for Laser Surgery


A number of laser procedures such as laser resurfacing or tattoo removal are associated with some discomfort.

Anesthesias provide a reversible loss of sensation and alleviate most of the discomfort.

The techniques most commonly used are topical anesthesia and regional anesthesia with or without systemic analgesics and/or anxiolytics.

Concomitant cooling, vibration or pinching of the area can be use to minimize the pain perception.




Introduction


Local anesthesia has been one of the most notable advancements in surgery for the past century. Prior to the advent of local anesthetics, patients had few options for dealing with pain. Inebriation was a common, albeit ineffective, practice.

In the early nineteenth century, it was reported that the Peruvian Indians experienced numbness around the lips after chewing leaves of the coca plant, Erythroxylon coca. In 1859, Albert Niemann, a German chemist, first extracted and isolated cocaine from the coca plant in a purified form.

Local anesthetics were first introduced into medical practice in 1884 when ophthalmologist Carl Kollar used purified cocaine as a topical agent by applying it to the cornea of animal models. In its first clinical application, cocaine was used in an operation for glaucoma. In the same year, Halsted and Hall infused cocaine into the brachial vein of a patient to achieve regional anesthesia.

Dentists used to dissolve cocaine hydrochloride pills in water and performed nerve infiltrations and blocks after drawing the mixture into a syringe. Although it provided profound local anesthesia that revolutionized dentistry and medical practice, the extreme vasoconstrictive action of cocaine often lead to tissue necrosis.

By the 1900s, cocaine’s narcotic effects had become well recognized, including its mood-altering effects and cardiac and central nervous system stimulation. In addition, due to cocaine’s severe physical and psychological dependence, its use for local anesthesia was discontinued.

In 1904, Alfred Einhoin synthesized procaine (Novacaine), an ester anesthetic, in search for a safer and less toxic local anesthetic. Novacaine was the gold standard for topical anesthetics for the following 40 years, until Nils Lofgren synthesized lidocaine. Lidocaine was the first of the amide group of local anesthetics, which exhibited greater potency, fewer allergic reactions, and a more rapid onset of action.

Proper local anesthesia is vital in laser surgery, as most laser procedures are associated with some discomfort, ranging from mild warmth to sever burning pain. An understanding of various local anesthesia indications, techniques, and side effects will provide a basis for the selection of the most appropriate anesthetic agent for the given procedure.


Classification and Mechanism of Action










Local anesthetics share a similar chemical structure: a hydrophilic amine portion, an intermediate chain, and a lipophilic aromatic ring.

They are divided into amide or ester groups due to the intermediate chain.

Anesthetics act by disrupting sodium channel activity and blocking electrical impulse transmission at nerve endings.

Most local anesthetics except cocaine have vasodilatory effects.

Epinephrine is often added as a vasoconstrictive agent and has the added benefit of minimizing systemic effects and increasing the length of anesthetic effect.

Local anesthetic agents are functionally divided into the amino amide and amino ester groups (Fig. 1). Both groups share a similar chemical structure that contains three components: a hydrophilic amine portion, an intermediate chain, and a lypophilic aromatic ring. The intermediate chain contains either an ester or amide linkage which categorizes the agent.

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Fig. 1
Chemical structure of local anesthetic agents

Pain sensation is carried via C fiber (unmyelinated nerve, 0.5–1 μm) and A-delta fiber (2–5 μm). These fibers are more sensitive to the actions of local anesthetics as compared to large nerve fibers. Consequently, patients may be able to feel sensations such as pressure and vibration while being insensitive to pain.

The effectiveness of a local anesthetic depends on its ability to diffuse across the nerve cell’s membrane (lipophilic properties) and then convert to a cationic form that results in better protein binding (hydrophilic properties). Higher lipid solubility of an agent increases its diffusion through a cell’s membrane, leading to higher potency and lower concentrations needed to produce the desired result. However, greater protein-binding ability leads to a longer duration of action due to a higher affinity for intracellular receptors.

Most local anesthetics except cocaine have vasodilatory effects, which increases chances of excessive bleeding during the course of the procedure. To counteract this, epinephrine is often added as a vasoconstrictive agent, which has the added benefit of increasing the local sequestration of the anesthetic, minimizing systemic effects and increasing the length of anesthetic effect.


Topical Anesthesia










Topical anesthetics are used for superficial laser surgery and minor dermatological procedures.

Quick procedures that require only a few seconds of anesthesia can utilize cooling agent.

Lidocaine is the most widely used topical anesthetics.

Occlusion with a plastic wrap is a way of enhancing anesthetic penetration and delivery to the dermis.

Methemoglobinemia is a major concern regarding the use of EMLA, particularly in neonates.

Topically-applied anesthetic agents are suitable for use in superficial laser surgery and minor dermatological procedures. Topical anesthetics act by disrupting sodium channel activity and blocking electrical impulse transmission at nerve endings. They can also be used to permit painless needle insertion when infiltrative anesthesia is required. These agents are usually encountered in an oil-in-water base or similar cream compound. For quick procedures, cooling sprays such as dichlorotetrafluoroethane or ethylchloride may be used.

The skin’s stratum corneum serves as a mechanical barrier slowing down topical anesthesia penetration. Thus, the vehicle is very important in helping the anesthetic traverse the epidermis. The thickness of the stratum corneum varies with anatomical locations, altering the time to achieve adequate anesthesia. Occlusion with a plastic wrap is one way of enhancing product penetration and delivery to the dermis. This method also hydrates the skin, which may help explain the lower incidence of side effects seen after its use in carbon dioxide resurfacing laser procedures.

The most widely used topical anesthetic is EMLA cream, a 5% eutectic mixture of lidocaine 2.5% and prilocaine 2.5% in an oil-in-water emulsion. It must be applied under an occlusive dermal dressing for 60 min for adequate dermal anesthesia. EMLA has been shown to provide adequate anesthesia for pulsed dye laser treatments of Port Wine Stains (PWSs) without affecting the laser treatment’s efficacy. It is also used in ablative laser resurfacing. The major concern regarding the use of EMLA relates to the potential risk of methemoglobinemia, also a known side effect of prilocaine. It is more likely in neonates, especially in pre-term infant.

LMX-4 (formerly called ELA-Max) is a 4% lidocaine cream in a liposomal vehicle that only requires 15–45 min of application time without the need of an occlusive dressing following its application. LMX-5 is the 5% concentration and although it is marketed for anorectal use, it can also be applied as a topical anesthetic agent.

Betacaine-LA ointment contains lidocaine, prilocaine and a vasoconstrictor in a liquid paraffin ointment. It has a recommended application time of 30–45 min without the requirement of an occlusive dressing.

Tetracaine gel is a long-acting ester anesthetic composed of 4% tetracaine in a lecithin gel. Its time application is 30 min under an occlusive dressing.

The 7% lidocaine and 7% tetracaine (LT) peel is a self occlusive topical anesthetic, presenting as a 1:1 eutectic mixture that is applied as a cream and air-dries to form a flexible membrane that can be peeled from the skin. The recommended application time is 30 min. LT peel has been successfully used in a variety of dermatological procedures such as PDL therapy, laser-assisted hair removal, non-ablative facial laser resurfacing, laser therapy for leg veins, cutaneous laser resurfacing and laser-assisted tattoo removal. It has shown to have a superior anesthetic efficacy in adult patients undergoing a variety of cutaneous procedures when compared to EMLA cream.

Quick procedures that require only a few seconds of anesthesia can utilize cooling refrigerant sprays, such as dichlorotetrafluoroethane or ethyl chloride. Ice cubes can also be used, especially to give painless injections in children.


Infiltrative Anesthesia










Local infiltration can be performed for procedures associated with more pain such as ablative laser resurfacing.

The ester-linked anesthetics have a much greater allergenic potential than the amide-linked anesthetics.

Cross reactivity exists among ester-linked anesthetics, PABA, paraphenylenediamine, and sulfo­namides.

Infiltrative anesthesia is the most commonly performed form of skin anesthesia. The concentration and selection of infiltrative anesthetics depend on the procedure to be performed, the speed of onset desired, and duration of action required. For quick and simple procedures, a short-acting anesthetic with rapid onset can be chosen. As for larger procedures, longer-acting agents will be needed.

When an extensive area of the skin is to be anesthetized, the anesthetic should be diluted in order to limit the total amount applied to the tissue and to reduce possible systemic adverse reactions. Conversely, higher concentrations can be used in smaller quantities for specific nerve blocks.

The ester-linked anesthetics (i.e. procaine, cocaine, tetracaine) have decreased in popularity due to allergic and cross-reactions with benzocaine, para-aminobenzoic acid (PABA), paraphenylenediamine, and sulfonamides.

Most procedures are performed using 1% or 2% lidocaine providing quick onset, long duration (45 min to 3 h without epinephrine), and low allergic reaction potential. When combined with epinephrine, an even longer anesthetic response can be achieved.

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Apr 27, 2016 | Posted by in Dermatology | Comments Off on for Laser Surgery

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