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Module 9 > General Anaesthetics > Flashcards

General Anaesthetics Flashcards

1
Q

what are the targets of general anaesthetics

A

1. GABAa receptor

2. NMDA receptor

  1. two-pore domain K+ channels
  2. glycine receptors
  3. Na+ channels
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2
Q

what is the overall mechanism of general anaesthesia

A

decrease in neurotransmission in the CNS –> loss of consciousness

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3
Q

what is general anaesthesia

A

reversible unconsciousness with reduced sensitivity and response to stimuli

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4
Q

what are the 3 required components of general anaesthesia

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

why do we anaesthetize animals?

A
  1. perform painful surgical or diagnostic prodecures
  2. minimize patient suffering
  3. reduce risk to vet and other individuals
  4. facilitate the procedure by immobilizing the patient
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6
Q

what are the stages of anaesthesia

A
  1. voluntary movement
  2. involuntary movement or excitement
  3. surgical anaesthesia
  4. medullary paralysis

modern anaesthetic drugs/protocols aim to avoid stages 1 & 2

GAs have narrow therapeutic index –> want to avoid stage 4

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7
Q

what are intravenous anaesthetic agents used for

A

to induce anaesthesia

occasionally used to maintain anaesthesia

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8
Q

what are the advantages IV anaesthetic agents used for induction

A
  1. rapid smooth induction (minimal excitement)
  2. rapid protection of airway (important in dyspnoeic patients & those risk of regurgitation/aspiration)
  3. no environmental pollution
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9
Q

what are the disadvantages of IV induction agents

A
  1. IV access required
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10
Q

what are the advantages of inhalational anaesthetic agents used for maintenance

A
  1. delivery/elimination depends on ventilation
  2. rapid adjustment of anaesthetic depth
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11
Q

what are the disadvantages of inhalational anaesthetic agents used for maintenance

A
  1. equiptment required
  2. endotracheal tube, carrier gas (oxygen), vapourizer, breathing system, etc
  3. environmental pollution
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12
Q

what are inhalational anaesthetic agents used for

A

maintenance of anaesthesia

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13
Q

what are the advantages of inhalational anaesthetic agents used for induction

A
  1. IV access can be secured after induction
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14
Q

what are the disadvantages of inhalational anaesthetic agents used for induction

A
  1. environmental pollution
  2. takes longer & delay in securing airway may be a problem in some cases
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15
Q

what are the effects of GAs on CVS and respiration

A

decreased contractility of isolated heart preperations

effects on CO and BP vary

potentially arrhythmogenic

decrease respiration

increase arterial PCO2

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16
Q

what are IV anaesthetic agents used in vet med

A
  1. propofol
  2. steroid anaesthetics (alfaxolne)
  3. dissociative agents (ketamine)

also

  1. barbiturates (thiopenone, pentobarbitone), imidazole derivatives (etomidate)
17
Q

what is TIVA

A

total intravenous anaesthesia

18
Q

what is redistribution

A

concentration of drug determined by lipid solubility, composition of tissue and blood flow

19
Q

what is redistribution

A

concentration of drug determined by:

  1. lipid solubility
  2. composition of tissue
  3. blood flow
20
Q

what is redistribution for IV anaesthetic agents

A

upon IV injection rapidly goes to brain because it is highly lipid soluble and has high blood flow –> rapid loss of consciousness –> but begins to redistribute and leave brain –> consciousness returns to normal

21
Q

what are the effects of GAs on the nervous system (3)

A
  1. inhibit conduction of action potentials
  2. inhibit transmission at synapses (decrease transmitter release, decrease action of transmitter, decrease excitability of post-synaptic cell)
  3. brain regions (reticular formation, hippocampus)
22
Q

what is the chemical structure of propofol

A

hindered phenol

23
Q

what is propofol at room temp

A

oil (emulsion)

24
Q

what is the mechanisms of action of propofol

A

enhanced GABA transmission

25
Q

why is propofol used

A

short acting

smooth and rapid recovery

26
Q

what are the pharmacokinetics of propofol (7)

A
  1. highly plasma protein bound
  2. large volume of distribution (>3 l/kg)
  3. redistribution and metabolism
  4. phase II metabolism: conjugated in the liver and another site (sulfate and glucuronide) 5. prior to excretion in urine
  5. rapidly cleared (>40ml/kg/min)
  6. suitable for TIVA
27
Q

what are the clinical relevance of pharmacokinetics for propofol

A
  1. effect may be enhanced in hypoproteinemia
  2. effect not prolonged if repeated IV doses are administered (suitable for maintenance)
  3. effect not prolonged in dogs with hepatic dysfunction
  4. a prolonged effect may be seen in cats
28
Q

what are the effects of ketamine (6)

A
  1. sensory loss with analgesia
  2. increased muscle tone
  3. eyes open +/- slow nystagmus
  4. active reflexes include laryngeal/pharyngeal reflexes
  5. less profound CVS & resp depression
  6. hallucinations/emergence delirium
29
Q

what is TIVA

A

total intravenous anaesthesia

anaesthesia maintained by intermittent boluses or continuous infusion of an IV agent

30
Q

why use TIVA (4)

A
  1. easy to administer (minimal equipment)
  2. pharmacokinetics are known/predictable
  3. inhalation anaesthetics may be unsuitable in some individuals
  4. avoids risk to people administering drugs (no environmental pollution)
31
Q

what are halogenated compounds

A

halothane, isoflurane, sevoflurane, desflurane

nitrous oxide, xenon

32
Q

list 5 pharmacokinetic features of isoflurane

A

licensed in non-food producing animals

  1. good speed of induction/recovery/change of depth
  2. pungent odour (not ideal for induction)
  3. minimal metabolism
  4. CO better maintained
  5. less arrhythmogenic
33
Q

list 3 pharmacokinetic features of sevoflurane

A
  1. rapid induction/recovery/change of anaesthetic depth
  2. pleasant odour & minimal airway irritation so suitable for induction
  3. low rate of metabolism

licensed in dogs

gaining popularity in vet anaesthesia despite higher cost

34
Q

what is the strucure of nitrous oxide

A

N2O

N=N

O

colourless gas, without taste or odour

stored under pressure in cylinders

35
Q

what are the pharmacokinetic properties of nitrous oxide

A

MAC (%) >100

oil: gas partition coefficient 1.4
blood: gas partition coefficient 0.47

% metabolized <0.01

Module 9 (43 decks)

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