Detail NOTE ON Local Anesthetics PDF

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LOCAL ANESTHETICSDRUGSINTRODUCTIONIn a small area of the body, local anesthetics block sensation and, in higher concentrations, motor activity. They are used to block nerve conduction of sensory impulses from the periphery to the CNS by applying or injecting them. When action potential propagation i...

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LOCAL ANESTHETICS DRUGS INTRODUCTION In a small area of the body, local anesthetics block sensation and, in higher concentrations, motor activity. They are used to block nerve conduction of sensory impulses from the periphery to the CNS by applying or injecting them. When action potential propagation is prevented, local anesthesia is induced, and sensation cannot be transmitted from the source of stimulation to the brain. Local anesthetics prevent the transient increase in permeability of the nerve membrane to sodium that is required for an action potential to occur by blocking sodium ion channels. Topical administration, infiltration, ring blocks, peripheral nerve blocks, and neuraxial (spinal, epidural, or caudal) blocks are some of the delivery methods. Local anesthetics are most sensitive to the action of small, unmyelinated nerve fibers that conduct pain, temperature, and autonomic activity impulses. Local anesthetics share fundamental structural characteristics. A lipophilic group is linked to a carbon chain by an amide or ester linkage, which is then linked to a hydrophilic group. Bupivacaine [byoo-PIV-ah-kane], lidocaine [LYE-doe-kane], mepivacaine [muh-PIV-ah-kane], procaine [PROkane], ropivacaine [roe-PIV-ahkane], and tetracaine [TET-tra-kane] are the most commonly used local anesthetic compounds. Lidocaine is probably the most commonly used of these.

Cardiotoxicity is a side effect of bupivacaine. Because of its increased toxicity to the neonate, mepivacaine should not be used in obstetric anesthesia.

A. Metabolism The liver is the primary site of amide biotransformation. Prilocaine is metabolized in the kidney and plasma, and one of its metabolites can cause methemoglobinemia. Plasma cholinesterase bio transforms esters (pseudocholinesterase). Patients with a deficiency in pseudocholinesterase are likely to metabolize ester local anesthetics more slowly. At normal doses, however, this has little clinical impact. Reduced hepatic function puts the patient at risk for toxic effects, but it shouldn't lengthen the time that local anesthetics work.

B. Onset and duration of action Several factors influence the onset and duration of action of local anesthetics. These factors include tissue pH, drug pKa, nerve morphology, concentration, and drug lipid solubility. The pH of the tissue and the drug's pKa are the most important of these. These compounds are charged at physiologic pH. The ionized form binds to the sodium channel's protein receptor, inhibiting its function and resulting in local anesthesia. The pH of infection sites may drop, causing onset to be delayed or even prevented. Higher concentrations and lipid solubility improve onset to some extent within certain limits. The length of time the drug can stay in the nerve to block sodium channels determines the duration of action.

C. Actions When local anesthetics are used alone, they cause vasodilation, which leads to rapid diffusion away from the site of action and a short duration of action. The rate of local anesthetic diffusion and absorption is reduced when the vasoconstrictor epinephrine is added to the local anesthetic. This reduces systemic toxicity while also lengthening the duration of action. The duration of action of local anesthesia is determined by redistribution, not biotransformation, and is unaffected by hepatic function. Some of these local anesthetics have additional benefits, such as lidocaine's antiarrhythmic effect when given intravenously.

D. Allergic reactions Patients frequently report allergic reactions to local anesthetics, but investigations reveal that the majority of these are psychogenic. Psychogenic reactions are frequently misdiagnosed as allergic reactions, and symptoms such as urticaria, edema, and bronchospasm can be mistaken for them. True amide allergy is extremely uncommon, whereas the ester procaine is slightly more allergenic. Because the allergenic component is the breakdown product para-aminobenzoic acid, which is produced by the metabolism of all esters, an allergy to one ester eliminates the use of another ester. An allergy to one amide, on the other hand, does not preclude the use of another amide. Other compounds in the local

anesthetic, such as preservatives in multidose vials, may cause an allergic reaction in the patient.

E. Administration to children and the elderly To avoid inadvertent overdosing, the maximum dose based on the child's weight should be calculated before administering local anesthetic. The response to local anesthetics is not significantly different in younger and older adults, and the doses required for each block are the same regardless of patient age. However, in elderly patients with compromised liver function, it is prudent to stay well below the maximum recommended doses. Because elderly patients are more likely to have cardiovascular problems, lowering the epinephrine dose may be prudent. Previous guidelines prohibited the use of specific local anesthetics in patients who are susceptible to MH, which has now been proven to be incorrect. All local anesthetics are now widely accepted as safe for these patients.

F. Systemic local anesthetic toxicity Repeated injections or a single inadvertent IV injection could result in toxic blood levels of the drug. The importance of aspiration before each injection cannot be overstated. Local anesthetic systemic toxicity manifests itself in a variety of ways, including signs, symptoms, and timing. The most important step in treating local anesthetic toxicity is to rule out the possibility in any patient who experiences altered mental status or cardiovascular instability after receiving a

local anesthetic injection. CNS symptoms (excitation or depression of the central nervous system) can be obvious, but they can also be subtle, nonspecific, or absent. Airway management, breathing and circulation support, seizure suppression, and, if necessary, cardiopulmonary resuscitation are all part of the treatment for systemic local anesthetic toxicity. Lipid rescue therapy, which involves administering a 20% lipid emulsion infusion, is a promising asset in treating local anesthetic toxicity....