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Clinical Pharmacology > 13.1 Introduction To Anaesthetics > Flashcards

13.1 Introduction To Anaesthetics Flashcards

1
Q

What are the 2 main categories of anaesthesia?

A

General

Local

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2
Q

What are the two main subcategories of general anaesthesia?

A

Inhalational / volatile

Intravenous

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3
Q

What is conscious sedation?

A

use of small amounts of anaesthetic or benzodiazepines to produce a ‘sleepy-like’ state. (Maintain verbal contact but feel comfortable)

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4
Q

Briefly describe the normal anaesthesia routine during surgery (7)

A
  • Premedication (Hypnotic-benzodiazepine).
  • Induction (usually intravenous but may be inhalational in children of if needle phobia).
  • Intraoperative analgesia (usually an opioid).
  • Muscle paralysis-facilitate intubation/ventilation/stillness.
  • Maintenance (intravenous and/or inhalational).
  • Reversal of muscle paralysis and recovery which includes postoperative analgesia (opioid/NSAID/paracetamol).
  • Provision for PONV.
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5
Q

What is PONV?

A

Post operative nausea and vomiting. Occurs as a side effect to anaesthetics and opioids

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6
Q

Give some examples of drugs used as inhalational general anaesthetics

A 
Chloroform
Halothane
Methoxyflurane
Enflurane
Isoflurane
Xe
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7
Q

Give some examples of drugs commonly used as intravenous general anaesthesia

A
  • Propofol
  • Barbiturates
  • Etomidate
  • Ketamine
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8
Q

How do we assess the stages of anaesthesia?

A

Guedel’s signs

  • muscle tone
  • breathing
  • eye movement
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9
Q

What are the 4 different stages of anaesthesia as defined by 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

Anaesthesia is a combination of :

A

Analgesia
Hypnosis ( loss of consciousness)
Depression of spinal reflexes
Muscle relaxation ( insensibility and immobility )

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11
Q

What determines the end - point of anaesthesia?

A

Anaesthesia concentration

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12
Q

In what order are the contributing factors of anaesthesia?

A

Memory
Consciousness
Movement
Cardiovascular response

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13
Q

What is potency?

A

The concentrational dose range over which a drug produces its affect

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14
Q

How do we measure anaesthetic potency?

A

MAC - minimum alveolar concentration

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15
Q

What is minimum alveolar potency?

A

The concentration in the alveolus of the lung at 1atm at which 50% of subjects fail to move to surgical stimulus (unpremeditated breathing of O2 and air)

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16
Q

What is the anatomical substrate for MAC?

A

The spinal cord

At equilibrium of MAC, the concentration in the alveoli is equal to the concentration in the spinal cord

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17
Q

What does the blood:gas partition cooefficients determine?

A

Determine the induction and recovery from anaesthetic. A low value indicates fast induction and recovery (desflurane)

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18
Q

What does the oil:gas partition coefficient determine?

A

Determines potency and accumulation

A high lipid solubility means there’s high potency and slow accumulation (halothane)

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19
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)
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20
Q

Why is nitrous oxide very often added to volatile anaesthetics?

A

To reduce the dosing amount

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21
Q

What are some rapid intravenous anaesthetics?

A

Proposal

Barbiturates

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22
Q

What are some slow intravenous anaesthetics?

A

Ketamine

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23
Q

What is TIVA?

A

Total intravenous anaesthetic

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24
Q

How do we describe intravenous potency?

A

Plasma concentration to achieve a specific end

point (e.g., loss of eyelash reflex a.k.a gabellar reflex)

25
Q

What is the glabellar reflex?

A

Repetitive tapping on the forehead eliciting a blinking response in the first few taps

26
Q

How is intravenous anaesthesia used in mixed anaesthesia?

A

Used as an induction bolus to end point and then switch to volatile

27
Q

What is the Meyer Overton correlation?

A

An observation that anaesthetic potency correlates with lipid solubility.
High potency anaesthetics have high lipid solubility

28
Q

What is the main target site affected by anaesthetics?

A

GABAa receptor

29
Q

What type of receptor is the GABAa?

A

A ligand gated ion channel allowing the flow of Cl- into the neurones. Opens on bonding with GABA, one of the major inhibitory neurotransmitters

30
Q

Describe how most anaesthetics work?

A

By opening GABAa channels, allowing Cl- ions to flow into cells and hyperpolarising neurones. This reduces the likelihood of APs firing.
They potentiate GABA mediated chloride conduction

31
Q

What are the normal effects of GABA?

A

Anxiolysis
Sedation
Anaesthesia

32
Q

Which anaesthetics do not operate by GABAa mediated chloride conductance?

A

Xenon
Ketamine
N2O nitrous oxide
- these block NMDA receptors (excitatory glutamate channels)

33
Q

What determines brain consciousness?

A

A balance between central excitation (glutamate) and central inhibition ( GABA )

34
Q

What are the main broad brain targets involved in anaesthetic action?

A

Reticular formation (hindbrain, midbrain and thalamus)

35
Q

How is the reticular formation affected by anaesthesia?

A

Reticular formation activity is depressed. The connectivity between the different regions of the reticular formation (hindbrain, midbrain and thalamus) is lost.

36
Q

What is the role of the reticular system?

A 
Reticular system often called “activating system” due to ability to increase arousal. Thalamus transmits and modifies sensory information. Hippocampus depressed (memory). Brainstem depressed (respiratory and some CVS). Spinal cord-depress dorsal horn (analgesia) and motor
neuronal activity (MAC).
37
Q

When are local and regional anaesthetics used?

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

Name some typical local anaesthetics

A

Lidocaine,
Bupivacaine,
Ropivacaine
Procaine.

39
Q

What is the basic structure of a local anaesthetic?

A

An aromatic ring linked to an amine group by an ester link or an amide link

40
Q

Local anaesthetics can contain an ester link or an amide link. How does this difference change the properties of the anaesthetics?

A

Plasma contain lots of esterase. Ester links are broken down quickly making those anaesthetics short acting. Amide links take longer to be broken down and therefore are longer acting

41
Q

What determines the characteristics of local anaesthetics?

A

• Lipid solubility – potency (higher greater potency)
• Dissociation constant (pKa) – time of onset. Lower pKa
faster onset
• Chemical link – metabolism
• Protein binding – duration of action (higher for longer duration)

42
Q

How do local anaesthetics work?

A

Block voltage gated sodium channels, the molecular drivers of the action potential

43
Q

Describe the mechanism of action of local anaesthetics

A
  • local anaesthetic molecules pass through the plasma membrane in uncharged form.
  • once within the cytoplasm of the cell it becomes charged
  • then enters the pore of the voltage gated sodium channel, blocking it
  • sodium ions cant move through and A.P. Process is stopped.
44
Q

Why is the local anaesthesia mechanism of action described as use dependent?

A

As the greater the degree at which the voltage gated sodium channels are firing, the greater the degree of block.

45
Q

What nerves are preferentially blocked by local anaesthetics?

A

Small myelinated afferent nerves in preference hence nociceptive and sympathetic block

46
Q

How do we increase the duration of action of local anaesthetics?

A

By adding adrenaline. Keeps the local anaesthetic by causing vasoconstriction and stops it from being cleared by the vascular system

47
Q

What does the Octanol:Buffer partition coefficient determine?

A

Octanol:Buffer partition coefficient is an index of lipid solubility
Therefore determines potency

48
Q

What doe the pKa of an anaesthetic determine?

A

The speed of action

49
Q

What does the linker of a local anaesthetic determine?

A

The metabolism

50
Q

What does the protein binding of an anaesthetic determine?

A

The duration of action

51
Q

What is the purpose of regional anaesthetics?

A

To selectively anaesthetise a part of the body

52
Q

What is the advantage of regional anaesthesia?

A

Patient remains awake

53
Q

What does regional anaesthetic use?

A

A local anaesthetic and an opioid

54
Q

Where is regional anaesthesia given in the upper extremity?

A

interscalene, supraclavicular,

infraclavicular, axillary.

55
Q

Where is regional anaesthesia given in the lower extremity?

A

femoral, sciatic, popliteal,

saphenous.

56
Q

What is intrathecal administration?

A

Injection into the spinal canal in the subarachnoid space so that it reaches the CSF

57
Q

What is an epidural?

A

An injection of local anaesthetic into the dural space of the spina cord

58
Q

What are the common side effects of general anaesthesia?

A

PONV (post operational nausea and vomiting) - may also by due to the opioids
CVS - hypotension
POCD ( post operative cognitive dysfunction) - increases with increasing age
Chest infection

59
Q

What are some of the side effects of local anaesthesia?

A

Generally well tolerated

Can cause cardiovascular toxicity if there is systemic spread as they are sodium channel blockers. - bradycardia

Clinical Pharmacology (26 decks)

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