Pharmacology of therapeutic blockades - anesthesia, anesthetics, etc. - Pain Clinic

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Pharmacology of therapeutic blockades - anesthesia, anesthetics, etc.

1. Local anesthetics.

The local anesthetics include those drugs which temporarily inhibit the excitability of receptors and the impulses conducting through nerve fibers. Most local anesthetics, and their are approximately 60, which are synthesized based on cocaine and nitrogen compounds forming two groups - ester (cocaine dicain etc.) and amide (lidocaine, trimecaine, bupivacaine, ropivacaine, etc). Each anesthetic is characterized by several parameters: the strength and duration of action, toxicity, latent period, the rate of penetration into the brain tissue and the strength of fixation to it, time and method of inactivation, elimination pathway, the stability in the environment and for sterilization. With increasing concentration of the anesthetic power increases approximately arithmetically, and toxicity - geometrically. Duration of action of local anesthetics is less dependent on its concentration.

The concentration of anesthetic in blood depends essentially on the method of injection, that is on tissue in which it is administered. Anesthetic concentration in plasma is achieved faster when administered intravenously or intraosseously , slower - in subcutaneous administration. So every time you hold a particular therapeutic blockade a careful selection of the concentration and dose  is required of to prevent vascular entry.

For local anesthetics are characteristic not only by analgesic effects. First of all, it is a persistent local vasodilatior for more than a day, it improves microcirculation and metabolism, stimulates reparative regeneration, resolves fibrotic and scar tissue, For local anesthetics are characteristic not only by analgesic effects. First of all, it is a persistent local vasodilatior for more than a day, it improves microcirculation and metabolism, stimulates reparative regeneration, resolves and fibrotic scar tissue, which leads to the regression of local dystrophic-degenerative process. Local anesthetics cause relaxation of smooth and striated muscle, especially when they are administered intramuscularly. At the same time remov pathological reflex muscle tension, eliminating abnormal posture and contracture, restored normal range of motion.

Features of anesthetics:

Procaine (Novocain) - ether anesthetic. Differs due to minimal toxicity and sufficient potency. Is the standard for evaluating the quality of all the other anesthetics. Many authors now prefer procaine in the blockade, for example, myofascial blockades. Their point of view, they justify the fact that procaine destroyed of mainly in the local tissues by pseudocholinesterase, thereby positively affecting the metabolism of these tissues. The main disadvantages of novocaine there are frequent diseases and allergies, lack of strength and duration of action.

Xylocaine (lidocaine) - amide type anesthetic, is metabolized primarily in the liver and to a lesser extent excreted through urine . Xylocaine is favorable then other of anesthetics due to rare combination of positive properties: increased stability in solution and to resterilization, low toxicity, high power action, good permeability, a short latent period after onset of action, expressed depth of anesthetic effect, almost absence of vascular and allergic reactions. Thanks to this Xylocaine is currently the most commonly used anesthetic.

Trimecain (mezocain). Very similar in chemical structure and action of Xylocaine is used quite often. It is inferior in all respects to xylocaine by 10-15%, identically having low toxicity and practically absence of vascular and allergic reactions.

Prilocaine (citanest). One of the few anesthetics which has less toxicity and approximately the same duration of anesthetic effect, as that of xylocaine, but inferior to the latter in the degree of penetration into the nervous tissue. It has a successful combination of two properties: a pronounced affinity for nervous tissue, which causes prolonged and deep local anesthesia, and the rapid decay in the liver under the influence of amides, which gives insignificant toxic complications and quick dissolution. These qualities allows use of tsitanesta it in pregnant women and children.

Mepivacaine (carbocain) - In strength the action is not inferior to xylocaine, but is toxic. Carbocain does not expand the blood vessels, in contrast to other anesthetics, which slows down bone resorption and provides greater duration than xylocaine. Carbocain is slowly inactivated in the body, so during overdosage  pronounced toxic effects are possible  , thus considered in the selection of the dose and concentration and is to be used with caution.

Bupivacaine (marcaine). The most toxic, but also the long-acting anesthetic. Duration of anesthesia may reach 16 hours.

2. Prolongators.

Vasoconstrictors are most often used to prolong the action of local anesthetic in the tissues. To a solution of anesthetic just before use, add adrenaline at a dilution of 1/200 000 - 1/400000, there is a small drop of 0.1% adrenaline in the syringe with 10-20 grams of the anesthetic solution. Adrenaline causes spasm of blood vessels at the periphery of infiltration and slowing down its resorption, prolonging the action of the local anesthetic, reducing its toxic and vascular reactions.

The other group prolongators are macromolecular compounds - dextran, blood substitutes, zhelatinol, protein blood products, autologous blood. Large molecules, adsorbing the anesthetic molecules on themselves. Dextrans prolong the anesthetic action about 1.5-2 times, autologous blood and blood products - in 4-8 times, and 8% gelatin solution - 2-3 days.

An ideal prolongator of this group can be considered – hemolysed autologous blood, which prolongs the action of the anesthetic to a day, moreover, it, unlike other large molecular preparations neither causes allergies nor is carcinogenic, free and available, has an immunostimulating effect and reduces the irritation in the local tissue while injecting the mixture. Other prolongatories are used less frequently.

3. Medications.

For the amplification and / or for special therapeutic effect of the blockade are used various medicaments.

Glucocorticoids - hormones of the adrenal cortex - the most frequently used for therapeutic blockade. Glucocorticoids play an important role in the metabolism of the body, affecting the carbohydrate and protein metabolism, less active against water and salt, which makes it different from the mineralocorticoids. Glucocorticoids have potent anti-inflammatory, desensitizing, anti-allergic, immunosuppressive, antishock and anti-toxic effect. From the point of view the preventive measures in therapeutic blockade, glucocorticoids are the perfect drug.

In dystrophic-degenerative processes of the musculoskeletal system, which is a major cause of pain syndromes in Neuroorthopedic diseases, the important role is played by non-specific autoimmune inflammatory processes taking place against the background of relative glucocorticoid deficiency in the local ischemic tissues. Introduction directly to a focus allows glucocorticoids to most effectively suppress therein these pathological processes.

To achieve a positive effect necessary to use a small amount of a glucocorticoid, which is almost fully implemented in the tissue degenerative focus, the resorptive effect is minimal but sufficient to eliminate the relative adrenal glucocorticoid insufficiency, which is frequently observed in chronic pain syndromes.

The use of steroid hormones in minimal doses, especially locally, is not dangerous. However, in patients with essential hypertension, gastric ulcer and duodenal ulcer, diabetes, purulent and septic processes, as well as in elderly patients corticosteroids should be used with extreme caution.

Often used hydrocortisone acetate or a microcrystalline suspension about 5-125 mg per blockade (varies with authors). Some authors point to the development of necrosis in the periarticular or intraarticular injection of microcrystalline suspension of hydrocortisone, explaining that the high concentration of the drug or lack of shaking before use. Therefore, hydrocortisone necessary to shake thoroughly before use, and introduce it in a solution with only local anesthetic.

Of the synthetic glucocorticoid dexamethasone increasingly used (soluble form - dexamethasone-21-phosphate sodium salt). Dexamethasone, thanks to the presence in its molecule, a fluorine atom, activates hydrocortisone 25-30 times, relatively little effect on the exchange of electrolytes. No known cases of soft tissue necrosis in its application. Per blockade 1.4 mg of dexamethasone is used.

Kenalog (triamcinolone acetonide), due to the slow absorption, long-acting local tissues. Therapeutic blockade with kenalog conducted primarily in chronic arthritis, arthrosis, to create a long-acting depots of glucocorticoid in the local tissues. Kenalog can be resused only in a week. Therefore, for its iadministration it is necessary to understand the exact localization of the pathological process. During the first blockades bears a great diagnostic burden therefore using   Kenalog is impractical.

Vitamin B complex most often used in medical blockade. Vitamin B1 - thiamine affects the conduction of nerve excitation at the synapses, in particular has a moderately severe ganglion blocking and curariform properties, potentiates the action of local anesthetics. Thiamine is generally well tolerated, but sometimes there may be a variety of allergic reactions up to anaphylactic shock. Usual daily doses for intramuscular administration: 0.025 - 0.05 g Thiamine chloride (1 ml of 2.5% or 5% solution) or 0.03 - 0.06 g thiamine bromide (1 mL of 3% or 6% solution).

Vitamin B6 - Pyridoxine is involved in biochemical metabolism of amino acids, lipids, histamine, plays an important role in the functioning of the central and peripheral nervous system. Pyridoxine hydrochloride is used as a 5% aqueous solution - 1 ml. Pyridoxine should be cautiously used in patients with gastric ulcer and duodenal ulcer, cirrhosis of the liver, coronary heart disease, adverse allergic anamnesis.

Vitamin B12 - Cyanocobalamin has high biological activity, is involved in the synthesis of amino acids, has a beneficial effect on the metabolism of carbohydrates and lipids, improves biochemical metabolism of the nervous system, improves tissue trophicity, has a mild analgesic effect. Cyanocobalamin is commonly used as 0.02% or 0.05% aqueous solution - 1 ml in blockade. Caution - should be used in patients with angina pectoris, a tendency to thrombosis, adverse allergic anamnesis. Cyanocobalamin is contraindicated in acute thromboembolism , erythremia, polycythemia.

Not recommended to co-administer vitamins B1, B6 and B12 in the same syringe. Vitamin B12 contributes to the destruction of other vitamins, can enhance the allergic reaction caused by vitamin B1. Vitamin B6 complicates the transformation of Vitamin B1 into a biologically active (phosphorylated) form.

4. Antihistamines.

In the development of any pain are involved histamine and histamine-like substances. They have both peripheral and central effects. Antihistamines relieves histamine-induced effects - smooth muscle spasm, swelling of the tissues, reduce the permeability of capillaries, prevents the development and facilitate the course of allergic reactions. Some drugs in this group (Diphenhydramine, Promethazine, suprastin) due to the central and peripheral cholinolytic activity having a pronounced effect on the nervous system - sedative, hypnotic, antiemetic effect, inhibit the conduction of nerve excitation in the autonomic ganglia, have a local anesthetic, anti-inflammatory and vasodilating effects.

Thus, antihistamines reduce some central and peripheral effects of pain , are prophylactic to toxic and allergic reactions, enhances the therapeutic effect of therapeutic blockade. Antihistamines are added to the anesthetic in the usual single dose: diphenhydramine 1% - 1 ml, or Promethazine 2.5% - 2 ml, or suprastin 2% - 1 ml.

5. Vasodilators

Are used to enhance the therapeutic effect of therapeutic blockade.

Papaverine, being myotropic antispasmodic, lowers the tone and reduces the contractility of smooth muscle, and this is due to its antispasmodic and vasodilatory effect. Normally added to a solution of 2 ml of anesthetic 2% papaverine hydrochloride.

No-shpa in chemical structure and pharmacological action differs little from papaverine, but has a longer and more pronounced vasodilating effect. Added to the mixture 2 mL of 2%.

For therapeutic blockade, we recommend using the following composition: lidocaine 1% - 5-10 ml, 1-2 mg of dexamethasone - 0.25-0.5 ml. You can add vitamin B12 - 0.05% - 1 ml, no-shpa 2% - 2 ml autologous blood - 4-5 ml.

A 20-gram syringe recruited consecutively these drugs, then produced a venipuncture and put autologous blood into the syringe. Contents of the syringe stirred for 30 seconds to complete hemolysis of erythrocytes, and then prepared mixture is injected into the painful area.

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