Module 2.1.1 (General Anaesthetics) Flashcards

1
Q

What are the stages of general anaesthesia?

A

Premedication

Induction

Intravenous anaesthetics

Maintenance

Inhalation anaesthetics

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2
Q

What is the purpose of GA?

A

Producing unconsciousness

Loss of sensation and reflexes

Facilitates surgery with much reduced distress to the patient

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3
Q

What are the FOUR stages of anaesthesia?

A
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4
Q

Premedication = given on the ward before the patient is taken to the operating theatre. What are the aims of premedication?

A

Relief from anxiety

Reduction of muscarinic effects bradycardia and secretions

Analgesia

Prevention of postoperative emesis

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5
Q

What is given for relief from anxiety? Why is it given? How to reverse ffects?

A

BZDs: diazepam, lorazepam, midazolam

  • To relieve apprehension and anxiety before anaesthesia
  • To lessen the amount of general anaesthetic required to achieve and to maintain unconsciousness
  • To sedate postoperatively
  • Effects reversible by antidote -flumazenil
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6
Q

What is given for reduction of muscarinic effects? Why is it given?

A

Atropine, Hyoscine, Glycopyrrolate

  • Muscarinic antagonists
  • Prevent salivation and bronchial secretions
  • More importantly to protect the heart from arrhythmias, particularly bradycardia caused by some inhalation agents and neuromuscular blockers
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7
Q

What is used for analgesia?

A

Fentanyl, Alfentanil, Remifentanil

  • Opioid analgesics
  • Often given prior to an operation
  • Adequate analgesia is important to stop physiological stress reactions to pain

NSAIDs

  • Useful alternatives and adjuncts to opiates
  • But inadequate for severe postoperative pain when used alone
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8
Q

What is given for postoperative antiemesis?

A

Ondansetron, Metoclopramide, Prochlorperazine

  • Provide postoperative antiemesis
  • Nausea and vomiting are common after general anaesthesia
  • Often due to opioid drugs peri- and postoperatively
  • Antiemetic drugs can be given with the premedication
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9
Q

What is used for the induction stage?

A
  • Intravenous (IV) agents - rapid induction of unconsciousness
  • Prevention of acid aspiration in emergency and obstetric operations is crucial
  • se either H2-receptor antagonist or a proton pump inhibitor prior to induction
  • Muscle relaxation

> Use Vecuronium, suxamethonium after induction

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10
Q

Explain the pharmacology of the following IV anaesthetics:

A) Barbiturates (thiopentone), Benzodiazepines (Midazolam)

B) Thiopentone

C) Midazolam

D) Propofol

E) Ketamine

A

A)

  • Potentiate the action of GABA on GABAA receptors
  • Produce a general CNS depression

B)

  • ultrashort-acting
  • Caution during administration – avoid severe medullary depression

C)

  • has anxiolytic, muscle relaxant and anterograde amnesic actions

D)

  • Exact mechanism uncertain
  • May potentiate the action of GABA on GABAA receptors (differs from barbiturates and benzodiazepines)
  • May shorten opening time of nicotinic receptors and sodium channels in CNS
  • Produce a general CNS depression
  • Rapidly metabolised more rapid recovery
  • Can be used for induction and maintenance

E)

  • Reduces neuronal excitability by blocking NMDA (N-methyl-D-aspartate ) receptors
  • Produce dissociative anaesthesia
  • Also stimulates opioid receptors in brain and spinal cord
  • Unusual increase in cardiac output via increased sympathetic activity
  • Produce unpleasant hallucinations
  • Rarely used today
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11
Q

What is used as muscle relaxants? Explain the MOA.

A

Vecuronium, tubocurarine, pancuronium

  • Competitive antagonists - nicotinic ACh receptor
  • Cause non-depolarisation of motor end-plat
  • Complete paralysis without fasciculation
  • Action reversible by increasing Ach levels with anticholinesterase
  • Antidote - neostigmine

Suxamethonium

  • Cause depolarising blockade at motor end-plate
  • Not reversible by anticholinesterase
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12
Q

What is used as maintanence? How to monitor?

A

Inhalation anaesthetic agents

Maintain a state of general anaesthesia after induction

Intravenous agents can be used via a continuous pump

Requires precise control of depth of anaesthesia in CNS

Level of anaesthesia is denoted by partial pressure of GA in CNS

Monitor using aveolar partial pressure

Ideal general anaesthetic provides a rapid and pleasant induction and maintenance of surgical anaesthesia, followed by a smooth and rapid recovery to a fully functional and conscious state

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13
Q

What is used as inhalation anaesthetics? What is the MOA?

A

Nitrous oxide, Desflurane, Isoflurane, Methoxyflurane, Sevoflurane

  • Typically act at high concentration
  • Potency is well correlated with liposolubility
  • Cell membranes - hydrophobic domains of proteins are likely sites of action
  • Excitatory transmission (glutamatergic and nicotinic) may be inhibited
  • Inhibitory transmission at GABAA receptors is potentiated.
  • Stereoisomers of some inhalation anaesthetics (e.g. isoflurane) - differences in potency
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14
Q

How do GA in body work?

A

The Lipid Theory (used to be the only theory!!)

GAs dissolve in membranes of neurons in CNS

Alter membrane function

The Protein Theory

GAs interact with hydrophobic parts of modulatory proteins eg receptors, ion channels

Alter ion conductance

Cellular and Receptor Mechanism

decrease functions of excitatory neurotransmitters

increase functions of inhibitory neurotransmitters

Affect potassium and sodium channels

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15
Q

What does the potency of lipid anaesthetics increase with?

A

increases as lipid solubility increases

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16
Q

What are the actions of propofol, thiopentone on ligand gated ion channels?

A

Potentiate action of endogenous agonists of inhibitory receptors eg GABA – A, glycine receptors

17
Q

What are the actions ketamine on ligand gated ion channels?

A

inhibits action of endogenous agonists of excitatory receptors eg glutamate, NMDA, nicotinic receptors

18
Q

general anaesthetic summary

A
19
Q

MOA of pancuronium

A

Pancuronium is a competitive, or non-depolarising agent

  • It binds to nicotinic receptors on the muscle endplate of the neuromuscular junction and thereby competitively blocking the action of acetylcholine.
  • Other agents include vecuronium and rocuronium. Their actions can be reversed by anticholinesterase agents such as neostigmine.
20
Q

How does the rate of induction of anaesthesia differ between children and adults?

A

Children have a higher alveolar ventilation rate, smaller lungs, and a lower capacity of tissues for anesthetic

This shortens the time to equilibration between inspired and alveolar partial pressure, and between alveolar and tissue partial pressure.