Local Anaesthetics

Question 1

Pharmacological ways of stopping pain - non-reversible

Answer 1

Phenol
Ethanol
Radiofrequency
Surgical

Question 2

Reversible pharmacological ways of stopping pain

Answer 2

Local anaesthetics

Question 3

Where are local anaesthetics injected? what does this mean for its movement in the body?

Answer 3

Around a nerve

Has to pass through epi->peri->endoneurium then through the nerves in the nerve fibre to reach central axons- takes time to act

Question 4

Mode of action of local anaesthetics

Answer 4

1. LA crosses membrane

2. binds intracellularly to Na channel

Question 5

Crossing the membrane requires what of LA? Why is this a problem?

Answer 5

Them to be uncharged

Problem as only binds when ionised

Question 6

Local anaesthetics bind to what subunit in an Na channel?

Answer 6

Alpha subunit

Question 7

3 constituent parts of cocaine molecule

Answer 7

Lipophilic
Intermediate chain
Hydrophilic

Question 8

Types of cocaine

Answer 8

Amides or esters

Question 9

Looking at general names between amides and esters

Answer 9

i is included before -caine in amides

Question 10

pKa wants to equal pH - why?

Answer 10

Ionised and non-ionised forms of local anaesthetics are equal

Quicker onset

Question 11

Sensory function lost in what order

Answer 11

Cold, warmth
Pain (Aa fibres, then second pair of C fibres)
Touch, deep pressure
Motor function

Question 12

What are often added to LAs?

Answer 12

Vasoconstrictors

Question 13

Why vasoconstrictors?

Answer 13

Prolong action
Reduce plasma levels
Reduced dose of anaesthesia
Reduced operative haemorrhage

Question 14

When not to add vasoconstrictors?

Answer 14

To areas supplied by end vessels

Fingers&toes, penis, ear lobule, ala of nose

Question 15

Which vasoconstrictors are used?

Answer 15

Adrenaline

Felypression - less effective but not effect on heart conduction/contraction

Question 16

Lipid solubility determines what

Answer 16

Potency of LA

Question 17

Adverse effects of LAs

Answer 17

Hypersensitivity - anaphylaxis, more common in esters, may be rxn to preservatives

Methaemoglobinaemia - prilocaine problem, metabolised 0-toluidine which oxidises ferrous to ferric ions, stops O2 binding, cyanosis, lethargy, resp distress which is not responsive to oxygen

Question 18

Treatment of methaemoglobinaemia

Answer 18

IV Methylene blue 1.5mg/kg

Question 19

LA toxicity affects what first

Answer 19

Highly sensitive areas of body e.g. eyes, face, ears

Moves to inhibitory parts of brain producing twitches

Question 20

LA toxicity progression of symptoms

Answer 20

Lightheaded, tinnitus, circumoral and tongue numbness

Visual disturbances
Muscular twitching
Convulsions
Unconsciousness
Coma
Resp arrest
CVS depression

Question 21

Treatment of LA toxicity

Answer 21

Stop injecting
Call for help
A: maintain airway, maybe secure with traceal tube
B: give 100% O2 and ensure lung ventilation
C: Confirm of establish IV access
D: control seizures

Draw blood for analysis
Assess CVS function
Start cardiopulmonary resus
Give IV lipid emulsion