Local anaesthesia

Question 1

What sensation are nociceptors involved in?

Answer 1

Pain

Question 2

What does general anaesthesia cause?

Answer 2

Loss of conciousness

Question 3

Whats does local anaesthesia cause?

Answer 3

Local reversible pain relief without loss of conciousness

Question 4

How is an action potential produced?

Answer 4

• 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

Question 5

What is the cycle voltage gated Na channels go through?

Answer 5

Open

Closed

Inactive

Question 6

What are the two anaesthetic pathways?

Answer 6

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

Question 7

In which form can molecules cross the phospholipid bilayer?

Answer 7

Uncharged

Question 8

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

Answer 8

70-90%

Question 9

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

Answer 9

10-30%

Question 10

Explain the hydrophilic pathway:

Answer 10

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

Question 11

Explain the hydrophobic pathway:

Answer 11

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

Question 12

What type of chemical are Local anaesthetics?

Answer 12

Weak bases

Question 13

Which group in the local anaesthetic structure is lipophilic?

Answer 13

The aromatic group with various residues depending on anaesthetic

Question 14

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

Answer 14

The amine group

Question 15

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

Answer 15

Ester or amide

Question 16

What breaks down the ester chains?

Answer 16

Broken down quickly by esterase’s in blood plasma

Question 17

What breaks down amide chains?

Answer 17

Enzymes in the liver

Question 18

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

Answer 18

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

Question 19

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

Answer 19

• interacting with the Na channel
• Anaesthetic effect

Question 20

What is the henderson hasselbach used to calculate?

Answer 20

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)

Question 21

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

Answer 21

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

Question 22

Which neurones are more sensitive to local anaesthetic?

Answer 22

Those with a smaller diameter and unmyelinated

Question 23

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

Answer 23

Aδ

Sensory afferents

Question 24

Which sensations to local anaesthetics block?

Answer 24

Pain

Touch

Temp

Loss of m. control

Question 25

Which of these sensations returns first?

Answer 25

m. control

Question 26

Which of these sensation returns last?

Answer 26

Pain

Question 27

Where is epidural anaesthesia applied?

Answer 27

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)

Question 28

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

Answer 28

30 mins - this is why if too late it will not be given in childbirth

Question 29

Where does epidural anaesthesia work?

Answer 29

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

Question 30

When is epidural anaesthesia often used?

Answer 30

Childbirth

Question 31

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

Answer 31

Intrathecal (spinal) anaesthesia

Question 32

When is intrathecal (spinal) anaesthesia often used?

Answer 32

In emergency C section

Question 33

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

Answer 33

Subarachnoid space close to the membrane in the lumbar area

Question 34

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

Answer 34

Blocks distal sensation (abdomen, legs etc.)

Question 35

What is intra-articular anaesthesia?

Answer 35

Anaesthesia injected into the joints

Question 36

What is intravenous regional anaesthesia?

Answer 36

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

Question 37

What is infiltration anaesthesia?

Answer 37

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

Question 38

What is a nerve block?

Answer 38

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

Question 39

What is surface anaesthesia?

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

Qx-314

Question 42

What are the 4 main side effects of local anaesthesia?

Answer 42

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!)