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Week 7 - 12 > Local Anaesthetics > Flashcards

Local Anaesthetics Flashcards

1
Q

When are local anaesthetics used?

A

When loss of consciousness is neither necessary or desirable

Post-operative analgesia

For major surgery, with sedation

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2
Q

Why are local anaesthetics used as an adjunct to surgery?

A

To avoid high-dose general anaesthetics

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3
Q

Structure of local anaesthetics:

A

Aromatic region

Basic amine-side chain

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4
Q

What bond is present in local anaesthetics?

A

Ester or amide bond

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5
Q

Difference between ester and amide local anaesthetics?

A

Esters are more unstable + can be metabolised into compounds associated with allergic reactions

Amides are more commonly used

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6
Q

Why are amide local anaesthetics more commonly used?

A

As more stable and extend duration of action

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7
Q

How do local anaesthetics work?

A

Reversibly block voltage-gated Na+ channels

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8
Q

What happens when local anaesthetics block channels?

A

Excitable membranes stabilise

Prevent membranes from being depolarised

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9
Q

Structure of peripheral nerve:

A

Consists of fibres of different function, diameter and insulation

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10
Q

What can peripheral nerves be blocked by?

A

Local anaesthetics but at different rates

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11
Q

Order of loss of function by local anaesthetics:

A

Pain

Temperature

Proprioception

Skeletal muscle tone

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12
Q

What does the probability that a local anaesthetic will block an impulse rely on?

A

Diameter of fibre

Myelination status

Length of nerve exposed to drug

Length of time exposed to drug

Concentration of drug

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13
Q

What size diameter of fibre are more easily blocked?

A

Smaller nerve fibres blocked more easily as smaller SA and lower number of channels

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14
Q

What amount of myelination makes a fibre more easily to block?

A

Myelinated fibres are blocked more easily than unmyelinated

Only need to block channels at nodes of Ranvier

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15
Q

Are local anaesthetics acids or bases?

A

Weak bases

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16
Q

In what conditions can local anaesthetics exist?

A

As neutral or protonated (become charged)

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17
Q

What are local anaesthetics dependent on?

A

pH

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18
Q

WHen can local anaesthetics block channels?

A

When they are ionised via intracellular binding site

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19
Q

When do local anaesthetics cross membrane?

A

When unionised

They can’t pass through membrane when ionised

20
Q

What is pKa?

A

The pH at which 50% of drug is ionised

21
Q

What do most local anaesthetics have pKa values between?

A

8 and 9

22
Q

Ratio of unionised local anaesthetic :

A

1:1 between extracellular fluid and cytoplasm of axon

Unionised local anaesthetic can cross membranes

23
Q

What types of channels do local anaesthetics bind to?

A

Open or inactive channels

24
Q

What are many local anaesthetics related to?

A

Frequency of neuronal firing

25
Q

When is there faster onset by local anaesthetics?

A

In faster firing neurons

26
Q

What’s duration of action of local anaesthetic dictated by?

A

Rate of removal

27
Q

What factors influence duration of action?

A

Blood flow

Action of plasma esterases (ester-linked local anaesthetics only)

Hydrophobicity of drug

28
Q

What do many local anaesthetics cause in the body?

A

Vasodilation - except coacain and prilocaine

29
Q

What effect does cocaine have?

A

Vasoconstriction

30
Q

What happens when blood flow is decreased to area?

A

Decrease in rate of removal

31
Q

What happens when a local anaesthetic causes vasoconstriction?

A

Can increase duration by 2x

Can decrease bleeding during surgery

32
Q

What’s a risk associated with local anaesthetics that cause vasoconstriction?

A

Ischaemic damage at extremities (e.g. in fingers and toes)

33
Q

Infiltration of locals anaesthetics:

A

Injection into tissues to reach nerve branches / terminals

34
Q

What needs to happen for local anaesthetics to nerve block?

A

Injection around nerve to cause small/large regional block

35
Q

What’s involved with intravenous regional local anaesthetics?

A

Double-cuff method to contain local anaesthetic to limb

36
Q

Where are extradural (epidural) local anaesthetics used?

A

In thoracic, lumbar and sacral regions

37
Q

Where are subarachnoid (intrathecal) local anaesthetics used?

A

Injected into subarachnoid space (CSF)

38
Q

What’s EMLA?

A

Eutectic Mixture of Local Anaesthetics

39
Q

What is EMLA used for?

A

Dermal anaesthesia

40
Q

What’s EMLA a mixture of?

A

Lignocaine and prilocaine

41
Q

Why can high concentrations of lignocaine and prilocaine be used in EMLA/

A

As melting point of mixture is lower than that of individual chemicals

42
Q

What does high concentrations of chemicals in EMLA allow?

A

More chance that more of it will get across the skin

43
Q

Why may there be unwanted side affects of local anesthetics?

A

Due to entry into systemic circulation

44
Q

Side effects when local anaesthetics get into cardiovascular system:

A

Dysrhythmias

Sudden fall in blood pressure - due to effects on heart and vasculature

45
Q

Side effects of local anaesthetics on CNS:

A

Restlessness

Tremors

Convulsions

Respiratory centre depression

Death

Week 7 - 12 (38 decks)

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