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Anatomy term 3 > Local Anaesthetics > Flashcards

Local Anaesthetics Flashcards

1
Q

What is general anaesthesia?

A

total loss of sensation

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2
Q

What is local anaesthesia? (3)

A
  1. regional
  2. local infiltration - cuts, skin incisions
  3. Topical - eye/skin
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3
Q

What are examples of non-pharmacological local anaesthesia methods? (3)

A
  1. cold
  2. pressure
  3. hypoxia
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4
Q

What are the 2 types of pharmacological local anaesthesia methods?

A
  1. not reversible

2. reversible

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5
Q

What are examples of not reversible pharmacological local anaesthesia? (4)

A
  1. Phenol
  2. Ethanol
  3. Radiofrequency
  4. Surgical
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6
Q

What is a local anaesthetic?

A

a drug

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7
Q

What does a local anaesthetic do? (2)

A
  1. reversibly prevents transmission of the nerve impulse in the region to which it is applied
  2. doesn’t affect consciousness
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8
Q

Where can a local anaesthetic block a neuron?

A

Anywhere along the pathway

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9
Q

How is an axon broken down (what components)? (4)

A
  1. epineurium
  2. perineurium
  3. endoneurium
  4. schwann cell
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10
Q

When does the local anaesthetic cross the membrane?

A

Only when ionised

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11
Q

What is an ideal local anaesthetic? (11)

A
  1. reversible
  2. good therapeutic index - ED50 and LD50
  3. Quick onset
  4. Suitable duration
  5. no local irritation even on repeated application
  6. no side effects
  7. no potential to induce allergy
  8. applicable by all rules
  9. cheap
  10. stable
  11. soluble
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12
Q

What is the structure of local anaesthetics?

A
  1. esters - Procaine
  2. amides - Lidocaine

RULE

  • no “i” = ESTER
  • “i” = AMIDE
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13
Q

What was the first local anaesthetic?

A

cocaine

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14
Q

What is the characteristics of local anaesthetics? (3)

A
  1. onset
  2. duration
  3. differential blockade
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15
Q

What does onset of action depend on?

A

pKa

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16
Q

In terms of pH what contributes to a quicker onset of the local anaesthetic?

A

pKa = pH

  • Ionised and non-ionised forms of local anaesthetic is equal

If nearer to 7.35-7.45 the quicker the onset

17
Q

In terms of pH what leads to a delayed onset of the local anaesthetic?

A

pKa > pH

ionised form > unionised form

18
Q

What is the pH of pus?

A

6.9

19
Q

What does duration of action depend on?

A
  1. Protein binding
    - the more protein binding the longer the duration

Bupivacaine - the longest

  1. Length of the intermediate chain joining the aromatic and amine groups
20
Q

What is potency?

A

dose required to produce desired effect

21
Q

What does potency depend on?

A

lipid solubility

  • the more lipid soluble drug penetrates the cell membrane more
  • hence a smaller amount is required to produce a given effect
22
Q

What is differential block?

A

ability to block neuronal conduction

23
Q

What does the ability to block neuronal conduction depend on? (2)

A
  1. type of nerve fibre
    - larger the fibre the slower the onset
  2. Location of nerve fibre
    - outside or in the mantle
24
Q

What are the types of nerve fibres?

A
  1. A
  • alpha - proprioception and somatomotor
  • beta - touch and pressure
  • gamma - motor to muscle spindle
  • delta - pain, cold and touch
25
Q

Why are LAs often given with vasoconstrictors? (4)

A
  1. prolong action
  2. reduce plasma levels - decrease risk of CNS effects
  3. greater anaesthesia at reduced dose
  4. reduce operative haemorhage
26
Q

When are vasoconstrictors not used? (4)

A

When the LAs target areas that are supplied by end-vessels

  1. fingers and toes
  2. penis
  3. ear lobule
  4. ala of nose
27
Q

What are examples of vasoconstrictors? (2)

A
  1. adrenaline (epinephrine)

2. Felypressin (analogue of vasopressin)

28
Q

What are the adverse effects of LAs? (2)

A
  1. hypersensitivity

2. Methaemoglobinaemia

29
Q

What is methaemoglobinaemia a toxic effect of?

A

Prilocaine

  • due to it’s metabolite 0-toluidine
  • this oxidised ferrous to ferric ions
30
Q

What are the symptoms of methaeglobinaemia? (3)

A
  1. cyanosis
  2. lethargy
  3. resp distress - doesn’t respond to O2
31
Q

What is the treatment of methaeglobinaemia?

A

IV methylene blue

32
Q

What is the treatment of LA toxicity?

A
  1. stop injecting the LA
  2. call for help
  3. ABCD
  4. Blood analysis
  5. Intravenous lipid emulsion
33
Q

What is the toxic dose of lidocaine with and without adrenaline?

A

WITHOUT

  • 3mg/kg

WITH

  • 7mg/Kg
34
Q

What is the toxic dose of bupivacaine/ levobupivacaine?

A

WITHOUT

2mg/kg

WITH

2mg/kg

35
Q

What is the toxic dose of prilocaine?

A

WITHOUT

6mg/kg

WITH

8mg/kg

Anatomy term 3 (4 decks)

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