DR RAHUL

LOCAL ANAESTHETICS

DEFINITION OF ANESTHESIA

• Anesthesia literally means “no sensation”

• Derived from the Greek verb for “to perceive” : Oliver Wendell Holmes, 1846

LOCAL ANAESTHESIA

• Loss of sensory perceptions by reversibly inhibiting the propagation of signals along nerve pathways in a specific area of the body.

• LAs block generation and conduction of impulse at all parts of neurons where they come in contact.

HISTORY

• Cocaine :

• First local anaesthetic

• Discovered by German, Albert Niemann (1860)

• Isolated from the leaves of coca

• First clinical use in 1884 by Sigmund Freud and Karl Kollar in ophthalmology as a topical ointment

INJECTABLE

• Low potency & short duration

• Procaine

• Chloroprocaine

• Intermediate potency & duration

• Lignocaine

• Prilocaine

• High potency & long duration

• Tetracine

• Bupivacaine

• Ropivacaine

SURFACE

• Soluble

• Cocaine

• Lignocaine

• Tetracaine

• Insoluble : Benzocaine

CLASSIFICATION

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GENERAL STRUCTURE

• Lignocaine

• Mepivicaine

• Prilocaine

• BupivacaineMore intense and

longer lasting anaesthesia

• Cocaine

• Procaine

• Tetracaine

• Chlorprocaine

• BenzocaineShort DOA, less intense

analgesia

TYPES OF LOCAL ANAESTHETICS

Esters Amides

• These get metabolized in the liver to inactive agents

• Binding to amides is provided by alpha 1 glycoprotein in plama

• No allergies associated with amides

• Hydrolysed in the plasma by a pseudo cholinesterase

• One by-product of this reaction Para-Amino Benzoic Acid (PABA)

• Allergic reaction are associated with PABA

TYPES OF LOCAL ANAESTHETICS

Esters Amides

MECHANISM OF ACTION

• Inhibits sodium influx through sodium-specific ion channels in the nerve cytoplasm

• Sodium ions cannot flow in, so potassium ions cannot flow out, thereby preventing the depolarization of the nerve

• Rate of rise of AP and depolarisation decreases with increase in concentration of LAs

• To do this the anaesthetic molecules must actually enter through the cell membrane of the nerve. This is where the differences in the time of onset and duration of the various local anaesthetics lies.

FACTORS THAT AFFECT ACTION OF LOCAL ANESTHETICS

• pH

• Cationic form binds to receptor site. The uncharged form penetrates membrane . Efficacy of drug can be changed by altering extracellular or intracellular pH

FACTORS THAT AFFECT ACTION OF LOCAL ANESTHETIC

• Lipophilicity• Main determinant of

anesthetic potency.

• Compounds with high lipophilicity penetrate the nerve membrane easily.

• This means less molecules are needed to inhibit the blockade of sodium ions. This leads to enhanced potency.

Lipid solubility and potency

Drug Relativepotency

Lipidsolubility

Procaine =1 100Prilocaine 1.8 129Lignocaine 2 366Bupivicaine 8 3420

VASOCONSTRICTORS• Blood absorbs the unused anesthetic. In

order to slow down this process many anesthetics are administered with a vasoconstrictor.

• These constrict the vessel and slow down the absorption of the anesthetic, by allowing less blood to enter/leave the site

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ADVANTAGES OF LIGNOCAINE ADRENALINE COMBINATION

• Decrease systemic toxicity (uptake by up to 1/3)

• Prolong local anesthesia (by ~50%)

• Decrease local bleeding (improve visualization of surgical field

DIS ADVANTAGES:

• Makes injection more painful

• Increases chances of local injury and necrosis.

• May raise BP and promote arrhythmias in susceptible individuals

PROGRESSION OF LOCAL ANESTHESIA

• Loss of:

• 1. Pain

• 2. Cold

• 3. Warmth

• 4. Touch

• 5. Deep pressure

• 6. Motor function

PHARMACOLOGICAL ACTIONS

• CNS :

• All can produce CNS stimulation followed by depression.

• Cocaine:

• Euphoria-excitement-mental Confusion-tremors-muscle Twitching-convulsions- Unconciousness -resp. Depression.

• Procaine, Lignocaine: safe at clinical doses

• CVS :

• Cardiac depressant at iv doses

• Antiarrhythmic action (procainamide)

TECHNIQUES OF ADMINISTRATION

• Topical Anesthesia

• Infiltration

• Conduction blockField blockNerve block

• Peridural

• Spinal anesthesia

TOPICAL ANESTHESIA

• Done by the administering the anesthetic to mucous membranes or skin. Relieves itching, burning and surface pain, i.e. sunburns.

INFILTRATION

• Occurs by directly injecting a local anesthetic to block the nerve endings under the skin or in the subcutaneous tissue. Used mainly for surgeries, i.e. cavities being filled.

CONDUCTION BLOCK

EPIDURAL ANESTHESIA

• This is accomplished by injecting a local anesthetic into the peridural space, a covering of the spinal cord

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SPINAL ANESTHESIA

• Here, the local anesthetic is injected into the subarachnoid space of the spinal cord

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TOXICITY

• CNS Toxicity: • Systematic absorption can lead to

excitement (tremors, shivering, convulsions),

• If absorbed in even higher amounts can lead to depression (coma, respiratory arrest and death)

• Cardiovascular toxicity: • If absorbed in excess systematically can

lead to depression of the cardiovascular system

• Hypersensitivity: Rashes to anaphylaxis• Local reactions: Combination with

vasoconstrictor (combination should be avoided-feet, fingers, toes,

pinna, penis)

Cocaine

Ester, tendency to cause allergy

Cardiovascular and CNS stimulant

Addictive

Used in ENT as a vasoconstrictor

Metabolised by plasma esterases

Lidocaine

Amide Standard agent against which others are

compared Antiarrhythmic Vasodilator, increases systemic toxicity Available as 0.5%, 1% and 2%

preparations

THANK YOU….