Session 7 - Anaesthesia

Question 1

Give examples of volatile general anaesthetics.

Answer 1

Nitrous oxide 
Chloroform 
Halothane 
Fluroxene 
Isoflurane 
Cyclopropane 
Xe

Question 2

Give examples of intravenous general anaesthetics.

Answer 2

Propofol
Barbiturates
Etomidate
Ketamine

Question 3

Describe the 4 stages of Guedel’s signs.

Answer 3

Stage 1: analgesia but still conscious, normal muscle tone
Stage 2: unconsciousness, breathing erratic, delirium could occur leading to an excitement phase, normal or increased muscle tone
Stage 3: surgical anaesthesia, with four levels describing increasing depth until breathing is weak, slightly to markedly relaxed muscle tone
Stage 4: respiratory paralysis and death, flaccid muscle tone

Question 4

Volatile anaesthetic potency is described using what measurement?

Answer 4

MAC (Minimum Alveolar Concentration) - the alveolar concentration of a volatile at which 50% of subjects fail to move in response to a surgical stimulus.

Question 5

What factors affect MAC?

Answer 5

Age (MAC higher in infants, lower in elderly)
Hyperthermia (increased), hypothermia (decreased)
Pregnancy (increased)
Alcoholism (increased)
Central stimulants (increased)
Other anaesthetics and sedatives (decreased)
Opioids (decreased)

Question 6

What factors affect induction and recovery from anaesthetics?

Answer 6

Partition coefficients (solubility)

• blood:gas partition (in blood)
• oil:gas partition (in fat)

Question 7

Why is nitrous oxide often added to other volatile agents?

Answer 7

Nitrous oxide reduces the MAC required for many volatile anaesthetics to work. Therefore adding nitrous oxide reduces dosing of the other volatile agent.

Question 8

What is the main target receptor for anaesthetic agents?

Answer 8

GABA receptors

Question 9

What effect do anaesthetics have on GABA receptors and what does this result in?

Answer 9

With the exception of Xe, N2O and ketamine, all anaesthetics potentiate GABA mediated Cl- conductance. This depresses CNS activity leading to:

• anxiolysis
• sedation
• anaesthesia

Question 10

What systems in the brain are targeted by anaesthetics?

Answer 10

Reticular formation (hindbrain, midbrain and thalamus) depressed.
Hippocampus depressed (memory).
Brainstem depressed (respiratory and some CVS).
Spinal cord - dorsal horn depressed (analgesia) and motor neuronal activity depressed (MAC)

Question 11

Of the main intravenous anaesthetics which are rapid acting and which are slower acting?

Answer 11

Propofol - rapid
Barbiturates - rapid
Ketamine - slower

Question 12

What is the main target receptor for ketamine?

Answer 12

Inhibits NMDA receptors

Question 13

What is TIVA?

Answer 13

Total Intravenous Anaesthesia (TIVA). When a intravenous anaesthetic is used as the sole anaesthetic rather than for induction.

Question 14

When are local and regional anaesthetics most commonly used?

Answer 14

Dentistry 
Obstetrics
Regional surgery (patient awake) 
Post-op (wound pain)
Chronic pain management (e.g postherpetic neuralgia)

Question 15

Give examples of local anaesthetics.

Answer 15

Lidocaine
Bupivacaine
Ropivacaine
Procaine

Question 16

What is regional anaesthesia?

Answer 16

Anaesthetising part of the body, often described as a nerve ‘block’. Patient remains awake. Uses local anaesthetic or an opioid.

Question 17

What are the main possible side effects of general anaesthesia?

Answer 17

Post-operative nausea and vomiting (PONV)
CVS - hypotension
Post-operative cognitive dysfunction (POCD) (increases with age)
Chest infection

Question 18

What is the main possible side effect of local anaesthetics?

Answer 18

Cardiovascular toxicity (due to systemic spread of anaesthetic, locals are Na+ channel blockers)