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semester 4 - CPT & Prescribing > 24. Anaesthetics > Flashcards

24. Anaesthetics Flashcards

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1
Q

WHat are the 2 types of anaesthesia?

A

General and local

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2
Q

What are the 2 types of anaesthesia used for general?

A
  • inhalation (volatile)

- Intravenous

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3
Q

what is the type of local anaesthetic?

A

regional

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4
Q

Define conscious sedation.

A
  • Conscious sedation: use of small amounts of anaesthetic or benzodiazepines to produce a ‘sleepy-like’ state. (Maintain verbal contact but feel comfortable)
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5
Q

what are the usual steps in anaesthetics?

A
  • Premedication (Hypnotic-benzodiazepine).
  • Induction (sleep) (usually intravenous but may be inhalational (needle phobics)).
  • Intraoperative analgesia (usually an opioid e.g. fentanyl).
  • Muscle paralysis-facilitate intubation/ventilation/stillness.
  • Maintenance (typically inhalational).
  • Reversal of muscle paralysis and recovery which includes postoperative analgesia (opioid/NSAID/paracetamol).
  • Provision for PONV
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6
Q

Give examples of volatile anaesthetics.

A
  • Nitrous oxide
  • Desflurane
  • Sevoflurane
  • Isoflurane
  • Enflurane
  • Halothane
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7
Q

Give examples of IV anaesthetics.

A
  • Propofol
  • Barbiturates
  • Etomidate
  • Ketamine
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8
Q

What are the range of effects on the CNS produced during general anaesthesia described by?

A

Guedel’s signs

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9
Q

What are the stages of Guedel’s signs?

A
  • Stage 1: analgesia and consciousness
  • Stage 2: unconscious, breathing erratic but delirium could occur, leading to an excitement phase.
  • Stage 3: surgical anaesthesia, with four levels describing increasing depth until breathing weak.
  • Stage 4: respiratory paralysis and death.
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10
Q

What is anaesthesia a combination of?

A
  • Analgesia
  • Hypnosis (loss of consciousness)
  • Depression of spinal reflexes
  • Muscle relaxation (insensibility and immobility)
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11
Q

As anaesthetic concentration rises, what is lost?

A
  1. memory
  2. consciousness
  3. movement
  4. cardiovascular response
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12
Q

Define potency.

A

Concentrational dose range, over which a drug produces its effects

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13
Q

What is MAC?

A

Minimum Alveolar Concentration

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14
Q

Define MAC.

A

[Alveolar] at which 50% of subjects fail to move to surgical stimulus (unpremedicated breathing O2/air)

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15
Q

Are higher or lower value MACs more potent?

A

A lower MAC value represents a more potent volatile anesthetic

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16
Q

When is a volatile anaesthetic at equilibrium?

A

[alveolar] = [spinal cord]

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17
Q

WHat is the anatomical substrate for MAC?

A

Spinal cord

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18
Q

What factor affects induction and recovery?

A

Partition coefficients (solubility):
• Blood:Gas partition (in the blood)
• Oil:Gas partition (in fat)

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19
Q

What is the blood/gas partition coefficient?

A

Reflects solubility of the volatile agent in blood and is defined as the ratio of its concentration in blood to alveolar gas when their partial pressures are in equilibrium

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20
Q

WHat does a higher blood:gas partition indicate?

A

More soluble: leads to greater uptake by the pulmonary circulation, but a slower increase in alveolar partial pressure of the agent and therefore more prolonged induction and recovery from anaesthesia

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21
Q

WHat does a lower blood:gas partition indicate?

A

Less soluble: lesser uptake by pulmonary circulation, therefore faster increase in alveolar partial pressure

– Low value = fast induction and recovery e.g., desflurane

22
Q

What is the oil:gas partition coefficient?

A

Determines potency and slow accumulation due to partition into fat - fat solubility

23
Q

What does a higher oil:gas partition value indicate?

A

More potent

24
Q

What affects MAC?

A
  • Age (High in infants lower in elderly)
  • Hyperthermia (increased); hypothermia (decreased)
  • Pregnancy (increased)
  • Alcoholism (increased)
  • Central stimulants (increased)
  • Other anaesthetics and sedatives (decreased)
  • Opioids (decreased)
25
Q

What is the effect of nitrous oxide on MAC?

A

NO Typically mixed with other volatile agents to reduce their MAC.

  • has little side effects, so can be used to reduce side effects of other agents
  • reduced MAC means reduced dosing
26
Q

what are the main rapid intravenous anaesthetics?

A

Propofol

Barbiturates

27
Q

what is the main slow intravenous anaesthetic?

A

Ketamine

28
Q

when are intravenous anaesthetic used as sole anaesthetic?

A

TIVA (Total IntraVenous Anaesthesia).

29
Q

How Do We Describe Intravenous Anaesthetic Potency ?

A
  • Plasma concentration to achieve a specific end point (e.g., loss of eyelash reflex).
  • For induction in mixed anaesthesia – Bolus to end point then switch to volatile.
30
Q

how is TIVA prescribed?

A

• TIVA uses a defined PK based algorithm to infuse at a rate to maintain set point. Pre-ceded by a bolus.

31
Q

WHat is the critical site of action of volatile anaesthetics? Exceptions?

A

GABA-A receptors

  • ligand gated ion channels
  • Cl- conductance - Cl- flows in so inside more negative which inhibits transmission of action potential - depress CNS activity

Exceptions: Xe, N2O, ketamine - block NMDA receptors

32
Q

What does potentiation of GABA receptors cause?

A

• Anxiolysis • Sedation • Anaesthesia

33
Q

how does anaesthetic potency correlate to lipid solubility?

A

higher potency = higher lipid solubility

34
Q

how does anaesthetic potency correlate to GABA-A interaction ?

A

higher the potency the greater the interaction

35
Q

in the brain, what is consciousness a balance of?

A 
between excitation (NMDA Glutamate) and inhibition (GABA).
Anaesthetics modulate this balance.
36
Q

What are the main systems of the CNS that are targeted by anaesthetics?

A

Loss of connectivity between systems:

  • reticular formation (arousal -consciousness) depressed
  • thalamus (sensory relay)
  • hippocampus depressed (memory)
  • brainstem depressed(resp and CVS)
  • dorsal horn (pain) and motor neuronal activity depressed
37
Q

When is local and regional anaesthesia used?

A
  • Dentistry
  • Obstetrics
  • Regional surgery (patient awake)
  • Post-op (wound pain)
  • Chronic pain management (PHN)
38
Q

What are the main local anaesthetics?

A

(most potent first)

Bupivacaine, Ropivacaine, Lidocaine and Procaine

39
Q

What is the basic structure of local anaesthetics, how does this affect its metabolism?

A
  • made up of aromatic ring and amine group
  • linked by either a ester (short acting)or amide(long acting)

We have lots of esterases in plasma, so these are broken down quickly - short duration of action

40
Q

What characteristics are important to consider in local anaesthetics?

A
  • lipid sol (higher = greater potency)
  • dissociation constant (pKa - lower = faster onset)
  • chemical link (metabolism)
  • protein binding (duration)
41
Q

what is the mode of action of local anaesthetic?

A

block voltage gated sodium ion channels - block action potential propagation
• Block small myelinated (afferent) nerves in preference hence nociceptive and symp block

42
Q

What is use dependent block (local anaesthetics)?

A

the degree of block is proportional to the rate of nerve stimulation
- more drug molecules enter sodium channels when they are open and cause block

43
Q

how does adrenaline impact use of local anaesthetic?

A

• Adrenaline ↑ duration

44
Q

which local anaesthetic is more potent and which has slower onset?

A

Compared to Procaine, Bupivacaine is more potent with a longer duration of action. Procaine is esterase metabolised and has a slower onset time but not much in it.

45
Q

WHat is regional anaesthesia?

A

WHat is regional anaesthesia?

Selectively anaesthetising a part of the body

46
Q

WHat does regional anaesthesia typically use?

A

Local anaesthetic and or an opioid

47
Q

What are the upper extremity regional anaesthesai?

A

Interscalene, supraclavicular, infraclavicular, axillary

48
Q

What are the lower extremity regional anaesthesai?

A

Femoral, sciatic, popliteal, saphenous

49
Q

how are regional anaesthesia given?

A

Extradural / Intrathecal / Combined (labour).

50
Q

What are the main side effects of general anaesthesia?

A
  • PONV (postoperative nausea and vomiting) (opioids)
  • CVS - hypotension
  • PO cognitive dysfunction (increases with increasing age)
  • Chest infection

general concern allergic reaction/anaphylaxis

51
Q

What are the main side effects of local anaesthesia?

A

Depends on the agent used and usually result from systemic spread (Locals are Na+ channel blockers so cardiovascular toxicity)

semester 4 - CPT & Prescribing (25 decks)

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