Lecture 4 - Nitrous Oxide Flashcards
What are the 4 main effects of anaesthesia, and what does each one mean?
Hypnosis - loss of consciousness
Amnesia - inability to form memories
Immobility - no movement in response to painful stimulus
Analgesia - no sensation of pain
What are some lesser important effects of anaesthesia, and what is an important property of all the effects?
Slowing of EEG
Slowed breathing
Stabilisation of heart rate
All effects are reversible
What are the 4 stages of anaesthesia, as experienced by the patient?
- Analgesia - dream-like, feels good
- Excitement (transient) - increased muscle tone and heart rate
- Anaesthesia
- Cessation of breathing (if you administer too much)
Which type of anaesthetic would you use to induce anaesthesia, and which would you use to maintain it?
Induction - an IV anaesthetic such as Propofol
Maintenance - an inhaled anaesthetic such as Nitrous Oxide
What are the desired features of anaesthetics that influences which one is used?
Fast induction & recovery No side effects Non flammable/non explosive High margin of safety Cheap Easy to store Easy to adjust levels
Name two inhaled anaesthetics that are no longer used today and explain why
Chloroform - colourless liquid. Causes vomiting and even death
Cyclopropane - very unstable compound and high cost
Name two inhaled anaesthetics that are commonly used today
Nitrous oxide - colourless gas, weak anaesthetic
Isoflurane - often used in conjunction with nitrous oxide
Name two IV anaesthetics that are commonly used today
Propofol - very rapid induction and recovery
Ketamine - NMDA antagonist. Short duration of action. Can cause hallucinations. Used on severely injured patients
Name two groups of medications that can also be used as IV anaesthetics, and and example in each group
Barbiturates e.g. thiopental
Benzodiazepines e.g. diazepam
Both positive allosteric modulators of the GABAa receptor, used for anti-anxiety and sedation
How is the potency of an anaesthetic measured?
Name the two measurements and how they are tested
In terms of minimum alveolar concentration (MAC)
This is the atmospheres at which it will have an effect in 50% of people
MAC (immobility) = loss of withdrawal reflex
MAC (awake) = hypnosis/loss of righting reflex
Why will an anaesthetic with a MAC above 1 atmosphere not have an effect?
1 atmospheres = normal atmosphere
What is the olive oil:gas partition coefficient?
A measure of how hydrophobic an anaesthetic is
Higher coefficient = can more easily dissolve in lipids
There is a positive correlation between the olive oil:gas partition coefficient and the potency of an anaesthetic
What is the unitary theory of anaesthesia?
All anaesthetics have a common molecular mechanism
All anaesthetics have a hydrophobic site of action
All anaesthetics work by perturbing the neuronal lipid membrane to affect neuronal activity
What are the 3 problems with the unitary theory of anaesthesia?
- Recently discovered anaesthetics are less potent than what would be predicted based on their lipid solubility
- Chiral enantiomer pairs of anaesthetic molecules have different potencies
- Mutations in some proteins can impair the effects of anaesthetics
What are the Group 1 anaesthetics and how do they work?
The intravenous anaesthetics e.g. propofol
Strong hypnotics/amnesiacs but weak immobilisers
Target beta-2 and beta-3 subunits of the GABAa receptor to potentiate the chloride currents
Also stimulates glycine receptors
