topical anesthesia

Topical Anesthesia 

Definition

Topical anesthesia is a condition of temporary numbness caused by applying a substance directly to a surface of the body. Loss of feeling occurs in the specific areas touched by the anesthetic substance.

Purpose

Topical anesthesia typically either relieves existing pain from a body surface or prevents pain during medical examinations or procedures. Body surfaces include both skin and mucous membranes, which are the moist linings of areas such as the inside of the mouth or nose. Occasionally, use of a topical anesthetic may help clarify whether a patient's pain comes from a body surface, which the substance is able to touch, or from deeper structures beyond the reach of the substance. A mucous membrane, an area of skin, or areas just beneath the skin's surface temporarily lose feeling during topical anesthesia.

Precautions

Topical anesthetic medications must be selected carefully and used in proper amounts in order to prevent harmful reactions. For instance, some topical drugs should be used only on intact skin to avoid rapid absorption into the body. Therefore, it is important to choose the right type and dosage of anesthetic for each specific purpose.

Description

Most drugs in the early 2000s used to cause topical anesthesia have at least some chemical similarity to cocaine, which was recognized as a topical anesthetic in the early 1900s. These drugs work by blocking nerve impulses that carry pain messages to the brain. Commonly used, twenty-first-century drugs include benzocaine, lidocaine, prilocaine, and tetracaine, These drugs come in several application forms, such as cream, jelly, ointment, solution, and spray, are available in varying strengths, and may be used alone or in combinations.

One common use for topical anesthetics is to relieve pain from problems such as sores in the mouth, skin scrapes, and hemorrhoids. A person typically applies a cream or jelly to the affected area. Numbness begins within a few minutes, and the anesthetic effect may last an hour or more. Repeated applications are often necessary.

The other broad category of use for topical anesthetics is to prevent pain from medical examinations or procedures on areas such as the eye, nose, throat, urethra, rectum, or skin. For example, even a single drop of anesthetic may allow examination of a painfully irritated eye or removal of a speck of dirt from the eye surface. Careful inspection of a nostril or insertion of a urinary drainage tube into the urethra may be difficult or impossible without the use of topical anesthetic spray or jelly beforehand.

Many uses of topical anesthetics involve application to the skin. Physicians and patients have long hoped for a way to numb an area of skin without having to use a needle to inject anesthetic. Original topical anesthetics were not effective in this way. A newer drug preparation called eutectic mixture of local anesthetics (EMLA, lidocaine 2.5%, and prilocaine 2.5%) can be used as a cream on intact skin. When applied for about 60 minutes, EMLA numbs the skin and penetrates as far as 5 mm below the surface. EMLA may help patients by decreasing the pain of needle pricks or simple skin procedures, such as repair of small lacerations. The main drawback to EMLA is that it takes so long for the anesthetic effect to begin, thus reducing its usefulness in settings such as the emergency rooms. Other drug combinations such as tetracaine, epinephrine (adrenaline), and cocaine (TAC), or lidocaine, epinephrine, and tetracaine (LET) have their own advantages and disadvantages.

The application of ice to a body area is a primitive method of producing topical anesthesia. Chemicals such as ethyl chloride can be sprayed onto intact skin to produce a momentary freezing and numbing effect.

Key terms

Anesthetic — Not having sensation; related to the loss of sensation; or, a substance that produces loss of sensation.

EMLA — Eutectic mixture of local anesthetics, a drug combination for use on intact skin.

LET — A topical anesthetic mixture containing lidocaine, epinephrine, and tetracaine.

Mucous membranes — Moist linings of body surfaces such as the inside of the mouth or nose.

Numbness — Loss of feeling or sensation.

TAC — A topical anesthetic mixture containing tetracaine, epinephrine (adrenaline), and cocaine.

Topical — For use directly on a body surface.

Covering the ointment with plastic wrap increases the absorption of the ointment through the skin. The use of plastic wrap, or other occlusive dressings, is the standard means of applying EMLA cream. Other techniques include using gentle heat or electric current to help the drugs penetrate intact skin.

Risks

Overall, topical anesthesia tends to be very safe. Minor problems might include discoloration of the skin at the application site or an uncomfortable feeling of numbness that lasts longer than expected. Repeated use of a topical anesthetic on a damaged eye surface may interfere with the normal healing process. Rarely, too much of the drug may be absorbed into the body in a short time and cause a reaction such as seizure or rapid heartbeat. Death related to topical anesthesia is extremely rare.

Normal results

Successful use of a topical anesthetic produces temporary loss of sensation in the area where it is applied.

Resources

Books

Hardman, Joel G., and Lee E. Limbird, eds. Goodman & Gilman's Pharmacologic Basis of Therapeutics. 10th ed. New York: McGraw-Hill, 2001.

Miller, Ronald D., ed. Miller's Anesthesia. 6th ed. Philadelphia: Elsevier/Churchill Livingstone, 2005.

Periodicals

Kundu, Suriti. "Principles of Office Anesthesia: Part II. Topical Anesthesia." American Family Physician 66, no. 1 (July 2002): 99-102.

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anesthesia /an·es·the·sia/ (an″es-the´zhah)

1. loss of sensation, usually by damage to a nerve or receptor.

2. loss of the ability to feel pain, caused by administration of a drug or other medical intervention.

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basal anesthesia  narcosis produced by preliminary medication so that the inhalation of anesthetic necessary to produce surgical anesthesia is greatly reduced.

block anesthesia  regional a.

bulbar anesthesia  that due to a lesion of the pons.

caudal anesthesia  see under block.

closed circuit anesthesia  that produced by continuous rebreathing of a small amount of anesthetic gas in a closed system with an apparatus for removing carbon dioxide.

crossed anesthesia  see under hemianesthesia.

anesthesia doloro´sa  pain in an area or region that is anesthetic.

electric anesthesia  that induced by passage of an electric current.

endotracheal anesthesia  that produced by introduction of a gaseous mixture through a tube inserted into the trachea.

epidural anesthesia  that produced by injection of the anesthetic into the extradural space, either between the vertebral spines or into the sacral hiatus (caudal block).

general anesthesia  a state of unconsciousness and insusceptibility to pain, produced by administration of anesthetic agents by inhalation, intravenously, intramuscularly, rectally, or via the gastrointestinal tract.

infiltration anesthesia  local anesthesia produced by injection of the anesthetic solution in the area of terminal nerve endings.

inhalation anesthesia  that produced by the inhalation of vapors of a volatile liquid or gaseous anesthetic agent.

insufflation anesthesia  that produced by blowing a mixture of gases or vapors into the respiratory tract through a tube.

local anesthesia  that produced in a limited area, as by injection of a local anesthetic or by freezing with ethyl chloride.

lumbar epidural anesthesia  that produced by injection of the anesthetic into the epidural space at the second or third lumbar interspace.

muscular anesthesia  loss or lack of muscle sense.

open anesthesia  general inhalation anesthesia using a cone, without significant rebreathing of exhaled gases.

peripheral anesthesia  that due to changes in the peripheral nerves.

regional anesthesia  insensibility of a part induced by interrupting the sensory nerve conductivity of that region of the body; it may be produced by either field block or nerve block (see under block ).

sacral anesthesia  spinal anesthesia by injection of anesthetic into the sacral canal and about the sacral nerves.

saddle block anesthesia  see under block.

spinal anesthesia 

1. regional anesthesia by injection of a local anesthetic into the subarachnoid space around the spinal cord.

2. loss of sensation due to a spinal lesion.

surgical anesthesia  that degree of anesthesia at which operation may safely be performed.

tactile anesthesia  loss or impairment of the sense of touch.

topical anesthesia  that produced by application of a local anesthetic directly to the area involved, as to the oral mucosa or the cornea.

transsacral anesthesia  sacral a.

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topical anesthesia

n.

Superficial loss of sensation in mucous membranes or skin, produced by direct application of local anesthetic solutions, ointments, or jellies. Also called surface analgesia.

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topical anesthesia,

anesthesia produced by application of a local anesthetic in the form of a solution, gel, or ointment to the skin, mucous membrane, or cornea. The most common agents include benzocaine, lidocaine, and tetracaine. Cocaine may be applied in solution to the mucous membranes of the nasal passages for certain surgical procedures. Also called surface anesthesia. Compare general anesthesia, local anesthesia, regional anesthesia.

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anesthesia (an´esthē´zē, an´esthē´zh),

n the loss of feeling or sensation, especially loss of tactile sensibility, with or without loss of consciousness, resulting from the use of certain drugs or gases that serve as inhibitory neurotransmitters.

anesthesia, basal,

n a state of narcosis, induced before the administration of a general anesthetic, that permits the production of states of surgical anesthesia with greatly reduced amounts of general anesthetic agents.

anesthesia, block,

n a local anesthesia induced by injecting the local anesthetic drug close to the nerve trunk, at some distance from the operative field. See also anesthesia, infiltration, and block.

anesthesia, conduction,

n a local anesthesia induced by injecting the local anesthetic agent close to the nerve trunk, at some distance from the operative field.

anesthesia, general,

n an irregular, reversible depression of the cells of the higher centers of the central nervous system that makes the patient unconscious and insensible to pain.

anesthesia, glove,

n an anesthesia with a distribution corresponding to the part of the skin covered by a glove.

anesthesia, infiltration,

n a local anesthesia induced by injecting the anesthetic agent directly into or around the tissues to be anesthetized; used for operative procedures on the maxillary premolar, anterior teeth, and
mandibular incisors. Also called field block. See also anesthesia, block.

Infiltration anesthesia.

anesthesia, intraosseous,

n the local anesthesia produced by the injection of a local anesthetic agent into the cancellous portion of a bone.

anesthesia, intrapulpal,

n the injection of a local anesthetic agent directly into pulpal tissue under pressure.

anesthesia, local,

n (regional anesthesia), the loss of pain sensation over a specific area of the anatomy without loss of consciousness.

anesthesia, regional,

n a term used for local anesthesia. See also anesthesia, local.

anesthesia, topical,

n a form of local anesthetic agent with which the surface free nerve endings in accessible structures are rendered incapable of stimulation by applying a suitable solution directly to the surface of the area. Used on the surface soft tissue before a local anesthetic injection to anesthetize surface soft tissues for minor operative procedures.

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topical,

adj 1. of or pertaining to the surface of a part of the body.
2. of or pertaining to a drug or treatment applied to the surface of a part of the body.

topical anesthesia,

n See anesthesia, topical.

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anesthesia

loss of feeling or sensation. Artificial anesthesia may be produced by a number of agents capable of bringing about partial or complete loss of sensation. It is induced to permit the performance of surgery or other painful procedures. See also anesthetic.

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balanced anesthesia

anesthesia that balances the depressing effects on the motor, sensory, reflex and mental aspects of nervous system function by the anesthetic agents. The philosophy encourages the use of several agents, each designed to affect one of the functions.

basal anesthesia

narcosis produced by preliminary medication so that the inhalation of anesthetic necessary to produce surgical anesthesia is greatly reduced.

block anesthesia

regional anesthesia. See also block.

caudal anesthesia

injection of an anesthetic into the sacral canal. See also caudal anesthesia.

central anesthesia

lack of sensation caused by disease of the nerve centers.

closed anesthesia

that produced by continuous rebreathing of a small amount of anesthetic gas in a closed system with an apparatus for removing carbon dioxide.

crossed anesthesia

loss of sensation on one side of the face and loss of pain and temperature sense on the opposite side of the body.

dissociated anesthesia, dissociation anesthesia

loss of perception of certain stimuli while that of others remains intact.

electric anesthesia

anesthesia induced by passage of an electric current.

endotracheal anesthesia

anesthesia produced by introduction of a gaseous mixture through a tube inserted into the trachea.

epidural anesthesia

see epidural anesthesia.

field block anesthesia

the anesthetic agent is injected around the boundaries of the area to be anesthetized, with no attempt to locate specific nerves.

frost anesthesia

abolition of feeling or sensation as a result of topical refrigeration produced by a jet of a highly volatile liquid.

general anesthesia

a state of unconsciousness produced by anesthestic agents, with absence of pain sensation over the entire body and a greater or lesser degree of muscular relaxation; the drugs producing this state can be administered by inhalation, intravenously, intramuscularly, or rectally, or via the gastrointestinal tract.

infiltration anesthesia

local anesthesia produced by injection of the anesthetic solution directly into the area of terminal nerve endings.

inhalation anesthesia

anesthesia produced by the respiration of a volatile liquid or gaseous anesthetic agent. Halothane, methoxyflurane, isoflurane, and a combination of nitrous oxide and oxygen are the common agents in veterinary use.

insufflation anesthesia

anesthesia produced by introduction of a gaseous mixture into the trachea through a slender tube.

intrasynovial anesthesia

injection of a local anesthetic agent into a joint or tendon sheath.

intrathecal anesthesia

introduction of local anesthetic agent into the spinal fluid by penetration of the spinal dura. Causes anesthesia in the tissues supplied by the nerves in the spinal cord zone that has been anesthetized. There is danger of injury to the cord and the technique is litte used in veterinary surgery. Called also subarachnoid, subdural or intradural anesthesia/analgesia.

intravenous anesthesia

the anesthetic agent, e.g. a barbiturate, is administered intravenously to effect. If an intravenous catheter is used, 'topping-up' amounts can also be administered as required.

intravenous regional anesthesia

see bier technique.

irreversible anesthesia

the loss of sensory and motor function of the part is permanent. The local injection of isopropyl alcohol has this effect.

local anesthesia

that produced in a limited area, as by injection of a local anesthetic or by freezing with ethyl chloride. Includes infiltration, nerve block, field block, surface, regional, retrograde regional, spinal, epidural.

mixed anesthesia

that produced by use of more than one anesthetic agent.

nerve block anesthesia

the anesthetic agent is deposited from a syringe and needle as close to the target nerve as possible. Several injections are often made if the landmarks for the location of the nerve are not outstanding.

obstetrical anesthesia

see obstetrical anesthesia.

open anesthesia

general inhalation anesthesia in which there is no rebreathing of the expired gases.

parasacral anesthesia

regional anesthesia produced by injection of a local anesthetic around the sacral nerves as they emerge from the sacral foramina.

paravertebral anesthesia

regional anesthesia produced by the injection of a local anesthetic around the spinal nerves at their exit from the spinal column, and outside the spinal dura.

parenteral anesthesia

anesthesia induced by the injection of the agent, either intravenously, intraperitoneally, subcutaneously or intramuscularly.

peripheral anesthesia

lack of sensation due to changes in the peripheral nerves.

permeation anesthesia

analgesia of a body surface produced by application of a local anesthetic, most commonly to the mucous membranes. Called also surface anesthesia.

rectal anesthesia

anesthesia produced by introduction of the anesthetic agent into the rectum.

refrigeration anesthesia

local anesthesia produced by applying a tourniquet and chilling the part to near freezing temperature. Called also cryoanesthesia.

regional anesthesia

insensibility caused by interrupting the sensory nerve conductivity of any region of the body: produced by (1) field block, encircling the operative field by means of injections of a local anesthetic; or (2) nerve block, making injections in close proximity to the nerves supplying the area.

saddle block anesthesia

the production of anesthesia in the region of the body corresponding roughly with the areas of the buttocks, perineum and inner aspects of the thighs, by introducing the anesthetic agent low in the dural sac.

segmental anesthesia

loss of sensation in a segment of the body due to a lesion of a nerve root.

spinal anesthesia

1. anesthesia due to a spinal lesion.

2. anesthesia produced by injection of the agent beneath the membrane of the spinal cord.

splanchnic anesthesia

block anesthesia for visceral operation by injection of the anesthetic agent into the region of the celiac ganglia.

subarachnoid anesthesia

see intrathecal anesthesia (above).

surface anesthesia

the application of a local anesthetic agent in solution, as in eye drops, or as a jelly, cream or ointment. The use of cold materials which freeze the superficial layers of skin is not much used in veterinary surgery. See also permeation anesthesia (above).

surgical anesthesia

that degree of anesthesia at which operation may safely be performed. There is muscular relaxation, and coordinated movements, consciousness and pain sensations disappear; many of the spinal neuromuscular reflexes are abolished.

topical anesthesia

that produced by application of a local anesthetic directly to the area involved.