Surface anesthesia

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. ... 

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 ... 

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. 

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. 

Other agents employed for surface anesthesia include the uncharged poli-docanol and the catamphiphilic cocaine, tetracaine, and lidocaine. 

EMLA cream (lidocaine 2.5% and prilocaine 2.5%) consists of a eutectic mixture of focal anesthetics. It is used to provide topical anesthetic to intact skin. Other topical preparations are effective only on mucosal surfaces. EMLA has been shown to reduce pain on venipuncture and provide substantial anesthesia for skin graft donor sites. No significant local or systemic toxicity has been demonstrated. 

Procaine is ineffective when administered through surface application, and is used only by injection. The onset of action for the drug is 2 to 5 minutes, and its duration of action is short. Vasoconstrictors are usually co-administered with this vasodilator drug to delay its absorption and to increase the duration of action. The drug is used for infiltration anesthesia, peripheral nerve block, and spinal anesthesia. 

The transplant of nasal mucosa was first prescribed by Naumann for the treatment of severe and bilateral conjunctival mucous shortages. In a study of 24 patients including 16 victims of a severe eye bum with symblepharons, Naumann has observed an improvement of the condition of the ocular surface in all of the cases. He has then concluded that the transplantation of nasal mucosa is better than the transplant of buccal mucosa. When the ocular damage is bilateral, the transplant of nasal mucosa would be perfectly recommended [11]. The nasal cavities are examined with an endoscope in order to find the zone to be sampled. The graft of nasal mucosa is taken from the septum, from the lower or medium turbinates. Under endoscopy and after local anesthesia, the anterior part of the turbinates is usually sampled. A hemostasis is cautiously operated and a gauze plugging of the cavity is set up. This... 

The induction of unconsciousness may be the result of exposure to excessive concentrations of toxic solvents such as carbon tetrachloride or vinyl chloride, as occasionally occurs in industrial situations (solvent narcosis). Also, volatile and nonvolatile anesthetic drugs such as halothane and thiopental, respectively, cause the same physiological effect. The mechanism(s) underlying anesthesia is not fully understood, although various theories have been proposed. Many of these have centered on the correlation between certain physicochemical properties and anesthetic potency. Thus, the oil/water partition coefficient, the ability to reduce surface tension, and the ability to induce the formation of clathrate compounds with water are all correlated with anesthetic potency. It seems that each of these characteristics are all connected to hydrophobicity, and so the site of action may be a hydrophobic region in a membrane or protein. Thus, again, physicochemical properties determine biological activity. 

The Duros implant requires implantation. To date, clinical trials have examined only one implant site, the mesial surface of the upper arm, - 10 cm above the antecubital crease. The procedure is performed on an outpatient basis using local anesthesia and requires less than 10 min tocarry out. The polished titanium surface minimizes any adhesions, permitting rapid explant and reimplant (at the same site) once the device is nearly expended. 

Clinical use Tetracaine is employed by ophthalmologists for surface anesthesia as a 0.5 % solution and by endoscopists for anesthesia of mucous membranes including airways as a 2.0 % solution. For topical anesthesia, a 4.0 % cream of tetracaine can also be used, which is, however, less effective than a lidocaine/prilocaine cream in preventing venipuncture-induced pain in children (van Kan et al., 1997). A combination of tetracaine with adrenaline and cocaine (TAC) is widely used for repair of... 

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. 

Anesthesia from intact surfaces requires that the drug must be absorbable. This excludes the intact skin. Cocaine, butyn, metycaine, and diothane are readily absorbed from mucous membranes, and are therefore efficient but also correspondingly toxic. Procaine and apothesine are relatively inabsorbable and therefore less applicable. Alypin and [3-eucaine are intermediate, but the order of absorbability varies for different mucosae. 

Those intimately familiar with bioassays have pushed these assays to their limits with respect to determining mechanisms of action at the whole animal level. Three obvious mechanisms are easy to discern. Two mechanisms, internal to the larvae, are toxicity and anesthesia.84 107 The third mechanism is external to the larva and involves preventing settlement by molecules adsorbing to the surface and changing its characteristics.29... 

One generally has to distinguish between surface anesthesia, infiltration anesthesia and conduction anesthesia (Fromherz 1922 Schaumann 1938 Camougis Tak-man 1971). Special local tolerance tests have been developed for each of these applications including peridural and intrathecal injections. 

PURPOSE AND RATIONALE Surface anesthesia is used to anesthetize the cornea and conjunctiva of the eye and the mucous membranes in the mouth. The classical pharmacological test is the blockade of the rabbit corneal reflex as described by Regnier (1923) that has become a standard test method for evaluating local anesthetics (FuBganger and Schaumann 1931 Ther 1953a Quevauviller 1971 Muschaweck et al. 1986). These pharmacological methods are only partially suitable to determine the irritancy potential of local anesthetic on mucus membranes. Luduena et al. (1960) compared the mucus membrane irritancy of mepivacaine and lidocaine by the eye irritation method according to Hoppe (1950) and Draize et al. (1944). 

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