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Specialites Summary > Principles and Pharmacology of Anaesthetics > Flashcards

Principles and Pharmacology of Anaesthetics Flashcards

1
Q

What does anaesthesia mean?

A

Without feeling/perception

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2
Q

Types of anaesthetic

A

General
Regional
Local

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3
Q

What does a general anaesthetic do?

A

Produces insensibility in the whole body, usually causing unconsciousness
Centrally acting drugs - hypnotics/analgesics

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4
Q

What does regional anaesthetics do?

A

Producing insensibility in an area or region of the body

Local anaesthetics applied to nerves supplying relevant area

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5
Q

What do local anaesthetics do?

A

Produce insensibility in only the relevant part of the body

Local anaesthetics applied directly to the tissues

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6
Q

Drugs used in anaesthetics

A 
Inhalational anaesthetics 
Intravenous anaesthetics 
Muscle relaxants
Local anaesthetics
Analgesics
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7
Q

Techniques and equipment in anaesthetics

A 
Tracheal intubation 
Ventilation 
Fluid therapy 
Regional anaesthesia 
Monitoring
USS 
fibre optics
BIS
Sensors
Modern anaesthetic machine
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8
Q

Triad of anaesthesia

A

Analgesia
Hypnosis
Relaxation

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9
Q

What types of drugs are used to form the triad of anaesthesia?

A

Opiates
Muscle relaxants
General anaesthetic agents
Local anaesthetics

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10
Q

What parts of the triad of anaesthetics do opiates effect?

A

ANALGESIA

hypnosis

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11
Q

What part of the triad of anaesthetics do muscle relaxants affect?

A

Relaxation

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12
Q

What part of the triad of analgesia does local anaesthetics effect?

A

Analgesia

Relaxation

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13
Q

What parts of the triad of analgesia does general anaesthetic agents effect?

A

ALL 3

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14
Q

Problems with anaesthetics

A

Polypharmacy
- including chance off drug reactions / allergies
Muscle relaxation
- requirement for artificial ventilation
- means of airway control
Separation of relaxation and hypnosis
- awareness

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15
Q

How do general anaesthetics work?

A

By suppressing neuronal activity in a dose dependent fashion

  • interfere with neuronal ion channels
  • hyperpolarise neurones = less likely to ‘fire’
  • inhalational agents dissolve in membranes (direct physical effect)
  • intravenous agents - allosteric binding (GABA receptors - open chloride channels)
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16
Q

What do intravenous and inhaled general anaesthetics do to the patient?

A

Provide unconsciousness

Small degree of muscle relaxation

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17
Q

What happens to the cerebral function in general anaesthesia?

A

Most complex processes interrupted first
LOC early - hearing later
more primitive functions lost later

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18
Q

What happens to reflexes in general anaesthesia?

A

Relatively spared
Primitive
Other autonomic functions spared also
small number of synapses

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19
Q

Features of unconsciousness in IV anaesthesia

A

rapid onset
1 arm - brain circulation time
Causes unconsciousness as soon as they reach the brain
Highly fat soluble drugs and cross membranes extremely quickly

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20
Q

Features of recovery in IV anaesthesia

A

Rapid recovery
Due to disappearance of drug from the circulation and moving to other parts of the body (compartments)
Very little due to termination of action of IV agent given as bolus

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21
Q

Blood concentration of anaesthetic dose

A

Blood level very high initially

Then falls straight away as the drugs move into highly perfused tissues

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22
Q

Muscle concentration of anaesthetic dose

A

Picks up the drug more slowly

The effect is large because of the relative mass of skeletal muscle in the body

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23
Q

Fatty tissue concentration of anaesthetic dose

A

Picks up drugs even more slowly than muscle

But can store large amounts due to the high fat solubility of these drugs

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24
Q

What does the Target Controlled Infusion (TCI) pump system allow?

A

Very accurate infusion to achieve specific blood or brain concentrations of agents

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25
Q

Using a TCI pump system, what is used to make calculations and assumptions about the patients physiology?

A

Age
Sex
Size

26
Q

What is used as inhalational anaesthetics?

A

Halogenated hydrocarbons

27
Q

How is the uptake and excretion of inhalational anaesthetics done?

A

Via lungs
concentration gradient - lungs > blood > brain
Cross alveolar BM easily
Arterial concentration equates closely to alveolar partial pressure

28
Q

What does MAC stand for?

A

Minimal alveolar concentration

29
Q

What is MAC a measure of?

A

Potency

Low number = high potency

30
Q

Induction speed of inhalational anaesthetics

A

Slow

31
Q

Maintenance of anaesthesia in inhalational anaesthetics

A

Prolong duration

Very flexible

32
Q

Awakening in respect to inhalational anaesthetics

A

Stop inhalational admin

Washout - reversal of concentration gradient

33
Q

Most common sequence of general anaesthesia

A

IV induction followed inhalational maintenance

34
Q

Induction of general anaesthesia involves…

A

Inhalation

Intravenous

35
Q

Maintenance of general anaesthesia involves…..

A

Inhalational
Intravenous
- Propofol
- opiate (remifentanil)

36
Q

CVS in general anaesthesia

A

Central = depresses cardiovascular centre

  • reduced sympathetic outflow
  • negative inotropic/chronotropic effect on heart
  • reduced vasoconstrictor tone -> vasodilation

Direct

  • negatively inotrophic
  • vasodilation (increased peripheral resistance)
  • venodilation - decreased venous return and CO
37
Q

Respiratory physiology in general anaesthesia

A 
All anaesthetic agents are respiratory DEPRESSANTS
- reduce hypoxic and hypercarbic drive 
- decreased TV and increased rate 
Paralyse cilia 
Decreased FRC (may be prolonged effect)
- lower lung volumes 
- VQ mismatch
38
Q

What do muscle relaxants to?

A

Relax (i.e. paralyse) skeletal muscle

39
Q

Indications for muscle relaxants

A 
Ventilation and intubation 
When immobility is essential 
- microscopic surgery 
- neurosurgery 
Body cavity surgery (access)
40
Q

Problems of muscle relaxants

A

Awareness
- due to separation of unconsciousness from hypnosis in the triad of anaesthesia which muscle relaxants allow
Incomplete reversal
- airway obstruction
- ventilatory insufficiency in immediate post op period
Apnoea - dependence of airway and ventilatory support

41
Q

What is analgesia usually used with in general anaesthesia?

A

Unconsciousness

+ / - muscle relaxation

42
Q

Why might using analgesia may mean you dont need to use muscle relaxants?

A

Because regional techniques usually provide a reasonable muscle relaxation by blocking motor nerves so spinal or epidural analgesia might not require additional muscle relaxation

43
Q

Why use intraoperative analgesia?

A

Prevention of arousal
- pain wakes you up
Opiates contribute to hypnotic effect of GA
- have a direct sedative effect
Suppression of reflex responses to painful stimuli
- e.g. tachycardia, HTN, gross movements

44
Q

What does regional anaesthesia not have?

A

No direct hypnotic / sedative effects

45
Q

What is the result of a local / regional anaesthesia?

A

Produce analgesia
No hypnosis
Retain awareness / consciousness

46
Q

How do local / regional anaesthetics work?

A

Blocking Na+ channels and preventing axonal action potential from propagating
Effects every tissue so toxic if delivered wrongly (IV)

47
Q

Effects of local / regional anaesthetics

A

Lack of global effects of GA
Derangement of CVS physiology
- proportional to size of anaesthesia area
Relative sparing of resp function

48
Q

Benefit of local / regional anaesthetics

A

Avoidance if reliance on opioid analgesics

49
Q

What is the colour of the needle and the nerve in an USS guided regional anaesthesia?

A 
Needle = yellow
Nerve = dark coloured
50
Q

Local anaesthetic drugs

A

Lignocaine
Bupivacaine
Ropivacaine

51
Q

Limiting factor of local anaesthetics

A

Toxicity

52
Q

How do local anaesthetics result in toxicity?

A

Produced by high plasma levels of LA
- IV injection
- absorption > rate of metabolism = high plasma levels - therefore vasoconstrictors reduce blood flow, reduce absorption
Therefore if high doses are injected into high absorption (well perfused) areas, then absorption will be high and exceed the rates of removal

53
Q

Toxicity of local anaesthetics depends on…

A

Dose used
Rate of absorption (site dependent)
Patient weight
Drug

54
Q

Most toxic to least toxic local anaesthetic drugs

A

Bupivacaine
Lignocaine
Prilocaine

55
Q

Presentation of local anaesthetic toxicity

A 
Circumoral and lingual numbness and tingling
Light headedness 
Tinnitus 
Visual disturbances 
Muscular twitching
drowsiness
Cardiovascular depression convulsions
coma
cardiorespiratory arrest
56
Q

How can we provide analgesia without paralysis?

A

LA differential blockage
- due to differential penetration into different nerve types
- myelinated, thick fibres are relatively spared
Motor fibres = relatively spared
Pain fibres = blocked easily

57
Q

CVS physiology in neuraxial block

A

Similar to CVS effects of GA but all effects of RA are due to sympathectomy due to t LA blockage of mixed spinal nerves

58
Q

What does sympathectomy result in?

A

Veno and vaso dilation

59
Q

Respiratory physiology in neuraxial block

A 
Inspiratory function (relatively) spared
- unless high block 
Expiratory function relatively impaired 
- cough dependent on abdo muscle function 
Decreased FRC 
Increased V/Q mismatch
60
Q

Blocks with increasing physiological impact

A 
Local anaesthesia
Field blocks
- hernia repair 
Plexus blocks 
Limb blocks 
- e.g. femoral and sciatic nerve 
Central neural (neuraxial) block 
- epidural 
- spinal

Specialites Summary (15 decks)

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