Local anesthetic prevention

Anesthetics fall into two broad classes local and general. They behave as then-names imply. Local anesthetics prevent pain locally. A dentist may give you a shot of procaine hydrochloride, Novocain, or other local anesthetic, to prevent the pain of hlling or extracting a tooth. But if you stub your toe getting out of the dentist s chair, your toe is going to hurt. Local anesthetics may help to alleviate the pain of sunburn but they will not help with that of a concomitant headache. 

Lidocaine hydrochloride Local anesthetic Prevent and control pain during certain medical procedures, numb and treat urinary tract inflammation (urethritis), and numb mucous membranes Xylocaine, Anestacon 2.0... 

Local anesthetics prevent the voltage-dependent increase in sodium ion conductance and thus block the initiation and propagation of action potentials. This occurs via two mechanisms. Firstly, non-specific activity on the membrane surface causes the membrane to swell, physically preventing sodium ions getting through the membrane pores. Secondly, blockade of sodium channels occurs. 

These agents are often combined with a vasoconstrictant such as epinephrine [51-43-4]. By using such a combination, the local anesthetic is held in the area for a longer period of time and its effect extended hemorrhage is minimized, blood loss prevented, and a better surgical repair obtained. 

Epidural analgesia is frequently used for lower extremity procedures and pain (e.g., knee surgery, labor pain, and some abdominal procedures). Intermittent bolus or continuous infusion of preservative-free opioids (morphine, hydromorphone, or fentanyl) and local anesthetics (bupivacaine) may be used for epidural analgesia. Opiates given by this route may cause pruritus that is relieved by naloxone. Adverse effects including respiratory depression, hypotension, and urinary retention may occur. When epidural routes are used in narcotic-dependent patients, systemic analgesics must also be used to prevent withdrawal since the opioid is not absorbed and remains in the epidural space. Doses of opioids used in epidural analgesia are 10 times less than intravenous doses, and intrathecal doses are 10 times less than epidural doses (i.e., 10 mg of IV morphine is equivalent to 1 mg epidural morphine and 0.1 mg of intrathecally administered morphine).45... 

However, local anesthetics may be helpful when abrasion accompanies the injury.39 Application of an over-the-counter antibiotic ointment containing an anesthetic may provide soothing relief, promote healing of abrasions, and prevent soft-tissue infection. Minor abrasions should be cleansed thoroughly with mild soap and water before application. More severe abrasions may require removal of debris or foreign bodies by a clinician followed by irrigation with normal saline. 

The answer is d. (Hardman, p T36J The addition of a vasoconstrictor, such as epinephrine or phenylephrine, to certain short-acting, local anesthetics is a common practice in order to prevent the rapid systemic absorption of the local anesthetics, to prolong the local action, and to decrease the potential systemic reactions. Some local anesthetics cause vasodilation, which allows more compound to escape the tissue and enter the blood. Procaine is an ester-type local anesthetic with a short duration of action due to rather rapid biotransformation in the plasma by cholinesterases. The duration of action of the drug during infiltration anesthesia is greatly increased by the addition of epinephrine, which reduces the vasodilation caused by procaine. 

Lignocaine, originally introduced as a local anesthetic, is now widely used for the treatment and prevention of ventricular arrhythmias. When used for this purpose, it is usually administered either by intramuscular injection, or as a bolus intravenously, or, more commonly, by constant intravenous infusion. For clinical purposes, lignocaine measurements arc usually carried out on plasma collected either while the patient is receiving a constant intravenous infusion or at a specified time after the last intramuscular injection. Colorimetric methods have been used in the past (S29), but, because they lack both sensitivity and specificity, may yield false and misleading results. They have largely been replaced by GLC techniques (A3, El, K5). 

Like chloroquine, quinine binds with plasmodium DNA, thus interfering in the synthesis of nucleic acids and preventing its replication and transcription. Quinine also suppresses a large portion of the enzymatic system and therefore it is characterized as a general protoplasmid toxin. This fact agrees well with the action of quinine on membranes, its local anesthetizing and its cardiodepressive effects. 

Local anesthetics are used extensively on the mucous membranes in the nose, mouth, tracheobronchial tree, and urethra. The vasoconstriction produced by some local anesthetics, cocaine especially, adds a very important advantage to their use in the nose by preventing bleeding and inducing tissue shrinkage. Topical anesthesia permits many diagnostic procedures in the awake patient, and when it is combined with infiltration techniques, excellent anesthesia may be obtained for many... 

Excellent and rapid anesthetization of an extremity can be obtained easily. Following insertion of an intravenous catheter in the limb of interest, a rubber bandage is used to force blood out of the limb, and a tourniquet is applied to prevent the blood from reentering a dilute solution of local anesthetic, most commonly lido-caine, is then injected intravenously. This technique fills the limb s vasculature and carries the anesthetic solution to the nerve by means of the blood supply. Because of the pain produced by a tourniquet after some time, this procedure usually is limited to less than 1 hour. The systemic blood levels of drug achieved after tourniquet release generally remain below toxic levels. 

Mechanism of Action An antiarrhythmicthat prevents sodium current across myocardial cell membranes. Has potent local anesthetic activity and membrane stabilizing effects. Slows AV and His-Purkinje conduction and decreases action potential duration and effective refractory period. Therapeutic Effect Suppresses ventricular arrhythmias. 

An ester group can be introduced into a local anesthetic, such as tolycaine (3.26), to prevent the drug from reaching the CNS if it is injected intravascularly hy accident or abuse. The ester group is fairly stable in the tissues but is very rapidly hydrolyzed in the serum to the polar carboxylic acid, which cannot penetrate the blood-hrain barrier. 

If seizures do occur, it is important to prevent hypoxemia and acidosis. Although administration of oxygen does not prevent seizure activity, hyperoxemia may be beneficial after onset of seizures. Hypercapnia and acidosis may lower the seizure threshold, and so hyperventilation is recommended during treatment of seizures. In addition, hyperventilation increases blood pH, which in turn lowers extracellular potassium. This action hyperpolarizes the transmembrane potential of axons, which favors the resting (or low-affinity) state of the sodium channels, resulting in decreased local anesthetic toxicity. 

Seizures induced by local anesthetics are usually treated with intravenous anesthetic drugs (eg, thiopental 1-2 mg/kg, propofol 0.5-1 mg/kg, midazolam 0.03-0.06 mg/kg). The muscular manifestations of a seizure can be blocked using a short-acting neuromuscular relaxant drug (eg, succinylcholine, 0.25-0.5 mg/kg IV). It should be emphasized that succinylcholine does not alter the CNS manifestations of local anesthetic-induced seizure activity. Rapid tracheal intubation can prevent pulmonary aspiration of gastric contents and facilitate hyperventilation. 

Anesthetics prevent neurons from transmitting sensations to the brain. Local anesthetics are applied either topically to numb the skin or by injection to numb deeper tissues. These mild anesthetics are useful for minor surgical or dental procedures. As described earlier, cocaine was the first medically used local anesthetic. Others having fewer side effects soon followed, such as the ones shown in Figure 14.39 on page 508. In general, molecules that... 

What does cocaine do in the brain First, it binds to sodium ion channels and blocks them from functioning. This action stops the flow of action potentials and prevents neurons from communicating with each other. Cocaine also blocks the conduction of pain signals, which explains why, after it was isolated from the coca plant ((Erythroxylon coca) in 1855, it was used as a local anesthetic, including for the eye and for toothaches. But ultimately, its anesthetic actions would be discovered to have... 

FIGURE 12-3 Schematic diagram showing mechanism of action of local anesthetics on the nerve membrane. Local anesthetics appear to bind directly to a site within the sodium channel, thereby locking the channel in a closed position, thus preventing sodium entry and action potential propagation. 

This involves considerable art, which must be learned in the clinic. It falls into two divisions (1) surface application to the mucous membranes, especially of the eye, nose, throat, and urethra and (2) injections about nerves, in different parts of their course and distribution, from their spinal roots to their ultimate fibrils. The advantages and disadvantages in comparison with general anesthesia and the selection of the local anesthetic agent also depend on clinical discrimination. Nervous, fearful, and excitable patients often suffer severely from apprehension, which also disposes toward accidents. They may be at least somewhat quieted by sedatives, morphine (0.015 g hypodermically) half an hour before the operation, or by barbiturates. The latter also tend to prevent convulsions. 

The treatment of poisoning by local anesthetics should begin with prevention and the selection, dosage, and technique of the administration gross errors and carelessness have caused many deaths. The previous administration of a sedative, especially of the barbituric series, diminishes the risk by suppressing the convulsions and their interference with respiration, so that animals survive one and a half to four times the ordinary fatal dose of cocaine or procaine if administered hypodermically. 

The test chemical should be placed in the conjunctival sac of one eye of each animal after gently pulling the lower lid away from the eyeball. The lids are then gently held together for about 1 second to prevent loss of the material. The other eye, which remains untreated, serves as a control. If it is considered that the chemical could cause extreme pain, a local anaesthetic may be used prior to installation of the test chemical. The type and concentration of the local anesthetic should be carefully selected to ensure that no significant differences in reaction to the test chemical would result from its use. The control eye should be similarly anesthetized. 

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