Anesthesia/anesthetics local

The onset of action is fast (within 60 seconds) for the intravenous anesthetic agents and somewhat slower for inhalation and local anesthetics. The induction time for inhalation agents is a function of the equiUbrium estabUshed between the alveolar concentration relative to the inspired concentration of the gas. Onset of anesthesia can be enhanced by increasing the inspired concentration to approximately twice the desired alveolar concentration, then reducing the concentration once induction is achieved (3). The onset of local anesthetic action is influenced by the site, route, dosage (volume and concentration), and pH at the injection site. 

Local anesthetics produce anesthesia by blocking nerve impulse conduction in sensory, as well as motor nerve, fibers. Nerve impulses are initiated by membrane depolarization, effected by the opening of a sodium ion channel and an influx of sodium ions. Local anesthetics act by inhibiting the channel s opening they bind to a receptor located in the channel s interior. The degree of blockage on an isolated nerve depends not only on the amount of dmg, but also on the rate of nerve stimulation (153—156). 

Specific Local Anesthetic Agents. Clinically used local anesthetics and the methods of appHcation are summarized in Table 5. Procaine hydrochloride [51-05-8] (Novocain), introduced in 1905, is a relatively weak anesthetic having along onset and short duration of action. Its primary use is in infiltration anesthesia and differential spinal blocks. The low potency and low systemic toxicity result from rapid hydrolysis. The 4-arninobenzoic acid... 

Lidocaine hydrochloride [73-78-9] (Xylocaine), is the most versatile local anesthetic agent because of its moderate potency and duration of action, rapid onset, topical activity, and low toxicity. Its main indications are for infiltration, peripheral nerve blocks, extradural anesthesia, and in spinal anesthesia where a duration of 30 to 60 min is desirable. Because of its vasodilator activity, addition of the vasoconstrictor, epinephrine, increases the duration of action of Hdocaine markedly. It is also available in ointment or aerosol preparations for a variety of topical appHcations. 

Toxic Reactions of the Skin Irritation is the most common reaction of the skin. Skin irritation is usually a local inflammatory reaction. The most common skin irritants are solvents dehydrating, oxidizing, or reducing compounds and cosmetic compounds. Acids and alkalies are common irritants. Irritation reactions can be divided into acute irritation and corrosion. Necrosis of the surface of the skin is typical for corrosion. Acids and alkalies also cause chemical burns. Phenols, organotin compounds, hydrogen fluoride, and yellow phosphorus may cause serious burns. Phenol also causes local anesthesia, in fact it has been used as a local anesthetic in minor ear operations such as puncture of the tympanous membrane in cases of otitis. ... 

Sate the uses of local anesthesia, methods of administration, and nursing responsibilities when administering a local anesthetic. 

Topical anesfliesia involves die application of die anes-flietic to die surface of the skin, open area, or mucous membrane The anesthetic may be applied wifli a cotton swab or sprayed on the area This type of anesthesia may be used to desensitize the skin or mucous membrane to the injection of a deeper local anesthetic. In some instances, topical anesthetics may be applied by the nurse ... 

Local infiltration anesthesia is die injection of a local anesthetic druginto tissues. This type of anesfliesia may be used for dental procedures, die suturing of small wounds, or making an incision into a small area, such as that required for removing a superficial piece of tissue for biopsy. 

Regional anesthesia is the injection of a local anesthetic around nerves so that the area supplied by these nerves will not send pain signals to the brain. The anesthetized area is usually larger than the area affected by... 

Spinal anesthesia is a type of regional anesthesia that involves the injection of a local anesthetic drug into the subarachnoid space of die spinal cord, usually at the level of the second lumbar vertebra There is a loss of feeling (anesdiesia) and movement in the lower extremities, lower abdomen, and perineum. 

A conduction block is a type of regional anesthesia produced by injection of a local anesthetic drug into or near a nerve trunk. Examples of a conduction block include an epidural block (injection of a local anesthetic into the space surrounding the dura of the spinal cord) a trails sacral (caudal) block (injection of a local anesthetic into the epidural space at the level of the sacrococcygeal notch) and brachial plexus block (injection of a local anesdietic into the brachial plexus). Epidural, especially, and trailssacral blocks are often used in obstetrics. A brachial plexus block may be used for surgery of the arm or hand. 

Epidural anesthesia is administered by injecting local anesthetic into the epidural space. Located outside the spinal cord on its dorsal surface, the epidural space contains fat and is highly vascular. Therefore, this form of anesthesia can be performed safely at any level of the spinal cord. Furthermore, a catheter may be placed into the epidural space, allowing for continuous infusions or repeated bolus administrations of anesthetic. 

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. 

J. E., Peray, P.A., Desch, G., Sassine, A. and Eledjam, J.J. (1996) Comparative electrophysiologic and hemodynamic effects of several amide local anesthetic drugs in anesthetized dogs. Anesthesia and Analgesia, 82, 648—656. 

Local anesthesia involves the blockade of nerve conduction in order to stop sensation. Because local anesthetics act on all nerve fibers they may also temporarily create motor paralysis. The usefulness of local anesthetics is their ability to completely block axonal transduction, which is reversible and without any apparent lasting effects. 

Forms of local anesthesia. Local anesthetics are applied via different routes, including infiltration of the tissue (infiltration anesthesia] or injection next to the nerve branch carrying fibers from the region to be anesthetized (conduction anesthesia of the nerve, spinal anesthesia of segmental dorsal roots), or by application to the surface of the skin or mucosa (surface anesthesia]. In each case, the local anesthetic drug is required to diffuse to the nerves concerned from a depot placed in the tissue or on the skin. 

In regional anesthesia (spinal anesthesia) with a local anesthetic (p. 204), nociception is eliminated, while consciousness is preserved. This procedure, therefore, does not fall under the definition of general anesthesia... 

Infiltration anesthesia The direct introduction of local anesthetic into the skin or deeper tissue for surgical intervention is called infiltration anesthesia. 

Spinal anesthesia Spinal anesthesia is the introduction of local anesthetics directly into the spinal fluid, which causes a sympathetic blockage, or loss of feeling as well as muscle relaxation resulting from the interaction of anesthetic with every spinal nerve tract. This method is used during major surgical interventions. As a rule, lidocaine, mepivacaine, and bupivacaine are used for this purpose. 

Epidural anesthesia This term is understood to be an introduction of local anesthetic into the spinal cord membrane of the intervertebral space. It is used during obstetrical and gynecological interventions that do not require a fast development of anesthesia. Drugs such as lidocaine, mepivacaine, bupivacaine, ethidocaine, and chloroprocaine are used for this purpose. 

A mechanism of local anesthetic action in which they serve as sodium channel blockers has been proposed. According to this mechanism, the molecular targets of local anesthetic action are the voltage-requiring sodium channels, which are present in all the neurons. The process of local anesthesia by respective drugs can be schematically represented in the following manner. 

Tetracaine is a strong, long-lasting local anesthetic. It is primarily used in spinal cord anesthesia. The most well-known synonyms of tetracaine are pontocaine and butylcaine. 

Lidocaine is the most widely used local anesthetic. Its excellent therapeutic activity is fast-acting and lasts sufficiently long to make it suitable for practically any clinical use. It stabilizes cell membranes, blocks sodium channels, facilitates the secretion of potassium ions out of the cell, and speeds up the repolarization process in the cell membrane. It is used for terminal infiltration, block, epidural, and spinal anesthesia during operational interventions in dentistry, otolaryngology, obstetrics, and gynecology. It is also used for premature ventricular extrasystole and tachycardia, especially in the acute phase of cardiac infarction. Synonyms for this drug are xylocaine, neflurane, and many others. 

Local anesthetics are used for topical anesthesia, local infiltration, peripheral nerve block, paravertebral anesthesia, intravenous block also known as regional anesthesia, epidural block, and spinal i.e. subarachnoid blockade. The local anesthetics may be divided into two main groups, the esters and the amide-type agents. 

Amide-type agents include articaine, lidocaine, bupivacaine, prilocaine, mepivacain and ropiva-caine. These are metabolized in the liver by microsomal enzymes with amidase activity. The amide group is preferred for parenteral and local use. If by accident rapidly administered intravascularly these agents, especially bupivacaine but also lidocaine, can produce serious and potentially lethal adverse effects including convulsions and cardiac arrest. They can more easily accumulate after multiple administrations. Intravenous lidocaine is sometimes used for regional anesthesia, for infiltration procedures, for the induction of nerve blockade and for epidural anesthesia. However, it is also used as an antiarrhythmic. Bupivacaine is a long-acting local anesthetic used for peripheral nerve blocks and epidural anesthesia. 

The vasoconstrictor actions of epinephrine and norepinephrine have been used to prolong the action of local anesthetics by reducing local blood flow in the region of the injection. Epinephrine has been used as a topical hemostatic agent for the control of local hemorrhage. Norepinephrine is infused intravenously to combat systemic hypotension during spinal anesthesia or other hypotensive conditions in which peripheral resistance is low, but it is not used to combat the hypotension due to most types of shock. In shock, marked sympathetic activity is already present, and perfusion of organs, such as the kidneys, may be jeopardized by norepinephrine administration. 

The first clinical uses of a local anesthetic agent occurred in 1884, when cocaine was employed as a topical agent for eye surgery and to produce a nerve block. These events inaugurated a new era, that of regional anesthesia. New applications were developed, including spinal, epidural, and caudal anesthesia. The search for a better local anesthetic led to chemical synthesis of a number of other compounds that have more selective local anesthetic properties and few systemic side effects. 

Although the characteristics of an ideal local anesthetic are easily identifiable, synthesis of a compound possessing all these properties has not been accomplished. The compounds discussed in the following sections fall short of the ideal in at least one aspect. However, the judicious choice of a particular agent for a particular need will permit the practitioner to employ local anesthesia effectively and safely. 

---