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Y2 CONTROL & MOVEMENT > General Anaesthesia > Flashcards

General Anaesthesia Flashcards

1
Q

What are the three types of anaesthesia?

A

general anaesthesia:

  • total loss of sensation

regional anaesthesia:

  • loss of sensation to a region or part of the body

local anaesthesia:

  • topical infiltration
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2
Q

What is an anaesthetic drug?

A

a drug that induces partial or total loss of sensation

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3
Q

What are the 3As as components to balanced general anaesthesia?

A

amnesia:

  • lack of response and recall to noxious stimuli (unconsciousness)

analgesia:

  • pain relief

akinesis:

  • immobilisation / paralysis caused by muscle relaxation
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4
Q

What are the three components of the triad of balanced general anaesthesia?

A
  1. unconsciousness
  2. analgesia
  3. muscle relaxation
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5
Q

What is meant by balanced anaesthesia?

Why is it used?

A

it involves a combination of agents being used

this is safer than a large dose of a single agent

it minimises adverse effects

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6
Q

What are the stages involved in one episode of general anaesthesia?

A

monitoring

intravenous access:

  • to give anaesthetic agents

start the process:

  • induction agents used for induction of anaesthesia
  • start the analgesia and muscle relaxation

maintain the process:

  • maintenance agents for amnesia / analgesia / muscle relaxation
  • replace fluid and blood loss

reverse the process:

  • reverse muscle relaxation
  • maintain post-operative analgesia
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7
Q

What are the roles of induction agents?

How quickly do they work?

A

induce loss of consciousness in one to two arm-brain circulation times

this is around 10-20 seconds

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8
Q

What compounds are used in amnesia as induction agents?

A

a diverse range of compounds:

  • nitrous oxide
  • halothane
  • sodium thiopentone
  • enflurane
  • isoflurane
  • sevoflurane
  • desflurane
  • propofol
  • xenon
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9
Q

What is the onset and duration of intravenous agents like?

When are they commonly used?

A

they have a quick onset and short duration

they are most commonly used as a bolus for induction

(but also for maintenance as infusion)

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10
Q

What is the potency of intravenous agents like?

How is it measured?

A

measured by Cp50

this is the minimal steady state plasma concentration of an intravenous agent required to prevent a somatic response in 50% of patients following skin incision

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11
Q

What is the main intravenous anaesthetic that has been used in the past?

How does it work?

A

barbituates

they work by prolonging the action of the neurotransmitter GABA on its receptors

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12
Q

In general, how do general anaesthetics work?

A

they modulate the activity of transmitter-gated ion channels

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13
Q

What are the sites of action of general anaesthetics?

A
  • peripheral nervous system and cerebral cortex
  • reticular activating system
  • basal ganglia, cerebellum, medullary centres, motor pathways
  • afferent neurones + monosynaptic pathways
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14
Q

What are the ideal properties of an intravenous induction agent?

A
  • simple preparation
  • compatible with other agents & IV fluids
  • painless on administration
  • high potency and efficacy
  • predictable action within one circulation time
  • minimal cardiovascular effects or other toxicity
  • depression of airway reflexes for intubation
  • rapid and predictable offset of effect
  • rapid metabolism for minimal hangover
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15
Q

What are the 4 main intravenous induction agents that are used?

A
  • propofol
  • thiopentone
  • ketamine
  • etomidate
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16
Q

What does propofol look like?

What are the benefits of its use?

A

it is a lipid-based white emulsion

it has excellent suppression of airway reflexes

it decreases incidence of postoperative nausea and vomiting (PONV)

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17
Q

What are the unwanted effects of propofol?

A
  • marked drop in heart rate and blood pressure
  • pain on injection
  • involuntary movements
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18
Q

What is the dose for propofol?

A

1.5 - 2.5 mg / kg

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19
Q

What are the benefits of using thiopentone?

What is it mainly used for?

A
  • faster than propofol
  • antiepileptic properties and protects the brain

it is mainly used for rapid sequence induction

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20
Q

What are the unwanted effects of thiopentone?

A
  • drop in blood pressure but rise in heart rate
  • rash / bronchospasm
  • intra-arterial injection - thrombosis and gangrene
  • contraindicated in porphyria
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21
Q

What dose of thiopentone is given usually?

A

it is a barbiturate and a dose of 4 - 5 mg/kg is used

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22
Q

When is ketamine used?

A

dissociative anaesthesia

anterograde amnesia and profound analgesia

it is the sole anaesthetic for short procedures

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23
Q

What is the onset of ketamine like?

A

it has a slow onset of 90 seconds

it causes a rise in heart rate and blood pressure and bronchodilation

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24
Q

What are the unwanted effects of ketamine?

A
  • nausea
  • vomiting
  • emergence phenomenon
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25
Q

What dose of ketamine is given?

A

1 - 1.5 mg/kg

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26
Q

What is dose of etomidate is given?

What is its onset like?

A

it has a rapid onset

the dose is 0.3 mg / kg

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27
Q

What are the benefits of using etomidate?

A

haemodynamic stability

lowest incidence of hypersensitvity reaction

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28
Q

What are the unwanted effects of etomidate?

A
  • pain on injection
  • spontaneous movements
  • adreno-cortical suppression
  • high incidence of PONV
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29
Q

What are examples of situations when ketamine should be used?

A

a patient requiring a burn dressing change

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30
Q

What are examples of situations when propofol should be used?

A

a patient undergoing arm operation under GA with an LMA

a patient with porphyria comes for an inguinal hernia repair

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31
Q

What are examples of situations when etomidate and thiopentone would be used?

A

etomidate:

  • a patient with a history of heart failure requires a general anaesthetic

thiopentone:

  • a patient with intestinal obstruction requires emergency laparotomy
32
Q

How long do induction agents last for?

How can amnesia be maintained?

A

they last from 4 to 10 minutes

amnesia can be maintained through:

propofol infusion:

  • this is total intravenous anaesthesia

inhalation agents:

  • this is inhalational anaesthesia
33
Q

When are vapours used for amnesia?

How are they administered?

A

inhalation agents are used to maintain amnesia

they are started after induction

they are administered via vaporisers or breathing circuits

34
Q

What are the physical properties of an ideal inhalation agent?

A
  • non-flammable
  • stable with materials (e.g. plastic, metal) with long shelf life
  • environmentally friendly
  • cheap and easy to manufacture
35
Q

What are the biological properties of an ideal inhalation agent?

A
  • pleasant to inhale, non-irritant
  • fast onset
  • high potency
  • minimal effects on other systems
  • no biotransformation
  • non-toxic to theatre personnel
36
Q

What is meant by the Meyer-Overton theory?

A

it describes the correlation between lipid solubility of inhaled anaesthetics and MAC

it suggests that anaesthesia occurs when a sufficient number of inhalational anaesthetic molecules dissolve in the lipid cell membrane

37
Q

What is meant by “MAC” of a general anaesthetic?

A

minimum alveolar concentration

this is the concentration of a vapour in the alveoli of the lungs that is needed to prevent movement (motor response) in 50% of subjects in response to surgical (pain) stimulus

it is used to compare potency (or strength) or anaesthetic vapours

38
Q

How was Meyer Overton theory proven to be false?

A
  • some predicted anaesthetics ineffective
  • lipid membrane effect reproduced by small changes in temperature in vitro
  • differing effects of stereoisomers
  • large molecular weight compounds less potent than predicted
39
Q

What are other theories about how anaesthetics produce unconsciousness?

A
  • critical volume theory
  • mean excess volume theory
  • multisite expansion theory
  • protein theory of anaesthesia
  • effect on channels
  • combination of above
40
Q

What is meant by critical volume theory?

A

solubilisation of a lipophilic general anaesthetic in the lipid bilayer of a neurone causes its malfunction and anaesthetic effect when a critical concentration of anaesthetic is reached

41
Q

What is meant by mean excess volume theory?

A

bulky and hydrophobic anaesthetic molecules accumulate inside the neuronal cell membrane

this causes distortion and expansion (thickening) due to volume displacement

membrane thickening reversibly alters function of membrane ion channels, producing an anaesthetic effect

42
Q

What is meant by multisite expansion hypothesis?

A

general anaesthesia may be the result of expansion of different molecular sites that are of a finite size and ultimately reach saturation

43
Q

What is meant by the protein theory of general anaesthetics?

A

general anaesthetics bind directly to a small number of targets in the CNS

these are mostly ligand-gated ion channels in the synapse and G-protein coupled receptors

this alters their ion flux

44
Q

What are the neurobiological effects of anaesthetics?

How can they be classified?

A
  • amnesia
  • hypnosis
  • immobility

can be classified by their effects on different receptors

there is an effect of genetic inter-individual variability

45
Q

What are group 1 general anaesthetics?

What are their clinical features?

A

etomidate, propofol, pentobarbital

clinical features:

  • strong hypnotics
  • strong amnestics
  • weak immobilisers
  • slow cortical EEG

molecular targets:

  • GABAA receptors
46
Q

What are the group 2 general anaesthetics?

What are their clinical features and molecular targets?

A

nitrous oxide, ketamine, xenon, cyclopropane

clinical features:

  • weak hypnotics
  • weak immobilisers
  • potent analgesics
  • no EEG slowing

molecular targets:

  • NMDA receptors
  • AMPA receptors
  • neuronal nAChRs
  • 2-pore K+ channels
47
Q

What are the group 3 anaesthetics?

What are their clinical features and molecular targets?

A

halogenated ethers and alkanes

clinical features:

  • strong hypnotics
  • strong amnestics
  • strong immobilisers
  • slow cortical EEG

molecular targets:

  • GABAA receptors
  • glycine receptors
  • glutamate receptors
  • neuronal nAChRs
  • 2-pore K+ channels
48
Q

What are the partition coefficients and recovery time for nitrous oxide?

A

blood: gas = 0.5
oil: gas = 1.4

MAC = 104%

recovery is fast

49
Q

What are the partition coefficients and recovery time for halothane?

A

blood: gas = 2.4
oil: gas = 220

MAC = 0.8%

recovery time is medium

50
Q

What are the partition coefficients and recovery time for desflurane?

A

blood: gas = 0.4
oil: gas = 23

MAC = 6.1%

recovery is fast

51
Q

What are the partition coefficients and recovery time for sevoflurane?

A

blood: gas = 0.6
oil: gas = 53

MAC = 2.1%

recovery is fast

52
Q

What are the 4 unconsciousness (amnesia) inhalation agents?

What are they used for?

A
  • isoflurane
  • sevoflurane
  • desflurane
  • enflurane

they are used for maintenancce

53
Q

What is the definition of MAC (minimum alveolar concentration)?

A

concentration of the vapour

that prevents the reaction to a standard surgical stimulus (traditionally a set depth and width of skin incision)

in 50% of subjects

it measures potency

54
Q

What is one MAC of the unconsciousness inhalation agents?

A

one MAC of:

nitrous oxide is 104%

sevoflurane is 2%

isoflurane is 1.15%

desflurane is 6%

enflurane is 1.6%

55
Q

When are inhalation agents used until?

What inhalation agents are used?

A

they can be continued until the end of operation

any inhalation agent can be used

commonly used agents are sevoflurane, desflurane and isoflurane

56
Q

What determines the characteristics and onset/offset of inhalation agents?

A

physical properties determine the characteristics of general anaesthetics

solubility in the blood determines the onset / offset

57
Q

What does it mean if an inhalation agent has low solubility?

A

low solubility means fast equilibration

agents with low solubility have a fast onset and quick recovery

they are most commonly used for maintenance (but can be used for induction)

58
Q

What is the problem with highly fat-soluble agents?

A

GA given for a long time accumulates in fat

this can result in a “hangover effect” for hours

59
Q

What is the difference in perfusion and equillibration of GAs in fat and lean tissues?

A

fat:

  • slow perfusion
  • large partition coefficient
  • slow equilibration

lean tissues:

  • fast perfusion
  • small partition coefficient
  • rapid equilibration
60
Q

When is sevoflurane used?

A

it is a sweet smelling inhalation agent

used for inhalational induction

61
Q

When is desflurane used?

What is its onset and offset like?

A

it is an inhalational agent used for long operations

it has low lipid solubility and rapid onset and offset

62
Q

What is isoflurane?

What is a benefit to its use?

A

an inhalational agent

it has the least effect on organ blood flow

63
Q

What are the general and specific adverse effects of inhalational agents?

A

general:

  • vasodilation
  • decrease cardiac contractility
  • can potentially affect organ perfusion

specific:

  • malignant hyperthermia
  • hepatotoxicity (halothane)
64
Q

What would be the preferred inhalational agent in an 8 hour long finger re-implantation?

A

desflurane

65
Q

What is the preferred inhalational agent in a chubby child with no intravenous access?

A

sevoflurane

66
Q

What would be the preferred inhalational agent in organ retrieval from a donor?

A

isoflurane

67
Q

After balanced anaesthesia is acheived, why is analgesia required?

A
  • insertion of airway
  • laryngeal mask airway
  • intubation
  • intraoperative pain relief
  • postoperative pain relief
68
Q

What category of drug tends to be used for analgesia?

A

opioids

69
Q

What short-acting drugs are used for analgesia?

A
  • remifentanil
  • alfentanil
  • fentanyl
  • remifentanyl given via IV infusion
70
Q

What analgesics are used for long-acting effects?

A

these are used for intra-op and post-op analgesia

examples are morphine and oxycodone

71
Q

What other opioids and analgesics are used in balanced anaesthesia?

A
  • paracetamol

NSAIDs:

  • diclofenac
  • parecoxib
  • ketorolac

weaker opioids:

  • tramadol
  • dihydrocodeine
72
Q

What is performed after amnesia and analgesia have been achieved as part of balanced anaesthesia?

A

muscle relaxation

this is required for intubation and surgery

73
Q

what is meant by akinesia?

A

the loss of the ability to create muscular movement

74
Q

What are examples of depolarising and non-depolarising muscle relaxant drugs (akinesis)?

A

depolarising:

  • suxamethonium

non-depolarising:

  • short-acting - atracurium, mivacurium
  • intermediate-acting - vecuronoium, rocuronium
  • long-acting - pancuronium
75
Q

What drugs are used to reverse the effects of muscle relaxants?

A

neostigmine & glycopyrrolate

76
Q

What are the stages involved in assessing unconsciousness?

A
  • clinical signs
  • measure level MAC
  • BIS monitor
  • isolated forearm
  • evoked potentials
77
Q
A

Y2 CONTROL & MOVEMENT (69 decks)

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