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Year Three - Specialities > Anaesthetics - Principle of Pharmacology > Flashcards

Anaesthetics - Principle of Pharmacology Flashcards

1
Q

What is the function of anaesthetic?

A

It is used during procedures and surgical operations to numb sensation in certain areas of the body or induce sleep

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2
Q

What are the four anaesthetic subtypes?

A

General anaesthesia

Regional anaesthesia

Local anaesthesia

Sedation

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3
Q

What is general anaesthesia?

A

It is a state of controlled unconsciousness, during which insensibility is produced in the whole body

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4
Q

Which two drug types are used in general anaesthesia?

A

Hypnotics

Analgesics

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5
Q

What is regional anaesthesia?

A

It produces insensibility in an area or region of the body

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6
Q

How is regional anaesthesia administered? What does this mean?

A

We inject anaesthetic near nerves supplying the relevant area

The effect is therefore remote to the injection

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7
Q

What are the two most common types of regional anaesthetic?

A

Spinal

Epidural

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8
Q

What is the difference between regional anaesthesia and regional analgesia?

A

Regional anaesthesia results in little or no sensation from the blocked area - warmth, proprioception, light, touch, vibration and pain

Regional analgesia will only remove pain sensation from that area, with other sensations being retained to varying extents

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9
Q

What is local anaesthesia?

A

It produces insensibility in a small part of the body where the operation is taking place

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10
Q

How is local anaesthesia administered?

A

We inject anaesthetic directly into the required tissues

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11
Q

What is sedation?

A

It involves using small amounts of anaesthetic drugs to produce a ‘sleep-like’ state

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12
Q

What is the difference between sedation and general anaesthesia?

A

Unlike general anaesthesia, sedation will result in some awareness of the procedure

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13
Q

What are the components of anaesthesia triad?

A

Analgesia

Relaxation

Hypnosis

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14
Q

What is the function of analgesic agents in anaesthesia?

A

They are used to provide pain relief, whilst also suppressing reflex autonomic responses to painful stimulus

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15
Q

What two drug classes are used in anaesthetic to cause analgesia?

A

Opiates

Local anaesthetic agents

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16
Q

What is the function of muscle relaxants in anaesthetic?

A

They are used to relax skeletal muscle enough that patients become immobile

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17
Q

What drug class is used in anaesthetic to cause relaxation?

A

Muscle relaxants

However, local and general anaesthetics also provide a degree of relaxation

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18
Q

What is the function of hypnotic agents in anaesthetic?

A

They allow a state of unconsciousness

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19
Q

What drug class is used in anaesthetic to cause hypnosis?

A

General anaesthetic agents

However, opiates also provide a degree of relaxation

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20
Q

Do individual anaesthetics require all three components of the triad?

A

No

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21
Q

What is the mechanism of general anaesthetic agents?

A

They work by suppressing neuronal activity

This is achieved through the opening of chloride ion channels, which hyperpolarises neurones and suppresses their excitatory synaptic activity

This means that they are less likely to reach their threshold potential and are therefore unable to send signals to other neurons

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22
Q

Which functions are inhibited with general anaesthesia first? Why?

A

Complex processes

This is because these processes are dependent on the greatest amount of neuronal activity

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23
Q

Which functions are relatively spared with general anaesthesia? Why?

A

Simpler, primitive functions

This is because these processes are dependent on a small amount of neuronal activity

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24
Q

What term is used to describe the order in which general anaesthesia affects cerebral function? Why is this advantageous?

A

Cerebral function is “lost from top down”

This allows unconsciousness to be achieved while automatic and autonomic functions are persevered, such as respiration and blood pressure homeostasis

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25
Q

Once general anaesthesia has been administered, why is it essential that we monitor patients?

A

We manage the impacts of anaesthetic agents on vital functions – such as airway maintenance, breathing and cardiovascular function (ABC)

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26
Q

In terms of the anaesthetic triad, what components does general anaesthetic provide?

A

Hypnosis

A small degree of muscle relaxation

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27
Q

What are the two mechanisms in which general anaesthesia can be administered?

A

Intravenous

Inhalation

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28
Q

List two intravenous general anaesthetic agents

A

Thiopentone

Propofol

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29
Q

What is the mechanism of intravenous general anaesthetic agents?

A

They undergo allosteric binding, which means that they bind to GABA receptors agonistically to open chloride ion channels

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30
Q

How do intravenous general anaesthetic agents produce a rapid onset of unconsciousness?

A

This is due to their highly lipid soluble nature allowing them to cross the blood brain barrier readily and access neural tissues

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31
Q

How do intravenous general anaesthetic agents produce a rapid recovery?

A

This is due to their imminent disappearance from circulation

This decrease in blood concentration is due to the redistribution of these drugs from circulation to other body compartments

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32
Q

How does the blood concentration of anaesthetic change after administration? Why?

A

Initially, the blood concentration is high, however this decreases rapidly

This is because the drug moves into highly perfused tissues

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33
Q

What does the blood concentration of general anaesthesia correlate to?

A

Brain concentration

34
Q

How does the muscle concentration of anaesthetic change after administration? Why?

A

Muscle absorbs anaesthesia more slowly, however the effect is large

This is due to the relative high mass of skeletal muscle in the body

35
Q

How does the fat concentration of anaesthetic change after administration?

A

Fat absorbs anaesthesia even more slowly than muscle, due to its lack of perfusion

However, it can store large amounts due to the high lipid solubility of these drugs

36
Q

What is the function of target controlled infusion (TCI) machines?

A

These machines automate the dosing of intravenous drugs during surgery

37
Q

What is the advantage of target controlled infusion (TCI) machines?

A

They allow accurate infusions of anaesthesia to achieve specific blood/brain concentrations

38
Q

What is the mechanism of inhalation general anaesthetic agents?

A

They dissolve in the lipid layer of cell membranes, resulting in a direct effect on transmembrane proteins to suppress neuronal activity

39
Q

What type of molecules are inhaled general anaesthetics?

A

Halogenated hydrocarbons

40
Q

Describe the mechanism in which inhaled general anaesthetic agents enters the body

A

At induction, a high concentration of the agent is administered

This creates a high partial pressure gradient in the lungs, allowing the drug to move into the patient’s blood and finally the brain.

41
Q

What is MAC (in terms of inhaled general anaesthesia)?

A

Minimum alveolar concentration

It refers to the drug concentration required in the alveoli to produce anaesthesia

42
Q

What does a low MAC value mean?

A

It refers to a highly potent drug, in which a small concentration is required to produce a state of unconsciousness

43
Q

How fast are inhaled general anaesthetic agents induced? In which circumstances could this be advantageous?

A

Slowly

In patients with obstructing airway disease

44
Q

How long is inhaled anaesthesia administered for?

A

It is administered for the duration of the procedure, and the patient will remain unconsciousness for as long as the anaesthetic is administered

45
Q

How do we awaken a patient on inhaled general anaesthesia?

A

Once the procedure has concluded, the anaesthetic agent is no longer administered, and the patient inhales a gas mixture with no agent in it – referred to as a washout mixture

This reverses the concentration gradient, producing a fall in alveolar concentration followed by blood and brain concentration

46
Q

How are inhaled general anaesthesia agents metabolised?

A

They undergo little metabolism in the body and are therefore almost completely exhaled again unchanged

47
Q

How do we monitor inhaled general anaesthetic agents?

A

We measure CO2 levels in expired gas, as this allows the end tidal portion of the gas stream to be identified and thus analysed

This represents alveolar gas

Due to the fact that inhalation agents are highly lipid soluble, the alveolar drug gas concentration is equivalent to the arterial drug gas concentration. This is because these drugs can cross the basement membranes readily

48
Q

What is the main advantage of inhaled general anaesthesia compared to intravenous?

A

We can reliably monitor inhaled general anaesthesia

49
Q

How is general anaesthesia administered in practice?

A

General anaesthesia induction is usually intravenous followed by inhalation maintenance

50
Q

What are the recent developments in the administration of general anaesthesia?

A

There have been developments in intravenous maintenance via computer controlled infusion mechanisms

They usually involve the administration of propofol with opiates, such as remifentanil

51
Q

What central effects does general anaesthesia have on the cardiovascular system?

A

It produces inhibitory effects on the cardiovascular centres and nuclei of the brainstem, resulting in the following effects…

  • A reduced sympathetic nerve activity
  • A negative inotropic/chronotropic effect on the heart
  • Vasodilation
52
Q

What direct effects does general anaesthesia have on the cardiovascular system?

A

It produces direct effects on vascular smooth muscle and the myocardium, which results in further vasodilation and venodilation

53
Q

Why does general anaesthesia decrease blood pressure?

A

Due to its vasodilatory effects, there is reduced venous return to the heart and therefore decreased cardiac output

The cardiac output is further reduced by the negative inotropic effects of general anaesthesia on the heart

In addition to this, arterial vasodilation leads to a reduced systemic vascular resistance (SVR)

Due to the relationship: MAP = CO X SVR, blood pressure is significantly reduced

54
Q

What two things maintain normal blood pressure after the administration of general anaesthesia?

A

We administer intravenous fluids

We administer vasopressor drugs

55
Q

What effects does general anaesthesia have on the respiratory system?

A

It produces inhibitory effects on the respiratory centres of the brainstem

This reduces the hypoxic and hypercarbic drive, resulting in reduced tidal volumes and an increased respiratory rate

In addition to this, general anaesthesia decreases functional residual capacity (FCR), which results in reduced lung volumes and VQ mismatch

This effect persists into the postoperative period

56
Q

Why do patients require oxygen after surgery with general anaesthesia?

A

The effects of reduced lung volumes and VQ mismatch persists into the postoperative period

57
Q

What anaesthetic agent results in no adverse effects on the cardiovascular and respiratory system?

A

Ketamine

58
Q

What is the mechanism of muscle relaxants?

A

They interact with the nicotinic acetylcholine receptors at the neuromuscular junction

59
Q

Do muscle relaxants produce an effect on smooth or cardiac muscle?

A

No

60
Q

In terms of the anaesthetic triad, what components do muscle relaxants provide?

A

Relaxation

61
Q

What other component of the triad has to be used in combination with relaxation? Why?

A

Hypnosis

This is because paralysation whilst being conscious can be extremely unpleasant for the patient

62
Q

What are the three complications associated with muscle relaxants?

A

Awareness

Incomplete Reversal

Apnoea

63
Q

Why do muscle relaxants have a risk of awareness complications?

A

This occurs when muscle relaxants are given in combination with an insufficient dose of the hypnotic agent

64
Q

What effects occur when muscle relaxants incompletely reverse?

A

The residual effects of muscle relaxants persist into the postoperative period

This may lead to immediate airway obstruction and respiratory insufficiency

65
Q

What are opiates?

A

They are substances with active ingredients that are naturally derived from opium

66
Q

What are the four opiates used in anaesthetic?

A

Fentanyl

Remifentanil

Morphine

Oxycodone

67
Q

What are the two features of fentanyl?

A

Short-acting

Potent

68
Q

What are the analgesic purposes of fentanyl?

A

It is an intra-operative analgesia

69
Q

What are the two features of remifentanil?

A

Extremely short-acting

Highly potent

70
Q

What are the analgesic purposes of remifentanil? Why?

A

This drug can be added to inhalation and intravenous agents to allow administration of lower doses and faster recovery rates

It is a highly potent drug

71
Q

What is the feature of morphine and oxycodone?

A

Long-acting opiate

72
Q

What are the analgesic purposes of morphine and oxycodone?

A

It is an intra-operative analgesia, which continues into the post-operative period

73
Q

In terms of the anaesthetic triad, what components do opiates provide?

A

Analgesia

A small degree of hypnosis

74
Q

List three examples of local anaesthetic drugs

A

Lidocaine

Bupivacaine

Ropivacaine

75
Q

What is the mechanism of local anaesthetic drugs?

A

They work by blocking sodium ion channels and thus preventing axonal action potential from propagating

76
Q

Why do we not administer local anaesthetic drugs intravenously?

A

Due to the fact that these drugs are not tissue specific, it is important that they are not prescribed intravenously as toxic effects can occur throughout the whole body

77
Q

How do we administer local anaesthetic?

A

Local anaesthetic injections are usually guided with ultrasound technology

78
Q

What is the advantage of ultrasound guided administration of local anaesthetic?

A

This allows for safer and more effective delivery of these drugs, reducing the likelihood of nerve or vascular injury

79
Q

In terms of the anaesthetic triad, what components do local anaesthetic drugs provide?

A

Analgesia

A small degree of muscle relaxation

80
Q

What are the physiological effects of local anaesthetic?

A

It produces some physiological effects; however, they are mainly cardiovascular with relative sparing of respiratory function

The cardiovascular effects produced lack global effect and instead become proportional to the size of the anaesthetised area

81
Q

In which patients are local and regional anaesthetic techniques preferred? Why?

A

In those with severe respiratory conditions

There are little respiratory effects

82
Q

What is a side effect of lidocaine?

A

Mental state change

Year Three - Specialities (15 decks)

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