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pharm + patient year 3 sem 2 > Local Anaesthetics > Flashcards

Local Anaesthetics Flashcards

1
Q

How are the different effects of cocaine produced?

A

Local anaesthetic- blocking sodium channels

Psychotropic- blockage of monoamine reuptake

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2
Q

What was the first pure local anaesthetic with no psychotropic effects called?

A

Amylocaine

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3
Q

Describe the features of type A alpha spinal nerve fibres.

A

Heavily myelinated
12-20um in diameter
Proprioception motor function

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4
Q

Describe the features of type A beta spinal nerve fibres.

A

Heavily myelinated
5-12um in diameter
Touch and pressure response function

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5
Q

Describe the features of type A gamma spinal nerve fibres.

A

Heavily myelinated
3-6um diameter
Muscle spindle function

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6
Q

Describe the features of type A delta spinal nerve fibres.

A

Heavily myelinated
2-5um diameter
Pain and temperature response function

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7
Q

Describe the features of type B spinal nerve fibres.

A

Light myelination
<3um diameter
Pre-ganglionic ANS function

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8
Q

Describe the features of type C sensory spinal nerve fibres.

A

Not myelinated
0.3-1.2um diameter
Pain response function

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9
Q

Describe the features of type C sympathetic spinal nerve fibres.

A

Not myelinated
0.2-1.3um diameter
Post-ganglionic function

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10
Q

What are polymodal spinal nerve fibres?

A

Able to respond to more than one type of stimulus

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11
Q

What is the major structural difference between motor and sensory neurones in the spinal cord?

A

Motor neurones enter the spinal column via ventral roots

Sensory neurones enter the spinal column via dorsal routes

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12
Q

Briefly describe the structure of dorsal route ganglion sensory neurones.

A

Cell bodies have a single axon that splits

One branch goes to periphery, other into the spinal cord

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13
Q

Briefly describe the structure of nociceptors.

A

Peripheral axon terminal is a bare nerve ending possessing receptors for noxious stimuli
May also be stimulated by protons and ATP released by damaged tissue

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14
Q

Describe the action of chilli peppers on nociceptors in the mouth.

A

Contain capsaicin which activates VR1 receptors
Normal function of these is to respond to high temperatures
Not water soluble therefore water does not cool mouth after spicy

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15
Q

What is the mechanism of action local anaesthetics?

A

Block sodium channels to prevent formation of action potentials and blocking nociception

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16
Q

Describe the structure of voltage gated sodium channels.

A

Alpha subunit is a long chain with 24 membrane spanning domains
Divided into 4 blocks of 6 transmembrane domains
Each pseudosubunit forms a structure with a charged 4th TM domain and membrane dipping domain

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17
Q

Describe how the structure of local anaesthetics aids their function.

A

Amine group allows local anaesthetics to become protonated
LA blocks sodium channels from within the cell therefore uncharged form must be present to allow passage through membrane

18
Q

Describe risk of use dependence with local anaesthetics.

A

Local anaesthetics block sodium channels more strongly in their open or activated states giving rise to use dependence
If LA dissolves through the membrane uncharged and then becomes protonated when reaching the channel binding site it does not require the channel to be open therefore does not show use dependence

19
Q

What is topical anaesthesia?

A

LA formulated as cream or spray and applied directly to skin surface
Allows blockage of signal close to, or at, the peripheral nerve terminal

20
Q

When is topical anaesthesia used?

A

Pain relief for minor conditions i.e. ulcers, haemorrhoids

21
Q

What is infiltration anaesthesia?

A

LA injected into tissue around area to be numbed

Usually affects only the more distal parts of the nerves (distal branches)

22
Q

When may a vasoconstrictor be used in local anaesthesia? Give an example.

A

To prolong duration of infiltration anaesthesia or nerve block
i.e. adrenaline

23
Q

When is infiltration anaesthesia used?

A

Dentistry

24
Q

What is a nerve block?

A

LA injected around a spinal nerve trunk, everything distal to this point will be numbed
Needle is often guided into place with the aid of imaging

25
Q

Why may a nerve block be used?

A

Can give better pain relief than infiltration or topical anaesthesia

26
Q

What is IV regional anaesthesia?

A

Pressure cuff used to cut off blood supply to a limb

LA is then injected and the cuff removed after 20 minutes

27
Q

Why is there a delay between administering IV regional anaesthesia and restoring blood supply?

A

Allows anaesthesia to develop and reduce concentrations of LA in the blood

28
Q

What is spinal anaesthesia?

A

Injection into the subarachnoid space just above the spinal cord causing pain sensation to be lost from all regions supplied by nerves below the level of injection

29
Q

Where can spinal anaesthesia be used?

A

Injection only into the lower spine due to the size of the subarachnoid space

30
Q

Describe the pros and cons of spinal and epidural anaesthesia.

A

Spinal is less versatile than epidural
Epidural shows less motor block
Onset of spinal is faster and less anaesthetic is required
Placement of epidural needle is easier than spinal so can be used anywhere along the spinal column

31
Q

What is epidural anaesthesia?

A

Injection into epidural space just below the vertebral column, usually via a catheter to facilitate further administration

32
Q

How does the effect of epidural anaesthesia vary with dose?

A

Low dose epidurals are often used for analgesia alone

Higher doses can be used for surgical analgesia where the patient needs to remain awake

33
Q

What are the 3 main properties of spinal nerve fibres that affect sensitivity?

A

Degree of myelination
Fibre diameter
Position within the nerve

34
Q

Why is there an allergy risk with LAs?

A

Ester linked drugs can be metabolised to para-aminobenzoic acid which can produce allergy

35
Q

Describe the risk of brain toxicity with LAs?

A

Neuronal activity depressed at low doses
As concentrations increase, activity of inhibitory neurones suppressed more than excitatory ones, can result in convulsions

36
Q

Describe the risk of CV toxicity with LAs?

A

Slow heart rate and reduce blood pressure
Can cause arrhythmia
Vasodilators with the exception of cocaine

37
Q

When may a LA be used in CV emergency?

A

Reduce heart rate in ventricular fibrillation

38
Q

Which LA has a duration of action of 1-3 hours?

A

Lidocaine

39
Q

Which LA has a duration of action of 30-60 minutes?

A

Tetracaine

40
Q

Which LA has a duration of action of 2-5 hours?

A

Bupivacaine

41
Q

Which LA is not safe in obstetrics?

A

Prilocaine

pharm + patient year 3 sem 2 (29 decks)

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