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.

anesthesia

[an″es-the´ze-ah] 1. lack of feeling or sensation.2. artificially induced loss of ability to feel pain, done to permit the performance of surgery or other painful procedures. It may be produced by a number of agents (anesthetics) capable of bringing about partial or complete loss of sensation.(See accompanying table.)Patient Care. Interventions of the health care team will be individualized based on the type of procedure the patient has undergone and the type of anesthesia administered. Patients recovering from general anesthesia must be assessed constantly until they have reacted. The vital signs and blood pressure are checked regularly; any sudden change is reported immediately. They must be observed to see that the airway is clear at all times. The observation is in specialized recovery rooms called postanesthesia care units that are equipped with a variety of monitors to measure such variables as blood pressure, respiratory and pulse rates, cardiac output, body temperature, fluid balance, and oxygenation. When necessary, patients are initially managed with ventilators that inflate the lungs mechanically through endotracheal tubes. Changes in breathing pattern, eye movements, lacrimation, and muscle tone are indicators for the depth of anesthesia. Breathing patterns are the most sensitive of these.
When patients are awakening from general anesthesia they may be restless, attempting to get out of bed or even striking out at those around them because they are afraid and disoriented. This state is called emergence delirium and should be assessed, as it can indicate hypoxia. Retrograde amnesia may be associated with the administration of anesthesia and adjuncts, causing the patient to forget events occurring in the immediate postoperative period.ambulatory anesthesia anesthesia performed on an outpatient basis for ambulatory surgery.balanced anesthesia anesthesia that uses a combination of drugs, each in an amount sufficient to produce its major or desired effect to the optimum degree and to keep undesirable effects to a minimum.basal anesthesia a reversible state of central nervous system depression produced by preliminary medication so that the inhalation of anesthetic necessary to produce surgical anesthesia is greatly reduced.block anesthesia regional anesthesia.caudal anesthesia a type of regional anesthesia that was used in childbirth between the 1940s and the 1960s. The anesthetizing solution, usually procaine, was injected into the caudal area of the spinal canal through the lower end of the sacrum and affected the caudal nerve roots, rendering the cervix, vagina, and perineum insensitive to pain. Called also caudal block.central anesthesia lack of sensation caused by disease of the nerve centers.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.compression anesthesia loss of sensation resulting from pressure on a nerve.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 regional anesthesia produced by injection of the anesthetic agent into the epidural space. It may be performed by injection of the agent between the vertebral spines in the cervical, thoracic, or lumbar regions. An old method was anesthesia" >caudal anesthesia, which involved injecting the agent into the sacral hiatus. Called also epidural block.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.gustatory anesthesia loss of the sense of taste.hysterical anesthesia loss of tactile sensation occurring as a symptom of conversion disorder, often recognizable by its lack of correspondence with nerve distributions.infiltration anesthesia local anesthesia produced by injection of the anesthetic solution directly into the area of terminal nerve endings. Called also infiltration analgesia.inhalation anesthesia anesthesia produced by the respiration of a volatile liquid or gaseous anesthetic agent.insufflation anesthesia anesthesia produced by introduction of a gaseous mixture into the trachea through a tube.local anesthesia that produced in a limited area, as by injection of a local anesthetic or by freezing with ethyl chloride.open anesthesia general inhalation anesthesia in which there is no rebreathing of the exhaled gases.paraneural anesthesia perineural block.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. Called also paravertebral block.perineural anesthesia perineural block.peripheral anesthesia lack of sensation due to changes in the peripheral nerves.rectal anesthesia anesthesia produced by introduction of the anesthetic agent into the rectum.refrigeration anesthesia cryoanesthesia.regional anesthesia insensibility caused by interrupting the sensory nerve conductivity of any region of the body; the two primary types are field block, the encircling of an operative field by means of injections of a local anesthetic and nerve block, the making of injections in close proximity to the nerves supplying the area. Called also block.saddle block anesthesia block" >saddle block.segmental anesthesia loss of sensation in a segment of the body due to a lesion of a nerve root.spinal anesthesia anesthesia due to a spinal lesion.regional anesthesia produced by injection of the agent beneath the membrane of the spinal cord. Called also spinal block.surgical anesthesia that degree of anesthesia at which operation may safely be performed.tactile anesthesia loss of the sense of touch" >touch.topical anesthesia that produced by application of a local anesthetic directly to the area involved.