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** Pharmacology - CF > Local anaesthesia > Flashcards

Local anaesthesia Flashcards

1
Q

What sensation are nociceptors involved in?

A

Pain

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2
Q

What does general anaesthesia cause?

A

Loss of conciousness

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3
Q

Whats does local anaesthesia cause?

A

Local reversible pain relief without loss of conciousness

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4
Q

How is an action potential produced?

A
  • Neuronal resting membrane potential = negative
  • Depolarisation = opening of voltage gated Na channels = positive membrane potential = action potential at threshold
  • Na channels inactivate within a few ms = repolarisation
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5
Q

What is the cycle voltage gated Na channels go through?

A

Open

Closed

Inactive

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6
Q

What are the two anaesthetic pathways?

A
  • Hydrophillic (use dependent = clinically most relevant)
  • Hydrophobic (non use dependent)
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7
Q

In which form can molecules cross the phospholipid bilayer?

A

Uncharged

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8
Q

What % of the LA is found in the charged form in the body?

A

70-90%

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9
Q

Which % of the LA is found in the uncharged form in the body?

A

10-30%

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10
Q

Explain the hydrophilic pathway:

A

INSERT PIC

N.B. this pathway can only work when sodium channels are being used (increased pain = more Na channels = more LA can access and bind the LA binding site)Equilibrium between charged and uncharged form

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11
Q

Explain the hydrophobic pathway:

A

Insert pic

N.B. the LA stays in the uncharged form and moves through the membrane to the LA binding side and inhibits Na channel from inside membrane

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12
Q

What type of chemical are Local anaesthetics?

A

Weak bases

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13
Q

Which group in the local anaesthetic structure is lipophilic?

A

The aromatic group with various residues depending on anaesthetic

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14
Q

Which group in the local anaesthetic structure is hydrophilic when it accepts protons?

A

The amine group

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15
Q

Which group in the local anaesthetic structure is the intermediate chain?

A

Ester or amide

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16
Q

What breaks down the ester chains?

A

Broken down quickly by esterase’s in blood plasma

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17
Q

What breaks down amide chains?

A

Enzymes in the liver

18
Q

What 3 things is the uncharged (unionised) form of local anaesthetic important for?

A
  • penetration of the neural sheath
  • crossing the plasma membrane (access sight of action)
  • rate of onset of effect
19
Q

what 2 things is the charged (ionised) form of local anaesthetic important for?

A
  • interacting with the Na channel
  • Anaesthetic effect
20
Q

What is the henderson hasselbach used to calculate?

A

The ratio of charged and uncharged form of local anaesthetic = how well it will reach site of action (can calculate the % of uncharged and charged)

21
Q

If a local anaesthetic is less uncharged, is it more or less effective than another local anaesthetic that has more uncharged?

A

It is worse because it is more difficult for the local anaesthetic to reach the site of action

22
Q

Which neurones are more sensitive to local anaesthetic?

A

Those with a smaller diameter and unmyelinated

23
Q

Which are the two types of nerve fibre mainly involved in pain?

A

Aδ

Sensory afferents

24
Q

Which sensations to local anaesthetics block?

A

Pain

Touch

Temp

Loss of m. control

25
Q

Which of these sensations returns first?

A

m. control

26
Q

Which of these sensation returns last?

A

Pain

27
Q

Where is epidural anaesthesia applied?

A

Injected epidurally (in the lumbar area) on top of dura mater (doesn’t interfere with nerves -> crosses membranes and sheaths of axons to take effect)

28
Q

How long does it take for epidural anaesthesia to start working?

A

30 mins

  • this is why if too late it will not be given in childbirth
29
Q

Where does epidural anaesthesia work?

A

Blocks distal sensation (abdomen, legs etc, - everything down!)

30
Q

When is epidural anaesthesia often used?

A

Childbirth

31
Q

What is the other type of local anaesthesia used at the spinal level?

A

Intrathecal (spinal) anaesthesia

32
Q

When is intrathecal (spinal) anaesthesia often used?

A

In emergency C section

33
Q

In intrathecal (spinal) anaesthesia where is the anaesthetic injected?

A

Subarachnoid space close to the membrane in the lumbar area

34
Q

Where is sensation blocked with the use of intrathecal (spinal) anaesthesia?

A

Blocks distal sensation (abdomen, legs etc.)

35
Q

What is intra-articular anaesthesia?

A

Anaesthesia injected into the joints

36
Q

What is intravenous regional anaesthesia?

A
  1. a pressure cuff is used to cut off the circulation in the limb (stops the anaesthetic reaching the heart and brain)
  2. Anaesthesia injected into a major blood vessel
  3. locally metabolised and then the pressure cuff is released
37
Q

What is infiltration anaesthesia?

A

The anaesthesia is injected into the mucosa near the periphery of nociceptors & it diffuses into the nociceptors e.g. in maxilla

38
Q

What is a nerve block?

A

Anaesthesia injected higher up the axons (anaesthetises larger areas than infiltration) e.g. in mandible

39
Q

What is surface anaesthesia?

A

Topically applied anaesthetic that diffuses into the tissue through thin mucous membranes

e.g throat losenges or Emla = used to reduce the pain of needle for anaesthetics

40
Q

Which local anaesthetic is permanently uncharged and used for surface anaesthesia only?

A

Benzocaine

(has no amine group = non-use dependent pathway)

41
Q

Which local anaesthetic is permanently charged and therefore only used experimentally?

A

Qx-314

42
Q

What are the 4 main side effects of local anaesthesia?

A
  1. = Paresthesia (long term numbness or altered sensation e.g. tingling)
  2. = hypersensitivity (local reactions, asthma, anaphylactic shock)
  3. = CVS -> decrease heart contractility, arrhythmia, vasodilation (except cocaine) = carries drug away quickly unless use with vasoconstrictor adrenaline (prolongs LA action, decreases LA toxicity BUT may cause ischaemia & adrenaline side effects need to be watched e.g. in individuals with heart problems)
  4. = CNS if in blood = agitation, confusion & excitement; convulsants & seizures = muscle relaxant & potentiates CNS inhibition (coma & respiratory depression = needs life support!)

** Pharmacology - CF (4 decks)

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