LOCAL ANESTHETICS Dr .Rupak Bhattarai

A local anesthetic is an agent that interrupts pain impulses in a specific region of the body without a loss of patient consciousness. Normally, the process is completely reversible--the agent does not produce any residual effect on the nerve fiber.

History The first local anesthetic was Cocaine which was isolated from coca leaves by Albert Niemann in Germany in the 1860s. The very first clinical use of Cocaine was in 1884 by Sigmund Freud who used it to wean a patient from morphine addiction.  It was Freud and his colleague Karl Kollar who first noticed its anesthetic effect.  Kollar first introduced it to clinical ophthalmology as a topical ocular anesthetic.  Also in 1884, Dr. William Stewart Halsted was the first to describe the injection of cocaine into a sensory nerve trunk to create surgical anesthesia.

TYPES OF LOCAL ANESTHESIA AMIDES: Bupivacaine(Marcaine) Etidocaine(Duranest) Lidocaine(Xylocaine) Mepivacaine(Carbocaine) Prilocaine(Citanest) Ropivacaine

Esters: Chloroprocaine .(Nesacaine) Cocaine. Procaine. Tetracaine .(Pontocaine)

Clinical Uses Esters Benzocaine:Topical Chloroprocaine : Epidural,Infiltration,Peripheral nerve block. Cocaine : Topical Procaine : Spinal, Infiltration,Peripheral nerve block. Tetracaine : Spinal,Topical

Amides: Bupivacaine: Epidural,Spinal,Infiltration,Peripheral nerve block. Lidocaine: Epidural, Spinal,Infiltration,Peripheral nerve block, Intravenous, Topical. Mepivacaine: Epidural,Infiltration,Peripheral nerve block. Prilocaine : Peripheral nerve block(Dental). Ropivacaine : Epidural, Spinal,Infiltration,Peripheral Nerve block.

Mechanism of Action Local anesthetics work to block nerve conduction by reducing the influx of sodium ions into the nerve cytoplasm. Sodium ions cannot flow into the neuron, thus the potassium ions cannot flow out, thereby inhibiting the depolarization of the nerve. 

Local Anesthetics Mechanism of action is by reversibly blocking sodium channels to prevent depolarization Anesthetic enters on axioplasmic side and attaches to receptor in middle of channel

Local Anesthetic Toxicity Central nervous system initially-- lightheadedness, dizziness, tinnitus, visual change later-- drowsiness, disorientation, slurred speech, loss of consciousness, convulsions finally-- respiratory depression

Allergic reactions-- rare (less than 1%) Cardiovascular Myocardial depression and vasodilation-- hypotension and circulatory collapse Allergic reactions-- rare (less than 1%) preservatives or metabolites of esters rash, bronchospasm

Prevention and Treatment of Toxicity Primarily from intravascular injection or excessive dose -- anticipation aspirate often with slow injection ask about CNS toxicity have monitoring available prepare with resuscitative equipment, CNS-depressant drugs, cardiovascular drugs ABC’s

Types of Local Anesthesia Local Infiltration (Local Anesthesia). Local infiltration occurs when the nerve endings in the skin and subcutaneous tissues are blocked by direct contact with a local anesthetic, which is injected into the tissue. Local infiltration is used primarily for surgical procedures involving a small area of tissue (for example, suturing a cut).

Topical Block . A topical block is accomplished by applying the anesthetic agent to mucous membrane surfaces and in that way blocking the nerve terminals in the mucosa. This technique is often used during examination procedures involving the respiratory tract. The anesthetic agent is rapidly absorbed into the bloodstream. The topical block easily anesthetizes the surface of the cornea (of the eye) and the oral mucosa.

Surface Anesthesia This type of anesthesia is accomplished by the application of a local anesthetic to skin. Surface anesthesia is used to relieve itching, burning, and surface pain (for example, as seen in minor sunburns)

Nerve Block In this type of anesthesia, a local anesthetic is injected around a nerve that leads to the operative site. Usually more concentrated forms of local anesthetic solutions are used for this type of anesthesia.

Epidural Anesthesia This type of anesthesia is accomplished by injecting a local anesthetic into the Epidural space. The Epidural space is one of the coverings of the spinal cord.

Spinal Anesthesia In spinal anesthesia, the local anesthetic is injected into the subarachnoid space.

Vasoconstrictors Vasoconstrictors decrease the rate of vascular absorption which allows more anesthetic to reach the nerve membrane and improves the depth of anesthesia. 1:200,000 epinephrine appears to be the best vasoconstrictor