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Year 3 - Specialties > Anaesthetics - principles + pharmacology > Flashcards

Anaesthetics - principles + pharmacology Flashcards

1
Q
  • Understand the mechanism, action and pharmacological kinetics of: local anaesthetic agents, general anaesthetic agents, opiates and muscle relaxants.
  • Describe the “triad of anaesthesia” and discuss how this relates to the concept of balanced anaesthesia.
  • Discuss the physiological effects of general and regional anaesthesia and how these may interact with patients’ underlying illness.
A

. Pharmacokinetics - ADME, how the body deals with the drug

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2
Q

Purpose of general anaesthetic

A

Produces insensibility in the whole body, usually causing unconsciousness

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3
Q

Purpose of regional anaesthetic

A

The agent is applied to the nerve and insensibility is produced in a distal area, remote from the injection, e.g. spinal or epidural block

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4
Q

Purpose of local anaesthetic

A

Agent applied directly to tissue and insensibility is produced in only that part

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5
Q

Types of anaesthetic drugs (5)

A 
Inhalational anaesthetics, i.e. general
Intravenous anaesthetics, i.e. general
Muscle relaxants
Local anaesthetics
Analgesics, e.g. opiates
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6
Q

What is the triad of anaesthesia

-an anaesthetic may consist of varying contributions from all 3 but doesn’t need to have all 3

A

Analgesia
Hypnosis
Relaxation

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7
Q

Describe hypnosis

A

Unconsciousness.

Necessary component of any general anaesthetic

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8
Q

Describe analgesia in terms of anaesthesia

A

Removal of perception of unpleasant stimulus

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9
Q

Describe relaxation in terms of anaesthesia

A

Refers to skeletal muscle relaxation necessary to provide immobility for certain procedures

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10
Q

Which components of the triad of anaesthesia do the following have

  • GA
  • LA
  • Opiates
  • Muscle relaxants
A

GA - all 3
LA - analgesia + relaxation
Opiates - analgesia + hypnosis
Muscle relaxants - relaxation

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11
Q

What is balanced anaesthesia

A

Means that you can control the individual components of the triad and allow different drugs to do different jobs, e.g. can use less GA by adding a muscle relaxant

Essentially allows doses of individual drugs to be minimised

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12
Q

Problems with muscle relaxants

A

Means that artificial ventilation is needed to maintain the airway

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13
Q

Patients can be awake but paralysed and unable to communicate due to the separation of hypnosis (unconsciousness) from muscle relaxation

What is this called

A

Awareness

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14
Q

Mechanism of GA agents

-what ion channels are opened

A

Suppress neuronal activity by hyperpolarising neurones (so they’re less likely to fire) - hyperpolarised by opening chloride channels or suppressing excitatory synaptic activity

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15
Q

How do inhalational GA agents hyperpolarise neurons

-what ion channels opened

A

Dissolves in the membrane and causes the Cl channel to open

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16
Q

How do IV GA agents hyperpolarise neurones

-what ion channels opened

A

Allosteric binding to GABA receptors which stimulates Cl channels to open

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17
Q

Action of GA

  • what is lost
  • what is spared
A

Removes cerebral function

  • complex processes lost first, primitive functions later
  • remove consciousness

Reflexes are spared (e.g. spinal reflexes) and other automatic functions

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18
Q

Cautions during GA use (2)

A

Need to maintain airway

Control breathing

19
Q

Name some IV anaesthetic agents

A

Propofol

Thiopentone

20
Q

How do drugs like propofol cause rapid onset unconsciousness and rapid recovery

A

Fat soluble so cross BBB very quickly and cause unconsciousness as soon as it hits the brain

Also leave the circulation very quickly

21
Q

Pharmacokinetics of IV anaesthetics

  • absorption
  • distribution
  • metabolism
  • excretion
A

Aborsbed into blood so blood conc. of the agent high initially then falls as it moves into highly perfused tissues

Distributed to organs, muscle and fat

Metabolised by liver

Excreted by kidney

22
Q

Does muscle or fat absorb IV anaesthetics quicker

A

Muscle, but the effect is large because of huge mass of skeletal muscle

Fat can store large amounts of the agent due to to high fat solubility of the drug

23
Q

Inhaled anaesthetics are what kind of compounds + name on

A

Halogenated hydrocarbons, e.g. sevoflurane

24
Q

How do inhalational anaesthetics work once inhaled

A

The gas moves down the conc. gradient into the blood (from the lungs) then to the brain to acheive a high enough partial pressure to produce unconsciousness

Continuously breathed during the procedure

25
Q

Inhalational drugs have a MAC (minimum alveolar conc.) which is a measure of

What would a drug with a low MAC mean?

A

the concentration of the drug required in the alveoli in order to produce any anaesthetic effect

A low MAC means the drug is potent as less of it is needed

26
Q

Is induction of inhalational anaesthetics fast or slow

A

Slow

27
Q

Main role of inhalational anaesthetics

A

To prolong or continue anaesthesia, i.e. MAINTAIN ANAESTHESIA

(usually to maintain IV induction)

28
Q

How are inhalational anaesthetics reversed

A

Machine is switched off and patient is given a gas mixture with no anaesthetic agent in it to reverse the conc. gradient and decrease the alveolar conc. therefore decreasing the blood conc. of the drug and subsequently the brain

29
Q

Most common sequence of GA uses what agents

A

IV induction followed by inhalational maintenance

30
Q

Physiological effects of GA
on the CVS
-central (3)
-peripheral (3)

A

Central effects

  • reduce sympathetic outflow activity
  • reduce contractility (negative inotropic effect)
  • vasodilation

Peripheral

  • reduce contractility of vessels (negative inotropic)
  • vasodilation leading to reduced peripheral resistance
  • venodilation –> decreased VR –> decreased CO
31
Q

Physiological effects of GA on resp function (4)

A

Reduce hypoxic and hypercarbic drive

Reduce tidal volume so increase RR

Paralyse cilia

Decrease FRC (i.e. decrease lung volumes so interferes with V/Q matching)

32
Q

GA agents decrease lung volumes so interfere with V/Q matching in the lungs and this effect persists post-op, so patients should be given what post-op

A

Oxygen (probably several days)

33
Q

Action of muscle relaxants

A

Paralyse skeletal muscle in an indiscriminate way, therefore airway muscles are affected too even though you don’t want to

34
Q

Indications for muscle relaxant use (3)

A

Ventilation & intubation

When immobility is essential
(e.g. microscopic surgery, neurosurgery)

Body cavity surgery

35
Q

Disadvantages of muscle relaxants (3)

A

Loss of awareness - awake but paralysed

Incomplete reversal - airway obstruction/resp insufficiency persists in immediate post-op period (i.e. at the end of the anaesthetic) but unlikely to persist when they’re back on the ward

Apnoea - hence the need for airway + ventilation support during op

36
Q

If the muscle relaxant is given systemically (orally) then also must provide which triad of anaesthesia

A

Hypnosis (unconsciousness)

37
Q

Analgesia is most commonly used in what way in terms of anaesthetising?

A

In conjunction with unconsciousness (i.e. GA) as part of ‘balanced anaesthesia’

38
Q

Does analgesia always have to be accompanied by GA ?

A

No, can use it as regional anaesthesia where it’s used itself, e.g. spinal or epidural analgesia

39
Q

What’s the point of intra-operative analgesia for someone who’s unconscious?
+ benefit of opiate analgesics

A

Prevents arousal from the pain

Opiates have direct sedative effect, contributing to GA

Suppress reflex responses to pain, e.g. tachycardia, hypertension

40
Q

Benefits of local + regional anaesthesia (4)

A

Retain awareness

Complete analgesia with no hypnotic effect

Can allow lower levels of GA to be used if GA is needed

Less physiological effects than GA, mainly effects on CVS

41
Q

Mechanism of local anaesthetic

A

Block Na+ channels so prevent AP from propagating

42
Q

Disadvantages of local anaesthetic

A

Lots of side effects and toxic if delivered wrongly

43
Q

Local + regional anaesthesia mainly have effects on which organ system

A

CVS, resp function spared

Year 3 - Specialties (17 decks)

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