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MD4001 Week 8 > 6. General anaesthesia > Flashcards

6. General anaesthesia Flashcards

1
Q

What is general anaesthesia?

A

Reversible, drug induced loss of consciousness, usually to allow a surgical procedure to be performed.

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2
Q

Two types of anaesthetic agents?

A

IV

Inhalation

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3
Q

What are Intravenous induction agents

A 
Agents which will induce loss of consciousness in one arm brain circulation time
e.g. 
• Propofol "magic milk|
• Thiopentone 
• Etomidate
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4
Q

What are inhalational anaesthetic agents?
Uses?
Examples

A

Gas or vapour, delivered to the patient via a breathing circuit.

Use:
• May be used to induce anaesthesia (children)
• More commonly used to maintain anaesthesia

E.g.
– Nitrous oxide
– Isoflurane
– Sevoflurane
– Desflurane
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5
Q

What is entonox?

A

50:50 Ni:O2

Found in: Labour and trauma wards

Analgesic effect

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6
Q

Different structures all have varying structure yet the _____ effect

A

Different structures all have varying structure yet the same effect

Thought that lipid solubility is the potency determiner

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7
Q

What is MAC?

A

min alveolar conc
min conc in the lungs that willc ause 50% of population to not respond to surgical stimuli

Low MAC means anaesthetic effect easily induced (high potency)

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8
Q

Lipid solubility determines…

A

Potency

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9
Q

In inhalaiton agents:
The _____ lipid soluble: the more potent: the lower the MAC
The _____ blood soluble: the slower the onset

A

In inhalation agents:
The more lipid soluble: the more potent: the lower the MAC
The more blood soluble: the slower the onset

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10
Q

Problem with lipid solubility theory?

A

Same structure BUT Different potency, so different clinical actions
Isomers have different potency’s so MAC/lipid solubility theory not true
Explanation: Basic protein provides anaesthetic effect, so anaesthetic effect due to effect on ligand gated GABA receptor

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11
Q

What current anaesthetic research is being looked into?

A

Research using knock-in mice
• Intravenous anaesthetics mediated by β3 subunit
• β2 subunit mediating IV hangover

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12
Q

Which anaesthetics excite:
GABAa receptors
Background K+ channels

A

GABAa receptors

  • All IV induction agents (etomidate, thiopentone)
  • Barbiturates
  • Inhalation agent

Background K+ channels
-All Inhalation agents

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13
Q

Which anaesthetics inhibit:
Na Channels
NMDA receptors

A

Na Channels
-Volatile anaestetics

NMDA receptors

  • NO
  • Xenon
  • Ketamine
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14
Q

Is anaesthesia just a chemical sledge hammer?

A

Thalamus IMPACT

–>
Cerebral cortex
Brain stem
Spinal cord

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15
Q

Main mechanism in waking up from anaesthetic

A

REDISTRIBUTION from brain to rest of body ***

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16
Q

Virtually all anaesthetic agents will have a negative inotropic effect on the heart and will reduce systemic vascular _______.
Exception: ________

A

Virtually all anaesthetic agents will to a greater or lesser effect have a negative inotropic effect on the heart and will reduce systemic vascular resistance.
Exception: ketamine

17
Q

Any drug causing loss of consciousness may lead to ________ of the airway

A

Any drug causing loss of consciousness may lead to obstruction of the airway

Respiratory depression is common with nearly all anaesthetic agents. With intravenous agents this tends to be a fall in respiratory rate and with inhalational agents a fall in tidal volume.

18
Q

Aims of an ideal anaesthetic?

A
  • Act rapidly
  • Pleasant
  • Cheap to manufacture
  • Stable (soda lime)
  • Analgesic effect
  • Amnesic effect
  • Minimal “hangover”
19
Q

Avoided features of anaesthetics?

A
  • Irritant on veins or airways
  • Emetic
• Minimal effects on other systems
– Breathing
– Cardiovascular
Produce toxic metabolites
Cause histamine release / anaphylaxis
20
Q 
Thiopentone, effect on:
Bp
CO
HR
SVR
RR
ICP
Pain?
A

IV anaesthetics

Bp- Decrease
CO- Decrease
HR- Increase
SVR- Increase/decrease
RR- Decrease
ICP- Decrease
Pain? No
21
Q 
Propofol, effect on:
Bp
CO
HR
SVR
RR
ICP
Pain?
A

IV anaesthetics

Bp- DECREASE
CO- DECREASE
HR- Decrease/-----
SVR- Increase/decrease
RR- Decrease
ICP- Decrease
Pain? Yes
22
Q 
Ketamine, effect on:
Bp
CO
HR
SVR
RR
ICP
Pain?
A

IV anaesthetics

Bp- Increase
CO- Increase
HR- Increase
SVR ------- 
RR- Increase
ICP- Increase
Pain? No
23
Q 
Etomidate, effect on:
Bp
CO
HR
SVR
RR
ICP
Pain?
A

IV anaesthetics

Bp ------ 
CO -----
HR ------ 
SVR ------
RR Decrease 
ICP --------
Pain? Yes

** Few side effects**

24
Q

Name the common IV anaesthetics used?

A

Etomidate
Ketamine
Propofol
Thiopentone

25
Q

Effect of Isoflurane as an inhaled anaesthetic on:
CVS?

Resp?

Other:
Cerebral flow flow?
Cerebral O2 requirement?
EEG?
Effect on uterus?
Potentiation of muscle relaxation?
Analgesia?
A

CVS?

  • Decrease in contractility, SVR, bp
  • Increase HR

Resp?

  • Increase RR, PaCO2
  • Decrease TV
Other:
Cerebral flow flow? Increase
Cerebral O2 requirement? Decrease
EEG? Burst suppression
Effect on uterus? Relax
Potentiation of muscle relaxation
Analgesia? Some
26
Q

Effect of desflurane as an inhaled anaesthetic on:
CVS?

Resp?

Other:
Cerebral flow flow?
Cerebral O2 requirement?
EEG?
Effect on uterus?
Potentiation of muscle relaxation?
Analgesia?
A

CVS?

  • Increase HR
  • Decrease in SVR and Bp

Resp?

  • Increase RR, PaCO2
  • Decrease TV
Other:
Cerebral flow flow? Increase
Cerebral O2 requirement? Decrease
EEG? Burst suppression
Effect on uterus? Relax
Potentiation of muscle relaxation
Analgesia? Some
27
Q

Effect of Sevoflurane as an inhaled anaesthetic on:
CVS?

Resp?

Other:
Cerebral flow flow?
Cerebral O2 requirement?
EEG?
Effect on uterus?
Potentiation of muscle relaxation?
Analgesia?
A

CVS?
-Decrease contractility, SCR and BP

Resp?

  • INCREASE RR
  • Increase in PaCO2
  • Decrease in TV
Other:
Cerebral flow flow? Increase
Cerebral O2 requirement? Decrease
EEG? Burst suppression
Effect on uterus? Relax
Potentiation of muscle relaxation
Analgesia? Some
28
Q

Inhaled anaesthetics?

A

Isoflurane
Desflurane
Sevoflurane

29
Q

Considerations when selecting drugs and techniques in anaesthetics?

A
  1. health & requests of the patient 2. the properties of the drugs
  2. the requirements of surgery
    to minimise patient risk and maximise patient safety and comfort.
30
Q

What are the stages of chemical synaptic transmission?

A
  1. Synthesis of NT and formation of vesicles
  2. Transport of NT down axon
  3. AP travel down axon
  4. AP causes Ca2+ to enter bouton, evoking NT release into cleft
  5. NT attachment to post synaptic receptors. Either excitatory or inhibitory effect
  6. NT and receptor separate
  7. Reuptake of NT
  8. Vesicles without NT transported back to cell body
31
Q

Where is the mainly action of general anaesthetics

A

General anaesthetic mainly act on the inhibitory channels at the Transmitter/ligand gated ion channels.

Mainly GABAa receptor: This is the major INHIBITORY pathways.
So general anaesthetics potentiate inhibitory effect of GABA.

This is a Cl- linked ion channel (2 x beta, 2 x gamma, 1 x alpha)

32
Q

What makes up the structure of the GABAa receptor?

A
  • Pentameric arrangement
  • Central ion channel pore
  • 18 possible subunits
  • Approx 30 forms of receptor
  • Some subunits location specific
  • Anaesthetics allosterically activate the receptor
33
Q

Balanced anaesthesia?

A 
A bit of this & a bit of that...
Selection of drugs and techniques bearing in mind the
1. health & requests of the patient
2. the properties of the drugs
3. the requirements of surgery

Purpose: to minimise patient risk and maximise patient safety and comfort.

34
Q

Which ligands are involved in the excitatory ion channels on CNS?

A

5-HT
ACh
Glutamate

Hence general anaesthetics downregulate these

35
Q

Outline the properties of ketamine

A

IV Anaesthetics

NMDA inhibitors

Side Effects:
Bp- Increase
CO- Increase
HR- Increase
SVR ------- 
RR- Increase
ICP- Increase
Pain? No
36
Q

Respiratory side effect of inhalation agent?

A

Respiratory depression is common with nearly all anaesthetic agents. With intravenous agents this tends to be a fall in respiratory rate and with INHALATION agents a fall in TIDAL VOLUME.

37
Q

Respiratory side effect of IV agent?

A

Respiratory depression is common with nearly all anaesthetic agents. With IV agents this tends to be a fall in RESP RATE and with inhalational agents a fall in tidal volume.

MD4001 Week 8 (7 decks)

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