Anaesthetics

Question 1

What are the 4 main effects that anaesthetics have on the CNS

Answer 1

Analgesia
Hypnosis (loss of consciousness)
Depressed spinal reflexes
Muscle relaxation

Question 2

Why are a range of adjuvant drugs used in anaesthesia, rather than one agent

Answer 2

No single agent produces all desirable effects

‘Division of labour’ between drugs = finer control of anaesthetic depth

Combination can reduce MAC/reduce risk of CNS depression

Question 3

Give an example of the range of agents used to anaesthetise

Answer 3

Benzodiazepine: sedation, amnesia
Propofol: sedation to unconsciousness
Nicotinic Ach receptor antagonists or depolarising agents (e.g. Succinylcholine): musc relaxation and reflex depression
Nitrous oxide: anelgesia

Question 4

What is MAC

Answer 4

Minimal alveolar concentration
% of inhaled anaesthetic (alveolar conc) that abolishes response to surgical incision in 50% of patients

Related to lipid solubility
Lower = more potent
Affected by age
Can be reduced when given in combination e.g. With nitrous oxide

Question 5

What is the broad mechanism of action of anaesthetics

Answer 5

Affect a range of ligand gated ion channels:
Modulate balance between excitatory (glutamate) and inhibitory (GABA) neurotransmission in the brain

(And lipid solubility for inhalational and IV agents)

Question 6

What are the molecular sites of action for anaesthetics

Answer 6

Post-synaptic transmission of inhibitory and excitatory ligand gated ion channels

Question 7

What are the systems targets of anaesthetics

Answer 7

Connectivity in Reticular formation (midbrain, hindbrain, thalamus)
Hippocampus (depressed memory)
Brainstem (depressed resp/CVS)
Spinal cord: dorsal horn (analgesia), motor neuron activity (MAC)

Question 8

How do anaesthetics affect inhibitory ligand gated ion channels

Answer 8

GABA and glycine:

Incase their potency

Decrease EC50 (lower amount of neurotransmitter needed to produce effect)

Increase chloride channel permeability = hyperpolarisation

Question 9

How do anaesthetics affect excitatory ligand gated ion channels

Answer 9

Unchanged potency but decreased efficicy of excitatory ligand

Non-competitive: once bound by anaesthetic, inactivates receptor

But affinity of remaining unbound receptors unchanged

Overall: reduces inward movement of excitatory channels

Nicotinic Ach receptors:
Reduces excitatory Na currents

NMDA receptors (Responsive to glutamate):
Reduces Ca current

Question 10

What are the main ADRs of anaesthetics

Answer 10

CNS depression
Resp depression
Arrhythmia with hypotension from reduced vascular resistance
Raiced ICP From increased vascular resistance
Post-op nausea and vomiting
Bronchidilation (malignant hyperthermia)

Question 11

What are the main stages of anaesthesia

Answer 11

Induction (begin inhalational agent, adjuvant administered IV)
Maintinence (keep adjuvants in balance)
Recovery (withdraw agents, monitor physiological function)

Question 12

What are Guedel’s signs

Answer 12

Stages of anesthesia:

1. Analgesia and consciousness
2. Unconscious, breathing erratic
3. Surgical anaesthesia
4. Respiratory paralysis, death

Question 13

What are the 2 main types of anaesthetics and give some examples

Answer 13

Inhalational agents
E.g. Nitrous oxide, isoflurane

IV agents
E.g. Propofol, ketamine