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PR3136 > GA > Flashcards

GA Flashcards

1
Q

What is General Anaesthesia used for?

A

To produce
1. unconsciousness
2. lack of responsiveness
to all painful stimuli (inhibition of sensory or autonomic reflexes)

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2
Q

General anaesthesia stages (6)

A
  1. Pre-assessment/Premed
  2. Induction
  3. Airway management
  4. Maintenance of anaesthesia
  5. Reversal/emergency
  6. Post-operative care
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3
Q

Ideal properties of GA (8)

A
  1. unconsciousness
  2. analgesia
  3. muscle relaxation (inhibit reflex)
  4. amnesia
  5. brief & pleasant
  6. depth of anaesthesia can be altered easily
  7. minimal adverse effects
  8. margin of safety large
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4
Q

Triad for balanced anaesthesia

A
  1. pain relief
  2. reflex inhibition
  3. unconsciousness (induction)
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5
Q

Why is there a need for balanced anaesthesia?

A

To ensure smooth and rapid induction & that analgesia and muscle relaxation are adequate

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6
Q

Types of GA (2)

A
  1. Inhalation anaesthetics

2. IV anaesthetics

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7
Q

Inhalation GA (3+1)

A

Volatile liquids

  1. Halothane
  2. Isoflurane (pungent)
  3. Sevoflurane

Gasesous
1. Nitrous oxide

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8
Q

MOA of inhalation GA (2)

A
  1. Enhance neurotransmission at inhibitory synapse via allosterically, increasing GABA receptors sensitivity to GABA itself (positive allosteric modulation)
  2. Depress neurotransmission at excitatory synapse via blocking glutamate neurotransmitter acting on NMDA receptors, prevent activation of NMDA receptors (negative allosteric modulation)
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9
Q

MAC

A

Minimum Alveolar Concentration

  • index of INHALATION anaesthetic potency
  • minimum concentration in alveolar air that will produce immobility to 50% of patients exposed to a painful stimulus
  • decrease MAC = increase potency
  • MAC alters with age, condition and concurrent drug use
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10
Q

Factors affecting absorption of inhalation GA

A
  1. conc of anaesthetic in inhaled air
  2. blood perfusion of lungs
  3. solubility of anaesthetic in blood

increase means increase absorption

BUT
increase solubility in blood means slower onset of action

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11
Q

Factors affecting distribution of inhalation GA

A
  • perfusion of organ/tissue

highly perfused organ (eg brain, lungs, liver & heart) will achieve equilibrium quickly after administration

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12
Q

Factors affecting elimination of inhalation GA

A
  1. conc of anaesthetic in inhaled air
  2. perfusion of lungs
  3. solubility of anaesthetic in blood
  • increase means increase elimination
  • most inhaled GA are eliminated through expired breath
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13
Q

Halothane

A
  • first modern inhaled anaesthetic
  • potent (MAC 0.75%)
  • medium rate of onset & recovery
  • little or no analgesic until unconsciousness supervenes
  • relaxes muscles & potentiates skeletal muscle relaxants
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14
Q

Halothane ADR (3)

A
  1. respiratory depression (dose dependent)
  2. bradycardia & arrhythmias (hypotension & dysrhythmia)
  3. halothane-associated hepatitis
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15
Q

Isoflurane

A
  • pungent smell
  • potent (MAC 1.4%)
  • medium rate of onset & recovery
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16
Q

Isoflurane ADR (2)

A
  1. bradycardia & arrhythmias
    - similar to halothane but reduced hypotension & arrhythmias
    - hypotension due decrease systemic vascular resistance
  2. metabolism of isoflurane produce inorganic F (nephrotoxic)
17
Q

Sevoflurane

A
  • potent (MAC 2%)
  • more rapid rate of onset & recovery than halothane
  • metabolised by liver
18
Q

Sevoflurane ADR (2)

A
  1. metabolism of sevoflurane produce inorganic F (nephrotoxic)
  2. usage of CO2 absorbent in vaporiser produce nephrotoxic agent
19
Q

Nitrous oxide

A
  • aka dinitrogen oxide
  • rapid onset & recovery but lack potency (MAC 110%)
  • analgesia & amnesia but no complete consciousness/surgical anaesthesia
  • only can used to supplement analgesic effect for primary anaesthetic
  • used alone for analgesic effect (eg dentist & labour)
20
Q

Nitrous oxide ADR

A

post-operative N/V

propofol have less post-operative N/V

21
Q

IV GA (3)

A
  1. Thiopentone
  2. Propofol
  3. Ketamine
22
Q

Advantages of using a combination of inhaled + IV (2)

A
  1. reduce dose of inhaled GA

2. produce additional effects that cannot be achieved with an inhalation alone

23
Q

Thiopentone / thiopental

A
  • high lipid solubility
  • MOA : enhance GABA binding to GABA receptors
  • rapid onset & recovery (high lipid solubility)
  • extensive plasma protein binding (mainly hepatic elimination)
  • duration of action depends on :
    1. elimination rate
    2. hepatic function (cirrhosis)
    3. Vd
    4. active metabolite (pentobarbital)
24
Q

Propofol

A
  • rapid onset & faster recovery
  • used for both induction & maintenance (continuous infusion of low dose)
  • used for day surgery
25
Q

Propofol ADR

A
  1. N/V (but lesser than nitrous oxide, anti-emetic)
  2. Cardiovascular effect (bradycardia & hypotension)
    - to be used in caution in elderly, compromised cardiac function & hypovolemic
26
Q

Ketamine

A
  • racemic but S- > R+
  • produce dissociative anaesthesia
  • produce sedation, amnesia, analgesia & immobility
  • rapid induction and recovery
  • used for both induction & maintenance (continuous infusion of low dose)
  • hepatic metabolism to less active metabolite
27
Q

Ketamine ADR

A
  1. psychological reactions (hallucination, delirium)
    - treat with premedication of diazepam & midazolam
    - dissociative anaesthesia
28
Q

Blood solubility and onset of action

A

Increase blood solubility, longer time taken for onset of action
Affect onset only, not efficacy

29
Q

Halothane vs Isoflurane in BP reduction

A

Halothane
- due to depression of cardiac output

Isoflurane
- due to decrease in systemic vascular resistance

30
Q

Advantages of Ketamine (4)

A
  1. Analgesia
  2. Sedation
  3. Amnesia
  4. Immobility
31
Q

GA with analgesia

A
  1. Ketamine

2. Nitrous oxide

32
Q

Opioid agonist used together GA

A

Remifentanil

  • 10min duration
  • 300x more potent than morphine

PR3136 (19 decks)

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