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Part 3 – PM3B COPY T > (PM3B) General Anaesthetics > Flashcards

(PM3B) General Anaesthetics Flashcards

1
Q

What is Lister’s carbolic spray?

A

Antiseptic

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2
Q

What are the aims of general anaesthesia?

A

(1) Loss of consciousness (+ amnesia)
(2) Analgesia
(3) Muscle relaxation (immobility)

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3
Q

Give an example of a halogenated hydrocarbon.

A

Isoflurane

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4
Q

Give an example of a barbiturate.

A

Thiopental

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5
Q

What is lipid theory?

A

Idea that general anaesthetics acted by integrating into the plasma membrane

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6
Q

How is anaesthetic action measured?

A

Minimum alveolar concentration (MAC)

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

Inversely proportional to potency

Lower MAC value = more potent volatile anaesthetic

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7
Q

What does a low MAC value indicate?

A

More potent volatile anaesthetic

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8
Q

What effect do general anaesthetics have on a cellular level?

A

Inhibit synaptic transmission

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9
Q

What are the actions of general anaesthetics on the CNS?

A

(1) Inhibit excitatory ion channels such as glutamate + ACh ionotropic receptors
(2) Activate inhibitory ion channels such as GABA(A) ionotropic receptors and two-pore potassium channels
i. e. to reduce excitation/ increase inhibition

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10
Q

How do general anaesthetics exhibit an effect on consciousness?

A

Act at midbrain reticular formation

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11
Q

How do general anaesthetics exhibit an analgesic effect?

A

Act at thalamic sensory relay nuclei

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12
Q

How do some general anaesthetics exhibit an effect on amnesia and memory?

A

Act on hippocampus

e.g. rohypnol

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13
Q

How do general anaesthetics exhibit an effect on loss of reflexes?

A

Acts on spinal level

Contributes to control of motor function

Leads to muscle relaxation

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14
Q

What effect do general anaesthetics have on the cardiovascular system?

A

Cause circulatory depression

Decreases cardiac contractility

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15
Q

What effect do general anaesthetics have on the respiratory system?

A

Profound respiratory depression

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16
Q

What effect do general anaesthetics have on muscles?

A

Action at neuromuscular junction (NMJ)

Causes muscle relaxation

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17
Q

What are the stages of general anaesthesia?

A

(1) Premedication
(2) Induction
(3) Maintenance
(4) Pain relief
(5) Muscle relaxation

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18
Q

What is premedication?

A

Combined drug treatment 1-3 Horus prior to anaesthesia

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19
Q

What is the purpose of premedication?

A

(1) Reduce anxiety/ pain/ secretions/ vagal reflexes/ postoperative nausea + vomiting
(2) Increase amnesia/ hypnotic effects of anaesthesia

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20
Q

What drug classes are used in premedication?

A

(1) Benzodiazepines
- e.g. diazepam
- increases inhibitory GABA release
- sedative + anxiolytic effect

(2) mAChR antagonist
- e.g. atropine
- prevents vagal reflexes + secretion

(3) Opioid receptor antagonist
- e.g. morphine
- sedative + reduction of pain

(4) PPI
- metoclopramide
- limits nausea + vomiting

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21
Q

What is induction?

A

IV bolus agents

Induce loss of consciousness + amnesia

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22
Q

What is the purpose of induction?

A

To induce loss of consciousness + amnesia

23
Q

What drugs are used in induction?

A

(1) Propofol
- activate GABA(A) receptors
- promote inhibition

(2) Barbiturates - e.g. sodium thiopental
- activate GABA(A) receptors
- promote inhibition

24
Q

What are some of the properties of drugs used for induction?

A

(1) Small
(2) Highly lipophilic
(3) Rapid distribution

(4) Fast onset
- ~20 seconds for circulatory blood to reach brain

(5) Action terminated by distribution into large compartments
- e.g. muscle

(6) Preferable to inhalation agents which have a slower onset of action

25
Q

What is propofol?

A

An induction drug

Favourable due to rapid metabolism

Lack of hangover effect

26
Q

What is thiopental?

A

An induction drug

Only remaining widely used barbiturate

Potent + acts within ~20 seconds

Lasts 5-10 minutes due to rapid metabolism

Can accumulate in fat which can cause a hangover effect

Associated with profound respiratory depression

27
Q

What is etomidate?

A

An induction drug

Favoured due to high therapeutic index

Lack of respiratory/ cardiovascular side effects because of high therapeutic index

28
Q

What is the only drug that blocks excitatory glutamate receptors?

A

Ketamine

NMDA glutamate antagonist

29
Q

Describe the onset of action of ketamine.

A

2-5 minutes

Relatively slow

30
Q

What effects does ketamine have in terms of anaesthesia?

A

Dissociative anaesthesia

  • sensory loss
  • analgesia

Can cause dysphoria + hallucination

31
Q

When it ketamine typically used in anaesthesia?

A

Paediatric medicine

Dysphoria + hallucination are less pronounced in children

32
Q

What is maintenance, with regard to anaesthesia?

A

Volatile inhalation agents

Used to maintain loss of consciousness + amnesia

33
Q

What drugs are used for maintenance in anaesthesia?

A

(1) Isoflurane
(2) Nitrous oxide
(3) Halothane

34
Q

What are some properties of maintenance drugs?

A

(1) Inhaled gases have fast onset + offset of action
- allows control of depth of anaesthesia

(2) Inhaled general anaesthetics freely cross BBB
- Kinetics are determined by rate of transfer from inspired air into blood

(3) Better than IV due to rapid elimination

(4) Fewer side effects than highly sedative drugs
- e.g. morphine/ hyoscine

35
Q

What is halothane?

A

Maintenance drug

Potent
- can lead to cardiovascular/ respiratory side effects

Can sensitise cardiac tissue to adrenaline
- can lead to dysrhythmia

Can cause hepatotoxicity

Hangover effect associated with high deposition in fat

36
Q

What is nitrous oxide?

A

Laughing gas – Maintenance drug

Low potency

Typically used in combination

Used for childbirth

37
Q

What is isoflurane?

A

Maintenance drug

Halogenated ether

Most commonly used inhalation anaesthetics

38
Q

What is pain relief, with regard to anaesthesia?

A

IV opioids

Used to provide analgesia

39
Q

What drugs are used in pain relief in analgesia?

A

(1) Morphine

(2) Fentanyl

40
Q

What are some side effects of opioids?

A

(1) Sedation
(2) Respiratory depression
(3) Nausea + vomiting
(4) Bronchospasm precipitation
(5) Anaphylaxis precipitation

41
Q

What is muscle relaxation, with regard to anaesthesia?

A

Agents acting at nAChRs at NMJ

Cause immobility during surgery

42
Q

How do neuromuscular blocking agents work?

A

(1) Competitive antagonists of nAChRs
- competitive blockers

(2) Agonists which cause depolarising lock of the muscle endplate
- depolarising blockers

43
Q

What are some examples of competitive antagonists of nAChRs?

A

(1) Atracurium
(2) Pancuronium
(3) Vecuronium

44
Q

What does binding of competitive antagonists of nAChRs lead to?

A

(1) Na+ entry
(2) Depolarises postsynaptic membrane
(3) Causes an excitatory postsynaptic potential

(4) Generates an action potential
- if threshold is reached

45
Q

Why are competitive antagonists of nAChRs used in obstetrics?

A

Do not cross the placenta

46
Q

How are competitive antagonists of nAChRs administered?

A

IV

47
Q

What is the duration of action of atracurium?

A

<60 minutes

48
Q

What is the duration of action of vecuronium?

A

<60 minutes

49
Q

What is the duration of action of pancuronium?

A

> 60 minutes

50
Q

What is the duration of action of rocuronium?

A

<60 minutes

51
Q

How is muscle paralysis caused by depolarising nAChR blockers?

A

Continual stimulation of NMJ

Causes muscle contraction due to depolarisation

Cannot repolarise as Na+ channels cannot inactivate

52
Q

What is an example of a depolarising nAChR blocker?

A

Suxamethonium/ succinylcholine

53
Q

Describe the duration of action of suxamethonium.

A

Short-acting

~10 minutes

As it is rapidly hydrolysed by cholinesterases

54
Q

What is the purpose of a combination of drugs being given in general anaesthesia?

A

(1) Rapid onset
(2) Rapid recovery
(3) Avoids periods of semi-consciousness
(4) No undue disruption of homeostasis

Part 3 – PM3B COPY T (33 decks)

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