Anaesthetics

Question 1

What are Guedel’s signs?

Answer 1

Stage 1:
Analgesia and loss of consciousness

Stage 2:
Unconscious
Erratic breathing
Delirium

Stage 3:
Surgical anaesthesia

Stage 4:
Respiratory paralysis
Death

Question 2

What are some examples of volatile GA?

Answer 2

N2O
Diethyl-ether 
Halothane 
Isoflurane 
Xe

Question 3

What is the minimum alveolar concentration?

Answer 3

Used to describe potency of volatile anaesthetics

Alveolar conc at which 50% of subjects fail to move to surgical stimulus
At equilibrium [alveolar] = [spinal cord]

Question 4

What are some factors that affect MAC?

Answer 4

Young age - increased
Old age - decreased

Hyperthermia - increased
Hypothermia - decreased

Pregnancy - increased
Alcoholism - increased

Central stimulants - increased
Other anaesthetics & sedatives - decreased
Opioids - decreased

Question 5

Why is N2O often added to other volatile agents?

Answer 5

Reduces MAC

Therefore reduces dose of primary anaesthetic needed

Question 6

What is the role of GABA receptors in anaesthesia?

Answer 6

GABA is a major inhibitory neurotransmitter
Most anaesthetics potentiate GABA receptors => increased inhibition in the CNS

Leads to:
Anxiolysis, sedation or anaesthesia

Question 7

What are some examples of IV anaesthetics?

Answer 7

Propofol
Barbiturates
Ketamine

Question 8

How is the potency of IV anaesthetics described?

Answer 8

Plasma conc required to achieve end point
Mixed anaesthesia: bolus used as induction, then switched to volatile
TIVA: bolus, then use defined algorithm to infuse to maintain set point

Question 9

What are some examples of local anaesthetics?

Answer 9

Lidocaine
Bupivacaine
Ropivacaine
Procaine

Question 10

What factors determine characteristics of LA?

Answer 10

Lipid solubility => potency
Dissociation constant => time fo onset
Chemical link => metabolism
Protein binding => duration

Question 11

What is the MOA of LA?

Answer 11

Blocks voltage gates sodium ion channels
Channel opens => LA enters channels => blocks entry of sodium => inhibits generation of action potential

Preferentially blocks small, myelinated afferent fibres
Hence blocks nociceptive and sympathetic fibres
Adrenaline increased duration of action

Question 12

What are some indications for local and regional anaesthesia?

Answer 12

Dentistry 
Obstetrics 
Regional surgery - pt awake 
Post-op 
Chronic pain management

Question 13

How is regional anaesthesia used?

Answer 13

Selectively anaesthetises a part of the body so pt can remain awake
Uses a local anaesthetic or opioid

Question 14

What are some side effects of GA?

Answer 14

Post-op N&V
Hypotension
Post-op cognitive dysfunction
Chest infection

Question 15

How do side effects result from local/regional anaesthesia?

Answer 15

Systemic spread

Eg local => cardiac toxicity due to Na channel blocker