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Clinical > Local Anaesthetics > Flashcards

Local Anaesthetics Flashcards

1
Q

When should you use local anaesthetics?

A

When loss of consciousness is neither necessary or desirable.

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2
Q

Should local anaesthetics be used in large operations?

A

For major surgery with sedation and as post-operative analgesia.

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3
Q

What are the two general structures of local anaesthetics?

A

Procaine and lidocaine (lignocaine).

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4
Q

Which type of anaesthetic is more common?

A

Amides are more commonly used, while esters are rarely used.

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5
Q

Which type of local anaesthetic is associated with allergic reactions?

A

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

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6
Q

What are examples of amide containing local anaesthetics?

A

Lidocaine, prilocaine, bupivacaine and articaine.

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7
Q

What are the properties of lidocaine?

A

Medium acting with rapid onset.

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8
Q

What are the actions of prilocaine?

A

Medium acting with no vasodilation.

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9
Q

What are the properties of bupivacaine?

A

Long acting with slow onset.

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10
Q

What are the actions of articaine?

A

Short acting with rapid onset.

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11
Q

What are examples of ester-containing local anaesthetics?

A

tetracaine, chloroprocaine and benzocaine.

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12
Q

What are the actions of tetracaine?

A

Long acting with very slow onset.

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13
Q

What are the properties of chloroprocaine?

A

Medium acting.

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14
Q

What are the actions of benzocaine?

A

Atypical mechanism of action.

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15
Q

How do local anaesthetics work in general

A

By reversibly blocking voltage-gated sodium ion channels.

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16
Q

What do local anaesthetics do to membranes?

A

Stabilises excitable membranes and prevents membranes from being depolarised.

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17
Q

What does a peripheral nerve consist of?

A

Fibres of different function, diameter and insulation.

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18
Q

Can the constituents of the peripheral nerve be blocked by LAs?

A

All can be blocked, but at different rates.

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19
Q

What is the order of loss in the peripheral loss due to LAs?

A

Pain, temperature, proprioception and finally skeletal muscle tone.

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20
Q

What are the factors that affect the probability that a LA will block an impulse?

A

Diameter of the fibre and the myelination status.

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21
Q

How does the diameter of the fibre affect the probability that a LA will block an impulse?

A

Smaller nerve fibres are blocked more easily.

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22
Q

How does the myelination status affect the probability that a LA will block an impulse?

A

Myelinated fibres are blocked more easily than unmyelinated ones.

23
Q

What other non-fibre factors affect the probability that a LA will block an impulse?

A

Length of nerve exposed to drug, length of time exposed to drug and conc of drug.

24
Q

What is the chemical status of LAs?

A

They are weak bases.

25
Q

When do LAs block voltage-gated sodium channels?

A

They block when they are ionised via an intracellular binding site.

26
Q

What is the side effect of ionised LAs?

A

They cannot pass through the membrane when ionised.

27
Q

What is the no use-dependence pathway?

A

The hydrophobic pathway.

28
Q

What is the use-dependent pathway?

A

The hydrophilic pathway.

29
Q

What is the pKa of most LAs?

A

Between 8 and 9.

30
Q

What is the Henderson-Hasselbalch equation for a weak base?

A

pKa-pH=log10((BH+)x(B)).

31
Q

How do use-dependence LAs work?

A

They bind to open or inactive channels.

32
Q

Why are they called use-dependence LAs?

A

Related to frequency of neuronal firing. There is faster onset in faster firing neurones.

33
Q

What is the duration of the use-dependent LAs dictated by?

A

The rate of removal of the LA.

34
Q

What is the rate of removal of an LA dictated by?

A

Blood flow, action of plasma esterases and the hydrophobicity of the drug.

35
Q

What do most LAs cause?

A

Vasodilation.

36
Q

Which LAs do not cause vasodilation?

A

Cocaine and prilocaine

37
Q

What is ischaemia?

A

An inadequate flow of blood to a part of the body, caused by a constriction or blockage of vessels supplying it.

38
Q

Why do some LAs aim to cause vasoconstriction?

A

Decreased blood flow to the area means decreased rate of removal of the drug, therefore longer lasting.

39
Q

What are the different routes of administration of an LA?

A

Surface, infiltration, nerve block, intravenous regional, extradural and subarachnoid.

40
Q

What are examples of surface routes of administration of LA?

A

Nose, mouth, bronchial tree, cornea and urinary tract.

41
Q

What are examples of infiltration routes of administration of LA?

A

Injection into tissues to reach nerve branches/terminals.

42
Q

What are examples of nerve block routes of administration of LA?

A

Small or large regional block by injection around the nerve.

43
Q

What are examples of intravenous regional routes of administration of LA?

A

Double-cuff method to contain LA to a limb.

44
Q

What are examples of extradural routes of administration of LA?

A

Used in thoracic, lumbar and sacral regions.

45
Q

What are examples of subarachnoid routes of administration of LA?

A

Drug injected into the subarachnoid space (CSF).

46
Q

What is in EMLA?

A

Mixture of lignocaine and prilocaine.

47
Q

What does EMLA stand for?

A

Eutectic mixture of local anaesthetics.

48
Q

What are the chemical properties of EMLA?

A

properties of EMLA?

The melting point of the mixture is lower than that of the individual chemicals.

49
Q

Why do the properties of EMLA allow it to work?

A

Because of the properties, a higher conc of both chemicals in the mix can be used.

50
Q

What causes side effects of LAs?

A

Unwanted side effects due to entry into systemic circulation.

51
Q

What side effects could occur in the cardiovascular system?

A

Dysrhythmias and a sudden fall in blood pressure.

52
Q

What is dysrhythmias?

A

An abnormal heart beat.

53
Q

What are the side effects in the CNS caused by LAs?

A

Restlessness, tremors, convulsions, respiratory centre depression and death.

Clinical (6 decks)

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