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Local Anaesthetics Flashcards

1
Q

What are local anaesthetics?

A

Drugs that reversibly blocks the impulse conduction and produces transient loss of sensation in a restricted region of the body without causing loss of consciousness

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2
Q

The order of block local anaesthetics?

A

Pain- temp- touch- pressure
Finally - skeletal muscle power

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3
Q

Properties of local anaesthetics?

A

Quick onset of action
Non-irritating to the tissue to which it is applied
Low systemic toxicity
Long duration of action to permit the completion of procedure
Free from allergic reactions
Should not cause any permanent damage to the tissue

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4
Q

Classification of local anaesthetics?

According to Clinical Use

A

Injectable anaesthetics

Surface anaesthetics

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5
Q

Classification of local anaesthetics?

According to Structure

A

Esters

Amides

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6
Q

Injectable local anaesthetics?

Short-acting with low potency

A

Procaine, Chloroprocaine

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7
Q

Injectable local anaesthetics?

Intermediate-acting with intermediate potency

A

Lignocaine, mepivacaine, prilocaine, articaine

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8
Q

Injectable local anaesthetics?

Long-acting with high potency

A

Tetracaine, Bupivacaine, Ropivacaine

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9
Q

Surface anaesthetics

Soluble

A

Cocaine
Lignocaine
Tetracaine
Benoxinate

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10
Q

Surface anaesthetics

Insoluble

A

Benzocaine
Oxethazaine
Butylaminobenzoate

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11
Q

According to structure

Esters

A

Cocaine, procaine, chloroprocaine, benzocaine, tetracaine

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12
Q

According to structure

Amides

A

Lignocaine, bupivacaine, dibucaine, prilocaine, ropivacaine

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13
Q

According to structure

Others

A

Pramoxine, Dyxlonine, Oxethazaine

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14
Q

Ester(Procaine) vs Amide(Lignocaine)

A

Ester(Procaine) - Ester type.
Short-acting, low potency. Metabolized by esterases.
Allergic reactions are common. Mainly for infiltration and nerve block.

Amide(Lignocaine) - Amide type.
Intermediate-acting and potency.
Metabolized by hepatic microsomal enzymes.
For Spinal, epidural, infiltration, nerve block

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15
Q

Mechanism of action of local anaesthetics?

A

local anaesthetics are weak bases > available as hcl salts (eg. Lignocaine hcl) > partially unionized (lipophilic) or partly ionized at tissue pH (7.4) > partially unionized (lipophilic) penetrates the nerve membrane>enters the adon>reionization takes place at axonal pH > *local anaesthetics block the voltage gated Na channels from inside; binds tightly to inactivated state and prolongs it>prevents the entry of Na into the neuron >no depolarization >no generation of action potential >no generation & conduction of impulses to CNS> local anaesthesia

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16
Q

Effects or actions of local anaesthetics

A

Bother sensory and motor fibers are affected

local anaesthetics block sensory nerve endings, nerve trunks, nmj, ganglia (*structures acting through increase na permeability)

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17
Q

Effects or actions of local anaesthetics

A

Smaller nerve fibers are more sensitive than larger fibres

Myelinated fibers are blocked first then unmyelinated fibres are blocked earlier than larger fibres

Autonomic fibres are more susceptible than somatic fibres

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18
Q

Factors affecting local anaesthetics?

A

pH

local anaesthetics are weak bases >*unionized at alkaline pH> increased penetrability through membranes >good local anaesthesia

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19
Q

Factors affecting local anaesthetics

A

PH

Inflamed & Infected Areas>decrease pH> local anaesthetics are weak bases *ionized at acidic pH>poor penetration of local anaesthetics through cell membranes > therefore
local anaesthetics are less effective in these areas

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20
Q

Degree of plasma protein binding?

A

Duration of action depends upon the protein binding

Procaine - poorly bound PP and has short duration of action

Bupivacaine - highly bound to PP and has a longer duration of action

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21
Q

Rate of diffusion from the site of administration?

A

Higher the concentration - rapid onset of action

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22
Q

Lipid solubility?

A

Higher the lipid solubility more is the Potency of the drug

Lignocaine is more potent than Procaine

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23
Q

Vasoconstrictors in local anaesthetics?

A

Drugs that constricts the blood vessels and thereby controls tissue perfusion

Are added to local anaesthetics to oppose the vasodilatory action of local anaesthetic agents

24
Q

Advantages of vasoconstrictor in local anaesthetics

A

LA + vasoconstrictor (adrenaline) > LA + Vasoconstriction leads to : increase action (increase duration); decrease systemic tixicity; and local hemostatic effect

25
Disadvantages & Contraindications due to vasoconstrictor with local anaesthetics
* Intense vasospasm & ischemia in tissues with end arteries may cause gangrene Eg: fingers, toes, penis, ear lobule, tip of the nose Absorption of adrenaline can cause systemic toxicity Delay wound healing by reducing the blood flow to the affected area
26
Adverse effects of LA CNS
Low doses - tongue numbness, sleepiness, lightheadedness, visual/auditory disturbance. Higher doses- nystagmus and muscular twitching, convulsions
27
Adverse effects of LA CVS
Cardiac depression, bradycardia, hypotension
28
Allergic reactions
* Skin rashes, itching, erythema, urticaria, wheezing & rarely anaphylactic reaction - The is more with Esters than Amides * Mucosal irritation - cocaine * Methemoglobinaemia - Prilocaine
29
Tetracaine?
Ester Highly lipid soluble Highly potent Highly toxic Has longer duration of action
30
Uses of Tetracaine
Spinal anaesthesia Surface anaesthesia (eye, ear, URT)
31
Action of Bupivacaine?
Amide Highly potent. Highly lipid soluble *Highly cardiotoxic, has slower onset and longer duration *Produces more sensory than motor blocked- hence used for Obst. analgesia
32
Action of Ropivacaine
Convener of bupivacaine Less potent & less cardiotoxic Duration of action is same as bupivacaine *Epidural ropivacaine is used to control - post-operative pain and labour pain
33
Dibucaine Use
Very potent, very toxic & *. longest acting Used for - spinal anaesthesia - for topical (surface anaesthesia) on mucus membrane & skin
34
Lignocaine use
Amide type local anaesthesia Rapid action, cam be used as antiarrhythmic agent in the *treatment of Ventricular arrhythmia
35
Lignocaine Pharmacokinetics
Absorbed rapidly after parenteral administration from git Metabolized in liver Half-life of 90 mins Excreted unchanged in urine
36
Prilocaine moa
Amide Intermediate onset and intermediate duration of action Has poor vasodilatory effect
37
Uses of Prilocaine
Topical & infiltration anaesthesia
38
AE of Prilocaine
Methemoglobinaemia
39
Eutectic Mixture of Local Anaesthesia (EMLA) moa
Lig 2.5% + Prilo 2.5% (cream) > The melting point of the mixture is less than either drug alone * At room temperature, exists as Oil Can penetrate intact skin up to 5 mm depth
40
Uses of Eutectic Mixture of Local Anaesthesia (EMLA)
*Venipuncture *Skin graft procedures *EMLA must not be applied to the mucus membrane * EMLA is CI Methemoglobinemia
41
Contraindication of EMLA
*EMLA must not be applied to the mucus membrane * EMLA is CI Methemoglobinemia
42
Benoxinate Use
Good surface anaesthetic *Used to anaesthetize cornea for tonometry
43
Oxethazaine Use
Topical anaesthetic * anaesthetize gastric mucosa *Produces symptomatic relief in gastritis *available with antacids
44
Benzocaine Butylaminobenzoate Uses
*as lozenges in sore throat *powder or ointment on wounds /ulcers *suppository for anorectal lesions
45
Techniques of local anaesthetics Surface anaesthesia moa
Sensory nerve endings are blocked Only superficial layer is anaesthetized Applied to mucus membrane & abraded skin - nose, mouth, eyes, throat, URT, urethra, ulcers, burns, fissures Eg: Lignocaine, tetracaine, benzocaine, cocaine
46
Techniques of local anaesthetics Surface anaesthesia uses
Tonometry, painful lesions, fissures, burns, iv cannulation duringendoscopies
47
Techniques of local anaesthetics Infiltration anaesthesia uses
Dilute solution of LA injected under the skin to block the sensory nerve endings *used for minor surgical procedures: incision, excision, suturing *Lignocaine, Bupivacaine can be used
48
Techniques of local anaesthetics Field Block
Injecting LA subcutaneously *Anaesthetizes the area distal to the inj. Uses: * for minor procedures on scalp, ant.abdominal wall, upper and lower limbs
49
Techniques of local anaesthetics Nerve block
LA is injected very close to or around the peripheral nerve or nerve plexuses Brachial plexus block-upper limb Cervical plexus block-neck Intercostal nerve block-ant.abdominal
50
Spinal Anaethesia
*LA injected in the subarachnoid space between L2-3 or L3-4 of the spinal cord *LA of choice - Lignocaine, Bupivacaine, tetracaine
51
*Spinal Anaesthesia Indications
Orthopaedic surgery of the lower limbs and pelvis Surgery of lower abdomen Gynaecological and obstetrics surgeries
52
* Spinal Anaethesia Complications
Hypertension Headache (PDPH)- due to leakage of CSF through the hole in dura mater. Prevented by using small bore needle PDPH is txt by lying down for 24hrs, plenty of fluids, abdominal compression
53
Other Complications of Spinal Anaethesia
Urinary retention Paralysis of cranial nerves Meningitis
54
*Uses of Epidural Anaethesia
Given in epidural space (between dura mater and bone) with Tuohy's needle. Indicated mostly for controlling: Postoperative pain, upper abdominal surgeries, thoracic surgeries, painless labour, chronic pain due to cancer and other conditions
55
* Spinal Anaesthesia vs Epidural Anaethesia
Spinal Anaesthesia is highly reliable, easy to place and has very quick onset of action It is indicated only for surgeries of limited duration, redosing cannot be done. PDPH is its complication Epidural Anaesthesia is less reliable, difficult to perform. Can be used for surgeries of any duration. Chances of PDPH is very less
56
*Intravenous Regional Anaesthesia Use
Indicated for any procedure on the arm below elbow or in the leg below knee that will be completed within 40-60mins LA is injected into the vein of the limb where flow is occluded by tourniquet *Mainly used to anaesthesize the upper limb * Lignocaine and Prilocaine

Pharmacology (8 decks)

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