6. General anaesthesia Flashcards
What is general anaesthesia?
Reversible, drug induced loss of consciousness, usually to allow a surgical procedure to be performed.
Two types of anaesthetic agents?
IV
Inhalation
What are Intravenous induction agents
Agents which will induce loss of consciousness in one arm brain circulation time e.g. • Propofol "magic milk| • Thiopentone • Etomidate
What are inhalational anaesthetic agents?
Uses?
Examples
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
What is entonox?
50:50 Ni:O2
Found in: Labour and trauma wards
Analgesic effect
Different structures all have varying structure yet the _____ effect
Different structures all have varying structure yet the same effect
Thought that lipid solubility is the potency determiner
What is MAC?
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)
Lipid solubility determines…
Potency
In inhalaiton agents:
The _____ lipid soluble: the more potent: the lower the MAC
The _____ blood soluble: the slower the onset
In inhalation agents:
The more lipid soluble: the more potent: the lower the MAC
The more blood soluble: the slower the onset
Problem with lipid solubility theory?
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
What current anaesthetic research is being looked into?
Research using knock-in mice
• Intravenous anaesthetics mediated by β3 subunit
• β2 subunit mediating IV hangover
Which anaesthetics excite:
GABAa receptors
Background K+ channels
GABAa receptors
- All IV induction agents (etomidate, thiopentone)
- Barbiturates
- Inhalation agent
Background K+ channels
-All Inhalation agents
Which anaesthetics inhibit:
Na Channels
NMDA receptors
Na Channels
-Volatile anaestetics
NMDA receptors
- NO
- Xenon
- Ketamine
Is anaesthesia just a chemical sledge hammer?
Thalamus IMPACT
–>
Cerebral cortex
Brain stem
Spinal cord
Main mechanism in waking up from anaesthetic
REDISTRIBUTION from brain to rest of body ***
Virtually all anaesthetic agents will have a negative inotropic effect on the heart and will reduce systemic vascular _______.
Exception: ________
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
Any drug causing loss of consciousness may lead to ________ of the airway
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.
Aims of an ideal anaesthetic?
- Act rapidly
- Pleasant
- Cheap to manufacture
- Stable (soda lime)
- Analgesic effect
- Amnesic effect
- Minimal “hangover”
Avoided features of anaesthetics?
- Irritant on veins or airways
- Emetic
• Minimal effects on other systems – Breathing – Cardiovascular Produce toxic metabolites Cause histamine release / anaphylaxis
Thiopentone, effect on: Bp CO HR SVR RR ICP Pain?
IV anaesthetics
Bp- Decrease CO- Decrease HR- Increase SVR- Increase/decrease RR- Decrease ICP- Decrease Pain? No
Propofol, effect on: Bp CO HR SVR RR ICP Pain?
IV anaesthetics
Bp- DECREASE CO- DECREASE HR- Decrease/----- SVR- Increase/decrease RR- Decrease ICP- Decrease Pain? Yes
Ketamine, effect on: Bp CO HR SVR RR ICP Pain?
IV anaesthetics
Bp- Increase CO- Increase HR- Increase SVR ------- RR- Increase ICP- Increase Pain? No
Etomidate, effect on: Bp CO HR SVR RR ICP Pain?
IV anaesthetics
Bp ------ CO ----- HR ------ SVR ------ RR Decrease ICP -------- Pain? Yes
** Few side effects**
Name the common IV anaesthetics used?
Etomidate
Ketamine
Propofol
Thiopentone
