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Year 1 Neurology > Anaesthetics > Flashcards

Anaesthetics Flashcards

1
Q

What are the three main effects of anaesthetic drugs?

A

Unconsciousness

(action on the reticular dormationa nd ARAS)

Loss of reflex’s

(Affects the sensory input to the reflex arc)

Analgesia

(reduced transmission of conscious sensation)

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2
Q

What are the two main groups of anaesthetics, and how do they differ in administration?

A

General

(Intravenous eg. propofol)

(Inhilation eg. isofluorane)

Local

(same as general but administered in low doses to affect small localised regions)

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3
Q

How are local anaesthetics grouped?

A

Split into 2 groups according to structure (normally have a ‘caine ending)

Amino-esters = metabolised in the plasma

Amino-amides = metabolised in the liver

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4
Q

What is the mechanism of local anaesthetics?

A

Via sodium channel block which dampens down neuronal activity and reduces sensory transmission to the cortex

2 ways:

Directly entering the channel when its open (more channels open the bigger the effect = use dependence)

Accessing channel by crossing the axonal membrane and binding from the inside

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5
Q

Give a clinical example of when local anaesthetics wouldnt work and why.

A

When the tissue is inflamed.

Local anaesthetics ability to work is pH-dependent - inflammatory soup in damaged tissue tends to be acidic

Local anaesthetics ionise in acidic pH = reduces their ability to cross the neuronal membrane and attach to the sodium channel

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6
Q

How is sensation affected by administration of local anaesthetics?

A

Local anaesthetics work more easily on smaller or un-myelinated nociceptive sensory fibres (A-delta and C-fibres) and unmyelinated autonomic fibers.

This is because the access to the sodium channels via the membrane is easier than across the larger and highly myelinated proprioceptive fibres

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7
Q

What 3 factors need to be taken into consideraton when selecting a local anaesthetic?

A

Needs to be:

Agent with low irritant effect and toxicity

Rapid onset of action

Half-life to allow adequate time to do a procedure

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8
Q

Name 3 commonly used local anaesthetics and their uses and half lives

A

Lidocane (amide) = 1-2 hours

(Local infiltratioin, nerve block, dental and topical)

Bupivacaine (amide) = 1-3 hours

(Local infiltration, peripheral nerve block, epidural, and sympathetic nerve block)

Benzocaine (ester) = <1 minuite

(Throat lozenges)

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9
Q

What are the main side effects of local anaesthetics?

A

Local irritation and inflammation occuring at the site of administration

Can be exasberated by the use of local vasoconstrictors or trauma to tissue on administration

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10
Q

Rarely there can be systemic side effects on the use of local anaesthetics.

What causes this and what are the systemic side effects?

A

Caused by overadministration of of the agent, leading to increased plasma levels of the drug

Cardiovasuclar changes

(Caused by local vasodialation or cardiotoxicity through binding in the heart)

CNS chnages

(Light-headedness, sedation, loss of consciousness)

Anaphylaxis

(Rare and only found with ester drugs)

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11
Q

What do general anaesthetics do?

A

Induce a loss of sensation, altered state of consciousness and a loss of memory for what happens under its influence

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12
Q

Name and explain the 6 steps in the process of anaesthesia

A

Premedicaion

Benzodiazepine to reduce anxiety and help with memory loss

Induction

Inhalation of IV administration of the anaesthetic

Muscle relaxation and intubation

Uses a neuromuscular blocking agent to relax the muscles during long surgical procedures

Maintenance

Inhilation or IV administration

Analgesia

Administration of agents to reduce pain on recovery from surgery

Reversal

Of both neuromuscular blocking agent and anaesthetic

Results in return of consciousness

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13
Q

What are some benifits of Inhilation anaesthetics?

A

Very potent and readily mixed with oxygen for administation (25% to prevent hypoxia)

Low blood solubility = rapid induction and recovery with fewer lingering effects

The speed of effect means anaesthetic levels can be quickly adjusted

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14
Q

Nitrous oxide (simple gas) can be used in combination with volitile liquids when administering inhilation anaesthetics.

Give an example of a volitile liquid and explain why NO is used.

A

Isoflurane

NO is not very potent but can be used in combiation with other inhilarion agents.

It provides some analgesia, so when used in combination it can mean reductions in the required doses of other drugs

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15
Q

What are the 4 factors that depth and speed of recovery from inhilation anaesthetics are linked to?

A

Rate of alveolar absorption

(depends on depth of inspiration and the concentration of the concentration of the agent administered)

Speed of equilibration

(balance of anaesthetic concentration in the air, blood and fats, which depends on solubility of the agent)

The relative concentations at equlibrium

Cardiac output

(controls delivery of drug o the brain)

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16
Q

Regarding inhilation anaesthetics, what is the activity of the agent linked to?

A

The blood:gas partition coefficent

Indicates solubility

The oil:gas partition coefficent

Indicates the relationship between concentration of inhaled ages and that in the fat (brain/lipid membranes)

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17
Q

What is the potency of an inhilation anaesthetic calculated as?

A

Minimum alveolar concentration (MAC) required to immoilise 50% of patients during noxious stimulation

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18
Q

What is the Meyer-Overton theory based on?

A

The correlation between lipid solubility of inhaled anaesthetics and minimum alvelolar concentration.

States that anaesthesia occured when a sufficent number of inhilational anaesthetic molecules had accumulated in the lipid cell membrane, regardless of the drug type

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19
Q

What are the main side effects of inhilation anaesthetic agents?

A

Reduce activity throughout the body, via depression of cardiac output and blood pressure

Cause respiritory depression through an action on teh brainstem respiritory centres

Cause irritation of the respiritory tract, resuting in bronchospasm and laryngospasm

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20
Q

Why are IV anaesthetics not used alone for long term anaesthesia?

A

IV is used to induce anaesthesia and maintainace is provided by inhilation or a combination of inhilation and IV

This is due to accumulation affects and slow redistribution

21
Q

What are the 5 most commonly used IV anaesthetics?

A

Thiopental

Propofol

Etomidate

Ketamine (slower acting)

Midazolam (slower acting)

There is not just one mechanism of action for all the drugs

22
Q

In general, how do IV anaesthetics work?

A

Supress consciousness through a reduction of activity within the CNS with agents acting on both the inhibitory and excitatory pathways

Thiopental and Midazolam increase activity at the GABA receptor (inhibitory)

Ketamine blocks glutamatergic NMDA receptors (excitatory)

23
Q

What are the side effects of general anaesthetics?

A

Vary according to the concentration, duration and drug used

Decreased cardiac contractitlity

Respiritory depression (in overdose, leading to respiritory failure and death)

Decreased CNS fucntion

Reduced sympathetic activity

24
Q

Why might opiods be given alongside anaesthetics?

A

When given at induction, opoids can provide analgesia and reduce the dose of antibiotic required to have a seditive effect

Their effect on the CV and respiritory system can also help counteract the effects of invasive treatments, reducing HR, BP and resp rate increases that are caused by the stress

25
Q

Name 3 fast acting opiods used in combination with anaesthetics

A

Fentanyl

Alfentanil

Remifentanil

26
Q

What are epidural anaesthetics used for?

A

Use general or local anaesthetics and sedatives to remove sensation

Use analgesics to block pain sensation specifically

27
Q

Why does epidural anaesthetic have more of a effect on sensory rather than motor functions?

A

Sensory neurons are significantly more sensitive to the effects of local anaesthetics than motor neurons

Linked to the levels of myelination and the ease of entry of the anaesthetic

Epidurals do have an effect on the motor system but it is drug and concentration dependent

Midazolam = seditive and muscle relaxant effects

28
Q

What sensation is removed during labour when a epidural is used?

A

Pain is removed, but pressure sensation is not

29
Q

Whar are the most commonly used anaesthetics?

A

Bupivacaine and Lidocaine

30
Q

Why may other agents be added to an epidural?

A

To prolong the duration of the block and decrease bleeding and toxicity

Adrenaine is the most commonly added

Opoids (fentanyl and morphine) can be added for muscle relaxing and analgesica properties

31
Q

What is the Bromage scale?

A

A scale used to determine the level of epiduaral block.

Asseses and grades the patients ability to move their legs following induction - 4 levels:

1) Complete block

Patient is unable to move the knees or feet

2) Almost complete block

Patient demonstrates an inability to flex the knees but has the ability to flex the feet

3) Partial block

Patient can partially flex the knees and resist gravity and has movemnt of the feet

4) No block

Patient can flex the knees and feet fully

32
Q

What are the two groups of neuromuscular blockers?

A

Depolarising

Non-depolarising

Both groups are used to relax muscle by blocking the activity at the neuromuscular junction

33
Q

What is the mechanism of depolarising neuromuscular blockers?

A

Non-competitive/agonist neuromuscular blockers

Also includes anticholinesterases

Depolarising NMB binds to the Ach receptor causing prolonged depolarisation (receptor closes and repolarises even though agonist is still bound) and the site to be blocked = prevents depolarisation and muscle contraction

Initial depolariation causes fasciculation of the muscles prior to relaxation occuring = increases likelihood of post-operative muscle pain

34
Q

What is the most common neuromuscular blocker used?

A

Suxamethonium

Only administered IV

Rapid acting = muscle relaxation within 1 min

Rapidly metabolised by plasma cholinesterase (5-10 mins) so requires a constant infusion to maintain the blockade

35
Q

What group of neuromuscular blockers do anticholinesterases fit into?

Give and example of one

A

Depolarising neuromuscular blockers

Neostigmine

36
Q

How do anticholinesterases work when used as neuromuscular blockers?

(Acetylcholinesterase)

A

Work non-competitivly to increase the levels of Ach in the junctional cleft by blocking acetylcholinesterase breakdown of Ach

Cause muscle paralysis by overloading the system = activating all Ach receptors at maxiumum and leaving no room for additional movement

(similar to neuromuscular blockers)

37
Q

What are the issuses associated with acetylcholinesterase inhibitors?

A

They increase activity in the PNS causing bradycardia, increased secretion and increased peristalsis

38
Q

Give an example of a neurotoxin that works in a similar way to anticholinesterases

A

Botulinum toxin A ( botox)

Works to reduce muscle activity by blocking pre-synaptic release of Ach

Used clinicnally to treat muscle spazams and tic

Also known for its cosmetic uses

39
Q

What is the mechanism of non-depolarising neuromuscular blockers?

A

Known as competitive or antagonist neuromuscular blockers

Compete with Ach to bind to the Ach receptors

Once bound they prevent depolarisation thereby blocking the effect of Ach

Also act pre-synaptically to reduce calcium entry = reduces the release of transmitter from presynaptic vesicles

Do not cross theh blood brain barrier = no effect on teh CNS

40
Q

Name 2 common non-depolarising neuromuscular blockers

A

Atracurium

Vecuronium

41
Q

Other than their direct mechanisms how do depolarising and non-depolarising neuromuscular blockers differ?

A

Non-depolarising have a slower onset time (2-5 mins) with a duration between 15-90 mins

Non-depolarising are also water soluble and show no accumulation with repeated doses = more suitible for long term use

42
Q

What can happen is neuromuscular blockers and inhilation anaesthetics are taken together?

A

Inhilation anaesthetics can increase the effects of neuromuscular blockers

Must talior the cocentrations used by correlating teh effects of multiple drugs

Need a balanced level of anaesthesia, analgesia and muscle relaxation

43
Q

Which group of neuromuscular blockers is always chemically reversed prior to recovery?

What are the drugs used to do this?

A

Non-depolarising

Neostigmine (anticholinesterase)

  • Specific for a non-depolarising blockade
  • Rapid (1 min)
  • Effects last for 20-30 mins

Sugammadex (Selective relaxant binding agent)

44
Q

Anticholinesterases work as a depolarising neuromuscular blocker (acetylcholineseterase inhibitors).

What other function can they have?

A

Also work to reverse the effects of some non-depolarising neuromuscular blockers eg. atracurium

But they can prolong the action of depolarising neuromuscular drugs eg. suxamethonium

45
Q

In the event that anticholinesterases must be given, what else can be given to counteract the side effects?

A

Bradycardia and increased secretions as a result of the muscuranic effects on the PNS are the side effects

Give Glycopyrronium or Atropine prior to, or with a reversing agent

46
Q

How do selective binding agents work to undo the blockade caused by neuromuscular blockers?

Give an example of one

A

Sugammadex

Selective relaxant binding agent used for raid reversal of NMB blockade and acts by forming a complex with the drug by encapsulating it to inactivate it

Well tollerated, no effect on the cholinergic nervous system, minimises the risk of residual paralysis and is rapidly cleared form the plasma and excreted within 24 hours

47
Q

What is the difference between moderate sedation and general anaesthesia?

A

In moderate sedation patients are conscious but relaxed and verbal contact can be maintained

With general anaesthesia there is no conscious awareness/the patient is without feeling/sensation

48
Q

Name the scale used to rank sedation levels.

A

The Ramsay sedation scale

Year 1 Neurology (26 decks)

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