Local Anaesthesia

Question 1

What is local anaesthesia?

Answer 1

Local anaesthesia is defined as a loss of sensation in a circumscribed area of the body caused by depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves.

Question 2

What is an action potential?

Answer 2

The AP is a transient depolarization of the membrane which causes an increased permeability of the membrane to Sodium ions with a delayed increase in permeability to potassium

Question 3

What is lost in “the loss of nerve function?”

Answer 3

Pain
Temperature
Touch
Proprioception
Finally sk muscle tone.

Question 4

What are the uses of local anaesthesia?

Answer 4

Topical (EMLA)
• Local/field
• IV block ( Biers block)
• Peripheral nerve block e.g. Radial N
• Plexus block e.g. Brachial
• Central neuraxial e.g. Epidural, Spinal.

Question 5

What are the two classifications of local anaesthesia?

Answer 5

1. Amides

2. Esters

Question 6

List amide LA drugs

Answer 6

*Lignocaine
• Bupivacaine
• Prilocaine
• Ropivacaine

Question 7

List Ester LA drugs

Answer 7

• Cocaine
• Procaine
• Amethocaine
• Tetracaine

Question 8

What is EMLA?

Answer 8

Eutectic mixture of local anaesthesia - Eutectic means a mixture of substances in fixed proportions , that melts and freezes at a certain temperature

Usually lignocaine and Prilocaine

Question 9

How is EMLA applied?

Answer 9

Applied topically and covered

• Needs an hour to take effect
• Good for IV access in children , but can cause vasoconstriction

Question 10

Side effect of EMLA on children

Answer 10

Vasoconstriction

Question 11

What is the other indication for Lignocaine?

Answer 11

It’s also an anti arrhythmic drug

Question 12

1. Describe the onset of Lignocaine.
2. How long does it last?
3. What concentrations does it come in?
4. Recommended doses
5. Side effects

Answer 12

1. Rapid!
2. 60 to 90 minutes
3. Comes in 1 % and 2 % solutions
4. 3 ~ 5 mg/kg W/o adrenaline
   7 mg/kg with adrenaline
5. Mainly neurotoxic

Question 13

1. Describe the onset of action for Bupivacaine
2. What concentrations does it come in?
3. Dosage
4. Side effects

Answer 13

1. Slower than Lignocaine but lasts longer , especially with a vasoconstrictor
2. Comes in 0.5% [] , also comes in as heavy or plain ( heavy contains dextrose)
3. 2-3 mg/kg with or without adrenaline
4. Mainly cardiotoxic

Question 14

How do we convert % to mg/ml?

Answer 14

We take % and multiply by 10

Question 15

Calculate the maximum dosage you’re going to administer to the patient:

40kg patient using 1% lignocaine

Answer 15

Remember : For 1% and 2% lignocaine , we give 3-5 mg/kg

1% Lignocaine is = 1 x 10 = 10 mg/ml

40kg x 5mg/kg = 200 mg

We want to convert this to ml , now we know 1% solution of Lignocaine is 10mg/ml , therefore:

200/10 = 20 ml

Question 16

List specific LA CNS side effects

Answer 16

Dizziness 
Tinnitus 
Circumoral numbness ( numbness around the mouth) 
Abnormal taste 
Confusion 
Seizures 
Decreased LOC 
Coma 
Resp depression

Question 17

List specific LA CVS side effects

Answer 17

Tachycardia with adrenaline ??
Otherwise - Bradycardia 
Heart block 
Vasodilation 
Hypotension

Question 18

Other side effects of LA that aren’t CNS or CVS

Answer 18

Allergic reactions : skin rashes ,itching

Question 19

How do we manage LA toxicity?

Answer 19

Stop injecting
• Call for help
• ABC
• A-ETT
• B-FiO2, hyperventilate
• C-defib, CPR, fluids, inotropes
• Prevent/control seizures (midazolam, propofol)
• Lipid emulsion (20% intralipid)
• 1ml/kg (over 1min) can repeat x3
• Infusion 0.25ml/kg/min