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Pharmacotherapeutics > General Anaesthetics > Flashcards

General Anaesthetics Flashcards

1
Q

What are general anaesthetics used for?

A
  • To produce unconsciousness and lack of responsiveness to all painful stimuli (inhibition of sensory and autonomic reflexes)
  • i.e. hypnosis, amnesia, analgesia
  • Provide condition for interventions (e.g. surgery to occur)
  • Control of physiology (elevated heart rate, control body temperature)
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2
Q

What are the different stages of general anaesthesia?

A
  1. Pre-medication assessment (PREMED)
  2. Induction of anaesthesia
  3. Airway management
  4. Reversal/emergency
  5. Post-op care
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3
Q

What are the ideal properties of general anaesthesia?

A
  • unconsciousness
  • analgesia
  • amnesia
  • muscle relaxation
  • brief and pleasant
  • depth of anaesthesia can be adjusted
  • minimal adverse effects
  • large safety margin
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4
Q

What are the different elements needed for anaesthesia to be balanced?

A

Possess optimal:

  • muscle relaxation properties
  • pain relief properties
  • sedation properties
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5
Q

Most commonly used anaesthesia

A
  1. Barbiturates (provide rapid onset of action)
  2. Neuromuscular blocking agents (relax muscles)
  3. Opioids and nitrous oxide (for analgesia)
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6
Q

What is the main concept behind issue distribution of inhalant GA

A

The more soluble the drug, the faster its onset of action.

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7
Q

Halothane vs nitrous oxide (states of anaesthesia)

A

Halothane - volatile liquid
Nitrous oxide - gases
Halothane is much more soluble in blood / has a faster onset of action than nitrous oxide.

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8
Q

What are the proposed mechanism of actions of general anaesthetics?

A
  • enhance neurotransmission at inhibitory synapses via allosterically increasing GABA receptor sensitivity to action by GABA itself (positive allosteric modulator)
  • also depressing neurotransmission at excitatory synapses via blocking glutamate neurotransmitter acting on NMDA receptor, thus preventing NMDA receptor activation (negative allosteric modulator)
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9
Q

What is the minimum alveolar concentration (MAC)?

A

The minimum concentration of gaseous anaesthetics required to achieve immobility in 50% of patients exposed to a painful stimulus.

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10
Q

“MAC is a fixed concept.” True or false?

A

False. Concept of MAC varies with age, condition and concomitant administration of medications

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11
Q

Absorption of volatile liquids anaesthetics

A
  • concentration of anaesthetics in air
  • solubility of anaesthetics
  • airflow in lungs
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12
Q

Distribution of volatile liquids anaesthetics

A

Determined by regional blood flow –> which tissue receive GA

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13
Q

Metabolism of volatile liquids and anaesthetics

A
  • Metabolites can be toxic

- Halothane: hepatotoxic, isoflurane + enflurane (nephrotoxic)

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14
Q

Elimination of volatile liquids and anaesthetics

A

Mainly via the export of expired breath

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15
Q

Halothane characteristics

A
  • Volatile liquid, non-flammable, non-irritating
  • Little or no analgesia until unconsciousness sets in.
  • Decreases BP due to depression of cardiac output. Bradycardia and arrhythmia can lead to hypotension and dysrhythmia
  • May cause halothane-associated hepatitis
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16
Q

Isoflurane characteristics

A
  • MAC potency (1.4%)
  • Medium onset of recovery
  • Decreases BP due to reduced systemic vascular resistance
17
Q

Sevoflurane characteristics

A
  • Potent (MAC 2.0%)

- Metabolised in the liver to release inorganic fluoride, also nephrotoxic

18
Q

Nitrous oxide characteristics

A
  • Non-flammable
  • Nitrous oxide alone gives analgesia and amnesia, but not unconsciousness and surgical anaesthesia
  • When used alone: as analgesic agent
19
Q

Dosing of different IV general anaesthetics

A 
Thiopentone: 4-7mg/kg 
Etomidate: 0.2 - 0.3 mg/kg 
Propofol: 2-4mg/kg 
Ketamine: 1.5mg/kg IV 
Midazolam: 0.02mg/kg
20
Q

Characteristics of general anaesthetics

A
  • induction agent is a substance that induces unconsciousness
  • most agents depress respiration: you will need to take over ventilation of patients
  • may be used to supplement the effects of inhalation agents
21
Q

Advantages of administering inhaled and intravenous anaesthetics together?

A
  1. Permit dosage reduction of the inhaled anaesthetic

2. More effective than administering inhaled anaesthetic alone

22
Q

thiopentone characteristics

A
  • enters the brain easily and rapidly, rapid onset of action (~10-20s after administration)
  • multiple doses/infusions: duration of action depends on clearance
  • extensively bound to plasma protein, eliminated renally via glomerular filtration and tubular reabsorption
23
Q

thiopentone MOA

A

allosterically modifies GABAa receptor so as to allow more GABA molecules to bind to it, depressing CNS effects.

24
Q

Propofol characteristics

A
  • induction rate is similar to thiopentone, recovery is rapid
  • rapid onset (kicks in after t60s)
  • extensively used in day surgery
  • significant cardiovascular effects (decreases b.p. and negative inotropic) –> hypotension
25
Q

Ketamine characteristics

A
  • can cause dissociative anaesthesia
  • rapid induction
  • large volume of distribution, rapid clearance –> allows for continuous infusion while lengthening the duration of action
  • risk of psychologic adverse effects associated with diazepam and midazolam
26
Q

What are the functions of anaesthetic adjuncts?

A

Augment GA –> sedation, analgesia, amnesia

Lower GA doses used –> reduce risk of adverse effects

27
Q

Benzodiazepine: Midazolam IV characteristics

A
  • used for sedation during procedures not requiring GA
  • metabolised in the liver (elderly are more sensitive, slower recovery)
  • side effects are compounded by concurrent usage of other agents
28
Q

Alpha-adrenergics: dexmedetomidine IV

A
  • short term sedation (<24 hours)

- little respiratory depression

29
Q

What are the different types of analgesics (NSAIDS)?

A
  • Opioids (fentanyl, morphine): used in the perioperative period
  • Relative potency to morphine [duration of action]:
    » Sufentanil, remifentanil, fentanyl, alfentanil
    » Remifentanil (ultra-short), the others are intermediate acting
  • Metabolised in liver
30
Q

Neuromuscular blockers characteristics

A

Non-depolarising (e.g. vecuronium)

Aids many surgical procedures and provides additional insurance of immobility

Pharmacotherapeutics (28 decks)

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