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Clinical Pharmacology > 13.2 Anaesthetics > Flashcards

13.2 Anaesthetics Flashcards

1
Q

How can anaesthesia be used ?

A

General
Local

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2
Q

How is general anaesthesia delivered?

A
  • Inhaled (volatile)
  • IV
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3
Q

How can local anaesthesia be used?

A

Regionally -can block an entire part of the body
Sometimes used if haemodynamically unstable and cannot use general

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4
Q

What is conscious sedation?

A

Small amount of anaesthetic or benzodiazepines used to produce a sleep state

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5
Q

What are the practical steps of anaesthesia?

A
  • Pre-medication to help anxiety- benzodiazepines
  • Induction -IV or inhalation
  • Intraop anaesthesia -opioids
  • Muscle paralysis for intubation
  • Reversal of muscle paralysis and recovery including post op analgesia
  • Post-op anti-emetics
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6
Q

Describe the structure of general anaesthetics

A

Lots of different structures

May have hydrocarbon with fluorine ring

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7
Q

What are some examples of inhaled general anaesthetics?

A
  • Nitric oxide (N2O)
  • Chloroform
  • Halothane
  • Fluroxene
  • Methoxyflurane
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8
Q

What are some examples of IV general anaesthetics?

A
  • Propofol
  • Barbiturates
  • Ketamine
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9
Q

What are Guedel’s signs?

A

Level of anaesthesia from the presentation of the patient

Eye movement and muscle tone

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10
Q

What are the different stages of Guedels signs?

A

Stage 1: Analgesia
Normal muscle tone
Some eye movement
Conscious

Stage 2: Excitement
Muscle tone normal to increased
Moderate eye movement
Uconscious
Breathing erratic
Delirium could occur

Stage 3: Surgical anaesthesia - Muscle relaxedness (slight, moderate, markedly, markedly ) increases until breathing becomes weak

Stage 4: Respiratory paralysis - Muscle tone flaccid
No eye movements
Death

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11
Q

What is anaesthesia a combination of?

A
  • Analgesia
  • Hypnosis - loss of consciousness
  • Depression of spinal reflexes
  • Muscle relaxation
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12
Q

What is anaeastheisa end point of determined by?

A

Concentration dependent

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13
Q

How do we describe potency in volatiles/inhalational agents?

A

MAC
Minimum alveolar concentration (EC50)

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14
Q

What order do responses go with anaesthesia?

A
  1. Memory
  2. Consciousness
  3. Movement
  4. Cardiovascular response
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15
Q

What is potency?

A

EC50

Concentration of drug needed to elicit half of the maximal response

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16
Q

What is MAC or minimum alveolar concentration?

A

Alveolar concentration of drug (1 atmosphere) at which 50% of patients fail to move to a surgical stimulus

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17
Q

What is alveolar concentration equal with at equilibrium?

A

Alveolar concentration of drug equals spinal cord concentration of drug at equilibrium

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18
Q

What are the different types of MAC?

A

MAC
MAC-Bar - autonomic response
MACawake

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19
Q

What is a main factor (compartment wise) affecting induction and recovery from anaesthesia?

A

Partition co-efficients - measures of solubility

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20
Q

What are some examples of partition co-efficients that can effect anaesthesia induction and recovery?

A

Blood Gas partition
Solubility in blood

Oil Gas partition
Solubility in fat

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21
Q

What is the relationship of Blood:Gas partition and anaesthesia?

A

Low value (so low solubility)

Fast induction and recovery as it is not in tissues and blood for long

E.g. desflurane

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22
Q

What is the relationship of Oil:Gas partition and anaesthesia?

A

Determines potency and slow accumulation due to partition in fat e.g halothane

Higher value so higher potency as it accumulates in fat

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23
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)
24
Q

How does nitric oxide affect MAC?

A

Nitric oxide decreases MAC

Need less of if you add nitric oxide

25
Q

What is the relationship of GABA and the potency of anaesthesia?

A

Increased interaction with GABA

Increases its inhibitory effects therefore increased potency of anaesthesia

26
Q

What is the main receptor target for inhaled anaesthesia?

A

GABA- increases effects of GABA (potentiates, GABA still needs to bind)
More hyperpolarisation, therefore further from threshold

27
Q

What is the exception to the GABA binding rule?

A

Xenon, Nitric Oxide and Ketamine
These work at NMDA receptors (glutamate receptors) and block them

28
Q

What systems is the main target of anaesthesia?

A

Reticular formation- controls consciousness

29
Q

What occurs to each part of reticular formation during anaesthesia?

A

Thalamus
Transmits and modifies sensory information before reaching PSC

Hippocampus
Depressed, memory loss

Brainstem
Depressed, respiratory and CV effects

Spinal cord
Depressed, analgesia ( dorsal horn) and Motor neurone activity decreased

30
Q

Howe can we see effects of anaesthesia on the brain?

A

PET scan

31
Q

Give examples of fast acting anaesthesia

A

Propofol
Barbiturates

32
Q

Give an example of slow acting anaesthesia

A

Ketamine

33
Q

What are IV anaesthetics often used for?

A
  • Induction in surgery
  • TIVA (total intravenous anaesthesia)
34
Q

What can Ketamine cause when you wake up?

A

Odd emergence reactions

35
Q

What is the main receptor target for IV anaesthesia?

A

GABA- potentiates

Not ketamine its binds to NMDA and inhibits GABA

36
Q

How is IV anaesthesia potency described?

A

Plasma concentration
Achieve a specific end point such as eyelash reflexes loss

For induction with mixed anaesthesia
IV bolus used to end point, then switched to inhaled agent

37
Q

What does TIVA use to calculate potency and anaesthesia end-point?

A

Total IV
Uses defined PK based algorithm to infuse at a rate to maintain a set point

Given a bolus before this

38
Q

When is local anaesthesia used?

A
  • Dentistry
  • Obstetrics
  • Regional surgery
  • Post-op
  • Chronic pain management
39
Q

What are some examples of local anaesthetics?

A

Lidocaine
Bupivacaine
Ropivacaine
Procaine

-caine suffix

40
Q

What is the common structure of local anaesthetics?

A

Aromatic ring with ester or amide connecting to amine group

41
Q

What are some characteristics of local anaesthesia?

A

Lipid solubility
If it was higher they would have greater potency

Dissassociation constant
Lower pKa leads to a faster onset

Chemical links (ester vs amide) Determines metabolism

Protein binding
More protein binding causes longer duration

42
Q

How do different bonds alter the duration of local anaesthetics?

A

Ester
Shorter acting, plasma contains esterases which break it down

Amide
Longer acting

43
Q

How does local anaesthetic work in wound analgesia?

Buvipacaine

A
  • Cocaine-like molecule
  • Cocaine enters channel via two ways - hydrophobic vs hydrophilic
  • Cocaine crosses plasma membrane if uncharged and picks up positiveve charge
  • Blocks Na+ channels that are open (hydrophilic pathway) or closed (hydrophobic pathway)
  • Na+ unable to travel through and depolarise resulting in decreased APs
44
Q

What do molecules block in local anaesthesia?

A

Dependent block
Only blocks channels if there is lots of firing

Blocks small myelinated afferent nerves in preference
Nociceptive and sympathetic block

45
Q

How does adrenaline affect local anaesthetics?

A
  • Vasoconstriction
  • Decreased blood flow
  • Increased duration of anaesthesia
46
Q

What is the difference between Bupivacaine and Procaine?

A

Bupivacaine
More potent
Longer duration

Procaine
Ester metabolised
Slower onset

47
Q

What determines potency of local anaesthesia?

A

Determined by lipid solubility
The higher the solubility the more potent

48
Q

Write out the strength of local anaesthetics from highest to lowest

A

Bupivacaine
Ropivacaine
Lidocaine
Procaine

49
Q

What is the speed of acting from fastest to slowest of local anaesthesia?

A

Determined by pKa
Low pKa means a faster onset

  1. Lidocaine
  2. Bupivacaine
  3. Ropivacaine
  4. Procaine
50
Q

Outline the duration of local anaesthesia from longest to shortest

A

Determined by protein binding
More binding causes a longer duration

  1. Bupivacaine
  2. Ropivacaine
  3. Lidocaine
  4. Procaine
51
Q

What is regional anaesthesia?

A

Anaesthetising a part of the body
Described as a nerve block
Patient remains awake

Uses local anaesthesia or opioids

52
Q

Where do you use regional anaesthesia?

A

Upper extremities
Supraclavicilar
Interscalene
Infraclavicular
Axillary

Lower extremities
Femoral
Sciatic
Poplitieal
Saphenous
Extradural
Intrathecal (spinal cord)

53
Q

What are the side effcts of general anaesthesia?

A
  • Nausea and vomiting acutely
  • Hypotension
  • Post operative cognitive dysfunction - increases with age and longer anaesthesia
  • Chest infection
54
Q

Why can you get a chest infection follow general anaesthesia?

A

Lack of coughing following surgery
Foreign tube with microorganisms directly into thoracic cavity

55
Q

Main concern generally of anaesthesia from public too

A

Anaphylaxis/allergic reaction

Clinical Pharmacology (45 decks)

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