Anaesthetics

Question 1

How can the different types of anaesthetics be split?

Answer 1

Question 2

What is concious sedation?

Answer 2

Use of small amounts of anaesthetic/ benzodiazepines to produce a ‘sleep like’ state

Question 3

What are the 4 stages of Guedel’s signs?

Answer 3

Typical course of conciousness:

Stage 1: analgesia and conciousness

Stage 2: unconcious, breathing erratic, delirium could occur leading to excitment phase (paradoxical excitment)

Stage 3: Surgical anaestheisa, with 4 levels describing increasing depth until breathing is weak

Stage 4: Respiratory paralysis and death

Question 4

How is potency measured in aneasthesia?

Answer 4

MAC - Minimum Alevolar Concentration

[alveolar] at 1 atm at which 50% of subjects fail to move to a surgical stimulus

Question 5

What happens when MAC is at eqilibrium?

Answer 5

At equilibrium [alveolar] = [spinal cord]

Question 6

What factors affect solubility (partition co-efficients) of anaesthesia?

Answer 6

Blood: Gas partition (in the blood)

• low value fast induction and fast recovery

Oil:Gast partition (fat)

• determines potency and slow accumulation due to partition in fat
• high potencu= high fat solubility

Question 7

What factors will affect MAC?

Answer 7

• Age (High in infancts, low in elderly)
• Hyperthermia (increased), hypothermia (decreased)
• Pregnancy (increased)
• Alcholism (increased)
• Central stimulants (increased)
• Other anaesthetics and sedatives (decreased)
• Opiods (decreased)

Question 8

Why are volatile anaesthetics typically mixed with nitrous oxide

Answer 8

• NO reduces the amount of anaesthesia needed
• Therefore, decreases side effects

Question 9

How do most anaesthetics interact with the GABA_A receptor?

Answer 9

• GABA_A is a major inhibitory transmitter
• Ligand gated Cl^- channel
• Most anaesthetics potentiate GABA mediated Cl^- conductance
• Cause neuronal hyperpolarisation to depress CNS activity

Question 10

Which anaesthetics do not target the GABA_A receptor?

Which receptor do they target instead?

Answer 10

• Xe
• N₂O
• Ketamine

Target the NMDA receptor blockin excitation

Question 11

Explain what happens to the brain circuitry when targetted with anaesthetics?

Answer 11

• Reticular formation depressed. Connectivity lost
  
  • usually causes increased arousal
• Thalamus transmits and modifies sensory information
• Hippocampus depressed (memory)
• Brainstem depressed (repiratory and CVS)
• Spincal cord depressed (dorsal horn) and motor neuronal activity

Question 12

Name some of the main intravenous anaesthetics and their speed of onset?

Answer 12

• Propofol (rapid)
• Barbituates (rapid)
• Ketamine (slower)

Question 13

What is TIVA?

Answer 13

Total IntraVenous Anaesthesia

Anaesthesia given by an infusion pump, no volatile gas required → benefical if doing surgery on airways/face

Question 14

How are IV anaesthetics Rx’d?

Answer 14

Usually given as a bolus then infused at a set rate calculated by PK

Question 15

When would you use local and regional anaesthesia?

Answer 15

• Dentistry
• Obstetrics
• Regional surgery
• Post op- (wound pain)
• Chronic pain management

Question 16

Name some local anaesthetics

Answer 16

• Lidocaine
• Bupivacaine
• Ropivacaine
• Procaine

Question 17

How to local anaesthetics work?

Answer 17

• Bind to the inside of voltage gated Na⁺ channel
• Need to become charged to pass through
• Block is use dependant → higher firing = more effective block
• Blocks small myelinated afferent nerves preferentially

Question 18

What are some of the main side effects of general anaesthesia?

Answer 18

• PONV - post operative nausea and vomiting
• CVS- hypotension
• POCD- post operative cognitive dysfunction
• Chest infection