General Anaesthetics Flashcards Preview

PM3B: Autumn > General Anaesthetics > Flashcards

Flashcards in General Anaesthetics Deck (24):
1

What are the three aims of general anaesthesia

Loss of consciousness

Analgesia

Muscle Relaxation (immobility)

2

What are the three main drug classes of general anaesthetics

Gases- Nitrous Oxide

Halogenated Hydrocarbons- Isoflurane

Barbiturates- Thiopental

3

Define minimum alveolar concentration (MAC)

The concentration of vapour in the lungs that is needed to predict movement in 50% of subjects in response to pain stimulus

4

What does a lower MAC value mean

More potent volatile anaesthetic

5

Describe how general anaesthetics inhibit the central nervous system at cellular level and give an example

1. Inhibits synaptic transmission through excitatory ion channels such as glutamate and acetylcholine inotropic and nicotinic receptors

2. Activate inhibitory ion channels such as GABAa and glycine inotropic receptor and two pore potassium channels

Example: general anaesthetics act to reduce excitation or increase inhibition

6

Where do general anaesthetics inhibiting the central nervous system normally act in the brain and spine

Brain:
Midbrain reticular formation- causes unconsciousness
Thalamic sensory relay nuclei (analgesia)

Spinal:
Loss of reflexes
Contributes to control of motor function and muscle relaxation

7

Where does flunitrazepam (Rohypnol) act on

Hippocampus to affect short term memory (amnesia)

8

What are the three things general anaesthetics act on in the peripheral nervous system and what they do to them

Cardiovascular- can cause circulatory depression via decreasing cardiac contractility
- Normally works on sympathatic nervous system, vascular smooth muscle to affect cardiac output or blood pressure

Respiratory- can cause respiratory depression

Muscular- acts on NMJ to cause muscle relaxation

9

What are the 5 stages of general anaesthesia (PIMPM)

Premedication

Induction

Maintenance

Pain relief

Muscle Relaxation

10

What is the premedication stage of general anaesthesia and the purpose of it

Combined drug treatment typically 1-3 hours before anaesthesia

Purpose:
Reduction of anxiety and pain
Promotion of amnesia
Reduction of secretions
Enhancing hypnotic effects of general anaesthesia
Reduction of vagal reflexes to intubation- slows heart
Reduction of post-operative nausea or vomiting centre

11

What are the drug classes used in premeditation, its role and give an example of a drug for each of them

Benzodiazepine:
Diazepam
Increases inhibitory GABA release for sedative and anxiolytic effect

mAChR antagonist
Atropine
Prevents secretion and vagal reflexes

Opioid receptor agonist
Morphine
Reduces pain and sedation

Proton Pump Inhibitors
Metoclopramide
Limits nausea and vomiting

12

What is the induction stage of the general anaesthetic cycle

IV bolus agents induces loss of consciousness and amnesia

13

What are the drugs used in the induction stage and the purpose of each

Propofol or barbiturate (sodium thiopental)
Activate GABAa receptors and promote inhibition (system shutdown)

Thiopental
Accumulate in fat which leads to hangover effect
Associated with profound respiratory
depression

Etomidate
Favoured due to high therapeutic index and therefore lack of respiratory and cardiovascular side effects

Ketamine
NMDA glutamate receptor antagonist
Produces conscious anaesthesia

14

What are the properties that make the induction drugs good for inducing consciousness

Small highly lipophilic compounds with rapid distribution

Very fast onset to brain circulation

Action terminated when distribution into large compartments (muscle)

15

Why are inhalation agents not used in the induction phase

They act slower and are prone to dangerous induction

16

What does the stage of maintenance involve

Volatile
Inhalation agents used to maintain loss of consciousness and amnesia

17

What are the drugs used in the maintenance stages of general anaesthesia and describe them

Isoflurane- halogenated ether

Nitrous Oxide- low potency- used in combination for reducing child birth pain

Halothane- can lead to adverse cardiovascular and respiratory effects

18

What are the properties that make the maintenance drugs good for maintaining loss of consciousness

Inhaled gases with fast onset and offset of action- able to control anaesthesia depth

Can freely cross the blood brain barrier so kinetics are not determined by rate of transfer from inspired air into blood

Has rapid elimination

Fewer side effects

19

What is appropriate pain relief in the general anaesthetic cycle

IV opioid agents used to provide analgesia

20

What are the drugs used in pain relief in the general anaesthetic life cycle

Opioids- morphine and fentanyl

21

What is muscle relaxation in the general anaesthetic cycle

Agents that act on the nicotinic acetylcholine receptors at the neuromuscular junctions to cause immobility during surgery

22

What is the mechanism of action of general anaesthetics that cause muscle relaxation via neuromuscular blocking agents

1. Competitive antagonists of nAchRs

2. Agonist that cause a depolarising block of the muscle end plate (depolarising blocker)

Examples: Atracurium, pancuronium, vercuronium

23

How do competitive nAchR blockers work via Na+ entry and give some examples

1. Depolarises the post synaptic membrane

2. Cause: excitatory postsynaptic potential

3. Generates action potential (threshold reached)

4. Drugs widely used as muscle relaxants alongside anaesthesia

24

How do depolarising nAChR blockers work and give some examples

They continually stimulate the neuromuscular junction by agonists and cause muscle paralysis

Muscle contracts due to maintained depolarisation but cannot repolarise and relax

Causes loss of excitability (Na+ cannot inactivate)

Example: Suxamethonium (succinylcholine)
Causes paralysis during anaesthesia for 10 minutes