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Local Anesthetics

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Drugs that produce a loss of sensation by Blocking afferent neural transmission along the peripheral nerve that carries sensation from a specific body part or region to the CNS

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An anesthetic drug can be administered:

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-Near the peripheral nerve that innervates a specific area -In the vicinity of the spinal cord >>This will block transmission of impulses at a specific level of the cord and affect a larger region of the body

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Local Anesthetics Are often used during minor surgical procedures

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This allows the patient to remain conscious during the procedure

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Analgesic

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A drug administered to reduce or eliminate pain

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Anesthetic

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A drug administered to produce a loss of sensation Example: An anesthetic may be administered prior to surgery or other painful procedure

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Local Anesthetics vs General Anesthetics Advantages of Local Anesthetics:

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-Faster recovery -Lack of residual effects >>Such as post-operative confusion and lethargy -Do not cause generalized depression of the entire nervous system >>Do not interfere with cardiovascular, respiratory and renal function

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Local Anesthetics vs General Anesthetics Disadvantages of Local Anesthetics:

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-Take a longer time to establish an anesthetic effect -Risk that analgesia will be incomplete or insufficient for the procedure >This can be resolved by >>>>Increasing the amount of the local anesthesia >>>>Switching to a general anesthetic

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Local Anesthetics Are sometimes used to provide analgesia for:

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Musculoskeletal Pain Joint Pain Cancer Pain Chronic Pain Complex Regional Pain Syndrome

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A local anesthetic is chosen depending on the:

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Operative Site Nature of the Procedure Type of Regional Anesthesia Desired >>Examples: >Single Peripheral Nerve Block > Spinal Anesthesia Patient's Size Patient's General Health Anesthetic's Duration of Action

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The suffix -caine (e.g. lidocaine, procaine, etc.) usually identifies ___________

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local anesthetics

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______Are administered through a variety of routes and techniques, depending on the specific clinical situation

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Local Anesthetics

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In local anesthesia, The drug should remain at the site of _________ for it to have optimal effect

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administration

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Therefore, local anesthetics are often administered in combination with a __________ agent (usually epinephrine)

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vasoconstricting

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The vasoconstricting agent Acts to:

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Decrease local blood flow Delay absorption of the anesthetic into the systemic circulation

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These effects of The vasoconstricting agent:

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Prolong anesthesia Reduce the risk of toxicity that can occur when sufficient amounts reach the systemic circulation

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The local anesthetic is metabolized by enzymes either in the _____or ______ and then excreted by the kidneys

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blood or liver

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Local Anesthetics All basically work the same way However, their clinical effects depend primarily on how they are administered

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Example: -Administering a local anesthetic to a small area of skin or near a single nerve ----Will produce a limited area of anesthesia -Administering the same local anesthetic near a nerve plexus or near the spinal cord ----Will produce a larger area of anesthesia

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Local Anesthetics can be Administered:

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Topically Injection

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Local Anesthetics can be Administered Topically:

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Topical Administration Transdermal Administration

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Local Anesthetics can be Administered Injection:

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-Infiltration Anesthesia -Peripheral Nerve Block -Central Neural Blockade >>>Epidural Anesthesia >>>Spinal Anesthesia -Sympathetic Nerve Block -Intravenous Regional Anesthesia

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Topical Administration

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A local anesthetic is applied to The surface of the skin A mucous membrane The cornea

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Topical Administration Uses

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Symptomatic relief of minor surface irritation Infection Sunburn Abrasions Insect bites

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Transdermal Administration

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A local anesthetic is applied to The surface of the skin The drug is absorbed into underlying tissues

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Absorption of a transdermal local anesthetic may be enhanced by the use of:

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Iontophoresis Phonophoresis

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Transdermal Administration Iontophoresis

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A therapeutic technique used to enhance the transdermal delivery of topical medicines through the skin via the application of a small electric current

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A charged, ionic drug is placed on the skin with an electrode of the same charge, allowing direct current to drive the drug into the skin

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May be used to produce topical anesthesia prior to certain dermatologic procedure (e.g. placement of IV catheter, lumbar puncture, needle EMG)

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This technique may be helpful in treating certain musculoskeletal injuries

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Iontophoresis & Phonophoresis

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Transdermal Administration Phonophoresis

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A therapeutic technique in which ultrasound waves are used to enhance transdermal delivery of topical medicines through the skin This technique may be helpful in treating certain musculoskeletal injuries

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Transdermal Administration: Local anesthetics can also be administered via a transdermal patch Used to treat:

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Localized pain in musculoskeletal conditions (e.g. OA, LBP) Neuropathic pain (e.g. diabetic neuropathy)

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Infiltration Anesthesia

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Anesthesia produced by injecting a local anesthetic solution directly into the immediate area of surgery Example: Used when performing a surgical repair (e.g. suturing)

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Peripheral Nerve Block

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Anesthesia produced by injecting a local anesthetic close to the nerve that supplies the surgical field The site injected is at a distance from the surgical filed Transmission along the peripheral nerve is interrupted

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Peripheral Nerve Blocks are Commonly used for

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Tooth extraction Surgical procedures of the hand, foot, shoulder

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Peripheral Nerve Blocks are Classified as

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Minor Nerve Blocks Major Nerve Blocks

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Minor Nerve Blocks

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Only one distinct nerve is blocked (e.g. ulnar, median)

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Major Nerve Blocks

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Several peripheral nerves or a nerve plexus is blocked (e.g. brachial, lumbosacral)

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_______ may be used to guide the needle so it can come as close as possible to the specific nerve without penetrating or damaging the nerve

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Diagnostic ultrasound

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Continuous Peripheral Nerve Block

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Nerve blocks can be continued after completion of surgery A small catheter is implanted near the nerve or nerve plexus so small doses of a local anesthetic can be administered continuously after surgery

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Continuous Peripheral Nerve Blocks are Commonly used after:

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Joint Replacement Ligament Reconstruction

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Prolonged administration of local anesthetics within skeletal muscle can:

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-Produce localized muscle pain and necrosis -Decrease a patient's ability to feel or move affected area -Could result in injury if the patient attempts to use the affected limb Example: A Femoral Nerve Block -Can affect the quadriceps muscles If the patient attempts to stand on the affected leg, the knee could buckle

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Central Neural Blockade

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The local anesthetic is injected within the spaces surrounding the spinal cord

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Central Neural Blockade Epidural Nerve Block

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The anesthetic drug is injected into the epidural space

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Caudal Block

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A variation of epidural administration The local anesthetic is injected into lumbar epidural space via sacral hiatus

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Central Neural Blockade Spinal Nerve Block

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Also known as Intrathecal Anesthesia The anesthetic drug is injected into the subarachnoid space

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Central Neural Blockade Used when anesthesia/analgesia is needed...

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-In a large section (e.g. obstetric procedures) -For lumbar spine surgery, joint replacement -For acute and chronic pain >>Epidural and spinal nerve blocks may be used to administer anesthetics and analgesics for relief of acute and chronic pain >>In some cases, a catheter may be implanted in the epidural or subarachnoid space to allow repeated or continuous delivery of the drug

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Local anesthetics are _____ when administered in high concentrations

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neurotoxic

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Epidural Nerve Block vs. Spinal Nerve Block Epidural Nerve Block

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-The anesthetic drug is injected into the epidural space -Requires a larger dose of anesthesia -The drug diffuses across the dura mater into the subarachnoid space and blocks conduction in nerve roots -Onset of anesthesia is slower with epidural analgesia -Can be performed anywhere along the vertebral column

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Epidural Nerve Block vs. Spinal Nerve Block Spinal Nerve Block

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-The anesthetic drug is injected into the subarachnoid space -Anesthesia is more rapid -Creates a more effective block of sensation with a smaller amount of anesthetic -Is typically performed in the lumbar region below the termination of the spinal cord (L2) to avoid piercing the spinal cord

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Sympathetic Blockade

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-An injection of a local anesthetic to block nerve signal transmission along nerves of the sympathetic nervous system -The injection is made into the area surrounding the sympathetic chain ganglion that innervates the affected limb

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Sympathetic Blockade is Used in cases of Complex Regional Pain Syndrome (also known as Reflex Sympathetic Dystrophy Syndrome)

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-This condition involves increased sympathetic discharge to an upper or lower extremity causing severe pain -Sympathetic nerve fibers innervate the smooth muscle of blood vessels -Pain can be due to vascular insufficiency

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Intravenous Regional Anesthesia

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Used for surgical procedures involving the Arm below the elbow Leg below the knee

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A local anesthetic is administered by IV into a distal vein of the arm or leg

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The local vasculature carries the drug to the nerves in that extremity

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Before giving the anesthetic, a _______ is applied to the limb proximal to the site of anesthetic injection to prevent the drug from entering the systemic circulation

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tourniquet

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Local Anesthetics: Mechanism of Action

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-Local anesthetics inhibit axonal conduction by: Blocking the sodium channels in the axonal membrane -If sodium channels are inhibited from opening An action potential will not be propagated past that point -Only a short portion of the axon needs to be affected by the anesthetic to block action potential propagation -If the axon transmits sensory --This sensory information will not reach the brain -----The result will be anesthesia of the area innervated by that neuron

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Differential Nerve Block

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The ability of a local anesthetic to block specific nerve fiber groups

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The characteristics of a neuron will affect the ability of a local anesthetic to block the propagation of an action potential. Neuron Factors:

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Diameter of Axon Myelination Length of a Neuron Distribution of Na+ Channels

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Based on fiber _________, the nerve fibers are classified as Type A, B and C

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diameter

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Type A Fibers

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The thickest and myelinated

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Type C Fibers

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The narrowest and unmyelinated

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Different fiber types transmit different information

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-Information transmitted by the smallest fibers will be lost first -Other types of transmission is sequentially lost as the local anesthetic effect increases

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The exact reason for the differential susceptibility of nerve fibers to local anesthetics is not known

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Axon diameter does not appear to be the reason

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Differential Nerve Block Type C Fibers

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-Narrowest diameter axons -Are more susceptible to block than large diameter fibers -Are blocked more rapidly -Transmit pain -The first sensory information blocked as the anesthetic takes effect

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Differential Nerve Block Skeletal Motor Function Is usually last to disappear

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This is because efferent impulses to skeletal muscles are transmitted via the large Type A fibers

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Differential Nerve Block Depends on concentration of the local anesthetic. A drug at:

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Lower concentration will produce only sensory block At higher concentration can produce motor block

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*The clinical importance of a differential nerve block is that certain sensory modalities can be blocked without loss of _________

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motor function

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Differential Nerve Block At the optimal dosage and administration...

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A local anesthetic can produce analgesia without any significant loss of skeletal motor function

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Local Anesthetics Examples:

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Generic Name: lidocaine injection (LYE doe kane) Brand Names: Nervocaine, Xylocaine Uses: Dental procedures Epidural and Spinal Nerve Block Intravenous Regional Anesthesia Generic Name: procaine (PRO cane) Brand Name: Novocain Uses: Dental procedures

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Although local anesthetics are administered for their local effects, they do get absorbed into the systemic circulation. Therefore, they can exert toxic effects on other organs and tissues

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This effect is known as Local Anesthetic Systemic Toxicity (LAST)

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Local Anesthetics Can affect the ________ and __________ if significant amounts of the drug enters the systemic circulation

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CNS and Cardiovascular System

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Local Anesthetic Systemic Toxicity (LAST) CNS Adverse Effects

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Initial Central Excitation which is followed by Depression Excitatory Effects: >Agitation >Excitation >Seizures Depressant Effects: >Drowsiness >Confusion >Impaired Respiratory Function >Coma

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Local Anesthetic Systemic Toxicity (LAST) Cardiovascular System Adverse Effects

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Decreased Cardiac Excitation Bradycardia Reduced Contractile Force Cardiac Arrest

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Local Anesthetic Systemic Toxicity (LAST) Risk of Incidence is Related to:

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-Excessive Dose >>>Of the local anesthetic -Accidental Injection >>>Of the anesthetic into the systemic circulation instead of the extravascular tissue -Type >>>Of local anesthetic used -Route and Method >>>Of administration

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Local Anesthetic Systemic Toxicity (LAST) Early signs and symptoms include:

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Tinnitus Agitation Restlessness Decreased sensation around the mouth, tongue and skin Bradycardia Fatigue

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Treatment for LAST

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Lipid Rescue

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Lipid Rescue Also known as Lipid Resuscitation

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Refers to the IV administration of a lipid emulsion to treat Local Anesthetic Systemic Toxicity (LAST) The circulating lipid emulsion compound will absorb the lipophilic local anesthetic Therefore, the anesthetic cannot bind to the sodium channels in the CNS, myocardium and other tissues

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Local Anesthetics Are often used for treatment of

answer

Musculoskeletal Pain Joint Pain Cancer Pain Acute and Chronic Pain

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Local Anesthetics

answer

Can be administered in various ways Can affect individuals differently

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OTs need to be aware of patients

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-Receiving local anesthetics -With transdermal patches >>Care must be taken not to disturb the patch during therapeutic interventions

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A patient may be receiving a continuous peripheral nerve block to control pain following joint replacement or ligament reconstruction

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A small catheter is implanted near the nerve or nerve plexus that innervates the surgical area

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Patient may lack sensation and motor control in affected area

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Therefore, care must be taken because the patient may not feel pain if joint tissues are being overstressed during therapeutic interventions

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Caution must be taken when ambulating a patient receiving a continuous peripheral nerve block affecting the lower extremity

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Buckling of the knee could occur Use of a knee brace may help prevent this from occurring

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Patients being treated with a central nerve block for acute or chronic pain May have a catheter implanted in the epidural or subarachnoid space to allow repeated or continuous delivery of the drug

answer

OTs should be aware that sensation and motor function might be diminished below the level of epidural or spinal administration

Chapter 12- Local Anesthetics – Flashcards

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