Peri-op Care: Anaesthetics Flashcards

1
Q

Name the 2 main types of general anaesthetics.

A
  1. volatile (inhaled)
  2. IV

(Usually use combinations - enhanced effects allowing smaller doses)

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2
Q

Describe the mode of action of volatile anaesthetics.

A
  • All volatiles exc. Xe and NO2 potentiate GABAa receptors, increasing Cl- entry on GABA binding. Causes membrane hyperpolarisation, central inhibition and thus anxiolysis, sedation and anaesthesia.
  • NMDA receptor blocking probably other site of action.
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3
Q

What is Minimum Alveolar Concentration (MAC)?

A
  • Alveolar drug concentration at 1 atm at which 50% Pts fail to respond to surgical stimulus.
  • Describes volatile agent potency.
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4
Q

Suggest factors that increase or decrease a volatile agent’s MAC.

A

MAC is increased by (so less potent in):

  • young age
  • pregnancy
  • alcoholism
  • hyperthermia
  • central stimulants

MAC in decreased by (so more potent in):

  • hypothermia
  • opiates
  • other anaesthetics and sedatives (NO2 often added to decrease dosing)
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5
Q

Name the 2 partition coefficients of a volatile agent that affect Pt induction and recovery.

A
  1. Blood-gas partition (= solubility in blood): low value indicates faster induction and recovery
  2. Oil-gas partition (= solubility in fat): high value indicates higher potency and slow accumulation due to partition into fat (obese Pts have longer recovery)
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6
Q

Which IV anaesthetic agent is usually used for induction and maintenance of GA? For rapid-sequence induction? What are their MOA and characteristic features?

A

Induction and maintenance of GA: IV PROPOFOL

  • moderate cardiac depression
  • pain on IV injection
  • little accumulation of metabolites and anti-emetic properties

Rapid-sequence induction: IV SODIUM THIOPENTONE (barbituate)

  • v. rapid onset of action
  • marked myocardial depression can occur and metabolites build up quickly (unsuitable for maintenance infusion)

Act by potentiating GABAa Rs… increased Cl- entry… membrane hyperpolarisation.

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7
Q

What are the respective advantages of bupivacaine and lidocaine as local anaesthetics?

A
  • Bupivacaine: longer acting (4-8hrs) but longer onset of action (5-10min). Prefered for spinal and epidural injections.
  • Lidocaine: rapid onset of action (2-5min) but intermediate duration action (2hrs without and 3hrs with adrenaline).
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8
Q

Which agent is typically injected alongside lidocaine? Why?

A

ADRENALINE: vasoconstricts arteries, reducing bleeding and delaying resorption of local (almost doubles duration of anaesthesia)

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9
Q

Describe the mode of action of bupivacaine and lidocaine.

A
  • Bind to intracellular portion of voltage-gated Na+ channels and block Na+ influx into nerve cells, preventing depolarisation and AP generation.
  • Use-dependent action as have higher affinity for open Na+ channels in inactivated state (hydrophilic pathway).
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