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C&M Neuroanatomy > Week 10: General anaesthesia > Flashcards

Week 10: General anaesthesia Flashcards

1
Q

What is general anaesthesia?

A

Total loss of sensation

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2
Q

Balanced anaesthesia requires 3 things. What are they?

A
  1. Amnesia
    Unconsciousness –> lack of response and recall to noxious stimuli
  2. Analgesia
    Pain relief
  3. Akinesis
    Muscle relaxation –> immobilisation/ paralysis
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3
Q

Explain the 7 steps carried out from arrival into anaesthetic room to recovery

A
  1. Anaesthetic pre-assessment which involves discussion about patients health and obtaining verbal consent
  2. Monitoring
  3. Intravenous access: to give anaesthetic agents
  4. Induction of anaesthesia: induction agents
  5. Start the analgesia and muscle relation
  6. Maintain the process: maintenance agents for amnesia/ analgesia/ muscle relaxation
  7. Reverse the process: reverse muscle relaxation. but maintain post operative analgesia
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4
Q

What is one to two arm-brain circulation time?

A
  • time taken for the anaesthesia to go from site injected into the brain
  • is usually 10-20 seconds
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5
Q

What is Cp50?

A

the concentration of the agent in the blood that can prevent movement after a skin incision in 50% of patient

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6
Q

How do GAs work?

A
  • by hyperpolarising the axon and therefore preventing conduction along the neurones
  • they modulate the activity of transmitter-gated ion channels
  • GA stimulate the inhibitory receptors and inhibit the excitatory receptors
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7
Q

Which 2 channels to GAs stimulate?

A

The inhibitory receptors:

  1. GABAa
  2. Strychnine-sensitive glycine
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8
Q

Which 3 channels to GAs inhibit?

A

The excitatory receptors:

  1. 5HT3
  2. Neuronal nicotinic
  3. Glutamate NMDA/ AMPA
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9
Q

What compounds are used for indection?

A

propofol and sodium thiopentone

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10
Q

What are the ideal properties of an intravenous induction agent?

A
  • simple preparation
  • compatibility with other agents and iV fluids
  • painless on administration
  • high potency and efficacy
  • predictable action within one circulation time
  • minimal cardiovascular effects
  • depression of airway reflexes for intubation
  • rapid and predictable offset of effect
  • rapid metabolism for minimal hangover
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11
Q

What are the four most commonly used GAs?

A
  1. Propofol
  2. Thiopental
  3. Etomidate
  4. Ketamine
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12
Q

What are two advantages of propofol?

A
  • excellent suppression of airway reflexes

- decreases incidence of PONV (post operative nausea and vomiting)

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13
Q

What are the unwanted effects of propofol?

A
  • marked drop in HR and BP
  • pain on infection
  • involuntary movements
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14
Q

What are the advantages of thiopentone?

A
  • barbiturate
  • faster than propofol
  • used mainly for rapid sequence induction
  • anti epileptic properties and protects brain
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15
Q

What are the unwanted effects of thiopentine?

A
  • drop in BP
  • increase in HR
  • rash/bronchospasm
  • intra-arterial injection: thrombosis and gangrene
  • contraindicated in porphyria
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16
Q

Ketamine is a dissociative anaesthesia. What does this mean?

A

anterograde amnesia and profound analgesia

17
Q

WHat are the unwanted effects of ketamine?

A
  • rise in HR/BP
  • N&V
  • patients go into ‘different worlds’
18
Q

What are the advantages of etomidate?

A
  • rapid onset
  • haemodynamic stability
  • lowest incidence of hypersensitvity
19
Q

What are the unwanted effects of etomidate?

A
  • pain on injection
  • spontaneous movements
  • adreno-cortical suppression
  • high incidence post operative N&V
20
Q

What are the ideal physical properties of inhalation agents?

A
  • non-flammable
  • stable with materials, long shelf life
  • environmentally friendly
  • cheap and easy to manufacture
21
Q

What are the ideal biological properties of inhalation agents?

A
  • pleasant to inhale, non-irritant
  • fast onset
  • high potency
  • minimal effects other systems
  • non toxic to theatre personaell
22
Q

Explain the Meyer Overton theory on how anaesthetics produce unconsciousness

A
  • related to lipid solubility
  • perturbation of lipid membranes
  • dissolve in plasma membrane affecting its fluidity, volume, surface tension
  • this effects the plasma proteins, causing the patient to stay asleep
  • agent with highest solubility = highest potency
23
Q

Why is the Meyer Overton theory shown to be false?

A
  • some predicted anesthetics ineffective

- lipid membrane effect reproduced by small changes in temp

24
Q

What theory of how general anaesthesia works is accepted?

A

A combination of all of these theories:

  • Critical volume theory
  • Mean excess volume theory
  • Multisite expansion theory
  • Protein theory of anaesthesia
  • Effect on channel
25
Q

What are the neurobiological effects of anaesthetics?

A
  • amnesia
  • hypnosis
  • immobility
26
Q

What is MAC?

A

Minimum alveolar concentration = concentration of the vapour that prevents the reaction to a standard surgical stimulus in 50% of subjects

1 MAC = all patients are asleep

27
Q

What are some commonly used inhalation agents?

A
  • sevoflurane
  • desflurane
  • isoflurane
28
Q

What are the adverse effects of GA?

A
  • vasodilation
  • decrease cardiac contractility
  • can potentially affect organ perfusion
  • malignant hyperthermia
  • hepatotoxicity
29
Q

Which inhalation agent is sweet smelling and used when we cannot establish I.V access?

A

sevoflurane

30
Q

Which inhalation agent has rapid onset and offset, lowest lipid solubility and can be used for long operations?

A

desflurane

31
Q

Which inhalation agent has the least effect on organ blood flow?

A

Isoflurane

32
Q

The next step after anaesthesia is analgesia. Why is this required?

A
  • insertion of airway
  • laryngeal mask airway
  • intubation
  • intra operative pain relief
  • post operative pain relief
33
Q

What is the next step after analgesia and what is this required for?

A

muscle relaxation

required for intubation and surgery

34
Q

Name some opoids

A
  • fentanyl (commonest, short acting)
  • morphine
  • oxycodon
  • paracetmol
  • NSAIDS
  • tramadol
  • dihydrocodeine
35
Q

Name some muscle relaxants for akinesis?

A
  • suxamethonium
  • atracurium
  • vecuronium
  • pancuronium
36
Q

How do we reverse muscle relaxants?

A

with neostigmine and glycopyrrolate

37
Q

How do we assess conciousness?

A
  • clinical signs
  • measure level MAC
  • BIS (bispectral index) monitor
  • isolated forearm
  • evoked potentials

C&M Neuroanatomy (44 decks)

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