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local anesthetic

This is an (incomplete) mind map about local anesthetics, which introduces detailed knowledge points such as structure-activity relationship and classification, mechanism of action (receptor theory), efficacy, pharmacokinetics, adverse reactions, etc.

Edited at 2024-11-27 23:39:43

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local anesthetic

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Outline

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inhalation anesthetic
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intravenous anesthetic
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MM

local anesthetic

Structure-activity relationships and classification

structure activity relationship

Aromatic group (benzene nucleus)

Lipophilic and hydrophobic, determines the lipid solubility of local anesthetics

Intermediate chain (ester bond or amide bond)

Determine the metabolic pathways of local anesthetics

Amino group (mostly tertiary amine)

Hydrophilic and lipophobic properties determine the degree of dissociation of local anesthetic molecules

Classification

intermediate chain

Ester local anesthetics (no i in English)

Amide local anesthetics (i in English)

Effect time limit

short acting

Procaine

Chloroprocaine

Medium effect

lidocaine

Mepivacaine

Long lasting

Tetracaine

Bupivacaine

Levobupivacaine

Ropivacaine

Mechanism of action (receptor theory)

site of action

Alpha subunit (main functional unit) on sodium channels

Amino acid residues on the S6 segment of the D4 region

Mechanism of action

Reversibly seals the inner port (not the outer port) of the sodium channel and binds to one or more specific sites

characteristic

Usage dependence (frequency dependence)

The higher the frequency of stimulation to the nervous tissue, the greater the number of open channels, the more obvious the blockage, and the stronger the local anesthesia effect.

It has a weak effect on resting nerves. Increasing the frequency of electrical stimulation will enhance the effect of local anesthetics.

Medicinal efficacy

Effects and adverse reactions

local nerve block

Effect (disappearance order)

Pain, heat, cold, touch, and deep sensations

condition

sufficient concentration

sufficient time

Reach the receptor site

There is sufficient long axis of the nerve in direct contact with the local anesthetic

central nervous system

normal function

inhibitory effect

toxic reactions

Excite first and then inhibit

If the local anesthetic is injected directly into the blood, it will not cause convulsions.

Cause

Local anesthetic concentration is too high

Central inhibitory neurons are more sensitive to local anesthetics than excitatory neurons

antagonistic

Benzodiazepines can enhance the inhibitory effect of GABAergic neurons in the limbic system

Cardiovascular (higher tolerance)

direct inhibition

toxic reactions

Excite first and then inhibit

Early stage: increased blood pressure and increased heart rate

Caused by central excitation

Late stage: heart rate slows, blood pressure drops, conduction block until cardiac arrest

Influencing factors

dose

Affects the effectiveness, depth and duration of local anesthetics

Increase drug concentration (commonly used in clinical practice)

increase capacity

Nerve block and epidural block use

injection site

Plasma concentration: intercostal > sacral canal > epidural > brachial plexus > subarachnoid space > subcutaneous infiltration

Hybrid application

Vasoconstrictor (epinephrine)

Slow down the absorption of local anesthetics, extend the action time of local anesthetics, and reduce systemic adverse reactions

Optimum concentration 1:200,000 (5μg/ml)

local anesthetic

Compensate the characteristics of different drugs with each other

Mixed application of fast-acting medium and short-acting local anesthetics and slow-acting long-acting local anesthetics

Pay attention to the maximum amount of local anesthetics used

rapid drug resistance

Concept: After repeated injection of local anesthetic, the nerve block efficacy is weakened and the duration is shortened.

If local anesthetic is added 15 minutes after subsidence, rapid drug resistance is likely to occur.

pregnancy

Progesterone causes increased neural sensitivity to local anesthetics

Drug generation

absorb

dose

injection site

Use of vasoconstrictors

distributed

Depends on physical and chemical properties, blood flow of various tissues and organs

Biotransformation and excretion

Ester local anesthetics

Pseudocholinesterase hydrolyzes, and a small amount of the original form is excreted

Amide local anesthetics

Liver microsomal enzyme, amidase decomposition

Only 5% of the original form is excreted in urine

Lidocaine is excreted in bile to a small extent

adverse reactions

Systemic

toxic reactions

hypersensitivity reaction

Receiving a small amount (1/3~2/3 of the maximum dose) of local anesthetic may suddenly lead to signs of toxic reactions such as syncope, respiratory depression or even circulatory failure.

idiosyncratic reaction

Receiving very small doses of local anesthetics can cause serious toxic reactions

allergy

Contact

neurotoxicity

Direct contact of the spinal cord or peripheral nerves with local anesthetics at too high a concentration or for too long a time may induce nerve damage.