthesia technique is violated, or when the anamnesis is not collected completely.

Other applications

Local anesthesia may also be used to diagnose some chronic conditions and to relieve pain after surgery.

Research has shown that local anesthesia may be more useful than opioids such as morphine for treating pain after total knee replacement surgery.

In 2010, results from a rodent study in Turkey showed that local anesthetics may reduce some symptoms of inflammatory bowel disease (IBD).

Anyone administering any type of anesthetic should be appropriately trained and qualified.

How does an appointment with an anesthesiologist-resuscitator take place and why is it needed?

• The anesthesiologist examines the patient before the operation, and not only pays attention to the main disease for which the operation is to be performed, but also clarifies in detail the presence of concomitant diseases
• If the patient is operated on as planned, then, if necessary, treatment of concomitant diseases and sanitation of the oral cavity are carried out
• The doctor finds out the allergy history (whether all drugs and substances are tolerated by the patient)
• Clarifies whether the patient has undergone operations and anesthesia in the past
• Pays attention to the shape of the face, chest, neck structure, and the severity of subcutaneous fat tissue
• Such a detailed consultation is necessary in order to choose the right method of pain relief for each individual patient.

Mechanisms of action and types of anesthetics

Anesthetics are divided into:

1. Local
2. General: a) inhalation - volatile liquids and gases b) non-inhalation (intravenous)

Table 1

1. Local anesthetics

Local anesthetics reversibly reduce the excitability of sensory nerve endings and block the conduction of afferent impulses in the nerve trunks in the area of ​​direct application, and are used to eliminate pain.

The first drug of this group, cocaine, was isolated in 1860 by Albert Newman from the leaves of the South American shrub Erythroxylon coca. Newman, like many chemists of the past, tasted the new substance and noted a numbness in his tongue. Professor of the Military Medical Academy of St. Petersburg Vasily Konstantinovich Anrep in 1879. confirmed the ability of cocaine to cause anesthesia. In experiments on frogs, he discovered that cocaine had a “paralyzing effect” on the endings of sensory nerves. V.K. Anrep studied the effect of cocaine on himself: an injection of cocaine in a dose of 1 - 5 mg under the skin was accompanied by complete anesthesia - a pin prick or cauterization with a smoldering match did not cause pain. A similar effect was observed when a cocaine solution was instilled into the eye and applied to the mucous membrane of the tongue.

Local anesthetics are classified into esters (anesthesin, dicaine, novocaine) and substituted amides (lidocaine, trimecaine, bupivacaine). Local anesthetics - esters are hydrolyzed by blood pseudocholinesterase and act for 30 - 60 minutes. Their effect is prolonged by anticholinesterase drugs (prozerin). The hydrolysis product, n-amino-benzoic acid, weakens the bacteriostatic effect of sulfonamides. Substituted acid amides are inactivated by the liver monooxygenase system within 2-3 hours. Bupivaquine causes local anesthesia lasting 3-6 hours, after its cessation the analgesic effect persists for a long time.

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

1. Agents used for superficial (terminal) anesthesia: Cocaine, Dicaine, Anestezin, Pyromecaine
2. Agents used primarily for infiltration and conduction anesthesia: Novocaine, Bupivacaine
3. Agents used for all types of anesthesia: Lidocaine, Trimecaine

Mechanism of action

Local anesthetics are tertiary nitrogenous bases. They consist of hydrophilic and lipophilic parts connected by ester or amide bonds. The mechanism of action is determined by the lipophilic part, which has an aromatic structure. For application to mucous membranes and skin and parenteral administration, aqueous solutions of hydrochloride salts of local anesthetics are used. In the slightly alkaline environment of tissues (pH = 7.4), salts are hydrolyzed, releasing bases. The bases of local anesthetics dissolve in the lipids of the membranes of nerve endings and trunks, penetrate to the inner surface of the membrane, where they are converted into an ionized cationic form.

Figure 1 | Mechanism of action of local anesthetics

Receptors for local anesthetics are localized in the S6 segment of domain IV of the intracellular part of sodium channels. By binding to receptors, local anesthetic cations prolong the inactivated state of sodium channels, which delays the development of the next action potential. Local anesthetics do not interact with closed channels during the resting potential period. Thus, action potentials do not develop in the area where local anesthetics are applied, which is accompanied by a block in the conduction of nerve impulses. The selective effect of local anesthetics on sensory afferent nerves is due to the generation of long-lasting (more than 5 ms) high-frequency action potentials in them.

First of all, local anesthetics block unmyelinated C and myelinated Aδ and Aβ fibers (afferent pathways conducting pain and temperature stimuli; autonomic nerves). Local anesthetics act on fibers surrounded by a myelin sheath at the nodes of Ranvier. Thick myelinated fibers (afferent pathways that conduct tactile stimulation; motor nerves) respond less well to local anesthetics. In addition, the resistance of motor nerves to anesthesia is due to low-frequency short (less than 5 ms) action potentials. In the focus of inflammation, under conditions of acidosis, the dissociation of hydrochloride salts of local anesthetics and the formation of their free lipid-soluble bases are disrupted, so the analgesic effect is lost. For example, local anesthesia may not be effective for tooth extraction in cases of severe periodontitis.

2. General anesthetics

2.1. Inhalational anesthetics

2.1.1 Volatile liquids

Theories of the mechanism of action of general anesthetics

The effects of inhalational anesthetics cannot be explained by a single molecular mechanism. Most likely, the multicomponent action of each anesthetic is realized through many targets. However, these effects converge on a limited number of changes underlying the physiological effects. At the moment, there are lipid and protein theories of anesthesia, but none of them yet describes the sequence of events occurring from the interaction of the anesthetic molecule and its targets to physiological effects.

Figure 2 | Inhalational anesthetics

The activity of inhalational anesthetics is assessed by the minimum alveolar concentration (MAC). A dose producing 1 MAC prevents movement in response to surgery in half of patients. The potency of general anesthetics correlates with their lipid solubility, suggesting the importance of interaction with hydrophilic targets. In particular, the discovery of a relationship between the strength of an anesthetic and its lipophilicity (Meyer-Overton's rule) gave rise to the lipid theory of the mechanism of action of anesthetics. The lipid theory of anesthesia states that anesthetics dissolve in the lipid bilayer of biological membranes and cause anesthesia by reaching a critical concentration in the membrane. The most sophisticated versions of the lipid theory require that anesthetic molecules cause perturbation (changes in properties) of the membrane.

Figure 3 | Meyer-Overton rule

Figure 4 | In the 20th century, it was shown that the potency of general anesthetics correlates with their ability to inhibit the activity of the soluble enzyme luciferase, which is not a physiological target of anesthetics but serves as a lipid-free model protein molecule for anesthetic binding.

Modern facts suggest that proteins, to a greater extent than lipids, are molecular targets for the action of anesthetics. The interaction of anesthetics with hydrophobic regions of proteins also explains the Meyer-Overton rule. The direct interaction of anesthetic molecules with proteins allows us to explain exceptions to this rule, since any sites of binding with a protein are determined both by the size and shape of the molecule, and by solubility. Numerous physical methods (X-ray diffraction, NMR spectroscopy) confirm that general anesthetics act by directly binding to the amphiphilic cavities of protein molecules, and the size of the bound region explains the effect of “chopping off” the properties (longer alcohols lose their anesthetic properties).

Mechanism of action

Thus, general anesthetics change the physicochemical properties of neuronal membrane lipids and disrupt the interaction of lipids with ion channel proteins. At the same time, the transport of sodium ions into neurons is reduced, the output of less hydrated potassium ions is maintained, and the permeability of chloride channels controlled by GABA-A receptors increases by 1.5 times. The result of these effects is hyperpolarization with increased inhibition processes. General anesthetics suppress the entry of calcium ions into neurons by blocking H-cholinergic receptors and NMDA glutamic acid receptors; reduce the mobility of Ca2+ in the membrane, therefore preventing the calcium-dependent release of excitatory neurotransmitters. The most sensitive to the action of general anesthetics are the polysynaptic systems of the central nervous system—the cerebral cortex (1013–1014 synapses), the thalamus, the reticular formation, and the spinal cord. The respiratory and vasomotor centers of the medulla oblongata are resistant to anesthesia.

Volatile inhalational anesthetics:

• postsynaptically enhance inhibitory transmission by potentiating ligand-gated ion channels activated by GABA and glycine;
• extrasynaptically by enhancing GABA receptors and ionic leakage currents;
• presynaptically by increasing basal GABA release.

Inhalational anesthetics inhibit excitatory synaptic transmission by reducing glutamate release and postsynaptically by inhibiting ionotropic glutamate receptors. The paralyzing effect of local anesthetics involves the spinal cord, while sedation/anesthesia and amnesia involve the supraspinal mechanisms of memory, sleep and consciousness.

2.1.2. Gas anesthesia

In anesthesiology, the inhalation gas anesthetic nitrous oxide (N2O) is widely used. At the end of the 1980s. The inert gas xenon entered foreign anesthesiological practice.

Nitrous oxide is a colorless gas with a characteristic odor, stored in metal cylinders under a pressure of 50 atm in a liquid state, does not burn, but supports combustion. Its mixtures with anesthetics of the group of volatile liquids are explosive in certain concentrations. In subnarcotic concentrations (20 - 30%) of nitrous oxide causes euphoria (laughing gas) and strong analgesia. At a concentration of 20% it provides pain relief to the same extent as 15 mg of morphine. Nitrous oxide does not affect GABA-A receptors. Used only in combinations, as the MAC is 104%.

The inert gas xenon is considered the best alternative to nitrous oxide, as it has a more pronounced anesthetic effect, indifference and environmental safety. The ability of xenon to cause anesthesia was discovered in connection with the practice of deep-sea diving and the development of hyperbaric physiology. Xenon is colorless, does not burn and has no odor; upon contact with the mucous membrane of the mouth, it creates a sensation of a bitter metallic taste on the tongue. It is characterized by low viscosity and high solubility in lipids, and is excreted unchanged by the lungs. A xenon-saving anesthesia technology has been developed that includes a minimum flow and a recycling system for repeated reuse of gas. This technology successfully solves the practically important problem of the shortage and high cost of xenon. In the mechanism of the anesthetic effect of xenon, blockade of cytoreceptors of excitatory neurotransmitters - H-cholinergic receptors, NMDA receptors of glutamic acid, as well as activation of receptors of the inhibitory neurotransmitter glycine are important. When interacting with cytoreceptors, xenon acts as a proton-binding cluster and forms complexes with the cations HCO+, NH2+, HNCH+. Xenon exhibits antioxidant and immunostimulant properties, reduces the release of hydrocortisone and adrenaline from the adrenal glands.

2.2. Non-inhalation (intravenous) anesthetics are divided into three groups:

Short-acting drugs (3 - 5 min)

• propanidine (epontol, sombrevin)
• propofol (diprivan, recofol)

Medium-acting drugs (20 - 30 min)

• ketamine (calypsol, ketalar, ketanest)
• midazolam (dormicum, flormidal)
• hexenal (hexobarbital sodium)
• thiopental sodium (pentothal)

Long-acting drugs (0.5 - 2 hours)

• sodium hydroxybutyrate

Figure 5 | General anesthetics for intravenous administration

Mechanism of action

The most widely used intravenous anesthetic is propofol. Its mechanism of action is associated with an increase in chloride conductivity of GABA receptors.

Methohexital is close to propofol in terms of the speed of onset and recovery from anesthesia.

Barbiturates were used for anesthesia before the introduction of propofol. Thiopental causes rapid onset and rapid recovery from anesthesia with a single injection, but it accumulates rapidly with repeated or prolonged administration and thus slows recovery from anesthesia. Barbiturates are ligands of barbiturate receptors. In small doses, they allosterically enhance the effect of GABA on GABA A receptors. At the same time, the open state of chlorine channels lengthens, the entry of chlorine anions into neurons increases, and hyperpolarization and inhibition develop. In large doses, barbiturates directly increase the chloride permeability of neuronal membranes. In addition, they inhibit the release of excitatory mediators of the central nervous system - acetylcholine and glutamic acid, and block AMPA receptors ( quisqualate receptors) of glutamic acid. Barbiturates have cerebroprotective properties and can be used for this purpose.

Benzodiazepines are used mainly as anxiolytics and for sedation with preservation of consciousness. All benzodiazepine receptors allosterically enhance the cooperation of GABA with GABA A receptors, which is accompanied by an increase in the chloride conductivity of neurons, the development of hyperpolarization and inhibition. The reaction with benzodiazepine receptors occurs only in the presence of GABA. Remimazolam is the youngest benzodiazepine and has a very short duration of action due to rapid neutralization by plasma esterases.

Ketamine is chemically a derivative of phencyclidine. The synaptic mechanisms of action of ketamine are diverse. It is a non-competitive antagonist of the excitatory brain mediators glutamic and aspartic acids in relation to NMDA receptors. These receptors activate sodium, potassium and calcium channels in neuronal membranes. When receptors are blocked, depolarization is disrupted. In addition, ketamine stimulates the release of enkephalins and β-endorphin; inhibits the neuronal uptake of serotonin and norepinephrine. The latter effect is manifested by tachycardia, an increase in blood pressure and intracranial pressure. Ketamine dilates the bronchi. When recovering from ketamine anesthesia, delirium, hallucinations, and motor agitation are possible (these adverse events are prevented by the administration of droperidol or tranquilizers). An important therapeutic effect of ketamine is neuroprotective. As is known, in the first minutes of brain hypoxia, excitatory mediators - glutamic and aspartic acids - are released. Subsequent activation of NMDA receptors, increasing the concentration of sodium and calcium ions and osmotic pressure in the intracellular environment, causes swelling and death of neurons. Ketamine, as an antagonist of NMDA receptors, eliminates ion overload of neurons and the associated neurological deficit.

The newest intravenous anesthetic is dexmedetomidine. It is a highly selective α2-adrenergic receptor agonist with sedative, sympatholytic, hypnotic and analgesic effects. Its main action is as an agonist at the a2 receptors in the locus coeruleus.

Sources:

1. Theories of the mechanism of action - https://en.wikipedia.org/wiki/Theories_of_general_anaesthetic_action and https://www.esus.ru/php/content.php?id=744
2. Vengerovsky A.I., Lectures on pharmacology for doctors and pharmacists 2007
3. Kharkevich, Pharmacology ed. 10
4. Miller's anesthesia / Ronald D. Miller; associate editors, Neal H. Cohen, Lars I. Eriksson, Lee A. Fleisher, Jeanine P. Wiener-Kronish, William L. Young. - Eighth edition. 2015

Why is anesthesia required for surgery?

• creating optimal conditions for the surgeon’s work during surgery, which determines the level of quality of surgical treatment
• providing safe, effective pain relief to patients during surgery
• ensuring and maintaining the life of the patient before, during and after surgery
• protecting the patient from aggressive environmental factors acting on his body (biological, infectious, physical, chemical, etc.)
• Are there any restrictions for anesthesia?
• Today, there are no restrictions for anesthesia based on age or the patient’s somatic pathology. But there are only indications and contraindications for performing one or another anesthesia technique. The choice of anesthesia technique is made by an anesthesiologist-resuscitator.

Principles of anesthesia in ophthalmology

Anesthesia in ophthalmology is used not only for pain relief; along with this, it solves several other problems and performs certain functions. Among them:

• Complete immobilization of the eyeball.
• Ensuring stable normal intraocular pressure.
• Blocking the flow of moisture to the eye through the tear ducts.

When choosing a method of pain relief in ophthalmology, the age of the patients must be taken into account. As a rule, these are elderly and elderly people who, in addition to eye diseases, also have some systemic diseases that require certain conditions.

What is meant by the term “Anesthetic care”?

Anesthetic care for patients includes:

• assessment of the condition of patients before surgery, determination of anesthetic and surgical risks
• determining the feasibility and carrying out, if necessary, intensive therapy in order to prepare the patient for surgery
• prescribing premedication (drug preparation for anesthesia)
• selection of anesthesia method and necessary funds
• anesthesiological support for planned and emergency operations, dressings and complex diagnostic studies
• monitoring the condition of patients during anesthesia and conducting corrective therapy in order to prevent and eliminate life-threatening functional and metabolic disorders
• awakening patients after general anesthesia, if there are no indications for prolonged maintenance of drug-induced sleep
• elimination of pain caused by various causes (including incurable diseases) using special methods