Local Anaesthesia Flashcards

1
Q

what is the MOA of local anaesthetics?

A

block the voltage-dependant sodium channels that depolarise the neuron

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2
Q

name 4 factors that influence local anaesthetic action

A
  1. local concentration of the LA
  2. the size of the nerve fibre
  3. nerve myelination
  4. length of nerve exposed to the LA
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3
Q

out of pain, sensory and motor fibres, whcih fibres do LAs block first?

A

pain fibres (myelinated A-delta and non-myelinataed C fibres)

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4
Q

what effect does hypokalaemia and hypercalcaemia have on LA?

A

it antagonizes the blockade.

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5
Q

what is the potency of a LA related to?

A

Its lipid solubility.

a lipophilic aromatic group is what enables the molecule to cross the nerve membrane.

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6
Q

what are the implications of a LA having a high pKa in practice?

A

it means it will be more ionised at physiological pH so its speed of onset will be slower but it will also re-ionise to a greater extent within the cell and produce mroe effective blockade.

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7
Q

what does the term use-dependence mean

A

the more channels are open, the greater the block becomes

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8
Q

name 5 clinical uses for local anaesthetics

A
  1. local infiltration e.g. for suturing
  2. topical
  3. nerve blocks (local and regional)
  4. epidural
  5. spinal
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9
Q

what is the most commonly used LA?

A

lidocaine

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10
Q

is an epidural given inside or outside of the dura mater?

A

outside

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11
Q

what is an epidural anaesthetic often used in combination with?

A

opiate

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12
Q

what space is a spinal aneasthesia given and between which vertebrae usually?

A

the subarachnoid space.

between L3 and L4 usually

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13
Q

what does the spread of the LA within the subarachnoid space depend on in a spinal anaesthetic?

A
  1. the density of the solution

2. the posture of the person during the first 10-15 mins while the solution flows up or down the subarachnoid space.

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14
Q

what does IV regional anaesthesia involve?

A

injection of a dilute solution of LA into a limb after application of a tourniquet

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15
Q

what is IV regional anaesthesia used for?

A

reduction of fractures or removal of ganglia etc.

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16
Q

why should the tourniquet not be released too early when a IV regional anaesthetic is used?

A

risk of systemic toxicity

17
Q

why are vasoconstrictors (e.g. adrenaline) sometimes added to LA solution for injection?

A

most LAs cause vasodilation at the site of injection whcih will enhance their removal. vasoconstrictors are added to prevent this.

18
Q

name 2 local unwanted effects of LAs

A

irritatation and inflammation, ischaemia from use of vasoconstrictor agents

19
Q

name 4 unwanted cardiovascular effects of using LAs

A

myocardial depression,
vasodilatation,
hypotension,
arrhythmias

20
Q

name 5 unwanted CNS effects from LAs

A
agitation, 
confusion,
tremors,
convulstions,
respiratory depression