Katzung 12th ed - Chapter 25 - General Anaesthetics - Intravenous (1)

Question 1

What class of drug is thiopentone?

Answer 1

Thiopentone is an ultra-short-acting barbiturate given IV.

Question 2

Describe the basic pharmacodynamics of thiopentone and phenobarbitone.

Answer 2

Bind to GABA receptors, prolong the duration of chloride channel opening, causing inhibition of action potential propagation. These can cause sedation, hypnosis, and anticonvulsant activity.

Question 3

Describe the distribution of thiopentone.

Answer 3

Thiopentone is highly lipid-soluble, and achieves plasma:brain equilibrium within one minute of IV administration.

Question 4

What is the duration of action of thiopentone? What pharmacokinetic feature of thiopentone determines the offset of its CNS effects?

Answer 4

Duration of action is 20-30 minutes, due to its rapid redistribution from CNS to skeletal muscle and adipose tissues.

Question 5

Describe the metabolism and elimination of thiopentone and phenobarbitone.

Answer 5

Both are metabolized SLOWLY in the liver to produce water-soluble inactive metabolites that are excreted in the urine.

Question 6

Describe the basic pharmacodynamics of propofol.

Answer 6

Propofol potentiates the inhibitory effect of GABA and glycine, causing hypnosis. It is used for both induction and maintenance of anaesthesia.

Question 7

What dose of propofol is given to achieve sedation?

Answer 7

0.5 - 1 mg/kg.

Question 8

What dose of propofol is given to achieve anaesthesia?

Answer 8

2-2.5 mg/kg.

Question 9

Describe the cardiovascular adverse effects of propofol.

Answer 9

Reduced PVR –> hypotension.

Negative inotrope.

Question 10

How is propofol presented?

Answer 10

As an oil in water emulsion.

Question 11

Describe the metabolism and excretion of propofol.

Answer 11

Rapidly metabolized in the liver (10 times faster than thiopentone) and excreted in urine.

Question 12

In one word, explain what largely determines the offset of CNS effect of propofol.

Answer 12

Redistribution.

Question 13

What is the distribution half-life of propofol?

What is the elimination half-life of propofol?

Answer 13

Distribution half-life 2-8 minutes.

Elimination half-life 30-60 minutes.

Question 14

What is the volume of distribution of propofol: small or large? Why?

Answer 14

Small Vd, due to being 90% protein-bound.

Question 15

What do we know about the mechanism of action of ketamine?

Answer 15

Largely unknown, but it may involve blockade of glutamate (NMDA) receptors.

Question 16

What is the IV dose of ketamine to achieve anaesthesia for a short surgical procedure?

Answer 16

1-4mg/kg, given slowly over 60 seconds.

Question 17

Describe the cardiovascular adverse effects of ketamine.

Answer 17

By causing inhibition of noradrenaline reuptake, ketamine causes increased HR, BP and cardiac output. It is a positive inotrope.

Question 18

Name one CNS adverse effect that happens in 12% of patients receiving ketamine.

Answer 18

Emergence phenomena: disorientation, sensory and perceptual illusions, vivid dreams.

Question 19

Describe the distribution of ketamine.

Answer 19

Highly lipid soluble, rapidly distributed to all tissues.

Question 20

How is ketamine metabolised and excreted?

Answer 20

Hepatically metabolized. Renally excreted.

Question 21

What is meant by an anaesthetic agent’s alpha half-life? And the beta half-life?

Answer 21

Alpha half-life refers to the Distribution half-life.

Beta half-life refers to the Elimination half-life.

Question 22

Which is metabolized more slowly: Ketamine or Propofol? Which one has a longer duration of effect?

Answer 22

Ketamine is metabolized more slowly (beta half-life 2.5 hours) than Propofol (beta half-life 0.5-1 hours).
Ketamine and Propofol both have a very similar onset (30 seconds) and duration of action (alpha half-lives both about 2-10 minutes)

Question 23

Which IV anaesthetic agent causes raised ICP?

Answer 23

Ketamine

Question 24

What is an “added bonus” effect of propofol, aside from its anaesthetic effects?

Answer 24

It has anti-emetic properties.